Engine bogs down above half throttle 1997 Sportster

[jwill19028]

Hello all,
I just put in an SBT rebuild 717 in my 1997 Sportster. I’ve properly broken the engine in, and have put a good 20 hours on it since then. It has run fantastic for those hours. However, just last weekend I had to get towed in on the lake for a dead battery after a full day of tubing. After some troubleshooting, I realized the battery was not charging and found the fuse for the charging system blown. I replaced the fuse then tested it again and it started charging but noticed a slight drop in rpm every so often. On my next trip, the boat was significantly loosing power. When full throttle it would hit full RPM but then bog down to what felt like less than half power, then back to full power. It randomly did this for power settings above 50% throttle, but would idle properly. It sounds like a carburetor problem, but I rebuilt both carburetors with mikuni rebuild kits over the winter, and it ran great the last 20 hours. The fuel selector was replaced about 2 years ago, but I’m going to replace it again. I’m wondering if somehow an ignition issue could cause this since the fuse for the charging system blew.

Any thoughts or input would be great,

Thank you!

 

[77Eltigre]

Hello all,
I just put in an SBT rebuild 717 in my 1997 Sportster. I’ve properly broken the engine in, and have put a good 20 hours on it since then. It has run fantastic for those hours. However, just last weekend I had to get towed in on the lake for a dead battery after a full day of tubing. After some troubleshooting, I realized the battery was not charging and found the fuse for the charging system blown. I replaced the fuse then tested it again and it started charging but noticed a slight drop in rpm every so often. On my next trip, the boat was significantly loosing power. When full throttle it would hit full RPM but then bog down to what felt like less than half power, then back to full power. It randomly did this for power settings above 50% throttle, but would idle properly. It sounds like a carburetor problem, but I rebuilt both carburetors with mikuni rebuild kits over the winter, and it ran great the last 20 hours. The fuel selector was replaced about 2 years ago, but I’m going to replace it again. I’m wondering if somehow an ignition issue could cause this since the fuse for the charging system blew.

Any thoughts or input would be great,

Thank you

I don't know the speedsters well but sounds like yours selector might be plugged or sucking air. If your on the water try switching from run to reserve. Or if you are on your way out the the lake try pulling the fuel line off the outlet of the selector and sticking it directly to the reserve fuel pickup. easiest way to tell if its a selector problem or not

 

[jwill19028]

I don't know the speedsters well but sounds like yours selector might be plugged or sucking air. If your on the water try switching from run to reserve. Or if you are on your way out the the lake try pulling the fuel line off the outlet of the selector and sticking it directly to the reserve fuel pickup. easiest way to tell if its a selector problem or not

I just bypassed the fuel selector and it’s still doing the same thing. Definitely feels like it’s a fuel problem. Idling perfectly. I think I’m going to take a look at the carburetors.

 

[jwill19028]

Here is a link of what’s happening! This was yesterday, after I bypassed the fuel selector. Still doing the same thing!

 

[77Eltigre]

When it bogs I would be tempted to pull the choke and see if it makes it any better.

Have you checked the fuel filter? it could be sucking air as well, otherwise Im wondering if the internal fuel filers on the carbs are restricted

 

[jwill19028]

When it bogs I would be tempted to pull the choke and see if it makes it any better.

Have you checked the fuel filter? it could be sucking air as well, otherwise Im wondering if the internal fuel filers on the carbs are restricted

That’s a good point, I’ll try pulling the choke. I also checked the fuel filter, and it was clean. I’ll probably take apart the carburetors and see if the internal fuel filter is clogged.