Backfiring through carb JS550

[velocity]

So my buddy picked up a couple JS550 hulls and an engine yesterday. The engine will run but is backfiring through the carb. The pipe has a crack in it that is letting water out. Can the lack of back pressure from the pipe cause that or should we look elsewhere? Air leak on the intake side maybe?

 

[cosander]

timing or woodruff key

 

[velocity]

Can you be a little more specific? We are both pretty mechanically inclined but this is the first time we have done any real work on a ski. Where is the woodruff key located, and are you thinking it may be sheared? How is the timing adjusted and which way would we need to go with it if it isn't they key?

 

[WFO Speedracer]

He is referring to the flywheel key that holds the flywheel in position on the crankshaft,it can shear if you jump it and keep the throttle pinned or crank it out of the water and back it in,I have seen both.

 

[Mouthfulloflake]

its a key that locats the flywheel on the crankshaft.

if its sheared, even slightly shifted, it will affect the ignition timing.

remove front cover, pull flywheel, verify key condition and flywheel alighnment with said key.

 

[velocity]

Sounds like the place to start. I am guessing there is a gasket in there somewhere though that will need to be replaced when we pull the cover? Will we need to find a replacement gasket or what do people use for their old ski's?

 

[Mouthfulloflake]

the kawi 750s used a long O ring around the front cover, you can reuse it if you dont break it.

maybe the 550s are the same?

 

[velocity]

Guess we will find out in a couple hours when I get home from work.:dunno:

 

[WFO Speedracer]

Yes 550's have the same o-ring setup on the cover,harmonic balancer puller with three bolt setup and a cpl of taps with a hammer on the end of the puller bolt should free the flywheel.

 

[velocity]

Well we got the cover off the flywheel yesterday, I think today we are going to try to figure out a way to time it. Have the timing light and I am sure we can fab up a pointer for TDC, just need to figure out how we can gauge the RPM's.

 

[velocity]

Well the other hull was in much better condition so we ended up just moving the motor into the nicer hull before we started messing with it. Once we got the flywheel cover off there was a small amount of oil in there that I think the previous owner may have put in to free up the starter. We cleaned it all out and put some new plugs in and some fresh gas. It fired right up and no backfiring now. Not sure what actually fixed the problem, could have been the oil messing up the timing, the old plugs, or the old gas. In any case it is running like a champ now.

 

[Mouthfulloflake]

cool!

tag and insure that BEEYOTCH, and maybe we can get to ride this weekend.

maybe we wont get shot at the boat ramp now that you have a water box.

 

[velocity]

I still need to get mine tagged lol. Might go do that today in preperation for the ozark invasion. Chad's still has good registration and even a fire extinguisher so I doubt he messes with it. His carb has the thumb throttle connection and he only has a finger throttle so we still have to figure something out there. Either need to find a thumb throttle or a finger throttle connection for his carb.

 

[Mouthfulloflake]

he should get insurance, there are some NICE boats out there... I wouldnt want to be liable for for damage to one of them.

but thats a whole other thread!

 

[velocity]

Alright guys, need some help we are at a loss on this ski. We pulled the flywheel and the key was fine. Put it back on and set the timing. Still backfiring through the carb at high RPM's. It has also developed a new problem where if we set the idle so it will run on it's own it will ramp up to WOT, giving it gas kills it. Thinking the revving to the moon is an air leak on the intake side somewhere, but we put new gaskets from where the intake mounts to the engine all the way to the carb so it is all fresh gaskets on the intake side and still doing it. Can it be any other gaskets causing the reving like maybe a headgasket or something? Also can anyone explain to me how it is backfiring through the carb with correct timing, because that blows my mind?

 

[WFO Speedracer]

Sounds like you have crankshaft seal leaks which will cause both the backfiring through the carbs and the runaway throttle issue.Pull the engine,pull flywheel and stator again and pull off the rear coupler.Separate the two case halves and replace the crank seals,seal it up with threebond 1104 or yamabond 4 reassemble and ride out.

 

[sflsurfrider]

insure your skis? hmmm.... never thought of it.

thatd make an interesting thread indeed.

 

[Mark44]

Bad reeds?

Mark44

 

[Mark44]

insure your skis? hmmm.... never thought of it.

thatd make an interesting thread indeed.

Insurance what is that crazy thing you speak of?:dunno:

Mark44

 

[velocity]

Bad reeds?

Piston port motor. We just changed out the entire intake and carb from another ski I had sitting in the garage that has the 38mm carb on it. It seems to run better, now it bogs when you give it gas but no revving to the moon.