VF500F - setting the float height after removing the fuel pump

Hi All,

Has anyone reworked the float heights after removing the fuel pump on the '84/'85 VF500F?

My hunch is that while the fuel pump is not required, i.e. there are no fuel starvation issues, the pump does help to even out the flow of fuel across the four carburetors.

I am wondering if a bit more fuel is needed in the bowls after removing the fuel pump (by decreasing the float height dimension as measured in the FSM).

On this note, has anyone added a second fuel line - adding a fuel inlet to the No. 4 throttle body - as this would also help to even out the flow.

Thx!

 

Setting the float height and removing the fuel pump are two different issues. By changing the float height you can affect the idle circuits along with the transition to off idle/low speed and low to mid speed circuits. level.It will make them richer. I would set the floats at mfg spec height, try the bike. Whether pump or gravity fuel feed the fuel in the bowls should maintain the proper level. If not that's a different problem.

Adding a second line might be a good thing as long as your able to pull fuel from a different source feed and be able shut it off when you want. By different source feed I mean not the same 3/16" line from just the petcock single outlet. Ex: splitting the current outlet line. If you are having a fuel starvation problem I don't think splitting the current single line will buy you anything. Same amount of fuel just going to two different places (1/2 each) instead of one place. Unless you can enlarge the single outlet feed tube.

 

To me the interesting part of this discussion and this application is that when Honda made the change to gravity feed on the 500 in 1986 the altered the fuel distribution point at the carbs. In the 84-85 fuel pump versions the fuel enters a single point at the end of the fuel bank. On the gravity fed 86 they split the fuel into two separate points: between #1 and #2 carbs and between #3 and #4 carbs. I believe that this is what has got IC thinking: Did Honda make this change to a more evenly spread distribution because there were slight reductions of fuel supply to the carbs on the opposite side of the bank (3-4) when using the gravity feed and the side fuel line inlet (1) on the 84-85 carb design?

 

Yes, this is what I am thinking.

What leads me to believe that the fuel level in the float bowls needs to be set a bit higher is that a creaky (in a recent post) noted that when he used an axillary tank his bike idled a bit rough. When he hooked up the stock fuel delivery system (with fuel pump) the idle smoothed out an the bike ran fine.

Though in full disclosure, as I understand, he did set the float height dimension a bit larger than the Factory spec - i.e. very slightly on the lean side.

My hunch is that the fuel pump helps to even out the fuel distribution and that when removed a float height adjustment should be made - or - a second fuel line should be added to help ensure a smooth engine response at idle.

I am wondering if any other owners have encountered this.

FSM specs:



Possible location of second fuel inlet:

 

I would NOT re- adjust the float levels.

Just change the fuel pump and see where you are at.

Float levels will not change just because you changed the fuel pump.

 

It is not that the float level is 'changing' rather when the fuel pump is removed the fuel is not 'as equally' distributed across all four carburetors. This may in part explain why Honda opted for two fuel lines on the '86 VD31A carburetors.

My question is, without running a fuel pump on the VD56A and VD56D series carburetors should you slightly increase the amount of fuel in the float bowls - or - add a second line to compensate?

 

NO no no.

I run my VF1000R WITHOUT a fuel pump. Not needed.

The amount of time for the float bowl to refill (if it was running completely dry)
would be milli seconds. Ride it first.

If you run for 1/2 mile on the freeway wide open and it starts sputtering THEN think about the exotic things.

Even on the Honda VF1000R the Honda workshp manual has discrepancies about float height. For instance, on one page showing float adjustment they say .330 thousandths.
On another page (specifications) it says .350 thousandths.
Both US model and 49 state or California -still a discrepancy.

I called Honda and they could'nt figure it, out and they never called me back (like they said they would), so I set them 1/2 way between the two measurements.

I have two 1/4 petcocks feeding a 3/8 line in to the carbs. To make sure when leaning the bike there is fuel.

Maybe they changed the 500 because of gas tank design not delivering gas when leaning left or right on a long sweeper curve. Not float bowl volume.


The DIAMETER of the line going into the carbs matters too.


ANYWAY Just ride it first then decide. If the float level is too high it can cause all kinds of problems. Worse than starvation on loooong high speed runs.

 

What has me a bit puzzled is creaky's post - with an auxiliary tank (gravity) there was a rough idle, with the stock delivery fuel system (fuel pump) the idle smoothed out.

 

I've been following this thread, so....today I bypassed the fuel pump on my 500 and let the fuel flow by gravity. The engine started, no problem, idled OK but when trying to run through the gears, starved for fuel. Hooked back up to the fuel pump, engine runs like it should. With the fuel line from the tank to the pump disconnected and vacuum applied to the petcock, fuel flows readily from the petcock, doesn't appear to be any flow restriction. If I can come up with a reason for why the engine will not run properly on gravity feed, I'll be sure to post.

 

Do you have an inline fuel filter?

 

Thank you for the post. This makes sense. I will look into the design of the '86 fuel delivery system a bit more (any '86 owners please feel free to post).

From what I have read the fuel line on the '86 splits downstream from the petcock and travels to two connection points between the throttle bodies (1|2 and 3|4). I don't know the spec on the petcock outlet or the fuel lines on the '86 - perhaps these are different dimensions when compared to the '84 and '85.

 

I do not think the fuel lines would split into two lines.
Check that out. One of the lines is a VENT FROm the float bowls not fuel feed.

Also find out how large the INSIDE of the fuel line is that comes FROM the petcock.
Sometimes those fuel filters are very restrictive. I use an auto fuel filter . A sheet metal filter with 5/16 or 3/8 outlets. Some of those mini motorcycle filters are only 1/8 inch inside diameter on the outlets.

 

What? are you the hall monitor? :flip: :flip:

I have an 86 700 and it has a fuel pump...unless the feed tubes inside the tank of the 500 are differentI don't see how gravity feed is going to work ..past a certain point.. my advice or opinion is, run it how they engineered it to run. I am all for modifications but if your having problems..... stay with the stock enginneering..

Good luck

 

I guess if the feed tubes are on the small size they may require a pump to keep enough fuel in the bowls. Going to gravity feed from there may not let enough fuel run in to all bowls in the time need. Raising the floats will correct that when running possibly. But will cause problems with idle and just off idle transitions.

I've run my 750 with just gravity feed aux tanks for carb adjustments and a quick run around the block without problems. If your feed line is that small I doubt slitting it after the petcock is going to buy you anything. Your not getting anymore fuel than the smallest restriction will allow. Possible it may get to the other two carbs faster with a split line. Though the amount will be the same and still not enough.

Sometimes you can enlarge the ID of a tube by drilling out a few thousands more. Just be careful of the wall thickness. It may be just enough to give you the fuel you need. You need to check the fuel tube size between the different years to see if there is a difference. As Donald said check the fuel filter ID size.

 

The '86 fuel line splits into two lines - this has been verified, please see posts 3 and 4 above.

Also please refer to this thread:

http://vfrworld.com/forums/1st-2nd-generation-1983-1989/32994-86-vf500f-keihin-carburetor-photo-showing-fuel-lines.html

 

The 700 is a different animal. This thread is specific to the VF500F and the fuel delivery changes between the '84/'85 and the '86 model years.

 

For the VF500F? Please post a link to the thread.

 

I see the 86 split lines. I also see a larger feed line to both of them. About twice the size of the ones going to each carb bank. What size feed line does the 84/5 use?