500 four reluctant to rev

[mickwinf]

out for a ride today and bike was going well mostly, except it doesnt seem to want to rev above about 5000 rpm. A bit of background for anyone who is new to the story of Lazarus the 500 four brought back from the dead. engine has had a full rebuld with rebore and pistons etc with about 200 miles on clock since. after working through a few snags it now runs nicely, carbs were also rebuilt, all standard jets and airbox etc. as i am running in the engine i havnt really given it the beans yet but today tried to accelerate a bit quicker but once at about 5000 rpm it seemed very reluctant to go any higher. there was no missing or spluttering it just would not rev any more. I am wondering if my float hight is wrong? it feels like its not getting enough fuel. any thoughts would be greatfully recieved. oh fuel tap is original honda not a cheap chinese and is clean and clear.

[florence]

are the throttles opening fully?

[neat street]

I would also check fuel flow from the stop cock, could be a build up on the internal filter??

[mickwinf]

Peacock filter is new and cable opening fully.

[Bryanj]

Restricted intake, trousers under seat?

[mickwinf]

All clear under there Bryan.

[mickwinf]

been thinking a bit more about this and looking online for similar problems. when i first got it on the road i had trouble with the vent on the tank cap which is a repro. in normal running it seems fine and rode 25 miles no problem, but what if it is restricting air enough to stop it revving over 5000. problem is if i open the cap at speed fuel will spill all over. thoughts?

[taysidedragon]

been thinking a bit more about this and looking online for similar problems. when i first got it on the road i had trouble with the vent on the tank cap which is a repro. in normal running it seems fine and rode 25 miles no problem, but what if it is restricting air enough to stop it revving over 5000. problem is if i open the cap at speed fuel will spill all over. thoughts?

When the bike won't rev over 5k, stop the bike somewhere safe and then open the fuel cap. If there is any air restriction you may hear the air rushing in. Wait long enough for fuel to fully fill the carb float bowls then close the fuel cap and try to rev the engine. If it still won't rev it's not a fuel cap issue.

[Bryanj]

If it was the cap it will rev with it open or just after starting untill the tank has a partial vacuum.
Q will it rev in any gear over 5000 or never over 5000

[Oddjob]

Just run the engine off a remote tank, that should isolate the tank vent question.

[mickwinf]

Will experiment further thanks for suggestions

[K2-K6]

Usually, when supply gets restricted, the longer it's ridden the worse it effects as float bowls aren't replenished at sufficient rate to fill demand.

Backing off power can then bring them back toward correct level and keep running. 

A plain ceiling that occurs always at 5000 rpm suggests more toward timing of ignition/ cam etc to cap any  advance in higher rpm use.

[exvalvesetdabbler]

If you on a mechanical advanced/retard are the bob weights free to move or get  a strobe light on the timing and watch the advance as revs increase from idle.

Second thing if you can get your finger up the carb inlets and feel that the slides are fully open when the throttle hits the stop.

Regards
Dave

[mickwinf]

I am sure the electrics are good as all new or reconditioned. Might have a bit of time to check in next couple of days.

[nairb]

I put a new after market air filter on my cb550 k3 and it ran very poorly.  For some reason the old genuine honda filter works best.