Topic: cb750k2 won't start - any help appreciated

[birdy]

Hi.
Battery fully charged, turns starter easily at first, then slower with repeated tries.
Also doesn't start on kicks (many).
Fuel flowing through from tank OK.No overflow from carbs.
Looks like poor quality spark though?
Any ideas- what should I replace first.
Ta

[Johnie]

Sounds like a bad battery to me. With a fully charged and good battery, repeated tries on the starter should not produce a slower starter. Weak spark...bad battery. You could be showing 12 volts on a tester but the battery is producing low amps. I would start with a fresh battery and go from there. Can you give us some history on the bike?

[mystic_1]

Need more history.  When was bike run last?  What work was recently performed, if any?  Has the bike been sitting a long time?  How did you gauge the "poor quality spark"?  Done a tune-up yet?

mystic_1

[greenjeans]

go though the usual tune-up while you're at it.

Set your valve clearance.
check your points, if they've been sitting they can oxidize.
set the timing.
check that battery - it could be as simple as that.
Check your spark - take out a plug and see what the spark looks like - I had to replace my coils - you should have a visible fat blue spark
New coils will show a noticeable to the naked eye spark vs old/bad coils

Still, if stored properly, it should fire up pretty easily.

[birdy]

Thanks for the replies so far guys.
Charged battery and previous owner advised to turn the idle screw up a bit from cold. Got it started on kick as starter  went sluggish again.
Started up finally, ran on fast idle so took to the road! Was reluctant to rev under load whilst riding (revved OK on the side stand though), then revved less and less until it finally died and refused to start even on kicking over.
It did start again on the push back on kicking over again, but wouldn't rev at all; stopped and then wouldn't re-start.
History - previous owner said he did points, gap on plugs OK, rebuilt and balanced carbs.

Will a new battery sort it? If so what do you recommend

PS the bike is missing the bottom metal lug for the side panel - David Silver advised they don't sell as a part- doesn't look like it should have come seperate- any ideas on this?

Ta

[Old75_ratafe]

Did it ever sit for any length of time after the rebuild... say over the winter without draining the bowls?

[birdy]

Previous owner has said he had it in fairly regular use, but I'll try draining the bowls. Does each carb have it's own drain point?

[Johnie]

Previous owner has said he had it in fairly regular use, but I'll try draining the bowls. Does each carb have it's own drain point?

Yes, the screw on the bottom of the bowl.

[rm56]

Gas will turn to varnish in about 90 days. If the last guy let it sit all winter without draining the carbs before storing it you will need to take them off, disasemble them, and clean them out. If a shot of ether makes it fire up then die, then you have a fuel delivery problem. My 74 has been sitting for months because I'm getting some part recromed. I pulled the battery and ran it out of gas in the garage first. Never park a bike for months with gas in the system, just causes trouble. Some use Stabil, I use it a little, keeps the gas from going stale. Causes a small amount of smoke but wont hurt the engine. Good luck.

[birdy]

Thanks so far.. I've drained 2 carbs, but middle 2 are a bit tricky as the screwdriver slots are a bit damaged.
The bike has started and revved up fine in neutral ( see previous mails on this subject). It's now a problem of failing when out on the road as I've since described.
I'll keep trying the middle 2 anyway, and have a new battery on order.