76 cb750k choking on 1st and 2nd gear

[exultant801]

i am lost.
just bought a really clean 76 cb750k with about 19k miles on it.

after a week or so, i started to notice 1st and second gear were struggling when i shift into them. kinda like when you upshift to soon and  it sputters and struggles a bit, like, say from 1st right to 3rd.

the carbs are spotless and don't seem to be the problem.
a friend replaced the spark plugs and checked the timing and that isn't the problem.

he seems to think its that the spark plug cables are stiff and corroded and that i may need to replace them and the coils...

or it might just need a valve adjustment?

does anyone else have any experience with this kind of issue?

please help

[vern401]

the books on here will give you the specs for the valves. Does it bogg in any of the other gears? If your plug wires are corroded inside then your resistance is high resulting in a week spark. How is the idle? without being in gear and you goose "quickly rev" the throttle does it rev right up and then quickly back down when you let off? You have a mechanical timming advance behind the timming plate the arms on it have been known to rust to the inner shaft stopping it from advansing.

[exultant801]

it bogs on pretty much all the gears at some point if i open it up.
out of gear, it seems to rev back down without issue.

a friend of mine said he went over the timing last week and it was just fine. i will check on that, though.

we are also thinking that the left side feels a bit weaker, like the two cylinders on the left aren't firing as well...would that mean a coil thing?

another friend is sure its a fuel issue. like a fuel-line clogged?

[vern401]

Ok for note I am a backyard mechanic so be Careful with this part!!!!
Warm up the bike some so it does not need the choke and will idle.
Now get a damp cloth, quickly tap the exhaust pipes and try to see if they are all the same temp. They each should steam the water off quickly. If 1 or 2 do not steam and the others do then you have 1 or 2 not firing right. check the plug color.
Make sure the carbs are clean clean. it dies not take much to plug them up. I sugest using an inline fuel filter too. what gap are your points set at? If you do not have a book for it there should be one here on this site for it you can download.

[exultant801]

ok. now when i rev it up in neutral it is not always revving right back down as normal???
and it seems now it is puttering more when i try to open up the throttle all the way in EVERY gear...whatever it is, it seems to be getting worse.

[Re-run]

Could be a few things.
First, what color are your plugs? If your a/f mix is too lean or rich, you can lose power when in gear as there is a load that does not exist in neutral.
If rpm does not drop properly, your manifold boots may have an air leak. spray wd-40 around both ends of each boot and listen for changes.
pull the airbox off and make sure your choke opens and closes all the way.
What filter do you have in the airbox?
Make sure the vent in your gas cap is clear and not creating a bit of vacuum.

[vern401]

Yes Re-Run is correct like normal. Check the color of your plugs they tell you allot about what the bike is doing. Check the intake boots and vacuume lines for leake with WD-40 or carb cleaner.
It does sound like you need a good carb cleaning. It sounds like there is something in the high speed port in one or more of your carbs. While cleaning them inspect the float needles closely. Make sure all the floats are at the right height. You should not have CV carbs on a 76 so holes in the diaphrams are not it.
That should be the rev up problem.
The rev down problem could be a vacuume leak or one of the carbs a little out of sync.
the sync should be done with the valves set to the right clearance and clean carbs.