477 BBC HIGH RPM MISFIRE
 

I have been fighting this for long enough... 477 BBC Dart pro 1 heads, Roller, 13:1, BG 400 pump (new), Quick Fuel 1050 Alch, MSD Distributor ignition.
Between the 1 -2 shift the car started popping slightly, steadily got worse. EGT was reading high. Put larger jet in carb. Kept getting worse as time went bye. Don't race alot so a few weeks go bye between attemts to cure. Thought it was a fuel delivery problem. Ordered new BG 400 pump and 4 port reg. Installed but no cure. Got up to almost 200 jets and still had hot EGT temps. Winter came a I said I'll see you next year.
Ordered new valve springs and installed. Went out today and problem still there. Any other things I am missing? I am probably looking over the problem so don't be afraid to mention some silly questions at this point.

Thanks in advance.

What kinda fuel pressure ?

Also when you were putting bigger jets in the carb was the egt going higher or lower ?

What fuel ya use ?

I have 8 to 9 lbs of fuel pressure. When I started changing jets, The EGT did not change or got worse. I am i at 1335 degrees and only running 1/8 mile.

Sorry. I use V/P alch.

changing jets didnt move the egt at all ? I assume you checked the float level already ?

Which VP fuel the normal m1 or m5 ?

Yes float levels been checked. I guess M1 on the fuel.

increase the fuel pressure some and see what happens, could be a bad gauge and be lower then actual ?

Did that. Put a second gauge on it and it is set now just before it runs past seat.

what high side chip does it have in it ?

Set to 7600. But now I can't even get to the shift point to make it shift it pops so bad. Shift point is at 6500.

Have ya tried a new chip in the shift side ?

Also it misses at no other point just before shifting ?

I keep coming back to this one ...
tell me more about the carbs your trying ? 1335 is likely the cause of it, thats very high. How about a vacuum leak ?

No. It is not even clean in the water anymore. I just talked to the engine builder to verify the springs I put on. I purchased this car turn key. I don't know exactly what cam is in it. I matched up the springs and purchased a set of K-Motions. He told me he was not a fan of them but he would pull the sheets and make sure the ones I had are o.k.
The carb is a Quick Fuel Alch 1050 Dominator. He also said I may have it too rich and the heat is from the fuel burning outside the exhaust ports now and giving me false readings on my EGT. The problem is that I can still build heat fairly easy and I do not have a lean out valve. I have checked for vacuum leaks and I do run a belt drive vacuum pump.

Go down to 6 1/2 or 7psi. Change the jets back to 180 squared, and try it.
At 8 or 9 psi your possibly misting fuel into your plastic vent in your bowl. With a BG 400 it can maintain 6 1/2 psi. 200 jets are way to big in my opinion.
Go down to 6 1/2 or 7psi. Change the jets back to 180 squared, and try it.

[quote="bajaboat32"]
The carb is a Quick Fuel Alch 1050 Dominator. He also said I may have it too rich and the heat is from the fuel burning outside the exhaust ports now and giving me false readings on my EGT. The problem is that I can still build heat fairly easy and I do not have a lean out valve. [quote]


The quick fuel alky carbs are a far cry from a good one, they are a weird deal to get right. Back the jet way off (180 like dparker said) and see what it does if that egt goes down you know, if it goes down some keep going with it. Remember egts arent "perfect" but once ya figure them out you can keep tuning to them. Where are you idle screws set at ?

If you have the wrong springs (springs for 750 lift cam 770) it could cause a issue like this also.

Good point guys.
Yesterday I started out at 164 front 176 rears. Car was bad. Popping very bad. EGT was High. I went to 180 front 188 rears. Car was better, Still popping. Did not make a full pass. Got out of it and EGT was 1129. So I went to 192 square, Still popping bad and EGT was 1330.

What MSD ignition?
Whats the plugs gapped at?
What plug wires?

what was egt with 164/176 ?

1295 degrees

Have you checked your distributor gear? Had one with a lot of wear and it wouldn't make it to the shiftpoint and popped like crazy.

Re: 477 BBC HIGH RPM MISFIRE
 

I'd probably go back to electrical. Check your distributor cap to see how it looks inside, maybe miss firing at higher r's and under a load.

Has the car always had a miss since you bought it? Have you added any new electrical extras to the car? See if you can find someone that has an MSD tester you can check the whole ignition system with out running the car and can eliminate components without buying unneeded parts. I went through a similar thing last year. Nearly pulled my hair out. Found out it was my 12 volt fan inside the car i would use when its hot out.

Some times you have to go back to the basics....
I was thinking the same thing. Go back to the ignition system, quit concentrating on valves or fuel delivery. Went down to the shop and popped the cap on the dist. and the center coil electrode is burnt flush with the bottom of the cap. The center tab on the rotor looks like it has been pretty hot also. Just got back from the parts store with new ones.

Won't be able to tell completely until we go back to the track this weekend but I think this may have had a little to do with the misfire problem. I will keep you posted and I truely thank you for all of the replies and direction that you all have supplied me with.

Steve

Try a different BOX!!! A friend had a 7AL3 that did that and they kept saying there was nothing wrong...we put it in my car and it did the exact same thing...hooked to the same wires as my box was hooked to. He got mad and bought a new box and the problem was solved. Hooked it to the same wires the other was hooked to. That was 7 years ago still no problems...it was a bad box...don't care what MSD said.