1998 Sportster 1800 needs help

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mgrant

mgrant

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I'm new to this forum so let me start out by saying hi to all. I just bought a 98 sportster 1800 in great shape for its age. it just has one problem and i can't figure out how to go about fixing it. i am by no means mechanically inclined and need help! it idles strong, runs low rpms strong, and runs high rpms strong. middle rpm causes the left engine to bog down and stall out if the throttle is not immediately opened up or let off of. the problem starts around 3500 rpms and continues to around 4000. when i increase throttle slowly, at 3500 rpms the motor will automatically back down to to around 2500 rpms and soon stall if no further throttle action is taken. the right motor runs great all the way around. i have replaced all spark plugs, put a can of sea foam into the remainder of the gas that came with the boat, and run the boat nearly empty of fuel. to the best of my knowledge the boat was not run often last season, and was not winterized last winter, so i am assuming from other things i have read that this is a gummed up carb problem, but i really have no clue. any troubleshooting help or help in general would be greatly appreciated. thanks!
 
yeah sea foam didnt do anything for me, but you read so many good reviews that you just hope the "mechanic in a can" will work for you. i was afraid of the carb issue, guess i'll pay my dues and take it to the mechanic next week. better to pay a little now and fix small issues before they becomes a major pocketbook cleaner.
 
you got 1 carb for each motor, with ampel amount of room to work in. Theres a total of 14 allen bolts for each motor to remove carb...besidesthe fuel in/return lines, and pulse line...

6-airlid assy
2-carb brace
4-flame arrestor housing
2-carb itself

10mm wrech to crack the nust off throttle/oil and choke cabes

Save the money, get a socket allen set, and you'd be surprise how easy/fast, after the first one, the second one will be...:cheers:
 
ok, haven't done anything yet, but just a quick add on comment. i took the boat out over the weekend and noticed something else. when i slowly throttle up, the motor runs great. it only bogs when i quickly throttle up to mid rpms. still sound like a carb problem? thanks. mark.
 
mgrant said:
ok, haven't done anything yet, but just a quick add on comment. i took the boat out over the weekend and noticed something else. when i slowly throttle up, the motor runs great. it only bogs when i quickly throttle up to mid rpms. still sound like a carb problem? thanks. mark.
Click to expand...

the excell pump and fittings are clogged. Pull the carbs, bud.
 
took the boat to the shop and had carbs cleaned and rebuilt, they said the same thing you said seadooya, and they got it fixed! but whatever they did, they caused a new problem to arise. now for no apparent reason, the motor automatically revs up. my throttle will be all the way back, and the motor will just shoot up to 2500 to 3000 rpms without me touching the throttle. any idea what this sounds like? i'd like to be able to talk to them about it a little, but i definitely don't want them to tell me some story and try to make me pay to fix what wasn't a problem before they started working on it. why would it just automatically rev up? thanks. mark.
 
both motors will rev up/idle to 3k, on the trailer. Once in water, the idle will be drawn down to 1500.
 
i never started the boat up out of water, i waited until i got in. the problem i'm talking about happens when the boat is in drive, at zero throttle. once i gave it some throttle, it stopped the sporadic auto rev. but once back down to no throttle, it started back up again...
 
whether in nuetral or forward, the boat, on the trailer SHOULD idle at 3k, once in water, it'll drop to 1500.

If in nuetral, on the trailer and try to throttle it, the motors wont go past 3500rpm, because of the rev limit switch.
 
once in the water it did idle at 1500rpms, but randomly automatically revved up to ~2500rpms once in gear at no wake speeds...
 
when i was talking to the service rep where i got my boat fixed, i think he said i may have a leak in an air line, or i may have air in some kind of line, or something to do with air. don't know if that can help anyone diagnose the prob but any response is appreciated.
 
well they said nothing is wrong with the boat. they said the boat is equipped with "steering assist" to help turn the boat at low speeds, and the reason it didn't do this before is that the carbs and accel pumps were so clogged up that not enough fuel could get through at low speeds to activate it. now that they are clean it works as it should.
 
mgrant said:
well they said nothing is wrong with the boat. they said the boat is equipped with "steering assist" to help turn the boat at low speeds, and the reason it didn't do this before is that the carbs and accel pumps were so clogged up that not enough fuel could get through at low speeds to activate it. now that they are clean it works as it should.
Click to expand...

soooo....whats the problem?
 
what does "steering assist", have do to, with high idle? Or is it idling now, correctly?
 
it wasn't a high idle, but rather a boost in rpms in forward or reverse at no wake speeds. with the steering assist, when you turn the steering wheel left or right to an extreme, one motor automatically boosts its rpms to better assist the boat in turning. the boat always idled correctly, but it caught me off guard when the rpms automatically jumped up in gear. and now that they told me it happens when the steering wheel is turned to an extreme in one direction, it makes sense.
 
I think what he is saying is that while idling he would steer the boat and the steering assist would kick in and the rpm would jump as the engines are used for extra thrust. he did not know this is how the steering worked and thought he had a problem.
 
bingo, i've never been on a boat with "steering assist" so it threw me for a loop when my boat began doing this (functioning correctly) after my carb rebuild.
 
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