78 -- 120 -- 120 -- 120

Re: 123 --124 --120--122

Petel

You have given me a list of things to go with, so I will check it out. I operate each of the intake valves while I had the valve cover off and none of them seemed to be abnormal. I am starting to lean towards the "lean fuel mixture" line of reasoning and plan on checking it out. Like I said, right after I adjusted the valves, the thing ran great. I accelerated it several times and no stutter, no backfire, nothing the way it shouldn't be. I let it reach normal running temp and ran it some more and then all of a sudden, this started. I will just have to take all possibilities, one at a time, and see what works.

 

Re: 123 --124 --120--122

I am mostly guessing, based on your description as "backfiring" and assuming you really do have fuel ignition going on in the intake manifold.

If on the other hand, it is actually just stuttering and stumbling from a lean mix, that would be a lot a lot easier to understand.

 

OK, here is what I have done so far. I have adjusted the intake valves to spec so I have the second set of compression readings which are now good (123--124--120-122). I have run the engine with the valve cover removed so I can watch the intake valve action and they are working fine. The rotators are working well, too. Interesting to watch them in action. The jeep idles smoothly as silk. No missing at all on any cylinder. I can push the accelerator and it runs smoothly until I get to about 2000 rpm or so and then it starts spitting and backfiring, BUT it also backfires out of the muffler, now. I have put a timing light on the timing mark and it advances when I accelerate. How many degrees should it advance?

I have also put the old distributor back on the engine just to make sure it was not something to do with the new electronic distributor, and I still have the same issue. Before doing so, I pulled the points and condenser plate out and checked the centrifugal advance mechanism, cleaned and lubricated it. I burnished the points and set them at spec. (Just to make sure I have the right spec, what is the gap?) The plugs and wires are new, so I don't think they are an issue.

I would assume a lean mixture in the carb could cause a backfire problem, too. I have been running the engine with an oversized fuel filter between the gas tank (which is also new) and the carb inlet. I doubt that anything got into the carb from this side of things. So what part of the carb should I look at, or would I be wasting my time with this? Can a lean run mixture cause backfiring?

Also I haven't looked at the exhaust valve adjustments, which I am going to do anyway, but I was concentrating on the intakes because of the backfiring through the carb. Can an out-of-adjustment exhaust valve cause this? I would think it would be unlikely at least.

Looking to the brains in here for an answer...

Thanks...

 

Timing should be 5º btc at idle, with 10º to 12º maximum of mechanical advance, at about 1700-1900 rpm, depending on the distributor. From my FSM.

You do have a FSM don't you?

 

I have a sheet with all the engine specs on it, but I couldn't find anything on the amount of advance. I probably need to get an FSM. Do you have a link and a estimate on cost?

 

Couldn't say where the best source is today, got mine forty years ago. But probably any of the jeep parts vendors, ebay, or Amazon.

I understand some of the recent reprints have poor photos, and it would be very important to find one with good pics. Maybe such as a used or NOS older reprint.

 

Reprint FSM just sold on ebay for under $10.

 

Didn't somebody post a link for the FSM downloadable in pdf form just a month or two ago?