Fuel Tank Vent

[DnKSeadoo]

I am working on diagnosing a surging problem I am having on my 96 sportster. I have cleaned the fuel filter, blew out the fuel shut off valve, took out the fuel tank baffle and cleaned the screen. There was not a lot of debris obvious in any of these areas. However I did find one of the fuel return tees that appeared to be cracked. Then when I touched the tee it completely broke. I am replacing that and putting it all back together. I also checked the carb linkage and all was working properly. I didn't go into the carb since I didn't find any debris anywhere else in the system.

So I'm wondering what the next step is. I'm confused on the vent on the side of the hull. Is this supposed to be a check valve or just a vent. I can blow into the valve and suck air out of it. Can this be sucking air into my tank and causing my surging problem? The surging happens over half throttle.

I'm new to this boat, just bought it last month and had it out twice. The first time out it was fine (on a full tank of gas), then the second time on about a 1/2 tank started surging over half throttle. When it was in smooth water I eased into the throttle and had my buddy go into the front of the boat to try to keep it level. As soon as the front came out of the water it started to break up. With the extra weight we were able to get it on plane and it was fine. But the second we came into choppy water and unlevel it started to surge again.

Please clarify if the vent on the side of the boat is supposed to let air in and out or just out. Any help is greatly appreciated. We are desperate to get it out on the water!

 

[voodoo]

The side vent works at about 3PSI so water can not just fill the tank, remove the carbs and put them in a cookie sheet to save any parts that fall loose, put shop towels over the holes so nothing drops in there while you clean out the tiny basket filters.

 

[DnKSeadoo]

Thanks for the reply. We tested it in the driveway just to make sure it started after I worked on it and it ran really good actually sounded the best since we got it. I am going to give it a try to see if what I have done will fix the problem. I thought it was something wrong with the baffle because it ran hard when the boat was level but when the front end would lift up it started again. If it is still doing the same thing I am going into the carbs.

 

[DnKSeadoo]

Still surging!!

Well, went for a test ride yesterday and the cleaning of the selectorand replacing of the fuel lines and filter helped a lot. But it was still surging over half throttle. So when I got home I pulled the carbs and found the mag carb basket filter was ok; but the pto carb basket was completely plugged with crap. I couldn't even blow through it! Also here is something weird I didn't find a carb base gasket under the mag carb. I looked all over for it not in the bilge or drive way or garage I looked in the intake too even though it would not fit in there. Off to find some base gaskets today.
On a side not during our test drive there was a guy with a late 90's Speedster trouble shooting in the bay near the dock so I turned him onto the forum. Spread the word!

 

[Bills86e]

Dump the fuel bowl of the water separator/filter and put a little vaseline on the
square o-ring and insure a snug fit and do not overtighten or it can crack the bowl cap and leak air into the drawing action of the carb fuel pump. Bills86e

This is a tell-tale if your supplier had water in the gas you bought. A water molecule
is very much larger than the gas molecule and can easily clog a carb oriface. Use a
Water Dispersant additive if detected.

 

[DnKSeadoo]

Thanks Bill I will take a look at that today and maybe try to get a new o-ring while I'm getting the base gaskets for the carbs. Should the fuel filter bowl be full of fuel when I remove it it has been sitting less than a day.

 

[Bills86e]

Hopefully just fuel, check that regularly.