2001 Sportster LE dies at speed randomly

[4x4Nick]

Hi folks, longtime powersports & 4x4 enthusiast, but new to boating. My wife & I picked up a 2001 Sportster LE last weekend, put it in the water for the first time today, and while it seemed to run fine at lower speeds it didn't want to go past half throttle or plane out, it just bogged.

I did a quick plug change on the water, front plug seemed fouled & wet but the rear was decent. Then engine woke right up & planed out no problem, but then it died 30 seconds later. Not like lost power & slowly sputtered out, but like someone pulled the lanyard/hit the kill switch. I put it back into neutral & it fired right back up.

Still sounded healthy, but this time I only got about 20 seconds on plane out of it before it died again in the same way. At this point we decided to head back to the ramp. It died twice more on the way back, but seemed ok if I kept it around 3000ish RPM.

I thought it may have been a grounding issue, as the negative battery terminal lead was kinda worn out when I put a new battery in it the other day. So I fixed that back at the house & we headed back to the lake. That didn't really help much, the front spark plug was still fouling & it still wanted to die if we tried to get into it, though it never completely shut off on us the second time out.

What do you folks think I should be looking at first? I was thinking it was an ignition issue at first, but now I'm thinking fueling or maybe a bit of both. It's a low hour engine, less than 50hrs I'm told with a receipt for the rebuild in 2019, but I still see light grey fuel lines from the sending unit to the carbs that I've been reading need to come off asap.

Right now my plan is to pick up a compression tester & some new fuel line for it, and pull the carbs to clean them up. Is there anything else I should be looking at? Is there any part of the cooling system that would cause it to run like this?

Thanks

 

[POPPS]

Is this a 951 DI?

 

[4x4Nick]

No, it's carbureted. I have them off now, will hopefully be able to dig into them a bit tomorrow.

 

[despower]

Was going to say that it sounds like what's happening to my 2006 LE DI. And my problem appears to be the injector compressor.

You didn't say if the boat was going into limp mode. When mine won't go past 5000 rpm, it's because it's in limp mode (that irritating loud computer beeping).

 

[4x4Nick]

I didn't think these things had a limp mode. It never beeped at me on the water, only when I first turn the power on with the lanyard hooked up.

 

[despower]

Mine does, but mine is a DI. I thought I'd ask in case.

 

[4x4Nick]

Update on this, still having issues.

So this week I:

Rebuilt both carbs with Mikuni kits
Replaced both needles, seats (2.0), & springs (95g)
Tested pop-off pressures, got 25psi on mag carb & 23 on PTO carb (seems to be within spec)
Set the Low Speed screws both at 1.5 turn out, and the High Speeds at 0 (per specs I found from SBT)
Replaced all main fuel lines between the carbs with generic powersports fuel line
Replaced the fuel return line to the sending unit with the same powersports fuel line
Replaced the pulse line with the same powersports fuel line (all were original grey tempo)

Noted that the pulse fitting on the carb end plate had been broken off at some point & replaced with a threaded barb fitting. The fitting was loose when I took the carbs off, so I put some blue threat locker on it & tightened it down. There's a small crack in the end plate where the fitting has been threaded in, but doesn't look like it's causing any issues, but I could be wrong.

It wanted to run away on me when I first test fired it on the trailer, but I choked it quick & it calmed down after that. It wanted to idle higher than before, close to 4000rpm on the trailer, but otherwise it sounded like it should. I did take some slack out of the throttle cable at the carb end when I re-installed them, it seemed awfully loose when I took them off. There's still enough slack in the cable that the throttle lever moves a bit before the cable engages the carbs.

On the water about 30 minutes later it didn't want to start or idle properly, but after a plug change it started to behave. It responded well to throttle inputs & planed out nicely. Cruised it for about a minute at 5500 rpm and then it died just like before I took the carbs off. It started right back up and I got it up to speed again but it still died out. It re-fired right away, but this time it wanted to bog & die anytime I moved past 1/4 throttle, and was idling very high at around 2200rpm.

Idled it back to the dock, backed off the idle screw on the throttle linkage but I couldn't get it to come down below 2000rpm. Called it a day at that point. Pulled both plugs, no fouling this time on either, though the PTO cylinder seems a little whiter than I'd like.

Not sure where to go at this point, still seems like a lean fueling issue. Where else should I be looking? Are my carb settings not what they should be? Is there anything up stream of the carbs that has a habit of restricting fuel? The boat does have a fuel selector, are those prone to failure? How is the tank vented, could it be getting vapour locked?

Any help would be appreciated.

 

[despower]

This is just a wild guess. I was having problems with no apparent solution until I replaced the voltage regulator. The boat would behave for a while, then go into limp mode. The shop replaced the MPEM, which did nothing until I swapped out the regulator. Any way of testing that? Again, just a wild guess.

 

[4x4Nick]

Aren't the voltage regulators on these integral to the MPEM? Hoping to avoid changing that if I can.

Another update though, still having issues.

I have since re-run the pulse line with more robust automotive fuel line, my thinking was the powersports line I had used was too soft and may have been dampening the vacuum pulses.

I also bypassed all the fuel system between the tank & carbs, I now just have one run of automotive fuel line with a shutoff valve going from the reserve pickup on the sending unit to the mag side carb.

It was a real treat when most of the threaded sheath part of the throttle cable end broke off when I was trying to re-install the carbs. The price on those is eye watering, lock wire & electrical tape are holding it together for now.

I coated the carb base gaskets with some fuel-resistant RTV thinking I may have had a vacuum leak there, but I'm still getting a really high idle while on the hose, which is still making me think vacuum leak. I'm trying to get it to settle down between 2800-3000 rpm, but it still wants to run at least 3500. It doesn't want to run away on me, which is nice, even if I blip the throttle. I've tried spraying carb cleaner around the base of the carbs while it's running to see if a leak presents itself, I've had mixed results. I feel like it's mostly just pulling the misted cleaner in through the air intakes, which are right there, and idling down on that.

Are there any other areas these things are prone to pull air from that they shouldn't? When I bolt the carbs on should I have the alignment plate a bit loose until the carbs are bolted onto the reed blocks? Is there a gasket between the reed blocks & engine case, or is that just sealed with RTV? I'm feeling like that's the next area I need to look.

Thoughts?

 

[despower]

My 2006 LE DI has a separate voltage regulator from the MPEM. It's mounted next to the MPEM. Someone with better knowledge than me could let you know if it's the same on the 2001 model.

 

[Raven888]

When you start the engine with the boat out of the water the engine will always rev very high. It will only idle normally in the water. The jet pump is always turning and needs the resistance of the water to idle down.

 

[bigtexan99]

Nick, how's the engine running? Check my post history, my 951 Carb would also cut out around 5500 RPM as well. No root cause, but the issue went away after I had the carbs rebuilt.