Pulse Problem

[Bt1223]

I have a 99 Sportster. One engine gets about 7lbs of pulse pressure, the other engine gets about 3lbs of pulse pressure. Any ideas would be appreciated. Compression is 150 in both motors.

 

[Dr Honda]

What's "pulse pressure" ???

 

[Bt1223]

I used a vacuum gauge the vacuum went on the motor that will not start. About 3 lbs of vacuum to pressure fluctuating. Also has a new fuel pump. On the motor that runs the vacuum is about 7lbs fluctuating to pressure.


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[Dr Honda]

OK.... so it's the vac that is being produced at the pulse port for the fuel pump??

I guess I'm confused since Vac isn't measured in "PSI". It's "in-mg". ALso... I'm not exactly sure what you are trying to find out with checking that. It's not a test that we normaly do, and any pulse will drive the fuel pump.


SO... I guess I should ask... What are you trying to find out? In your second post, you say one engine won't start, but you didn't say anything about things not running in your first post.

 

[Bt1223]

Sorry I'm new too posting on here. My one motor won't start. If I crank it I can feel a pulse on my finger. So I figured the pump was bad. Put new pump on. Hook the hoses up crank, still no start. If I hook a extra piece of hose up to the pulse port. And apply pressure and vacuum it will pump fuel. So I guess my question is. What could cause this.


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[Dr Honda]

OK... now we are getting somewhere.


SO.... if you hook up a "Mighty Vac" (hand vac tool) you can drive the fuel pump and get fuel up the hose? BUT, the engine won't drive it? BUT, the engine has 150 PSI compression.


If that's right... then there could be crank seal leak on that engine. Basically... the pressure/vac being produced by the piston is not being held in the crankcase.

OR....

your rotary valve isn't spinning, or it's very out of time.


A quick test for that is, put a little mixed fuel directly down the carbs, and see if it will start. If it doesn't... then pull the carbs, and verify the valve.

 

[Bt1223]

How do you verify the valve with the carbs off? It was running great than died. Wasn't pumping fuel. So I changed pump.

I'm used to cars and trucks, not 2strokes.


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[Dr Honda]

The simple way is to just make sure it's spinning as you roll the engine over by hand. (Spark plugs out) If the gear stripped... you will see it hop... or even stop.


If it's running smooth, and without skipping... then there's no reason why the pump should be driven.

But... as I was saying before... a little mixed fuel directly into the carbs will let you know if there is more to it than a bad pump.

 

[Bt1223]

I had to leave town for a few weeks. Can I get back to you than?


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[Dr Honda]

I had to leave town for a few weeks. Can I get back to you than?


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Sure... we will be here when you get back.