Matt Tries – 1984 VF500F Overhaul

This doesn't solve your problem now, but when I bench synch carbs I use a strip of high quality heavy stock printer paper cut into a strip about 6 - 7 mm wide and use it as a "feeler gage". I set the idle on the base carb for a nice drag on my strip. Open the butterfly, insert the strip in the center, let the butterfly close on the paper and pull. Again, just a nice drag that you can get a feel for. Now I move on in my progression matching that feel, periodically going back and rechecking the "drag" on the ones I've already done. Using this method I have rarely had to make adjustments on the bike. The paper gives you really good feedback even on very minor adjustments.

Good luck!

 

I like this a lot. This sounds like it would be far more accurate than the method I used and the same level of work. The good news is that I should get to try this out pretty soon because I'm going to reassemble my buddy's 500 carburetor hopefully this weekend. Probably depends on how stuck I get with my own bike.

I would have taken the bench sync a lot more seriously if I had known how hard access was going to be! I'd just sync'd my Bandit recently which is like a 2-3 minute job once the tank is off. Conveniences of an inline I suppose. Now I'm eager to try out the paper feeler method. Thanks again.

 

How about a piece of fuel hose that stays stiffer than regular hose, insert socket and snake it up there.

 

This is good advice...Thanks. I will try this tomorrow.

 

judging by the synch gauges, i think you might have lost a synch spring on the throttle linkages. also, i think you're going the wrong direction with slow jets as it should run fine with #35 or #38 if everything else is ok.

if carbs are bench synched by eye (throttle plate and progression hole) there is never a need to turn a synch screw more than 1/16 turn for final synch.

maybe check the tightness of carb boot clamps cuz you may be sucking in air from somewhere.

 

Squirrel, I've put 40s in VF500F with full systems no prob. It puts the mixture screw in the sweet spot IMO. A 38 is what the bike should have came with stock, so a 40 is not a huge leap with mods.

All the VF/VFR should have came with one up on the pilot. That's how they met the idle emission standard for US DOT approval.

My 1998 ST1100 came with 40, same bike Euro got 42. (Now has 42 and PAIR removed)

You are very knowledgeable and have worked/tuned on plenty. I'm not saying you're wrong, just that I'm not either. I've tuned many customer VF500F on stock 35 no problem with the right tweaks.

 

^^ ok we need to work together to get this one running well.

 

Little diversion from the synchronization I started earlier this week and was hoping to finish. I back-filled and bled the new rear stainless line without any issue. So I've got rear brakes. Good!

In true two steps forward, one step backward... realized I used way too much grease when reassembling the master cylinder for the fronts, and I wasn't pushing any fluid. Spent two days just putzing and pumping the lever trying to make anything happen. Was really perplexed. Then I decided to start loosening the banjos at different points and pushing fluid through the the syringe to see that I was getting pressure everywhere, and I haven't found any issues. Decided to pull the master cylinder off, pull everything out, clean it all up in the ultrasonic, and put it back on the bike. The lever feels a whole lot better now. I reverse filled the lines all the way up to the master cylinder, but I can't actually push fluid into the reservoir if it's attached to the lines.

I still haven't been able to develop any pressure in the front brakes yet. Going to leave that aside and hope some air bubbles start to move their way towards the top as a handle it.




Back to the task at hand. I found out I can position the flexible screwdriver to access the #1 and #2 synch screws pretty easily by wrapping a wire around the top and pulling it. I feel confident I can get to those two.

I still can't figure out a way to get to that #3 synch screw without the fancy tool. Going to try a few more things and hopefully get it done this weekend. If not, buying that tool.

 

So I was able to figure out a way to hit all three synch screws with the bendy screwdriver + wire; however, it was still so far off and my idle was ~3000rpm, and the gauges look as wonky as before. I started to think you might be right about missing a synch screw spring... so I gave up on running it. Brought it back in, and I've pulled the carburetor back off. Might as well see if there's something obviously wrong.

The carb boots I was pretty confident in that they weren't pulling air as I'd gone around with starter fluid earlier and checked for air leaks. I found one on carb #3 (when I first did this) and realized I could tighten them down a lot harder than initially thought.

Anyway, I am not missing a synch screw spring luckily. And from what I can see, the springs on all #1,2,3 are the same--I counted 6 turns each. I was thinking #3 might be different because it's not paired with a second one.

In regards to the paper feeler gauge, I understand how this would work with carbs #1,2,3 that have adjustability. Manual says #4 is non-adjustable. Synch #3 to #4, and then do #1 and #2 in either order. I can do a feeler with the adjustable ones. #4 is basically closed solid and can't be changed. I put a piece of paper in there, and I cannot remove it without tearing the piece of paper. I now see that #1,2,3 were WAYY too open comparatively, and it took about 4 full turns to get them to close completely.

I guess my question is: Should a butterfly ever close completely like #4 is by default? I don't see any way this could be changed. This would explain why the vacuum reading was ~2 times as high as the others. But the others lined up very close to where I expected them to be based on my limited experience of balancing other bikes. My plan is to just set them all like #4 since that's how I interpret the manual. But it seems like they could have just said "close all the valves completely" and saved some ink if that's how it truly should be done.

Action Mark Martin came in a box from my friend with all his carburetor that I need to clean. I was sending him a few pictures picking his brain, so that's why he's in the shot.



Lastly, I was feeling pretty defeated since now I've got a carburetor I can't figure out and a front brake system I have been unable to get pressurized after messing with it all week. The mail man brought me some new coil wires from Billy's Outback. They are so nice and soft and easy to route compared to the old ones that were really not feeling good. I cut them long in the expectation I'll trim them once I figure everything out.

A purist is going to hate the yellow wires, hah. But this bike lost its stock paint job a while ago and I thought it might be fun. Definitely second guessing if I should have just ordered black, but we'll try this out for a while. Fired it up once before pulling off the carburetor to make sure I didn't fuck that up too. It fired.



*Edit--forgot to mention that the exhaust from the left side (#1,3 both adjustable) felt considerably stronger when I put my hand behind it compared to the right (w/ #4 non-adjustable). That would jive with the super strong vacuum pull on #4, but it also makes me suspect even more that #4 throttle valve shouldn't be resting closed solid shut. I did not pull the butterflies off when I cleaned it, so that setting of the carburetor shouldn't have been disturbed.

 

I said the base carb is adjusted by the idle screw. Set the "idle" so you have a nice drag on the paper. Then adjust the remaining to match that feel. When you are all done, you will have to adjust the idle back up quite a bit, but they will all be opening at the same time, the same amount.

And cut that paper in a nice strip, not torn and jagged. Like a litmus test strip.

 

ooooooo. Jesus that makes so much more sense. Set #4 with the idle screw... set #1,2,3 accordingly.

I'd dropped the idle all the way back trying to bring it down because my #1,2,3 were all so far open.

I promise I'm listening. The meaning of "Base carb is adjusted by the idle screw" went over my head until this moment. I will set carb #4 with the paper feeler. Then I'll set the other 3 after that. Then I will put the carburetor back on the bike, allow the engine to warm up, set the idle close to 1,300 rpm as the manual states, and fine tune in the synchronization using the vacuum gauges.

I can do that.

 

yes, all butterflies should be able to close completely. as capt80's says, use idle adjusting screw to set the minimum opening (with feeler gauge) and match the other carbs to that one for bench synch. setting synch while idiling is different, so reread the manual.

it helps alot to blip the throttle a couple times every time you adjust a synch screw, and remember that the sequence of screw adjustment is very important.

 

Excellent. Just making them all closed wouldn't give the fine adjustment you actually need. And look at the linkage and make sure you are doing the right progression. Everything builds off of the last carb you did. But the paper will tell you, go back and recheck as you go.

You'll get it. Isn't this "fun"?

Yes and what squirrel said. As I go thru my bench synch, I will occasionally gives the butterflies a nice "snap" and make sure everything is seating nicely, and re-check my work.

 

Nice tutorial on bench sync going. Really appreciate this.

 

It isn't, but it is. The fun part is doing it the second and third time quickly with an understanding of why. The frustration is the first time. But I know it's worth struggling through. I went on my first motocamping trip last year, and my buddy's bike wouldn't fire. We started tearing parts off that big ass Harley and troubleshooting everything we could in the middle of the woods. The bike wasn't getting fuel. We got it resolved, and that beast fired up. If I didn't struggle in the garage trying to figure these things out, I'd have never had the experience to even begin diagnosing that kind of issue, and the trip would have possibly ended there. Instead it's just a funny story now on one of the best weekends I've ever had.



Anyway, I found some gasket paper and used the paper feeler method as best I could to bench sync the carburetors. I've got it back in the bike using the hair dryer and 2 tiny flathead screwdrivers. Should be able to run it tomorrow to figure out if I got it any closer.

 

For me other than riding my bikes the best part is doing all the work myself.....learning and helping others.

 

Pretty sure they're just a bunch of damn wizards with their paper feeler gauges and other tribal knowledge sorcery. I tried out the paper feeler gauge method last night and mounted the carburetor. I fired it up today--with the air filter in and 38 pilots 2.5 turns out--and the damn thing sounds 100x better than before. I can put the idle wherever I want, and it'll stay there now. The throttle is only hanging a little bit, and I'm positive I can work some of that out once it's fully synchronized and I play with the A/F screw.



I was curious to see how close I got. Granted, I've still got a lot of room for improvement on bench synching, but the bike isn't running bad. I don't think I'll be having to pull off the carburetor again for a while which is a relief. I'm still struggling to hit synch screw #3, so I'm just going to wait to do a proper synch once I get the right tool. I've got a bunch of other items I still need to tend to.

Had to check it though.


Can anyone cast a spell and rid my front brake system of air? Just kidding. I'll figure it out. Thanks again for the help.

 

Just in case someone stumbles across this and wonders why synch screw #3 is so difficult to access:




#1 and #2 are easier from the other side, but by no means easy. I can do them consistently though with the bendy screwdriver and wire. #3 I have to luck into after much swearing and sweating. The right tool for the job will make all the difference. Or just nail the paper feeler bench sync and don't worry about it.

 

I have the crappy tool & also the correct tool. Honestly, once you get the correct tool you will understand. Its a night & day difference & I only wish I had bought it years earlier. The back of my hands have been burnt a 'few' times - even whilst wearing gloves. Since I got that tool I don't even need gloves..

On the Synch tool I find that if you set the gauges so the cylinders are next to each other 'in the front pair & the rear pair it makes it easier to read.. You can label them but its pointless. Just make the left pair the front cylinders & the right pair the rear cylinders.

 

I've already got enough scars on my hands. I've made up my mind to buy the tool. Revzilla about to make some money off me this week, since I need to buy tires for two bikes as well.

Do you concur that the Motion Pro 90 Degree Hex Driver Carburetor Tool is a good choice to go with? https://www.revzilla.com/motorcycle/motion-pro-90-degree-hex-driver-carb-tool