1986 vf500 Idle goes up to 3K rpm then down to normal.

I'm posting this on behalf of my buddy. So he got him self a 86 vf500, no battery so he just took some jumper cables and ran them from his car battery to the bike to see how it runs. The bike will idle at about 1000 rpm, then go up to 3000 rpm then back down. He isn't sure if it's the choke that causing the weird idle or if it's something else. A google search didn't provide any answers. Hopefully some one here can help us out.

 

Doncha think the carbs might need cleaning ?? How many miles on the wee blighter, and how long was it sitting abused and unused ??

 

Not sure on how long it's been sitting for or the miles. That's what we were thinking is the carbs need cleaning. He hasn't really worked on a v4 before, so he's thinking of taking it to a shop and have them tune it up.

 

Good luck with that !! Shops today mostly know zilch about older bikes, and many refuse to work on them. I would look for an old man with a beard, nobody younger than about 45, to work on those carbs.

 

Hey, it could be something like air leakage around the mounting boots, loose clamps maybe.

Can you get the bike to idle around 1200 with the choke off ??

 

I'll ask him, he's gotta wait till payday to get a battery. Luckily he got a manual with the bike, so he could always try rebuilding the carbs. He has never done that on a bike before just simple fixes on the carbs. Also he isn't sure if he could get a rebuild kit for the carbs. He isn't complaining for 500 bucks.

 

Carbs are not difficult at all, just be organized. To do a good carb clean. Have him read this...


***DO NOT remove the aluminum plate that holds the 4 carbs together. You can do a pretty good job of cleaning without separating the carbs. The guide shows them completely apart but you don't have to get that crazy. When Billy does them, everything does get broken down.***



From V4BBS, for quick reference...
"The V4 engines use 4 constant velocity (variable venturi) carburetors to supply fuel to the engine. The constant velocity refers to the air speed through the throat of the carb. The velocity is controlled by a slide mounted to a diaphram. The diaphram is sensitive to vacuum created by the flow of air across a hole(s) in the needle end of the slide. As the engine speed increases, the vacuum above the diaphram increases due to venturi action and the slide is raised.

There are three circuits (paths) in the carb.
The starting circuit (choke) provides extra fuel when the choke is open. It uses a fixed jet and a choke plunger to control the flow of fuel to the port in the carb throat. The restriction is the fixed jet at about 0.021 inches. The choke plunger also provides an air bypass around the throttle plate to increase the engine speed during warm up.

The low speed circuit provides the primary fuel for operation below 4000 to 5000 rpm. When the engine is pulling vacuum the fuel is drawn through a passage to the low speed needle valve, and then to a large hole on the bowl side of the throat on the engine side of the throttle plate. The needle valve controls flow to the large hole. This path also feeds the 4 tiny holes on the float side of the throat and under the throttle plate. Both paths continue to function at all engine speeds. The restriction is the low speed needle or the low speed jet.

The high speed circuit provides fuel above 4000 rpm. It uses a fixed orifice and a needle connected to the slide to control the flow of fuel to the needle valve opening in the carb throat. As engine speed increases the slide raises the needle and allows additional fuel to flow. The restriction is the needle valve on the slide. Since the needle valve never completely closes, the circuit provides fuel at all engine speeds.

It should be verified that fuel is getting to the carbs. Verify you are getting a flow of fuel at the inlet hose to the carbs. No flow can be caused by delivery problems due to tank venting, plugged screen in the tank, pinched hoses, fuel pump problems or fuel filter plugged. Or you could be out of gas.

The main symptoms of carb trouble are.
1. Hard cold starting that is caused by restricted choke circuit, low speed circuit or improper fuel level in the float bowl. Failure modes that cause this are.
a. Plugged low speed jet. The jet must be removed and cleaned.
b. Plugged choke jet. The jet cannot be removed, it must be cleaned in place.
c. Plugged low speed circuit and choke circuit passages from the jet to the carb throat. The carburetor must be removed and the passages cleaned.
d. Improper fuel level in the float bowl. The float valve and screen must be removed and cleaned. The float must then be set to the correct level.
e. Improper setting of the low speed needle valves. In most cases resetting them to the factory recommendation will be satisfactory.

2. Poor idling and hesitation when accelerating up to 4000 rpm caused by restricted low speed circuits or improper fuel level in the float bowl. . Failure modes that cause this are.
a. Plugged low speed jet. The jet must be removed and cleaned.
b. Plugged low speed circuit passages from the jet to the carb throat. The carburetor must be removed and the passages cleaned.
c. Improper fuel level in the float bowl. The float valve and screen must be removed and cleaned. The float must then be set to the correct level.
d. Improper synchronization of the 4 carburetors. They may synced while on the engine using vacuum gages or mercury sticks.
f. Improper setting of the low speed needle valves. In most cases resetting them to the factory recommendation will be satisfactory.

3. Poor operation above 4000 rpm caused by improper slide operation or improper fuel level in the float bowl. Failure modes that cause this are.
a. Ripped diaphram. Ripped diaphrams must be replaced, usually with the carbs off the bike.
b. Leaking diaphram. If the diaphram is not seated correctly in the cover it will leak air and defeat the vacuum action.
c. Sticking slide. The slide must be removed and any contamination removed.
d. Choke valve not closing completely.
e. Incorrect high speed jet or emulsion tube installed. Verify correct parts.
f. Incorrect spring installed over the slide. Verify correct springs.
g. Incorrect high speed needle installed. Verify correct needle.


Carburetor Cleaning and Rebuild

There are 3 approaches to cleaning the carbs.
Use an additive in the gas tank such as Techtron or Sea Foam.
Do the disassembly and cleaning yourself.
Send them to a professional for a super cleaning.
The additive route sometimes works if the plugging of circuits is not too bad.
The do it yourself method will achieve well functioning carburetors that looks like they did when you took it off.
The professional cleaning by Billy Carr will make them shine and function like new with the added advantage that he has any needed replacement parts. BBS friendly carb cleaning service

To quote Billy, "being the local carb guy means I get mine either way. I rebuild them... I get paid. You do them yourself with my cheap carb kit ... I get paid. Buy the carb kit and in a few hours and you can have a resealed long lasting set of carbs. Never be afraid to delve in to a set of carbs unless you do not possess the simple ability to tell which end of a combination wrench is which. Worst case scenario is you mail me a bucket full of parts when you realize you got in over your head. Saves me teardown time."

Sample of his work.





Helpful hints if you do them yourself.

Take photos of the carbs installed, cable routing, removed still on the plenum from all angles. You will treasure them when you put things back together.
Remove all 4 carburetors and the plenum (air box) as an assembly.
Drain the fuel from each carb through the drain nipple by opening the needle screw in the bottom of the float bowl.
If the carb rack (all 4 carbs bolted to the plenum) is dirty clean it with a degreaser before you start to take things apart.





When you disassemble your carbs keep the parts separated by individual carb as they are different from front to rear in many cases (baby food jars are great). Note, after 30 years and many owners the parts may not actually be in the correct location. Always refer to manual for the correct placement and part. The model number will be stamped on the flange above the float bowl.
Do not be afraid to use a permanent marker in an out of the way spot to keep the carbs straight (number the baby food jars too). They are numbered #1- #4 left to right as you sit on the bike.
If you do not split the rack you will not have to hassle with the linkages and the throttle plate synch will be much easier. You will not be able to change the fuel and air tube o-rings however, your call.
Use a good #3 Philips tip screw driver bit or impact bit to loosen all screws. Tap each one a couple of times with a hammer and bit before you try to loosen them
Your work area should someplace where you can track down parts that may escape you.

Do It Yourself Rebuild

Buy a carb rebuild kit from Billy C at BBS friendly carb cleaning service
It has everything you need plus a DVD filled with information.


One carb at a time, remove the 4 screws that hold the float bowl on. Check condition of the o-ring seal. If hardened, get new ones. If they have never been replaced they will be hard and flat.




Remove and clean the drain plug and clean the drain nipple if plugged.
Remove the pin holding the float in place, remove the float and needle.
Remove and check the condition of the needle seat and screen.
Remove the high speed jet and holder (emulsion tube). Make sure all holes are clean.
Remove the low speed jet. Make sure all holes are clean especially the one through the center, clean with a 0.015 inch wire or #79 pin drill for 38 size jets. The size of the jet is stamped on it. 38 stands for 0.38 mm or about 0.15 inches.
The choke jet cannot be removed, pressed in. Clean the hole through the center of it, clean with an 0.021 inch wire or a #75 pin drill.
Inspect all passages and blow air or a solvent through them. Look into each hole with a good light and a magnifying glass.

Login 20pc Drill Bits #61-80 and Pin Vise





Remove the low speed needle from the side of the carb just above the float joint. It may be covered with an aluminum cap to prevent tampering. If it is, drill a 1/8 inch hole in the cap, drive in a sheet metal screw a couple of threads and pull the cap out. Before unscrewing the needle, turn it in counting the number of rotations until it seats lightly. The needle will have a spring, flat washer and o-ring behind it, remove them.
Inspect all passages with a good light and a magnifying glass and blow air or a solvent through them.






Remove the choke valve by removing the black plastic nut, the linkage plate, the black linkage sleeve and spring. Work it out as an assembly. Be careful, the black nut is fragile.
Take some more pictures of where all the linkage goes.




Blow air through all the passages to clean, including the choke jet.

On the other side of the carb, remove 4 screws holding on the chrome cover. Be alert, it is spring loaded.
Remove the diaphram cover and spring.
Remove the diaphram slide assembly. Carefully inspect the diaphram for any tears or cracks. If any found, big and expensive problem to replace. Clean the slide and its bore of any residue. Don't use carb cleaner on the diaphrams, it will damage them. Use a 0.018 inch wire or pin drill #77 to clean the brass orifice located under the diaphram cover. This orifice appears to be a drain for any fuel accumulated in the top of the diaphram.

With all the jets, needles, slides and chokes removed, blow air through all the passages including the choke jet. Blow air through the small ports in the carb throat to verify that they are clear. Soaking in a cleaner may now be done safely.




***THIS IS NOT MANDATORY, I WOULD SKIP THIS UNLESS YOU HAVE FUEL LEAKAGE FROM THE TUBES***

Now is the time to replace the o rings on the fuel rail if you plan on doing it. Be very careful with the tubes as they can be broken with sideways pressure. The o rings are included in the Billy C kit.
Use a quality #3 Philips head screw driver to loosen the 8 screws holding the carbs to the plenum. Tap them with a bit and hammer to break them loose. Leave all screws in place until they all have been broken loose.
Take pictures of all the springs on the throttle linkage.
Remove the 8 screws and remove the plenum. There are locator dowels on each carb that may require prying out for separation. BE CAREFUL the sync and shaft springs will fall out when you separate the carbs. You did take those pictures right? The tubes are unique so keep track of what goes where.
Remove the o rings from the tubes and replace with the new ones.
Clean the holes that the tubes insert into. Did you notice that the fuel path runs straight through the bottom of all 4 carbs?
Carefully insert the fuel tubes back into the carb bodies along with the vent tubes if your model has them. Do not let the o ring roll out of the groove. The throttle adjuster plates and shaft springs must also be lined up for each carb. Do not worry about the sync springs at this point.
Replace the plenum with new socket head cap screws M6-1.00 x 20. You do not want to mess with the Philips the next time. They are available at most hardware stores for about $.50 each. Evenly tighten the screws making sure that the tubes and shafts are not binding. Boiling the air funnels makes them easier to install. Old ones shrink and are a pain in the ass to get in place. Make sure the line on the funnel is between the two index lines on the airbox.

When you are satisfied that everything is clean, begin reassembly.

Assemble the diaphram slide assembly into the carb, make sure the hole(s) in the diaphram align with the holes in the carb.
Assemble the spring and cover. Short vacuum piston springs install in the rear carbs, long springs install in the front carbs. Make sure the diaphram seats into the groove. Tighten 4 screws. To test seating, hook a shop vac up to the engine side of the carb and open the throttle plate. The slide should rise, then fall when the throttle is closed. If it doesn't the diaphram is not seated.





Gently flex the floats to check for cracks. They like to crack where the lattice meets the float---and then they fill up with gas. You'll notice the float full of fuel if you tear down quick after carb removal. Otherwise you won't know without careful inspection.

Inspect your float needles. The rubber tip on can pull out of the metal needle and bind up the valve.

Carefully clean the choke plungers. It makes them operate smoother and prevents them from hanging up. Some fine emery paper works well for this. Inspect the end of the choke valve for the condition of the rubber insert. If it is badly worn in may be removed and flipped over. Replacements are not available.
Assemble the high and low speed jets in the carb tightly. Verify the correct size is used in the correct location. The fuel emulsion tubes that the main jets thread into are different between front and rear carbs. There are low drilled holes and high drilled holes in the tubes. The tubes with the holes located furthest away from the main jet install in the rear carbs.








Set the float height by holding the carb on its side until the float just stops closing. Then measure the distance from the top of the float to the bowl surface. If you lay the carb down it will distort the reading. Adjust the height by bending the metal tab on the float. A dial or digital caliper back end works well for setting the height. If you get different readings on each side of the float, use an average of the two readings.
Install the float bowl with gasket and 4 screws tightly. Tighten the drain plug in the bowl.

Assemble the spring, washer and o-ring in that order on the slow speed needle. Screw in the needle assembly until it just bottoms out. Then open the number of full turns recommended.





Assemble the choke valves, lifter arm, spring, black sleeve, black nut and linkage plate. Don't break the plastic nut. Test by moving the choke lever (where the cable attached) and verifying that the valve opens about 3/8" and closes with a slight clearance between the head of the valve and the fork. You may need to wait to do this until all 4 valves are assembled. If they don't function correctly, adjust the linkage by bending.

Install all sync springs at this time. Remember there is a spring on the sync screw and a spring between the two tabs. Use those pictures you took for reference.













Bench check the sync of the carbs.
#1 carb is adjusted with the black idle knob. Place a 1/8 inch wide strip of printer paper between the throttle plate and bore on # 1 carb. Adjust the black idle knob until there is a slight drag on the paper.
Next, place a strip into #3 carb. Adjust the screw on the linkage for the same drag. There must be 2 springs on the adjuster for it to work properly. One on the screw, one in the linkage.
Verify that the linkage between the front and rear carbs is in place and that the bushing are tight.
Next, place a strip into #2 carb. Adjust the screw on the linkage for the same drag. There must be 2 springs on the adjuster for it to work properly. One on the screw, one in the linkage.
Next, place a strip into #4 carb. Adjust the screw on the linkage for the same drag. There must be 2 springs on the adjuster for it to work properly. One on the screw, one in the linkage.

An alternative method uses the small hole in the carb throat to set the plates. The plates should be set so that half the hole is visible. The hole is opposite the paper shown in carb #1.





Cycle the throttles to make sure the settings repeat.

With the carbs mounted to the plenum do the following before you put them on the engine
1. Do a bench sync and make sure all the little springs are in the throttle linkage. Make sure that the linkage bushings are not worn out, this can cause sync problems. All 4 throttle plates should move at the same time.
2. Move the choke lever and verify that all 4 choke valves are opening and closing fully. Adjust (bend) linkage to get them all working and have clearance at the valve to fork when closed.
3. Hook up a shop vacuum to the engine side of each carb. Open the throttle with the vacuum running. The slide should open, and close quickly when the throttle is closed.
4. Some people fill the carbs with fuel before installing to make sure there are no leaks.

Now is the best time to change the o-rings on the 2 coolant tubes in the V of the engine. It can be done with the carbs in, but not easily.
After reinstalling the carbs on the bike and before you hook up the fuel line, FLUSH the fuel lines to remove any debris. Or you may be doing this procedure again.

After reinstalling the carbs on the bike a sync of the carbs should be done using gages. This will compensate for the minor differences in flow to each cylinder. With a good bench sync, most people find that there will not be much change needed. Do this sync in the same 1,3,2,4 order.

The manuals describe an idle drop method to adjust the low speed needles. It is somewhat difficult to do and the results people have had are varied. Give it a try if you want, but most people get back to just about the recommended settings. I prefer to start with the recommended and then close each needle a quarter turn in. Ride the bike and verify that acceleration has not been affected. Try an additional quarter turn and verify acceleration. If performance falls off, go back one step. This leaning of the mixture procedure will improve your mileage and improve hot starting in high temperature conditions."

 

Golly Jee !! You and BC,huh ?? Last complaint i heard about him, he forgot to tighten main jets and they all fell out on a VF750. Does he answer his phone ever ??



I clean carbs for member here too and charge way less, work faster.

 

Thank you very much for the info, i'll show this to my buddy. By the time he's done with this bike he's gonna know it better then honda

 

No problem. It looks more involved than it really is. It takes awhile your first time but then it's not bad after that. Let us know how he made out.

 

Me and BC? HA! It's more like, You and BC,huh? It's glaringly obvious that even you feel your reputation can't stand on it's own, forcing you to post 2nd hand gossip followed by "Oh, it just so happens I do carbs too." That is soo cheezy man. Clearly you weren't a marketing major. Put it in your sig that you do carbs and be done with it.

Try this on...since I've been wanting to make some extra cash, I decided to help some people out with their bikes.

I met a guy who had Squirlboy do his carbs. He striped out half the float bowl screws and forgot one of the gaskets. He sent them back and hasn't heard from him again. Buyer beware. Oh, it just so happens I do carb rebuilds now. I've been working on V4 carbs for 30 years. It's only $10 for a complete rebuild and I can have them back on your bike over night.

Sound cheezy? You bet it does.

 

Hopit, you been pimpin' for BC, getting a discount ??otstir:

My labor is about $65 less, and that has to count ! Most complaints i've heard about his work is that it takes too long.

BC never comes here to help riders with specific problems (although his almost-complete instructions above are much appreciated) or answer questions here, but i try to, most days.

What may seem cheezy to you looks to me like a old guy who loves working on bikes with alot of 'cycle 'sperence just trying to help members here and supplement his meager SS monthly retirement income by doing what he is great at and enjoys doing in his retirement. Plus, i like to keep my hands busy doing useful things.

 

Please tell me this is a joke...seriously...a joke, right? So, you're "helping" people when a new member comes on to share their thrill of buying a new 1st gen, while all others say welcome and congrats, you call them a moron and tell them they should buy something newer. Or when you tell a noobie that it's a good thing he's an engineering major cause that's what it'll take to get his 500 to make him happy. I can find dozens of examples of this kind of "help", with most of them coming in a thread that's not even asking for help, merely introducing themselves. You are really quite the welcome wagon for VFRW.

What's cheezy is bringing up hearsay to promote yourself. I'm not talking about you wanting to supplement my monthly check to you.