Triumphrat

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My misfire has returned. I previously posted about it here.

I thought I fixed it months ago, but it must have been a coincidence. The number three cylinder quits randomly. The cylinder will refuse to ignite for several minutes and then randomly it will start running again. It does not matter what type of throttle input I give it.

When the engine is missing I pulled each plug wire. When I pull #3 no difference is noticed. If I pull #1 or #2 the engine quits. I installed brand new spark plugs. Next, I swapped #1 and #3 coil and plug wires. The dead cylinder did not move when I swapped the components. This eliminates the coil and wires. When #3 was not firing I pulled the plug wire and put a spare spark plug in it. I held the jacket of the sparkplug to the nearest ground ( some nut ). It was firing.

Perhaps the quality of spark is my issue. The spark on all three cylinders looks yellow and smallish. Could a failing ignition pickup be causing this? I don't know what to do next. If the #3 carb was fouled I would expect the problem to be consistent, not random.

Please help!

jimmyj900

A weak yellow spark on all three cylinders points toward a problem within the ignition system that's common to all three cylinders -- low voltage to the igniter, internal igniter failure or failure of all three coils.

If you've had all the coils out at the same time or replaced them with Nology coils, it's possible you've reversed the coil leads -- the red wire should go to the terminal farthest from the frame. Reversing the leads can cause a weak spark.

I'd say the highest probability would be a weak battery or dirty/corroded battery terminals. Clean and grease the terminals, check the fluid, charge the battery and see if the problem clears up.

Check the battery voltage with the ignition off and again with the ignition on and the engine not running. If there's a significant voltage drop the battery may be on it's way to the recycling yard.

Disconnect the igniter plug and take a close look at the terminals. You could have a corroded or burnt connector pin.

I doubt a failing ignition pickup is the problem. Since the pickup coil output is processed by the igniter electronics the igniter should shut down if the pickup signal is weak or intermittant.

Anyhow, check the above and get back to us.

Jim

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Cuppa500

I hesitate to say this. I've said it before when everyone else was saying 'coils' & in that instance it *was* coils.....but humour me.

Next time this happens get to a compressed air supply. Turn off fuel tap, & open up & gently blow air up each carb drain plug. (You need a long allen key, 3mm I think, & a bit of plastic tubing helps) This won't fix the problem but it may well get you home. I would suggest that if you try this & find that the 'interval' between misfing episodes is increased, it is indicative of a partial fuel blockage.
This occurred on my T'bird. Randomly misfiring/dying on one cylinder (Left -hand one IIRC). Leave it a minute or two & it started right up again, . Next 'episode' could be in 1km or 40km.

Blowing with the airline just 'mixed up' settled sediment, temporarily restoring flow.
When I stripped the carbs there was a *little* sediment in each bowl, but the real culprit was the hidden in-line fuel filter *inside* the fuel line behind the carbs. It takes *very little* sediment to lodge here to cause the problem you describe. And yes I did/do also have an aftermarket inline fuel filter fitted. The sediment that got through was extremely fine.

I was suprised that when fuel flow was 'centrally restricted' that each carb/cylinder wasn't 'equally affected', but that's what happened. I also *know* it was the inline fuel filter. First time I cleaned out the carbs/fuel tap/aftermarket inline filter, I didn't know about the 'hidden' one. Put it all back together & problem remained. Cleaned the 'hidden' filter. Problem solved. No misfires for past several thousand kms.

regards
Cuppa

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My girlfriend's father was nice enough to let me use his garage this evening. I hopped on the Legend and promptly drove over. The misfire did not appear on the short nine mile ride to his house.

I stripped the bike down. I previously eliminated the spark plugs, coils, and wires. The coils measured 600, 700, and 700 ohms across the primary contacts. I was receiving battery voltage at the primary leads for each cylinder. Also, the + side of the coil is connected to the green wire with red tracer. This is the case for each coil. The battery is less than one year old. It is a sealed Westco and has been maintained with a Battery Tender. The battery contacts are clean. The battery drops half a volt when the ignition is turned on.

I located the ignition unit. It is mounted on the forward face of the battery box and has a locking connector. The connector consists of three offset rows of contacts. The female and male surfaces were clean and not burnt or melted.

Next, I turned my attention to the fuel filter Cuppa mentioned. It was a real pain. I hate that air box and chamber! After removing the fuel hose I was bewildered. Where was the fuel filter!? Upon further inspection I located it inside the plastic fitting. The filter is a small cone with a white, plastic frame. The filter element is a very fine screen. At the bottom of the cone I found 3mm of dense sediment. I used compressed air and starter fluid to clean the filter.

The misfire usually takes 20 miles to appear. The trip home wasn't long enough to prove that I had solved the problem. I will update you when I am able to take a longer ride.

It was 33F tonight. I can still feel the cold in my legs.

Jimmy and Cuppa, thanks for the suggestions.

Cuppa500

3mm! That's way more than I had. I have my fingers crossed. You did clean the rest of the fuel system (carbs & fuel tap) whilst you were there didn't you? 33 degrees here as well today. Centigrade. :wink:
regards
Cuppa

[ This message was edited by: Cuppa500 on 2006-03-02 00:24 ]

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I confess. Having never taken a carb apart I wasn't ready to do so in a friend's garage. I didn't want to run the risk of not getting the bike back together and out of his garage by the end of the night. I have technical drawings of my carbs. They appear to disassemble quite easily. How far do I have to tear them down in order to inspect and clean them?

Also, the petcock and carbs may require replacement gaskets if I damage them during disassembly. I don't have any spares, yet.

I'll save those chores for a fair day when I'm on my own turf.