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hard starting sportster


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Just picked up a '98 sportster with 300 hrs. Ran great when I test drove it but now it seems to have a fuel delivery problem. I put a new fuel pump and filter on and the only way I could get it to start was by dis-connecting the fuel line from the carb rail and pouring gas back down to the pump. The thing ran great all day, so I figured the new pump just needed to be primed. Went to start it the next day, same thing, the line was dry and would only start by priming the fuel line. It happend several times that day.

1) On the carburated engine should the fuel pump come on when I turn the switch to "on"? Its not, just when cranking.

2) When I pull the input line to the filter should I expect to see free flowing gas? There is gas in the line but its not pouring out. possible blockage?

3)Unless there is a leak to allow it to bleed down, shouldnt the gas stay up at the carb? or at least up to the pump. ( the line from the filter to the pump goes dry too.

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I've had problems in the past priming those carter pumps in the past.

Beyond that I would try running the boat off a remote tank to eliminate any other fuel problems.

Also is the fuel filter full of fuel?

-Chris

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It has a Holly carb.

I filled the filter when I installed it but have not checked it since. The line from the filter to the pump and from the pump to the carb is dry when it wont start. I'm wondering if there is a malfunctioning check valve somewhere in the system.

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Can u tell us what technique you use to start the boat? The pump should turn on when the key is on (before you start cranking the engine). I have a 99 sporty with the 310 carb motor and have found when the motor is cold I need to pump the throttle 2 times, put it back to fast idle position and it starts great every time. Once the motor is warm, there is no need to da anything except turn it on.

Gibbo

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The pump does not run until the motor cranks over, then it stays on for about 15 seconds after I stop cranking. I can pump the throttle untill I'm blue in the face, I dont think there is any gas in the carb to pump. The only way I can get it started when cold is by filling up the fuel rail with gas. When its warm it starts right up most of the time.

thanks

Craig

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i have a 95 response with the 350 monsoon, and my fuel pump runs when the boat is turned to the on posision w/o cranking. I need to leave it in this position for about 5-10 seconds or else the boat will have a hard time starting. From what I've read and understand it's because of vapor lock. Not sure if that is your problem, but I would say yes, your fuel pump should be running before you crank the engine.

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The fuel supply pump turns on during cranking & when the engine has oil pressure . The oil pressure switch is mounted beneath the distributor. I don't know if the fitting at the tank has a check valve . It seems like it probably should . Check valves are a great place to collect debris . A loose or damaged hose could allow the pump to pull air. If you could get your hands on a mighty vac hand vacuum pump you could pull fuel from the tank & look for signs of air or high inlet restriction.

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There is both a screen at the pickup that can get clogged and a check valve in the gas tank.

That is why I suggested the OP run the boat off a remote tank to eliminate (or identify) the tank as the culprit. Especially since getting to some parts of a gas tank in a sport can be soooo much fun.

-Chris

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Thanks for the input! That makes sense about the pump not pumping until there is oil pressure for safety reasons. And I dont think I have any blockage because it runs good when it starts.

The more I think about the symptoms the more I suspect the check valve. I think I will try to blow low pressure~5psi into the tank from upstream of the fuel filter. Would that be a good indicator if the check valve is working?

How do you get to the gas tank on the sportster, or more specifically, how do you get the rear seat out? It looks like it might be kinda tight.

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By the disscussion, you must have an electric fuel pump, correct?

If so, there must be a fuel pressure regulator somewhere. It may have a screen on it also that could be clogged. Just throwing some suggestions out there. My '95 only has a mechanical fuel pump with a carb.

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Pulling the fuel tank out isn't too bad. The rear seat back is held in place by a bunch of 1/4 studs. Remove the blower cover & the little box to access the bolts in the center . Long arms help with the ones on the side. The studs stay in the seat back & could gouge the boat if you aren't careful prying the seat out.

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Doug, I would have thought it had a pressure regulator but I cant find one.

Pup, I don't think I will have to pull the seat out as I did a pressure test last night. I put about 5psi into the fuel line before the filter and didn't hear any air going into the tank and the line seemed to hold pressure. I did not do a leak down test just a quick check. I did check the float bowls and the primary was empty and secondary was full. I still cant detect gas in the oil and see no external leaks. I think I'm going to rebuild the carb as I cant figure where the gas is going. Anybody have any suggestions about where to get a rebuild kit?

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Curious how the boat could run fine an an empty primary. If you shut the motor off, it should be up to the float level.

Random thought but if that's empty, could be an issue with a stuck float or stuck or sticky needle / seat? Not sure it's even possible for your engine to run mostly off the secondaries but I can't see why the primary would be empty out each time you shut off the motor, assuming it was running fine up to the point where you shut it off (ie, it didn't sound like you were starved for fuel)

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Chris, Do you mean power up the pump to see if it pulls fuel, or bypass the pump to see if the engine will suck fuel?

Once started it runs fine, you can shut it down restart it an hour later its seems to be just when it sits for any length of time ~ 3 plus hrs.

Anybody have any clue as to where the fuel in the primary float bowl is going? my guess is its sitting in the manifold until startup.

A quick fix might be to put a check valve just after the filter to keep the pump primed just to get by for the weekend, any thoughts?

thanks,

Craig

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does your tank experience a "suction" condition while running, so after shutting off, there is vacuum in the tank. Longer it sits, the more fuel it pulls back into the tank (slowly) emptying out the carb, down the line, past the pump so it's not primed anymore? Did you ever crack open the filler cap right after running hard for a while and listen for the sound of air rushing in? I still don't know how that could suck fuel out of the bowl since I think it enters from the top, not the bottom...?

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Chris, Do you mean power up the pump to see if it pulls fuel, or bypass the pump to see if the engine will suck fuel?

Once started it runs fine, you can shut it down restart it an hour later its seems to be just when it sits for any length of time ~ 3 plus hrs.

Anybody have any clue as to where the fuel in the primary float bowl is going? my guess is its sitting in the manifold until startup.

A quick fix might be to put a check valve just after the filter to keep the pump primed just to get by for the weekend, any thoughts?

thanks,

Craig

I would try powering up the pump and verify it pulls fuel before going anywhere and run the boat off a remote tank to eliminate any weird fuel tank/check valve stuff.

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I believe the primary if full once the the pump is primed and boat is running. It runs great, the problem is after it sits for a length of time, I believe the primary float bowl is draining down slowly (accelerator pump?), the float drops, allowing air into the fuel rail thus allowing the fuel to run down to the filter......its a theory at this point.

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Good idea, just cause its buzzing dosn't mean it's suckin. I'm going to try to power up the pump tonight. I'm going to pick up some fittings to run it off of a remote tank too.

thanks!

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I believe the primary if full once the the pump is primed and boat is running. It runs great, the problem is after it sits for a length of time, I believe the primary float bowl is draining down slowly (accelerator pump?), the float drops, allowing air into the fuel rail thus allowing the fuel to run down to the filter......its a theory at this point.

Ok, A Holley carb is known to leak fuel into the intake if the gaskets are old.

Is there any black smoke coming out of the exhaust at slower speeds? If so that is an indication of an internal carb leak.

A carb rebuild will correct this problem and it may perform better.

Fuel can not be siphoned out of the bowl because the needle and seat is at the top of the bowl and the bowl is vented.

Fuel "prime" could be draining back to the tank if there is no check valve to prevent it from doing so, but once the key is turned on, the electric fuel pump starts, the carb should be refilled with fuel rather quickly.

If there was a vaccumn building in the fuel tank, eventually the fuel pump would no longer be able to supply fuel pressure to the carb and the boat would stall. I believe you said that once it starts it stays running and runs well... so that's not it.

I have a mechanical pump on my '95, even when it sits for a month, it will start after ~10-15 sec of cranking.

Borrow a fuel pressure gauge and see if your pump builds pressure. Check a manual for the spec on that.

My $0.02 worth.

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The carb could be leaking through the power valve. If the valve is loose or damaged it would allow the fuel in the bowl to drain into the intake . You would never see it. Try jumping the pump as Chris suggested at the oil pressure switch . You can hear the pump load up when the float closes . After the bowl is full the boat should start right up.

The carb rebuild kit I used did not come with the correct power valve. Check the #'s on the valves to be sure.

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thanks for all the help everybody! just tested the fuel pump. This was the first thing I suspected and put a new one on so I thought I had that eliminated but now I don't know. I powered it up when it was on the boat and waited for it to "load up". It ran for about a minute and never sounded like it was straining. I dis-connected the line from the carb and waited for fuel but nothing came out. Took it off and bench tested it (dry)and it only pulled 1.0" hg on my tester and less than 1psi on the outlet. I dont have a service manual (any one know where to get one?) but it seems weak to me. If I did get a bad pump or it went bad all ready, would you expect the boat to run so good once I prime the fuel line?

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from the symptoms you're describing, it seems the block only gets propper fuel delivery when it's running, which means it's pulling fuel.

-Prime

-Runs when warm (read, fuel in line, no prime required)

I vote pre-pump blackage.

Try running an external fuel source to the pump, or replacing the line from the tank to the pump. When its dry, try starting it. If it fires up, that's your answer.

Shouldn't you have a regulator on or near the rail?

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If your primary bowl is empty after sitting over night , the powervalve in the carb is bad , that is a common failure area of a holley , it is a vacumn enrichment diaphram which will fail if your carb ever backfires, the diaphram ruptures and dumps the gas into the intake manifold, slowly overnight, also you will normally here some spark knock under hard accelleration due to the diaphram not riching up the mixture.

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