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Discussion Starter · #1 ·
'76 CJ360T with 759A carbs. I've put close to 2k miles on it since restoration last spring. The carbs have got new diaphragms, needles, jets, gaskets, etc. last year. I'm reasonably certain this is not an ignition issue - new points, coils, battery, electronic regulator/rectifier, advance springs, and the advance works correctly according to a dynamic timing light.

Towards the end of a ~50 mile ride the other day it started missing during acceleration at about 3.5 - 4k rpm in traffic. Up shifting smoothed it out and I got home OK. I suspect crud in carb jets, so have taken things apart for cleaning. Whilst doing that I noticed that the plug on the end of the throttle shaft on the right side is missing (see picture). Could that air leak on one side be the cause of the mis-firing? (By the way, I know that there is silicone in the test port; both plugs were missing when I got the thing and I sealed them like that.)

I'm going to make a new plug for the throttle shaft and pien it in place. I don't know when that plug fell out, or for sure if it's missing is responsible for the right ride looking leaner than the left (picture attached, right on right, left on left).

Also, according to the spark plugs it's been running kind of rich all along (since I've had it). I've put one grade hotter plugs in it just before this latest 50 mile ride (7's instead of 8's). I know that's not a perfect solution to an over-rich issue; what should I do with jetting? It's currently got #68 primary main, #100 secondary main, and #35 slow.

I think we need to go a bit leaner at speed, but is that the main or the secondary, and what change would you all recommend?

Oh, and the fuel consumption seems excessive to me - around 35 mpg.

Thanks!



DSCF5595.jpg

DSCF5594.jpg
 

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Discussion Starter · #2 ·
Got that plug on the end of the throttle shaft replaced. It's nice to have a lathe :)

DSCF5596.jpg

Any advice on jetting?

By the way, the float levels were both off - one at 1", one about 7/8". Have adjusted both to the correct 3/4". Unfortunately I don't know which was on which side...

Thanks
 

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Crazy PJ is the expert ion your carbs, I'm sure he'll be along. In the mean time, I'll throw my own thoughts out there.

If both plugs looked like the one on the left I'd leave it alone. A little bit rich is not necessarily a bad thing. Now that you have replaced the missing plug I would put it back together and go for a ride (with a new pair of spark plugs), then see what they look like.
 

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Discussion Starter · #4 ·
Thanks, J-T. That's kinda what I was thinking, but would certainly welcome more opinions. I'm going to set the carbs aside for now and check other stuff (valves, compression, etc.). The weather's not going to be good for a while anyway.
 

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Discussion Starter · #5 ·
Compression test results (dry): 155 psi both sides. According to the manual perfect is 171 and too low is 149. Note that this is a kick-start only bike, and I'm a 60 year old smoker who has had several beers.

I'm declaring the compression OK. :)
 

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If your Float both had larger setting measurements than spec that would account for your lean condition.

The floats hangs upside down in the fuel bowl.
A greater gap means it hangs lower and shuts off earlier resulting in the low fuel level and lean condition.
The jets have to work too hard with the vacum sucking the fuel up the tubes to the intake.
 

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Discussion Starter · #7 ·
So far so good; got it all back together and rode around the block a couple times. Starts right up, idles well, and no more hesitation on acceleration (although I didn't get out of 3rd...). It's rush hour, the roads are wet, and I just popped open my 3rd beer so we're not going on a longer ride today. Wednesday is looking good.

Oh, the left side intake valve was tight (no clearance), left exhaust was loose maybe 2-3 thou. Right side was good all around.

Hopefully fixing all the little niggles I found has done it :)

Come on summer!
 

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Discussion Starter · #8 ·
So far so good; got it all back together and rode around the block a couple times. Starts right up, idles well, and no more hesitation on acceleration (although I didn't get out of 3rd...). It's rush hour, the roads are wet, and I just popped open my 3rd beer so we're not going on a longer ride today. Wednesday is looking good.

Oh, the left side intake valve was tight (no clearance), left exhaust was loose maybe 2-3 thou. Right side was good all around.

Hopefully fixing all the little niggles I found has done it :)

Come on summer!
 

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Discussion Starter · #10 ·
OK, looks like I've been barking up the wrong tree here. On the test ride this afternoon it ran great for several blocks, then started missing on acceleration again, just as before. Then it just died altogether. Could not get it re-started, walked it home (less than a mile, mostly flat, thank goodness). No spark on either side here in the garage. I've got 12.6 v at the battery, only 6.4 at the connection to the coils. Sparks fine with a jumper from the battery + to each coil in turn. So, electrical issue. (Wrong sub-forum too, eh?) But this is good - at least I know exactly what the problem is :)
 
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