99 Sportster starboard engine cutting out

[Mickey butler]

I have a new to me 99 Sportster with the 720 engines. The port side engine runs great but I am having some problems with the starboard engine. It starts up fine and idles but it cuts out around 3500 rpm and either drops to an idle or stops altogether. I cleaned the carbs and that helped for about 5 minutes. After that, it went right back to cutting out. The port engine revs fine all the way to 7500. The intake grate was also cleaned out but that had no effect. Does this sound like anything common? Someone else mentioned it might be the rotary valve but they weren't sure. I have heard that is a pretty tough job. Any help or advice would be greatly appreciated. Thanks!

 

[Sportster-2001-951C-Stock]

I vote for a fuel system problem. 1st, make sure there are no air leaks in all the components upstream of the fuel pump, else the engine won't receive a steady supply.

If you have the fuel pump that's divorced from the carburetor (not attached and part of the carburetor) those are known for wearing out and the replacements are of slightly larger capacity. You don't need a giant fuel pump but the replacement will have slightly more capacity.

In the case of an air leak in a fuel line, a low pressure check (less than 5psi) might reveal a component or fitting that isn't sealing thus as the fuel pump operates it's only sucking air and not much fuel. Usually this problem type will not allow the engine to make power at high speed and will cause general running problems (such as lean stalling) throughout the entire operating range.

Remove the fuel line supplying fuel to the fuel pump and pushing air into this line, should hear the air bubbling up from the bottom of the fuel tank at the pickup tube that's submerged in the fuel. IMPORTANT: Remove fuel cap from the tank first, to avoid air pressurizing the fuel tank.

 

[ialonso]

Is your 717 Single Carb or dual? Best $200 per engine is a NEW carb. You can by BN-40-38-24 for around $200 or less, and take the new carb's pump parts off and use your current carb's pump block off plate. If you have the same single carb set up I do, this carb is jetted the same, but has a built in fuel pump.) Your OEM carb from SeaDoo is much more, but BN40-38-24 has more parts (some you don't need) and costs much less. (The OEM has no built-in fuel pump, but instead a block off plate. to convert 40-38-24 to yours, you take the built-in fuel pump off and cover with the plate from your OEM carb, and BAM!, that's the carb you need)

Since it worked fine for a few minutes after cleaning it, I would bet it is carb related. It's your money and only you suffer the consequences and enjoy the fruits of spending it. definitely check all that can be checked without shelling out $200 bucks. (How did the internal carb filter look when you pulled it? any chance something is really dirty and plugged it again right after? It has happened to me with a bad fuel line and bad filter. I long ago replaced the carb' blocking plate screws with 8mm bolts so I could examine the internal filter in the carb with only flame arrestor removal. (It is very tricky but can be done) Ethanol fuel played a bad season on me long ago, so I know what dirty fuel can do.)

Fuel Cleanliness is EXTREMELY important for carb life and function. dirt can clog minute passages or leave your needle valve stuck open, flooding your engine on some restarts. (as in 30-90 minutes after last ride, engine is flooded.) I replaced the built in filters with Spin-On fuel filter/water separators, and I have never looked back.

Good Luck!