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No start, backfire thru carb

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SeeJayTwo View Drop Down
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    Posted: 16 Apr. 2023 at 9:26pm
Early 1946 CJ2a. Probably a replacement motor. L134. Not started for 25 years. Water pump off, fuel pump off. Rebuilt WO on. Can't get the screw off of the timing hole cap without going nuclear. I have spark. No. 1 plug fires at approx TDC. All other plugs fire. Distributor wired 1342 CCW. No.1 at 5 oclock.  Squirting gas down carb throat and filling bowl thru carb inlet. Carb is mostly out of the equation. For three days trying things, I get the same backfire with flames out carb and out bottom of Exhaust manifold. Removed tail pipe at manifold thinking I had mouse blockage. Heat riser broken but hanging open. Ballast bypassed, direct 12V to coil. Using remote starter. I have a lot of experience with motors. None with L134. It's either my age and I'm missing something or it's valve issues. I think I have a timing gear motor. I don't want to open this motor.

 Previous owner died, his friend was given the Willys and he did nothing for 25 years and sold to me. So silly me thinks nothing could be very wrong. being here in AZ all it's life. Hood closed, air cleaner and oil filter in place. Probably was running. No signs of dist. removed or any funny business. All bolts tight, some rusty tight. Turned dist CW and CCW while cranking. I can not imagine carbon would not allow any fire, albeit I am getting "fire" :). can't imagine one valve sticking would not fire motor. Please correct me and give some ideas. My present plan is new plug wires and new plugs. The wires are really bad and plugs real old. Coil is old, points old, condenser old. Spark seems bright enough to fire. It is exploding gas. So I guess I'm thinking weak spark, Wishfully. I really can't believe it still has spark. Motor was soaked thru plug holes after I got it, because I thought motor was frozen, then realized it was the water pump that was frozen and belt holding crank. This was months ago. 


Edited by SeeJayTwo - 16 Apr. 2023 at 9:57pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SeeJayTwo Quote  Post ReplyReply Direct Link To This Post Posted: 16 Apr. 2023 at 9:39pm




Edited by SeeJayTwo - 16 Apr. 2023 at 9:56pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 16 Apr. 2023 at 9:53pm
Not started for 25 years?

My first thought is stuck valves. 

You can find this out by removing the tappet cover and watching while the engine is turned over. Sometimes you can free stuck valves by placing a thicker feeler gage between tappet and valve stem while turning over the engine. 


Edited by Oldpappy - 16 Apr. 2023 at 9:58pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SeeJayTwo Quote  Post ReplyReply Direct Link To This Post Posted: 16 Apr. 2023 at 9:58pm
Stuck as in....................rusted? When I said I have a lot of experience with motors, not fixing internals.
Thank you
So are tappets getting stressed?


Edited by SeeJayTwo - 16 Apr. 2023 at 10:05pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cpt logger Quote  Post ReplyReply Direct Link To This Post Posted: 16 Apr. 2023 at 11:49pm
I would start with the new wires & plugs. The wires may be arcing between themselves & the plugs may not be firing. With new wires & plugs we know that they are not our issue. Unless, of course, you buy Chinese junk! Then all bet are off.

To diagnosis this issue, we really should do a compression test... However, IME, Oldpappy is on the right track, stuck valves.

It could be rusted or just gummed up valves. Either way it needs some serious penetrating fluid, NOT WD-40, nope, no way. I do not care that they say it is a penetrating fluid, it is a Water Dispersent, thus the WD in it's name. Spray the valves while turning the engine. The trick of placing a stack of feeler gauges between the valves & the lifters forces the valves to move up further then they do normally. This gets the penetrating fluid up further in the valve guide. It will take a lot of time and patience. Often this will loosen the valve in the guide which will help with sealing the combustion chamber. Thus, eliminating the "backfire" through the carburetor.

Yes, if the valves are stuck in the closed position, it creates a lot of stress on the lifter. The only solution to damaged lifters is replacement. IMHO, This is best done with the engine out of the rig.

IHTH, Cpt Logger.

PS, What is meant by a lot of experience with motors?

Edited to add the PS.


Edited by cpt logger - 16 Apr. 2023 at 11:54pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpoole Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 1:51am
Agree on the stuck valves, which seem likely after 25 years. 

Incorrect timing via bad adjustment or mixed up wires can also lead to backfiring through the carb and should be pretty easy to evaluate as a possible cause.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lee MN Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 9:39am
X3 on stuck valves, but it’s also easy to mix up #2 & #3 plug wires with like results, double check that.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SeeJayTwo Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 1:55pm
Yes, all is double checked. thanks to everyone. I now have a direction. I will be removing the manifolds and then side cover to do valve check and feeler/spacer procedure. Will report when complete. Plugs, wires and gaskets ordered.

Edited by SeeJayTwo - 17 Apr. 2023 at 1:57pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TERRY Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 2:48pm
It is possible to remove the valve access cover without removing the manifolds. Less risk of breaking studs thatway.
May need to undo the exhaust pipe.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cpt logger Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 4:04pm
First, just for grins, please do a compression test. You do not want to remove the manifolds +/or the head if you do not need to. If the compression test shows good, we are all wrong as to stuck valves.

Removing the access cover might work, but the space for working will be very limited, as will the ability to see the valves and lifters. Your call.

If you choose to remove the manifolds, be sure to soak the bolts & studs with penetrating fluid for a day or five before torquing too hard on them. They break easily. Not good, very very bad! Seriously, one might have to remove the entire engine to fix a broken stud.

Removing the manifolds gets one great access to the valves top end. This will make it easier to apply the penetrating fluid to the valve stems. Plus it lets you see what is happening. I would also remove the left fender for the same reason. OTOH, I might remove the head first. That also gets one access to the top of any open valves, stuck or not.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SeeJayTwo Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 4:49pm
Forgot to mention I did a compression test at beginning of troubleshoot. 125+ psi all cylinders. I need to remove manifolds anyway for prevoious owner broken bolts. I'm aware of the danger and being very careful. Fender and tire off. What is dangerous about taking head off? broken bolts? Sure would let me de-carbon some.
It seems to me at this point I have to eliminate valves no matter what. The spark and time is there. My memory of doing the compression test was...seems high for an old motor, something fishy. Could be massive carbon or valve train or both. I know I need to get the timing hole cover off before going nuclear on the motor.


Edited by SeeJayTwo - 17 Apr. 2023 at 4:58pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lee MN Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 5:21pm
Well then, if you have 125 psi across the 4 that rules out any stuck valves, I would then guess the distributor is set 180° off, very common.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SeeJayTwo Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 5:26pm
Read original post. Had thumb on no. 1 hole, plug laying on head, crank motor with starter, plug fired at every compression stroke.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 5:30pm
If you did a compression test and got a reading of 125+ psi on all cylinders on an L134 engine that hasn't ran in 25 years I suspect your compression gauge is giving a faulty reading, but still if you are getting compression on each cylinder the valves are not stuck.

The L134 does not produce that high of compression. A fresh F134 might, but I have never heard of that high of compression on the flathead.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SeeJayTwo Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 5:42pm
I'll do it again. I agree.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cpt logger Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 5:53pm
" I have to eliminate valves no matter what."

You just did. As the compression numbers are good, so are the valves. If the valves were stuck or not sealing we would have 0-50 PSI, not 125.

There is no need to look at the valves for sticking. They are fine.

There is also no need to remove the head. If carbon is the cause of "excess compression pressure" that can be done after the engine is running well.

IMHO, Compression at 125 PSI indicates a fresh overhaul. As does the non-stuck valves. Are you sure that this is a "tired" engine?  We know it is old, but is it worn out or is it a fresh overhaul?

When I overhaul an engine that may sit for a while before it is put into service, I "pickle" it. This procedure uses a lot of oil and other lubricants. If your engine was pickled before storage, those fluids may be the cause of the higher than expected compression readings. When It first started, did it billow out blue smoke like a mosquito fogger? If so, you are so lucky!

I suspect that it was pickled and your "backfiring" may be caused by now oil fouled plugs.

However, the broken manifold bolts could be the cause of the "backfiring" due to a massive intake leak between the manifold and the block. This would lean out the fuel/air mixture and cause the"backfire" and it would also cause the engine to run fairly hot fairly quickly. 

This is why I ask a lot of questions. We did not know about the compression test & it's results. We also did not know about the broken manifold bolts. It is all starting to make sense now. lets keep going!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cpt logger Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 6:02pm
A freshly overhauled L-134 with a high compression head will produce 125 PSI of compression.

I should ask Mark W. what the compression is on Chug a lug. I have not had the time to keep up on his thread about Chug, my fault.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SeeJayTwo Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr. 2023 at 6:08pm
I don't like it when I'm helping someone and they "forget" to tell me things. very frustrating. now I'm doing it.
  One broken bolt where exhaust meets intake. 4 bolts on a square pattern. Connection still very tight. The other bolt I just did on the tail pipe flange. Of course the one threaded into the manifold. Thought I could fix both on the bench.
 I don't know the "freshness" of the motor. Top of pistons look black. Maybe my soaking with oil and blaster during the "thought it was stuck" era did something. No wetness seen in plug holes. Appreciate all the ideas and diagnosis. your questions are invited. they jog my memory.
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