84 vf500f running on 3 cylinders

One other thought.
Some timing lights do not like this type of ignition on these bikes (the pulse trigger) really it is a Magneto with a modern name.

So one thing you can do is find another spark plug and remove the spark plug wire from one cylinder and plug that spare plug into the wire that you have taken off that cylinder and ground it on the engine and watch to see the spark.

Do not ground the wire directly to the engine to watch for spark because that can ruin an ignition part. The spark plug has the correct resistance.

And make sure the spark plugs on the motorcycle have the correct gap because too large of a gap will cause irratic spark when the plug is in the engine and under compression pressure.


They used to have spark plug testers that would test the plug under compression and you could watch through a plexiglass window. I do not see those much anymore.

Never sand blast a spark plug. It ruins them because a piece of sand can get jammed between the electrode and insulator and cause the plug to over heat. If you do not believe me send an email to Champion spark plug company and ask them.

 

Those are cool but what I meant was they had a plexiglass BOX that you screw the spark plug into and you hook compressed air into the box to equal the compression pressure (around 155 PSI).
Then you screw the spark plug into the box.
See what happens is a spark plug may look like it is working, then when it is under compression pressure it actually has the spark suppressed (snuffed out) by the compression of the engine.

Probably with the newer type plugs it is less of an issue.

Some of these had a plastic viewing window too.

But don't buy those spark plug sand blasting machines!!!

 

The other thing you can do is when it is running is just point a infared heat sensing gun at each cylinder and it will show the cool cylinder. Mystery solved.



$100. or less. Sometimes $40.00 on sale.

 

Cylinder '2' is the front left cylinder.

One spark unit controls 2 & 4 and one controls 1 & 3.

 

The VF500 might be different, but on the VF1000F/R cylinder numbering is as follows.

left rear#1 .....Right rear#3........Left front#2......Right front#4

I have the HONDA workshop manual right in front of me.

 

Thanks INVISIBLE CITIES.
I am surprised that tinkerinWstuff made that mistake. Usually he has his self together.

But i have made mistakes too.

 

Those three boilermakers at lunch add up Tink!

 

Still wokring it through

Hey Guys

just an update on where I am up too.

The carbs have been stripped, soaked, cleaned and re assembled, 'as a side there was no blockages anywhere but it feels good to know they are not the problem'

I have replaced the carbie insulators - 'chunks of rubber between the carb and the head' - these were cracked and definitely causing vacuum leaks.

I have re checked the leads and plugs and they are all in good condition- so with it all re-assembled I fired her up and low and behold- problem still exists, it is better now, at least it will idle, so I went about checking the vacuum balance and number 2 is low so I am starting to suspect a broken valve spring or bent valve even though it has definitely never hit while I have had the bike.

-the reason I am suspecting valve train is that at crank speed we have good compression, at idle we have erratic [read intermittent] running and at 2k and above the cylinder may as well not be there, so I am thinking a valve spring that is weak or cracked that can hold compressions at crank but fails as the RPM's rise.

Anyway the next step is to pull the tappet covers and double check springs and things, I could not see any problems when I had them off earlier but I must not be looking close enough.

oh well, looks like the old girl may have to retire as I need a daily rider and with parts being what they are in Australia I can not keep her going reliably, I would like to hold on to her so I will keep looking for the problem while I look for a newer Gen to use for the daily rider.

I will try to update when I have more information to add. Once again thanks for all the input, it has been great just watch and listen to guys that have obviously been there before.

 

You make the wildest assumptions!!! "cracked valve springs" Crazy.
I have worked on engines all of my life and I have not seen one yet.
I have only seen weak valve springs in high compression engines with high lift drag racing cams.


When you had carbs apart did you remove the float needles . Did you look at them with a magnifying glass? I would have replaced them. It is 90% why carbs do not run right. DID you know that? The float needle.

Do you have calipers to measure the height? When the carb is upside down?
DID YOU MEASURE THE FLOAT HEIGHT????

Vacuum balance was low. On which carb???

When you do a vacuum balance you have to calibrate first .
If you have the fluid type like motion pro you have to hook it up correctly and get that right FIRST.
Also the #4 carb cannot be adjusted. only the other 3 carbs in relationship to that carb.

Do you have the special 90º bevel drive screwdriver, if it is need on the 500?

But lets back up a step.

Did you see even consistant spark on all cylinders?????

 

Never heard that, but if valve springs break that would be a factory defect. That means they are getting work hardened from being the wrong metalurgy.
There were some HONDA CB350 's that had countershaft sprockets that broke from not being hardened correctly.

 

Well finally got time to pull the front tappet cover off the old girl and guess what,

retainer on number 2 exhaust valve is missing, the valve spring retainer is hard up under the tappet and I can only guess what the valve is doing. I think this problem was mentioned right back at the start of this thread, but none of my diagnosis would have suggested this problem, the motor has compression, it just fails under load.

I am going to have to drop the head as it's got to have bent a valve but why it has got compression is beyond me.

Can anyone direct me to a replacement head gasket, I am not having much luck locating one in Australia, do we have access to any patterns for the 84 front head gasket, maybe I can find someone local to make a gasket for me??

I will have to chat to my local wrecker to see if he has any head components etc.

Anyway thanks for all the help, I will let you know how I get on with the repair.

 

Bummer about the valve. Here is a link to a thread on head gaskets for the VF500F. As you have no doubt found out they are NLA from Honda but there are a few other sources available.

http://vfrworld.com/forums/1st-2nd-generation-1983-1989/31074-scan-em-if-you-got-em-vf500f-head-gasket-patterns.html

 

Were both halfs of the retainer/KEEPER missing?
If the valve is up but will not push down by hand then it is bent.
But do not push it down then turn the engine over!!!

If the engine has compression -then it just means the valve is closed and the valve is NOT bent if it has full compression.

Is the flat washer like retainer in place on top of the valve spring and the KEEPER parts missing? NOT CLEAR. If a KEEPER is missing you need to find it and take it out of the engine.

If a valve is bent it will be stuck in the down position OR it will be in the up position and stuck. Most of the time bent valves are always found in the down position.

The springs cannot bring it to the up position if it is bent. That is why the piston hits the valve sometimes.