I have a couple of hundred miles on my rebuild and this problem just doesn't seem to be going away. The problem's not as bad as it used to be when the carb had been sitting for 18+ months unused.

If I'm cruising along at about 2k RPM (40 mpg in 4th gear) on a slight hill I am getting a stumble and an occassional pop (backfire?). The timing should be right unless I didn't set it the right way. You don't need to unhook anything do you when doing the timing? I've put some fuel system cleaner and even some Heet through thinking I had water but there wasn't much of an effect. I seem to have decent power despite the altitude and it seems to decently otherwide.

Any hints would be appreciated! <img src="/forums/images/graemlins/cheers.gif" alt="" />

so after it sat for that long did you rebuild the carb? that may be a good idea, I have never let a car or truck carb sit that long but I had that same problem on a motorcylcle I had after sitting through a winter. I rebuilt the carb and replaced the fuel filter and it was back to normal, sounds like your problem resides either there or in your timing. where did you set it to? I know my manual calls for something like 10 degrees before TDC.

Mine used to do that, and it was always when it was under load climbing a hill. Then one day it quite completely (on a hill of course). A mechanic found the coil was shorted out. New coil and the problem was fixed for good.

Did I rebuild it? What do I look like, a sadist?? <img src="/forums/images/graemlins/scared.gif" alt="" />
No, it just sat in a bag. I suspect it might be the carb, but from what I've read that's a pain to rebuild. Maybe I'm wrong?

Timing's set to 7? BTDC. At least it was. I suppose it's worth checking it again. I did pass my emissions, so that was a good sign. <img src="/forums/images/graemlins/kewl.gif" alt="" />

I can definitely check the coil. My manual says it needs to be clean and dry to work correctly, and it's quite possible it's got some grime or is going bad.

Thanks for the tips!

That is what my 90 LWB is doing too!....and I dont even have a carburetor!

From every thing you describe, i would say it is ignition related. Check wires, coil and distributor cap for carbon tracks. If you know anyone that has an oscilloscpe, the problem can be pinpointed.

Or a lean condition will cause a backfire......

You could try and read the O2 sensor with a volt meter under cruise. And yes check the ignition too. Make sure the mechanical advance s not sticking while you are at it.

Kevin

Yes, but it will be lean at other speeds also. not just when under load in overdrive. Reading the O2 during the misfire will tell you nothing as when there is an ignition misfire, there is a rush of oxygen which will lead you to believe the engine was running lean.

When my ECU was going out in my Raider, it would sputter and backfire under load around 35-40mph. Then I would let off of the gas and let it idle and it would do fine until under a load again. Pull the codes from the ECU using a volt meter. Look in the Tech section. That is funny that the ECU will give you a constant "beat" if it is ok, but a "flatline" if dead. <img src="/forums/images/graemlins/lol.gif" alt="" />