1986 VF 500 Starting, Idling, Tank issues

Hello Guys,

Ok I recently purchased a bike off a friend of mine, who purchased it on Craigs List. I believe the bike sat for a while and my friend an aircraft mechanic bought it running, he rode for about 15 - 30 mins using 100 octane gas. then it died on him. He cleaned the carbs, the throttle intakes, and then broke his leg and gave up. I bought it off him and have been trying to work on it.

He believes the tank has a problem, I took the tank off and JB welded a couple leaks, and ran parts cleaner thought the whole thing. Cleaned the gas cap took the petcock apart and cleaned it too. because i was waiting for JB weld to cure i used a Poweraid bottle attached to the carbs as a fuel tank. After his cleaning I can get the bike to start after 10 to 20 mins of cranking and resting with the throttle full open the engine would rev to 5,000 - 6,000 rpms, then slow down and run at 2 to 3,0000 rpm. after several attempts to fix that i can ride the bike around with the bottle and then eventually it will run out of gas.

So no ive taken the carbs apart after buying the service manual, reset the floats to Spec. cleaned the jets, found a a jet slightly broken on carb #3 (only the metal used to unscrew the jet is broken) and everything else seems fine. After that and putting the carbs back, the engine has same problem wont start gets flooded eventually starts with throttle full open and then runs at 2 - 3,000 rpm dies when trying to idle. today i bought new plugs NGK DPR8EA9 ( I live in MA) and the engine started right up stays at low rpm, will rev, dies when idled. My friend the aircraft Mechanic says it sounded like it wasn't running on all cylinders. So checking the exhaust pipes it appears as thought the bike runs on cylinders 1 and 2 but not three and four. Checked coils resistance per manual and checked ok, dyanmic check shows the coils, cables and plugs all good, (Holding plug on frame and hitting the starter) spark on all four. the old plugs were carbon fouled but cold be from several flooded starts. Compression checks on all cylinders were excellent each cylinder held at least 60 PSI. First im a I am thinking of moving the carbs over so carbs 1 and 2 are on cylinders 3 and 4 to see if its a carb issue. i might also check the cables by moving those around. after that im thinking of rejetting the carbs, then adjusting the floats for less fuel. all this done with air filter off, which also looks clean but ill be replacing anyway. Looking for advice, tips, tricks and possible problem eliminating tests i can do.

As for the tank. Ive removed the fuel filter cleaned it, and thought i had the tank working but it doesn't seem to drain gas. tried attaching vaccum hose to both openings and nothing. check with hand held vaccum pump. I am going to buy and replace the filter.

Looking for possible new tank if anyone selling for cheap. any advice would be helpful. Im not an idiot when it comes to mechanical workings, my friend is an aircraft mechanic and can help me but i am new to bike, and major engine maintenance.


Thanks so much.

SkyPilot

 

Compression should be at least about 160 psi according to service manual.

Run engine with airfilter in place, not removed.

Be sure the wires on coils and to plugs are going to the RIGHT plugs.

Tank must flow with a strong, full stream of fuel without rust.

are the vaccum slides moving or stuck ?

switching carbs around is not a good idea. Can you easily see light through pilotjets?? If not, they're clogged, and you could replace them for less than $10 each.

if an aircraft mechanic can't sort it, please don't fly on his planes.......

 

+1 squirrelman.. also sounds like you tank cap is not venting to allow fuel to flow . when you flip the cap over there is a small hole in it spray LOTS of carb cleaner in it and let it sit.

 

after you remove the fuel filter throw it in the trash as they are not needed and on the 86's which run the small carbs need the flow and could cause a lean condition (spark nock) put to this way if it should have been on there honda would have put it on from the factory..



throw up some pictures of it

 

Just to clarify Matt's comments: the 86's came without a filter from the factory.

As SM mentioned, you can't "move the carbs around", they only go on one way. I'd pull the whole rack and do a throrough cleaned and inpection. That sounds to me like where your problem lies.

 

Bike.

The fuel cap sat at least one hour in parts cleaner and i used shop air to clean seems to vent fine.

when i disassembled the petcock all pieces appeared fine moved back and forth. I have to try a couple other things but otherwise its a mystery why it wont flow fuel.

the fuel filter is in the tank and was installed by the factory.

The Number 1 and Number 2 cylinder work fine. So cables are going to the correct cylinders. As the #1 coil sparks cylinder 2 and 4 and coil 2 does 1 and 3. how can i get Half the coils and cables correct and not the other?

the pressure test i did was putting compressed air into the cylinders at close to if not TDC and it held up to 60 at least psi didnt try more than that, i dont know if the pressure gauge the mechanic has goes higher than 100.... ill have to check.

I was going to slide the carbs over to the left so carb 1 is on cylinder 3 and carb 2 is on cylinder 4 but thinking now i bet the frame is in the way and wont allow me to do that.

Looking at the manual which jet it the pilot jet? It said i would have to drill out the pilot jet and not to do it if i didnt suspect a problem.

also the aircraft mechanic just got lazy. he didnt try anything other than cleaning the carbs.... He thing was.... he fixes engines all day he didn't feel like doing it in his spare time.

Also ill take some pictures this weekend if i have time.

 

That's just a screen and not considered a 'filter'.


If you are not getting spark out of one coil I'd check the pulse generators. The coils rarely if ever go bad, so don't waste your time thinking it could be the problem. My guess would be the pulse generator for those cylinders, they are known to fail. You can't really blame them though, considering the environment they have to live in I'm surprised and electrical device can last as long as they do.

 

Coils

During dynamic check all cable and all plugs produce spark.

 

take a look at this it might help with the fuel flow. just make sure that all the jets are clear( see through) Daugherty Motorsports - Tank Valve Petcock Modification
there is a post about checking the pulse gen. you'll have to do a search.

 

Fuel Tank

Hey guys, sorry no pictures yet. Turns out it was a carberator vent problem. But now only two cylinders are firing i think thats a carb problem. But i need a fuel tank.
the previous owner, not the mechanic, decided to fix the swiss cheese holes in the fuel tank with JB weld and patched a 2 inch long hole with JB...... Sigh.

Looking for a tank anybody got any ideas.

 

motorcycle junkyard or check fleabay