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Discussion Starter · #1 ·
We're stumped. We have a nicely built 351w runs strong except for some "pinging", "knocking", or what ever you want to call it. Here's what I have:

650 mighty deamon carb
edelbrock air-gap intake
afr 185 63cc heads
flat top alum pistons
flat tappid cam, w/ mech lift
msd ign and distributor
10.6:1 comp
approx 14-16 initial timing
32 deg advance (wanting 36)
running 91 octane w/ octane booster

As the engine gets fully warmed the detonation seems to increase. It is primarily below 3000 rpm when under a load. We then decided to pull plugs and look at them. We found the #5 and #6 plugs were wet and not the chocolate color of the other 6 plugs. When the engine does miss or hic-up, it does seem to be on the drivers side exhaust (which also has the most black soot in the side pipe).

We have yet to pull the valve covers and check valve train, including lash.

I'm sure there is something else you guys will need to know that I'm not telling you so any help and/or suggestions would be appreciated.
 

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You have way too much timing. If I read your thread correctly, you have 48º total timing. You should have no more than 34-36º
 

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Discussion Starter · #4 ·
No, we only have a total of 32 at this time. The distributor is retarded back to about 12-14 at start-up. We want to have 36 when all is correct.

Yes, it can have vacuum advance. We are running mechanical at this time.
 

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Try this

Raise your intial up to around 16. Back off the throttle screw to where it idles mostly on the timing. Stay under 1k idle. If you have to put more timing into it, do it.

Now adjust your Air Fuel screws. They are going to be more responsive when the throttle screw is backed out as far as you can go. You'll get a more acurate mixture, you should notice this right off when adjusting again.

Im guessing your too rich at idle and lean out with throttle input. Hence the popping noise.

I say too rich and heres why. If your trying to get the car to idle by adding throttle instead of timing. Your adding to the total fuel being dumped into the intake. Your Mixture screws will be toward the lean side because of the added fuel.

Unless theres a bigger problem, im guessing timing may be the root cause.

16 degrees is not alot. Think of the vacum advance adding 10-12 degrees to a base of 6 degrees.

Then again, Im probably wrong.
 

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They are putting a lot more ethanol in fuel right now-that might have something to do with your pingng. I had the same problem with a 327 with 11.1 forged pistons recently. I ended up changing the pistons out to 10:1 because it even started detonating on flat roads while under very mild acceleration. Ut never did that before even when i had 11.5:1 compression ratio with domed pistons, so i assume it has something to do with the quality of the gas in the region that you are located.
 

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Hi,
Did you retorque your intake?
Mike
 

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First I would drop down to a coldest plug possible before I did anything else. Start to increase your heat range after you get the misfire taken care of. Scrutinize your plugs closely for heat. From the description above it could be both ignition and burn, why take the chance?

Check the carbon ball condition inside the cap, material buildup on the cap posts, and the rotor condition. Also look for cross firing in the cap, check the mag pickup wiring +/-, temporarily reroute your distributor pickup at another location to the box, check those two particular wires resistance, and rotor phasing last. I've had quite a bit of luck wearing out the cap ball and would check it first.

How fast are you pulling in your advance? Some motors don't like it coming in at lower revs. Double check your springs and see where your at on the advance curve.

All the advice above too.
 

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What spark plug are you running? heat range?
Since only 2 plugs are wet I would check plug wires to be sure there not open or shorted.
What is your idle speed when having 14* initial timing?
What is the rpm when you have your total sdvance?
May have timing advancing too fast,along with the 2 dead or weak cylinders thats causeing the problem. Popping from exaust is the 2 bad cylinders.
Can you supply a vacum reading?
 
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