Triumphrat

tbh9088

I just purchased a '98 TBS, and because the bike is new to me I have no reference to judge whether a noise is normal or something that deserves attention. So, perhaps someone can help me identify my mystery noise.

The bike was dealer-fitted with FCR 39's by the previous owner only 200 miles ago. I understand that the rattle coming from the carbs at idle is normal - and I dig it, actually.

The rattle disappears off idle, but a new noise appears predominantly from the left side of the engine during cruise regardless of rpm range (3500-5500) when the throttle is just over 1/8 or so. It is the exact same pitch as the idle carb rattle and appears to be coming from the carb area, but sounds like a subdued jackhammer. If I open it up to 1/4-1/2 throttle, the noise seems to quiet a bit, but it could be that the intake noise just drowns it out. If I back off the throttle slightly, the volume drops off very quickly until it is inaudible. Onset from first audible to maximum volume is 1/8-3/16 throttle (these are all estimates, of course).

I tend to think this is just carb noise, but I want some assurance that the noise isn't due to something like a lean mixture. It's colder here than when the carbs were installed in the summer, and the idle lopes a bit indicating a slightly lean mixture. But, the bike makes good power, and there is no popping during deceleration that would support my accusations of a mixture problem.

Unfortunately, I'm not skilled enough to tuck my head under the tank to narrow down the source. It is definitley coming from #1 cylinder/carb, though.

1. Could it just be carb noise, or is carb noise only at idle?
2. If the noise was related to mixture, would there be other symptoms as well?

BigAl8295

I have a '99 Legend with FCR-39s. There is a normal rattle from idle to about 4000 rpm. I have been told that it is normal and the carbs are meant to be run at higher rpms.

I do not have any particular sound that only comes from one carb, so I wonder if one is out of sync.

Since you just purchased it, why don't you take it back and have the dealer take a look at it?

I'm sure one of the more experienced guys will chime in.......

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tbh9088

The dealer that installed them is 1200 miles away, so access is limited at best.

Guess I"ll try my hand at synchronizing the carbs and see if that works. I've been wanting to build a balancing rig anyhow. Where are the vacuum ports on the FCRs?

gregp

Your noise may not be carb related at all.
Just to be safe, I would pull the alternator and check the coupling bolt! You can also pull the right side (clutch) cover and inspect the alternator drive bolt that is directly behind the large clutch basket gear (up near the top). If it is broken, like mine was, it will be loose, flopping around, and polished by rubbing up against the clutch basket gear.
The noise you are describing sounds just like the noise that I experienced when my alternator drive bolt broke.
There are lots of threads on this problem here, and I am not sure if the problem was remedied by '98.
If your bolt is broken, there is an upgrade kit available from Triumph for $90 US.