1994 Yamaha VXR minor issues - Page 4 - PWC Forum: The best hang-out for Personal WaterCraft enthusiasts
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post #31 of 34 (permalink) Old 12-12-2018, 01:23 PM Thread Starter
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I set it to 32psi according to a SBT chart i found online which is now deleted (the adjustments it suggested were wrong, so i don't see why the pop-off would be right). I dug through every inch of the manual and couldn't find anything about popoff. I also can't find anything online. What would you recommend for pop-off pressure on the 650? and on the 700?

Also, on a different note... What is the difference between the 650 and the 700? My best guess would be that the 700 has a super BN44 and the 650 has the super BN38, but I never verified this and everything seems identical.
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post #32 of 34 (permalink) Old 03-26-2019, 07:07 PM Thread Starter
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Here's another update in case anyone has been following or is looking for potential solutions. 1st off, i picked up a 1992 vxr with aftermarket head, exhaust, and all for $250 so i could have parts and a trailer for the 650. The parts ski ended up running after cleaning the carb and changing spark plugs. Its problem was that it sputters anywhere after 1/2 throttle and didn't rev any higher after that point. I rebuilt the top end and all the cooling/water channels (the outer rings surrounding the cylinders) in the head were full of shells. I cleaned everything and put it back together. Still had the sputter, so I decided to redo my fuel lines and shorten them, so I plugged my ON line and ran a line from my RES to filter to carb (this was to guarantee my fuel switch wasn't bad and to reduce the time it takes the fuel system to pressurize after starting). I also tried different known working ignition coils and they made no difference. It still goes up to 1/2 throttle and doesn't really rev higher, but it seems to go slightly faster (30-35mph) and no longer sputters, it just doesn't rev up. I was thinking maybe the temp sensor is bad and acting as a rev limiter. Thats what i'll look into next.
Also, the 650 i figured out had a stripped bolt on the head and a bad head gasket leak, which explains the wet plugs, terrible starting, and terrible running. I tried to re thread the cylinder block and my tap broke off into the block, so I'll be buying a new one of those off ebay when i find money. Lastly, the 700 would only kinda start like once a month. My friend suspected it was ignition coils, so i let him try one of mine, and before we knew it he was flying across the lake going 45mph! His only problem is carbs right now. It idles great and goes full speed, but everything else is sketchy. So here are some questions that i can't figure out...

If his ski is set at the exact point where the low speed screw is at its highest possible idle (it wont hardly run on any other setting) but when he give is gas it starves (I believe it is starve because he needs to poor gas in the carb to start it again), than his popoff must be decreased in order to allow more fuel, correct?

Also, is it possible that a bad heat sensor would restrict the engine from reving past 1/2 throttle? Or is there another likely source?
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post #33 of 34 (permalink) Old 03-27-2019, 06:06 AM
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If the cyl's are in good shape, any reputable machine shop can remove the tap, drill the hole, and install a insert. I would take it to a pwc engine builder though.

His ski: sounds like either pop off or a bad fuel pump. It's running lean, so I would find the problem asap. If he hasn't done a carb rebuild, I highly recommend it.

Try setting the screws to 1 7/8 low and 1 5/8 high and set pop off at 35-45 preferably just doing a spring swap.
Again, make sure the kits are true Mikuni kits. Off brand kits can cause issues from poor quality materials. make sure the little round check valves in the fuel pump are installed with the strip facing out. Make sure every little passage and orifice is clear and you use the new inlet filters.
Yes a bad temp sensor can cause that. It actually limits the rpm to about 3k, but should act like it's bouncing off a rev limiter, which it really is.
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post #34 of 34 (permalink) Old 03-31-2019, 04:37 AM
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Just found this lurking around. New I had something somewhere.
Has the screw and jet settings you are needing for both ski's.
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