Hey everyone,

New thing for me today. Nice spring day hanging in the 70's. So decided to take her out. I get about 15 yards down the drive and the motor makes a sound simular to near wot then dies. I start it up and it does the same thing again. So I start it again and back it up and put it in the garage.

Engine starts and idles fine.
The symptoms:
1 rev engine in neutral and release throttle engine drops down to approx 200 rpm or so, knocks like crazy then speeds back up to normal idle or dies.
2 sounds like a small knock between #1 & #3 can't really pin it down though if I advance it a bit a degree more I think it goes away or the rpm change masks it.
3 vacuum is around 8hg. I found one leak at the carb and took care of it. I sprayed all around the carb and manifold and found nothing else.
Last time I had checked it(roughly 2 weeks ago) it was right at 14hg and gently rocking with the cam.
4 Some popping in the exhaust when cold then fades off.

Cupping the carb horn stalls out the motor so I believe at least all exterior leaks are gone.

Nothing had been done to the motor since last time I ran it.
I've checked the fuel filter and removed some garbage. I had cleaned the bowls last time I timed it and removed anything that was inside.
I disconnected pb and closed that port, no change in hg.
idle responds to a/f screws. they are 1.5 turns out

engine specs:
327 .040 over
.465/.465 lift .224/.224 @ .50 on a 114 installed straight up.
holley 670 street avenger .69's in front .72's in secondaries.
Pv is a 6.5
timing is msg 6box with 6883 dizzy set at 16btdc

I've got not a clue as to whats going on how bout you guys

This sounds fuel related to me. You said you had crap in the filter and carb. I would check the filter again. It could also have gummed up the sock in the tank. I would hook up a fuel pressure guage and see if the pressure drops under load. An easy try would be to shoot some air through the fuel line from the intake side of the pump back toward the tank. It will blow any crap off the sock and sometimes things will be fine for awhile, until the sock gets plugged again anyway.

Update:

Switched to my 750vac secondary carb and played with timing. Runs a bit better. Vacuum hanging around 9-10 and steady. Pulled the tank, the sock is ripped and letting trash by. Not sure if it will solve the issue, but will have to wait and see monday or tuesday when I can get to NPD and pick up a new sock. So, guess I'll just clean the tank and paint it.

Disconnect the line at the fuel pump and blow it out good with air in case there is junk laying in there. I think you just might have taken care of your problem.

Well, new sock on sending unit, new fuel filter. This didn't solve the issue either. Raising rpm and trimming back the idle to keep from diesling. Made it somewhat better. Vacuum at 9hg now and not improving any. Through in a 4.5 pv still no difference. May be over carbed now with the 750 as when I remove the vacuum line to the dizzy the motor speeds up. May have to try it back again with the 670 and see if there is any difference that way. That will have to wait for tomorrow.

If the engine had 14" of vacuum before and only 9" now, a manifold leak somewhere, leaking fuel, or late valve timing, I would think.

Not sure.. Started it up today and sprayed starter fluid all over it and nothing. Shot a tad at the carb and it bogged right after. Pulled the line off to the dizzy and she actually spead up. So I'm sure this carb is big for it with the present cam. I'll retry the 670 tomorrow and see how she acts with it. I picked up new cover gaskets today. So I can recheck the valve lash and see if anything has changed.

Have you checked the spark plugs. At this point, I would check the plugs and do a compression check while I was at it. Something happened to cause that vacuum to drop that much that fast. If you have headers, you could do the crayon check. Start it up and rub the crayon on each header tube close to the head and see if they are all heating at roughly the same rate. I would closely check both 1 and 3 since you said there was a ticking noise there.

Have you checked the spark plugs. At this point, I would check the plugs and do a compression check while I was at it. Something happened to cause that vacuum to drop that much that fast. If you have headers, you could do the crayon check. Start it up and rub the crayon on each header tube close to the head and see if they are all heating at roughly the same rate. I would closely check both 1 and 3 since you said there was a ticking noise there.

Well will have to try that in a couple of days then. Reset timing mark after relocating TDC (was off by 4*). Reset valve lash though nothing seemed to shift at all. Letting the gasket sealer finish setting between cover gaskets and heads then will put the covers back on. Probably get the covers back on tonight then pull the plugs thursday after work.

Let you know what I find out then.

Didn't feel like waiting so went out and buttened it up.. Started her up and she melts a crayon a good 3-4 inches out from the heads on the headers on all 8 tubes.

The crayon trick sounds like you are getting adequate fuel and spark at idle. That is a good sign. Do you have a gas smell in your engine oil? Maybe check the fuel pressure to see if maybe there is a crack in the diaphragm or junk stuck in there. When you put the 670 back on try plugging all of the vacuum ports and see what happens to your vacuum reading. If you do have good fuel pressure, the vacuum stays at 9, and your compression checks out, I am stumped.

Compression check of a couple cylinders shows ______?
Low compression, compared to an earlier check, would show late valve timing.
Vacuum reading at idle is presently 9 in., Vacuum reading at more rpm?

Well, today changed out the fuel pump and the line from the pump to the carb. No change.
Rev the engine and vac raises accordingly.


Pulled all lines off of carb and capped. Oddly enough vac went up to 11. Went wot and let off and she went back to a normal idle.:o This is strange as I had pulled everything the other day and it had no effect. Soooo, I change out the hose to the brakes reconnect everything start it up and hit it....... went right back to normal idle. So, not really sure if it was the hose, or perhaps that the seal on the powerbooster was just a hair cockeyed and was causing a minute leak. I still need to pull the 750 off and go back to the 670 as when I pull off the vac line to the dizzy it still speeds up. At least she's running right again. Just to bad I couldn't get it straightend out last night.. Today was a perfect day to drive to work and back as it only made it up to 75* today. Now I'll have to wait til' this weekend to drive and monday to scoot it to work.

Thanks for the input, guestimations and head scratchings.:yes::yes::yes:

So perhaps the findings show that there were possibly two leaks that reared their heads at different times.

Good job! I am really glad you got things going your way finally! Are you running your advance canister to a ported or manifold vacuum source? I have the best luck with manifold.

Have always run it to manifold.