Strange throttle behavior. - Triumph Forum: Triumph Rat Motorcycle Forums
Trophy Trophy 3 & 4 - for all 900 and 1200cc models 1991- 2004

 
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post #1 of 8 (permalink) Old 11-06-2012, 04:37 PM Thread Starter
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Strange throttle behavior.

It doesn't make much sense to have to roll back the throttle to gain acceleration when trying to go WOT, does it?
Meaning, at WOT the acceleration from 60 to 80 mph is somewhat sluggish until I roll back on throttle about 1/4 of a twist. Then it comes alive and pulls hard. It seems I have to feather the throttle to get full acceleration.
Is it a problem or just part of a business of being carburetor-ed bike?

Thanks guys...
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post #2 of 8 (permalink) Old 11-06-2012, 05:27 PM
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This is a classic, classic symptom of a too large main jets. Did you just get the bike by chance? Do you know any history? Unless you've had it for awhile and have not gone to larger jets and the problem just came on. Ask the previous owner about his carburator work.
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post #3 of 8 (permalink) Old 11-06-2012, 06:42 PM Thread Starter
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I've had my 900 for nearly 2 years.
I bought it from dealership. They didn't have any records of repairs/maintenance.
Could it be due K&N filter I've installed last service(about a year ago)?
I filled it with Premium last time to see if there will be difference in performance. IMHO premium is a waste of money...
Could the premium be TOO much for it?
It gets decent MPG, 38 MPG average.
It has decent power on take off. The top speed right where it should be, a healthy number.

I can't take my Trophy out of service for long time because it is my ALL-IN-ONE transportation.

How would I find if my 900 has oversized jets w/o taking carbs apart?
Is there a way ?

Thanks...
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post #4 of 8 (permalink) Old 11-06-2012, 11:23 PM
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Well if your bike has been doing this for the 2 yrs you've owned it, I'm still thinking it could be too large main jets but if it's a recent development I'd look elsewhere. I seriously doubt if too high an octane (or too low for that matter) would cause this. I've heard different stories about K&N filters but don't have any experience with them to say one way or another. K&N filters supposedly flow more air though so if any thing would make wot leaner. I don't have a clue what jets are in your bike stock. You don't have to dismantle the carbs to access the jets, you just have to remove the float bowls, but of course you have to remove the carbs to do that.
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post #5 of 8 (permalink) Old 11-08-2012, 12:45 AM
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Too low octane will cause ping or knock under some circumstances. Too high will cause carbon buildup over time. There's nothing better about "premium," it's just harder to ignite. Usually best to stick with the recommended mid-grade unless you've installed high-compression pistons or a turbo or some other mod that needs higher or lower.

K&Ns flow gobs more air than stock when clean, but let lots of junk through. Gradually, they fill up with said junk, which improves filtering but decreases airflow to about the same level as a stock filter. They definitely add an air of mystery to the proceedings, I'll give them that.

Might be slightly easier to pull the up-side float bowl without pulling the carbs, but only slightly on the Trophy.

Cheers,
-Kit
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post #6 of 8 (permalink) Old 11-08-2012, 01:32 PM
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Another thought on your wot issue is a pin hole in one of carburator's diaphram. Matter of fact I would check that first before Ifool with the jetting, especially if the problem happened rather quickly and wasn't always there from the start of your ownership. I think diaphrams can be checked and changed without taking off carbs.
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post #7 of 8 (permalink) Old 11-08-2012, 03:41 PM Thread Starter
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Great information guys!
It is inevitable I have to down my horse for a time to sort his ailments ...

Cheers!
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post #8 of 8 (permalink) Old 12-28-2012, 01:22 PM
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+1 on checking the diaphragm rubber. Small holes or breaking the seal around the outside edge would definitely attribute your symptoms to this.

Please let us know what the final outcome was, or was it the fact that one header was colder than the other from your other topic?
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