VF500F - setting the float height after removing the fuel pump

It seems like the '86 petcock is at least double in external piping!



Thanks IC! If you hadn't triggered me with your post I would have missed this '86 petcock.

 

Thank you for the post and the accompanying photos blitzas.

It is very helpful to see a side by side comparison between these two versions.

On this note - do you think an '86 petcock could be modified to mount onto an earlier '84/'85 gas tank?

 

With just petcock modification the answer IMHO is definitely NO.
The brass tube of the '86 barely enters the '84/'85 tank and the mounting plate - knob axle distance difference is 1cm.

If cut and welding of tank is considered then I reckon it is feasible with tank modification, only if the '86 petcock mount area is transferred at the '85 tank, and the level difference of tanks is compensated somehow.
It will be a major high risk cutting/welding exercise though.

Reconsidering all findings I believe removing the pump in a '84/'85 in order to convert to gravity feed is a no go.

 

I guess that answers the question of going gravity feed and why some had problems and some didn't.
It looks like there is enough material in the 86 petcock to oval the mounting holes to fit the 84/85 tank, no? Would the base need to be reshaped also to fit flush to tank? Or is an 86 tank really needed?

 

I'm not sure that it does. I've converted several VF's to gravity feed and never changed the petcock on any of them. I've never had a single fuel delivery problem on any of them. The original 84-85 VF500F line size can supply way more flow than the 500cc's will ever be able to consume.

My opinion has always been that folks will try converting to gravity feed to fix a problem. Since the fuel delivery was not part of the problem, the bike still doesn't run right. It doesn't have anything to do with gravity vs. pump feed. This is just what I've gathered over the years.

 

Here is a lengthy -1000 words- reply:



If it doesn't come out clear or if any questions please ask. Scale is 1:1

I do respect your experience and it seems quite reasonable your argument "The original 84-85 VF500F line size can supply way more flow than the 500cc's will ever be able to consume." though it is not just the size it matters as any restriction such as filters and fuel level will just reduce delivery.
My experience from a year's gravity feed conversion is just one fuel starvation under "difficult" conditions otherwise I had no problem in normal use.
Nevertheless it is not easy to verify if the last fed carb on a '84/'85 converted bike is running a bit lean.

My point is that under fuel demanding conditions there might be an issue with fuel delivery. If you want a 100% sure gravity feed the '86 solution is the way to go.
It is not just myself claiming that; honda's engineers think the same.

 

Thanks for the sketch.

If you could machine/fabricate a different base for the '86 petcock would this then be able to be mounted to the '84/'85 tank or is the body, of the ‘86 petcock, too large to fit - i.e. was the side wall, on the ‘86 tank, reworked to accommodate this?

If you are able to mount the ‘86 petcock, on the ’84/’85 tank, would it be advisable to install a second fuel line to the ‘84/’85 carburetors to take advantage of the larger fuel line i.d.?

Thx!

 

I tried to enter the brass tube of the '86 petcock in a '84 tank just for taking photos but it is slightly bigger so it cannot fit in. I believe there is no way in modifying the '86 petcock to make it fit in a '84/'85 tank. Only the tank modification might work. On the '86 the mounting plate place is reworked, probably lowered by around 5mm, but I cannot compare sidewalls at the moment. See next:



Here is the petcock's mounting plate- knob axle height difference:

Although I have no idea what the internal fuel passages differences between the '84/'85 and '86 carbs are I intend to do so. It cannot do any harm for sure.

 

Thanks blitzas!

It is very helpful to see the two versions side by side in this photo.

 

Wow.....what a difference between the 2

 

Difference is quite big but I believe the '86 petcock is over engineered. The diaphragm of the '86 petcock is the same as the one of the VTR1000!

 

Guys, I'm still struggling to understand what the fuss is all about. The stock 84-85 petcock works fine for gravity feed - what more do you need to know? Why would you want to go to the trouble of making an 86 part fit a 84-85 tank?

 

I wasn't trying to make work here - more I was wondering if the stock '86 petcock could be modified without too much trouble.

It looks like it can not, so I guess this idea is a non-flier.

This said I am still a bit puzzled by creaky's findings related to the engine performing better with the fuel pump...

On a fuel delivery system note:

I am currently restoring the gas tank on my '84. I found a few pin holes under the surface after sandblasting (they hadn't made it through the paint yet) so I decided it was best to address these.









The Factory paint was near mint and I was able to keep the original decals and the original Candy Aleutian Blue color as the painter carefully cut in the Shasta White to the original decal line.



Next up is to seal the inside with Casewell epoxy. Once this is complete the tank will be rust free.

I'm thinking I may not run an inline fuel filter at this point - instead relying on the stock petcock filter screen...

 

I have seen these holes quite a few times. The adjacent area is unfortunately not much better.
That's the VF500; a bike with great handling and pin holed tank hwell:

 

I think the Casewell (or similar) epoxy liner is the way to go here.

http://www.caswellplating.com/aids/epoxygas.htm

On this tank the pin holes were filled with weld first. The tank was then primed and painted (Shasta White). Next up is the epoxy liner then back to the painter for a final wet sand and clear coat.

The paint on this tank was about a nice as you could find yet those pin holes were lurking under the surface.

The good news is that with a skilled resto shop (or if you have the skills/equipment in house) you can fill the pin holes and restore one of these tanks without having to get into a full repaint/decal restoration project.

 

ic......you apparently are still wondering why I had a fuel starvation problem with gravity feed. When I tried the gravity feed, the tank only had about 2 gallons of gas in it. The petcock was thoroughly clean & unobstructed, fuel lines unobstructed, vacuum line connected to the petcock, fuel filter unobstructed, gas cap vent not obstructed. So, the only conclusion that I can come to is that with the two gallons in the tank, gravity just wasn't enough to keep the bowls full under full throttle. Since it did run on gravity, if the pump takes a dump I'm sure that converting to gravity as a field expedient will at least keep me going to get back to the barn.

 

Thanks Creaky.

I am going to try running without the fuel pump on my '84. I am puzzled by what you have encountered but I have also read from many owners (and as noted above in the thread) that the fuel pump is superfluous.

I was hoping the '86 petcock would be a plug and play for a larger i.d. but this is not the case.

I think running a single line from the petcock to the carburetors without an inline filter will work okay but I will know more after a few test runs.

This won't happen until next season though as my VF500F is in the hanger bay for the winter.

 

I took my chances with POR15 tank sealer this time. Though my '86 tank was in near perfect condition I knew without sealing I would eventually get pinholes someday.
I had tried KREEM in a different tank many years ago, tank never used afterwards and after 6-7 years I had a look at it and liner was converted to flakes.

Anyway, fingers crossed and time will tell.

 

C'mon, don't let a little cold weather bother you, I put in 125 miles today.:smow:

 

I am an Easterner for sure though 80mph in 40F weather isn't for the faint of heart.

Kudos!