1983 VFR fuel starvation issues at highway speeds after 20-30 minutes of riding

I have a 1983 VFR that just came back from the shop, new fork seals and carbs gone through, cleaned, synched etc. It idles right about 1200rpm, under highway speeds it seems fine, out on the highway after about 20-30 minutes you begin to notice the rpm's dropping and the speed until it is barely running. It has happened twice so far. Tank was "creemed" by previous owner, not sure if it was done correctly or not. Pulled fuel line, fuel flowing well, it has an inline filter under the tank. I can stop the bike, let it sit for a few minutes, then start up and run with choke on about 1/4 of the way and limp it home. Any ideas on this issue guys? I think I'm going to send the tank out to the shop in Pennsylvania who will cut it from the bottom, completely clean it, seal it , reweld it, prime it and send it back. But I would like to stay with the original paint even with the scratches it has, (only original once)! I really do not know what is causing this issue, cannot ride it the way it is and it needs ridden! Second owner and it has 8115 miles on it, all original except front brake lines, tires, battery. If anyone has any ideas, PLEASE advise!!! Thanks!

 

I would suggest you verify the fuel pump is operating correctly, it is not uncommon for them to work correctly when cold and fail to operate when heat soaked. I would also check that the tank is venting correctly, if the gas cap was replaced at some point and it was off a California model then it is not a vented cap.

 

OK, who do I "verify" the pump is operating correctly? Gas cap is original, not been replaced. Best way to check it for proper venting?

 

The fuel pump testing procedure is outlined in the FSM. I would also suggest searching around the forum. These are issues that a lot of 1st and 2nd gen owners have dealt with before.

 

What's an '83 VFR ?? Rare bird indeed !

Try the standard fuel pump relay bypass. If you haven't tested for sparks on at least one plug when she quits, couldn't it be a possible electrickal problem like failing cdi or charging system insufficiency. Test fuel flow from tank, draining into a fuel-proof DOT-approved bucket, etc. to observe output flow as tank drains to near-zero. Sometimes some tanks just won't sip near the bottom reliably.

 

try opening the fuel cap when it starts doing it. If it picks up again then the tank breather could be blocked

 

Thanks! A friend who owns an FJ1200 said to try the same idea. If it isn't venting properly, how do I fix that?

 

The cap will have a vent somewhere, blow compressed air or better yet carb cleaner through it to get the gunk out. Wear glasses while doing this, I got a nasty squirt in the eye when I didn't.

 

Toe interesting point you make there, how did they vent the tank?

 

I'll check that tomorrow and see if that works

Haven't really looked at the cap, just figured it was venting since it idles and runs well at normal speeds.

 

+1

This is most likely your problem. I would be concerned about the Kreem too but one thing at a time.

 

Tried that, no help

That did not solve the issue, it seems more like no spark to some of the cylinders, slight backfire when it does start up again. I think by putting on the choke it gets enough fuel to the two firing cylinders to run, although not well! I'll check spark and see if that is the issue when it starts acting up, it takes a while for it to run badly though. I am really thinking that as the coil gets hot, it is starting to lose spark. If it is that, I think I'll do the replacement coils from a newer Honda like I have heard others have done.

 

OK, checked spark, yes, plugs were correct ones and in good shape, fuel filter clean, fuel clean, coil/spark wires good seals, grounded properly and connectors fine. What about voltage regulator? It gets warm when running, which I am sure it is supposed to. How would I test that to make sure it is sending enough voltage to the coils? And if coils are putting out correct spark voltage? I do not have a service manual.

 

Testing of coils isn't easy particularly if you think they are breaking down when they warm up, only thing you can do is get a a good known coil and start swapping it around or replace the coils and go from there. That is what any shop would do and you just have to pay the bill.If you are convinced it isn't fuel, it must be electrical and that can be all sorts of things and if it was easy we could give you an answer straight away. As for the rec/reg get a volt meter and fit it to the wiring somewhere and then you can see what is going on with the charging. rec/reg has nothing to do with the spark unless the battery is flat and then it is another ball game

 

It is never, ever the coils.

At this point I would suspect the pulse generators. Their failure mode is exactly what you describe. The only way to test would be to take a volt/ohm meter with you. When the bike dies you have to immediately find the connector and check the resistance. If they cool off any at all the resistance will be normal - they must be checked asap after the engine dies.

Of course, if you just keep riding it they will degrade to the point they check bad all of the time, so that is an option too!

 

Sounds like a good idea

I'll look into that next, see if I can find some to swap out. Thanks for the idea!!!

 

Well the problem has been resolved. The fuel filter below the fuel pump was found to be in bad shape. I am guessing that the previous owner left it full of fuel and after sitting for many many years, it was ruined. Apparently enough fuel would flow through it for a short time, then it would starve for fuel and die. Local vintage bike mechanic figured it out for me, thanks Hoy's Vintage Bikes Brownsburg Indiana!