hey guys i have a 1978 honda cb250 t dream and im having bother with it wen i change into 3rd 4t and 5th gear i cant go above 5000rpm. the timing is set perfectly and it still wont play ball any1 know chat can cause this
2007-06-30 02:52:58 · 8 answers · asked by Anonymous in Cars & Transportation ➔ Motorcycles
Not being able to spell?
2007-06-30 11:22:50 · answer #1 · answered by MIKEnJAPAN 5 · 0⤊ 0⤋
I think this has vacuum carbs - the ones with the big chrome tops (possibly a screw at each corner). If I'm right then it might be the carb diaphragm, which is under this cover. If I'm wrong then ignore the rest of this answer.
The diaphragms need not to have holes in them. With time they will get a tiny perforation - then the card stops working because the slide can't rise (it's pulled up by vacuum, not by the cable).
It's a very easy job to replace them, and they used to be quite cheap. It's fairly obvious what to do. I'd look at both diaphragms. If you can see an obvious hole then change that one. If you can't, it might just be too small. Buy one diaphragm and try it in each carb. I'd be surprised if both went at once, but it's possible.
Good luck.
Keep everything spotlessly clean, and be gentle with all parts. Normal care will be fine.
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Some time later.....
Assuming you've checked all the usual service stuff....
If the carbs on your bike are NOT vacuum carbs but have sliders that are both pulled by cable then there may be a cable problem. Look in the back of both carbs by just removing the wide rubber hose that connects to the card air intake (the engine does not need to be running). Look down each carb body as you operate the throttle - do both slides move up and down as you move the throttle? If only one moves properly then the problem is with the part of the cable going to that carb. I seem to recall there's a cable divider under the tank - a small black cylinder where the single throttle cable is divided into two - one for each carb.
If there is a single cable operating a solid mechanical linkage then forget the above.
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yet more thoughts....
The valve clearances on this are set with small screws and locknuts. Are the gaps okay - not too tight / loose? On higher mileage machines you can get small indentations in the tops of the valve stems that the feeler gauge goes over the top of. So the actual gap gets set too big (the thickness of the gauge, plus the depth of the dip). That aside - if the gaps are too big you'll hear rattling at the top end. If they are too tight then the valves will not fully close and you'll get loss of power (then burnt valves if it goes on too long).
2007-06-30 11:00:16 · answer #2 · answered by philipscown 6 · 0⤊ 0⤋
Fuel starvation.Check your petcock to see if it is working properly.Put in new plugs and clean you air filter.There is only 3 things a bike need to run,fuel,air,and spark,check all of these.
2007-06-30 10:07:02 · answer #3 · answered by tconroy 2 · 0⤊ 0⤋
Might be time for an engine rebuild.
Cylinder bore, piston & rings.
Check the compression.
2007-06-30 18:14:09 · answer #4 · answered by guardrailjim 7 · 0⤊ 0⤋
all of the above plus check your ht leads. all ways start with plugs first
2007-07-02 03:25:21 · answer #5 · answered by peter s 2 · 0⤊ 0⤋
i woild check it again and make sure your spark plugs are in correctly
2007-06-30 12:29:04 · answer #6 · answered by salsa 2 · 0⤊ 1⤋
have you checked air filter is clean
2007-06-30 11:27:15 · answer #7 · answered by mikebsa 1 · 1⤊ 1⤋
have you put the right spark plug in it.
2007-06-30 10:01:27 · answer #8 · answered by peter p 5 · 0⤊ 2⤋