XJ900F Rebuild Carb Gremlins

Hi Again,

Slowly sorting out the engine after a rebuild and cleaning of the carbs. All prior work has been done...valves clearances, cam chain, timing marks aligned etc. Had a small problem with a stuck enrichment valve on #4 which has now been rectified.

But now it seems I might have a stuck float valve on #2 and just needing some expert confirmation.

Firstly, exhaust header on #2 is barely warm...probably warmed by heat of the engine on other 3 cylinders.

Took spark plug out and grounded it against the engine and it has a healthy spark.

At this stage no gas tank on yet so fuel is being fed via an extended clear fuel line. I used a syringe on the fuel line to fill the carbs but after several goes the fuel level in the line never built up, and when it did look like it was filling it would slowly reduce disappearing eventually below the fuel filter.

I took the metal cap off #2 carb (a short cut to see if anything visible could be the problem) and sure enough, each time I pumped fuel into the line it would slowly come bubbling up through the main jet where the round slide and needle rest.

I'm guessing here but with the fuel level so high does this have the effect of blocking some air passages so the atomisation of the fuel can't occur and therefore cylinder #2 fails to fire???

So...problem is float or stuck float valve?

And I guess theres no way of getting #2 carb bowl off while on the bike ? )):-(((

 

Additional information...Mikuni Carbs.
Rebuilt. Cleaned. Everything except float valves removed as it was from a working bike before I tore it down.
Perhaps months of sitting dry and then even with the rebuild, something inside the float valve may have dried out?

 

Have you tried giving the bowl a sharp tap with the handle of a screw driver? Can help to dislodge stuck valve/float. Other than that I think
it's carbs off time. You lucky devil.. Could also be old o-ring on the float valve brass 'holder' - I've had some success with 7mm x 1.5mm on Mikuni BS series
(28,30,32)

 

The carbs have been off the bike for 12 months and the rebuild was 6 months ago. My guess is that the I ring has dried out. All the float systems seemed in good operational condition when I had them apart so it must be a dried out leaking o ring. Lucky me. And those carbs were spotless when I put them back on.

 

Try tapping on it. Have the cap off so you can observe at the same time. Additionally...with all the raw gas that has flooded the cylinder, you'll want to do an oil change before running the motor very much as your oil is now thinned with all that fuel.

 

when you pull the carbs off and find your problem . put them in a holder and check fuel levels off the bike and for leaks before you reinstall them

will save you some time in the end

 

rubber bits do dry out when the carbs are off the bike. I realized it last year with my 900 carbs, After having the carbs off for several months, they started leaking at the fuel rail seals as soon as I put the petcock on PRIME. It was the very first time the carbs leaked like that. Luckily, the seals swelled up tight a few hours later, no leak since then.

 

fill them with seafoam when off the bike for a long time.

 

Current investigations see to indicate a sticking float needle...not seating properly.

The floats look OK. No gas inside them so therefore not leaking. Can only be the needle. Will take a closer look later. Thanks for the helpful feedback.

Cheers

 

I did forget...There is the golden rule of carburettors...though shalt remove them at least three times before all is well again!

 

Could still be that pesky o-ring. If the carbs are like mine it's floats off to access the float needle. If the pivot pins are stuck a good tip I picked up here was the use of an auto centre punch - works like a charm. Be careful also to offer some opposite resistance to the float post.