Another Uncle Phil Interesting Running Mystery

It sure sounds like the fuel pump operating intermittently. When I had a failing pump on my ST1100 it acted exactly the same way. If it were a bad coil you would only lose two cylinders and run on two. Unless the connection fed both coils.
 
The 97 eh?
I had similar issues with my 97 when I first got it. I suspect the gas cap. Apparently you can rebuild them, I just got a new one and it resolved the issue.
I was at OHSToc when it happened. GreenZR and Ohio Deer suggested I run the bike home with the fuel cap slightly ajar, that got me home.
 
bdalameda said:
It sure sounds like the fuel pump operating intermittently. When I had a failing pump on my ST1100 it acted exactly the same way. If it were a bad coil you would only lose two cylinders and run on two. Unless the connection fed both coils.
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That's what I thought at first - I've had the same 'symptoms' the multiple times I've had fuel pump failures.
 
kiltman said:
The 97 eh?
I had similar issues with my 97 when I first got it. I suspect the gas cap. Apparently you can rebuild them, I just got a new one and it resolved the issue.
I was at OHSToc when it happened. GreenZR and Ohio Deer suggested I run the bike home with the fuel cap slightly ajar, that got me home.
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I usually run with the fuel cap loose anyway but it's easy enough to replace since I have a few laying around ... ;)
 
Esti1300 said:
Hey Phil, I’ve had similar issues in the past. Symptoms were similar to yours. Running nice and strong then, out of the blue, it would hesitate and slow down, then pick up again and run well for several miles. At one point it became more serious causing me to pull over.
Long and ugly story short, it turns out it was a loose coil connection.
Now Frost’s issues might not be a loose coil connection but the symptoms you describe sure sound like they are related.
Good luck with your investigation.
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That's sort of what I thought next but when I pulled all the plugs they were the 'correct' color.
If I was having coil 'failure' I would think they evidence lack of fire and be sort of sooty colored.
 
Uncle Phil said:
I just blew through the gas cap and the vent hose and did not sense any back pressure at all.
For good measure, I then took an air hose and did the same thing just in case.
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my point was that the fuel tank, capped, get pressurized from the heat. At that point it acts as a fuel pump. When it cools down it looses pressure and fuel won't be forced out as much therefore the engine is starving for gas. It sits again get hot and pressurized , runs till till the tank cooled down by driving. The fuel pump may be working cold but not hot. I'll ques it runs longer and better on a full tank.
 
I can't say which of the possibilities is causing your problem, but you can't tell much about the condition of ignition coils by doing a simple resistance measurement. Coils are very dynamic, the best way to test them is with an ignition scope when the bike is running and exhibiting symptoms, but since you probably don't have one a coil swap is the next best thing. And ignition problems don't stop at the coils, the plug caps and plug wires are also suspect, but given that your description sounds like more than one cylinder cutting out its probably not likely that you have two (or more) bad wires/caps. But it could indicate a bad power wire to a coil.

Since you have several parts bikes to choose from, swapping out the coils and plug wires/caps from a good running bike would be a good move, and while you're in there check the condition of the power wires to the coils.

whether or not it fixes the problem, its one of a few possible causes that needs to be crossed off the list. The fuel pump is another suspect, and since you've swapped those before it might be less work to try that first.
 
Have you moved any fuel lines lately? Also sounds like vapor lock. Fuel vaporizing in the line before the injector's. Just a couple of degrees variation will cause this. Had a Chevy that would do this a long time ago.
 
dwalby said:
I can't say which of the possibilities is causing your problem, but you can't tell much about the condition of ignition coils by doing a simple resistance measurement.
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I wonder about that. The definitive answer would be to the question, how does heat affect an ignition coil? If it is a breakdown in insulation, maybe a high voltage tester is the answer.When I was installing gutter ice melting cables and pavement warming cables, Raychem's instructions were to use a meter that measured the resistance to ground when 1000 volts was applied to the conductors in question. I ended up buying a $700 Fluke MM to do exactly this. Might such an instrument be able to find one defective coil out of 4?
 
Had an issue with a buddy's Aermacchi Sprint dirt track racer where spark would get weak during longer, hot races. Apparently the coil plates were heating and expanding, and caused fractures in the winding. Worked fine cold, got crappy when hot! We replaced the coil with a newer one and the issue went away.
 
Well, what I know so far -

1. New fuel pump - no difference
2. New fuel filter - no difference
3. Bypass fuel pump relay - no difference.
4. Visible fuel in fuel filter - appears to be flowing fine.
5. Fuel cap loose.
6. Coil resistance after engine hot and missing - 26-27 both sides.
7 Proper Iridium plugs installed about 40,000 miles ago - tips look to be proper color and in good condition.
8. Still not running right.
 
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If it had a catalytic converter, I would suggest checking that for obstruction. But I don't think the ST1100 does. Maybe just double check the exhaust is exiting consistently on both sides once it starts running poorly?

I had an older carbureted vehicle that would act up when it got hot (backfire, no power, etc) and turns out it had been running rich and partially clogged the exhaust (and more than one dirt dauber had built a home in there). I think it took a long highway trip "wide open" before it burnt everything off and all was happy.
 
Howdy. Although my fuel pump acted just like yours when it was going south, my bike had no black smoke. My experience has been when a vehicle starts throwing black smoke------->> 02 sensor. Fwiw.
 
It seems you've eliminated most of the fuel delivery problems (electrical too), what about the ignition key wiring and the kill switch along with the red wire bypass area? Could it be expansion cracks in solder or connectors/fuses as things heat up?
 
you might want to try the igniter box and/or pulse generator as these can have heat related issues.
 
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