Fuel in Pulse line and Fuel overflow from Mikuni square pump

Martin Colligan

I have a Rotax 125 and the Pulse Line gets gas in it ... was wondering what causes that ...

Also on the Mikuni fuel pump there's a tiny hole witch I gues is an overflow ...
gas comes out of there. Any help would be appreciated !!

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Roger Miller · Posted: Wed Nov 07, 2012 3:03 pm Post subject:

Start by rebuilding the pump with new soft parts.
Sounds like you have a diaphragm that is leaking.

Martin Colligan · Posted: Wed Nov 07, 2012 3:28 pm Post subject:

It's been always doing that ... It's the 3 rebuild that I do ...

Why is there gas in the Pulse line ?

Running too rich ?

Thanks !

Chris McGinley · Posted: Wed Nov 07, 2012 8:45 pm Post subject:

Are you sure it's gas and not some oil blowing back up from the gear case?

I see you have a zip tie on the pulse line; make sure that's very tight so no fuel finds its way in there from drips when you change the jet or drain the carb.
_________________
Chris McGinley
Monster Raceworks
Rotax Masters
"Always stay one step ahead of the storm" - JZS
http://www.njkarting.org
http://www.btbsecurity.com

Martin Colligan · Posted: Wed Nov 07, 2012 8:54 pm Post subject:

When I start it ( at idle ) if I give it some gas i see gas slowly coming thru the pulse line ...

Then when it's entering the fuel pump the excess gas comes out of the little hole on the side of the fuel pump ... ( underneath the JAPAN marking )

Chris McGinley · Posted: Wed Nov 07, 2012 9:05 pm Post subject:

Sounds like something is wrong with the pump. Have you tried replacing the complete pump with a new one?
_________________
Chris McGinley
Monster Raceworks
Rotax Masters
"Always stay one step ahead of the storm" - JZS
http://www.njkarting.org
http://www.btbsecurity.com

Martin Colligan · Posted: Wed Nov 07, 2012 9:32 pm Post subject:

Will try a new pump ... but I clearly see gas coming from the Crankcase ( pulse line ) going in the pump ...

Chris McGinley · Posted: Thu Nov 08, 2012 5:27 am Post subject:

Brian Wilhelm · Posted: Thu Nov 08, 2012 6:52 am Post subject: ?

It's very normal for a small amount of mixture to find it's way down into the pump, from the crankcase. it does reduce the pumping action somewhat as it is "dampening" the pulses that make the pump work.
Two solutions:
1-Clean the pump out partway through each day.
2-Drill a .030 hole through the outer housing into the bottom of the pulse chamber (the air side). The mixture that accumulates drains out and the pump work just fine. Actually the pumps used to come that way, I have no clue why they aren't now.
I've put the hole in dozens of pumps with zero issues.
_________________
Brian

Greg Lindahl · Joined: 13 Jan 2011 Posts: 264

Interesting that you've put a hole in the pulse line at the pump that creates a crankcase leak and you've had no trouble with running, especially idling.
Locating the pump above the crankcase pulse fitting will help with oil filling the pump chamber. Turning the pump on its side/front so the pulse line enters at the bottom can help somewhat with oil accumulation in the pump chamber. Oil in the pump chamber reduces fuel volume delivery.
NOTE: Even with the pump mounted above the crankcase fitting, I've had to resort to different length pulse hoses to "tune" harmonics to NOT pump oil to the pump chamber. The oil will go up to a higher mounted pump if the hose is the "wrong" length.
Harmonics are the real issue.

Greg Lindahl · Joined: 13 Jan 2011 Posts: 264

Interesting that you've put a hole in the pulse line at the pump that creates a crankcase leak and you've had no trouble with running, especially idling.
Locating the pump above the crankcase pulse fitting will help with oil filling the pump chamber. Turning the pump on its side/front so the pulse line enters at the bottom can help somewhat with oil accumulation in the pump chamber. Oil in the pump chamber reduces fuel volume delivery.
NOTE: Even with the pump mounted above the crankcase fitting, I've had to resort to different length pulse hoses to "tune" harmonics to NOT pump oil to the pump chamber. The oil will go up to a higher mounted pump if the hose is the "wrong" length.
Harmonics and uneven pulse strengths are the real issues.

Brian Wilhelm · Posted: Thu Nov 08, 2012 11:55 am Post subject: