..........Tuning the mm x450.........new ? post 59

[Steptoe]

I had a little ping under load, so i turned the timing back and it stopped( i dont have a timing lite and have to get one asap).The timing could be way off,

OK there are still a lot of 'old school' people who can tune timing by ear.....in 40 yrs I have never meet one.
Tuning timing by 'ear and or vac gauge ends up with the engine over advanced and carb out of adjustment.
Over advanced as mentioned above is slow death ..detonation...and you dont have to be able to hear it for it to be happening....
Turn the dizzy back to a rough stable idle. tune the carb as best as possible...get a timing light, mark out the balancer to 40 deg.
An easy way to do so, is get a taylors tape...the missus sewing box, measure the circumferance (360 deg) divide by 36 that is 10 deg...mark on a bit of good duck tape 5 and deg deg increments.. and stick to the balancer.

They make a advance kit which is springs and keys for my dist that i can change to get my advance where needed, is it better to use the hei instead of my unilite and 6al..?

my veiw..why use a mac truck to do the shopping?....dont use a mini to do long haul freight.
LPG is more sensitive to something wrong in the ign..on the other hand ign should be kept in good condition.
Yeah hei s u can get spring kits but they dont come with adjustable cent degs....that has to be done in the hei as I describe previuos....and if you screw up a counter weight, grab some more out of the local wrecking yard rubish bin.
And you dont have to just use THE special hei springs... most dizzys spring will fit its just finding the 2 that work.

OH when increasing cent in a hei...you can put enough (depending on the specs of the hei you are starting on) so the counter weight will just top of the end of the slide plates they slide on...I use a brown fiber resin stuff, make a larger slide then epoxy on in place of the old ones....

Tuning the 450 ..sry never played with one, only know the impco 425...sounds like the principle is basically the same thu???

[flatblack]

I just had it running today, It took a while when it was cold to start but it started. I adjusted the idle and it seems at a decent low rpm, when its up to temp and i shut it off if i bump the key and give it pedal it fires right up, if not it just cranks about ten to twelve times then it will start. The new plugs were a little dark inside, the electrode is clean tho. I adjusted it some and got it to keep temp, making me believe that it was lean. I should get the 02 installed this weekend, would setting the carb a little lean at idle help cold start ups..?

I tried messing with the timing but i couldnt get the lite my dad had to work, a friend has a dial back mac tools lite and will help me get it set this weekend.


I did notice tho every start up it idles at a different speed, varies about 200 rpm. I just checked for vac leaks and didnt find any, maybe like said it is my base plate, i even disconnected my booster to see if that even has a leak. I used carb cleaner to check, i did find a crack in a mew vac hose and replaced it.

[Steptoe]

It sounds like you timing, mixtures everything is out of wack...As I said before , you cant get anything right without at least a timing light, vac gauge and O2 helps greatly.

would setting the carb a little lean at idle help cold start ups..?

No engines have chokes for cold start (I dont) chokes make the engine run rich.

[storm]

For those that dont know, I am in the US where the V-8 is still the predominate engine. When I did that Oldsmobile, it was in the late 1970's where low compression was the rule rather than the exception. The ignition would not fall into the next cylinder but we routinely saw timing advances in these low comp engines in the upper 40's degrees. The larger the combustion chamber and lower the compression, and with wide lobe centers (old emission engines) the longer the combustion cycle.

When that engine was swapped to LPG, the exhaust valves would routinely burn through and would not stop until the CR was bumped.

Franz

Franz, I am well aware that Lockhart Texas is in the US, I am also well aware of the American penchant for the V8 engine.

Having worked on many GM V8s from Chevrolet, Holden, Oldsmobile and Pontiac (also Ford and Chrysler V8s as well, love Windsors and Chrysler 340s can't stand Clevelands but that's another debate altogether) I understand that each has its own particular timing curve. Having said that I am yet to see a regular V8 with a regular crank and distributor setup be able to go past 45 degrees without pulling into the next cylinder on the distributor. My own Trans Am had that problem if the vacuum advance was hooked up. I am more than willing to learn how it is possible so please feel free to explain it to me, and no I'm not being smart I am genuinely interested. I just think I have missed something obvious

[Steptoe]

and distributor setup be able to go past 45 degrees without pulling into the next cylinder on the distributor.

Are you not confusing Dizzt degreees with crank degrees?
When on is working on a dizzy ...setting up on a dizzty machine...one works in dizzy degrees
When one gets to putting the timing light on the ctank its engine degrees. ???????

[storm]

and distributor setup be able to go past 45 degrees without pulling into the next cylinder on the distributor.

Are you not confusing Dizzt degreees with crank degrees?
When on is working on a dizzy ...setting up on a dizzty machine...one works in dizzy degrees
When one gets to putting the timing light on the ctank its engine degrees. ???????

Ah different revolutions of crank and cam/dist, 2 to 1 or 1 to 2 whatever way round were working, that's it.

Now that begs the next question then, aren't we confusing both when we are talking timing? It seems we are going from crank degrees to dist degrees, and possibly back again, in the one topic without it actually being clear what one is being discussed. It does to me anyway

Thanks Steptoe, I kinda knew it was something I was missing. (No not my brain )

[flatblack]

Is there a base to set the timing at with a 12:1 comp engine..? Ive just read that if you set the idle a little rich it helps with cold starting, is that accurate..? I noticed when i was out messing with it if i have someone crank it while im turning the idle mixture i can get it to fire. Im going to get a timing lite and a vac guage today, i should have the 02 hooked up to a narrow band fuel/air on the weekend.

[Steptoe]

Is there a base to set the timing at with a 12:1 comp engine..?

I would start total cent (no VA) 32 feg all in then work back and 4th from there for thepwer range and establish a low idle Total (cent + VA) around 600/700 rpms anyting from 8 to 16 deg.

[franz]

Storm, dont assume that when the dist is at "0" degrees that the distributor rotor is sitting directly adjacent to the corresponding post. The rotor may trail the post by up to 22 degrees, then advance up to the total amount. In some cases, cross fire was a problem, one reason distributorless ignition came in. Look at some of the rotors on Fords, the tip was shaped in a "tee". When I was teaching advanced automotive theory in the 80's at our local college, we had a distributor machine. We had a transparent distributor cap for a GM HEI, and we could load the secondary side to max voltage. Quite a lightening storm inside, especially when dark.

When calculating timing, the indicated distributor degrees is the same as crankshaft degrees, that is what is referenced. The distributor rotates at camshaft speed, not crank speed but the timing referenced by the distributor is shown in the crank pulley.

Franz

[franz]

1) Lets move the ignition timing discussion to a new thread, good stuff here though!

2) Flatback, LPG is very temperature related. When cold, LPG is more dense and fuel mixtures may tend to be a bit richer. This is why a closed loop fuel system is very helpful at maintaining fuel mixtures. Cold engine low speed engine rpm variations is common, due to cold engine friction, increased lube oil viscosity, fuel mixtures, etc. A worn baseplate only adds to the problem. As for a baseline ignition timing for 12:1, I think I might try around 5 degrees btdc and see how that works.

One thing to toss in. We have gotten spoiled with modern vehicles electronic fuel injection, and their ability to almost start instantly. I drove an older vehicle last weekend and forgot I had to pump the throttle to set the choke, and restart it when it didnt start and run properly on the first twist of the key, and baby it for the first couple of seconds until it warmed up. Not many mechanical carbed propane fuel systems start and run perfectly on the first twist of the key, some do, most dont.

Franz

[flatblack]

1) Lets move the ignition timing discussion to a new thread, good stuff here though!

2) Flatback, LPG is very temperature related. When cold, LPG is more dense and fuel mixtures may tend to be a bit richer. This is why a closed loop fuel system is very helpful at maintaining fuel mixtures. Cold engine low speed engine rpm variations is common, due to cold engine friction, increased lube oil viscosity, fuel mixtures, etc. A worn baseplate only adds to the problem. As for a baseline ignition timing for 12:1, I think I might try around 5 degrees btdc and see how that works.

One thing to toss in. We have gotten spoiled with modern vehicles electronic fuel injection, and their ability to almost start instantly. I drove an older vehicle last weekend and forgot I had to pump the throttle to set the choke, and restart it when it didnt start and run properly on the first twist of the key, and baby it for the first couple of seconds until it warmed up. Not many mechanical carbed propane fuel systems start and run perfectly on the first twist of the key, some do, most dont.

Franz

ok ill try 5 btdc, ill be changing the baseplate to a new one but not sure what to buy. i wasnt totally sure how a propane powered vehicle was supposed to start, so it being a little rough till it builds some heat sounds normal. Then i know that much is normal, ill be trying to get it all set up this weekend(weather permitting). id like to get this setup and get the hang of the propane to prove people wrong, guys here say no way it works good and it sucks so far......ill fix that...lol. thankyou, ill let you know what i come up with.

[Frank]

If you have to crank it a lot when it's cold, it could be that the converter is too far from the mixer. You'll get a quicker cold start if you can move the converter as close as possible to the mixer. There are cold-start assist devices available that can help too.

[flatblack]

If you have to crank it a lot when it's cold, it could be that the converter is too far from the mixer. You'll get a quicker cold start if you can move the converter as close as possible to the mixer. There are cold-start assist devices available that can help too.

To move my converter closer id have to fab a bracket that goes over the valve cover, i dont have room on the firewall with the heater box there. Ill try to see what i can do with moving the converter. I have 30 inches of hose and two elbows on each end, that prob doesnt help either. What do they make for the cold start assist, do you even mean cold start assist even when its 80 degrees out or meaning when its cold like in the 30s..?...or when the engine is cold period...? and thanks

[Steptoe]

30 " thats huge..I rem , maybe reading something about being to long throttle response becomes slow???
Keeping the pipe short as possible is a major consideration on any fresh install design.

LPG is no different to changing a petrol engine carb..its actually easier in many ways...very little/nil ...re jetting messing with accel pumps,doesnt exist..still have to reset the sec butterflys and delay for them to come in thu, and timing has to be right.

Timing is critical...think of timing like this.
Out deer shooting, there is a slight cross wind, and the deer is moving.....
get the shot right right lead/height(advance) and the deer drops
Get it a bit off, you have a few hours tracking it down (engine runs ok but ineffiecent)
Get it way off, either wound the deer (runs real rough) or miss all together.(will not fire)

[Frank]

The cold start assists would work whenever the engine is started. To have a better idea of what they look like, download the Impco Catalog and go to page 147. The extra fuel doesn't hurt when the engine is hot but does help when the engine is cold.

The Start Assist Valve (Impco PN SV) provides extra fuel to the mixer when the starter motor is engaged.

The Vacuum Power Valve (Impco PN VPV) provides extra fuel to the mixer when manifold vacuum is low and is probably better suited to Impco mixers as they don't have a built-in enrichment system like the OHG/MM X450 mixers.

Try moving the converter closer to the mixer before buying an enrichment device.