1996 sportster throttle issue

[physicistkev]

I posted this in the PWC catagory by mistake. I am reposting it here so if an admin sees it in the PWC section please delete it there.

So I just picked up a 1996 speedster that has a throttle/power issue. It is a bit difficult to start but not unbearable. All cables (throttle, choke and direction) are smooth and clean. Rear cylinder has 142psi and front cylinder has 140psi compression. Spark plugs look good, slight charcoal color and are not excessively wet. If anything they are a bit on the lean side.

The problem goes like this. Once started the boat will use up to 1/4 throttle and not really exhibit any issue. Maybe a slight bog, but nothing really out of the ordinary. Once you pass 1/4 throttle the engine will either bog down or it may carry the RPM up to full throttle, usually bog. If it continues to gain RPM, I have no idea if I am reaching peak RPM or not, but it starts to plane and then the engine just bogs down. It might maintain high RPM for 2 - 3 seconds. If you leave it at WOT it will run for at least a few more seconds. I really haven't left it there to see if it actually stalls or not. If it bogs down the RPM drops, but it continues to run.

I can get it passed the bog by rapidly going from 1/4 to 3/4 throttle until I hear the RPM climb above a certain point and then it will really rev up. However, it only maintains high RPM for a few seconds and then slowly, over a second or 2, drops down to barely 1/4 throttle speed.

It feels like a rich condition, but the plugs don't show it. I guess it could be bad gas as I don't know how long the gas has been in the tank, but it's unlikely. It is most likely a fuel delivery issue, as though the tank isn't staying pressurized or the fuel lines are clogged. The carburetor was rebuilt last year, and the seller had the receipt. The exterior of the carb looks terrible so I am very tempted to tear it apart and clean it, but I wanted to see if anyone here had a better place for me to start looking.

Thanks,

Kevin

 

[physicistkev]

Follow up question. Through some trouble shooting I have noticed that when the boat is running there is no appreciable difference if I remove the gas cap. i know that the fuel tank should be able to hold a 5psi pressure. I haven't been able to test that yet, but wondered if removing the gas cap would affect how the boat ran. If it does then I have a pretty good idea that there is a pressure leak in the fuel system. Since there is no fuel leaking on the boat, the pressure loss has to be in an area where it is backed by air not fuel. So the filler spout, breather or bundle of stuff that goes into the fuel tank is most likely where the leak is.

Sound logical?

Thanks,

kevin

 

[roneagan@cfl.rr.com]

Carbs

Sounds like the carbs may need to be rebuilt, I have found it's the most common problem.. If it has not been used much they tend to get really filled with corrsion, there are also little filters in the carbs that can get all gunked up.. Don't know if it has gray fuel lines, but if it does they need to be changed or you will just continue to have problems.. There are some great post in here on how to rebuild the carbs... It is not that difficult to do and should clear up your problems....Do a search on gray fuel lines...

 

[physicistkev]

It appears that the previous owner replaced all the lines except the pulse line with black fuel line. The boat did not get much use this year or last, after the carbs were rebuilt. I am hesitant to rebuild them for this reason, but if I don't find a major air leak in the fuel system then I am going to to replace everything.

$100 for a carb rebuild kit
$20 in fuel lines
$12 in hose clamps
and a few hours of my time are well worth it on the boat.

We shall see.

Thanks,

Kevin

 

[seadoodude1]

At the very least check the internal carb filters. Don't continue to run engine with it running like it is or severe damage will occur due to a very hit lean burn that will melt piston top edges.

 

[Dr Honda]

The fuel tank doesn’t get pressurized while the boat is running. There is actually a vent on the starboard side of the hull. (the right) The 5psi thing is so you can find any leaks after you are done working on the fuel system.

For your problem… I would say don’t have a rich condition… it’s going lean. The filters are probably plugged up, and the carbs need opened up, and cleaned. This type of carb doesn’t like to sit unused for long.

 

[physicistkev]

Dr. Honda, thanks for the answer on the vent. I was just about to ask if it's supposed to be a check valve or just a regular vent. The manual isn't real specific on it. It would seem that a carb rebuild is in order. The lines are a bit dirty but the pressure test checks out. Just looks like it sat to long and now it just needs a refresher.

Thanks for the info.

Kevin

 

[snookdcoochi]

so I have a 97 speedster with dual 717's and trying to identify the idle screw and low speed screw? any help please. and also is there a way to sync both carbs at the same time from one place to idle at the right rpm????