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Uneven fuel distribution #2780238
06/01/20 03:01 AM
06/01/20 03:01 AM
Joined: Dec 2019
Posts: 138
Sweden
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Mopar493 Offline OP
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Mopar493  Offline OP
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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 somehow. Last time i checked the plugs it was number 6 that looks black same cylinder 7 does now so it must be about the fuel distribution

20200601_083538.jpg20200523_142729.jpg20200523_142242.jpg20200531_171130.jpg
Last edited by Mopar493; 06/01/20 03:15 AM.
Re: Uneven fuel distribution [Re: Mopar493] #2780241
06/01/20 05:26 AM
06/01/20 05:26 AM
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N.E. Ohio
6bblFLASH Offline
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What spark plug are you using?
Looks like cold plug based on the thick base.
Off the wall opinion:
Idle too rich,idling cold.and plugs never cleanup twocents
What type of fuel are you using?

Almost any manifold will wet the the floor at low speed and or cold.
Then depending on shape and angles a couple cylinders are very rich cold/idle...
These issues are why stock stuff has high idle on the choke and heated manifolds.

Last edited by 6bblFLASH; 06/01/20 05:52 AM.

70` Cuda`,440 6BBL Jerico,Dana 4.56 Still on 93 Pump Gas
9.87 @ 136/1.31-60ft.`09 Mopar Nationals PASSON PERFORMANCE "Stick-Shift" Champ!
2013 StickShift Challenge Winner@ Mopar Nationals!
Re: Uneven fuel distribution [Re: 6bblFLASH] #2780254
06/01/20 08:01 AM
06/01/20 08:01 AM
Joined: Dec 2019
Posts: 138
Sweden
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Mopar493 Offline OP
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Mopar493  Offline OP
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Sweden
Originally Posted by 6bblFLASH
What spark plug are you using?
Looks like cold plug based on the thick base.
Off the wall opinion:
Idle too rich,idling cold.and plugs never cleanup twocents
What type of fuel are you using?

Almost any manifold will wet the the floor at low speed and or cold.
Then depending on shape and angles a couple cylinders are very rich cold/idle...
These issues are why stock stuff has high idle on the choke and heated manifolds.

Thank you for your answer! Im running Ngk 6 now, thats one step colder than stock. I have a o2 censor in the drivers side exthaust, the afr gauge is a Aem and by looking at that the engine running a bit rich at idle, betwen 12-13. The thing is the afr reads rich on cruice and wot too, but 5 of the plugs looks really good by reading them and im scared to lean it out more. I have tried to screw in the idle mixture screws at idle but the engine starts to idle bad so i just leave them where i have the highest vacuum. I use same yours 93 octane and in this tank of gas i fill in a boutle of Torco unleaded accelerator to, just for test it.

Re: Uneven fuel distribution [Re: Mopar493] #2780256
06/01/20 08:08 AM
06/01/20 08:08 AM
Joined: Aug 2011
Posts: 2,842
Pattison Texas
CSK Offline
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CSK  Offline
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Originally Posted by Mopar493
Originally Posted by 6bblFLASH
What spark plug are you using?
Looks like cold plug based on the thick base.
Off the wall opinion:
Idle too rich,idling cold.and plugs never cleanup twocents
What type of fuel are you using?

Almost any manifold will wet the the floor at low speed and or cold.
Then depending on shape and angles a couple cylinders are very rich cold/idle...
These issues are why stock stuff has high idle on the choke and heated manifolds.

Thank you for your answer! Im running Ngk 6 now, thats one step colder than stock. I have a o2 censor in the drivers side exthaust, the afr gauge is a Aem and by looking at that the engine running a bit rich at idle, betwen 12-13. The thing is the afr reads rich on cruice and wot too, but 5 of the plugs looks really good by reading them and im scared to lean it out more. I have tried to screw in the idle mixture screws at idle but the engine starts to idle bad so i just leave them where i have the highest vacuum. I use same yours 93 octane and in this tank of gas i fill in a boutle of Torco unleaded accelerator to, just for test it.


A lean missfire will make a plug black.


1968 Charger COLD A/C Hilborn EFI
512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim
2020 T/A 392 Stock 11.79 @ 114.5

Re: Uneven fuel distribution [Re: Mopar493] #2780257
06/01/20 08:09 AM
06/01/20 08:09 AM
Joined: Aug 2009
Posts: 1,314
Ohio
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jlatessa Offline
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Ohio
Not an uncommon problem w/dual plane manifolds,
some times the easy fix is to try a one step hotter plug in those cylinders.

Easy to try and can't hurt anything.

Joe

Re: Uneven fuel distribution [Re: CSK] #2780259
06/01/20 08:16 AM
06/01/20 08:16 AM
Joined: Aug 2009
Posts: 1,314
Ohio
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jlatessa Offline
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Ohio
Originally Posted by csk
Originally Posted by Mopar493
Originally Posted by 6bblFLASH
What spark plug are you using?
Looks like cold plug based on the thick base.
Off the wall opinion:
Idle too rich,idling cold.and plugs never cleanup twocents
What type of fuel are you using?

Almost any manifold will wet the the floor at low speed and or cold.
Then depending on shape and angles a couple cylinders are very rich cold/idle...
These issues are why stock stuff has high idle on the choke and heated manifolds.

Thank you for your answer! Im running Ngk 6 now, thats one step colder than stock. I have a o2 censor in the drivers side exthaust, the afr gauge is a Aem and by looking at that the engine running a bit rich at idle, betwen 12-13. The thing is the afr reads rich on cruice and wot too, but 5 of the plugs looks really good by reading them and im scared to lean it out more. I have tried to screw in the idle mixture screws at idle but the engine starts to idle bad so i just leave them where i have the highest vacuum. I use same yours 93 octane and in this tank of gas i fill in a boutle of Torco unleaded accelerator to, just for test it.


A lean missfire will make a plug black.



I haven't heard of that, how does that darken the plug?
Not trying to be a smart a a$$, just curious.

Joe

Re: Uneven fuel distribution [Re: jlatessa] #2780261
06/01/20 08:18 AM
06/01/20 08:18 AM
Joined: Aug 2011
Posts: 2,842
Pattison Texas
CSK Offline
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it is just an incomplete burn so no heat & the plug can get dirty


1968 Charger COLD A/C Hilborn EFI
512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim
2020 T/A 392 Stock 11.79 @ 114.5

Re: Uneven fuel distribution [Re: CSK] #2780262
06/01/20 08:23 AM
06/01/20 08:23 AM
Joined: Aug 2009
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Ohio
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jlatessa Offline
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How would you diagnose that condition?

Thanks, Joe

Re: Uneven fuel distribution [Re: jlatessa] #2780263
06/01/20 08:26 AM
06/01/20 08:26 AM
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Pattison Texas
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Originally Posted by jlatessa
How would you diagnose that condition?

Thanks, Joe


a four gas analyzer,,,,, just set the idle mixture screws for a smoothest idle with new plugs & see how it goes.


1968 Charger COLD A/C Hilborn EFI
512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim
2020 T/A 392 Stock 11.79 @ 114.5

Re: Uneven fuel distribution [Re: CSK] #2780269
06/01/20 08:46 AM
06/01/20 08:46 AM
Joined: May 2019
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nowhere
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Sniper Offline
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Originally Posted by csk
Originally Posted by jlatessa
How would you diagnose that condition?

Thanks, Joe


a four gas analyzer,,,,, just set the idle mixture screws for a smoothest idle with new plugs & see how it goes.


A much cheaper solution than a 4 gas analyzer is using a colortune.

Re: Uneven fuel distribution [Re: Sniper] #2780271
06/01/20 08:52 AM
06/01/20 08:52 AM
Joined: Dec 2019
Posts: 138
Sweden
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Mopar493 Offline OP
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Thank you guys for all your answer, im greatful for all ideas. Maybe i should try with one step hotter plugs and set the idle mixture for best idle and see how it looks after some driving.

Re: Uneven fuel distribution [Re: Sniper] #2780287
06/01/20 10:01 AM
06/01/20 10:01 AM
Joined: Dec 2019
Posts: 138
Sweden
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Mopar493 Offline OP
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Originally Posted by Sniper
Originally Posted by csk
Originally Posted by jlatessa
How would you diagnose that condition?

Thanks, Joe


a four gas analyzer,,,,, just set the idle mixture screws for a smoothest idle with new plugs & see how it goes.


A much cheaper solution than a 4 gas analyzer is using a colortune.

I have looked at the Gunson colortune and it seems to be a nice product but is not a vacuum gauge good enough for the idle mixture job? And with a 4 bbl carb that feeding 8 cylinders its not so much to do for a single cylinder or a few that running rich. My number 7 spark plug lookes totally black and 5 and 6 are to rich but the rest are good, i just wonder how it can be

Re: Uneven fuel distribution [Re: Mopar493] #2780297
06/01/20 11:33 AM
06/01/20 11:33 AM
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West Coast, USA
jbc426 Offline
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Originally Posted by Mopar493
Thank you guys for all your answer, im greatful for all ideas. Maybe i should try with one step hotter plugs and set the idle mixture for best idle and see how it looks after some driving.


If possible, attach some pictures showing a side shot of your plugs so we can see how many threads are getting colored from the heat etc. Ideally, they should have color down to 3 or 4 threads. I have to run a different heat range on several of my cylinders to get the same thread coloring.

I haven't messed with that type of car before, but 12 to 13 A/F ratio is too rich. Can you lean that out a bit? Maybe by dropping the float level a touch, or altering the jetting?


1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
Re: Uneven fuel distribution [Re: Mopar493] #2780327
06/01/20 12:56 PM
06/01/20 12:56 PM
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Bend,OR USA
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Cab_Burge Offline
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I like to use 14.5 AFR or leaner at idle and part light throttle cruise below 2500 RPM warmed up or hot up
How much mechanical, actual, compression ratio do you have?


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Uneven fuel distribution [Re: jbc426] #2780342
06/01/20 01:59 PM
06/01/20 01:59 PM
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Mopar493 Offline OP
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Originally Posted by jbc426
Originally Posted by Mopar493
Thank you guys for all your answer, im greatful for all ideas. Maybe i should try with one step hotter plugs and set the idle mixture for best idle and see how it looks after some driving.


If possible, attach some pictures showing a side shot of your plugs so we can see how many threads are getting colored from the heat etc. Ideally, they should have color down to 3 or 4 threads. I have to run a different heat range on several of my cylinders to get the same thread coloring.

I haven't messed with that type of car before, but 12 to 13 A/F ratio is too rich. Can you lean that out a bit? Maybe by dropping the float level a touch, or altering the jetting?

I have no good picture of that, maybe you can see on this one but it is about 2 threads slighly colored. But by leaning out the carb more going to make the good cylinders running to lean, or have i wrong here?

20200601_195345.jpg
Re: Uneven fuel distribution [Re: Cab_Burge] #2780351
06/01/20 02:15 PM
06/01/20 02:15 PM
Joined: Dec 2019
Posts: 138
Sweden
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Mopar493 Offline OP
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Originally Posted by Cab_Burge
I like to use 14.5 AFR or leaner at idle and part light throttle cruise below 2500 RPM warmed up or hot up
How much mechanical, actual, compression ratio do you have?

The compression ratio is 10,04:1, pretty mild cam for the cui, 231/237@050, i have 18 hg/inch of vacuum at idle in park at 900 rpm, snap the throttle the gauge needle drops to 5 and bounces back to 25 and then go back to 18, the needle slightly floating within a half hg at idle. Im thinking that leaning out the carb more makes the 5 good plugs to running lean, like i said there is a rich condition in only 3 cylinders so the distribution must be uneven. Its strange, 5 plugs lookes really good and 3 to rich and the afr shows to rich, how can it be?

Last edited by Mopar493; 06/01/20 02:18 PM.
Re: Uneven fuel distribution [Re: Mopar493] #2780373
06/01/20 03:10 PM
06/01/20 03:10 PM
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jlatessa Offline
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On a dual plane, it is sometimes difficult to get all cylinders equal. Runners differ depending on the design.
Some try jet staggering with mixed results DAMHIK.

Some times you just have to go the easy way and mix heat ranges
to get a good plug color, it's not blasphemy.

Joe

Re: Uneven fuel distribution [Re: Mopar493] #2780391
06/01/20 04:16 PM
06/01/20 04:16 PM
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Bend,OR USA
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I like the looks of that plug up
I would lean down the thicker step on the primary metering rods by .002 to .004 and see if it drives good and makes the plugs run cleaner at part throttle cruise or not.
I'm assuming you don't have a lot of choices on where to buy or get Carter or Edllebrock metering rods in Sweden so I hope you can find some like I'm suggesting, don't change the bottom step if you can twocents
If you get a set of rods like I'm talking about drive the car enough to warm it up without getting on it hard , drive it easy and then check the plugs, listen or feel for detonation or pinging, if you hear it or feel it let off the off of the throttle and put the old rods back in it as soon as you can twocents wrench

Last edited by Cab_Burge; 06/01/20 04:19 PM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Uneven fuel distribution [Re: jlatessa] #2780421
06/01/20 05:07 PM
06/01/20 05:07 PM
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Posts: 138
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Mopar493 Offline OP
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Originally Posted by jlatessa
On a dual plane, it is sometimes difficult to get all cylinders equal. Runners differ depending on the design.
Some try jet staggering with mixed results DAMHIK.

Some times you just have to go the easy way and mix heat ranges
to get a good plug color, it's not blasphemy.

Joe

Thanks, i will try it

Re: Uneven fuel distribution [Re: Cab_Burge] #2780422
06/01/20 05:08 PM
06/01/20 05:08 PM
Joined: Dec 2019
Posts: 138
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Mopar493 Offline OP
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Originally Posted by Cab_Burge
I like the looks of that plug up
I would lean down the thicker step on the primary metering rods by .002 to .004 and see if it drives good and makes the plugs run cleaner at part throttle cruise or not.
I'm assuming you don't have a lot of choices on where to buy or get Carter or Edllebrock metering rods in Sweden so I hope you can find some like I'm suggesting, don't change the bottom step if you can twocents
If you get a set of rods like I'm talking about drive the car enough to warm it up without getting on it hard , drive it easy and then check the plugs, listen or feel for detonation or pinging, if you hear it or feel it let off the off of the throttle and put the old rods back in it as soon as you can twocents wrench

Thanks, i will try and see how it goes

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