IMPCO 100 too lean idle circuit and load

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jono
Posts: 346
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

IMPCO 100 too lean idle circuit and load

Post by jono » Wed Feb 24, 2016 4:17 pm

now that I think about it, may even be a copy of a 100

bought it new some years ago, used it once to test it in place of a 125

it ran too lean on idle yet drove well, could not fault it without an analyser up the tail pipe

fast forward to now - has been installed on similar vehicle and engine Subaru 1800 cc OHC EA81 - all pretty factory, no special cam just using a manifold of twin Hitachis for its nostrils.

Still idles too lean, so lean you'd swear wind was blowing up the tailpipe reader VANE AFR807WB - is going off the scale at idle stationary.
starts no worries, set timing at 14 DBTDC instead of factory wetrol 8 DBTDC

The idle adjust screw is now wound all the way in tight to max rich, power valve about midpoint and drives quite nicely, cleanly cruising around desired 15.5:1 on cruise, high 14's on hard acceleration on level road.

But, if the revs are not up high region and I boot it, goes to high 17 or low 18 lean and bogs down on the flat or even load it to go up inclines
So, have a lean idle which really needs sorting before the rest of it can be tuned.

If I tickle the throttle to keep the mix under 17:1 it pulls well and increases speed up inclines

What I have not told you yet is that I am running an L converter in prep for a turbo conversion to run the L and a 200.
Am wondering if the little 100 is struggling to entice fuel from the L converter the problem more than the lean condition of the 100 ?

Have read posts in here where some have said they have no problem running 100 series mixers off L converters ( there may have been a turbo in their applications and same or smaller engine capacity
any ideas, experience ?
My immediate plans are to pinch a known god 125 from something to try - see if it has troubles pulling fuel from the L, or to try a known 200 mixer that was working on an 1800cc engine just it had a turbo to speed up the fuel supply

the mixer is too lean for starters - never experienced a new mixer being so off the mark in mixture !


C3H8
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Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: IMPCO 100 too lean idle circuit and load

Post by C3H8 » Thu Feb 25, 2016 5:58 pm

This is a very common problem with the 100 (125) and 200 (225) series mixers. During my days as a distributor we sent several cases of 100 and 200 mixers back to IMPCO because they were too lean at idle. New stock arrived with the identical condition. We gave up on returning it as futile. It was a waste of shipping time and money.

The first action you have taken already. You turned the idle screw all the way in to limit air getting past the air/gas valve.

The next item you need to check is for any shimming rings that might have been installed. Remove them if they are there. These are installed under the solid ring under the diaphragm. Installing them lowers the gas valve further into the vapour outlet and leaning the mixtures. This was a common practise on forklifts to reduce pollution from idling FL in the warehouses. Installing shims also caused the cruise mixtures to be leaner.

The next thing to do. While you are checking for the shims make sure you mark the solid ring prior to removing it. These are stamped out by a metal press by the thousands likely. The ring (spacer) can have a slight concave shape that is not even visible. A couple of thousands of an inch. When reassembling just flip the ring over and sometimes this will make a difference.

Third the air bypass channel gets its bypass air from above the gas valve. Try blocking the channel as air gets past the screw even when it is turned all the way in.

That's the standard changes you can look for without actually modifying any section of the mixer that is irreversible.

An easy richening procedure is to take the spacer ring, set it on a steel surface such as an anvil, and using the ball on a ball peen hammer tap along the inside diameter of the ring. This will cause the ring to concave slightly. You have to be very careful as too much and there is little chance you can reduce the concave. Err on the side of caution and install the ring several times to get the idle mixtures right. Install the ring with the concave up causing the set position of the gas valve to be higher. If you were to pre-set the idle screw at 1 to 2 turns out and get the mixtures close at that point it would leave adequate adjustability to richen or lean the mixtures from there. Be aware though that this will change your mixtures during acceleration, cruise and WOT. The WOT is adjustable with the power valve so that is not a problem. If you find you concave the ring too far by only a little amount you can use shims to lean it out or replace the ring and start over.

There are a couple of other possibilities but I would prefer not to go into those as they permanently change the mixer requiring a brand new mixer if done incorrectly.

jono
Posts: 346
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: IMPCO 100 too lean idle circuit and load

Post by jono » Sat Feb 27, 2016 6:26 am

thanks C3 for the good comments. I had a sneaky suspicion that it had a light idle for fork use, but did not think it would have a leaning ring from new, but maybe so - I need one for another application and had run out so would be a useful find if there is one. Am doubting the after market hand flows and marks the diaphragms but if they have may find a useful number to quote for a richer or just try my other options first. Be easier just to buy another mixer by IMPCO this time, and maybe the 125. Maybe some thread tape on the idle screw to see if that can be riched up a tad - you are right in that having a possible fuel leak - quite a coarse thread they are uhuh ?

I am glad I found this was a lean unit on another car at a time that was convenient to me and not in a rush I am likely to put self in soon :)

OK so you are encouraging a slight spill over of the diaphragms seat by a slight buckling of the seating 'washer' - good thinking

I gues could also try using a fine number drill hole so some fuel can escape bypassing the washer. Be almost no harm if it did not work, tap and plug hole up - almost a throw away if it not work right ....

jono
Posts: 346
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: IMPCO 100 too lean idle circuit and load

Post by jono » Sat Feb 27, 2016 5:52 pm

Image

my guess is this would be a possible culprit - the outer ring is not machined , or not machined with greatest accuracy and sports a few lips, see the shiny bits ? Surely this is just a spillway for air to seep over and into the fuel delivery stream as it is simply a similar track that the idle screw air would take. Wouldn't you think as the fuel seat gets great care during manufacture that this seat would get same diligence to getting a perfect seal ?
I may be able to scrape a knife blade accross it without damaging the fuels dam wall machined surface and see what I can achieve.There is no leaning ring to remove C3.

C3H8
Posts: 1000
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Location: Winnipeg, Canada

Re: IMPCO 100 too lean idle circuit and load

Post by C3H8 » Sun Feb 28, 2016 10:10 pm

Ok, so no leaning ring.
The lip you indicate is an interesting thought but this does not really control the fuel delivery volume. You obviously have it apart. Visualize the metering rod (bullet) fitting down into the opening in the vapour outlet in the picture. Note that the bullet gets larger the farther you draw it out of the opening. Also note the bullet has three ways of increasing fuel flow. At idle the widest area of the bullet is the area still in the opening. To richen or lean the idle mixture without turning the air bypass screw the bullet has to be lifted further (richer) or inserted further )leaner) into the opening. The opening is a very precise measurement. This is where the shims work as they are only .003 inches thick. Moving the bullet up or down causes a change in the mixtures. Unfortunately you don't have any to remove. As I stated a minor change in the deflection of the steel ring will change the mixtures as it changes the idle position of the bullet in the vapour outlet.

In drastic cases we corrected the idle mixtures by lightly sanding the inside upper edge of the vapour outlet. This enlarged the gap between the wall and the bullet allowing more fuel to get past the bullet with the same amount of lift. This required extreme caution using a fine emery cloth and taking apart of the mixer to test the fuel mixtures. Removing to much material and the mixer became scrap metal because there is no way to reverse it.

I don't think grooving or sanding the lip you are pointing at will change anything although I cannot be certain. I've never tried that. The same amount of fuel will still be available between the vapour outlet wall and the idle portion of the bullet. Also changing that wall height in any way may lower the bullet further into the opening making the mixer even leaner.

I hated having to do any of these things that permanently changed the mixer. It should not have been required. My preference was the reshaping of the ring because it was easily replaced if we got it wrong.

jono
Posts: 346
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: IMPCO 100 too lean idle circuit and load

Post by jono » Sat Mar 05, 2016 4:46 pm

Still yet to test after my blade scrape.

Thinking a slight nick in the top of the inner fuel ring might add fuel to needed rate, add another nick to increase rich :)

Got a new IMPCO 125 in transit for me now, see if that is any better, forgot to order the 'bell' so may need to borrow from another application.
The n need for a bell of the 100 variety is why I went 100 in the first place !!

jono
Posts: 346
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: IMPCO 100 too lean idle circuit and load

Post by jono » Tue Mar 15, 2016 5:27 pm

OK, the blade scrape does not seem to have done anything, or enough. The next trick will be to try flipping the marked :) washer and see if that is enough.

Then, have tried gas thread tape on the adjust screw but it did not stay with threads to get to internal hole block. May try closing it on some electrical tape held in place

Am also considering just making the smallest nick in the top of the metering body that faces the diaphragm to bleed some fuel in, increase the nick until I get idle right. Also picked up a new 125 - the real stuff this time - IMPCO so got another diaphragm to borrow :)
fuel use on a tank of some hard test driving returned 375km 41. something litres . Possibly the best I have got from one of these 1800 cc flat fours on gas :)

jono
Posts: 346
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: IMPCO 100 too lean idle circuit and load

Post by jono » Fri Mar 25, 2016 4:54 pm

just an update - suspecting that the 100 may have been struggling to pull fuel from the larger spec L converter on an 1800cc 8 valve boxer - cobbled up a 200 to replace the 100. The 200 previously ran fine on another 1800cc boxer just it was more twin port inlet ( one port per pot instead of one port per 2 pots) and turbo - runs better, but still has a milder flat spot/ hesitation type bog if I floor it - so not look like the lean idle of the 100 the cause of the hesitation /bogging .

Reckon I get the lean reading because the converter is just too hard to pull instant fuel change needs out of it from the 1800cc.

I have bigger issues with this engine - despite fitting new valve stem seals to the heads when they were off - this baby draws oil from somewhere on downhill runs. Not likely to be valve guides. The poor thing sat for eight years as a newly installed used engine complete with a warranty melt disc displaying sellers confidence it would outsee the warranty period - it did just under 30 miles in eight years. Its intake valves copped black sticky gunk from either old oil or old fuel or fuel stuff stick to sides of tank - caused bent push rods also :(

Again, not such a worry as ute was purchased with a turbo engine transplant in mind. The donors organs laying about the place already ....

jono
Posts: 346
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: IMPCO 100 too lean idle circuit and load

Post by jono » Sun Mar 27, 2016 5:49 pm

but with this in mind it still does not stop my curious tinkering - getting the odd dead spot in making traffic turns in second gear - still not tail pipe analysed mixtures (so serves me right :) ) but gosh, if I just tramp it in most situations the little ute goes as quick as it can shove me along the road :)

jono
Posts: 346
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: IMPCO 100 too lean idle circuit and load

Post by jono » Fri Dec 01, 2017 3:42 am

yeah, here we go. This is my post from some time ago when I ran a 100 mixer and got results above.

Now, more recently I tried the 100 on similar engine, same capacity just better breathing and could hardly start or run it, so I upped it to the 200 off the L converter and even though mixtures are great, fuel consumption is not - must be me taking advanttage of the induction roar and the fact this engine revs out a grand or two more.

Had an idea this week, to try the 100 off the L without a balance tube. same result, actually , worse. Could not start it.

So, I bunged a 125 on with and without a balance tube and she starts, runs and drives.
Now the 100 and 125 are so close in spec its not funny, yet so different in results!

Wont be buying plastic adapters again either, dont know my own strength :(

jono
Posts: 346
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: IMPCO 100 too lean idle circuit and load

Post by jono » Sat Dec 09, 2017 8:06 pm

On my na 1800 cc flat four revs to 6500 have tried lots of combos of converters and mixers and still get some lean flat spots, back off until mix Richens to about 17:1 and she takes off again

Running an L converter with a 200 was most fun, intake roar fantastic

Run the 200 off the Cobra J did not get same induction roar

100 could not even run off the L this engine

125 off the L converter not much remembered

100 of the Cobra J very quiet, lean idle 16.5 fully screwed in but pleasant to drive but leaner than stoich most of the time

125 off the Cobra J is best driveable but not as good as have had in the past with same engine and others similar

Then this morning disconnected the 5/16 balance tube.

I think it is more driveable no flat lean spots as yet

The Peel indash mixture display is indicating a more normal reading from the O2 pre-cat position.

Time to tune it again from tailpipe and see what I get.

Maybe a despise for the old faithful balance tube!?

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