Poor running bike trouble shooting help

[Tomcatt]

Originally Posted by Racepres

And I thought that simply running on Reserve, deleted al that crap... as a Troubleshooting aid..to eliminate Vacuume problems

Some vacuum petcocks had a "Prime" position (On, Prime, Reserve positions) that flowed fuel with no vacuum when on "Prime", just like a conventional petcock. But, you were still screwed if the diaphragm was damaged.

[IXL2Relax]

To my knowledge, no HD vacuum petcock ever had a 'prime' setting. Only RES-OFF-ON.

If the carb float bowl is empty, the engine needs to run long enough to create vacuum enough for the petock to open far enough to refill the bowl. If the valve is leaking, it might eventually fill the bowl, but when working as designed, the petcock requires vacuum to let any fuel reach the carb. (Big Mother must protect you from yourself!)


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[Tomcatt]

Originally Posted by IXL2Relax

To my knowledge, no HD vacuum petcock ever had a 'prime' setting. Only RES-OFF-ON.

If the carb float bowl is empty, the engine needs to run long enough to create vacuum enough for the petock to open far enough to refill the bowl.

I couldn't remember if HD ever had the "Prime" petcock. One of the nice things about the "Prime" petcocks was that on prime they'd fill the float bowl of a freshly rebuilt carb. Not a big deal on electric start bikes but it took quite a few kicks to fill the float bowl with a RES-OFF-ON vacuum petcock...

[brucstoudt]

will the oem petcock flow fuel through it in the reserve position without the motor running,as mentioned previously?i like to drain the fuel from my tanks at the end of the riding season.haven't been able to do it with the vacuum model.

[IXL2Relax]

Originally Posted by brucstoudt

will the oem petcock flow fuel through it in the reserve position without the motor running,as mentioned previously?i like to drain the fuel from my tanks at the end of the riding season.haven't been able to do it with the vacuum model.

The OEM STOCK PETCOCK does not flow fuel unless the engine is producing vacuum - like turning over or actually running. In the OFF position, it does not flow fuel even when there is vacuum.

The RESERVE position DOES NOT FLOW fuel unless there is vacuum to open the valve in the petcock.

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[Iron Mike]

Originally Posted by brucstoudt

will the oem petcock flow fuel through it in the reserve position without the motor running,as mentioned previously?i like to drain the fuel from my tanks at the end of the riding season.haven't been able to do it with the vacuum model.

Use your vacuum pump to manually open petcock to drain.

[Racepres]

Originally Posted by IXL2Relax

The OEM STOCK PETCOCK does not flow fuel unless the engine is producing vacuum - like turning over or actually running. In the OFF position, it does not flow fuel even when there is vacuum.

The RESERVE position DOES NOT FLOW fuel unless there is vacuum to open the valve in the petcock.

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Had to go educate myself... The unknown origin 1994 I been riding, will flow on Reserve but not in On, nor Off (of Course).. It does tho, have a chrome Petcock, so that makes me suspicious... So Checking two other (one late one early) '90's XL's , neither will flow anything in any position without vacuum
Apologies for my Ignorance..

[IXL2Relax]

Originally Posted by Racepres

Had to go educate myself... Apologies for my Ignorance..

HD made various changes over the years - It's hard to track every one - They even had a bulletin on the fact they reversed the indication of ON & RES. They also some times used the long handle as the indicator and sometimes the other (pointy) end of the switch handle.

http://sportsterpedia.com/doku.php/t...ck_fuel_outlet

The first STOCK use of the vacuum petcock was on 1995 models (previously only an option). So 1994, OEM STOCK, would have had the older, non-vacuum, petcock.

That's one of the reasons for the Sportsterpedia. Even after we figure stuff out, it's hard to remember everything you once learned.

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