The Stovebolt Site Forums The Parking Lot Big Bolts won't idle, backfires through carb

I thought I had the 409 where it would run again but I can't get it to idle. It will stay running at 2,000 rpms but when I let off it backfires through the carb and dies slowly. When it is running it pops through the exhaust. It's got a new fuel pump and a clear filter so I can see it's getting gas. I don't have any vacuum leaks that I can find. I can't mess with the timing because of the steel governor line from the distributer to the carb. Who's got ideas?

It sounds as if it may be retarded you may have to bend that steel vacuum line a little.
Also how dose the compression seem with the combustion camber being in the cylinder in the 409 it is common for the rings to get damaged by carbon. If you rebuild this motor and have it bored be sure the machinist puts the lip back in the top of the bore for the combustion chamber or your new top ring will drag carbon down into the cylinder casing premature failure.

On any GM, that has a distributor "window"
they are prone to get damp inside. Remove, thoroughly clean and dry the cap. check for cracks, replace it and try again. Keep us posted.

Time it with the steel line disconnected. That is for the govener. Then when you get it right you can reshape the line. If it is too far off the dist may be a tooth off. Have you cleaned out the carb?

I've had this same problem for the 5 or 6 years. It runs just long enough to get out of the driveway, then I usually have to tow it home. I've had the carb apart several times. A couple of weeks ago it was flooding and blowing gas out the top of the back barrels. The rear floats had a little gas sloshing in them so I replaced them. All the lines and filters are new. I've tried to stay away from the timing even though I know most problems that are blamed on the carb are usually electrical. I don't see how the time could have got off. The distributer hasn't been out to get off a tooth. I'll take the governor line off and try advancing it and see if it makes a difference. I can't get it to run long enough to use a timing light. I decided I wanted to show it at our show in town next month and I want it to make there and back under its own power.

How old is your gas? Stale gas will cause symptoms like you describe.

I've run it out of gas several times the past few weeks. This morning I unhooked the line and drained the tank, then put a couple of gallons of fresh in it. I also by passed the cannister filter under the cab, so now it goes straight from the tank to the new fuel pump. The clear filter won't get more than half full but I don't know if it really needs to fill up or not. On top of all that, I think I've about cooked the starter. The battery has a full charge but it won't hardly turn over without the charger hooked up and on boost. Either the solenoid is going or the windings are.
Working on these old things is my only hobby (obsession) and even when I'm stumped it's still better than being at work.

Run a compression check, don't worry about the steel line, it can stay hooked up and bend with the swing of the dist, almost sounds like you have a burnt valve or one stuck open, but try turning the dizzy first.

Mearl: This just came to me after reading your last post. I had very much the same problem with my 64 GMC. I chased this problem for quit a wile even put a new distributor in the truck. This may seem dumb but it turned out that I had enough sediment in the tank that it would block the pickup screen after running a short wile. The sediment would not come past the pickup so the filter was always clean. In order to get my tank clean enough to stop this from happening I had to remove it put about 1/2 a gallon of diesel in it with some clean drain rock and roll it around and empty it, I repeated this multiple times put the pickup and fuel level sending unit back in with some fresh gas and the problem went away. Even if it doesn’t help it not a bad thing to do to an old truck anyway.

I believe I'll try that. I worked at a logging machinery place in 79 & 80 And was sent to fix a Detroit diesel in a skidder that would run for a few minutes and die. I finally ran a temporary fuel line and it ran. Come to find out there was a shop towel on the pick up tube. The guy called back the next day with the same problem, we told him to check the tank again and he found 3 more towels. When we had the skidder in the shop it had no fuel cap and people would stuff a rag in it, apparently it got several stuffed in it. But you're right it acted like my truck does.
I also had to take off my starter today, I thought it would be like the one you asked about on your 64 C-60. Mine is still different, it has 2 mount bolts to the bell housing. The snout of the starter is square (kinda) and the bolts are diagonal from each other.