Mikuni carbs

[twangin4u]

What's up guys!? Long time..
   The other day I decided to tune my carbs. As I was letting the bike warm up I grabbed a can of carb cleaner and gave little squirts around any spots that might be sucking in air. I found that on the shafts that pivot the throttle plates are sucking air in. Quite a bit actually. The two middle carbs are OK, but the two outside ones are leaking. The previous owner wasnt much of a patient mechanic. I know he had the carbs off before, and I know that I've already found a list of things I've had to correct since having the bike. Anyway, there's a seal on each side of the shaft on the carb. Almost looks more like a small lip seal than a square o ring. Does anyone know which way this goes. Mine have the lips facing outward. Also, what hardware goes on the shaft after the seal. By that, I mean, is there a small washer that compresses that seal a bit? Cause to me it just doesn't seem like there's a way for it to keep from sucking air in. Any knowledge would be much appreciated..
   

[JPaganel]

Anyway, there's a seal on each side of the shaft on the carb. Almost looks more like a small lip seal than a square o ring.    

Not almost.

It is a lip seal, like you would find on many other kinds of shaft. It's small and completely rubber, no metal inserts or springs.

Does anyone know which way this goes. Mine have the lips facing outward.   

Lip goes to the side where there is higher pressure, the stuff you are trying to contain.

For oil seals, that's inside of the engine. For carbs, it's the outside, the atmosphere.

Also, what hardware goes on the shaft after the seal. By that, I mean, is there a small washer that compresses that seal a bit? Cause to me it just doesn't seem like there's a way for it to keep from sucking air in.

There may be a washer, but it does not compress it. The washer is only there to protect the seal. The rubber seal is what keeps the air out. The lip against the shaft is what does it. It's why replacing it with an O-ring doesn't work.

If the seal is sucking air, it means the rubber has hardened and worn.

Yamaha does not list this seal as a separate part on the FJ, or on any other bike with a 4-carb rack. I think Randy stocks the seals now. 

It can be replaced, but it's a royal pain in the butt. I have two sets of FJ600 carbs in pieces because of this operation. I can just about guarantee you the previous owner never had them out.

Removing seals involves not only breaking apart the rack, but also removing the butterflies. Butterfly screws are peened over. They are also soft metal and strip out when you look at them too sternly.

[racerrad8]

We do indeed have them in stock

Carburetor Throttle Shaft Seal

If the screws weren't screwed up on the throttle shafts, the previous owner never had them out. As JP said they are peened and without the proper knowledge on how to get them out they would be stripped out because they are soft JIS screws that are peened over so as to not come out(Also, shouldn't be re-used as the threads are usually screwed up from the peen). The lips face outwards but there is no washer to hold them there except on the outside of the carb bodies where the c-clip is.

Robert - RPM

[Pat Conlon]

Robert, are there throttle shaft bushings that can be replaced?
If so, if you are going to the trouble of removing the throttle plates and shaft to replace the seals, I think some new shaft bushings would be prudent.
(if possible)

Pat

[racerrad8]

Pat, there are no replaceable bushings there. If dirt gets in there from either poor filtration, he was running K&N type air filters with the hard backing plate, or from the throttle shaft seal being bad the shaft just eats the aluminum of the carb bodies away. (The ol' which metal is harder steel or aluminum problem.) We see this every once in awhile in with the legends car guys who dirt race. I just recently had a set come in the door that was off a dirt track car and he was saying that no matter what he did the idle would always be different. We got the carbs here to check them over and found that you could move the throttle shaft all around which was changing where the throttle plate would rest at idle, every time the throttle was applied. After breaking them down and getting the seals off the shaft you could see the carb body had been worn and elongated. He elected to change the seals on them and rebuild as they were and simply use them as a back up set of emergency carbs. For the race car this will be fine as it doesn't really matter to the race car guys how it idles. Now if they were on a bike I would say they would be no good as sitting in traffic idling low enough to die or racing up to 1500 RPM would be a royal PITA to deal with. He will now be running the RPM Dual Pod Foam Air Filter on all three of his cars to prevent the fuel washout that the filters that are plate backed like K&N type filters cause.

Robert - RPM

[Pat Conlon]

Ok, thanks Robert. I've learned something today....

So it sounds like there is not enough meat on the carb body to drill out the elongated hole and press in new shaft bushings.

[racerrad8]

Pat, I'm sure there is enough there to drill it out and press a bushing in but it is not a common enough problem to worry about. If we were to have it done, we would probably have to make 1,000+ to break even on them, after the set up fee and this and that and every thing else from the machinist to have to bushings made. Then add the labor to drill them out and press them in at the proper tolerances. It wouldn't be cost effective(At least for us). Now if you had nothing but time on your hands and were a machinist or had a friend to make them for you it could work. But this set I have just built and two other sets that I have seen were this bad. Another thing I would worry about is, that if they aren't perfect and for what ever reason they are off a little bit either from machining or pressing them in crooked and the throttle gets stuck wide open, someone could be in for a real thriller of a ride.

Robert - RPM

[Pat Conlon]

Ok, thanks Robert....yea, the line drilling would have to be precise....

As long as a rack of new Carbs are available to the consumer, this would not be cost effective. I was thinking down the road...

[FJ_Hooligan]

I have yet to give it a try, but I think that the first gen FZ1 carbs could possibly work on an FJ.  I remember measuring the intake spacing and as close as I could tell, it matches the FJ.  The carbs are also a bit smaller in vertical height so that's another positive.  I want to say the cables are swapped, but I'm not sure. 

[Pat Conlon]

Hey Hooli, I'm not sure the narrow ('01-'05) FZ-1 engine matches the 77-85-77 cylinder spacing of the FJ. I know the FZ-1 header tubes don't fit.
It would be great if they did as they are 37mm diameter BSR Mikuni.....More air for our big engines vs the 36mm FJ carbs.
However, I seem to remember years ago that someone was saying that they (FZ-1 carbs) were a PIA to work on?

There is a guy down in San Diego, Bill Cain, an old school FJ owner (and overall good guy) who has done some interesting carb swaps on the FJ
He recommends these Keihin CV36's off the Kawasaki ZRX1200....



http://powaymotorcycle.com/SanDiego/

[FJ_Hooligan]

But Pat, intake spacing is not necessarily indicative of exhaust spacing.  By my best measurements with a tape measure I get ~78 - 85 - 78mm.

I recall holding an FJ assembly of carbs up to an FZ set and the spacing was almost exact.  Why I have 2 extra sets of FZ carbs is a mystery when I only have 1 extra set for the FJ.  :-)

The FZ carbs are more complicated than the FJ carbs, but still very similar, and a lot less complicated than the last set of Keihin carbs I worked on

[Pat Conlon]

Good point on the exhaust spacing, I didn't think of that

Yea, I don't know enough about the differences between the Keihin vs Mikuni to invest in a set of ZRX carbs.

Those 37mm FZ-1 carbs do sound interesting Hooli...

[twangin4u]

We do indeed have them in stock

Carburetor Throttle Shaft Seal

If the screws weren't screwed up on the throttle shafts, the previous owner never had them out. As JP said they are peened and without the proper knowledge on how to get them out they would be stripped out because they are soft JIS screws that are peened over so as to not come out(Also, shouldn't be re-used as the threads are usually screwed up from the peen). The lips face outwards but there is no washer to hold them there except on the outside of the carb bodies where the c-clip is.

Robert - RPM

☺ One of the butterfly valves has two different screws on it so... But I see what you mean. I'll come by when I get a chance and pick up some goodies.

   Encountered another issue.. lol
The needles on carbs 1 & 4 have pooched out at the ends. Anyone ever had this problem? It's preventing gas from flowing into the carbs. See attached

Don't know if you can tell but one needle is from carb 2. It's working fine, but the other one has pushed itself out a little bit

[twangin4u]

We do indeed have them in stock

Carburetor Throttle Shaft Seal

If the screws weren't screwed up on the throttle shafts, the previous owner never had them out. As JP said they are peened and without the proper knowledge on how to get them out they would be stripped out because they are soft JIS screws that are peened over so as to not come out(Also, shouldn't be re-used as the threads are usually screwed up from the peen). The lips face outwards but there is no washer to hold them there except on the outside of the carb bodies where the c-clip is.

Robert - RPM

☺ One of the butterfly valves has two different screws on it so... But I see what you mean. I'll come by when I get a chance and pick up some goodies.

   Encountered another issue.. lol
The needles on carbs 1 & 4 have pooched out at the ends. Anyone ever had this problem? It's preventing gas from flowing into the carbs. See attached

Don't know if you can tell but one needle is from carb 2. It's working fine, but the other one has pushed itself out a little bit

[JPaganel]

The needles on carbs 1 & 4 have pooched out at the ends. Anyone ever had this problem? It's preventing gas from flowing into the carbs. See attached

Don't know if you can tell but one needle is from carb 2. It's working fine, but the other one has pushed itself out a little bit

Needles are just about the easiest and the most common thing to fix.

Replace them all. That way you won't have to go back in next year when 2 and 3 take a crap.

Also, replace the needle seat o-rings.