running lean

[terzmo]

340 motor with mild cam/msd ignition. Demon carb ran like crap so I bought a 750 proform...double pump. Running lean as plugs are gray to white. Original jets were 74/80(primary,secondary) Changed to 78 and 84...#1 and 2 plugs are gray...and 7 looks just about right as brown,bordering on black. (performer intake) Ran car at idle and sprayed intake with carb cleaner and besides being much cleaner, I saw/heard no leaks or increase/decrease in idle.

I can up the jets some more but would like all plugs to look like #7

air jets also need changing ? timming ? outside of a manifold leak,why the difference in color from #1 and #7 ??

Thanks to any in advance...

 

[70rr-brian]

Are you running any lead additive? That crap they sell today will leave tiny white speckles on your plugs. Perhaps that is what you are seeing? Although not seeing consistency on all the plugs is a bit odd if you were running additive. Nevertheless a 750 I would think would be almost too much carb for a 340 with a mild cam.

You stated the demon ran like crap....how does the new carb run? The same? I would think a healthy MSD ignition on a healthy motor would make all plugs look pretty good. Maybe just for fun do a compression and leakdown test to see if anything is going on inside there.

 

[terzmo]

the proform runs great...and actually, the previous person was running NGK4...somthing and had them gapped at almost 060. I installed champion 12YC and gapped at factory specs. No fuel addiive.....I placed My hand over the carb at idle and it stalled instantly so I'm pretty sure a vacum leak is not happening. Thanks for Your thoughts

I also had two 493 strokers and the first ran extremely rich and the second one ran normal. Both had the same 950 proform carb(blew the first one up....few to many RPM's)

also as far as running...it starts almost instantly cold or warm and with the proform it feels like I gained about 50 ponies...not a 12 second car but definetely woke it up.

 

[Meep-Meep]

When you say mild cam what are we talking here? Lots of overlap will cause low vacuum, which could dilute the fuel charge at idle. What you may be seeing with the different color plugs is fuel distribution issues.

 

[terzmo]

no ideawhat cam...in before purchase from estate auction...appears to be a fuel distribution issue as 1 & 2 are gray...#7 is brown to slightly black

 

[godfatherofchry]

you are doing the plug reading after a hard flat out run arn't you ?? just asking...........Artie

 

[hendo0601]

Artie is correct in asking that. You will need to clean the plugs up, start the engine and let it warm up to operating temperature then do a flat out balls to the wall blast, then shut the engine down and check the plugs. Checking the plugs after just letting it idle wont give you an accurate reading. If you are really wanting to get technical and get some hard numbers you can have your local muffler shop weld an o2 sensor bung into each headpipe and install a wide-band o2 sensor and read them with a laptop. This will tell you if you have one bank running lean/rich etc. It is kinda overkill but it works. I am sure that you are not new to the game based upon your previous posts, but even the most experienced mechanics sometimes forget to go back to the basics...treat the problem and not the symptoms and only change one thing at a time. I have been a professional mechanic for over 12 years now and I still have to remind myself to do that.

Let us know what you find/change and how it comes out! I am curious about this one!