'91 VXR Bogs In Water

[Ramskull]

I just bought a '91 Yamaha VXR 650. It runs great except when you first start off. If you give it any gas, it will die. The previous owner replaced the choke with a primer. The only way I can get it to go is pump the primer once & give it at least 1/2 throttle. Then it runs great as long as I don't go below 1/2 throttle. The strange thing is that it has great throttle response out of the water. I have checked the fuel filter. I have taken the carb apart & it is clean, as is the internal filter. The diaphams are great. I pulled the low idle needle out & it's fine. No matter how I set it, it doesn't name a difference. Please help!!!

[wmsky]

Re: '91 VXR Bogs In Water

Sounds like the engine is starved for fuel coming off idle. Most likely the pop-off pressure is too low and/or the pilot jet is too small. Does the carb by chance have an aftermarket flame arrestor on it? If so, the carb probably needs to be rejetted, and/or the pop-off pressure lowered. If the original owner didn't do this, not only is your engine running too lean at low rpms, it might also be running too lean at higher rpms. There are plenty of threads in the SBT forums about rejetting your carbs, adjusting your pop-off, and tuning your carbs. It's a good idea to do a thorough inspection of the engine, and tune the carbs, of any used pwc you buy. Never assume that a used jetski is tuned properly. Even if it seems to be running well, there could be problems that will manifest themselves slowly over time, or suddenly when the engine siezes because you pushed it that last little bit one day.

The throttle response out of the water is easy to explain. There is no load on the engine when the ski is out of the water. The engine requires much less fuel to spin up when there is no load on it, so a too small pilot jet could easily be supplying enough fuel in that case.

[Ramskull]

Re: '91 VXR Bogs In Water

Thanks for the response! I was figuring it might be the pilot jet, so last night I took the carb apart. It looked like the pilot jet was clogged. I cleaned it & everything else. I put it all back together & started it up. It now idles much higher than before. I will take it out Saturday & test it in the water. As for the flame arrestor, it is stock. If it still gives me problems, do you know what size jet I should go to?

[wmsky]

Re: '91 VXR Bogs In Water

If the flame arrestor is stock, the stock pilot jet should be the right size. If you are still having problems after cleaning the pilot jet, you might have a sticking needle and seat, or a clog somewhere else in the carb. I've seen others on the forum mention that the factory set pop-off pressure for a lot of pwcs is set on the high side. This would also cause a bog from idle. You might want to look into lowering the pop-off pressure with a weaker spring or a larger needle and seat. There are plenty of threads on these forums about adjusting your pop-off too.

[Ramskull]

Re: '91 VXR Bogs In Water

The clogged pilot jet was it! It runs great now. Thanks for your help!!! Thanks to you too SBT for having agreat site. :emoticonb