85 VFR Engine Revving Issue VIDEO

YouTube - VFR700 Interceptor Engine Problem.3gp

Getting my bike out for the spring and have discovered a problem where the engine doesn't want to rev higher than 5500 RPM's. It won't cut out but it strains to go higher and runs rough at that speed. Also the tach will drop down to zero. Problem only persists until I release the throttle. It idles well and runs fine below 5500. This wasn't a problem when i put it away for the winter. Please see video. Any help is greatly appreciated. Thanks.

YouTube - VFR700 Interceptor Engine Problem.3gp

 

Have you checked the pipes to see if they are all running at the same temp? Did jump start the battery? Have you check for spark on all four cylinders when the tach fails. I am thinking CDI failure but it is difficult to tell from this distance. They do tend to run better than you expect with a failed CDI.

 

Faulty spark unit or pulse generator

 

not sure if pipes are the same temp but when the bike is idling there is thicker/ blacker smoke coming out of the left pipe than the right. Battery is fine, I had it on a charger all winter. Also, spark plugs are brand new. Sorry for my ignorance but could you explain how to go about checking the spark? Also, what is the CDI? Thanks

 

CDI, Capacitor Discharge Ignition

Do you have a Factory Service Manual handy? The FSM will give you more info on how to troubleshoot this.

Here is a page from the VF500F manual which is likely similar to your bike:

 

Hey thanks a lot for the quick replies and helpful info guys. I guess I'll start by replacing the CDI and pulse generator and get back to this thread if it solves the problem. Do you think I can rule out ignition coils?

 

Coil failures are very rare but CDI's and pick up coils are not. Easy to check but you will need a multi meter. Do you have one ? The tach failure is a nice clue. A failed coil will have no affect on the tach. It is in the ignition signal circuit or CDI to be sure.

 

checking for spark is an easy one..... you can pop out the spark plug plug the wire back in and then ground the plug to the frame and turn it over you should be able to see a nice spark...... you said you put new plugs in?..... did you check the gap... (not the cause of your problem but might as well make sure) and you should give the carbs a little bit of a cleaning after all the bike sat all winter.....

And I would go with what IC and TC have suggested....IC TC= Guru
good luck

 

You did not give the miles. I would not just start replacing parts.
FIRST Get a workshop manual and and do the test for those components.

Does it backfire on start up? When you say it won't rev is that while on the road OR when it is sitting still? Very important distinction.

I would bet the idle jets are clogged as usual from sitting during the winter.
Components do not just start failing while it is not even in use.

BUT NOI ONE wants to take the carbs off and take the idle jets out and clean them DO THEY?? You have to see daylight through them.

Just spraying something in the carbs, or putting something in the gas tank WILL NOT CLEAN the gunk out of the idle jets.

And in that VIDEO the bike is idling very high probably because it will not idle at 1000-1500 RPM right?

YOU SAID It ran fine before you put it away for the winter right?
That is your clue.

The idle jets are as small as a human hair.

 

So I got a chance to look at the bike today. The general consensus on this thread seems to be a bad CDI box. Also, this guy claims that if the box controlling CYl #'s 1 and 3 is bad it will make the tach goofy so it was the first place I looked. Wouldn't you know that as soon as i pulled it out of the bike a bunch of water poured out and the board is completely corroded.


So I guess that's my problem. I think it was from an afternoon last October when I was forced to ride an hour from Philly through a really bad storm. Actually, based on how bad this thing looks I'm surprised it was running at all. So does anyone know a good place to acquire these? They seem very rare and expensive. Also, are the two boxes interchangeable, for example if I can only find the one that controls Cyls#2&4 could i use it to replace the box for Cyls#1&3?

Should also note that I tested the pulse generators to rule them out and they check out fine. If it's still runnin rough after I replace CDI I'll take the carbs out and clean them up good. Also, FYI, the bike has 26,000 miles and is overall well taken care of. The guy who sold it to me last year was a honda tech but dang, why did I buy such a complicated machine for my first ride? Love at first sight I suppose. Thanks for all the help guys.

 

New CDI box fixed it. Runs good as new. Thanks

 

Good deal! Glad you are up and running.