help i have twin 350 mag carb when i start the portside motor it feels like its running on six cylinders.after running for about ten minutes at 2000 rpm which it won't exceed any way it smooths out and get up to 4800 rpm like it was bran new.if i shut it down for a half hour no problem but over that it goes back to the original problem. i disconnected the choke no diffrence. could it be a valve in the head ?its a quadrajet

ttt

Did you try swapping the carbs side to side? Did you buy these carbs from me? One thing to look at is the little vacuum canister on the side of the carb. Make sure it is actuating when the engine starts. This canister does two things, holds the choke open a predetermined amount to make the engine run good cold, and holds closed the secondary air valve. Other than that, sounds like the float is hanging up or possibly the secondary metering rods are not seating correctly. I'd check out the vacuum canitster though. Sometimes when the rubber vacuum hose or diaphram warm up they will start working.

BT

I had a problem similar to this last year in my small block powered 28 cigarette. It ended up being a hole in my exhaust manifold (Gil) and was trickling water into the #8 cylinder until I got to a high enough rpm to blow it out then it would clear up. But yours doesn't sound like that, just check your oil for water and maybe pull the plugs and see what they look like.

hi bt yes i bought them from you but they are on my other boat and run fine.iwas going to switch but i wanted to eliminate other problems if there are.i might do what dave said after i do a compresion check.
thanks guys

Glad they worked for you Sonic... you had me worried there. Doesn't sound like a compression problem to me. Why do you think that?

BT

BT
i always look at the worst.it could be as you said float or metering rods.
thanks again paul

there is fuel in the oil!!!!!!!!!! whats that mean?

I would say that means that "blue thunder" is probably right in that your floats are stuck or you have dirt in the carbs or something that is carb related. The symptom is usually an erradic idle. I think quadrajets come with some sort of screened fuel filter within the carb. When this happens fuel is dumping into the engine, running past the piston rings, and into the oil system. Once you fix the carb problem, don't forget to change the oil that has become contaminated with the gas and then change the spark plugs because they most likely have become fouled.

Don't run it like that Sonic, you can wreck the ring seal having fuel flushing past like that. Then you will have a compression prob!

BT