Another Carb Question Thread VF500...

Well, here I am again, back working on my bike, and hopefully getting close!

I just got done re-doing my carbs using the best parts I have from my 2 sets. I feel that I have good pieces everywhere except boots, but i'm working on that, and don't think that is my real problem at this point. (spraying wd-40 on and around them while it's running does not change the way it runs)

As for the internal parts of the carbs, out of the 2 sets, here are the jets I had

Main Jets:
-- 4 * 98
-- 2 * 105
-- 2 * 108

Slow Jets:
-- 4 * 38
-- 4 * 35

Needles:
-- 2 Marked 2VD
-- 2 Marked 2VF
------These 4 are all very close to the same size, visually they look the same
-- 3 Non-Marked with clips and something like 6 slots for clips, much bigger around than the VD & VF ones.
-- 1 Marked 68E that is the same length (where the clips are placed) but slightly larger around at the bottom than the non-marked needles.


So, based on what I found in this thread http://vfrworld.com/forums/1st-2nd-generation-1983-1989/31843-rejetting-vf500f-2.html, and the fact I have a full Yoshi Exhaust and a K & N Air Filter.

I went with this for my set-up

Mains:
105F
108R

Slow:
38

Needles:
2VD- Front
2VF- Rear



From here is where it gets weird (IMO)

So I put the carbs back on, just like this, started it up w/ choke on and it runs really decently. Hit the throttle and everything seems fine, Haven't ridden it or anything, just let it sit there, haven't done much adjusting with the idle setting to get it to idle w/o choke and here is why...

The Pilot Screws are turned all the way down, to the soft bottom out point. This has me rather confused, shouldn't that be shutting off the fuel? Or do I have my interpretation of how this works wrong?

I tried to turn the adjustment out 2.75 turns out like suggested by Factory Pro, and it seems like it is way to rich, turning the throttle basically kills it instantly.

So does anyone have some suggestions on where to head with this?

As always, any help is appreciated!

 

Need a bit more info.

What year bike do you have? What year carburetors are your using?

The idle mixture screws control the output of the idle outlet. They should be gently seated and then turned out 2 ½ turns.

The idle mixture screws do not control the bypass outlet. The bypass circuit is an intermediary circuit that works just of idle, when the butterfly exposes it to the engine.

In terms of jetting – the recent thread you mention notes the owner using larger main jets for the front carburetors – on an ’86 VF500F – per Factory Pro’s instructions.

To be honest, I am not sure I understand why FP has the ’86 setup this way and we are waiting the hear back on why they do.

For reference, V4 carburetors typically have the rear (#1 and #3) carburetors setup for a richer operation. This includes a thinner jet needle, a main jet emulsion tube with holes in a different arrangement and a larger main jet.

On a side note – Factory Pro does not supply new emulsion tubes with their VF500F jet kit but they do supply new jet needles.

Hope this is of some help. Let us know how you make out.

 

i.c. is right. the emulsion tubes are slightly different front to rear, and mixture screws must be open at least 2 turns. use the #35 slow jets. you'll need to do a few plug readings before things are sorted.

 

Thanks for the post. I am curious about the #35 slow jet recommendation...why not #38's?

 

I think half of the parts that he has are from a Jet kit, the obvious give away is the needles with clips. I suspect that the 35's were part of the kit, as 38's are stock.

It is weird and too bad that you don't have all 4 of the needles with the clips as they offer better tunability than dinking around with washers, etc. Since one is missing and there is this other odd-ball needle it is tough to know what was done.

 

Also, the slides are a different part numbers on all three model years. Part of the quirkiness of the VF500F.

I believe - though haven't confirmed this yet - that the difference is in the dimension of the small hole next to the jet needle that regulates the rate at which the slides rise in response to the vacuum created by the airflow.

This is the infamous hole that the DynoJet kit requires you to drill - as noted, the FP kit does not.

Carburetor Slide (aka Vacuum Piston) OEM part numbers:

'84 16111-MB1-771
'85 16111-MF2-781
'86 16111-MF2-711

 

I fixed a misprint in my post, I put the larger Jets in the rear because of Jamie's suggestion post #46 in that thread, 108's in the rear 105's in the front.

First, my bike is a 1985 with 85 carbs, although some parts may have been swapped with my 84 carbs, but they were either all 4 switched or none switched.

As for the Pilot Screw, So you are saying that should only affect the idle on the bike, and not when the throttle is actually opened? And having it all the way down (gently seated) should do what exactly?

As for the main jet emulsion tube's, there were 3 different types of emulsion tubes with my carbs.

Had 4 the same, and all with the 98's in them, they had 1 hole, 2 holes, 1 hole, 2 holes if you turned it in a circle.
2 of them had 1 hole, 3 holes, 1 hole, 3 holes if you turned it in a circle
and 2 of them had the same, except the 2 sides that had 3 holes, the lowest hole was dropped to the distance where a 4th hole would have been, but skipped the 3rd. So still 3 holes.

I put the later of the sets on the 105's, and the other 3 hole set up on the 108's if I remember correctly.

Jet Needles, should I make adjustments to what I did with these?

As for plug readings, anyone want to give me some insight on how to do this, I know it deals with taking the plugs out, looking at them, and making adjustments based on how they look, but I'm not sure what adjustments do exactly what yet...

Putting washers on the needles, richer?

Adjusting pilot screw out , richer?

How do you mix and match these?


Thanks for the input so far!

 

Re. the pilot screw (AKA idle mixture screw) - this is a 'fuel' screw meaning that when you turn it out, it increases or 'richens' the mixture.

 

On a follow up note regarding the idle mixture screws AKA pilot screws - to adjust these:

First set all to 2 turns out from being - gently - seated.

With a warm engine, turn the screws out (typically an additional 1/2 turn) and carefully listen for an RPM increase. That's all there is to it.

Honda does have an 'Idle Drop Procedure' in their FM but this has more to do with emissions politics than the actual practice of making an engine run better - IMO.

 

Further to the above, there is a link to a jetting tutorial in the recent jetting thread.

Raising the needle with a washer is like lowering the clip on a needle with clip slots = richening

See tutorial and other jetting articles on the web for info on what does what and how they interact.

 

+1

Here is a link to the Factory Pro Tutorial:

CV Carb Tuning Procedures

 

Another way to dial-in mixture screws is to slowly turn each screw clockwise (one at a time) while the engine is idling. At some point that cylinder should stop firing; then open each screw the same amount (usually about 1 to 1 1/2 turns) from that exact position to get smoothest running.

Did you check float height in each carb ??

 

Checked the float height, think they are set right.

The weird thing is, with the screws all turned down, to a soft bottom, is the best I could get it to idle, note, the choke was slightly on.

When I open the screws up, it is too rich when in the mid range, and bogs down very bad...

This is why i'm having so many woes about adjusting these carbs.

Any Tips Based on that info?

 

Did you carefully inspect and clean all the circuits when you had the carburetors off?

 

Weird problem, clearly something not right and obstructed somewhere.

Incidently, did you sync the carbs or at least bench sync them before installation?

 

............

Things are totally messed up if the bike runs with screws turned fully in.

don't blame idle circuit for poor midrange (3000+ rpm) running, and why do you think it's too rich rather than too lean ??

whatever mods have been made, you need to go back to stock factory jets/needles to get the bike running right.

remove air filter and watch slide action up and down in response to throtte with engine running as it's easy to pinch diaphrams if you've had carb tops off.

 

All circuits, and I mean ALL circuits were clean when I put it back on the bike, and that is when it started right up when I forgot to turn the pilot screws back out. I'll probably pull the carbs again this weekend

My Thoughts Exactly

So just to clarify 1 more time, the Pilot Screw only changes the idle jet?

Initially (the time before this when I had the carbs off and cleaned) I had left the pilot screws where they were, at 2.5 turns out. Went for a ride, realized it was bogging down so bad, tried 2.75 turns, wasn't any better, unsure if it was worse, tried 3.25 turns, was definitely worse, and then ever tried 3.75, way worse. Then when I decided to go the other way, it was gradually getting better, then overnight it wouldn't start again before I could finish testing it all. And this is where i'm at now...

Short Answer- turning the screw out made it worse, so i'm assuming it is running rich.

Did this, everything seemed normal to me, although I'm not positive what normal is (they were moving up in down very fast, vibrating, at the same height)

 

The idle mixture screw controls the output of the idle circuit.

It is a fuel screw meaning 'in' leans and 'out' richens. The idle mixture screw does not control the bypass outlet.

The bypass circuit is an intermediary circuit that works just off idle - when the throttle butterfly exposes it to the engine.

I know it is not welcome news but I think you are going to need to pull the carburetors and re-inspect everything.

 

Already have time planned for it this weekend

By now it takes me >5 Min to take them off and >5 Min to put them back on, and going through them isn't much work either...