Mystery 1980 Honda CB750ka

[nielsva]

Hello everyone! New to the forum, i already found some interesting info here but appearantly nothing that suits this problem:

As I said a 1980 Honda CB750ka with VB52A(B) carbs.. I will tell the whole story later but this is summoning up the problem. If i start it up it runs at 2500rpm, after 10 seconds of idling it revs up to about 4-5k. We changed the spark plugs and coils, and tested them and they work. I think the problem is the float height: the floats are non-adjustable and were hanging at the bottom (carb upside down) so I bought a set of new float needles off louis.de, a german website, and put them in. I measured the height and it was too high, at about 20mm instead of 15,5. So i fugered they weren't the right needles. So I went to the official honda dealer and bought 1 new needle for this type of carb. I put it in and this time the height was about 10mm, so too low.

I examined the needles and the previous one is the same as the last one I bought, but still the height isn't right. How can I fix this? I'm still not pretty sure this is the problem.

Hope you guys can help me?

Thanks in advance,
Nielsva
Belgium

[seestheday]

Can you send pics?  Not of just the carbs, I'm interested in the whole bike - but pics of the carbs will help with diagnosing the issue.

Is the KA a German model?  I have an 81K in Canada, and I've heard of the KZ being sold in the UK, but I've never seen a KA.

[Larry spillman]

If your carb floats are adjustable you can bend tap that contacts needles and adjust floats height that way some times a high rev for no reason is a VACUUM LEAK

[cdaiscool]

Non-adjustable, not sure exactly what you're doing to measure 'em. Show us?

Meanwhile, a high idle could be from your idle screw too far in. Could also be your choke isn't releasing, or a vacuum leak, or excess fuel getting in there/not tuned properly.

When did it start? What other work was done when this showed up?