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Uneven fuel distribution

J

Jimmy Jakobsson

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Hi! I have done alot of tuning with my Mopar 493 stroker engine, Edelbrock avs2 800cfm, Edelbrock rpm intale, Edelbrock E-Street heads 84cc, Comp cam xe275hl camshaft(231/237@050), 10,04:1 scr, Fbo distributor set at 18 initial and full manifold vacuum brings it to about 30 at idle, 34 degrees full mechanical advance. The engine running pretty good now with no hesitation or stumble, its just some slight misses at idle. I reading my spark plugs and they all looks good, except cylinder 5, 7 and 6 running richer than the others, is this about the rpm intake(dual plane) or what? The engine do not use any oil or anything like that and i have about 500 miles on it from new rebuild, i did a compression test a mounth ago and i have 200psi on all cylinders cold engine. The blackest one is number 7 and the 2 other rich ones are 5 and 6. The whitest plug is how the other 5 cylinders looks like. So the distribution must be uneven. Last time i checked it was number 6 that looked black like the 7 do now so it must be the distribution of fuel
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Swap your vacuum advance to ported and see how it runs. There's no reason for you to have 30° advance at idle.
 
Bill Monk said:
More likely idle mixture side to side. They should be the same on both sides. I disagree with ported vacuum, I run manifold vacuum. I know this is an old debate and all I can tell you is that it works well for me and the logic behind why is sound. You can find it here.
http://4secondsflat.com/Ported Vs Constant Manifold Vacuum.htm
Click to expand...
Im going to check mixture and change to hotter plugs, these are a bit to cold, only 2 threads slightly colored. The engine not running bad, its running great actually with the Fbo distributor, 18 hg of vacuum at idle, i just checked the plugs and see there was uneven colored, 5 plugs looked good and 3 to rich, number 7 really rich so the distribution of fuel must be uneven.
 
Bill Monk said:
More likely idle mixture side to side. They should be the same on both sides. I disagree with ported vacuum, I run manifold vacuum. I know this is an old debate and all I can tell you is that it works well for me and the logic behind why is sound. You can find it here.
http://4secondsflat.com/Ported Vs Constant Manifold Vacuum.htm
Click to expand...

i am running a stroker and the engine is much happier with the higher timing at idle using manifold vacuum. also had a distributor tuned on a machine and that made the difference for me.
 
I don't mean to hi-jack this thread but just had a question about the spark plugs. I am running kind of a similar set up to the OP. My sparks plugs look about the same as the spark plug in the upper left pic. In years past I would have thought that was lean and they should be a tanish color. You can watch 10 videos on spark plugs and get 10 different views of what they should be. I was wondering what everyone thought about that spark plug in the upper left pic whether it is a good color or on the lean side.
 
chargermll said:
I don't mean to hi-jack this thread but just had a question about the spark plugs. I am running kind of a similar set up to the OP. My sparks plugs look about the same as the spark plug in the upper left pic. In years past I would have thought that was lean and they should be a tanish color. You can watch 10 videos on spark plugs and get 10 different views of what they should be. I was wondering what everyone thought about that spark plug in the upper left pic whether it is a good color or on the lean side.
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Hi i wonder about the same thing and nobody seems to have a proper answer, im also running a wideband a/f gauge and that one tells me really rich but by reading the plugs the distibution is uneven, that means if someone just tuning by what a/f ratio gauge say its very possible its running rich or lean in some cylinders anyway and because nobody really dont know how to read the plugs it must be same playing on the lottery to just looking at a A/F gauge. If some of my plugs here really is on the lean side than leaning out the carb more just for make the A/F gauge happy just going to make those plugs even leaner, so it is like a lottery even with a A/F gauge if you not running 8 coils and 8 injectors, one mixture for each cylinder.
 
After another test drive it was number 6 that was totaly black instead of number 7 and still 3 fat cylinders so its not just a single one of them thats running fat so i belive the problem is and i have always belive it that it is the distribution of fuel in this intake that is uneven, maybe its just so that the dual rpm intake not working properly for my combo. Im going to try a street dominator intake, i know the single plane are better for distribution and are more forgiving in the low end on a stroker engine, if it is better for even distribution and i maybe have to give up a few lbs in the bottom end so let it be so, the bottom end is huge on this engine and im not a race driver so i belive im not even notice the different, the engine have more power than i ever use, i want the distribution even and the engine feeling well.
 
I've never heard of an intake manifold that flows unevenly; it either flows or it doesn't. How does that even happen? Debris inside of the runners? You mentioned the engine missing at idle; I would be thinking an ignition problem would be the real culprit here. Are you sure you're getting adequate spark on all cylinders?
 
myk r sanchez said:
I've never heard of an intake manifold that flows unevenly; it either flows or it doesn't. How does that even happen? Debris inside of the runners? You mentioned the engine missing at idle; I would be thinking an ignition problem would be the real culprit here. Are you sure you're getting adequate spark on all cylinders?
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You have never heard about uneven fuel distribution depending on intake/engine combo? Ok than you maybe should try to study that topic some .Why do you think there is alot of different manifolds to fit the specific engine, dual, single and so on. I not believe it myself before i talked to some known engine builders about it and they put me into the topic more. You must have see sometime that one cylinder run leaner/richer than another and now im not talking about only WOT driving. A little reading here in the link, there is alot more about it in different forums and so on
https://www.enginelabs.com/engine-tech/engine/intake-manifolds-single-plane-or-dual-plane/

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the OP states that engine runs fine except for slight misses at idle. if one side of idle circuit is trying to supply whole engine for fuel, might explain the rich bank of plugs depending on how the runners are going from plenum. just my two cents for something to look at. might be something preventing fuel to flow through that idle circuit on one side.
 
Jimmy Jakobsson said:
You have never heard about uneven fuel distribution depending on intake/engine combo? Ok than you maybe should try to study that topic some .Why do you think there is alot of different manifolds to fit the specific engine, dual, single and so on. I not believe it myself before i talked to some known engine builders about it and they put me into the topic more. You must have see sometime that one cylinder run leaner/richer than another and now im not talking about only WOT driving. A little reading here in the link, there is alot more about it in different forums and so on
https://www.enginelabs.com/engine-tech/engine/intake-manifolds-single-plane-or-dual-plane/

View attachment 959167 View attachment 959172
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https://www.trifive.com/forums/showthread.php?t=60876
Heres is a persons experience with a dual plane Edelbrock air gap intake worth reading, there was a few experts involved that have to scratched their heads for a bit.
 
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