Needle jet wear and sloppy slides

[andrewsw]

As we all know (or should know), needle jets wear and cause funky richness problems. Part of this is caused by the slide and/or slide carrier wearing. Has anyone given thought to fixing that by building up the sides of the slides to improve the fit? I"ve got an extra set of slides and might play with this. A little bondo or jb weld or similar smeared along the flange and then sanded smooth might be just the ticket to remove some of that play from the slides and thus help with the needle jet wear. It would only take a little tiny bit to make it work.

thoughts?

A

[PitterB4]

How do JB Weld and Bondo react to fuel?  I certainly don't know but I'm thinking that over time, that would deteriorate and make a mess. 

[andrewsw]

yeah, it would have to be fuel safe. I think JB weld is okay, don't know about bondo though. Any kind of fuel safe, sandable putty should work though. It's not like it's a high stress part. It doesn't have to be structural at all, just stick there. I know there are a variety of gas-tank repair compounds, maybe one of those would be appropriate.

Hell even some kind of tape might do the trick...

just thinking out loud, I guess.

[Banditmax]

I tried this with tape and found it didnt work too well i think the jb weld would have to be the best option. But each slide would then have to be matched to its carb and you could find it would be constantly be pulling at the needle / jet and wear it faster.

[tomacGTi]

Remember as well that some of that play is designed into the carb itself.

Ever rev the engine with the airbox off? Notice the slides do not come up smoothly?

By tightening the tolerances, you risk binding the system. I've thought about it before and just decided to lightly oil the slides and wipe off the surfaces instead of going down that road.

Ideally, a rollerbearing setup would be great but that's alot of BS for a mass produced carb.

[andrewsw]

I tried this with tape and found it didnt work too well i think the jb weld would have to be the best option. But each slide would then have to be matched to its carb and you could find it would be constantly be pulling at the needle / jet and wear it faster.

I'm not sure how this would happen, unless you "shim" it on the wrong side? You'd want to shim it on the engine side to push the slide forward slightly to keep the needle centered in the hole better. The excessive wear issue comes when the slide or carrier wear to allow more slop in the slide. The vacuum pulls the slide back towards the engine causing the needle to rub against the engine side of the emulsion tube more. By shimming the engine side of the slide, you'd pull it forward again.

At least that's how I see it.

Remember as well that some of that play is designed into the carb itself.

Ever rev the engine with the airbox off? Notice the slides do not come up smoothly?

By tightening the tolerances, you risk binding the system. I've thought about it before and just decided to lightly oil the slides and wipe off the surfaces instead of going down that road.

Ideally, a rollerbearing setup would be great but that's alot of BS for a mass produced carb.

I agree that binding could be a problem. It would have to be the barest minimum of a shim job. Not enough to bind, but enough to take out some of the slop. In my carbs, which are the best fitting combo of slides and carriers I could come up with out of two complete carb banks, some of them are loose enough that when you tap on the front of the slide, you can hear it hit the back of the slide carrier. The other two are tight enough that this doesn't happen.

I'm not sure how a coat of oil is supposed to help with this, btw. I suppose a coat of some heavy fork oil or something might provide a little buffer to keep the slide slightly forward, but I'd be afraid of it slowing the response of the slide.