B1 runs well for 5-7 minutes, then won't respond to throttle

I have a 94 Blaster, 61x, with a Riva pipe, TDR waterbox, and Boyesen reeds. JetManiac and I have been trying to get it back on the water all summer with nothing but frustration.

So far I've replaced the coil, CDI, and have run 3 different stators (2 used replacements from JM). The symptoms I'm describing below have occurred with 3 different stators. The CDI and coil I replaced earlier in the summer when the B1 didn't want to rev while in my garage. The CDI and coil seemed to solve this.

When it's cold and I drop it in the water, I'll get about 5-7 minutes of ride time before it starts to act up. During those first few minutes, it runs great and responds to all throttle inputs. I've had a similar issue in the past with my SJ, and a new stator solved it. Once the B1 is warm, anything more than about 1/3 throttle and it won't respond but it won't quite die. Just doesn't want to rev. It will idle fine and always starts right back up.

If you let it it sit for an hour or so to cool off, then try again, you might get 30 seconds to a minute before it starts to not respond to any throttle inputs. If you keep trying, more than about 1/4 throttle will actually cause it to die. Again, it always starts right back up and idles fine.

Fuel tank check valve is in working order, allows air into tank but not out.

I've stood in waist deep water and let it ride around in circles with the hood up around me while I checked for exhaust leaks and all seems good.

JetManic and I are stumped what to try at this point.

Fuel selector valve? Bypass the fuel selector? Carb rebuild?

Since it seem so temperature dependent, we keep thinking it's electrical.

I'd like to get it back on the water for a few more weekends this summer, but I'm already in the process of acquiring the needed parts for a 1200 swap.
 
To me it sounds like a fuel starvation issue as well. Did you replace the check valve, or just blow through it? I had one on my ski that seemed to be working fine when i tested it off the ski by blowing through it but something internally caused it to fail while riding. Replaced that and now were good. Worth a shot for the $10 or less it will cost if you haven't replaced it.
 
To me it sounds like a fuel starvation issue as well. Did you replace the check valve, or just blow through it? I had one on my ski that seemed to be working fine when i tested it off the ski by blowing through it but something internally caused it to fail while riding. Replaced that and now were good. Worth a shot for the $10 or less it will cost if you haven't replaced it.

I just blew through it. It's not new, it was on my SJ a couple years back.

I've ordered the following from JetManic and it will be here on Fri and I'll install before yet another test session on Sat.

Check valve
Inline fuel filter
OE fuel line to bypass the selector for now
Mikuni rebuild kit

Hopefully this does it.

Can anyone explain why the issue seems so temperature dependent? That's why JM and I were so convinced it was electrical. Does it have to do with the tank building up pressure as it warms up, and some partial blockage or leak somewhere (or both) not allowing the carb to suck enough to overcome that pressure?
 
I believe I’ve had the same problem with my superjet. I replaced the temperature sensor and it worked just fine. What it does to a SJ is shut down one cylinder when it overheats (don’t worry your engine isn’t overheating that’s just what the sensor thinks)
 
I believe I’ve had the same problem with my superjet. I replaced the temperature sensor and it worked just fine. What it does to a SJ is shut down one cylinder when it overheats (don’t worry your engine isn’t overheating that’s just what the sensor thinks)

Temp sensor has been deleted and blank ebox grommet installed. Sorry, should’ve mentioned that in my thread.
 
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I found a ton of tiny little fibers in a tank once....glogged up the carb filter. Would cause similar symptoms. Also rebuild the carb. Could have a worn diaphragm and clogged filters and gummed up needle and clogged fuel selector......
 

ScottS

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I’m going to throw this out, awhile back my buddy was having a similar problem, ski ran great cold for 5-10 minutes then started breaking up. He borrowed some plugs and the problem went away. The original plugs looked like new, nice and clean because they were new. They were solid top NGK’s. He checked the gap and I believe they were gapped at I think 0.030”. Solid top plugs come with a wider gap than the screw top plugs. He closed them down to the recommended 0.023” and the ski ran great. Yamaha has a weak ignition and do not like wide gaps. Try it.

Also, always try unplugging the start-stop switch and run it, a dirty one causes all kind of strange issues.
 
I ended up replacing the tank check valve, fuel filter, bypassing the fuel selector switch, and replacing the carb diaphragm and now she's running great!

The check valve I had on the tank would allow some air in, but wasn't as free flowing as the new ones I got from JM so I went ahead and swapped them.

The carb diaphragm in the ski wasn't OEM, either.

Hard to say what exactly solved the problem, but I finaaaaally have 2 running skis again, just in time for the end of summer.
 
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