help backfiring through carb and exhaust!

[power=speed1]

hi guys im new 2 jetskis but have delt with many 2stroke motors. ok so my cousin gave me a 1991 seadoo xp ( i think ) he said the jet drive was locked. went 2 crank it and of course nothing so i tried another battery and it turned right over. after i cranked on it for a while it started and run for about 15 minutes then bogged down and shut off. he had just recently quit using the oil tank and switched 2 premix. there was barely any oil in the tank when i first got it. and its completely empty now so im wondering if the rotary valve ran out of lube when the tank got empty and frose or stripped out the gear. and if so would it cause it 2 backfire through exhaust and intake. sorry so long and thanks in advanced.



sorry 4 posting in the wrong thread im new and if i new how 2 move it i would.

 

[timmyboy76]

hey power...its cool to run premix, but you'll need to keep oil in tank, like you said, to lube the RV assy. If your losing oil, then pull plugs out, and ground them, and crank motor. Lost oil would more than likely, seep thru RV seal and exit thru plug holes while cranking, if so, then rebuild/sbt in the worx. You might wanna take gander at fuel system,..clean/replace the fuel selector, replace grey lines, rebuild carb/s...Its a start, stud...:cheers:

 

[seadoosnipe]

Backfire?

Back fire through the exhaust is probably due to a fuel and oil mixture so great that it ignited.

Like timmyboy said......your oil tank is now only used to keep the rotary valve lubricated. You should rarely see an oil drop in this tank unless the seals are shot...........:cheers:

 

[power=speed1]

sorry i wasnt clear. he switched 2 premix but didnt remove the oil pump. does that make a difference about the oil disapearing? it should right?

 

[timmyboy76]

what your describing, even if he forgot to disconnect the oil line going to injection pump, the resivoir bottle shouldn't lose the oil that fast, on what your describing. Might check for leak/s, if you can, pull plugs and crank motor over with rag over holes, if oil blow'n out, then my guess the RV seal bad...

 

[seadoosnipe]

Rotary Seal?

:agree:........hit the nail right on the head!:cheers:

 

[power=speed1]

so if the seals are bad would it cause it 2 backfire? it wont start, it will turn over and backfire.

 

[seadoosnipe]

Backfire?....

Normally, about the only way a 2 Stroke Rotax will backfire is because the rotary valve is out of timing. If this has been apart, then it may have been re-installed incorrectly.

As for backfiring through the exhaust? You allow any buildup of a combustable liquid to accumulate in the exhaust system and the vapor finally reaches the spark of the plug during a stroke, then yes, it's possible that you'll create ignition, exploding the vapor buildup.

So, the two part answer is, yes, with a build up, a backfire caused by vapor buildup is possible but, the more likely cause of a backfire is from an improperly set rotary valve.

See if you can find out if this plate was removed. Also, the possibility of the rotary worm gear pin being sheared from the shaft is possible.

 

[power=speed1]

i dont believe the rv plate was pulled it was running fine for 15 minutes or so and it baughed down and shut off. i hope its the worm gear as u mentioned. in a few days i can start pulling it apart, ive been waiting for my arm to heal, 23 staples.

 

[power=speed1]

ok so im back checked the rv plate its correctly timed. when i try 2 start it, it spins slowly and builds up speed faster and faster and right when it seems its going 2 start it backfires and sometimes stops the motor completely, could this be due to incorrect ignition timing? maybe a sheared woodriff key?

 

[timmyboy76]

maybe a bad brass gear, down in RV assy...

 

[power=speed1]

if it was a bad brass gear wouldnt the timing on the rv assembly be off? also i would like to thank everybody 4 welcoming me and for all the advice, it is much apreciated.

 

[timmyboy76]

no offense, but how you check the timing. Maybe its 180* off

 

[Chester]

ok so im back checked the rv plate its correctly timed. when i try 2 start it, it spins slowly and builds up speed faster and faster and right when it seems its going 2 start it backfires and sometimes stops the motor completely, could this be due to incorrect ignition timing? maybe a sheared woodriff key?

Bingo!
A sheared woodruff key is what you have. That and a rotary valve are the 2 most likely causes of the backfiring you describe.

Chester

 

[timmyboy76]

some were/weren't

...............

 

[power=speed1]

front cylinder at tdc the valve is set at 132* i believe that is correct, please correct me if i'm wrong.

 

[power=speed1]

ok so im stuck because i dont know the exact year of the motor each year timing is different and i believe 132* is incorrect thanks timmyboy. now how do i figure out the year ?

 

[timmyboy76]

alright, you should have a 132*RV, with 115* opening and 65* closing. As for oil, hows that doin, bottle draining somewhere still?

While i'm thnking of it, take 2-long pencils, and remove the spark plugs. Insert pencils in the holes, and then turn the pto counterclockwise. while doin that, take a gander at movement of pencils, make sure that at any time, they didn't movet he same way. If so, you have a twisted crankshaft, which would cause backfiring. I know, did it to my banshee...

 

[robin savell lloyd]

Bingo!
A sheared woodruff key is what you have. That and a rotary valve are the 2 most likely causes of the backfiring you describe.

Chester

If I am not mistaken Chester knows pwc's more advanced than most people. He is famous but many do not know this. He has alot to offer to this forum. I have read many statements by him and he seems to be very wise. But I can allways be wrong so good luck. Robin :rofl:

 

[power=speed1]

thanks for the info its much apreciated i will check everything out 2marrow. this is been a greate forum with lots of help and advice from friendly people. thanks.