Noticeable miss at mid-throttle

[BiltByMe]

I'm running a 350 with a MSD StreetFire distributor, Weiand dual plane intake and Holley 650 double pump carb. At idle the truck runs alright but there is a very slightmiss that you can hear if listening closely. I cant blip the throttle without it bogging hard and I don't believe its a problem with my advance. Im thinking a vacuum leak at the intake since i never retorqued the bolts after my break in period of the engine. The miss is very noticeable about 2500 rpm and there is a slight lurch that I can feel while driving. I've also seen fuel stains on the outside of the intake that would indicate a leak in the top of intake manifold but I've got the carb mounting nuts well torqued on top of a new gasket so I don't know why there would be fuel there.

[garyd1961]

The fuel stains may be gas boiling in the carb. You can try an insulator gasket under the carb if that's what it is.
How do you have the vacuum advance hooked up. Do you have the vacuum advance restrictor plate hooked up. If not you probably have too much timing advance.

[YoungPup1977]

Newly rebuilt engine.... is the carb new ?
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[Mike C]

I'm a broken record with this, but most carb issues are ignition. Most likely you have a plug, a wire, the cap, maybe the rotor, etc. that is whacked. It's firing MOST of the time, or some of the time. But fix that and most likely (never say never, right?) your carb issues go away.

[BiltByMe]

Originally Posted by Mike C

I'm a broken record with this, but most carb issues are ignition. Most likely you have a plug, a wire, the cap, maybe the rotor, etc. that is whacked. It's firing MOST of the time, or some of the time. But fix that and most likely (never say never, right?) your carb issues go away.

That's what we initially thought. I used a timing light to check that I have spark on all cylinders and it all checked out. Now I'm not positive on whether each cylinder is firing every single time it should be and I don't know the best way to check that but with the timing light on the signal was staying in constant rhythm with engine rpm.

[geezer#99]

Did you check your timing when you had the light on there?

[YoungPup1977]

check the exhaust manifold for temp. see if each exhaust manifold port is the same temp....

firing order is 18436572
check to make sure you do not have 5 and 7 swapped and/or on wrong.......

I may have missed something here, but can anyone add to what has been done to this vehicle lately ? What work has been done lately ?

my 2 cents...good luck !!!

[BiltByMe]

Originally Posted by geezer#99

Did you check your timing when you had the light on there?

yes i did check and it was right on the money from where I had previously set it. I don't remember now exactly what it's set at off the top of my head but I do know it hadn't changed.

[geezer#99]

We need to know what your initial timing is.
And pics of the fuel leakage on the intake will help.

And what Cam?

[Chevyrestorerman]

New engine that you just broke in ? No idea what you put the timing at and you think its a intake gasket leaking....

Good Luck !!!!! I do like the 5/7 plug wires swapped idea mentioned above.

[Wrenchbender Ret]

Try driving it with the vacuum hose to the dist. disconnected & pluged. Like Gary says, Sometimes too much advance can cause a surge at part throttle.
George

[Chevyrestorerman]

What was the issue on this thread, so many of these threads go out to space and never resolved. Hate for someone doing a search and they read thru these threads and they go no where. i must be the only one that happens to.

[68gmsee]

Originally Posted by Chevyrestorerman

What was the issue on this thread, so many of these threads go out to space and never resolved. Hate for someone doing a search and they read thru these threads and they go no where. i must be the only one that happens to.

Nope. Happens to everyone. I see that a lot in other forums also.

I've always encouraged everyone to please post a resolution whenever possible to help others with the same problem. Doesn't matter if there wasn't a resolution or if it was something simple. It's nice to know what happened.

[Chevyrestorerman]

Originally Posted by 68gmsee

Nope. Happens to everyone. I see that a lot in other forums also.

I've always encouraged everyone to please post a resolution whenever possible to help others with the same problem. Doesn't matter if there wasn't a resolution or if it was something simple. It's nice to know what happened.

Are you the forum cop, just wondering who is the WHO on this forum....are you the one to go to for issues ?

[68gmsee]

Originally Posted by Chevyrestorerman

Are you the forum cop, just wondering who is the WHO on this forum....are you the one to go to for issues ?

We call them moderators. And no, I'm not a moderator. Just someone who has experienced what you mentioned above where a posted problem has no resolution.

If you have an issue about something go to the specific site and at the very bottom there should be a member moderator. You could send them a private message.

Correction... Not every forum has a moderator at the bottom. Best to click on Forums above and on the right is a column that shows the moderators.