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Discussion Starter #1
When accelerating hard, my stock 2004 T100 runs well up to about 4000 rpm, then, like a switch was turned, the power drops and a vibration (engine miss?) starts. This occurs most frequently when going up hill or into a strong headwind. Typical scenario -- on I-80 headed up Parley's canyon, 5%-6% climb. Change lanes to pass truck and open throttle fully at 3000-3500 rpm in 4th or 5th gear. Bike accelerates to just past 4000 rpm and then the rate of acceleration suddenly drops noticeably and I feel a slight vibration in foot pegs and bars.

The vibration does not occur going downhill at similar speeds/rpm's so I think I'm feeling an engine miss.

I'm a poor mechanic, but I'm guessing this sounds like an electrical problem and I should start by replacing plugs, wires, and coil.

Would anyone care to offer other suggestions?

Thanks.
 

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Discussion Starter #3
I appreciate the thought.

Would the fact that my problem is rpm dependent, rather than speed related, seem to point away from the breather problem? 4000 rpm in 4th is quite a different speed than 4000 rpm in 5th, yet the affect is the same.
 

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Clearly a load-dependent issue...roll ons downhill at 4000 rpms not an issue, but uphill are an issue. Makes me wonder if your clutch is slipping under high load conditions...but that should be worse at low rpms when you whack open the throttle. Does it do the same thing when you knock it down a cog and run the revs up? IMHO, rolling on full throttle at 3000 to 3500 isn't optimal...I generally keep the rpms up more than that or downshift to get her up into the powerband.

I'd start by checking to see if your carb's float levels are correct/that silly vent tube is tucked away since the bike sounds like its fuel starving a bit under demand. Or possibly if the air filter is overly dirty. Or maybe you've developed a small vacuum leak...check your vacuum caps on the intake manifolds. The diaphragm on one of the carbs could also be starting to go south and not lifting the slide as well as it used to...the increased vibrations point to your carbs going out of sync/one side is working harder than the other. This would point to differences in slide lift one side to the other (vacuum leak on one carb) or fuel starvation on one side (float level out of whack).

Regards,

---Rich
 

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A sun scope and a dyno this would be solved in about 5 mins.

CV carbs are tricky SOB's.

Stock air filter still in place? Could be dirtied up. If the air filter is stock and clean, remove it and make the same run. If your bike runs worse you are running lean, if it runs better, it was running rich. If you seem to notice no change, then you are most likely looking at electrical.

How many miles are on the bike?
 

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I'd do what Rich suggested. Almost all of it is visually easy to inspect.

Did your bike sit for any length of time? (even as little as 3-4 weeks?) Maybe while you are checking the things Rich suggested (diaphragms, etc) pop out your main jets and have a look. Take something like a small paperclip and gently make sure there's nothing gumming them up, careful not to gouge the soft brass that the jets are made of. The main reason I was thinking jets is that your problem seems to be more at WOT. Also, have you checked your fuel filters? It does sound like it's starving for fuel, as Rich pointed out. And maybe look out for any unusual amount of trash in the bowls. (unusual=more than a tiny bit)

I'd look into what he said about the vibes. Definitely sounds as if the problem is in one carb. (in other words, make sure you rip into both carbs)
 

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Discussion Starter #7
Thanks for all of the tips. I will certainly check out what you all have suggested but I struggle to think it's carburetor or fuel related because the power drops like a switch was flipped. I actually can feel myself lurch slightly forward when it happens from the sudden decrease in acceleration. (not total loss of power, but a slowing in the rate of acceleration)
 

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Thanks for all of the tips. I will certainly check out what you all have suggested but I struggle to think it's carburetor or fuel related because the power drops like a switch was flipped. I actually can feel myself lurch slightly forward when it happens from the sudden decrease in acceleration. (not total loss of power, but a slowing in the rate of acceleration)
Don't be fooled by that feeling. I chased what I would have bet my life on as being electrical with a set of CV carbs and it turns out the air filter was slightly over oiled.

It would get to 4G at over 1/4 throttle and she'd pop and spit and fall all over itself. I pulled the air filter out on the side of the road, made another pass, hung the tire in first, popped it in second and third as it kept revving past 9500 faster than I could bat an eye...This was on my GS1100 of course. I had changed coils, traced wires, looked at pick ups, replaced ignition modules and it turned out to be an air filter.

Food for thought.
 

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I had the exact same issue with my 1970 Triumph Bonneville. I accelerate in any gear and when I reached 4000RPM, the engine would start to misfire. When continuing to accelerate, at about 4500RPM the misfire ended and the engine ran smoothly when running over about 4500RPM. After struggling with over carb tuning and replacing the stock ignition with electronic ignition, the problem continued and actually got worse. The solution ended up being a $3 ignition plug wire cap. The bike runs perfectly now!
 
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