1996 Sportster that has never run quite right

[physicistkev]

So I got this boat about 2 years ago for a song. I have worked on it enough to get it running and out on the water occasionally. I decided this year to tear into it and make it right, reliable and as close to stock as possible. I don't think there are any mods to the engine. The engine was a new from the factory unit in 2002. Previous owner put a few hours on it, had some issue with the carbs and stopped using it. When I got it, 2 years ago, I tore down the carbs and the fuel lines and put all new lines, cleaned the fuel selector and did a minor carb rebuild.

When I tore down the cabs a few nights ago, there was white powder stuck to everything. It was stuck on all of the o-rings and seals. I had to use a brass brush and brass wire wheel on a Dremel tool to get it off of all the carb parts. It was like cement. My first question is what is the white stuff? Is it aluminum oxide from carburetor rust/oxidization?

I ask because I want to know if I should tear out the tank and check it for sediment. I remember when I originally took the fuel selector out and cleaned it, it had the same stuff in it. I drained the tank last time and found nothing, so I don't think it's sediment, but I can't quite be sure where the white stuff is coming from.

The running issues are interesting. It starts up fairly well and idles well. Up to 1/4 to 1/3 throttle it responds OK. It's not smooth as you push the throttle. Feels like there are about 3 settings from idle to 1/3 throttle, this is not a cable feel, but a motor response feel. From 1/3 throttle to WOT, there is nothing. It sometimes bogs a little and after 3 or 4 seconds takes off. Sometimes, it just hangs at the 1/2 throttle state, not getting on plane but acting like it wants to. Once I get it wound up, it will run like that until you use most of the tank. I have run it for 15+ minutes at WOT without issue.

I have a nice Mikuni rebuild kit with new pop off springs, main and slow jets (stock sizes), new screws and clean carburetors (after the whole brass brush and wire wheel combo). Is there anything else I should be looking at? Boat is not premix. The slow jets were butchered, as though someone chewed them up trying to get them out and gave up. The passageways looked OK, but I am replacing them out of principal.

Thanks for your input,

Kevin

 

[Dr Honda]

The fuel tank is plastic... so there shouldn't be anything "White" in the fuel system. I would say that's it's probably decay from the aluminum parts. But... if you think it's junk in the tank... put a large, automotive fuel filter in the hose before the carbs.

As far as the poor throttle response... I'm going to say it's the carbs. Sometimes... when they wear out... they are hard to tune. But... if you verify that every passage is clear, and that all the parts are sealing... you should be OK. The critical parts are the seats on the fuel pump check valves... the high speed check valve... and the transition ports in the pilot circuit.


As a final note... have you checked the compression of the engine... or verified the rotary valve timing?

 

[SKETSEA]

If you haven't. replace the fuel line do so.

 

[physicistkev]

Replaced the fuel lines.... completely.

The tank is plastic, but didn't know if there was some reaction with the ethanol or something I hadn't thought of.

I did not check the rotary valve timing. I checked the compression when I first got it and it was fine. I don't remember what the value was but I checked it against the service manual and it was an appropriate value. I will check again when I go to put the carbs back on.

Is there a way to flush the aluminum oxide out of the system? I have a fuel filter in place but it doesn't seem to have much of anything in it. I guess I could go to a finer material or put a water fuel separator on it. Does the fuel system have enough oomph to put a restrictive water fuel separator inline?

Thanks for the input. I have worked on 4strokes for a long time and have an HPDI 250 on a larger boat, but this is the first 2stroke carburetor I have worked on.

Kevin

 

[physicistkev]

Update

Compression test on both cylinders. 140PSI on each. It thought that was pretty impressive, maybe I'm wrong.

After putting the carbs back on, syncing them, syncing the oil pump, spilling a gallon of fresh fuel in the bilge, cleaning up the fuel and reattaching the fuel return line to the PTO carb (grrrrr). I took it to the river and had a go.

Worked great. HAd the best throttle response I have ever experienced with it. It was almost magical . However, after 10 minutes of running around I made some sharp left and right S's and the engine bogged down. I had experienced this before, left turns and I lose a decent amount of power. I assume that this is from pulling fuel from the main jet and starving the engine. Got going straight again and it ran for about 30 seconds at WOT. Then, all I could get was half throttle. It sounded like it wanted to go but just couldn't make it. This went on for a few minutes. I then idled around for a few minutes and, voila. I had full power again. I am thinking its a fuel starvation issue. Maybe the fuel selector switch is clogged, maybe the inline fuel filter is clogged or something else is restricting fuel.

Anyone think of anything else that would do this?

Thanks,

Kevin

 

[griz400]

steering left and right, i suspect a problem with the fuel pickup inside the fuel tank, you could fill tank completely and if it works good then, then you know problem is in the tank,

 

[Lifted5.4Lariat]

There is a cable on the backside of the wheel that bumps rpms up when turning and idling and also brings the rpms down when going wot and turning.

 

[physicistkev]

steering left and right, i suspect a problem with the fuel pickup inside the fuel tank, you could fill tank completely and if it works good then, then you know problem is in the tank,

Tank was full today. Minus the gallon I spilled into the bilge.

There is a cable on the backside of the wheel that bumps rpms up when turning and idling and also brings the rpms down when going wot and turning.

Sorry, I wasn't clear. The loss of power is only when making left turns. They have to be pretty aggressive to see the effect. I would say you are correct if it happened both directions, all though, maybe the cable is only working for right turns and is not working for left turns. I will have to check into this to see if there is something to it.

Is it acceptable to bypass the fuel selector switch? I can just as easily cap the main or reserve fuel pickup and run off of the other. That would test the selector switch, but will that mess with the fuel system? The system is simple so I can't see an issue, but this is new territory for me.

Thanks for the input,

Kevin

 

[Dr Honda]

Is it acceptable to bypass the fuel selector switch?

Thanks for the input,

Kevin

Yes... it's fine for a test.

 

[physicistkev]

Excellent! I will bypass the switch and see if it gets better. I will also check the fuel system for holding pressure, but I don't think this is an issue as I wouldn't get symptoms of this nature or at least I would expect it to not be able to maintain WOT for very long with inadequate fuel pressure. I am certain it's not the carbs. It can't be the pistons or top end with 140PSI on both cylinders. Rave valve or reeds would not be this intermittent. Oil pump is working fine. It really has to be a fuel delivery issue.

Thanks for the help thus far,

Kevin

 

[physicistkev]

The update.

I pulled the fuel selector switch. I took the "ON" fuel line and capped it with a brass 1/4in nipple/cap combination. I pulled the "OUT" line from the inlet of the fuel filter and put the "RESERVE" line directly to the fuel filter. I did this so I would know exactly what line was what in a few weeks when I reassemble it all.

I plunked it in the river and off I went. It ran great. I was able to do a sustained 20 min 3/4 - WOT throttle run with no issues. I also had no RPM drop on left turns. This seems to have solved the major issues I was having.

I am now into smaller problems. For example, after the WOT run I noticed that when I went down to idle, the engine has a tendency to stall. Also, there is quite a bit of hesitation when throttling back up. No bogging, just a 1 second lag. I will look into the carb settings to see what I can do about this.

Due to some thunder storms I had to pull the boat, and when I went to start it out of the water, to remove water from the lines, it wouldn't start. I only had a few minutes so I couldn't troubleshoot, so I will have to try it again tomorrow or Sunday.

All in all, good progress.

Thanks,

Kevin