Triumphrat

tbh9088 · 03-30-2009, 01:33 AM

Thought I'd tap the knowledge and experience of the group here to try and resolve a minor engine issue on my '98 TBS. . .

Sorry for being so verbose, but it sometimes saves time to state all the relevant facts up front.

At lower RPMs, the engine is silky smooth. Then, around 3600 rpm, it feels like one cylinder is doing something "different." The engine still seems to pull strong, but there is a definite mechanical pulse (vibration) and an audible exhaust note change from about 3600 rpm and up. The pulse is very regular, like a missing cylinder, but not as severe. It seems to get a little better as the rpms rise above 5,000, but that may be because the pulses are closer together. If I close the throttle and coast down through this rpm range, the engine is again very smooth - so this is only occuring under load (steady cruise and above).

A little background:

To address the problem I decided to perform a quick tune-up by replacing plugs, and cleaning the FCR39s. I also lowered the jet needle clip one notch and adjusted the slow air jet towards lean based on the lightly carbon-fouled condition of the plugs (all plugs looked identical in fouling - no oddballs to indicate one cylinder was doing anything dramatically different). The engine runs even smoother now below 3600 rpm, and pulls stronger, but the higher-rev pulsing is still there.

I noticed that the #3 plug wire doesn't grab the threaded plug post as securely as the other two. Could a poor contact between the plug wire and the plug terminal cause the symptoms described (smooth low rpm operation and pulsing at high rpm)? Wish I had another plug wire to test :\.

Could I also be imagining this? Because cylinders 1 & 3 share a silencer, and cylinder 2 has a dedicated pipe and silencer, could this just be a characteristic of the engine/exhuast setup? Still, the consistent and pronounced change at 3600 rpm leads me to believe otherwise.

Thanks for any input.

Regards,
Bruce

denny · 03-30-2009, 01:48 AM

It could be a coil just beginning to break down.
Have you replaced any of the coils?

Mine did that intermittently for awhile, then a coil failed. after replacing that coil it went away. But other things could cause similar symptoms. Loose plug wire connection is also a good possibility.

Slinky · 03-30-2009, 04:01 AM

There is a "rumble" on these engines around 3500rpm, but only under load. The higher the load, the worse it gets. It is a charaxteristic of these engines.

It may not be what you are describing, but it certainly seems like a strong possibility.

tbh9088 · 03-30-2009, 10:19 AM

I read of the Gill coil issues, and replaced them with Nology when I first bought the bike.

Slinky - that rumble is probably what I'm hearing. I'll embrace the character of the engine and stop worring about it. Thanks!

I will replace the plug wire just to be certain. Anyone know where I can source just one? Seems a huge waste to spend $120 for a set of three when the other two are in great shape.

IrlMike · 03-30-2009, 11:28 AM

Quote:

Originally Posted by tbh9088

I read of the Gill coil issues, and replaced them with Nology when I first bought the bike.

Slinky - that rumble is probably what I'm hearing. I'll embrace the character of the engine and stop worring about it. Thanks!

I will replace the plug wire just to be certain. Anyone know where I can source just one? Seems a huge waste to spend $120 for a set of three when the other two are in great shape.

+1 on the 'rumble'.

I bought my plug wires from Sprint Manufacturing in UK. Helpful enthusiast run outfit, good guys to deal with. Way cheaper than $120 !

http://www.triumphparts.gbr.cc/70231...?p=2&cat=34958

Mike

ssevy · 03-30-2009, 12:04 PM

Also +1 on the rumble. Especially in 5th gear and under load - sort of like a wet dog shaking itself off.

IrlMike · 03-30-2009, 12:50 PM

Quote:

Originally Posted by ssevy

- sort of like a wet dog shaking itself off.

good description!

:

tbh9088 · 03-30-2009, 01:34 PM

In the last 12 hours I've gone from, "what the h3ll is wrong with this?" to, "sweet rumble!"

Thanks, all.

BigAl8295 · 03-30-2009, 05:30 PM

I'm about to pee on your wheaties.

That rumble/hum/harmonic hasn't existed on my bike since I switched to the FCR-39s.

When I had it on my stock setup it would disappear after it got up over 4000 rpm, didn't exist up to 5000 rpm.

Maybe you have something loose.

tbh9088 · 03-30-2009, 06:13 PM

Grrrrr. Loose exhaust, maybe?