• 4 Stroke Husqvarna Motorcycles Made In Italy - About 1989 to 2014
     TE = 4st Enduro & TC = 4st Cross

  • Hi everyone,

    As you all know, Coffee (Dean) passed away a couple of years ago. I am Dean's ex-wife's husband and happen to have spent my career in tech. Over the years, I occasionally helped Dean with various tech issues.

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Low Fuel Pressure, possible causes?

canuk

canuk

Husqvarna
Other than a bad fuel pump, what can cause low fuel pressure?

If I remove the pump and put 12v to it and it hums along does that mean anything? Will that indicate its good or is it impossible to judge?
 
Blocked fuel line, or mal-functioning pressure regulator.

You can get an idea by putting 12v to it while under gas level, in a clear plastic jug, the stream coming out should be strong enough to splash around pretty good, my pump measured at about 50 psi, and the regulator would knock that down to 40-42.
 
OlderHuskyRider said:
Blocked fuel line, or mal-functioning pressure regulator.

You can get an idea by putting 12v to it while under gas level, in a clear plastic jug, the stream coming out should be strong enough to splash around pretty good, my pump measured at about 50 psi, and the regulator would knock that down to 40-42.
Click to expand...

Thanks. i'll try that. PSI though the whole assembly was 15-30 psi and variable (according to dealer)... once I removed the pump I see it has already been replaced (ca custom) so I wonder if maybe the pump I ordered wont fix the issue. I will buy a fuel pressure gauge and isolate the pump to see if it might be the regulator.. or somewhere else.
 
canuk said:
Thanks. i'll try that. PSI though the whole assembly was 15-30 psi and variable (according to dealer)... once I removed the pump I see it has already been replaced (ca custom) so I wonder if maybe the pump I ordered wont fix the issue. I will buy a fuel pressure gauge and isolate the pump to see if it might be the regulator.. or somewhere else.
Click to expand...


Stupid question but how do I use the fuel pressure tester? There is a clear overflow tube on this tester and when I run the pump, my fuel just pours out the overflow on the tester... What am I doing wrong?

tester is "T'd" on the line between pump and filter.
 
Just pulled out my new pump because of the same issue, this is the old one with 4 rides on it:
View: https://youtu.be/lDiTCCWmIdo

The older one seemed to flow a small amount more psi, dismantled it and noticed about 40% of the positive terminal's brush missing. I suspect that may have been the cause.
 
That was a bucket of gas.

Don't be surprised if it's a pain in the ass to pull apart. You've got to pry the crimped lip back up and slip the impeller and motor out, mine was not reusable afterwards. It's clearly obvious why these things fail since the fuel actually flows through the electric motor, hence the gum up. If it's not for cooling purposes it's totally an idiotic design, I mean come on you don't submerge a jet ski engine to propel it. A side inlet plumed straight to the impeller bypassing the motor would probably have made these last forever.
 
Using gasoline is the way to go for sure.

When I tested mine, I kept the assembly together, on the plate, so I could put my thumb over the outlet and see that the pressure regulator was working. This pump design is what is in all newer cars, but the cars never get the heat and vibration exposure that the pumps gets on a dirtbike thumper. I went thru 4 pumps in 20,000 miles.
 
Agreed, definitely test it in the housing first. I tested it like that after to be positive I didnt have a pressure regulator failure of some kind.
 
I don't think the larger tanks on the 2012 and newer bikes help any.

I've seen 2013-4 red heads boil the gas in the tank as there is even less airflow under the tank due to the bigger head on those motors.

In any case the small tanked 2010's are the best looking dirt bikes ever IMHO.
 
Just a note on low fuel pressure. If the bike has a plastic filter in the tank, be sure it is not leaking at the seam. I have seen quite a few with this problem. The bike needs at least 35 psi pressure to run right.
 
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