(86-87) carb options

I picked up an 86 vfr700 a couple weeks ago for a steal. The only thing wrong with it being the carbs leaked. I got it it home cleaned the tank and and started on the carbs when I noticed that they had already been into and it looked like parts were missing. 2 standard thread screws were used on the bowls. Rather than trying to track down all the necessary and expensive parts, Im looking into just changing the whole set up. I found a couple of sets on ebay but they were pretty expensive. Im wondering If it is possible to adapt the 3rd gen. carbs to my second gen?

 

Not gonna happen, two different animals. Have had poor luck with E-bay carbs so be sure you ask aboot condition and are able to hold their feet to the fire if they are not.

 

Im thinking about doing away with that whole set-up and running flatsides anyway. Ive got a set of 34mm mikunis that I think I can make work, all Im really worried about is the angle of the carb bowl. Ill have to make a throttle cable but I think its possible. What is so different about the 3rd gen. carbs? Are the angle of the cylinders different? Im pretty good at fabrication, was just wondering if I was heading into uncharted territory. It would be nice if I knew someone had tried it before I go and spend money on a set gen. 3 carbs.

 

All four generations the carbs have the same basic VD design made for vertical downdraft applications.

3rd gen has the throttle cable bell crank on the outside of #2 carb, 4th gen has it on #1, so cable lengths are different, but 3rd and 4th can interchange.

On 2nd gen the bell crank is on the #2 carb also, same as 3rd gen. The 1st gen bell crank is on inner side of carb #4 and comes out the central interior region--major pain to access.

1st and 2nd gen intake spigot diameters are 1.50" and 3rd4th spigots are 1.655", so the rubber boot insulators are different.

For 3rd and 4th gen the center to center (or edge to edge) spacing of the carb spigots is 5.70" for F or R banks.

Unfortunately i don't have a spare set of 2nd gen carbs to measure their spacing-- but you do, so get out your tape measure, get a reading and post it back here, then we will know.

EDIT Update: i have a 1st gen engine on a pallet and the intake spacing measured 5.610" and the spacing on the carb plenum plate was 5.540", best that i could measure using redneck squid tools.

i believe you could make any of them work if you made custom rubber insulators to mount carbs to the intake, of course the plenums are all different and use different air filters and housings, etc. and the fuel tank wouldn't fit right, but if you are a clever fabricator it wouldn't be a problem to make your own air filter.

 

Flatslides on a streetbike ?? :crazy: It will NEVER run as smoothly or as well as the OEM CV setup.

Easiest, most practical solution is to fix the carbs you have, otherwise you'll need to solve many problems and spend a bunch of money with any other setup.

 

I actually fixed the stock carbs already. Had to make some fuel tubes for it. ( I don't know what the big deal about taking the intake plate off is, makes things way easier.) As for flat sides on a street bike, The mikunis that i have came off of my gs750 "street bike" they are not as smooth low in the rpm range but, in my opinion its worth it just for the simplicity factor, not to mention the gains possible with some exhaust mods. The only problem I can see with the flatsides is the angle of the cylinders and how the gas would sit in the bowl.

 

Also, Thank you KennyBobby for being the only one with some good ol' southern optimism.lol. I will measure the spacing and post it when I go back to work tomorrow just to be sure.

 

Can't get good results using any diameter carbs other than stock, too much turbulence and inefficient flow at transition point.

 

Hey nightrider,

Here's the reason--there are about a dozen little springs between all the linkages that keep the butterfly valves aligned and synched--most folks don't realize it and the springs jump out and get lost when they dismantle the carbs from the plenum plate, then it never runs right ever again. Also most folks will crack or break the fragile fuel tubes when they separate the carbs from the plate. It's easy to remove the entire rack with the cables attached if just making a jet change.

 

I had to to take it off to get to the ever so fragile fuel tubes. (they were all busted up) I didnt have any springs pop out at me, but these carbs have been into before and its possible they were already gone. Nothing really looked out of place but i did notice that the rear butterflys seem to open a little before the front ones. Im gonna look at a fiche and do some inventory of all those little parts.

 

Sounds like somebody was already in there and lost some springs and broke the tubes for you--then you have no choice but to separate at the plate. There are at least two springs at each synchronizer screw, one above and one below the link. There are some axial thrust springs between the carbs on the ends of the throttle valve shafts.

The venturi diameter is basically the same for all four gens, 32mm for 1st and 2nd, 34mm for 3rd, and 33mm for 4th. Same size motor in each case breathing thru the same size windpipe.