[camaro man]

Under light to normal driving the motor has a slight mis to it, more noticeable if you hold the tranny in gear. It starts around 1800 rpm and goes away as you build up the rpm over 3000. When you get on it a little or even at WOT the motor runs fine. It was time for a tune up anyway so I have installed a new cap, rotor, plugs, adjusted the carb, valves and the timing and it still misses. The plug wires are near new with less than 1000 miles on them. I have not ruled them out yet. I'm running a MSD ignition system. Any idea's? Bad gas? It's been doing this since around the time I took it out of storage, but I'm not sure If it actually started when I took it out. It might have started shortly after. I'm still on the first tank of gas since storage.

[BreathWeapon]

Are you sure it isn't a slight ping like what I am having right now? Same symptoms anyway. What you might want to try is adding some octane booster to your existing fuel, then top it up with the good stuff and see if it smooths out a bit. If so, it might be a timing advance problem like what I have, and I am working on that with the help of others here to hopefully solve the problem.

[CFunK]

Bust out the ohm meter and check the wires. I had a similar symptom and it turned out plug wire 6 was toast.

[gm torch red]

i had the same problem, it turned out to be a bad plug. and it had less than 300 miles on it. hook your timing light to each plug wire, one at a time, and watch the light blink and see if it misses.

[camaro man]

I checked all of the plugs with the timing light and the all seem to be firing right. I also checked the plug wires with a ohm meter and they all were O.K.

[RickD]

Try looking at the wires in the dark while the car is running to see if you can dtect any cross firing or leakage. What did your old plugs look like? At cruise you're under light load, max vacuum (if you have vac advance) and running alot of timing.

[camaro man]

My distributor is a MSD mechanical advance. The timing is correct At 36 degrees. I added a sump to the gas tank this winter. I washed the tank out good. I check my screen type fuel filter yesterday and I found a few small metal pieces in it. If some small pieces of metal made it through and into the carb (quick fuel 950) could it get stuck in the carb and cause a slight lean type problem till the secondarys start to open?

[camaro man]

I had my carb gone through and there was some small metal flakes in the carb. I put the carb back on and I still have the same problem. I switched carbs and put on a Holley 750 on and the problem was gone. Now I have to have the local speed shop go through the carb again.

[CFunK]

Thanks for the update camaro_man. So it does indeed sound like a carb issue?

Post back with the end result.

[camaro man]

The speed shop tested the carb on a 350 ci motor on a dyno. They could not reproduce the problem. Now I'm lost.... I will be putting my carb back on later today and I'll try it out again. If I still have a problem I think I'll be looking for another speed shop. If it works fine then it's time and I'll still be looking for another speed shop.

[BreathWeapon]

Hmmm.... maybe just a mildly lean condition; can you richen 'er up a tad?

[camaro man]

I put the carb back on and I still have the same problem. The shop is telling me that it's common with the type of carb. They say that at low rpm the carb is starving for air till the throttle plate opens more. The also said that they could send the carb somewhere and have the metering blocks modified to fix the problem. $100.00 to do it. I didn't have this problem last year, they said I should have had the problem from the beginning. If what they are saying is true then it makes me think if switching from a AN-6 fuel line to a AN-8 fuel line could have brought this problem to the surface. I think I will still consult another speed shop.

[camaro man]

I took my car to another speed shop. They took my Quik Fuel 950 off and put a Holley 850 on it and it ran a little better. Since it still wasn't right I started working on it again a couple of weeks ago. The new shop adjusted each of the air fuel mixture screws 1 turn out. I decided to reset the carb air fuel mixture screws to the suggested factory starting point (1 1/2 turns out). The motor almost died. I screwed them back in till the motor seemed to run best and they are now set at 3/4 turns out. Currnetly the motors is running better than either of the shops could do, but it's still not smooth like last year. Over the winter I upgraded the fuel system. I added a sump to the factory tank and moved from -6 an fuel line coming out of the factory pickup tube going to the pump to -8 an line from the sump to the pump. I aready had -8 an line from the pump to the carb. The pump is a mechanical Carter 120 gph preset @ 8 psi. Now I'm wondering if upgrading the fuel line the pump has caused the motor to be running too rich. I appears to me that the smaller the carb and the leaner the mixture the better it runs. Since there is more fuel now getting to the pump could the pump be over powering the needle and seat in the carb and forcing more fuel into the motor? One thing that lead me to think of this was that I installed a liquid filled fuel gauge before the fuel log and the gauge would drop in pressure as the motor warmed up. It would go from 8 psi to 1 psi after the motor was hot. I replaced the gauge and the same thing happened. The roughness of the motor also seems to be more noticeable after long WOT runs. The plugs that I changed from last year were a little black, the tailpipe is very black and powdery. The tailpipes angle downward behind the rear tires and will leave black rings on the driveway while the motor warms up.

I have been thinking about installing a regulator with a return line after the pump to bleed off the excess pressure and gas.

It seems like a lot of regulators have 3/8" npt fittings. Is -8 AN id the same as 3/8 npt id? I was thinking -8 AN was 7/16".

[Joekool1234567]

AN fittings go by 16th of an inch. 8 is 8/16 or half an inch, 6 is equal to 3/8". As for the engine problem, mabey you just made the common mistake that most hot rodders make and you over carbed the engine. I had a proform 750 DP on my camaro and while it did make a ton of power gas mileage sucked and anything beside WOT and idle the engine just didnt run its best. Now I have a 3310 on there and while WOT performance is lacking every other aspect of engine performance has increased ten fold. Sometimes building an engine for ultimate preformance means you have to deal with odd driveability issues that usually cant be resolved unless you "detune" the engine some to make it liveable on the street.

[camaro man]

I fired up the motor for the first time a year ago last march and the motor purred like a sowing machine all last year with a jetted out Quick Fuel 950 cfm carb. Since upgrading the fuel line the motor hasn't ran smooth at low rpm and I have two gauges that say the fuel pressure is dropping off as the motor warms.

Can't seem to find a 3 port regulator with a fuel return and 1/2" NPT fittings.