345 v8, 727 trans, new summit racing brand carb (spread to square conversion). Mostly stock. Was running beautifully. Drove about 70 miles and realized I was down a cylinder when I came to an idle at a stop light. Pulled plugs (see picture) and realized that it looks like I'm running both Rich and lean at the same time. Those plugs are sitting in order. I'm thinking maybe I have an intake leak? Any thoughts? I've never seen anything like this before.
Running on seven?
- Thread starter OSUBEAVER
- Start date
Scout-It-Out
Member
Maybe it's the picture but they all look lean to me.
What size carb?
Is the engine all stock?
If your new carb has a choke, you can manually close it a little and see if the engine smooths out. Also if you have an ir temp gun you can check exhaust temp. At each port. You could also take it to a smog shop and ask them to sniff it. (with the machine) that would tell you if it's Rich or lean.
What size carb?
Is the engine all stock?
If your new carb has a choke, you can manually close it a little and see if the engine smooths out. Also if you have an ir temp gun you can check exhaust temp. At each port. You could also take it to a smog shop and ask them to sniff it. (with the machine) that would tell you if it's Rich or lean.
Scoutboy74
Moderator
While two of the electrodes appear darker in color than the others, they don't look fuel fouled or even that sooty. From those four I'd say you're more lean than anything else.
Robert Kenney
Super Moderator
First the clean plugs look fine especially if you were running at cruise power settings. They are usually lean of stoichiometric during cruise on emissions applications. If you don't experience any surging or running issues leave it. If you don't mind playing with your jetting fatten it up 5% in cruise and see if you pick up throttle response. Only one way to get reliable plug readings. Fly down the road at what ever range you are interested in checking for 5 + minutes and immediately kill the engine. Coast to a stop and pull the plugs. Any time idling will ruin the plug readings. 3/4- wot readings need 30+ seconds at normal operating temps to get any kind of good readings on a street engine
as for the 7 cylinders firing, do a compression check. You May have also possibly spit a push rod.
Does it seem to smooth out under power like in gear and loaded? Could be a fouled idle fuel circuit.
as for the 7 cylinders firing, do a compression check. You May have also possibly spit a push rod.
Does it seem to smooth out under power like in gear and loaded? Could be a fouled idle fuel circuit.
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Besides the carb and rebuilding certain things to factory, yes the engine is stock. This is a 600cfm summit racing carb that I have jetted down. My primary is 62, secondary 67. It seems to run steady w/o any surges.
What really intrigues me is that every other cylinder is that ash gray on the electrodes, and the others are black.
Scout-it-out: good idea, I will check to make sure the electric choke is functioning properly.
Robert: it does smooth out in gear and loaded. Is there an easy way to do a compression check, or would I need to take it to a shop (I have basic tools only).
Thanks for helping me everyone, I'm signed up for the Binder Bee and want this thing running top notch for it!
Here is the carb I have on it if anyone is interested:
summit racing sum-m08600vs - summit racing street & strip® carburetors - overview - summitracing.com
What really intrigues me is that every other cylinder is that ash gray on the electrodes, and the others are black.
Scout-it-out: good idea, I will check to make sure the electric choke is functioning properly.
Robert: it does smooth out in gear and loaded. Is there an easy way to do a compression check, or would I need to take it to a shop (I have basic tools only).
Thanks for helping me everyone, I'm signed up for the Binder Bee and want this thing running top notch for it!
Here is the carb I have on it if anyone is interested:
summit racing sum-m08600vs - summit racing street & strip® carburetors - overview - summitracing.com
Robert Kenney
Super Moderator
You already have the plugs out and that is half of the battle. You need a compression tester which you can borrow or rent from one of the major auto parts chains. Disable the ignition (no sparking. Remove the - point to distributer wire. Crank the engine with the ignition switch or get a remote starter switch.
Hold the throttle open and crank for each cylinder till the pressure reading peaks. I like to attach a battery charger to the battery while I do the test so the battery will have a better chance of maintaining a consistent cranking potential.
Log your readings and post them so we can see and help.
Hold the throttle open and crank for each cylinder till the pressure reading peaks. I like to attach a battery charger to the battery while I do the test so the battery will have a better chance of maintaining a consistent cranking potential.
Log your readings and post them so we can see and help.
Robert Kenney
Super Moderator
That would be cool if it was as simple as that!
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Take a look at your manifold, half the cylinders are fed by one side of the carb, the other half by the opposite side of the carb, every other one. Makes it a pain to tune a carb with a sniffer as you get a bit of both barrels. Your carb is not adjusted the same on both sides. That will explain the different colors on your plugs, however the misfire I can not help you out with.
FDChappie
Well-known member
On both of my carbureted IH rigs, water in the fuel will cause fuel not to flow in one of the idle circuits. An easy check for this is to see if the mixture adjustment screw makes a change to the idle. The one with no response is the problem side. A shot of carb cleaner down the affected carb bore will cause the engine to run smooth for a moment and also confirm the problem.
On my rigs one solution is a full throttle run through the gears.
but that doesn't always do it. A quart or 2 of denatured alcohol in the tank will cause any water tank to emulsify/mix with the gas and flow through the carburetor.
The reason this happens is that water has a higher surface tension than gas and will not flow easily through the small orifices in the idle circuits. In a well tuned carb the loss of the additional fuel from the idle circuit can cause surging during part throttle.
On my rigs one solution is a full throttle run through the gears.
but that doesn't always do it. A quart or 2 of denatured alcohol in the tank will cause any water tank to emulsify/mix with the gas and flow through the carburetor. The reason this happens is that water has a higher surface tension than gas and will not flow easily through the small orifices in the idle circuits. In a well tuned carb the loss of the additional fuel from the idle circuit can cause surging during part throttle.