My 77 CJ7 has run for years without any attention, not that I put any great miles on it. This summer it decided it was going to be difficult, so now I have to remember how a carb works, with very small success.
I took it all apart and cleaned it, and blew out the jets. Put it all back together and tried it, no dice. When I come off of throttle, it dies unless I very carefully feather it down to idle. I’m clueless about what’s wrong, and have run out of dead chickens to wave over the necromantic device.
I think it would be less trouble to pull the engine and put in a spare 4.0L I have on the shelf.
When you took it apart and cleaned it, did you put a new carb kit into it? People talk lovingly about the older generation of cars, but the thing they skip over is all the wearable parts. As in parts that are fully expected to just wear out and stop working. There’s tons of them too in old generation cars!
For your case a carb kit would replace all the gaskets, seals, and give you a new needle and seat. This became a kit because all these parts get old and brittle and wear out. Because the carb is a precise device that depends on the vacuum of the engine to operate, any tiny little gasket leak or poorly closing value causes all manor of performance problems.
I didn’t but the carb is pretty low-miles. I might have put 500 miles on it in the 10 years since I replaced the carb. I did blow it all out and cleaned out the float bowl. Maybe I missed blowing something out.
Even without miles, age can make the seals get brittle. Also, have you checked the idle setting? If it’s misadjusted you can have all sorts of odd behavior.
Been fiddling with the idle mix adjustment screws a lot. Doesn’t seem to make much difference.
Yah, I get that age will do it as well, but really 10 years isn’t much for a rebuilt carb unless it was truly subpar materials. But possible I guess.
Been fiddling with the idle mix adjustment screws a lot. Doesn’t seem to make much difference.
That’s usually a sure sign you still have an obstructed pilot or air jet.
Edit: So you apparently don’t have a pilot jet, it’s called an “idle pickup tube” in the diagram below. Make good and sure it and the 2 air bleed passages are clean (there is one pickup tube and 2 air passages per “barrel”).
That’s a very helpful diagram. I was blocking off holes while it hit it with air and trying to figure out what the flow was. I’m going to go over it again with this on hand.
Keep in mind that only shows the idle circuit. But that’s probably where your problem is. Also double check float height if you haven’t.
Float height, you mean? Yah, I did that.
I had a pinhole leak in the diaphragm of one of my two Mikuni carb, and my twin cyl bike would act really weird.
In that case, it wouldn’t evenly provide power with throttle, but just as telling was when I got going and suddenly let the throttle go, the engine would die.
Point is, look at your rubber, old stuff gets destroyed by ethanol, mileage irrelevant.
Hows your anti-stall diaphragm (aka dashpot)? my buddy’s old truck kept stalling coming to a stop, that was the issue with his.
I don’t have one, it’s a MC 2150 but it’s ran for years without issue. It is an auto so you’d think it would have one. But even just sitting still, it’ll snuff itself if I jam the throttle and let it go.
I can’t help with the problem since you’ve covered most of the things I would know about. Last carb I worked on was my beloved VW Beetle, and I understand how things can run fine and then suddenly just stop for no reason. But in the end, there IS a reason, somewhere.
I just commented to point out if it helps, a carburetor is just a mechanical computer. It changes the input of fuel and air based on other variables. So somewhere in the code something is now not calculating the same as it was, or the variables themselves are different. I know that doesn’t answer the problem, but it’s something I’ve always been in awe about since being told my my dad that a automatic transmission is just a fluid computer. Which is funny, since he could tear down one of those, but never could “get” how an electronic computer worked.
I don’t have experience with that carb, but two old vehicles: One was some slime goo had clogged one of the small carb holes. Looked like maybe a rubber gasket had reacted to something and liquified and been sucked into the hole. The other car having the issue you mention was actually a faulty EGR valve getting stuck.
