A troublesome 1998 gtx limited

[ddanster]

I'm about to give up on this machine and cut my losses..really don't want to spend the on season tearing this thing apart. Anyways to refer to previous posts I ran this machine last summer and had issues with starting it up. It would run at full speed just fine and had plenty of power. I spent the winter replacing all the fuel lines, rebuilding the carbs and verfying all systems. The carbs pass all tests according to the manual and are as clean as can be. Also replaced the fuel selector valve and recently bypassed it to see what would happen with running.

The issue I'm having on the water now as it seems to hesitate and flatten out at halve throttle. I'll fully throttle it and it stays at half speed then suddenly it will take off and reach full power and run well for a few seconds then abruptly cut out as if its running lean or starving for fuel. When it cuts out like that its hard to start but eventually starts. It definitely feels like its struggling at times. This particular engine does have a compression inbalance..one cyclinder is about 140..other about 127, at least when I tested it during the winter. But it ran fine at idle, mid and full speed last summer with those compressions. Perhaps I have a leak at the crank seal? I didn't take apart the fuel baffle should have I? Fuel pump seems to work just fine. Any help is appreciated!

 

[Dr Honda]

127 is low, and you can be fighting that. When the compression drops, the combustion gases push past the rings, and displace the incoming fuel/air mix. Have you checked the compression this year?

Yes... there are a lot of engiens that run at 127 PSI... but when the spec is 150... the seals (rings) are done.

You can have a crank seal leak... and that causes issues.


AND... you could have a rotary valve clearance issue.



Lastly... when you cleaned the carbs... did you verify the high speed check valve? Did you verify 100% that the transfer ports are clear? Did you make sure the bolts holding the carbs on are tight, and use new base gaskets?? Just recently, we had a guy chasing tuning issues, and the carb bolts became loose. AND... I can't tell you how many times guys say the carbs as good, but once I get my hands on them... I find issues.

AND FINALLY... when you cleaned the carbs, did you use all OEM/Mikuni parts? the aftermarket kits are hit-or-miss.

 

[- BiRkS_]

Dr Honda, I believe this is a 951. Aren't the compression readings supposed to be around 130-135 psi?

As for the mid range issues, check the accelerator pump and see if its squirting fuel in each carb. Also, when you replaced the fuel lines, did you replace the 1/4'' grey one in between both carbs?

 

[ddanster]

127 is low, and you can be fighting that. When the compression drops, the combustion gases push past the rings, and displace the incoming fuel/air mix. Have you checked the compression this year?

Yes... there are a lot of engiens that run at 127 PSI... but when the spec is 150... the seals (rings) are done.

You can have a crank seal leak... and that causes issues.


AND... you could have a rotary valve clearance issue.



Lastly... when you cleaned the carbs... did you verify the high speed check valve? Did you verify 100% that the transfer ports are clear? Did you make sure the bolts holding the carbs on are tight, and use new base gaskets?? Just recently, we had a guy chasing tuning issues, and the carb bolts became loose. AND... I can't tell you how many times guys say the carbs as good, but once I get my hands on them... I find issues.

AND FINALLY... when you cleaned the carbs, did you use all OEM/Mikuni parts? the aftermarket kits are hit-or-miss.

Yes carb bolts are tight, I took it out last weekend and had problems so spent this week removing the carbs and checking everything again. I took it out this morning and it has the same problem. They do have new base gaskets and it is tight..I did use aftermarket parts on the carbs so perhaps something there. I haven't checked the compression this year as of yet....think I will to see if it has gotten worse.

 

[ddanster]

Dr Honda, I believe this is a 951. Aren't the compression readings supposed to be around 130-135 psi?

As for the mid range issues, check the accelerator pump and see if its squirting fuel in each carb. Also, when you replaced the fuel lines, did you replace the 1/4'' grey one in between both carbs?

Yes I did replace the lines between the carbs. I also checked the pump to verify it was squirting fuel into both barrels. Flicking the throttle helps it take off when its hesitating however it will always cut out on me.

 

[Dr Honda]

Dr Honda, I believe this is a 951. Aren't the compression readings supposed to be around 130-135 psi?

.......

Yep... sorry about that. 127 is still OK on that engine. (I guess I shouldn't have read it over so fast)


With that said... and with a new thought...............


You could have a cracked, or broken reed.

 

[ddanster]

Yep... sorry about that. 127 is still OK on that engine. (I guess I shouldn't have read it over so fast)


With that said... and with a new thought...............


You could have a cracked, or broken reed.

I just did another compression test and the cyclinder that had 127 now has just a hair above 121-122 psi, and the other cylinder is about the same 139-140 psi.

 

[ddanster]

Thanks for everyones comments..I sprayed carb cleaner randomly to see if i had an air leak. I sprayed on the exhaust joint right after the rave vale and it nearly dies. Being this is the exhaust this shouldn't happen right?