VFR750 Electrical or fuel problem?

Hello all,
I need your help in order to sort out a "issue" with one of the bikes in our family. It's the older one a VFR750 from 1990.

The problem occurs only now and then without any regularity.
It appers just like it's running out of fuel, the engine start to jerk and if ju unclutch it dies immediatly. However when engine has stopped you can just turn the key off and back on and release the clutch and roll-start it again. Works like it did before the "issue". Or if at stand still you can push the starter and give it some choke and it works fine again.

This problem can happen once or many times during a trip of 100km or it could be that it doesn't happen at all.
Some things I have checked already:
- Measured coils and plug HV cable
- Cabling to/from ICM
- Fuel pump works when jumped
- Plugs changed during winter service, also battery (old one was 7years)

Thanks in advance

 

Fuel filter been changed recently? Could be partially clogged.

 

Doubtful, because sometimes it works good and sometimes not. Our last trip we rode for 500km and home again, then it stopped 5 times on the away trip, on the way back home it worked fine without a single stop.
I have checked the filter and fuel flows nicely through it. None the less I'll change it.

I just opened the fuel pump and the contact surfaces that moves the pump had some bumps not much but anyway. I slightly tired to smoothen them with some sand paper.

Anything else?

 

If fuel flow is OK, then seems to point to electrical problem in ignition circuit. Since it's 20 years old, could simply be a bad / corroded connection somewhere. That could cause the issue intermittently. So maybe try taking apart and cleaning connections associated with getting energy to the plugs. Check / clean ground connections too.

 

At least the connections on the coils are ok, those I checked when I measured the coil restsances.
So I have checked the following and are still coming up with nothing:
I followed the service manual.
- Measured ICM, all ok but the "ignition pulse generator coil" value was ~320ohms, the specification says 450-550ohms.
- Measured coils, within specification.
- Measured the 4pin black connection, within specification.
Fuel side:
- Filter
- Pump is working, (should it click all the time or only when the engine needs fuel?) also did some maintenance on the connectors.

I'm still fumbling in the dark.....

 

I wish I had more specific ideas for you to try, but my '97 Viffer has run like a champ since I bought it a few years ago. I've spent MUCH time tracking down electrical gremlins on my old cars, but not my bike. And in many cases, bad connections / relays / fuses rather than faulty major components have been the culprits.

Anyone else out there with ideas to try??

 

Yeehaw, another intermittent snag. I luvs these.:wink:

It wouldn't hurt to inspect and clean the clutch, kill and sidestand switches. They have been known to create similar mayhem.

So the bike won't start without the choke, when already warm? Is this normal for your bike, or another symptom?

:crazy:

 

Possible same old problem that no one really wants to fix.

The idle jets get clogged or a little moisture.
It will run with choke on. gas will not go though them. The hole in the idle jet is almost the size of a human hair.

Only one way to fix it , put Sea foam in the tank to help keep moisture in suspension.
It is condensation build up in the tank.

You have to take the carbs off (which you will not want to do) and remove the idle jets and clean them and make sure you can see daylight through them.
And like others have said, change the fuel filter.

You did not tell us the mileage.

Charcoal cannister??? Float bowl vent clogged?

Question - Does it idle perfectly? No backfiring?
If so, it may not be the idle jets. I would check that first. Take any lines off of the float bowl vents and vent to atmosphere temporarily. It it does not have the problem then it is something in the float bowl vent system, like the vacuum switching valve, or charcoal canister.

 

Try riding with the gas cap open. Some old bikes have a vented gas cap. Look for a small hole in the gas cap. If it has one make sure it is not clogged.

 

I have checked the sidestand and kill switch. I also checked the gear in & start switch (neutral switch or whatever it is called) wgen I measured the ICM.

If the engine is stopped by driver and then started again while warm no choke is needed. Only need the choke when this "issue" has happened for easier starting directly, also in this case the choke can be taken off when the engine is running stable.

 

The viffer has ~134000km/83000miles on the meter.
Charcoal cannister?? Is this the same as sub air cleaner??

The idling is ok, I haven't noticed any problems with that. The jets where changed in 2003 @90000km. The engine works fine and is wonderful to drive as long as this "issue" stays away. Then like a flash from a clear sky the problem appears, also when hot weather (25-30degC) it is more sensitive.
I'll check the float bowl venting.

 

Along with Dave's suggestion about the plugs, try a wire wiggle test, with the bike idling.

Do you have a clock? Has it lost it's time?

 

If you need the choke when the issue appears and not at other times it is defenitely a fuel problem. The choke creates higher vacuum to draw more gas. Your bike is starving for gas.
Rust in tank?
Check all fuel lines, vent lines, gas cap, filters. clogged jets. dirt in float bowls. Also check routing of fuel lines to see if they run too close to a heat source, this could cause vapor lock in the fuel line. Look for a spot for the fuel to get pinched after something heats up.

 

You didn't mention if this bike is a 49 state bike or a California bike.

I had the same symptoms with my '91 Suzuki Katana 1100 (California bike).

After taking off all the Califonria smog stuff and plugging a few hoses the problem was fixed.

The bike ran sooooo much better after doing this.

 

Yesterday I spent the whole day in the garage and did some searching. So I have now checked all the vents, the fuel line is checked, the pump works (shouldn't the pump run all the time as the fuel cut relay gives info to run when engine is running. Or does the pump itself regulate when it runs even if the relay gives "green" light to operate?). Wiggle test are made. Also connections are checked to rule out bad connections.
I disconnected 1cyl when running, continues to run (but notice that only three are doing the work), this isn't even close to how the engine dies when fault appears.

The engine is a European model, so neither 49state or California issues can be a problem.

As I didn't find anything that might cause this, I went over to the battery side, I found out that the charging voltage only was 12.9V @5000rpm. I loaned the R/R from our VFR800FI and plugged it in and I then got 14.6V. Appearantly the R/R is faulty, will order a new one.
But before you all start to say there's the problem, is it actually the R/R that is causing this problem?
Could this faulty R/R cause the engine just to die on an irregular basis? Could the faulty R/R cause the ignition or fuel pump to die and then come back to life just because a turn of the key? How come no lights or fuses blow? Why no start problems? Why does it kill the engine more in warm weather?

 

The fact that it will still start right back up, leads me to think it is not the problem. The battery obviously has still got lots of juice left, so logically it should not be the cause. R/R problems, unfortunately, have had a history of being illogical. It has to be changed anyways, so you might as well play the wait and see game. Hopefully, you won't get stranded, if it rears it's ugly head again. You haven't so far, so just playing the odds.

Good luck

 

You have done some good investigative work.

You still have not told us about one VERY important thing.
If this is a carb model you need to find out HOW the float bowls vent.

It is like if you have liquid in a straw and you have your thumb over the end of the straw . The gas cannot flow if the vent line is clogged.

Some float bowls vent to atmosphere and the end of the hose has a little rubber flap to keep the wind rushing by from sucking the gas out of the float bowl. Check that flap to make sure it is working.

Some models have the float bowl vent line go right back into the air box but there is a metal plate over the end of the vent tube to keep the intake air from sucking the gas out of the float bowl.

The third one is more complex. It has the float bowl vent line going to a vacuum valve. The valve is normally closed and only opens when you start the bike and vacuum coming from one of the intake manifolds(high vacuum) goes to the vacuum switching valve and opens the valve so the float bows can vent while the bike is running. Find out which intake manifold it is coming from. Make sure it has vacuum. Some models had a brass fitting and it was in aluminum and got a lot of corrosion. Could be clogged.

If that vacuum valve does not work right the bike will not run very well. You can remove it and check that valve with a hand held vacuum pump or with your mouth.

The hardest thing for any engine to do is to idle.
Also if it wants to die at idle it could be as simple as not enough air because the air filters are dirty OR it is a foam filter with too much heavy oil on it.

 

Your 1990 model does not have a cannister on it or any of that bogus emissions junk.