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Low torque at midrange revs

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Jaksmart
Newbie
Newbie

Posts : 2

Low torque at midrange revs

Post by Jaksmart on Mon 22 May 2017, 10:15 pm

Hello everyone,

New on the forum. I own a 1996 CB 500 (about 38.000 kilometers on the clock). I bought it six years ago but have (dare I say it) largely ignored the maintenance schedule (except for chain/sprockets, tyres, and engine oil/filters which have been diligently cared for and serviced/replaced when needed...). Since I've never owned or driven any other bikes than my trusty old CB since driving school, I am curious about a particular aspect of the bike that you other CB 500 owners might know a thing or two about. 

When accelerating from, say, 30 km/h in 2nd gear on full throttle, the bike has lots of low-end torque and starts accelerating quite strongly. However, when entering the 5000-6500 rev range, I usually notice quite a dip in power (and a surge in vibration), until it takes off like the spirited little bee it is once more around 7000 rpm (with noticeably less vibration). When I bought the bike, due to Danish license legislation, I had to have a professional mechanic install a 34 hp restriction set (washers in the carbs, matched to the frame and engine number and everything), which was removed (by the same shop) after the mandatory 2 year seniority period. In this low-power setting, the described torque-dip was noticeably more profound than it is now, but I'm wondering if I should be doing something to mend what seems to remain of it. 

Do any of you have similar experiences with your CBs, or is this simply how the engine runs? As a one-horse-kind-of-guy, I wouldn't know. I'm sure carb sync, ignition timing and valve clearance checks are way overdue, but I'm currently trying out some of the easier replacements (air filter, spark plugs etc.) before going into those tasks.

Thanks in advance!
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Jameshambleton
Moderator
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Posts : 1878
Location : Bedale, North Yorkshire

Re: Low torque at midrange revs

Post by Jameshambleton on Mon 22 May 2017, 10:22 pm

The Honda 33bhp restrictor washers also required different size jets so this could be causing your issue. 

There is a power drop about 5500 to 6000 if I remember correctly across all models
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Melitos
Godly
Godly

Posts : 64
Location : Vaasa

Re: Low torque at midrange revs

Post by Melitos on Mon 05 Jun 2017, 7:16 pm

Hi,

My -95 was really unwilling to accelerate at 6krpm full throttle. The bike was running too lean, fixed now with #130 main jets on carbs along with optimisation of induction and exhaust pressure losses. Have a look at your plugs to see if they are too light coloured.

BR,
Antti

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Re: Low torque at midrange revs

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