Modern setup vs. ancient factory propane specs on tractor

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evranch
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Modern setup vs. ancient factory propane specs on tractor

Post by evranch » Fri Dec 14, 2018 1:58 am

Hi all,

I'm from Saskatchewan and have done a few propane conversions on the farm, small engines and one large implement (a MF36 swather). I'm working on a MH44 tractor now.

The interesting thing about the MH44 is that it could be bought as a single-fuel LPG model way back in the early 1950s. The main differences from gas:

- compression greatly increased from the very mild 5.65:1 to a reasonable 8.7:1. This was done with domed pistons rather than different heads.
- different valves and seats. Perhaps hardened, but I have no information on this. Only the exhaust valves have seats, this is the same for the gas model.
- spark plug heat greatly decreased from the Champion 8-Com. to the Champion 5-Com (Or Autolite BT8 to BT4)
- complicated old Ensign propane carburetor with multiple jets and power valves. Mixture is to be set to 14.9-15.5 under part load and 14.3 under full load i.e. barely rich.

Surprisingly the timing remained the same at 0 degrees.

SO...

I'm doing this as a dual-fuel with a simple Impco 225 mixer before the carb, mainly because my local junkyard has a surplus of Impco 225 units. I know it is too big for it. So far it's running well tuned by ear, though. At first I couldn't get it to stop idling rich, so I added a PCV valve to lean it out a bit and also get rid of the oil mist blown everywhere. Seems to have done the trick, though I still can't lean it out enough to really get it to stumble, so I don't really know where I'm at. Unfortunately I don't have a sniffer. I also converted the tractor to 12V negative ground, mounted a 10SI alternator, put on a hotter ignition coil, new condenser and new wires as the spark was super weak.

Questions:

- Usually we would drop one heat range for the plug. Why have they dropped to such a cool plug? Is it due to the increased compression, and since I'm keeping mine 5.65:1, should I just drop one heat range? Right now it has Champion D21 plugs from the last owner - these are too hot for serious work and are going to come out anyways. From factory specs, 8-Com would be D16, 5-Com would be D9.
- It's going to spend most of its life as a working tractor on LPG, so should I add a lubrication system? The different valves and seats for the LPG model kind of scare me.
- What should I do with the timing? What the heck is up with 0 degrees of advance? Especially on LPG? It runs smoother and the exhaust is cooler with 5-10 degrees of advance. Switching between gasoline and LPG, gasoline starts to not ping but misfire towards 10 degrees, which I've never seen. Right now it's sitting at 5 degrees for dual fuel. It has an extremely lazy cam, max RPM 1500, it's definitely not a race motor. I heard a rumour that these old machines had 0 or retarded timing to avoid backfires that break arms on the hand crank. I am never going to crank it by hand, who wants to hang onto a 4.3L motor? Scary.
- Tractors spend a lot of time idling. Since I can't get my idle mixture perfect, am I risking my valves? I still don't know if propane is safer rich or lean, I've read that it can get hot at both ends. EGT thermocouple reading right out of the manifold is about 220C at idle, which is actually cooler than on gasoline.

Thanks for any help and I hope I can gain more knowledge and be helpful on this forum as well!
Alex

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BigBlockMopar
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Re: Modern setup vs. ancient factory propane specs on tractor

Post by BigBlockMopar » Fri Dec 14, 2018 2:12 pm

The wrong LPG mixture can only be dangerous at a load.
Too rich mixture at load is what (I recall) can burn valves as the mixture is still burning up hot when the ex. valve opens.

I've had my 318ci (8.6:1) car engine idling/cruising at around 17AFR for long times. General driving around 16 and full throttle at around 12.5-13 AFR.
I'm now running a 11.3:1cr 360ci engine with same plugs.
AFR's are fairly similar, maybe just a tad richer, but since my AFR-sensor craps out after a few minutes of driving I can't keep an eye on it all the time anymore.
Using factory mid '80s heads which probably have induction hardened seats, or what's left of them after all these years..

As for the 0-degree timing and pinging on gasoline, I would double check TDC on the balancer/flywheel.
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'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

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Re: Modern setup vs. ancient factory propane specs on tractor

Post by C3H8 » Fri Dec 14, 2018 5:20 pm

Pretty neat sounding project. The engines in the first 7 decades of the century had valves of relatively soft materials compared to the time when lead free gas was introduced. Lead in the gas provided substantial protections against valve recession. Anyone converting in that time could usually expect valve recession, especially on the exhaust valves to occur quite rapidly. That's why the tractor companies went to hardened valves and seats if the customer wanted to run propane. The speed of the recession was directly proportionate the the amount of continuous high loads the vehicle operated under. As for setting your mixtures it's interesting you are having difficulty getting to the lean side on a 225. They are notorious for being biased too lean. I am assuming you are turning the idle crew in the correct direction. Out or CC to lean. The addition of the PCV is a good choice but again it will only make the idle mixtures richer since the engine now has some oil to burn also. An added benefit of the PCV will the oil will provide a minor amount of lubrication for the intake valves and possible a smaller amount for the exhaust depending on valve overlap and slow the recession a little. You should always do mixture adjustments with the PcV drawing air and then install it into the valve cover after.

The additional heat range drop was because of the increased compression. 3 points is quite a bit. In your cases you will need to experiment a little. Start with the factory recommendation. Because you have installed a PCV system you may actually have to go up a heat range to compensate for the oil being burned through the engine now. Run the engine a month or two and then check the plugs to see how they are doing and make adjustments from there.

Yes, a top oiler would be a good idea. Again though this may be another reason to maintain the factory recommended plug before making any changes. More oil being burned. The higher heat may be required to keep the plug from forming deposits.

For the timing I expect a tractor distributor s easy to access. If it is I would mark the distributor clamping plate at 0 and 10 degrees. If your running gasoline just change the timing back to factory. Since the engine only runs at 1500 10 degrees on propane sounds very good.

As mentioned by BB your temperatures at idle are no concern. I'm used to dealing in F degrees. Your only running 413F at idle. The critical temperatures for valves using non leaded gas was approximately 1400F I would expect that on this older engine you should be watching the temps under load to be 1000 or less. You can reduce exhaust temperatures by advancing the timing within reason. Minor changes can make a big difference. In the days prior to unleaded fuel three things affect exhaust temps. Fuel mixtures, timing and valve lash. According to literature from IMPCO two of those things after to be out to significantly affect exhaust temperatures. You may not be sure of your mixtures but the full load one is the critical one. Once your satisfied with your timing close the power valve on the mixer a little at a time between runs until you begin to lose power. Then open it until you achieve maximum power. At that point open it just a slight additional amount.

Lastly the valve lash is very important. Adjust your valves to the maximum allowed clearance. Gas is a wet fuel and helps to cool components like the stem and seat surfaces. Propane is dry and even though it burns cooler than gasoline the valve temperatures typically remain higher. Picture what happens when your grinding a piece of metal and you dip it in water vs just trying to cool it in air. Because of this the valve expends a certain amount especially on the valve stem length. Setting at the maximum limit instead of minimum ensure the valves close completely allowing as much heat as possible heat to transfer to the block.

In a lot of testing we did we found that mixtures actually have a fairly small impact on exhaust temperatures. The biggest affect was due to timing and valve lash.

evranch
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Re: Modern setup vs. ancient factory propane specs on tractor

Post by evranch » Fri Dec 14, 2018 7:31 pm

Wow, great input from both of you guys addressing a lot of my concerns and validating some of my thoughts. It's definitely a fun project, and the tractor is ending up pretty heavily modified in general, being farm and not show. I'll have to post some pics once I get it put back together a bit.

Yes, soft valve materials is my greatest concern, but I also wonder if this engine could have been designed to run on unleaded fuel. I know some of the similar vintage aircraft engines have hardened seats and don't require leaded avgas. In fact this quote is from an FAA bulletin about Continental motors that were very similar to this motor:
Small engines from the 1940s were designed for fuels with octane ratings of 63 to 73 octane. These fuels contained no lead at that time.
This gas model shares the valves with yet another variant, the carbureted kerosene / "low-grade" model. This variant drops the compression even further, to a meager 4.68:1, and retards the timing for a fuel that obviously has very little resistance to preignition. This was a cheap farm fuel that I doubt would have been leaded? Ancient history by now.

In any case, I'm sure there's benefit to adding an oiler. I've never done one before, though. C3H8, also being on the Canadian prairies, do you have a source for propane components out here? Most people look at me funny when I even ask about such things. I've been considering building my own oiler from a windshield washer tank and a needle valve, as that looks like what Flashlube basically is. I've read that people are using 2-stroke oil either straight or mixed with diesel.

I'm glad you mentioned the oil mist from the PCV helping as that was one of the reasons I installed it! The other reason was that the factory breather discharged the oil mist directly at the driver's face. When setting clearances, I noticed this motor seems to have zero overlap, which is one reason I deemed the cam to be super lazy. I hope this still means the exhaust valve can be lubricated.

Interesting that the 225 usually runs lean. I'm turning the screw the right way, and until I installed the PCV I could remove it entirely without the motor even slowing down! I've been tuning with the PCV out of the valve cover so that I can put my finger over it to momentarily richen the mixture. Horsepower-wise though, the 225 is vastly oversized for this motor and I've read that can make mixers run rich. Despite being a 4.2L motor, the tractor is only rated at around 40HP due to its low RPM and all-around mildness. I called Century on the phone awhile ago to ask a few questions and they told me they doubt my power valve will ever come into play, since the mixer will never be anywhere near WOT. Mixture should be changed by swapping the gas valve if necessary. Does that sound sensible? (I just realized I never checked to see if I have a rich gas valve in there, I suppose I should pop the top off and check).

I will install the factory plugs (D16) and see how they work. I tend to prefer a hotter plug on older equipment anyways as they tend to burn a little oil.

As far as timing goes, it's really easy to access the distributor and I already marked it for 0 degrees. Sounds like a good plan. And as far as the timing marks go, they are etched right into the flywheel, annoyingly observed through a port behind the carburetor where you can't really use a timing light, so I don't see how they could have slipped. I guess when I go over the clearances again I can check that they correspond to the valve positions. While playing with the thermocouple I noticed I can easily take the idle EGT over 400C (750F) just by pulling it a couple degrees retarded, timing definitely has a huge effect on EGT. I probably should mention that this tractor has no vacuum advance at all.

That's really interesting that valve lash is so critical. I just set all the valves a couple days ago, 1 thou loose at a moderate temperature. They only give hot clearances, and I don't want to warm it up all the way in the shop and fill the place with exhaust. Right now the front end is on blocks as I'm reworking the steering, so it's kind of stuck there. The manual doesn't give a range - do you have a ballpark figure how much looser to set them?

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Re: Modern setup vs. ancient factory propane specs on tractor

Post by C3H8 » Fri Dec 14, 2018 11:55 pm

:lol: Your right. Finding a top oiler may be difficult. Most of the tractor or farm supply places new what they were prior to 1990 or so. There are still companies advertising these. Here's a link to one. http://www.ampcolubes.com/. The write up mentions Marvel Mystery oil which I am sure all the farmers referred to back in the 80's and 90's. The site claims this oil is available at most auto parts stores. Also I believe Princess Auto used to carry these. They might still.

Centuries statements on the 225 are probably correct. 40 HP is really low for that mixer. A much better choice would be a 125 or even a CT60. The CT60 will handle up to 73 HP. The only issue here is this mixer requires a remote air cleaner so the 125 might be better. Also you can probably find the 125 the same way you found the 225 however the new cost of the 125 is pretty cheap anyways. It also has an adapter available to go from a 225 mount to the 125.

As for the valves typically a hot and cold setting is 2 to 3 thou difference. I would probably just add 2 thou to the factory setting.

As you have noted timing has a significant impact on your exhaust temps so use it to your advantage on propane. The octane of propane is a minimum of 97 and as high as 104 RON. There are some differences of opinion on how to calculate it. The range is 97 to 110 so in theory it has a 104 RON. For some reason Chrysler says because it is a dry fuel you should use the lower 97 number. It doesn't really matter since both are substantially better than gasoline. This gives you a few degrees to work with keeping in mind the older design of this engine and as you noted its lack of valve overlap.

Propane parts you can get anything you need from Proquip sales Inc. in Calgary. 866-692-8132.

evranch
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Re: Modern setup vs. ancient factory propane specs on tractor

Post by evranch » Sat Dec 15, 2018 12:16 pm

Those old glass Ampco units would look great on the tractor and would be really easy to install into the same manifold port I put the PCV into. Looks like there were many brands of these back in the flat-head days, so I just need to track one down here in Canada. I know MMO well enough though I've never thought of this use for it - which seems to be the original use as Marvel made their own oiler for it!

Your mention of Princess made me think of a cheap and off-the-shelf solution though: install one of their common air tool lubricators and fill it with MMO. A very similar device. They are adjustable at low flows so it should be possible to hit that 6 drops per minute recommended by Flashlube. I could either put it in my existing PCV line (where it might foul up) or tee it off as another small vacuum leak and adjust the idle mixture accordingly. Actually... I suppose I could feed it from one of the downstream ports on the mixer, where it would be getting mixture rather than air. Then I would just need to decrease my idle speed setting. I think I'll do some experimenting with this.

After doing the math this tractor only needs 95CFM so even a model 55 would work. If I wanted to go LPG only, an updraft 55 would replace the gasoline carb perfectly. A remote air cleaner would be ideal actually, since I have to either buy an air horn for my 225 or tilt it at 45 degrees to fit the air cleaner beside the block. Unfortunately my junkyard has lots of 225s for a reason - they specialize in old school buses, many of which were propane. However with the supplier you shared I should actually be able to buy a new model CA100 that's configured to fit my application. I've actually been pulling off the throttle bodies and welding up my own air horn adapter plates for the bases of the 225s so that I can mate them to the side intakes of my gas carbs, so it would be nice to just buy one off the shelf!

evranch
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Re: Modern setup vs. ancient factory propane specs on tractor

Post by evranch » Sun Feb 17, 2019 3:19 pm

Update: The tractor project is basically done except for an air filter. The regulator is plumbed in to the cooling system and it's running on liquid propane. I swapped the main thermostat from 160 to 180 for extra heat. I've been plowing snow and have some initial performance results to share.

Driveability: Excellent. It's greatly improved from gasoline, especially at cold temperatures. Startup is immediate with no smoke, hunting or stumbling. It will idle far lower and it also has greatly improved lugging performance. In snow it is basically impossible to stall it, while on gas it would stall readily if I overloaded the hydraulics or pushed into a big drift without enough speed. Is this something to do with burning dry gas rather than atomized gasoline in the cold? It's also a lot quieter than it was on gasoline and has a really nice deep growl to it.

Efficiency: I weighed a 20lb tank, hooked it up, plowed my yard and my neighbour's yard out, then weighed it again. Steady working for 73 minutes pushing snow and cutting large drifts. I burned 6.8lbs of propane. This works out to 5L or 1.31 US gallons.

According to the Nebraska tests for this tractor it will burn 1.3 gallons per hour of gasoline at high idle delivering 1.43HP. Another test result was 1.78gph to deliver 10HP. Considering that I was pushing snow the entire time and still only burned 1.3 gallons of propane, I'm going to consider this conversion a definite success when it comes to efficiency.

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Re: Modern setup vs. ancient factory propane specs on tractor

Post by storm » Mon Feb 18, 2019 12:49 am

The fuel efficiency is interesting. The timing must be pretty well spot on for LPG for it to do so well.
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Fuel flow requirements calculations viewtopic.php?f=5&t=1638

evranch
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Re: Modern setup vs. ancient factory propane specs on tractor

Post by evranch » Mon Feb 18, 2019 7:23 pm

I was really happy to see those numbers (though idling through 1.3gph is thirsty compared to any modern engine)

I've found that every propane conversion I've done has had better efficiency than it did on gasoline. It's kind of odd since propane has lower energy content. I've blamed it on the old carbs being in bad shape or disliking ethanol fuel, but in this case, it's meeting factory specs - 70 years later, and with a compression ratio that was mild from the factory.

I wonder if it could be something to do with my altitude? I'm at around 2500' which would naturally favour somewhat leaner mixtures - that's getting to the point where you would start to consider adjusting the mixture on a light aircraft. However propane is not really "leaner", it just has lower energy content... though it will burn well at a broader range of mixtures than gasoline... hmm.

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Re: Modern setup vs. ancient factory propane specs on tractor

Post by storm » Tue Feb 19, 2019 2:20 am

evranch wrote:
Mon Feb 18, 2019 7:23 pm
However propane is not really "leaner", it just has lower energy content...
No and yes.
LPG is by definition leaner. Lambda 1 on petrol is 14.7 yet 15.5 on LPG. Full power .85 Lambda is about 12.5 (12.47 to be exact) on petrol and 13.2 (13.17 to be exact) on LPG.

LPG does have lower calorific value but when push comes to shove pumping energy is required to convert liquid petrol to a usable atomised fuel while LPG is converted from a liquid to a gas via the usage of waste heat.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

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Re: Modern setup vs. ancient factory propane specs on tractor

Post by C3H8 » Tue Feb 19, 2019 1:35 pm

Fuel efficiency on gasoline in older vehicles could be very erratic. They typically had very rich mixtures to keep them running cold using a choke. This was because of really poor atomization of the gasoline and much of the liquid droplets would get stuck on the intake manifold walls until the engine warmed up. On older engines this could take 5 to 10 minutes. In addition the intake manifold designs, especially on an engine like yours, was very poorly designed. They were normally cast with very rough surfaces on the way to the intake valves. The reason why racers would port and polish there heads and polish the intakes or change them to better designed ones. Due to the poor design the manufacturers would also set the carbs to the rich side, especially for 3/4 to wot. It was common to see very lean mixtures on the cylinders farthest from the carburetor. On engines with very poor designs it was common to see LPG run better than gasoline. LPG is a true vapour and other than the first minute or two of operation it's vapourization can be very consistent. It also distributes better than atomized gasoline ensuring each cylinder is more likely to gets its fair share of fuel. The farthest cylinders may still be leaner but they are better than on gasoline. Storm's points are all valid but with the engines from decades ago the main advantage of LPG over gasoline (petrol) is the gasoline engines were quite inefficient. That's why today we see the true difference in BTU values with the injection systems. It is very common to see up to a 25% difference in fuel use between LPG and gasoline. Gasoline systems have come a long way since they began commonly using injection around 1985. Gasoline systems only require enrichment the first 30 seconds to a minute when cold and the wot enrichment is much more refined. In addition all the cylinders get the same amount of fuel with the introduction of port and direct injection.

evranch
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Re: Modern setup vs. ancient factory propane specs on tractor

Post by evranch » Wed Feb 20, 2019 6:32 pm

That explains it then, since everything I've converted has been older equipment. I've thought about slapping a mixer onto the intake of my 2002 GMC Sierra farm beater but I think all it would do is complain and throw codes, and not really be worth the effort. These older motors are definitely worth the effort.

The MH44's Y-shaped, cast iron intake manifold is certainly a poor design, with uneven distances to the cylinders, rough surfaces and sharp turns. Below it all is a long drop to an updraft carb, so the path is even harder for cold droplets to make. No wonder that when running gas this tractor needed at least 5 minutes to warm up at a high idle before it would do anything but bog and sputter, and idled poorly at low RPM, since most of the fuel likely would end up on the walls of the manifold. Running gas at low temperatures that lower funnel section to the carb would grow a good shell of ice before it was warmed up.

That also explains the torque boost as all cylinders are getting a proper mixture on propane and firing strongly. After adjusting the governor and throttle linkage today, I have it smoothly revving from 650rpm to the rated 1500rpm and back, at idle and under load. I took it out to see how low I could go, set the governor to idle and lugged it up the driveway hill in 5th gear at maybe 100-200rpm. It sounded like an old hit and miss engine, puff puff puff. I only quit because it was starting to lurch pretty bad, not because I ran out of power - the throttle plate was probably only a quarter open. Then I pushed around some snow in second gear at well below idle speed. Unthinkable when this was a gas tractor.


One thing that I'm curious about is why it will lug so low but it won't idle any lower than 650rpm. The governor is in play at 650, and there is still a little room to the idle stop screw on the throttle. Adjust the governor lever in a little more, and it stumbles down and quits. But put it in gear, the revs drop way lower and it will lug all day. Not that I really want to idle lower, the alternator quits around 500rpm, but I'm curious why it would behave like that. Idle mixture? Flow too low for the mixer?

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Re: Modern setup vs. ancient factory propane specs on tractor

Post by C3H8 » Thu Feb 21, 2019 1:21 pm

All to do with the basic operation of an IMPCO mixer. At no load the airflow through the mixer is very slow and the gas valve barely open. Lowering the idle speed reduces the air flow and the gas valve virtually closes. With the load the air flow is higher and the air/gas valve is pulled open a lot further. This leaves room for lower RPM operation as the gas valve is further open and has room to close a little with out shutting off the fuel flow completely. On another note I would not recommend overdoing this. The stress on the crankshaft can be significant when lugging an engine putting additional load on the rods, and bearings also. Remeber that low speed operation also means low oil pressure and will increase bearing wear quite a bit. They're fun tests but don't overdo it.

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Re: Modern setup vs. ancient factory propane specs on tractor

Post by jono » Sat Feb 23, 2019 8:10 pm

it is some while since I looked into the forum - has been so quiet. Am only using a 7" tablet hot wired to my cell phone so have not read the contributions fully
I have taken in some figures such as engine size is 4.2 litre but lost the comp ratio. What are idle, working and max rev specs of this project? I was going to say capacity wise the 225 should be fine as I have seen on351 F100 and now recently made my 200 with L converter work on my Subaru flat four 1800 cc work brilliantly , contains both a miser and the devil !!

I was going to suggest but too late to make a manometer to ensure your low comp was going to be able to work the diaphragms correctly but you have succeeded in a good set up which is often the case adapting these basic, crude old components. But I guess 4.2 litres at low comp must be able to suck like my low comp 1.8 running 7.7:1 but then I have an IHI hair dryer assisting now up to no more than seven psi.

I use one grade colder than standard for gasoline and plug gap I reduce to 0.6 mm to reduce the load on ignition components coil and module. You may be able to open up the P!ug gap with such low comp without loading your ignition bits? Check with the smarter ones first :)

Good read these posts

Oops EDIT......seen max revs of 1500 holy cow ! And 4.3 litre so no need to answer my silly questions/b]

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Re: Modern setup vs. ancient factory propane specs on tractor

Post by jono » Sat Feb 23, 2019 8:29 pm

Your idle speed may be depending on how much air slips past throttle butterfly when in no load situation

I once used an Impco throttle plate body that is a stretched out circular shape like a round dining table that has rectangular extensions in the middle section - so it was a replacement for a single stage two barrel Stromberg WW of the 60s and 70s

It was fine on 250 cube six inline that idled right and revved to billy'O - 6000

Then when I tried it on 110 cube flat four, so much extra air snuck past the not so close tolerances of the butterfly to body - it idled at no less than 1200 rpm instead of desired 750 or 800 unless load her up to drive off which is where I guess you also get lower revs

I knew of at the time the same throttle body and same car and they played with butterfly to get great idle. I tried twice making my own butterflies but failed to achieve same.

Twenty years later it turns out the next owner of modified throttle plate and body is promising to give it to me as no further use for it, though I am a bit the same having moved onto EFI throttle bodies in my conversions

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