VF500F - setting the float height after removing the fuel pump

Sorry....I'll try to stick to the subject at hand.

 

Always being a fan of slight detours...

VF500F Keihin floats

 

No worries at all creaky!

 

Continuing on a slight detour, I wrote to carb guru Mike Nixon about adjusting the float drop. He recommended to leave the Factory setting.

As many may know the tang (noted above) controls how far the float needle comes out of its seat. If set too far the float needle will come completely out of the seat - potentially getting stuck to one side and subsequently it will not go back into the seat when the float rises.

This can lead to a fuel overflow issue that can't be stopped.

Based on the above, I am guessing this is the reason why Honda does not post the drop spec in the FSM.

The drop tang can get damaged but this is rare.

So it looks like, while adjustable, it is best not to re-adjust the tang unless it is damaged.

 

I have had that exact problem with dirt bike carbs in the past, that is the float dropping too far causing the needle to bind and stick resulting in a constant carb overflow. That is why I was concerned about the drop dimension for the VF carbs particularly since the float levels and drop were not the same in all 4 carbs when I disassembled them. I arrived at an ?educated? guess drop dimension based on my experience with dirt bike carbs.

 

Makes sense. I am curious now to see if I find a difference in the float drop settings on the VDA sets that I have...

On the fuel pump/float topic I think I am going to stay with the Factory setting, though I am still giving some thought to adding an additional fuel line.

 

I have learned from the discussion that Honda went to the two inlet system when they dropped the fuel pump. That is telling me that most likely a fuel delivery problem cropped up with the single inlet and no pump.

 

I kind of agree.

Though I haven't heard of other owners experiencing fuel starvation or idle problems when removing the fuel pump on the '84/'85, I think I may add a second fuel line. I don't see what the drawback would be...

Any thoughts would be most appreciated!

 

Okay, I may have been overly broad in saying 'any thoughts' would be most appreciated.

 

ic.....I just read a post on another forum concerning switching to gravity feed. The poster states that an '86 petcock has a larger outlet tube than the '85 petcock. Also, I neglected to mention that when I tried the gravity feed with the fuel tank installed, there was no rough idle problem like when I had the temporary fuel bottle hooked up. The fuel starvation showed up when accelerating through the gears.

 

Thank you for the post.

Yes, I believe this is correct - though I don't know the actual spec for the '86.

This makes sense as the larger petcock outlet and subsequent fuel line, on the '86, splits into two smaller diameter lines (probably matching the i.d. of '84/'85 single line) before arriving at the carburetor.

 

To answer the first question, setting the float height lower after removing the fuel pump is NOT the way to go.
Main problem in '84-'85 arrangement is the fuel delivery under fuel demanding conditions and it is solved by the pump. '86 arrangement uses a different tank petcock hole, different petcock, different fuel lines, different carbs and all contribute in resolving the gravity feed fuel delivering problems.
I had removed the pump in my '84 bike, and got fuel starvation issues when fuel was low in tank and throttle was in more of than let's say 70% for long periods. Other factors such as inline filters, dust and flake filter and tube blocking, insufficient tank ventilation etc tend to make the problem worse.
I am against removing the pump in a stock '84-'85 although I do like the simplicity of the gravity feed. Having an '86 tank - petcock would be the proper solution IMHO as the most restrictive item is the petcock. Just splitting the line feed in a gravity modified '84-'85 will help a bit fuel distribution resulting in a "more even" work of cylinders but cannot solve high load leaning.
Removing the pump and setting the float height lower will give a quite rich mixture when in idle and low load (when fuel delivery is enough) a more or less ok mixture in mid to high load (when fuel less restrictive flow will somehow compensate the reduced fuel delivery), and a lean mixture at high load because the fuel delivery cannot just be enough.

 

Thank you for the post blitzas.

I agree, reconfiguring the float height seems problematic.

I am giving some thought to modifying the stock '84/'85 petcock to increase the fuel outlet diameter - or - modifying the mounts on an '86 petcock to fit the '84/'85 tank.

 

The fuel outlet diameter of the '84/'85 petcock is probably the only non restrictive part of it. Internal petcock piping have half of outlet's diameter.

Modifying the mounts on an '86 petcock to fit the '84/'85 tank I believe is just not possible as the '86 petcock is 5mm "taller" than the '84/'85 and the knob axle won't be at center of the hole then. I wouldn't even consider cutting and doing welding modifications at the tank unless I had a dozen of them.
On the contrary an '84/'85 petcock at an '86 tank seems reasonably feasible and is also in my "to do someday" list unless I will find an '86 petcock as the pair 86 tank with 86 petcock is the only way out towards reliable gravity feed.

 

Out of curiosity have you opened up an '84/'85 petcock and compared the internals to an '86?

 

No. I didn't have an '86 petcock yet, only an '86 tank which is on the way to be finished. I have opened/modified an '84 petcock which is placed aside. I have studied though some external photos of the '86 petcock, and I am pretty sure every external piping is quite bigger than the '84/'86 petcock so I assume the internals follow a fixed proportion. Maybe I will be able to justify my thoughts soon, and in this case I will keep you updated.

 

Sounds good. I'll look into sourcing an '86 petcock as well.

It will be interesting to see if the internals (along with the external piping, as noted) are indeed larger when compared to the '84/'85.

 

If only I still had my VF and all my parts bins I would be able to answer so many of your questions! I had an 86 tank on mine and a few 84 petcocks...

 

After digesting all this info, I have decided not to consider at anytime to convert to gravity fuel feed. I am going to buy a spare fuel pump and ride.