Idle issues

[Wenman]

I know this may be a vaugue question but I am experiencing idle issues. I have a cb550 and have completed a top end rebuild replacing all gaskets, purchased a set of completely overhauled carbs from carburettor Keith in Oregon which were jetted at 100 mains 40 idles, synced and bench tested with a 'bolt on and go' promise! Static timing is adjusted spot on, valve clearances done new plugs etc.
It starts and runs up through the rpms fine however for it to start and run in this manner I need the choke on at 20% all the time?? Idle/air screws turned out 1 revolution!
The engine is running very hot too, after a 10 minute slow ride I cannot touch the rocker cover at all as it will scold my hand and could prob cook my breakfast on it?
The project is almost complete I'm just trying to resolve this problem so I can enjoy the fruits of my labour!!
Please help!!

[philgresty]

Have you vacuum synced them whilst on the bike? that usually helps to smooth out the idle, bench syncing them gets it close but it needs to be done on the bike really. I would double check all the valve clearences, vacuum sync and see how it is then.
Phil

[JamesH]

Sounds like you're running lean. Check your inlet rubbers (carb to head) for air leaks...

[Wenman]

Thanks for your comments so far! Haven't had them vacuum synced in the bike yet so will look into that, a friend has a vacuum sync device so I'll borrow it hopefully it's not too difficult to do myself??
Also has original rubbers between carb and head, nothing obvious apart from what looks like surface cracks, wonder if replacing these would be be worth while anyway?

[JamesH]

Definitely replace the head to carb rubbers and my advice is use genuine honda parts not repro. Also try to use the original clamps. Get vacuum synced and report back.

[Wenman]

The only stockist of genuine inlet rubbers hasn't any in stock.. although they do have aftermarket ones? Is there that much difference? Should I hold out for oem?

[K2-K6]

I'd stay well away from syncing the carbs for now. If as James suggested it's got an air leak, then syncing will do nothing but put error onto your carb setup.
If it's leaking air into the engine after the carbs have metered out the fuel, then it will run lean and no amount of syncing will correct it. Air leaking in has no fuel added to it, you have to make sure you've got no leaks first.

If you just want to add fuel to make it run better while you do further diagnosis, then consider lifting the needles one notch to help avoid over heating. Get the engine warm and while ticking over spray something like wd40 onto the intake rubbers, if you get a change in rpm then it proves it's sucking unmetered air in through those carb mounts.

Syncing really is the icing on the cake IF everything else is confirmed as correct first.

[totty]

+1 for the leak test, but also test the seal between the manifold and the head as one of those o-rings might have failed.

[philgresty]

the inlet o rings are the same as the tappet cover o rings, if they are easier to get hold of?

[Wenman]

I assume by replacing the head to carb rubbers you mean the boots that actually connect the carbs to the head via the two jubilee type clips per boot. I've already replaced the rubber Oring seal at the inlet manifold!!??

[philgresty]

In that case spray some starter fluid around all carb to head rubbers and where the manifold bolts to the head to see if theres a leak anywhere. Sometimes the carb rubbers can be overtightened, pinching them and allowing a tiny gap

[K2-K6]

Be careful with flamms / volatile liquids around it in case it goes wrong. Don't do it in a garage and have some means of extinguisher available.

Some people use brake cleaner or carb cleaner to do this and some brands have acetone in them, obvious risks to paint and plastics.

[Wenman]

So rather than mess around trying to discover any potential air leaks I've decided to order new rubber boots (genuine oem). This will mean carbs to head everything new!!
Professionally rebuilt carbs, balanced and synced on test motor, new boots with original clips, new manifold o'rings at the inlet manifold! This will hopefully mean no leaks! I can then put the balancer on and check there synced correct! Fingers crossed once the boots are changed the problem will be solved! I've added a pic of the carbs if anyone is thinking of ordering from this guy I highly recommend!!

[Johnwebley]

lovely pic of the carbs,

 I notice you have non-standard filters,do they have internal bell mouths? some times carbs need a bell mouth to smooth the intake air flow,

 I hope others here can explain more,and better

[Wenman]

I hope someone else can explain too as I have no idea what a bell mouth is?
Waiting patiently.....