'84 Vf700f jetting question and general carb questions

Got a jet kit from carbjetkits.com mains are +2 sizes and comes with one shim per needle, I also have the option if reusing the 112 mains and going up only one size on the mains.

According the the jet kit instructions and labeling the smaller jets are supposed to feed the front cylinders.

According to the service manual and the current state of my carbs the smaller jets feed the rear cylinders.

Stock according to service manual 112 front 110 rear

My carbs now -Stock as best as I can tell 112 front/ 110 rear

+2 according to jet kit instructions and jet labeling 115 front/ 118 rear.
Also I believe I read somewhere that the smaller jets went to the front, since the downdraft carbs tend to flow a little more fuel.



So who is right? Where do the smaller sized jets go?



Also another quick question. If (and that's a big if) my carbs were synced before cleaning/ rejetting and I don't separate them or change individual throttle settings, will they remain synced the same after rejetting?

I am not even sure how this thing was running, as the pilot jets in the two carbs I cleaned up were both nearly plugged and the pilot screw covers are still in place. Despite this it manage to idle at 800-1200 rpm nearly in spec?

I got alot to learn here......it's much, Much different than a single cylinder carb, where the slide and needle are raised by the throttle cable.


Would a visual check for slides raising at the same time and speed, be a good visual indication or carb balance or synch?

What else should I be aware of / look out for while I have the carbs off and partially apart?

 

what size pilot jets were in the "kit"?

What has been done to the engine or cams/valvetrain/intake manifold/exhaust to require such a large jump in the main jets?

There is a good thread on here about cleaning carbs,
http://vfrworld.com/forums/showthread.php/22449-Cleaning-carbs

 

No change in the pilot , I actually got the 118/115 kit as it was the same cost as the 115/112 (+1 size) ,but I already have 112 mains stock. For that matter I have some shims laying around somewhere that I use for half jumps on clip adjustable needles of Keihin power 2 strokes. I probably could have went to the Honda shop and gave $8 for two 115 mains and been good.

As soon as I can verify that the service manual is correct in calling for one size smaller in the rear I plan go with one needle shim and 112/115 (+1) mains , to support a K&N filter, riding near sea level <750 feet, and the probability that I won't always have straight ethanol free fuel in the tank.
I also have plans to open up the stock mufflers or fit aftermarket cans in the near future hence the reason I wanted to have the 118 mains on hand.
If I can't get enough fuel at idle with just fuel screw adjustment or get up over 3 turns by much, then I will go for the #40 pilots.

Maybe I am going about this backwards though, since K&N is my only real mod at the moment maybe I could get by with going to a #40 pilot and counting on the little bit of extra fuel it provides to cover for low altitude and the inevitable gallon or so of non eth free fuel that finds its way into the tank.

Your thoughts?

Will definitely check out the link tho' . I did manage to dig up some good info and educate myself a bit on multi carb setups, throttle sync and such.

Still didn't get a definite answer as to where the smaller jets go. Hopefully the rebuild post will clear that up.

Thanks for the reply, and please feel free to correct any of my flawed thinking.
This is my first shot at both multiple and variable venturi carbs I would be quite interested in hearing what someone with some v4 experience would suggest.

I kinda got the impression that the stock jetting may be a bit lean due to emissions concerns, particularly for riders at a lower altitude.

 

Just to answer your question regarding the synchronisation, what this does is adjust all the throttle plates so the same amount of flow passes through them all at idle. Messing with the jetting or need/slides shouldn't affect the sync, but jostling the carbs on and off the bike might cause some change. In my experience the synch is very sensitive to even 1/16 turn of an adjusting screw. You can eyeball-adjust the throttle plates so that they all sit in the same location relative to the pilot jet orifice in the carb floor, but best is to use a set of vacuum gauges. There are some DIY synch tools made from tube and bottles that can be made up if finances are tight, a googling should find those fairly easy.

 

Thanks for the replies the carb rebuild link helped and had lots of good info.

I am still a bit confused about which carbs get the larger/ smaller jets. I guess I will have to go with the manual and current setup and say the smaller jets go in the back.
This is how it was when I took it apart and it didn't run too bad as long as I had straight eth free fuel and the bike was good and warm.

 

Seems like that is an error in the manual, the larger jets go in the rear cylinders since they run hotter. Here is discussion for the VF500

http://vfrworld.com/forums/showthre...-and-Slow-Jets-Emulsion-Tubes-and-Jet-Needles

Where is the SquirrelMan?

 

OK gonna swap them, funny the 112 jets were in the front and 110's in the rear. that means I will be putting 112 jets back in the front and 115's in the rear.
Soo.... strange.
Gotta wonder if they were like that from the factory or someone swapped them following the manual?

Found this thread also.... final word from a trusted VFR guru says exactly what the manual says regarding diaphragm springs and needles, except he also says bigger mains in the rear....
http://vfrworld.com/forums/showthread.php/25321-Carburetor-main-jet-holders-(diaphragm-springs)

I trust there are those who have tried both ways and I have yet to see anyone say that the smaller go in the rear.....only that the manual says this.....
No one has refuted through experience that the bigger ones are in the rear.

Time to swap them back out , not gonna go against the recommendations of both the forum and the supplier of the jets.

Appreciate it! You, the forum and the fact that my new carb boots (insulators) haven't showed up yet have saved me from having to tear down and pull the rack again or worse yet loose performance and efficiency and not even know it.

So far 3 for 3 on plugged slow jets and somewhat plugged enrichment jets. Not to bad otherwise, a bit of very fine rusty powder in the bowls, but little to no buildup on the needle valve filters. Should have probably bought a set of bowl gaskets or O-rings tho , don't think the ones on there will leak , but I would sleep better with new.
Guess I will save that for when I separate the carbs and do a full cleanup.

 

Don't ever separate the carbs from the plenum plate just for cleaning--nothing good will come of it.

 

Yes, some Honda V-twins and possibly V-4's do have bigger jets in front, the Honda Hawk NT650 for example. :eek-new:

Also, be sure if your 4 main jet holder tubes (emulsion tubes) are the same or different, high holes vs. low holes, and that they are positioned right. :courage:

 

Been studying and thinking on this pretty extensively. It seems the issue has to do with the way the cylinders and carbs are positioned on the '83-'85 vf7X0f, different from the '86 on vfr and most other v45's. The front cylinders are nearly flat where the rears are mostly vertical.
They also differ from the earlier v4 motors, if not in positioning then in the fact they are water not air cooled making the temperature difference between front band rear cylinders non-issue.

That said it is the type (side draft vs down draft) and positioning of the carbs alone that dictate the difference of the in jetting for the '83-'85 v45 variants.

I don't have any pictures or drawings to refer to. But it has to do with the way the fuel is picked up and flows. The longer and softer spring also helps with this. Longer to keep the needle valve less open at light vacuum, where gravity alone allows slightly more fuel down into the cylinder, and softer to let the needle open more (than the shorter stiffer spring) and further under overall increasing flow and vacuum where the greater angles the fuel must flow around (more resistance) requires a slightly larger orifice to get the same amount of flow.

I apologize for the poor explanation of this as it really has more to due with flow of dry air versus flow of air fuel mix (wet air), and advanced fluid and gas dynamics that I really don't have but the most elementary understanding of.

Long story short I could not bring myself to leave stock 112 jets in the front, while shoving 2 sizes bigger (115's) in the rear. So it was quite a relief to hear squirrel say that this particular model might well be the exception to the rule.

Now if those damn rubber boots would just show up so I can get it together and go for a ride. I can forget about all this headache inducing jetting stuff.
I am sure after a good warm-up and some twisting with a small flat head on a flex shaft that it will run at the very least as good as it did with nearly all the pilot jets plugged one carb no where near bench synch.

Hopefully all goes well and I can finish up the last few details (fork seals, valve/tensioner check and adjust)
and get to twisting the grips not wrenches. I am getting so tired of missing out on my daily 30 minute R&R ride.

Worst case at least I will have soft boots to make pulling the rack to swap jetsam bit easier.

Thanks all and I will definitely report back and leave info as to whether the cylinders are running evenly on the top.


Later
Deebee