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When I first start it when it is cold it runs fine at idle.But when it gets to normal temp. it starts running rough at idle. When I step on the gas it react like it should with no problem. The same at speed no problem. It is a weber carb. The hitachi I had on it before did the same thing. It has a 1/2 Inch hard rubber gasket between the manifold an the carb. Just wondering if it has a vacuum leak.

Yep... sounds like a vacuum leak. If it turns out that it isn't, it could be that the carb has some dirt pugging up a jet in the idle circuit.

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Previous setup: 4.1 Buick V-6/TH 350
Current setup: 400 Small Block Chevy V-8/TH 350
9" ford rear end/short bed/blue
What do Water, Electricity and Humans have in common... They all travel the path of least resistance.

I don't know what year truck you have, but it could be a smog control of some kind that is opening when the eng. is warmed up and creating a vac. leak.

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OK, I'm over it. Where's the beer?

Mine is doing the same thing and this is what I have boiled it down too.
-I know that the webers fuel pressure is regulated at 2.5 to 3PSI. The pressure recieved by the Hitachi is 4.5PSI.
-I bought the pressure regulator today.

-Also the hitachi came with a granite plate to help with heat.
-The adapter plate doesnt have long enough screws to use the granite plate. will be looking for screws tomarrow.

-Reason to use granite plate... The weber gets real hot and begins boiling the fuel. the fuel becomes insufficient there for not actually providing correct gas to the intake. (MAKING HIGH RISE CARB) You should have a heat gaurd as well.

I let you know if this corrects my problem.

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1974 stock engine
New: Accell Coil/Accell Plugs/Platinum Wires/Pertronix Pointless System/Fuel Pump/Weber 2Barrel Downdraft/ES3000 Explorer Pro Comp

If the power brake diaphram is leaking or the EGR valve doesn't seat, you'll have that problem. The vacuum spark advance diaphram, too.

If it were a 76 or newer, I'd suspect the EGR valve or the vac lines to it. There is a thermal switch that opens up at operating temperature to allow the EGR valve to work. I forget exactly how it is hooked up on the 75 and older motors though. Pull the vac line to the EGR at the carb and plug the port on the carb. If that gets it running right you'll know where to look.

Or if you want, smack the E.G.R. valve with a hammer 1 or 2 times. If it's stuck open, it wont matter if you have a vacuum line to it or not.

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Previous setup: 4.1 Buick V-6/TH 350
Current setup: 400 Small Block Chevy V-8/TH 350
9" ford rear end/short bed/blue
What do Water, Electricity and Humans have in common... They all travel the path of least resistance.