problems with my 83 vf750f

so i've got this bike that i picked up that sat cold in a garage for years and years.. it's only got 700 miles on it. but there's been problems. starting with a realllly rusty tank (which i replaced) amongst other things. i've got a good guy on the job now (who mostly restores old honda v-twins... you could check out his website www.ssclassics.net if you'd care to), but we're still having difficulties. here they are:

the only way the bike will start and idle is on full choke.. the mech has been looking for what the carb jetting should be. he thinks maybe the carbs we're rejet oddly. anyone know the jetting for an 83?

a tube leads off the carb but goes nowhere.. are we missing something? maybe we're not getting vacuum on the air intake? i'm no mechanic so you could call me clueless.

i love the bike, i just want to ride it! any help with these issues would be of great assistance. thanks...

 

I know it ain't much but I didn't see any body else offering up any assistance, so I thought I'd get it started and maybe some other folks will want to play too :biggrin:

 

I found a picture of the carbs in the VFR Wiki.........It's not great but at least you can tell me which tube it is by number, LOL?

 

thanks a bunch norcal, i'm forwarding this link to my mech.. i looked for the carb pic in the vfr wiki and could not locate it.... any chance you could link? thanks a million...

 

Just doin' my part! :biggrin:

http://www.vf750fd.com/vf750f/83VF750F.PDF

 

Danimal:

Where are you located? Maybe a 1st gen owner is nearby to assist you in person?

Just a thought.

BZ

 

On the '83, the front and rear carb tubes vent to the airbox.

On the 84-85 those front and rear carb tubes are tied together under the airbox with a hose. Another vent between the two rear carbs has a hose in a "J" shape that is vented to the atmosphere behind the airbox. It is "J" shaped to prevent water from getting into the carbs.

Or you may have a California bike with some of the emissions crap missing - the VIN should tell you if it's a Cali-bike.

Let me know if you have a Cali bike and I'll send you the instructions I have for removing the emissions.

 

just talked to mechanic again.. the tube connects to all carbs and ends in a t-joint sticking out under right coil...

and to reiterate: great spark on all 4, fuel into carb great, but doesn't get from carb to motor unless all air choked out...

thanks again for all the help.. i'm from venice, california by the way and seriously wish i was riding right now. patience is a virtue though.. or so i've heard. and this is super early vf, bike number 1605 off the line in dec of 82 so i don't think it's cali em.

 

Check for fuel flow by opening all float bowl drain screws (with petcock ON) and looking for adequate flow rate.
IF the tank was rusty before then suspect a clogged fuel screen or filter, possibly the fine screens above the float inlet needles.

this sounds like a classic case of plugged jets in carbs, which should have been fully and properly cleaned. Or air leakage around the carb mounting sleeves (manifolds) causing a too-lean mixture?

there are usually only 2 hoses assoiciated with most carbs: fuel inlet and air vent. vent line must be open to atmosphere, not important whether it's connected to air box or not. Cali models may have extra lines. If you had the manual you would likely have made more progress.

if your restorer can't sort this out his status as such is somewhat suspect despite nice website.

 

Dude, you said it in your very first sentence: the bike sat for a long time. That's a guaranteed recipe for varnished carbs. In fact, it's likely so bad that you will have to get a completely new (good used) set. I've found that very bad carbs cannot always be brought back to life.

The hose you are referring to is most likely the bowl vent. It should run down and exit in front of the rear tire.

With bikes this old, ultra-low miles is not a good thing. Bikes need to either be ridden regularly or stored properly. Bikes that sit for long periods often were not properly prepped for long-term storage.

I hope this helps!

 

Not to sound contrary, JD, but iv'e never seen a set of carbs that cannot be properly cleaned, and iv'e seen the WORST!!
New jets are cheap.

Takes longer, yes, but you might want to go through any replacement carbs too!

 

Well, I've got a couple of sets that even my ultrasonic cleaner cannot get to budge. If the carbs are left full of fuel for a couple of years they are gone. You are right, nothing is impossible, but the work/time/parts/money it would take is just not worth it.

 

i'll start here by saying thanks again.. but this mechanic is a guy that i can trust.. i did have the carb rebuilt by someone else before it got to him.. he's still taken it apart and said that things look ok. he's just not really 100% familiar with bikes after 1978. he's been having fun working on this project, but it's the first vf'er that he's worked on. he got into it cause he saw the bike and realized that it was the first one he ever wanted as his friend had one in high school. he's always coaching me not to trust anyone and you guys seem be of the same mind.. my opinion is that you find someone you can trust and you put your faith in them.. maybe i've been burned a few times along the way, but all in all.. i found it's the way i'm happiest. i'm know, i'm a sucker.

i've been passing all this info on to him and i'll let you know how it goes.

thanks again..

 

The hard part about old carbs, in my experience anyway, is never the jets. It is the tiny cross-drilled passages inside the carb bodies that get corrosion in them. Varnish is bad enough, but a good chemical bath can remove it. The only caution I would throw out there is that some '80's bikes have an anti-backfire nylon valve, located on the side of the main body, that can only be removed by destroying a pressed-in cover. The nylon piece will most likely be damaged by a chemical bath, so it should come out.

The corrosion can be really difficult. There used to be a place in Antioch or Pittsburgh (California) called "RECARBCO" that resurrected some tough-to-replace marine carbs for me, years ago, for reasonable prices. I do not know if they handle bike carbs, but they might know who does.

By virtue of the fact that the choke has to be on for it to idle suggests that the low speed internal passages are clogged, and the only way for fuel to enter the airstream is up through the main jet. The difficulty in cleaning the passages is that they are cross-drilled, as I mentioned above. Two or more holes are drilled at opposing angles to intersect, and a plug is put in place to seal the passage at the common intersection. The plugs have to be removed, and a solid piece of wire (or whatever) needs to be ran through the passages to clear them. Then the plugs have to be replaced to seal the passage again. Certainly not hopeless, but professionals have the experience and the tools.

And for what it is worth, I have cleaned some carbs multiple times with conventional cleaners, such as Berryman's, to no avail. Many times a person who "rebuilds" a carburetor, myself included, has assumed that a general cleaning and new gaskets will be sufficient if there are no immediate signs of internal corrosion.

So I guess what I am suggesting is although the carbs were rebuilt, they still have issues. As the other members have suggested, I would look for any vacuum leaks first.

And now a silly question; have you checked to make sure that the idle speed adjustment is working? Part of the choke circuit kicks up the idle speed; it is possible when you disengage the choke that the carb butterflies are just closing all the way.

 

Main jet size for an 83 VF750F A is Kehin #128, slow jet size is #38. I am not too sure about your mechanic only because he does not know what the correct jetting is, you can get that information very easily from a number of sources including the web. I no longer make my living as a motorcycle mechanic but I would not (and still will not) work on a mechanical system when I don’t even know what the proper set up specs are. Anyway I agree that the carbs need to be checked over (he says they look good, if he knows anything then his comment would indicate the carburetors are salvageable). Check the fuel filter, check the fuel pump, fuel lines and fuel petcock (make sure it is not clogged – I have seen this happen). Do you or your mechanic have a shop manual for an 83 Interceptor, it doesn’t sound like it; get one. The routing of hoses is clearly shown in the Honda Factory shop manual, there are hoses that vent to the atmosphere you will only know which ones they are when you consult the shop manual. JIM

 

Bingo!

Not these carbs, luckily.

 

I have learned some useful carb tricks from Bernoulli, Eduardo Weber, and Smokey Yunick and test carb fuel flow patterns and float needles using compressed air and kerosine before rebuilt carbs are mounted........
Seriously plugged jets can be replaced with new ones cheap!

Remember that the "Sea Foam" fuel system cleaner has done more miracle cures than Mother Theresa and, unlike her, is available at most autoparts stores.

I'm guessing this is a gravity-feed setup and does not use electric fuel pump, right??

 

No the 83 VF750F has a fuel pump. JIM

 

in that case, hotwire fuel pump using jumper wire, drain carbs, close drain screws and wait for pump clicking to stop.........then try starting again.

 

Squirrelman, is there a link, book, or article you can point me to that covers the kerosene/compressed air stuff? I read Smokey's "Power Secrets" many moons ago, but don't recall anything on this (like I said, many moons ago...). I have my own semi-primitive techniques, but I am always on the lookout for better ways to do things. Thx!