Carb Slide Won't.....SLIDE.

jbeebe

Member
79 CB650, Keihin mechanical carbs, not the later CV style carbs.

After pulling them in/out a few times in a row to clean the pilot before riding season and adjust the choke cable that I shortened and moved to the side of the carbs I must have caused some sort of damage to the #4 carb body. The slide will not move freely in the chamber. To get it out I had to heat up the chamber and pry it out. It will not go in without a mallet (just to give an example of how messed up it is). I've swapped slides and narrowed it down to the chamber itself, not the slide. (The #4 slide works fine in other carbs, but other slides won't work in the #4 carb.)

Both the slide and chamber are free of burrs or gouges. Things i've tried so far:

- Sanded the inside walls with 300, then 500 sandpaper to ensure it's smooth.
- I measured the slide at 15/16", made a steel rod of the same size with a chamfered leading edge. My plan was to ram this in the chamber to correct any deformities in the wall. The round steel stock must be a couple thousandths shy of what the slide is, because it slides freely.

I'm just not sure where to go next with this....


Here's a poser shot of the bike last season before doing some more work.

Thanks!

 

SONICJK

Reminds me of...me No, I'm sure of it. I hate him
So the slide slides freely in the other 3 bodies?
Does a slide from one of the 3 working carbs slide into the nonworking? (just to narrow it down further)

How far does it go in before it binds? Can you narrow it down to a specific point?
 

jbeebe

Member
So the slide slides freely in the other 3 bodies?
Does a slide from one of the 3 working carbs slide into the nonworking? (just to narrow it down further)

How far does it go in before it binds? Can you narrow it down to a specific point?
The #4 slide does slide freely in the other bodies. Other slides do not slide into the #4 body.

It goes in 1/8" before it hangs up. It doesn't seem to hang up on any specific spot or side. This is why I thought the entire body might be slightly deformed from prying on it.
 

jbeebe

Member
alright, it was probably a bit aggressive, but I just about had enough, haha. I used a sanding drum and managed to get the unconformity out of the bore. After using the drum I went with progressively finer sandpaper by hand.

Now the slide functions properly, but when turning the linkage to operate all 4 slides, there is a lot of resistance and it does not return properly. All the springs and seated properly, I think the linkage is bent or something is just a little tweaked causing the throttle linkage not to "roll" smoothly.

I suppose I'll try to narrow it down to which part of the linkage is hanging up and see what I can do. Because these Keihin carbs were only used for a few years, 79-81 I believe, they aren't too common on ebay.

 

SONICJK

Reminds me of...me No, I'm sure of it. I hate him
Did you drop them at some point? I can't see how putting them in and out could cause either problem without being dropped.
Maybe someone picked them up curiously off the bench when you weren't around and dropped them and didn't tell you? :rolleyes:
 

jbeebe

Member
Did you drop them at some point? I can't see how putting them in and out could cause either problem without being dropped.
Maybe someone picked them up curiously off the bench when you weren't around and dropped them and didn't tell you? :rolleyes:
I put pry bars on each side to get them to fully seat into the cylinder boots. I just couldn't get them to "click" in by pushing or with a ratchet strap around the engine. That's probably what did them in. I wish I could blame someone else...ha.
 

Maritime

Well-Known Member
prying on cast aluminum is never a good idea, I learned the hard way on that. If you have to I always block with wood or something to spread the force over a larger area of whatever cast thing I may be prying on. As for you linkage issue if you tried to move the stuck slide using the linkage then you likely stretched or bent something that will need to be re-adjusted to get it back to working correctly.
 

SONICJK

Reminds me of...me No, I'm sure of it. I hate him
I put pry bars on each side to get them to fully seat into the cylinder boots. I just couldn't get them to "click" in by pushing or with a ratchet strap around the engine. That's probably what did them in. I wish I could blame someone else...ha.
yep that'll probably do it lol.
For my 400f a 2x4 against the carbs and then a prybar was the only way I could get the damn things to go in there.
 

pidjones

Well-Known Member
Next time, try a little thick silicone grease on the rubber and carb (like Dow Corning High Vacuum Grease) and heat the rubber with a heat gun until bathwater warm.
 

jbeebe

Member
Thanks for the replies everyone, i'll probably get to the carbs tonight or tomorrow and will let you know what I find/fix/break.
 

jbeebe

Member
Update:

Already folks, turns out the slide "cylinder" on carb 1 and 4 were both deformed from prying. This now makes sense because I had a pry bar on both sides of the carb bank to try to push them into the cylinder boots, haha. I used the previous method of the drum sander and then finer sanding by hand (or finger in this case) to get the walls smooth.

I heated up the cylinder boots with a heat gun for a good amount of time (I was actually patient for once), lightly coated the inside of the cylinder boots with grease, then they went in without the need of the prybars.

Thanks for your help, even if it was for mostly moral support, haha.
 

Snout

Active Member
My buddy did the same thing on a set of SU carbs on a British MG. One tap with a hammer did enough deformation that it could not be seen, yet the slide did not move. Glad you got yours ironed out! I always have trouble with mating those buggers, especially if the boots are getting stiffer.
 

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