Super Jet Carb issues

Hey guys,

First off, thanks in advance if you read this novel:

'90 superjet 650. When I picked it up for 250 off of craig's list it fired right up and ran. Brought it down to the river and it ran to a peak of about 25mph. It was coughing and sounded like crap. Took it home and replaced all fuel lines, fuel filter, and put in a primer kit. Then it wouldn't start at all unless the primer fed it some gas. The gas tank has positive pressure (not sure if it should) because it shot gas out of the "on" hose when I pulled the hose so I figure it isn't the fuel pick up. I bypassed all filters and switches and ran the "on" line directly to the carb. Still no go unless primed while starting. Spark is there, compression is 149 150. Pulled the carb off and rebuilt it, replacing every gasket on the intake side in the process. Mikuni carb rebuild kit used. It did the exact same thing once reassembled. Wasn't sure if it was an exhaust leak so I pulled the entire exhaust off and cleaned it, and then I replaced every gasket on the exhaust side. Still the same.

Description of exactly what happens:

Prime twice and visually see fuel enter carb. Press starter and it fires a couple times, but it doesn't sound to healthy. Then it backfires and will not fire again unless primed. If primed while the starter is turning the motor over it will fire a couple of times, but, again, it doesn't sound like a healthy 2-stroke.

So......Do I just suck at rebuilding carbs :banghead:? Low speed needle is at 2.5 turns and high speed is at 2.5 turns.

Kept the high speed at 2.5 turns and went 1/4 turn at a time on the low speed until 5.5 turns. Then repeated with the high speed at 3.0 turns.

Again, I'm questioning my rebuild skills because to me, everything seems to be pointing at the carb and a lack of fuel.

At this point I'm thinking about having the carb professionally rebuilt. Any thoughts/suggestions?

Thanks again
Mitch
 

Philip Clemmons

Owner, P&P Performance
Location
Richmond, Va
1st off, screw settings are measured from full closed. Turn them all the way in, then out 1 turn on low and 1-1/2 to 2 on the high to start.

Second, be sure your lines are on correctly. The top returns to the tank, the bottom is the inlet from filter/valve, and the middle is the pulse from crankcase.
 
That was turns from in to out. It still seems like its running lean, but I'll give it a whirl. Many, many, many thanks for the quick replies.

Lines are on right. With the low speed at 1 turn out and the high at 1.5 turns out it does the same thing. Always ends its little firing run with a funny sounding whoosh out of the exhaust. I've tuned a seadoo 800 (removed carbs, added some go fast parts, and then re-tuned them) and have never run across anything like this.

How hot/intense should the spark look? I wouldn't say it looked weak on mine, but it definitely wasn't up to par with car plugs. Again, thanks for the patience with a superjet newb.
 
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Well.......just saw there is oil spray from the drive shaft? I'm guessing the case seal is now blown and bleeding air into the system giving the back fires?

With the new settings and new plugs it backfires. Alot. Like its louder than a .22. Time for a rebuild kit or seal kit or? Plugs are wet too.
 

Kohldanielzimmer

Sierra Nevada Runoff Rider
Site Supporter
Location
Ahwahnee, CA
Yes if you can visually see the crank seals leaking it's time for a split and seal. I would hit up jet maniac for oem seals and a full gasket kit
 

Kohldanielzimmer

Sierra Nevada Runoff Rider
Site Supporter
Location
Ahwahnee, CA
Clean and prep for new gaskets carefully ( to avoid marring the sealing surfaces) and thoroughly. Use proper torque values for all bolts. Get a good case sealant yamabond 4, threebond 1211. I apply all gaskets dry but have heard of other methodologies. Make sure to remove your coupler before you take the crank out of the cases. I personally love the cold fusion flywheel lock. Makes life super nice for removing the coupler and flywheel bolt. You will also need a harmonic balancer type puller to remove the flywheel frame the crankshaft. Take your time. This link can be helpful. http://www.x-h2o.com/threads/68398-How-to-assemble-a-701-motor
 

Philip Clemmons

Owner, P&P Performance
Location
Richmond, Va
Might wanna consider a crank while you're at it. Jetmaniac has those as well for 250 or less I believe. Cheap insurance if you're going that far into it.
 

Shonuff

I've got the glow
Site Supporter
Location
Memphis
You might have eaten a flywheel key. Also, you have a super awesome screen name as you're on my lap at all times.
 
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