Virage: Will 1 bad hall effect sensor cause just a bog off idle?

[casey67]

Have you tried manually controling the squirter. After it was running,try putting your finger over the exit-trying to seal it when releasing throttle. See if that helps the spray any.

[Bluedmax]

I'm guessing you rebuilt the carb, do you remember if it had 4 jets or 3 jets ? ( that will be 3 jets on front, 1 larger jet on rear of jet block-

Yes I rebuilt the carb (several times now). Set the pop off, set the lever height, rebuilt pump, cleaned everything out, etc. My carb has 4 jets all in the jet block.

[Bluedmax]

Have you tried manually controling the squirter. After it was running,try putting your finger over the exit-trying to seal it when releasing throttle. See if that helps the spray any.

When I had the carburetor apart and was checking the accel pump components, I had the small hose off the nozzle and was doing that procedure to prime the diaphragm. I'd seal the end of the hose with my finger when releasing the throttle, then cycle that way a few times. When I reconnected the nozzle and thought it wasn't working as good, that's what prompted me to disassemble and clean the nozzle, then vacuum test it once put back together.

With everything back on the ski and engine running I tried your suggestion of covering the nozzle hole when releasing the throttle a few times and doesn't seem to improve anything.

I'm wondering if I should open the carburetor back up and try a lower pop off setting?

[casey67]

There are carbs without accell pump. With proper adjustment they do not bogg. The Keihin carbs w/accell are set rather lean,the accell pump over comes the leanness to prevent a bogg.

So having pop off at it's lowest spec will help. Turning out low mixture screw - I think it's adjustable range ends at like 2-3 turns out,then a larger low speed jet is needed.


Did the carb appear to be "completely" disassembled ? Like powder coat worn off shaft nuts, any possibility the pump cam was messed with/replaced ?

[Bluedmax]

My neighbor has a 93 Yamaha 650, I believe without an accel pump. I'd be curious to go see if his carb would bolt up to mine just to try...?

Pop off spec is 18-20. I have it set at 19 (using my own setup with a gauge from ACE). So not much of a “range” to play with. The only way to lower the pressure is to cut the spring down right?
Low screw spec is 1-3/4 turn out. I'm already at 2. It seems to help the bog but also seems to load up at idle.

The carb has never been completely disassembled. My dad and I bought the ski new and I'm the only one that's ever worked on it. I've tried to look closely at the cam / linkage / plunger rod and see if there's anything that seems off. It all looks good though.

What I still don't get is how the original engine ran without a bog (even with 1 piston coming apart), SBT replacement engine #1 ran fine (exhaust manifold surfaces were machined wrong but the engine didn't bog), but now SBT replacement engine #2 I can't get to run without bogging. And I don't think I had even started messing with the carb yet (the sequence of events is now starting to get fuzzy). I've pressure and vacuum tested the new crankcase (with the intake and exhaust manifolds on). The pressure test held 9psi for 5 minutes. I left it on longer just for fun and it bled off slightly so I squirted some soapy water around everything just to see if I could see anything. I found a few small bubbles coming from where the flywheel housing bolts to the crankcase. Super small though and held pressure longer than most instructions indicate to perform the test for. Am I missing something here maybe and seeing bubbles trumps a passing pressure test?? I also vacuum tested it and held with no loss for like 30 minutes.
The only other place I found a “leak” was through the throttle shaft bore. I can get the engine to change rpm when I spray chemtool around where the shaft exits the carb. If this is a problem though, I’m not sure why this wouldn’t have affected the other 2 engines.
Could there be anything SBT did in the rebuild that would have changed the mixture requirements… larger bore size, higher compression, wrong components, ???
I guess worst case scenario if I can’t find anything else wrong and lowering the pop off doesn't work is I could start upsizing the jets and see if I can get it dialed back in. It still seems like a band aid though that is masking an underlying issue.

I really appreciate all the help and info! I've tried to be so thorough and yet this one is still just kicking my butt!

[casey67]

Even the service manual recommends "checking fuel mixture" after carb work, which to me suggests it may need adjustment away from factory spec.
The spec was when everything was new, which was along time ago.
In my opinion, carbs are not perfect-never have been. They are the cheapest/easiest way to meter fuel. When more precise control is wanted or needed, it's electronic fuel injection. And even that gets updated/perfected every year.

Every 1/8 turn of the mixture screw will make a difference,if you feel it or not. 3 turns or more might be the threshold for single carb,I dont know, I switched to twin carbs, you need to try. Need to find HOW far off it is to even guess what if anything is really wrong with it and if it gets rid of the problem. Personally I don't worry about being 1 or 2 sizes higher on jets on my 20-25 year old machines.

Sbt does bore all cylinders, IIRC 1.0 mm over and lower compression. Don't know what difference that makes with the tune. Probably a bigger difference with single compared to duals.

[Bluedmax]

I think my next step is going to be reducing the pop off pressure to see if that helps. Just to confirm, is cutting the spring the correct way to do this?

[casey67]

The fuel mixture screw is located outside the carb. On a single carb it is insanely easy to get to and adjust,readjust-return to "factory setting ".

Factory spring is correct size/pressure.
Aftermarket "kits" will probably have wrong pressure pop-off springs. When aftermarket springs need to be "adjusted", they will need to be trimmed. No going back to original setting ,presumed "correct".

[Bluedmax]

Yes on the mixture screw. I've already adjusted that several times and not achieved the results I needed. That's why I was thinking my next step would be to reduce the pop off pressure and see how it responds.

I used an aftermarket carb kit, so yes I had to trim the spring originally to get my pressure down to spec. Just wanted to make sure that was the correct way to do it. If I trim the spring down to lower the pressure more and it gets worse, I'll try to find an "original" rebuild kit to redo everything again.