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machine gun back firing - no power

Over the past 7-10 days I have been loosing power with my '83 258 engine to the point where it is difficult to drive and keep running. It feels like I am pulling a trailer, and I am getting rapid machine gun style backfiring through the muffler when I get around 2000 RPM. It has 215,000 miles so it is a little tired anyways. It felt like the timing had slipped, like possibly the timing chain had slipped, but when I use a timing light the mark is still in the ballpark of where it should be, so I don't believe that is the case. I re-adjusted the timing using only a vacuum gauge to get the max vacuum and it now idols better, but I still get the machine gun type back firing when I get over 2000 RPM.

A few months ago I replaced the valve cover from a plastic cover to an aluminum cover to stop the constant oil leak I was having. In the process I swapped the valve bridges with the non-bolt style bridge since they were not needed any longer. When did replace those I torqued them down, and used the original nuts.

The vacuum advance is still moving properly and has been well cleaned.

Any ideas what is going on? My first idea of timing seems to be more or less ruled out. I am now leaning towards one of the rocker bolts has come loose. Any other ideas of what to look for or check?

83 CJ-7

258 I-6 engine

MC2100 carb

stock and original distrubutor

Reply to
Rusted
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Bad distributor cap? There are a bunch of bad caps and rotor sets out there. The rotors are too short so they work for a short time, then arc out all over the place.

Oil drip onto the coil power connection or loose almost broken wire there?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
Reply to
Mike Romain

Also a longshot, but a very weak valve spring will show these symptoms as well.

Chris

Reply to
c

Add plug wires to that.

Earle

Reply to
Earle Horton

I was hoping that you would respond. The cap is approx 4 months old, I will replace cap and rotor tonight to see if that changes anything. cool call. There is oil all over the palce in that motor, I will try to engine clean it as well to see if anything changes or I can see anything.

Reply to
Rusted

Close, but not yet. I took off the distributor cap to see a ball bearing on top of the distributor. The top of the cap had come uncrimped and the parts had fallen out. New cap and rotor later and I have much more power, but I still get the machine gun effect at 2000 RPM.

I have not cleaned the coil yet, but will do that the next time I get a minute. Other ideas??? Being a natural pessimist I am thinking that I need to remove the valve cover and check that the bolts that hold down the rocker arms have not worked loose.

Side note. When I ask for rotor they always ask if it is a manual or auto. There are different part numbers. The rotor for the auto is about 1/8" shorter than the rotor for the manual for some reason. I think that the short rotors you speak of are probably the parts guy grabbing the wrong one.

Reply to
Rusted

I am now wondering if this is a valve issue. Not so much a weak spring, but I wonder if nuts that hold the rocker on (right under the valve cover) have come loose. I did remove 4 of them to swap to the bolt-less style bridge when I changed my valve cover. I wonder if they did not get torqued down properly, of if reusing the old nuts was an issue. Anyone have torque specs for those nuts and/or know if there are issues of using the old nuts or if I need to just buy all new to make sure

Reply to
Rusted

I would suggest that you purchase a bottle of STP gas treatment and put it in your tank before the next fill up. You may have picked up some water in your gas. I have had this happen several times. And after 1 bottle, things smoothed out.

david 91yj 05 sport.

Reply to
David Drum

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