Topic: At a bit of a loss...4000rpm and struggling

[Thunder]

Hi guys

1974 cb740k

I recently completed an engine(valves, skimmed, rings, pistons,gaskets).I also installed the original pipes and airbox with K&N Filter.

Carb jets were checked 110 and 40's. (Standard i presume as they were  the same as other Carbs i got).

She goes fine up until about 4000rpm, then she struggles to go higher, then she seems to wanna go alot better around 6000 (don't wanna take it higher, running in) , is this the "Flat" spot?
I though it was  points, so i replaced em. Same as before.
Cut the plug cables to new wire.
The carbs i took out of a running bike (with pods however), i have done the fuel/Air to one and a half turns out.
I also tested her by dropping the airbox bottom and it didn't seem to make a difference.

She idles a bit rough but it's all good until 4000(smooth), after she just seems to struggle.

Any futher ideas...

Thanks
Thor

[Thunder]

Hi, just to update

I ran her hard and did a plug chop.

 Inspected plug 1 and 4.
1 was dark, almost black
4 was black on one side and nearly white on the other.

Checked with the plugs connected and they are sparking.

thinking it might be a blocked jet, or a couple, as the last time i had the carbs out (yesterday) they had a fair amount on gunk in em from the tank?
Taken the petcock off and re-cleaned the filter(did it yesterday) and it was very clean.

These carbs came off a 4into1 and podded bike, they got 110 and 40 jets, is there anything else i need to check after getting the carbs out?

The bike runs, but the power/running curve is lumpy, and at higher rpm's it struggles.

[scunny]

is your ignition advance moving freely ?

[Thunder]

Heya

Tx mate, you talking about the timing plate?

 If so, i tightened it by the three screws after setting it with the timing light.
Tearing my hair out,as i've gone through the tuning steps. With the plugs different colors i reckon fuel?
I'm thinking taking the carbs and airbox out and checking the carb needle position?, then putting her together with cones/pods just til the gremlins are sorted (easier), or do you think it's spark?
She's lurching along alot worse than my old engine with pods and 4 into 1, i though going standard would be the answer.

Thor

[scunny]

the advance unit is behind the points plate, at about 3000rpm it advances the timing.if it's not advancing, bikey ni likey. you should be abkle to turn the can that the points run on by hand and it should snap back into place when let go

[Terry in Australia]

If it's "lurching" under load Thor, check your float levels mate, they could be too low. Cheers, Terry.

[Thunder]

Terry n Scunny.

Cheers on that , will check the points advance(change em out), and gonna put a different set of carbs in and see if there is a difference.

Shot for the help

I Will update as soon as i have done it