Superjet - Bogging down after 3-5 mins at full throttle


Appreciate any help!

i bought a superjet last year, pretty much stock. RN - 2003

Put it almost to pieces this winter, checked all parts for wear, and fitted a b pipe, primer, tachometer, bilge, ++

The only engine mod is b pipe and MSD - I used the recommended b pipe settings on carbs and headpipe.

This season it has been going strong for 4 hours.

but last time i was out it bogged down and died completely - After 4-5 mins at full throttle. (This was after about 1-1,5 hours of run time) I started it again, and it run for 20 meters than died. started again, and run for 100 meters until i reached a dock, where i died it myself, to take a look in the engine room.

After a check and waiting for 10 minutes it run like normal again..
The only thing i can find that is wrong is a small exhaust leak from the b pipe expansion chamber. I can see a small stream of smoke coming up from underneath the chamber when running at idle. (bought the b pipe used).

I checked the fuel hoses for blockage, also took the went line off to make sure there was no wakuum/pressure in the fuel tank, everything was normal.

It has nevner happened before, not this season and also not last, where i run it completely stock for about 20 hours..

the thing is..last year i was a complete beginner and probably never runned it 5 mins at full throttle. so im not sure the problem has always been there..

My guess is, that small exhaust leak has nothing to do with my problem? It was there at least 2 running hours before my bog down. I will fix it by welding the hole shut, or might try some jb weld..

but at the moment i rather want to find out why my superjet booged down after a few minutes with full throttle..

Apart from the bog-down after full thottle at 5 minutes, It runs great.. tons more power than stock.. After it died, i waited 5 minutes, and it runned great again. Drow it for another 30 miutes without issues. but i never tried 5 mins straight at full throttle again..

So my guess is, i have some kind of fuel starving issue at full throttle for a extended period of time? I put the carbs to bits this winter, all gaskets/filters looked OK..

My plugs also looks good, dark brownish. i would say good. Not to white (lean), and also not black, (rich)

Any ideas?

I added a couple of pics from the engine bay.. im a complete noob, so if anyone can see something bad, please let me know!

Appreciate any input!

Best Regards,


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Perhaps the Chamber Leak allows Unmetered Air back into the Cylinder, diluting the Unburnt Fuel Mixture that is being stuffed back into the Combustion Chamber causing a Lean Condition in the Cylinders, which can cause Piston Seizures...

What are the Cylinder Compression readings?
I hope not..! I havent tested this season after b pipe, i did a couple of compression tests last year, it was 156 psi on cyl 1 and 158 psi on cyl 2.. Both times.

Havent checked after bogdown, i will get back with result, hope my engine isnt damaged:/

I thought a small exhaust leak wasnt able to damage the engine.. The pulse back has to be good, otherwise it wouldnt run so good.. Its alot more powerful than before bpipe - with the leak.

I will get back tommorrow with compression results, appreciate reply!
Kind of had a similar issue with my son's blaster a while back. Check that both jets are clean and clear and not gummed up. Then check the internal fuel filter(the one under the fuel pump)

My issue was a a combination of the above plus the cdi. Thinking it was a heat thing..once the cdi got hot enough it would fault. Let it cool down and it would run good, then fault again after a few minutes.

Sent from my SM-S767VL using Tapatalk
Lot of good theorys here, thanks!

I guess i Will start with plugging the hole in the chamber. maybe the engine didnt get enough air because of the leak, and thats why it died?
Do you think jb weld will do the trick or should i get it welded at a shop?

I did a compression test today, 158PSI on both cylinders.

mthomps: it didnt die imediately, it kind of gargled down to zero.. Sounded like it didnt get enough air or fuel

Bored@stroked: arent these engines designed to be driven hard? So what you are saying i should only have full throttle for short burts? I dont want to kill my engine
Stock you can ride it wide open all day. With b-pipe and an enhancer you should be careful. A lot of it depends on where you set the rev limit and your prop.

I would start with the exhaust leak and deal with that first. If you were a sprinter running a 100 meter do you think you'd run better breathing fresh air or a mixture of fresh air and your own farts


Urban redneck
Bored@stroked: arent these engines designed to be driven hard? So what you are saying i should only have full throttle for short burts? I dont want to kill my engine
Yes, but you've modified it.
Im not an expert. Lots of guys on here are, so I'd ask a professional. I also run like 220psi on 94 octane so short burst are the only thing keeping my engine alive lol


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Sacramento Delta
@ultraclearance I am glad your thread popped up again. Saturday and Sunday, I think my '95 FX-1 with the 61x 701 engine had the same problem you are describing. My wife had to tow me back in both days. Saturday we skied for an hour and a half, then the ski started bogging down and eventually would only start and run for a second after I primed it. So, I took the carb out checked the screen in the Mikuni SBN 44 and it was clean. Then I notice that the intake tube in the tank had detieriorated rubber flakes clogging it up, so I cleaned that up, notice that there were also some in the fuel filter but was not restricting flow and started it on the stand where it ran problem free. On Sunday, I got one WOT racing my wife (who now is consistently beating me, but I used to be able to beat her because I was able to hook the pump up - now it makes no difference) and then the ski died and would bog down and then back to only starting for 1 second after prime.

Hey guys.

I don't think it is a fuel issue. I have a 6m6 CDI I can put in (is that ok guys?) and try it.

Do you think that the CDI or charging or ignition coil on the stator heats up and starts to fail causing a loss of spark?

I would think a carb obstruction would not let it run WOT for quite a while and then cause it to not run?

Let me know what you think.

Manual says Engine Runs Irregularly or Stalls can be four things: Compression, Fuel, Ignition or again Compression.

Manual says "Sparking But Weak" apparently usually causes a no start condition. It is caused by fouled or defective spark plug, defective plug cap, ignition coil, charge coil, or CDI.

I don't know if the spark is in fact weak. Because I don't want to head back out to the river with my spark plug checker. (But maybe I should, that way I could compare initial spark strength running with later, when hot or warmer, running.)

I have to pull the spark plugs and look at them and also open the electrical box up, but I think it may have the original CDI in it. If so, I will replace it with a MSD Enhancer.

But my wife's '94 SN SJ required a rebuild of its stator by Jet Ski Solutions. So, maybe that it what is required. It also required a new CDI (MSD Enhancer).

P.S. I run WOT until I beat my wife, she beats me, or it gets sketchy and I get scared . . . My wife runs her SN SJ 61x WOT with impunity.

UPDATE: I just swapped in another CDI and same thing but now on the stand: Ski starts, runs a little longer than just on primer fuel and then dies. HEI in-line spark tester shows great spark until it dies. Ordering a oem Mikuni SBN 44 rebuild kit from @JetManiac or @john zigler and will go from there. BTW my fuel tank check valve was totally clogged, but taking it out does no good. Also it is the check valve hose that is deteriorating and putting black flecks in the tank so am replacing it with blue fast flow fuel hose 1/4".
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I found the problem. I took it out again yesterday, and after a few minutes of riding it died again. But this time i wasnt able to start it, i Just heard this buzzing noise from the ebox, probably the starter relay.

I wiggled the plus cable, and tighten it up, after that the problem has been gone. Drove it for more than 2 hours after without problems

All my faults are thanks to a bad terminal on my battery. The positive side. Last year when i took the battery out for the Winther i partly deformed the terminal because the screw was corroded. Didnt think more about it until now.

Its working now, but i will get a new battery Just to be safe.

Appreciate all feedback, thought i should post this in case anyone else get the same sympthoms.

Note: I did a test on the trailer where i disconnected plus terminal while engine was running. your engine wont die imediately if you loose power from battery, it kind of bogs down.. At least with MSD enhancer. So easy to think its something else, like fuel or air
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