Seadoo GTX RFI won't start on cranking. Just backfiring loud from manifold and exshaust.

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sgivanth

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I bought an GTX rfi with a wiring problem which now have sorted. Now the motor runs for 1 or 2 seconds and cuts out with a huge backfire loud from both manifold and exhaust. After investigating I found the rotary valve shaft got a free play 1/4 -1/2 of an inch (approx 5-6mm movement). Is this normal or could be this cause not start symptoms. Got 155 psi compression on both cylinders. Also got good spark and fuel in each cylinders.
 
No, that is not normal. While there is a measurement of clearance, it is between the plate and cover. The rotary gear is brass, and is a worm gear where it makes contact with the crankshaft in the center, between the connecting rods. It's brass so that if you damage something, it's that rotary shaft gear, and not the crankshaft. Make sure this play you suspect, is actual play; in other words, if the rotary shaft is moving, the crankshaft is not. If this gear is worn out, then it will cause the backfire your getting.
 
Thanks Seadoosnipe. Yes the valve moves freely about 5mm left or right without moving the crank shaft. Can the brass gear wear out rather than breaking the gear teeth? Causing the free play? Also could this cause me no start and backfire symptoms? Sorry I’m a car mechanic but not expert on rotax and rotary valve engines.
Also what I noticed when cranking on full throttle the engine starts and revs full without backfire for 5 secs and then it cuts out. Spark plugs were more oily wet and loads of oil or petrol mixture have thrown out from the throttle body. Exhaust manifold looks dry.
Is it safe to pullout the shaft using the puller without dismantling the crank case?
 
Cranking at full throttle shuts off the fuel pump if I remember correctly, I know for sure it does on the DI skis.

No, you shouldn’t have play on the rotary valve.

I have heard both ways but have only split the cases to pull the rotary shaft so I can’t say for sure you can do it without splitting them.

You also can’t inspect the cavity or clean out any debris without splitting the cases and when the brass gear goes it makes a brass mess inside.

Also if the engine is flooding from bad injectors it can make big backfires from all the fuel in the exhaust.
 
Thanks mikidymac..... I will pull it out whilst the engine on ski. I got a inspection camera to check for debris. I don’t think there will be brass shavings as the worm gear might have just worn out. Anyhow will check for any in oil out of crank case.
Injectors seams to be good as I checked the spray pattern leaving the rail outside.
I assume the engine gets flooding due to free play movement and letting both cylinders suck up air and oil from the valve openings.
Once again thanks a lot for information and now I’m confident that valve play isn’t normal and it’s causing backfire with no start symptom.
 
I would first check the injectors. They may be leaking fuel into the cylinders because they are not sealing properly. Where are you measuring the movement of the rotary valve? At the furthest point from center?? I have a little slack one one I recently checked... enough to cause me some concern and make me wonder about the condition of the rotary gear. The engine ran fine.

If you are pulling the rotary valve shaft with the engine inside the ski please start a thread with pictures. I'd sure like to know if this works for you. I dislike pulling engines. That said... pulling the engine makes every job so much easier. LOL
 
I pulled the rotary valve shaft out today. Brass wheel looks ok but maybe teeth are worn to cause free play.
Also how to check injectors are leaking fuel or not on to cylinder head.
What do mean by the shaft is toast?
There are a plenty of YouTube videos about pulling the shaft without removing the engine.
 
I pulled the rotary valve shaft out today. Brass wheel looks ok but maybe teeth are worn to cause free play.
Also how to check injectors are leaking fuel or not on to cylinder head.
What do mean by the shaft is toast?
There are a plenty of YouTube videos about pulling the shaft without removing the engine.

I sent my fuel injectors off for rebuilding. Cost me $48 total for both. You get a print out on initial tests and results when the injectors are cleaned and ready for service. I have the contact info. The company is in Florida. I am well pleased.

I thought it would be a pain in the butt to get in there to pull the rotary valve shaft with the engine in place. I still wonder if you needed to do that but you'll be glad you did I'm sure. Good luck !!
 
Can someone explain me if the attached picture looks correct??? I guess someone have used a wrong valve plate as the manual reads the duration should be 159 degrees. This one reads 172 degrees which may cause the issue for back fire.
 

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Many thanks etemplet.... is the valve on the engine pic is correct then?

If you check the manuals it gives you that information and I don't have one in front of me. I will look later today if that will help you. I am anxious to hear of your adventure in installing the rotary valve shaft with the engine in the ski. I had the most difficult time pulling the rotary valve shaft out of the engine and mine was on the bench. :) I'd love to be able to remove and replace that shaft with confidence. :) Get R Done !!!
 
Etemplet the above image is with my replacement shaft installed. It wasn’t a difficult job to pullout with a correct sized socket and a m8 bolt.
 
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