Author Topic: Vaccum Pressure  (Read 2712 times)

TecCrash

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Vaccum Pressure
« on: September 23, 2013, 01:16:01 PM »
Hi all, New to the site and to the Oddy.  Picked up a couple of 83's and I'm working my way through the fuel system issues on them,  One has a new fuel pump, lines, hose clamps, filter and I'm waiting on new jets.  The strange thing is that I'm not getting hardly any fuel into the filter, I'm wondering if it could be a vaccum issue from the crankcase.  Anyone know what the Vaccum pressure should be at?

Thanks!

Chris

LiveWire

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Re: Vaccum Pressure
« Reply #1 on: September 23, 2013, 04:19:41 PM »
Check your cylinder compression. The vacuum at the crank case pulses with positive pressure between. If your compression is below spec, the loss also means less vacuum under the piston. Also check for air leaks in case gaskets and seals. If air is leaking in, that will reduce your vacuum. Worse is it will lean out your engine.

TecCrash

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Re: Vaccum Pressure
« Reply #2 on: September 23, 2013, 10:29:55 PM »
Thanks for the reply!  I have 125 PSI, cold with WOT.  I'm not sure how to check if the case is leaking.  I haven't ran across that procedure on the board or in the manual yet, but it was one of my thoughts. 

I had an interesting thought this evening, I need to check to make sure I'm getting good flow from the tank.  I checked the pitot valve and it wouldn't turn, so I need to pull it and make sure it clear enough to flow the required amount of flow.  I'm working late the next few nights, I'll let you know what I find.

Thanks again for responding!

TecCrash
aka Chris

LiveWire

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Re: Vaccum Pressure
« Reply #3 on: September 24, 2013, 09:09:06 AM »
If the engine is running, you can check for air leaks by spraying carb cleaner at the gaskets and seals listening for a change in idle speed. On a non-running engine, you plug the exhaust, intake and fuel pump pulse line connecting a gauge and schraeder valve at some point to be able to pump 6psi of air in. It should take at least 6 minutes to leak down to 0. Spray soapy water to locate the leaks if they exist.

TecCrash

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Re: Vaccum Pressure
« Reply #4 on: September 24, 2013, 09:13:57 AM »
Thanks!   I found the "Non-Running" method this morning and I should have figured out the other one on my own.   You think there is any validity to the flow issue causing my issue?  IT idles fine, but has ZERO bottom end won't hardly move from a stop, 3/4 throttle up it seems better if you can get the rpm's up that far.  The slow jet was trashed so I need to get one, hopefully that helps.

LiveWire

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Re: Vaccum Pressure
« Reply #5 on: September 25, 2013, 08:01:01 AM »
If it is not getting fuel, that is a problem. 125 psi sounds low for compression, although I don't know the FL250's stock compression off hand.

TecCrash

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Re: Vaccum Pressure
« Reply #6 on: December 02, 2013, 09:02:05 AM »
OK Took me forever to find time to work on this, but I did over the weekend.  Problem ended up being that I was using a fuel filter that was designed for automotive, and it was too big, It wouldn't bring enough gas through it.  I went to a small see through style and started flowing fuel.  Runs it out pretty well now.  Thanks for your help!