Combustion Theory- Triumph Trophy- parsley1938

[Aquaduct]

Couple more days riding the wayward Triumph Trophy, some observations and possible conclusions.

Friend of mine says that State-side Triumphs are set up lean for 1% CO. UK Trophy's are 2.5-3% CO, not as lean, but still pretty lean. Mixture screws are sealed, so good luck messing with that (well beyond the ken of my mechanical experience).

Riding in the morning, 37-40 deg F (3-4 deg C), without the choke it bucks wildly at 60-75 mph. Prodigious amounts of choke make it tolerable.

In the evenings, 60 deg F (15 deg C), I can get the choke off if I stay above 75-80 mph (4500 rpm). About 70 mph (4000 rpm) the bucking comes back.

Almost impossible to maintain idle under any circumstances.

Hasn't been consistently warmer than that yet, but it seems to run OK when warmer.

So my theory is that a lean mix combined with cold intake temps, light loads, and weak spark is causing missing. To address it, I need to wring out the ignition system.

And that is the difficult part. I'll try to get a wire resistance spec out of the dealer, but after that I don't have any good ideas to diagnose weak spark and trace it to a component. Any good ideas? May just have to throw on coils and wires. Plugs are relatively new, but if I get into the rest, I'll do those too.

So, any comments?

[Quick 350]

Getting to the sealed mixture screws isn't hard at all.

When you put on an aftermarket exhaust you need to install a jet kit in the carbs.

One of the things need to be done at the time of jet replacement is drilling out the set screw plugs with a 1/8" or smaller drill bit.

Your only going in a 1/16" or so just to get through the plug.

Don't ram the drill bit through the plug or you will hit the mixture screw.

The mixture screw does sit back from the plug an 1/8" so chance of hitting it isn't that great.

Just take your time!

Using a self taping screw insert it into the drilled hole.

With a little wiggling use the screw to remove the rest of the plug.

I've done this on many bikes including a Triumph Trophy I installed a jet kit in to.

Good Luck!!!

and post back!

Mike

[Aquaduct]

Well, while calling looking for resistance specs, I ran into a very knowledgable dealer tech in Frederick, MD. He went about looking up the answers to my stupid questions and then we started chatting about my problem.

He said that the ignition systems in these are very Japanese (no Heart of Darkness goofiness anymore) and are usually quite reliable. I told him what was going on and what I've done and he said that because the choke seems to have an effect, he doubted it was electrical. More than likely, I was still missing something in the carbs. His bet was either the idle mixture screws or the pilot circuit.

During the chat he mentioned that he had the factory ignition tester and had an Exhaust Gas Analyzer. I asked him how much he charges and he said it's $70/hr. He said he could run a diagnosis for at most 1 hour and if it were a simple adjustment, that would take care of it. If it turned out to be something else, we could order parts and come back and be sure we nailed it.

His approach was frankly amazing. I've talked to a bunch of other dealer guys who won't tell you squat until they open it. And then all they have to offer is parts swaps until the problem goes away. If this hits, the guy's got a customer for life. And believe me, since he's at least an hour away from both my work and my home, that's no small feat.

So, rather than shooting in the dark at $130 per coil, I'll let him run the diagnostic. It may be nothing much and then I'll spend $70 to know it's been done right. The appointment is next Thursday. I'll keep y'all posted.

[parsley1938]

Wouldnt even know where to start to look for mixture screws, let alone take a drill to them! No change in the performance of mine, starting to get whiplash of the neck with all this bucking about though! Thanks for keeping the info coming, its very much appreciated for those of us with no mechanical knowledge and little money! Dave

[Aquaduct]

Parsley, actually, I think the idle mix screws are exposed. They might be the ones you can see if you look straight in from either side on the bottom of the carburetors. If'n that fixes mine, I'll pass along what was done and how. Perhaps it's just a matter of twisting those screws.

[Gadjet]

Parsley, actually, I think the idle mix screws are exposed. They might be the ones you can see if you look straight in from either side on the bottom of the carburetors. If'n that fixes mine, I'll pass along what was done and how. Perhaps it's just a matter of twisting those screws.

be careful, those might actually be the float bowl drain screws. At least they are on my bike.

[Aquaduct]

be careful, those might actually be the float bowl drain screws. At least they are on my bike.

That's why I'm paying someone who knows what they're doing to turn them!

[TechTMW]

There's no way the screws are exposed unless the bike has POD (Previous owner disease) Idle mix screws have been "Tamper proof" by law since the late 70's.

Your mechanic friend sounds like a real person. Congrats on finding him, and hopefully he lives up to your expectations.