Carb Rebuild Problems

[f15radar]

I bought a genuine Mikuni rebuild kit. On one of the carbs, the pop off doesn't really "pop" like the other. It just starts losing pressure around 24PSI. The other carb does pop (24PSI), but its doesn't hold the 10 pounds. Its a slow leak and takes about 5 minutes but it goes to 0. Is it ok that the first carb doesn't really "pop" and do I need to try and find the leak on the second carb? Also what type of screw (stainless steel?) should i use. Thanks.

 

[etemplet]

Are you spraying WD-40 on top of the seat? Also, I like to the seat to seal up tight pretty quick after the pop.. You may have have to pop it a few times to verify that it is sealing properly. If it is leaking all the way down it will leak fuel and flood the engine.

 

[f15radar]

Yes I am spraying WD-40

 

[etemplet]

Did your carb kit come with the new seats and needles? I find problems like this go away when I replace those parts. Generally cost me about $17 for one carb but I find it worth it. That with the correct spring and I don't have to wrestle with anything. Spot on and ready to roll.

 

[f15radar]

It did come with new seats and needles.

 

[etemplet]

Strange. Did you trying bringing the pressure up a little quicker? When I have an issue I pop it a few times till I get some consistency. Perhaps there is some debris under the seat. From another angle...Are you sure the parts are Genuine Mikuni? I've challenged a vendor of mine because the package didn't look right

 

[f15radar]

Ok, so I looked at it really close and the needle seat was coming up a little. So I unscrew the bracket and looked it all over and it looked OK. I screwed it back down and was using very little pressure but the screw busted inside. I drilled it out and cut new threads (4x.70). Now seat screwed down OK and it holds the 10lbs now but it still wont pop. The other card holds and pops now after fiddling with it. If I loosely screw the screw that holds the small rod it will pop but sticks up way too high. Any ideas? I don;t know how to proceed at this point.

 

[FL-Rider]

Possibly bent lever arm rod...roll it on a flat glass table or granite top to see if it rolls smooth.

 

[f15radar]

It doesnt look bent

 

[FL-Rider]

Maybe the lever arm is pinched where the rod goes through it? If the lever is sticking up, something must be binding.

 

[f15radar]

That's with the screw not tight. But if I screw it tight, it will not pop but doesn't stick up. Needle and seat are new and genuine Mikuni. Something has to be radically wrong.

 

[FL-Rider]

Wait... did you mean it was sticking in the up position, or just the lever arm is sticking up like bent up higher than it should?
Maybe swap the lever arm and rod from your other carb to see if it does the same thing.
One other thought...when the screw broke, was there any liquid (wd-40) in the blind hole where the screw threads into?

 

[etemplet]

It won't pop. Is it leaking. Too much spring? Take the spring out and see what happens. Gotta find out what it ain't.

 

[FL-Rider]

After re-reading your post, now I'm thinking that what you are saying is the needle seat is sticking up like its not down in the hole all the way. Is that what's happening?

 

[f15radar]

yes but when i make sure its in the hole it wont pop. it just kinda starts losing pressure but no pop like the other carb.

 

[POPPS]

If your carbs have brand new mikuni parts, exactly the same needle and seat, and spring, and the pivot arms look exactly the same, (the top and bottom are parallel to each other), and you have not jammed the spring, then your results should be very close to each other, I like to use a mixture of gas and a bit of 2 stroke tinted oil, for pop off, since the fuel in the carbs is straight gas from your tank. Also, I am assuming that you are not leaking past the O ring on the brass seat.

 

[f15radar]

I agree. That is why I don't know how to proceed.

 

[FL-Rider]

The seat should press down in the hole all the way with just finger pressure and stay there. It shouldn't require tightening the screw to force it down. It sounds like the hole is dirty or the o-ring is pinching.

 

[f15radar]

The oring on the seat?

 

[FL-Rider]

I think what you're saying is that the needle seat doesn't stay down in the hole all the way and you have to tighten the screw to force it down. Is that what is happening?

 

[f15radar]

yes when pressure is on it. With no pressure it sits fine.

 

[mikidymac]

Try swapping the needle, seat,arm and pin from the good carb and see if it works correctly. If it does start swapping parts back until you find the part that doesn’t.

 

[FL-Rider]

It sounds like something is preventing the seat from going all the way into the hole. Either corrosion, dirt, etc., or pinching needle seat o-ring. If the seat is not seated all the way down, the lever arm will bind against the needle valve when you tighten the screw for the lever arm rod. This can bend your lever arm out of adjustment. The explanation for why it pops when you loosen the screw for the lever arm, is because it relieves the pressure off the needle.
Find out why the needle seat is not seating all the way into the hole, and I think you'll solve your problem. Then recheck the lever arm to make sure its adjusted. Also, check for a groove in the needle tip, because its had pressure applied to it and that may have caused an indentation.

 

[FL-Rider]

I re-read your post again and have a new idea. You ask what type of screw to use in the first post because it snapped. If your talking about the screw that holds the needle seat in, then you need to get an original mikuni screw. This screw will fit the retainer that holds in the seat. Other types of screws may be shaped differently and may not hold it in place correctly. Just a thought....

 

[f15radar]

I believe that may be the problem, however, I can't use an original Mikuni screw because after the screw broke halfway into the hole, I had to drill it out and I ruined the threads. I still have the original screw because my Kit had a new screw that came with it. It must have been junk tho to break off like that and I wasn't putting any pressure on it. Anyways, I put an M4 in which I believe is the next size up. I believe the original was a M3. It looks like the new thread isn't working good as the head of the screw may be hitting the seat and not coming down on the bracket to hold it.. Can I just fill the hole in with JB weld and then drill, thread back a M3? Is their something else I could use on such a small hole besides JB weld? Or do I need to find a machine shop to repair it?