Hi all, My first posting here in the HAMB asking for help after reading a ton and trying to make all kind of changes to the float, air mixture and idle. I have had the carburetor off over 10 times now. Really appreciate any help on this as it a bit challenging revving the engine with your hand every time I have to come to a stop The car: 1959 GMC shortbed with original straight six 270, floor starter, 4 speed manual, original drum brakes all around, no booster. Stromberg one barrel carburetor. The problem: The idle speed drops really quick and the truck dies when braking hard. The idle also drops quick when making a sharp left turn a very slow speed but does not necessarily die. It happens at all times no matter if I am on a hill or not, going up hill or down hill. It also happens when going in reverse. Standing still idling is fine and the truck starts right up every time. If I brake down slow it works fine/better. It is as if I hit a bad spot while pushing on the bake pedal and all of a sudden the idle drops. When putting less pressure on the brake pedal after braking slow the idle picks back up but pretty slowly. Sorry for the long description here, just trying to provide as much info as possible. Thanks for any input on this I really appreciate it! -Fred
Look for a va***m leak. That is normally the problem. if it began to stumble and miss I would say that it was a loose electrical connection but first look for a va***m leak. get some starter fluid and when the car is idleing start spraying it around. if you speray it somewhere and it revs up you just found your leak.
Could be a lot of things, including loose screws holding the carb together or to the intake manifold, fuel system issues like pump/lines/filter from one end to the other, wiring problems (yeah, these are fun), misadjustment of the carb, etc.
Did it ever run correctly? If yes, what was the last thing you touched? Go back to that. Stalls at weight shift, Fuel delivery obstruction, check from tank to carb jet including fuel pressure. Jack up side while running while fuel pressure guage is being monitored. Wiggle test the harness while running, check everthing from the battery thru ignition switch to distributor. Too many keys play havock on the ignition wsitch. The added weight act like a pendulum and break contact. You'll find it
On the 6-bangers, I've seen plenty of carbs that needed to be tightened up. The top 1/2 is notorious for loosening up where it attaches to the bottom 1/2. I'll also go with a low float or one that hangs up. Bob
Had a similar situation that drove me nuts. turned out to be warped throttle body. Check the flatness of your mating surfaces & if required, lap the mating surfaces (using a black marker) & check untill perfectly flat. Also good to put a light coating of silicone spray on your gaskets so they don't stick if you need to pull your carb apart.
First, is the intake mated/sealed properly to the head? You know there's rings/sleeves that slide into the intake & head ports both. Sometimes preventing the intake from matting properly. THIS IS VERY IMPORTANT.
Symptoms sound real familiar. A friend of mine had a 66 Nova 6 Cyl, did the same thing. I tore my hair out trying to pinpoint the problem. Get this, it turned out to be a bad ignition switch. John had a ton of keys on his key ring, and that weight moving around acted like a pendulum, shutting off the ignition off when braking. We replaced the ignition switch and cured the problem.
Thanks for all the help on this! I think it turned out to be the carburetor pump. The new one was too short at the bottom and could move too far downwards. I put the old one in and that fixed it. I also adjusted the float a bit and made sure it was properly mated like you all suggested. Thanks 31Vicky with a hemi for asking this: Did it ever run correctly? If yes, what was the last thing you touched? Go back to that. I will apply this to all my work going forward. Thanks! Fred
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