SX/SXi/SXi Pro Throttle and acceleration problem

[Mitchell]

Ok so i give my ski full throttle from going no throttle and it either bogs down or stalls. I thought the choke was on but no. Maybe old gas? But ran the old gas out. Anybody hAve an idea?

 

[Mitchell]

It's a 1992 750 sx

 

[ratboy120206]

carb! bog is rich, stall is lean!

 

[joshp]

Anyone have an idea on issue below:
I had a 1/2 tank of fuel and filled ski the rest of the way with fresh fuel. Power was great as usual for about 10 minutes. Then in the miidle of the ride I suddenly had a huge loss in power. Low end torque is gone and top speed is about 8-10 mph slower. Can bad fuel or a poor mixture cause this drastic of a change. I would expect a fuel issue to cause the motor to not run before an 8+mph power loss? Could something have damaged the impeller? Could it be afuel pump issue? Tried running on reserve with no change. Power is gone regardless of whether engine is warm or cold. Thanks!

 

[SNOWMAN]

make sure you have NO WATER at all in tank. water tends to collect in tank and then separate...then it gets a big gulp of water and bogs. empty tank. refill and run ski. i heard the cylinders will rust as well if water is in the gas and then it sits

 

[joshp]

make sure you have NO WATER at all in tank. water tends to collect in tank and then separate...then it gets a big gulp of water and bogs. empty tank. refill and run ski. i heard the cylinders will rust as well if water is in the gas and then it sits

What would water in the gas look like? I've syphoned as much as I could. I also pulled the carb to check for a clogged jet but didn't notice a clog.

 

[jMike]

You can see a separation in the bottom of the tank where the water will sit. Check your needle and seat for wear as well while your rootin' around in the carbs, look for wear rings or marks on the needle tip. Hmmm what else.. look for exhaust leaks under the hood, the fumes can build up and choke out the engine. Check your reeds for chips/cracks.

 

[SNOWMAN]

yeah like jmike said. the water sits in a small catch basin type thing in very bottom of tank. make sure you get ALL the water/fuel out. if you dont want to take the tank out, connect a shop vac to a gas can and syphon it out that way, it will be bone dry. i learned it on youtube. no fuss. no mess. no taking tank out. i was surpised. mine had like 1/3 of a gallon of pure water in the tank and was running ok...it bogged a little but not much. if you use the shop vac method, you will see the water come out of tank...it seprarates and looks like spring water. cant miss it. drain it.

 

[joshp]

We found one of the fuel pickups is cracked in two where it hooks into top of tank. I don't know if there was a pre-existing crack there that I disturbed when checking the filters in the tank. I now have it running on reserve but power still isn't up to normal. Should the ski have the same amount of power running on reserve? I've also disconnected/bi-passed the priming system in case it was causing a vaccum leak.

 

[joshp]

Update: I replaced the fuel pickup and the ski still lacks power. Reeds look okay. Fuel diaphragm/pump isn't torn. Engine compression was tested and both cylinders are pretty even in compression.

I know it is not the fuel at this point.

Does 92 750SX come with a single Mikuni carb from the factory? The ski has a R&D intake manifold.

Thanks.

 

[sxipro02]

Mine started doing that when my wires were bad. Might be tine to cut them back or get new wires put on your coil.

 

[joshp]

I have a new coil and wires that I never got to putting on. I'll try swapping in the new one.

Where do you guys get new spark plug boots? Originally I was going to go factory but I think they're like $32 each.

Does 92 750SX come with a single Mikuni carb from the factory?

 

[sxipro02]

Don't know about the carb but I do know you can get msd boots or off brand msd looking ones cheap on jeggs or summit.com.

 

[eeerieski]

those come stock with a keihin 38mm carb stock, mine would bog every time and no amount of carb adjustment would fix it, come to think of it carb adjustment really didn't do anything. I bought a 44sbn and waiting on the intake, should run great after.

 

[Hirschfelt]

19 years old: Many options - Time for spring tune up
Keeping stock 38 - 7/8 turn out for high and low screw. Thats stock meaning stock everything: pipe and are filter
I would ditch the 38 keihin and get a mikuni. Or pick up a set od sxr takeoffs.
Make sure you pressure test the low end.
Crank case drain can leak. Block that off.
Rusted up flywheel ans stator can rob power. Pull the cover and clean and reseal.
Cut plug wires as stated above and get new plugs BR8ES NGK or B8ES NGK
New fuel lines are cheap,
I would regasket the entire engine and inspect all internals. Might be able to just hone and get new rings to liven up the top end. or get a complete new top end.
Good luck

 

[Hirschfelt]

PS: just cut back the plug wire about 1/4" and push the boot back on. Use dielectric grease in the boot. Auto store NGK have a screw on top make sure that is tight.

 

[joshp]

I bought the ski used about 3.5-4 years ago and had great power until last summer.

It has a Mikuni carb on it and it has a Bad Bones aftermarket head. Compression test showed no signs of a weak topend.

I'm going to try new coil and wires (the two came as a unit).

If this doesn't do It, it may be worth taking to a shop to avoid the high cost of replacing part by part...

 

[kevbo]

It was due for a complete round of maintenance about 3.5-4 years ago.

 

[joshp]

Is there any other type of Mikuni carb other than SBN series? I'm looking to rebuild the carb and I plan on purchasing the kit on ebay.

 

[jhammett89]

I second the wires, mine were cracked and caused it to cutout. Trimmed them back and good to go!