CJ360 Carburettor help

Trevor May

Been Around the Block
I have been having problems with my carbs for a while. She starts terrible, idles terrible, and is generally crap until warm. When she's warm, she is great. Last fall I changed out a low speed jet, and immediately ran better than before when just cruising about 50 km/h. Unfortunately didn't solve the big issue.

Here is the meat of the issue: When I try to set my idle fuel screws, the right side works exactly as the factory intended. Turning the left side has almost no effect on the idle rpm at all. In fact, only when I turn the screw in fully does it change, and then it revs up slightly. I tried switching idle screws, but no change. I also switched the low speed jets, and no change. So I pulled the carbs and took pictures of the inside of the idle screws.

I suspect that my left idle screw isn't reaching the hole to stop fuel from going in, either from wear or damage. I believe that if I'm careful, and drill a TINY amount of material out of the larger diameter of the hole, then the throttle screw with its tapered end will go deeper into the hole and possibly allow me to control my idle fuel again. I could really use some input.
 

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Maybe bottom out both and measure what you got sticking out as a comparison. To see if the suspect side isnt penetrating as deep.

then pull the suspect out and coat the suspected area w black marker then screw it back in.

The marker should rub off and reveal a shiny spot on the needle. So you can pinpoint exactly where the stopping contact is being made.

You may need a magnifying glass as the clean contact area may be very very small.
 
Also, if you have aftermarket rebuild kit springs you may need to grind the ends flat. At the un-finished cut ends can cut and grind into the body causing burrs and badness.

heres a comparison shot of the springs I made. Notice the Honda springs are ground flat on the ends.
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My springs are definitely Honda. I haven't changed them and the PO was mechanically inept so I doubt that would have occurred to him. He was more of a "ride to failure" type of owner.

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The taper on the tip of the screws are not perfectly straight on either. Both show one side of the taper totally rubbed off. The "good" side does have a faint ring on the thicker part of the taper. The left doesn't have that ring. Kind of what I was expecting.

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Then yep, looks like your right, you will just have to do your very best to remedy the discrepancy in carb body.

Take your time, use your magnifying glass and good lighting.
Ide hate to see you get into a situation where enough material has to be removed that the O-ring cant do its job.

My local Honda dealer has the A/F mix needle kits available for the CJ. So, I imagine they are available at most all dealers.

Good luck and keep us up to date.
 
Quick update. We're enjoying some beautiful spring weather and my bike is out of commission. I'd love to get out and enjoy the sunshine but unfortunately I haven't had an opportunity to finish the carb mod.
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Alberta! Last year we set a record high 26°C, 78.8°F today. It's still snowing and miserable, although the roads are more like driving in rain. Tomorrow is the start of seasonable weather. I'm not putting my snow brush away yet.

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Update:

So I did drill the seat for the idle screw landing and it looks much better in there. That was truly a butt clenching experience. I was fully prepared to have ruined my carb body irrevocably at that point. As it turns out, I didn't! Since I don't have a drill press, I used a little trick of taping up the drill bit with electrical tape to make a bushing that just fit in the body. This kept the drill bit centered as I used my hand drill to mutilate the mixture screw head landing.

The result? No improvement. At least I didn't make it worse. It might be a tiny bit better, but generally the same. The left idle screw gets a little better when it is all the way in and the right is still about 1.75 turns out. Not sure where to go next right now with these bodies. I made a doodle of my needle and compared it to a doodle of the opening in the carb. These would indicate that the idle screw is seating at the bottom like its supposed to be. I also posted this pic of the Honda service manual that shows the path of fuel/air mixture during idle. This indicates that the bypass holes are supplying more than enough fuel/air to keep that side running. Any suggestions where to go next?
 

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Sync,
Ensure the butterfly is centered up in the body. This can be a bit of a pain, since they can slide a bit from side to side. Use a flashlight to shine through from the filter side as best you can, eyeball any gaps around the butterfly. Make sure its circumference is centered in the body and free to close without scuffing on the body.

Then use gauges to sync. Then swap the gauges on the carbs to ensure gauge accuracy/discrepancy.

Double check to ensure pilots are the same size. 35 if I recall. If new great. If old, its possible po drilled one or both. Not very likely these have been drilled as they are tiny.

Make sure pilots both have the same size air holes in them. rebuild kit has small holes. Old Honda has larger holes.

I drilled mine out to old honda size. I dont recall it making much difference. Just make sure they match.

slowjet35.jpg


Also if yours has screw out air correctors under the diaphragms. Ensure these didnt get mixed up and swapped. As all 6 have the same thread size. They are easily mis-installed.

11494-220714063350.jpeg


Ensure floats are the same. And the small spring "wishbone" tab is installed correctly on the float needle seat. If installed upside down, the seat can drop down a bit. Causing a fuel height discrepancy. Even though floats measure the same.
The spring tabs have a small bow to them and must apply pressure to the seat.

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Seals over the butterfly shafts? Avoid leaks.

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Do you have pods on her? If so is it possible one is over oiled (decreasing air flow) than the other?

Put your bike on its center stand for any carb tuning.
 
Please disregard the following post - I made the following assessment(s) without thinking through about the actual bike.

Sounds like the carb body is dirty. I doubt there is/was anything wrong with the pilot air needles or their bores. Spray carb cleaner into the hole where the needle of the pilot air screw goes. A strong spray of cleaner should come out of the well where the pilot emulsion tube fits. The pilot emulsion tubes are permanently made onto the pilot jets and have holes in the sides of the tube - evidently of various sizes per trek97's pic. These holes are where the air from the pilot air screw goes through to mix with the fuel before it goes into the main bore to mix with even more air limited by the throttle plate. The fuel supply is fixed by the pilot jet size, but the air is variable and determined by the pilot air screw/needle. The holes in the emulsion tubes do not impact the air volume (unless they were to become super small) because the air screw is the part that determines the air supply. However, treks picture is a good example of factory carburetor brass compared to aftermarket kits. When I get a set of carbs, I check for aftermarket brass and toss any I find in the trash and replace with factory brass straight away. Commonly the owner has just "rebuilt" (or had it done) and I always ask if they kept the old parts and very often the answer is yes. 90% of the time, I put all the old factory brass back in after cleaning everything and they work perfectly.

Compare the carb cleaner flow through the two carb bodies - obviously they should be the same. The trouble could also be farther downstream past the pilot emulsion tube, so with the pilot jet and tube out, blast carb cleaner into the hole where the end of the pilot emulsion tube seats and compare how it blasts into the main bore between the two carbs. Obviously it should be the same. If these two passageways are clean and the parts are not damaged, the pilot system is fine. You can check the function of the pilot air needles by blowing compressed air through a rubber tipped air blower nozzle into the pilot air inlet in the intake bell of the main bore. Air should blast out into the pilot emulsion tube well and you should be able to throttle it down to zero when you turn the air screw all the way in to where it contacts its seat. You should get the same behavior from both carbs.

You say the bike runs fine once warmed up so why so much focus on the pilot system? Maybe more attention to the starting system? Trek97 makes some excellent points - I'd check through all of them.
 
On this particular pair of Keihin carbs there is no air "adjustment" to the pilot system or seperate A/F mix.

The air is controlled solely by the corrector "jet". Under the diaphragm.

The troublesome adj needle valve simply meters how much atomized air/fuel mixture is allowed into the system when the butterfly is closed.
 
Duchat, I guess I should asked. LOL This is a stock pair of 745 or 754 keihins, Correct?

If you screw the adj needle all the way down does that cylinder want to cut out? Or does it continue to run the same?

If it runs the same, Either the needle isnt seating properly and still open OR its got to be sync or something not letting butterfly close (air/fuel mix getting around butterfly). through the 3 tiny holes directly under butterfly.

If it wants to cut out it is working. Then begin turning adj out (allowing more air/fuel mix) rpm should increase at some point. Keep turning out until you pull it out. Cylinder should cut out again because its not getting any fuel mix only open air through this circuit.

Liquid fuel should NOT come out the screw needle adj opening under any circumstance. Engine running or not.

Like jpm said make sure the circuits are clear and clean. The 3 small holes and the larger single hole (connected directly to the needle adjustor.)
 
I'm running 759A, which I relieve is stock on the CJ360.

The idle screw mixture on the right affects the engine as you described. Screwed all the way in, engine shuts down. I haven't unscrewed it until it comes out, but I have followed enough of your builds to know you're not talking out of your butt. I

The right side isn't like that. I start at 1.5 turns out and turn it in until it stops. The idle doesn't change until I almost bottom out and then it gets a little faster.

I have replaced one of the idle jets with a new Honda jet because it was bent slightly, and I was having trouble getting it clean. That improved idling but still having this issue.

I'm focusing on this because it's keeping the engine from performing properly. It takes dozens of kicks to get running, and I can't trust it to go anywhere in case it won't run when I have to leave. I can't proceed to the next step until it's properly running and I know more improvement is worth the effort. I won't sell and move on because it will haunt me that I sold a crappy runner. I'm log jammed at this point.

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trek97 said:
Sync,
Ensure the butterfly is centered up in the body. This can be a bit of a pain, since they can slide a bit from side to side. Use a flashlight to shine through from the filter side as best you can, eyeball any gaps around the butterfly. Make sure its circumference is centered in the body and free to close without scuffing on the body.

Then use gauges to sync. Then swap the gauges on the carbs to ensure gauge accuracy/discrepancy.

Double check to ensure pilots are the same size. 35 if I recall. If new great. If old, its possible po drilled one or both. Not very likely these have been drilled as they are tiny.

Make sure pilots both have the same size air holes in them. rebuild kit has small holes. Old Honda has larger holes.

I drilled mine out to old honda size. I dont recall it making much difference. Just

Also if yours has screw out air correctors under the diaphragms. Ensure these didnt get mixed up and swapped. As all 6 have the same thread size. They are easily mis-installed.

Ensure floats are the same. And the small spring "wishbone" tab is installed correctly on the float needle seat. If installed upside down, the seat can drop down a bit. Causing a fuel height discrepancy. Even though floats measure the same.
The spring tabs have a small bow to them and must apply pressure to the seat.

Seals over the butterfly shafts? Avoid leaks.

Do you have pods on her? If so is it possible one is over oiled (decreasing air flow) than the other?

Put your bike on its center stand for any carb tuning.

I'll look at the butterfly's to check for alignment. I have a mercury tube tool for checking carb balance. Bought it in the 90's. My air correctors are not screw out type. I have set the float heights, but now I'm wondering if I have a leaky float. Not sure, but I suspect the wishbones are installed properly. One of my butterfly seals had come out, but I put a plug in it. The troublesome carb has the original shafts seal. Original airbox and filters.


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Quick update: pulled the carbs off again. Drained the carbs first. Used a very crude graduated cup to measure fuel drained from bowls and left had quite a bit more than right. Pulled whole float assembly out and found a small gouge in the o-ring around thefloat valve seat. Of course I'll replace it. Is this a smoking gun?

9217dd804366a088f3da1468fd701ea8.jpg
 
Ah, It may very well be. Im surprised you didnt have fuel running out of the carb an onto the floor.
and look in there to make sure it doesnt have a burr inside the body that did the gouging.
And yep youre right w the 759. Its just been a few years and I cant recall them all.
Which is good. Atleast we know the correctors didnt get mis-matched.
 
Duchat said:
The idle doesn't change until I almost bottom out and then it gets a little faster.
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Thats the weirdest thing I ever read. I will have to think about that one.

Once you hit bottom does it cut out?

Just get floats set, check butterflies then sync them.

We will come back to this after those things are done. Sorta Sounding like the needle seat is toast bro. But keep going for now.
 
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