96 GTX carburetor throttle shaft kit

[esahlin]

I looked it up and I have Mikuni BN-40I caburetors on my 96 GTX 787. I believe I have a throttle shaft leak causing misfires at idle and part throttle. I am trying to figure out what throttle shaft kit will work for these carbs if any. All I can find are these throttle shaft kits listed:

MK-BN/038 TV, MK-BN/044 TV and MK-BN/046 TV. Doesn't seem like any of these will work for the 40I or will they.

Thanks for the help.

 

[stephensimmons]

clean your carbs first. Sounds more like you have a clogged low speed jet or carbs are slightly out of sync.

 

[esahlin]

Thanks...heres a long description of whats going on.

96 GTX didnt start or run when I bought it. 200 hours on original engine.

Removed carbs and filters full of black crap. Replaced all fuel lines, removed the fuel tank and cleaned. Original fuel selector and original fuel filter/seperator.

Rebuilt carbs (Didn't buy original Mikuni kit used the cheaper WSM kit found on ebAy) , used original needle arm springs, new needle and seats. Tested pop-off to around 38 psi.

Compression was 150/152
Cut back the spark plug wires and reinstalled.
New plugs

Low speed screws set at 1.25 out high speed 0.
Ski misfires at idle in water a bit but mostly at part throttle positions (under 1/2 throttle) it misfires with a pop pop through exhaust.

Once I get past about 3/8-1/2 throttle and above about 4K ski runs great with awesome power.

Thus, I thought it was the three holes in the low speed circuit. I cleaned another set of 96 XP carbs (carbs had been sitting on a defunct ski for 5 years no guarantee these were good carbs) I had and placed them on and tested with similar results maybe a tad less misfiring.

Plugs were darker tan after the last outing.

I just went through the original carbs again blasting a ton of air and carb cleaner through the low speed circuit and the three holes. Just placed them on the the ski again and ran on the hose...doesnt seem much different but will need a water test to verify.

Other thoughts:
I have air bubbles showing up in the fuel delivery line to the carbs. Not sure how or if this could cause my part throttle misfire.

tachometer bounces around at idle speed on the hose seems pretty erratic but I never had a ski before so not familiar.

Just did an idle test on the hose and sprayed WD40 around the carb base gaskets and throttle shafts....WD40 made the motor want to die. So I replaced the base gaskets and used a smear of ultra black around gaskets to make sure they seal. Di the WD40 test again and engine wants to die with WD40 sprayed on the carb shaft ends.

This problem is killing me .......but I'm at the point of trying to reseal the shafts and Ive ordered some different sized low speed jets to try if the shaft sealing process doesn't work.

 

[stephensimmons]

Are the shafts loose in the carb bodies?

 

[esahlin]

Are the shafts loose in the carb bodies?

The shafts did not seem unreasonably loose when moved up down side to side.

 

[stephensimmons]

The shafts did not seem unreasonably loose when moved up down side to side.

hummmm. I wounder if there it a seal in there?

 

[stephensimmons]

http://www.seadoopartshouse.com/oemparts/a/sea/500d90b2f8700209082587fc/carburetor-mag

The shafts do carry seals on them.

 

[esahlin]

Thanks for the link

 

[soccerdad]

It really seems odd that you have two sets of carbs giving you the issue. The air is not supposed to be in the fuel line. That is a big problem and could cause your issue. Easy test. Run a line directly from the fuel tank RES fitting to the inlet of the carb. This bypasses your fuel selector and filter/strainer (which both often leak air and you said you did not change either one.).

I have no idea why the 4d40 test did what it did. But I suspect some is finding its way into the inlet of the carbs, even as a fine mist. Try the test. I bet your issue goes away.

 

[esahlin]

Thanks soccerdad for mentioning this test.....I'll do this test this afternoon and see what happens. I hope that's the case in that the original selector and water separator are the issue....ive got some new ones arriving in the next couple days.

 

[mikidymac]

Those WSM carb kits and not replacing the fuel selector and fuel strainer are probably causing all the problems.

 

[esahlin]

I did the soccerdad mod and ran the reserve line direct from the tank to the carbs.....no bubbles in the reserve line going to the carbs. This cleaned up the idle noticeably and I went for a water test today and the idle in the water and anything around 1/8 throttle or less was much cleaner than before. THanks to soccerdad and when I get my new water seperator and selector valve Ill install and test again for air. in the line from the new seperator and valve.

Anything 1/8 throttle to about 1/2 throttle before 4K rpm there is still some misifre even after going with the direct reserve line. I have a new genuine Mikuni kit with Mikuni needle and seats coming in so I think I will install that this week and see what happens.

Plugs were dark tan in the center and dont seem to indicate a lean condition trending more rich than lean.

 

[soccerdad]

I did the soccerdad mod and ran the reserve line direct from the tank to the carbs.....no bubbles in the reserve line going to the carbs. This cleaned up the idle noticeably and I went for a water test today and the idle in the water and anything around 1/8 throttle or less was much cleaner than before. THanks to soccerdad and when I get my new water seperator and selector valve Ill install and test again for air. in the line from the new seperator and valve.

Anything 1/8 throttle to about 1/2 throttle before 4K rpm there is still some misifre even after going with the direct reserve line. I have a new genuine Mikuni kit with Mikuni needle and seats coming in so I think I will install that this week and see what happens.

Plugs were dark tan in the center and dont seem to indicate a lean condition trending more rich than lean.

I'm glad you made progress. Always glad to help.

 

[esahlin]

I plan to keep updating my thread with what I do until I find a solution maybe it will help someone else someday:

So here is what I did today:
I installed my new fuel selector valve (aftermarket brand) and new water seperator (OEM Bambardier unit)....hooked up the fuel lines back to where the out from the seperator is feeding the carbs. Now I am getting air in the out line to the carbs again. Turned the selector to reserve (bypass water seperator) and now there is much less air but a few small bubbles show up every now and then.

I rebuilt my second set of carbs with new Mikuni Needle and seats and new Mikuni black 80gram springs....one of the new Mikuni black 80 gram springs was defective in that I could only get a popoff of under 20psi.....tried the spring in two different carbs with same low result. In its place I ended up using an original spring that was already in the original 97 GTX carbs. This spring provided a 38 popoff. THe other new Mikuni black 80 gram spring provided a 35 psi popoff. Used New Mikuni diaphragms and gaskets.

Rebuilt carbs going on this week:
Mag carb pop off 35 psi
PTO carb pop off 38 psi

Before I take it to the lake I'll look into the air making it into the fuel lines. I think its sucking air into the lines from the tank or somewhere. Ill try to tighten the clamps etc.

Carbs removed from last weeks test.....with the reserve line run directly to carb inlet creating a better smoother idle but still had sputtering up to 1/2 throttle. Tested today after removal and Pop offs were both about 30psi (original 96 GTX springs) on both carbs with the aftermarket (not original Mikuni) needle and seats.

 

[esahlin]

Well, after all the struggles finally have it running good.....read on some old thread that problems with the water regulator valve can cause issues with part throttle driveability. Opened up my water regulator and the spring was broken in three pieces. Lower clamp was rusted out.....used a spring from my 96 XP, replaced rusted clamp with zip tie, Bellows checked out fine. Tested on the lake this weekend and its running great. Cleared up the part throttle issues .