86 VFR stalling intermittently

Hey guys, haven't been on here much in the last year or so. Really haven't been riding much, other than to work. I have a recurring problem but until lately hasn't been bad enough to irritate me enough to fix it. Here are the symptoms....(I hate intermittent problems)

The VFR stalls out occasionally as if it's out of gas. Usually at highway speeds. By the time I can pull over and hit the starter a couple times, it starts up and runs normal. It may not do it again till the next ride or even weeks away. I rode last week to work and it stalled 3 times to work and 4 times home. Still start back up every time. Just causes me pull to the shoulder till it restarts. It runs fine and smooth any other time.

It soesn't seem like a kill switch or similar electrical issue related to spark cause it sputters first as if it's out of gas. It's as if the bowls don't get filled fast enough. I checked the fuel pump and relay and they work at idle at least. The spark box activates the relay and seems ok. I haven't checked the actual fuel flow yet to see if it's in spec. I will do that next I guess.

I should note that it has CA emissions on it and I've been studying the vacuum routing to see how it works. I will check the fuel tank vent hose next to see if it's clogged since it's tied in to that. I noticed the Air Vent Control Valve and the Purge Control Valve seem to work opposite each other to recycle fuel vapors. If one of these doesn't work, how does it affect the engine performance? If I remove the system wil it work better? I'm looking at it and have an idea but I need to study further which lines to plug and which to vent, etc.

So, any ideas on which it could point to for the problem? I figure I'll check the fuel flow and put an iar hose on the fuel vent line to try to blow it out. It would be nice to temporoarily mount a voltmeter somwhere tied to the pump to see if it is actually pumping when the bike stalls. I don't have any test gauges to test the AVCV or the PCV. Is there a way to test those without vacuum gauges?

Check the fuel filter?

this has happened to SO many 86/87 vfr 700/75-
if the filter is not clogged up..
its the fuel pump.
99.9999999999999999999999 % sure of that.
if your not a a high speed gun and run squid, then you can bypass the pump. either buy a LONG new line and a install a new filter or get a curved pipe from a radiator shop to plug in where the r/r is now.
the draw back..
with this set up. 1 of 2 things must be considered.
1) punching a hole through the pipe INSIDE THE TANK at the outlet bung..(take a awl and put in the the pipe and hammer it)

2) running the bike as is but have less reserve as the gas inside the tanks go UP then flow to the petcock then down to the outlet bung.

i would get a new pump thats the best option. :fing02:
howeber..
i would get a one made for a newer model. the 86 set up never lasted long. seemed like i needed a new pump every 2 years.
i put on a cbr600 pump and all was well. :fing02:

[image: View Post]SEBSPEED, on 29 November 2010 - 10:58 AM, said:

Check the fuel filter?


Yeah. Rebuilt the carbs, new boots, new fuel line, new fuel filter a couple years ago when it bothered me then. Had no effect. just ran better. Still stalled at seemingly random times. They're just much more frequent lately.

[image: View Post]gll429, on 29 November 2010 - 11:35 AM, said:

this has happened to SO many 86/87 vfr 700/75-
if the filter is not clogged up..
its the fuel pump.
99.9999999999999999999999 % sure of that.
if your not a a high speed gun and run squid, then you can bypass the pump. either buy a LONG new line and a install a new filter or get a curved pipe from a radiator shop to plug in where the r/r is now.
the draw back..
with this set up. 1 of 2 things must be considered.
1) punching a hole through the pipe INSIDE THE TANK at the outlet bung..(take a awl and put in the the pipe and hammer it)

2) running the bike as is but have less reserve as the gas inside the tanks go UP then flow to the petcock then down to the outlet bung.

i would get a new pump thats the best option. :fing02:
howeber..
i would get a one made for a newer model. the 86 set up never lasted long. seemed like i needed a new pump every 2 years.
i put on a cbr600 pump and all was well. :fing02:


So, you're saying that it won't pump enough to meet spec? Or that it occsionally quits working? The relay worked fine when it got the signal from the spark box and I could feel the pump working. I was thinking the pump might be the culprit. It was odd though because it did work at idle.

I forwarded your orig post to a good friend of mine that made my '86 run better than it ever has after having similar issues... here's what he had to say:

Definately sounds like it could be a fuel pump problem. It could also be a float height issue or a pinched vent line for the fuel tank. Since it has steadily gotten worse, I'm going to guess fuel pump. Maybe it's not pumping enough fuel when the motor is spinning at higher rpm's. The only way to really tell if that's the problem is to replace it and hope for the best. If he's mechanically inclined he might want to do a visual on all of the lines for the fuel system and/or even check the floats and fuel passages in the carbs. Hope this helps.

:fing02:

[image: View Post]Wheatie, on 29 November 2010 - 12:23 PM, said:

I forwarded your orig post to a good friend of mine that made my '86 run better than it ever has after having similar issues... here's what he had to say:

Definately sounds like it could be a fuel pump problem. It could also be a float height issue or a pinched vent line for the fuel tank. Since it has steadily gotten worse, I'm going to guess fuel pump. Maybe it's not pumping enough fuel when the motor is spinning at higher rpm's. The only way to really tell if that's the problem is to replace it and hope for the best. If he's mechanically inclined he might want to do a visual on all of the lines for the fuel system and/or even check the floats and fuel passages in the carbs. Hope this helps.

:fing02:


I'm seeing a recurring theme here.


I'll look at a newer CBR pump to see if it matches up and go from there. I'm still gonna check the pump out of curiosity. The service manual give a certain minimum acceptable flow that I'm curious to see if it meets.

Thanks guuys. This helps alot.

[image: View Post]crepitus, on 29 November 2010 - 08:30 AM, said:

Hey guys, haven't been on here much in the last year or so. Really haven't been riding much, other than to work. I have a recurring problem but until lately hasn't been bad enough to irritate me enough to fix it. Here are the symptoms....(I hate intermittent problems)

The VFR stalls out occasionally as if it's out of gas. Usually at highway speeds. By the time I can pull over and hit the starter a couple times, it starts up and runs normal. It may not do it again till the next ride or even weeks away. I rode last week to work and it stalled 3 times to work and 4 times home. Still start back up every time. Just causes me pull to the shoulder till it restarts. It runs fine and smooth any other time.

It soesn't seem like a kill switch or similar electrical issue related to spark cause it sputters first as if it's out of gas. It's as if the bowls don't get filled fast enough. I checked the fuel pump and relay and they work at idle at least. The spark box activates the relay and seems ok. I haven't checked the actual fuel flow yet to see if it's in spec. I will do that next I guess.

I should note that it has CA emissions on it and I've been studying the vacuum routing to see how it works. I will check the fuel tank vent hose next to see if it's clogged since it's tied in to that. I noticed the Air Vent Control Valve and the Purge Control Valve seem to work opposite each other to recycle fuel vapors. If one of these doesn't work, how does it affect the engine performance? If I remove the system wil it work better? I'm looking at it and have an idea but I need to study further which lines to plug and which to vent, etc.

So, any ideas on which it could point to for the problem? I figure I'll check the fuel flow and put an iar hose on the fuel vent line to try to blow it out. It would be nice to temporoarily mount a voltmeter somwhere tied to the pump to see if it is actually pumping when the bike stalls. I don't have any test gauges to test the AVCV or the PCV. Is there a way to test those without vacuum gauges?



mine has been doing the same thing.. when I get off my lazy butt a fuel pump swap is in order.