VF750F Carb Throttle synchronization

Hello all,
I recently got my first Interceptor and reassembled the carburetors however I cannot figure out the throttle opening positions on these. I can only get two throttle valves to open on time and after much more throttle, the other two will open. Are these designed to only run on 2 cylinders at little throttle and then all 4 will open up with more throttle?

Let me know, This doesnt seem right.

Isaiah

83 Vf750F RED

 

are you refering to the slides with the air box lid removed? your watching these as you give the bike gas?
if you are; the answer is yes, they should all rise in unison. Best bet is to bench synchronize them before you re-install, this gets you in the ball park.

 

Seems that you lost a couple springs (or never got them) that go between throttle shafts to lock them in position throughout the linkages' movements. Each shaft interlocks with another through the missing spring/s, and throttle plates must move together.

 

Awesome. That'll explain it. Thanks again, I'll keep an eye out for those springs on ebay or something.

 

I have the same issue. The front carbs open fully, but the rear carbs only open 60% of the way. I have all the springs in place but still can't get them to open all together 100%.

 

Here are some photos of a spare set of 83' carbs:

Hope this helps.

 

Thanks for the pictures. Looks like I am missing one spring. It is the spring that butts up to the throttle cable holder. Not sure if that will be the difference maker. I've removed my carbs twice and both times I have to remove one carb at a time and springs go flying!

 

Removing one carb at a time is a sure way to f' things up !!

Don't remove carbs from the airbox base when removing or replacing !!!!!! If you do, springs get lost, and you might crack a fuel tube or drop a spring into the intake manifold.

Despite your claim, i believe you're still missing the lower spring (at the front) on the rod that links front carbs to rears. All this stuff needs to be checked and confirmed BEFORE installing carbs.

 

Hello All,

I have a 83 VF750F which I bought new. It spent a lot of time unused for other considerations. I recall that even then, it took the bike forever to warm up sufficiently to idle without the choke. It has gotten worse over time, and the gas mileage gone to hell. Low speed throttle response is terrible. I am now going through the low speed pilot circuit. I have removed the block off plugs and screws, squirted Gumout liberally through with the the little spray tube fully inserted, blown them out with a canned air duster, but I still get no idling w/o choke even at 4 turns open. I have done this many times to revive old small engines, but have used high pressure shop air. I am thinking this might do the trick but I am worried about blowing out the diaphragms.
I presume the circuit is only connected to the float bowls (and vents) and not the intake port which connects to the diaphragm, and that I may be safe with a very brief blast of shop air to clear them. Any thoughts or recommendations? I have also read that the bowl vents should be disconnected from the airbox and vented to the atmosphere?
The washer and o-ring only came out on one screw. O-ring looked ok, screws were discolored at the end, but no crud. How critical is it to replace these o-rings? What are the sizes?
I also noticed that the rubber velocity stacks inside the airbox each have a tiny hole which pointed to by a crayon mark on the inside and outside. Does anyone know what orientation these holes are supposed to have with respect to the carb inlets?

I offer my profuse thanks to in advance to anyone offering help to get the wind back in my face,
Friendly regards,
Ike

 

Sparky firstly congratulations on owning a bike for 36 years!

When cleaning carbs you want to be careful of damaging the diaphragms and other rubber parts with carb cleaner. I would suggest that you pull the diaphragms out while using carb cleaner and compressed air.

You should pull the carbs off the bike, and remove the float bowls and then the jets so you can blow carb cleaner through them. The low speed jet is very fine and easily clogged, as are the passages that lead to the floor of the carb throat under the butterfly. If you can, buy new carb mounting rubbers to make the refitting job a little easier and to ensure you get a good seal.

For o-rings, if you can't get OEM, just go to a local industrial seal supplier.

I did the above recently with my ST1100 carbs, and here is a link to a site with great pictures and explanations that might be of some help.

http://www.st-riders.net/index.php?topic=10249.0

 

Sparky needs to clean his slow jets with a steel wire (.010") poked clear through; compressed air isn't much good for cleaning gunked-up jets.

 

Thanks for your advice, Squirrelman. The bowls and slow jets are next. Probably my biggest problem is my own decrepitude. I am almost 60, and have a disability with the discs in my lower back being all ruptured. (hey, if I knew I would live this long, I would have taken better care of myself...) Three days of bending over the carbs left me in pain for 5 days. I have sprayed carb cleaner around the tubes between the carbs and heads, no sign of a vacuum leak, so I am thinking to leave the carbs in place and take off the float bowls and clean from underneath. At that point I will sync them with home brew manometers. I will need to get a set of those extension tubes to screw into the vacuum ports. Are those an M4 thread?

I just put fresh rubber on. The choices were few, but I decided to go with stock size Avon Roadriders. Not many miles on them yet, but they felt a little greasy on the ride home from the shop. In the course of mounting the front tire, the speedometer cable sheath broke right near the front. The core is intact, so I guess I will fix with some heat shrink and ultrablack. (NY State troopers and NYC police are not terribly bike friendly, and traffic tickets are hideously expensive.) I didn't even bother looking for a replacement.

After that, I will need to clean up the front brakes, which appear to be saturated with fork oil. The seals were leaky from day one. I did change them way back when... put in Golden Spectro #5 oil, but they still leaked. This time I am thinking to drain and clean them with a plastic shim, and refill with Bel Ray 15W. I weigh about 190.

Regards and safe riding to all,
Ike

 

If the brake pads have any traces of fork oil it's best to scrap them, and you'll need to clean the discs with lacquer thinner on a rag too.

You really think you can remove the float bowls while carbs are on the bike ?? Best of luck !

 

Hello again,

Popped the float bowls off carbs 1&2, took out the slow jets. The second needle in the wire kit was a very tight fit, but I forced it through them. I was figuring the problem was mostly the back carbs, (1&3) judging from low temp readings on the exhaust pipes right near the heads. On the right side of the engine there are coolant pipes which block removal of float bowls 3&4. This will require draining of coolant and greater disassembly which my elderly decrepitude does not tolerate well. I figured I would do the easy ones and see if there was any difference. I set the pilot screws at 3 turns out for those carbs. It started right up, and after 5 minutes I was able to turn the choke all the way off! It would not do that when it was new! In a few days I'll drain the coolant, remove the plumbing and take a crack at 3&4.

I have not been able to find the pilot screw o-rings in nitrile or viton, which incidentally are 1.1mm thick and 3.2mm i.d., but at this point I wonder if they would make a big difference since the leakage of air past the threads cannot be much. As for the diaphragms, I would expect their failures to cause problems at larger throttle openings and higher speeds, which my bike fortunately does not exhibit.

I drained the fork oil, cleaned the seals with a strip of plastic, hit the shiney spots w/sandpaper, and refilled with BelRay 15w. They seem to be leaking even worse than before. There was a spongelike ring between the seal and the dust boot which were deteriorated and thrown away. Could this be failing to wipe the oil missed by the seal? I am seriously considering dirtbike type accordian boots... The roads in my area are terrible, (Queens, NY,) but the bike only has 9300 miles.

Sincere thanks to all for your pictures, info and suggestions. Keep them coming.

Friendly regards,
Ike