Rejetting the VF500F

I am getting my '86 California bike back on the road after it has had a long rest. I have a Factory Pro kit in it, but I was wondering what the differences are between the 49 state and California bikes to require different jetting. I know the California bikes tend to have all of the fuel vapor stuff, but was there anything else? Did the California bikes have different cams?

Mine has Yoshimura slip-ons with a K&N in the stock airbox, and due to my neglect after the bike has been idled the last few year I was going to replace the pilot jets and main jets, although a recent move to the Colorado front range from the flatlands of California would probably make some jet changes a good idea anyway.

I think I will start with 95/98 and go from there.

 

Well, I've got clogged pilot jets and need to finish the valve adjustment, and get new tires. The F2 wheel swap will have to wait. Getting pretty jazzed about getting it back on the road.

I did dig up my box of stuff from Factory Pro, and although the card in mine shows a date of August 99, none of the information on it has really changed. Still, I'll try and scan it and post it anyway.

 

I was wondering if my email to FP was answered. Turns out my wife logged onto my computer in NY and the message got pulled off the server. I never saw the message in VA.

Here's Marc Salvisberg's response from Factory Pro:

Hi Greg (I remember you, btw).

Now..... I'm saying this in all great humour..........

There's sure a lot of people who talk and look up specs and postulate and raise doubt.......

The specs on what we have on our sheet are what worked best on the bikes that we tuned here.
Sea level, moderate temps and humidities with stock exhausts and USA aftermarket exhausts.

If I remember correctly, the "perfect" main jet on all those years would have been some non existent 1/2 size jet (like 91.25 or something).
I was 100% correct on the bikes that I tuned - and it's possible and probable that someone has a bike and pipe combination that wants some different main jet stagger.

But bantering and scanning spec sheets won't provide perfect jetting. They have to change jets.


Why might the jetting be different front to rear?
Same reasons inline 4's might have different jets in each cylinder......
Airbox resonance and flow rates, heat, cooling, exhaust resonance and flow, - almost any thing that you can think "might" cause a different the engine actually wants a jet to be required, probably is a reason.

Learned many years ago that it's better to put the jet in the carbs that the engine wants (ending up with something that runs well).
Later you can try to figure out why it might want that different jet.

You mentioned that the bike "can handle" some jet size - it's not that some bike "can handle" something without signs of distress - it's that you need to put in the jet that pulls the best at high rpm -

Great subject -

Marc

 

The problem I have with all of this, is without a dyno, how can you tell which jet really pulls the best? (granted, they're in the business of selling both jet kits and dynos...). But for someone that doesn't have ready access to a dyno, what to do? And their road-dyno instructions are vague..

I have two bikes that I think need some re-jetting/needle-height adjustment (wife's HawkGT and my VFR700). But swapping jets puts enough downtime between runs, how can you really tell the difference (or is it really THAT dramatic of a change with each jet size?).

 

Thanks for the follow-up post.

 

True! And these are keys to tuning a bike. Every bike is different. Bikes are at different temperatures, elevations, and mileage. Different bikes have different equipment on them such as filters and exhaust. There is no one setup that will work with everyone. There is, however, a good BASELINE setup that will work for many, and people can use that to tweak their own setup based on THEIR bike. That's what I was searching for when I originally posted the question in Post #1.

It's not easy to get the best power from a carb setup without the use of a dyno. Most people just don't have that kind of sensitivity. Driveability, good idle, and cool running are things that you can feel and see though, and that's what I'm using for tuning this one.

Keep in mind that peak power is not what you're always looking for.

Lean mixtures give good power as long as it's not too lean. However, lean runs hot and can burn valves and cause overheating. "Lean is Mean" Ever heard that saying? It's true but it's not safe. It also causes problems with driveability and throttle response.

Conversely, rich running is safer because the extra fuel helps cool the combustion chamber. Too rich though and you can wash oil off the cylinder walls, foul plugs, muddy throttle response, and have poor mileage.

Again, it depends on the bike. Sometimes you CAN feel the difference between two main jets, IF you ride the bike often enough and have that muscle memory (or is it "sensation memory"?). Some bikes have a very narrow band of "good running", where all it takes is one needle position or one main jet to make all the difference in the world.

I had a Yamaha XS750 Cafe that I just sold that was the same way. It seemed the carb setup on it was such that it was extremely sensitive to mixture screws settings. 1/2 turn one way and it ran great, but anything other than that it would either foul the plugs rich or go lean and die. You couldn't ride it anywhere the elevation changed because of this.

I don't think our Hondas are that way, as most Hondas typically aren't, but yeah it's possible.

 

I normally just use the plug reading technique. That seems to work just fine without requiring a dyno.

 

The "plug chop"? My area makes that really difficult (I live in the mtns, all 2-lane twisties), and then you need to pull the plug on the side of the road, not exactly fun... (or do I have how to do it wrong?)

 

All it takes is about a 1/4 mile stretch close to your house. Just rip it through the first couple of gears then shut it down right away. Coast into your driveway and proceed from there. It's ok if you have to idle a bit, just try to minimize that if possible. I like to wire wheel the plugs right before doing this so you know that your readings are accurate. It's not science but it gives you an indication of what's going in there.

 

My "driveway" is a 1/2-mile long grade, 20% in places, with about a 700ft climb overall. Maybe just romp it up the hill? The switchbacks at the top will complicate things, though...

I need to live someplace a bit more flat.

 

No response. Not unusual.
Many people are just lazy. They want info -but are too lazy to help others.

 

You do NOT have to have a dyno to tune a bike.
Matter of fact many WINNING bikes have not been on a dyno, or have ignored dyno advice.

 

Really??? How much more information do you need beyond what is in this thread?

 

Originally Posted by Michael E
I posted jetting questions for the 500 a few times with no response. I don't know that a lot of people here have gone away from stock, based on responses. It might even be tougher go with the 86. I wonder if Matt changed his jetting?

I do not need any information about jetting.
I was just saying WHY there is no response to some forum members questions.
Some people have helpful information, but will not take the time to help others.
I try to help when I can.

I have worked in motorcycle shops since I was 16 years old. I am 61 now.
It is a mystery to those that grew up with fuel injected cars and motorcycles.
It is no mystery to me.

 

That was nine months ago! This thread evolved well with good information and contribution by many.

It's funny when you look back at old posts and you barely remember writing them or sometimes not at all! I must be getting old.

 

tinkerinWstuff...........What jetting did you find best for the '85 VF500F that you had? Mine still has the stock jetting and for me it runs just fine and delivers very good fuel mileage. Should I be going a bit richer to keep exhaust temps a little cooler? Or for any other reason?