Flathead doesn’t idle right

[Flathead86]

Hi guys, I am lost, I’ve tried everything and can’t get my flathead to idle right, it’s spitting from the exhaust, like a soft back fire, I’ve tried Adjusting my timing, can’t really adjust my dual carbs bs of this issue, what you think might be the problem, any advice would be great? Thanks

[petehoovie]

Sticking valves....Drizzle some MMO down the carb at fast idle (out in the sticks someplace) and add some to the gas tank....

[Flathead86]

[QUOTE=petehoovie;1883510]Sticking valves....Drizzle some MMO down the carb at fast idle (out in the sticks someplace) and add some to the gas tank....[/QUOT

It’s a fresh engine built,

[petehoovie]

It could still be a valve hanging up or maybe its that nasty cam you put in it....

[Flathead86]

Originally Posted by petehoovie

It could still be a valve hanging up or maybe its that nasty cam you put in it....

What about the cam, it’s a race cam, form h and h flatheads?

[petehoovie]

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"race cam"? Race cams don't idle like a stock cam....they don't idle so smooth
Tell us about the build and the cam....

[Flathead86]

Originally Posted by petehoovie

"race cam"? Race cams don't idle like a stock cam....they don't idle so smooth
Tell us about the build and the cam....

It’s 80 over, Navarro heads, bubbas gmc distributor, dual 97, adjustable lifters, what else would you like to know, the cam is 3/4

[my4dv8]

We need to know exactly the specs of the cam . Just a race cam from H&H is not sufficient info. How does it sound when sped up to say 1800 rpm??

[Flathead86]

Originally Posted by my4dv8

We need to know exactly the specs of the cam . Just a race cam from H&H is not sufficient info. How does it sound when sped up to say 1800 rpm??

I can’t really hear the engine right with it spitting like that, but it’s sounds nice,

[KiWinUS]

https://youtu.be/SXvnDP25924
Bryan he needs one of these cams
Cheers

[KiWinUS]

I suggest a leak down test or at least a compression test. Have you double checked valve lash.

[Flathead86]

Originally Posted by KiWinUS

I suggest a leak down test or at least a compression test. Have you double checked valve lash.

All 8 cylinder have more than 100psi I haven’t done a leak down test yet but that’s my next step,

[KiWinUS]

Look at plugs if they are black & sooty that will cause your issue. Carbs or too much fuel pressure could cause plugs to be this way.
Have you asked Mike at H&H for his opinion.

[Flathead86]

Originally Posted by KiWinUS

Look at plugs if they are black & sooty that will cause your issue. Carbs or too much fuel pressure could cause plugs to be this way.
Have you asked Mike at H&H for his opinion.

My plugs are black, but I can’t adjust my carbs with this problems,

[Flathead86]

Originally Posted by Flathead86

My plugs are black, but I can’t adjust my carbs with this problems,

Mike told me it could be carbs, or timing but I feel my timing is right and I just rebuilt the carbs,

[KiWinUS]

Okay if plugs are black there’s a carb issue but there’s no adjusting of idle screws that will fix it. Carbs build correctly with correct fuel pressure should not soot plugs no matter where idle screws are. Start idle screws 3/4 to 1 1/4 turns out both same. Them black plugs won’t fix themselves. Need to glass bead or replace or will continue to misfire.

[Talkwrench]

Carb leaking down ..?

[chap52]

I would close down one carb totally and see how it runs on one carb. Then get a uni-sync and go through the dual carb sequence. Worked for me years ago with a 3/4 cam, dual 94's. Chap

[Flathead86]

Where would you guys have your timing at? Considering it has a race cam?

[tubman]

On a modified engine, I use a vacuum gauge to set initial timing. Get it as close as you can, and then adjust the timing until you get the highest vacuum reading at idle. Then retard it just a small amount and you should be all set.

You're not done yet. This will produce the correct timing at idle, but really has nothing to do with timing at higher rpm's. That depends on the advance curve in the distributor. That is another subject entirely.

[flatjack9]

Does your distributor have a vacuum advance cam? An engine with a more aggressive cam generally needs more initial advance. I would say in the 6 - 8 degree range. But this may give you more advance than needed at higher rpms.

[Flathead86]

Originally Posted by flatjack9

Does your distributor have a vacuum advance cam? An engine with a more aggressive cam generally needs more initial advance. I would say in the 6 - 8 degree range. But this may give you more advance than needed at higher rpms.

No It doesn’t, this might be stupid question which way on the distributor is advance?

[tubman]

We need more information; Early (front-mounted) or Late (conventional "post"type"). If the former, it should be set up and timed on a machine intended for that purpose. If the latter, CCW to advance, CW to retard.

[Flathead86]

Originally Posted by tubman

We need more information; Early (front-mounted) or Late (conventional "post"type"). If the former, it should be set up and timed on a machine intended for that purpose. If the latter, CCW to advance, CW to retard.

It’s a later motor with the distributor on the side of the motor,

[KiWinUS]

What distributor are you using? Stock is a bad choice

[Flathead86]

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I got it from gmc bubba from the forms?

[tubman]

Originally Posted by KiWinUS

What distributor are you using? Stock is a bad choice

Especially if you are not running a bone stock carburetion system.

And who does that with a "hot cam"?

If the distributor is from "Bubba" it's most likely a modified SBC unit. Is it mechanical advance only or vacuum over mechanical?

[Flathead86]

Originally Posted by tubman

Especially if you are not running a bone stock carburetion system.

And who does that with a "hot cam"?

If the distributor is from "Bubba" it's most likely a modified SBC unit. Is it mechanical advance only or vacuum over mechanical?

I wish I could understand what does this mean, I am confused on this distributor,

[tubman]

Most modern distributor have two methods of advancing the spark timing. There is a set of internal weights that move outward when the speed increases that causes the timing to be advanced as engine speed increase (this is called the "mechanical advance"). In addition, they usually have a vacuum advance unit that also advances the ignition timing as manifold vacuum increases. Vacuum is highest at engine idle and steady cruise, and the additional advance it adds to the mechanical advance provided by the weights serves mainly to increase fuel economy. In periods of low vacuum (acceleration), the advance is limited to that provided by the mechanical advance only to prevent detonation under load.

Just about all SBC distributors come with vacuum advance. You can tell because they have a vacuum line running from the intake manifold to the advance unit on the side of the distributor. The attached picture is not very good, but you can see part of the vacuum advance. It is the round silvery-gray unit at the back of the distributor. I mention this only because I believe "BUbba" is kind of a fan of mechanical only setups so it may have been removed from your distributor.

[Flathead86]

Originally Posted by tubman

Most modern distributor have two methods of advancing the spark timing. There is a set of internal weights that move outward when the speed increases that causes the timing to be advanced as engine speed increase (this is called the "mechanical advance"). In addition, they usually have a vacuum advance unit that also advances the ignition timing as manifold vacuum increases. Vacuum is highest at engine idle and steady cruise, and the additional advance it adds to the mechanical advance provided by the weights serves mainly to increase fuel economy. In periods of low vacuum (acceleration), the advance is limited to that provided by the mechanical advance only to prevent detonation under load.

Just about all SBC distributors come with vacuum advance. You can tell because they have a vacuum line running from the intake manifold to the advance unit on the side of the distributor. The attached picture is not very good, but you can see part of the vacuum advance. It is the round silvery-gray unit at the back of the distributor. I mention this only because I believe "BUbba" is kind of a fan of mechanical only setups so it may have been removed from your distributor.

It does not have a vacuum like the picture,

[KiWinUS]

You have a very good distributor. I doubt it is creating your sooty plug issues. You will always have misfire with sooty plugs.

[Flathead86]

Originally Posted by Flathead86

It does not have a vacuum like the picture,

Attach are pics. It’s dark in my garage so I couldn’t take good pics, my plugs have been replaced and still have the problem at idle,

[KiWinUS]

If you have excessive fuel running into engine from just one or both carburetors could cause your misfire at idle.
Because you have plug fouling issues I personally believe it’s a carburetor problem.

[tubman]

Originally Posted by KiWinUS

If you have excessive fuel running into engine from just one or both carburetors could cause your misfire at idle.
Because you have plug fouling issues I personally believe it’s a carburetor problem.

If this is the case, I think this might be a good time to install a stock manifold and run each carburetor separately to get a better handle on it.

Also, since the distributor seems to be mechanical only, I'd go with my first suggestion for timing.

[Flathead86]

Originally Posted by tubman

If this is the case, I think this might be a good time to install a stock manifold and run each carburetor separately to get a better handle on it.

Also, since the distributor seems to be mechanical only, I'd go with my first suggestion for timing.

Ok, I think I know what might be my problem, one of my carb doesn’t shoot as fuel out of two port, as my other one, I am thinking it could be my power valve,

[KiWinUS]

Power valves must function correctly & be sure you used the correct gasket for power valve.. could very possibly be your issue.
cheers Mate

[tubman]

After all of this, we are missing one important piece of information. Has this engine ever run well? It sure sounds like a fresh rebuild that you can't get to run right. Unlike the pros ("RonnieRoadster" in particular), most of us have a problem getting a new engine up and running with multiple carbs.

Do yourself a favor and beg, borrow. or steal a known good stock intake system.