Honda Shadow Forums banner

engine starts fine, dies suddenly, starts fine, dies, runs great, repeat

900 Views 53 Replies 5 Participants Last post by  madshadow
Hi all,
I feel really stumped. My 1986 Honda VT1100 starts on like three revs, runs perfect, then dies like someone hit the kill switch. Push the starter, it starts right up, runs perfect, then dies. Rev it to 3000, it runs great. and it might keep running. I then might be able to ride hard 50 miles, stop-n-go or highway, then pull up to a stop sign, at idle, it dies. Rinse, repeat. Always has gas in the bowls (checked by turning drain screws out). New battery, always has about 13 volts at rest measured at battery terminals, and near 14 with engine running. At higher revs, I've seen it hit 15, but seems usually to remain mid 14s. Coils primary leads, tested at harness connectors, show 2.5 ohms each (Haynes book says approx. 2 ohms is spec.) Ignition pulse generators 455 and 437. Haynes spec is 450 to 550, so one is low, but my other engine ran fine and its IPGs had like 427. Camshaft pulse generator at 630 ohms is within spec (Haynes: 570 to 690). I have recently cleaned the carbs, changed the fuel filter, the air filter was replaced a year ago and looks 95 percent spotless. I have swapped new and old fuel pumps in and out and bypassed and unbipassed the fuel pump relay. It does what it's supposed to do. I long ago removed the air vent control valve and plugged the orifices. Even with the valve gone, my idle air screws are out only 1 turn each, and very little backfire on decel. And it runs fine, pulls hard, doesn't miss, except when it just shuts off. I've also cleaned the kill switch and ignition switch, and replaced the little springs in the ignition switch. They test out like they're supposed to function. I have no kickstand switch. I replaced the clutch switch (and the similar brake light switch on the other side). The front cylinder plugs look gray and dry, the back cylinder plugs are black like that cylinder had been rich (I adjusted that carb).
I've looked for shorts in wiring, I haven't found any, probably because I recently replaced the harness with a good used one after experiencing faulty connection problems. My bike lives outside in Florida, only occasionally it gets to sleep under a pole barn. I ride daily, though, so that dries it out. What could make it shut itself off and then start just fine the next second? Can the spark units fail intermittently? Should I throw money at the pulse generators?
See less See more
1 - 20 of 54 Posts
After reading a previous post about a kill switch, I remembered something I didn't understand about mine. When the key is on, the kill switch connects black wire, which carries battery voltage, with with black/white wire which, if I recall, goes to spark units and coils. All good so far. But, if key is off, black wire at KS has continuity with ground (it beeps with one lead on KS and one on negative battery post). (And if kill switch is on "run" both wires are grounded). So, it doesn't just disconnect a hot, it connects to ground. Is it supposed to do that?
I also found it interesting in the recommended reading that the spark units have a low-voltage cut off (possibly 9.7 volts). So I checked. My bike climbed in voltage from 12.5 to 13 when it died (within 15 seconds of starting). BTW; I previously replaced the infamous (melted) triple yellow connector.
Is your idle low? Try raising it a bit and see, then back out the mixture screws 1/2 turn and see if it helps.

Pretty strange about the black wire going to ground on the hot side and not blowing the ignition fuse.
Your meter may be beeping from the resistance of the other units that the ignition fuse supplies. The black wire also goes to the fuel relay and voltage regulator.
Here is a trick you can try - have it running at idle and heat the ignition units with a hair dryer to see if they get warm and open up. And wiggle the terminals going into the units.
Did you measure the pulse gens when they were warmed up also?


See less See more
Now my idle is about 1000. I had turned it up to 1500 to keep it from dying, but then it cycled into its "no problems" mode, so I readjusted, lowering idle and air screws. Then it started acting up again and hasn't "fixed" itself this time. It starts right up and within seconds, shuts off. I don't think it was hot when I tested the coils. But, the problem happens within about 15 to 20 seconds after first-start, before warm up. If I wanted to bypass the ignition and kill switches to test them, to see if it runs without dying on just a wire to battery pos., how would I do that?
Just run a wire off the battery positive post through a toggle switch (and a fuse is a good idea) to the black/white wires on the ICU.
That goes to the coils too so it should power everything just like the key.
Just use it for testing and make sure the wires are protected from damage.
I also have a little diode that pops out of the harness along the left frame rail just before the rear fender support that has no continuity either way. Two-spade, meter reads OL wither
Thanks for your relies, Swifty. I'll try a couple of your suggestions and report back.
That diode is part of the safety system for starting.
With no kick stand switch it won't kill the power.


See less See more
Engine acted the same when operated on toggle wire instead of key. Starts, dies. The diode did show .496v going one way, so I just didn't test it properly the first time.
I put a hair drier blowing on the bigger spark unit, started the bike and tried to keep it from dying. It would run steadily only at 3000 rpm, so not exactly idle. But it ran without dying for over a minute, so I backed off the throttle gradually. At 2,000 it died.
So, it seems to need hi revs, and possibly heat. A few days a go, I was able to ride it for quite a while after warming it up under high revs, but now it seems more like to die at even high idle. I'm thinking of opening up the clutch cover to see if my pulser gaps are good.
The gaps shouldn't change. I suspect fuel pilot passages blocked/debris in carb. At the higher rpm, you're running on the main jet, lower rpm/idle, on the pilot circuit.

Also verify carb bowl vent hoses are clear as well as tank vent hose.
Do you have an old timing light?
Put it on a cylinder and hold the trigger down and watch the light as you go through your tests.
Or get one of these cheap ignition testers as a visual of what the spark is doing.

I decided not to pull case off to check gaps... I swapped in a pair of old coils, no change. I'm going to check bowl vents. Are they the internal pipe in the bowl or external? I'll be looking at the manual now.
I remember taking out two jets and cleaning them, the slow and main, but not a third pipe that didn't seem to be readily removable. I also plugged orifices on the outside because I removed the air control valve a long time ago. So I hope I find a problem so I can get it right this time.
Don't try to remove the solid pipes.
The pilot jets have really small holes, you may want to re-check them and blow carb cleaner through the passages to verify it's coming out in the venturi area.

If the bowl vents are blocked, it can build up fuel vapor pressure in the float bowl which causes flooding and dying at stop signs etc. You might smell fuel when it dies, If it's not that I'd keep looking.
Another way to prove the pilot circuit is the problem would be to have it running and when it tries to die, spray carb cleaner or starting fluid into the intake. To see if fuel is lacking.
cleaned them again, no luck. I've been just blowing them out with carb cleaner. It starts right up, runs at high revs, cuts off like a kill switch as I ease up. No pops or misfires. I'm going to walk away for a bit, but I'll be back.
1 - 20 of 54 Posts