Fuel Flow on 1986 VF500F

This is for any other bike that is NOT an 88-90 VTR 250.

Fuel Flow on 1986 VF500F

Postby Guaire » Wed Nov 01, 2017 2:19 pm

I'm not getting any gas through my petcock while on the bench.

This bike was in the shop. I found out the needles weren't closing the fuel flow. They are replaced. Floats are set to 7.3 mm. Replaced the float bowl gaskets.
Back in my garage, while the tank was off, I noticed the Off On Reserve ring was 180 degrees wrong. After turning it around and orienting the dial properly, I blew air into the petcock and the air was blowing out the fuel lines. I re assembled with a gasket between the petcock and the tank.
I added fuel to the tank, on the work bench. I turned it to RES. No flow. I closed off one carb connector and attached my brake fluid pump on the other one. While set to RES, I have tried to get gasoline through the petcock and into the fuel line. No go.
The spring and diaphragm in the petcock are new. I won't re connect the tank and lines if there is no gas flow.
What could be wrong?

Tonight I will pull the petcock and see if there is an obstruction in the tank.
I'll try to post a pic of my fuel lines.
Attachments
Fuel Line 1.jpg
Fuel lines with two outputs.
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Re: Fuel Flow on 1986 VF500F

Postby Alan_in_WA » Wed Nov 01, 2017 8:09 pm

From your description, there may be a little misunderstanding involved. The picture shows a petcock with a vacuum diaphraghm. No fuel is going to flow unless you apply vacuum to it, REGARDLESS of what position the petcock is in - Reserve is NOT a 'prime' position that bypasses the diaphraghm valve - it just pulls fuel from lower in the tank than the 'on' position. Try applying vacuum to the port on the petcock while it is in either 'on' or 'res' - you should get flow.
At least that's the way my 84's work.

Alan
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Re: Fuel Flow on 1986 VF500F

Postby Murdo1 » Fri Nov 03, 2017 1:22 am

Is the diaphram and spring in the right way?
That little filter will not flow enough fuel when riding at high speed, better to change it for a bigger one with more flow before you spend lots of time and $$$ trying to find a 'carb jet' problem.
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Re: Fuel Flow on 1986 VF500F

Postby Guaire » Fri Nov 03, 2017 2:15 pm

Hi Murdo - I changed the petcock, just to be sure.
Alan - With the tank back on the bike, it started. I can rev it for awhile then it runs weak and stops. Or, it starts and runs weakly with choke on.
I attached a brake bleeder pump on the breather tube on the diaphragm and that helped the flow. But, it wasn't enough to keep the bike running.
I'll look for a new/used petcock. Maybe that will work. I'm stumped.

Thanks for helping.

Bill
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Re: Fuel Flow on 1986 VF500F

Postby Murdo1 » Sun Nov 05, 2017 1:57 am

I ended up throwing the diaphram away and making mine a manual tap. Just had to epoxy up the tube holes and it worked fine.
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Re: Fuel Flow on 1986 VF500F

Postby Guaire » Sun Nov 05, 2017 8:44 am

Hey, Murdo - You got that right. That's what I'm going to do. I found this article on the web, posted on vfrworld.com.

daughertymotorsports.com/howto/tankvalve/tankvalve.html

Anyone who has to fight this design problem on the VF500F should know this solution.
I'll be working on this mod, asap.

Cheers,
Bill
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Re: Fuel Flow on 1986 VF500F

Postby Guaire » Sun Nov 05, 2017 2:39 pm

Minus Fairing.jpg
Outer Diaphragm Cut.jpg
What's left of the Inner
Inner Diapragm Cut.jpg
What's cut, what's left
Got it done. Here's pics of the diaphragm cut outs.
Sitting in the driveway after a short test run on wet roads. After a few minutes of riding. It idled at 1200 rpm.
In the midst of all this carb work, I repaired the rear and upper fairing. The rear needed a mounting hole. The upper needed the same. Plastex to the rescue.
At least now it's a runner. I can tune and sync when it's convenient.
Looking to freshen the turn signals and change the front brake lines to steel braid.
Pics are the cut diaphragms.
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Re: Fuel Flow on 1986 VF500F

Postby squirrelman » Fri Dec 08, 2017 1:27 am

geeze, man, just step up to a big boy's better, more reliable, faster VFR ! :o you've suffered enough with Vf500 problems i think, and VFRs are way under-valued in the market now. :shock:
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044_44 2vfrhill.JPG
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