CB550 Tuning Advice

[Neilw]

Could the rubber bits be coming from the rubber sealing washer inside the petcock?

On the auxiliary tank fuel supply ?

I don't know what config is there, but running some fuel i to clear container should show anything not desirable.

I'm using a clear auxiliary tank with a clear pipe.

[K2-K6]

I was wondering if scottly was questioning if there was a petcock on the auxiliary tank, and if that had any parts in it with this potential.

I know some have a metal petcock as others have a simple plastic clamp external to the feed pipe.

[Neilw]

I was wondering if scottly was questioning if there was a petcock on the auxiliary tank, and if that had any parts in it with this potential.

I know some have a metal petcock as others have a simple plastic clamp external to the feed pipe.

Ah, yes, sorry, yes it has a petcock - i'll check that too!

[McCabe-Thiele (Ted)]

I have an online filter on my Auxiliary tank, just in case of contamination from the petrol can, my cans all have rubber type seals on the caps.

Must be very frustrating.

[deltarider]

In general: do not position an auxiliary tank much higher than the bike's own tank. This to prevent floatvalves opening and as a consequence carbs overflowing.

[Neilw]

In general: do not position an auxiliary tank much higher than the bike's own tank. This to prevent floatvalves opening and as a consequence carbs overflowing.

Got that; tried to keep the differential the same.

Got the float heights about right; fuel is settling a few mm below where the float bowl joins the body of the carb.

I've double-checked the drain screws for debris and cleaned them with carb cleaner and compressed air.

Also flushed the carbs through with petrol, and for the most part the fuel is clear. I flushed about a litre of petrol through; there may be two really tiny black bits, which you can barely see with the naked eye. It's as good as I can get it, so accept that perfect doesn't exist, and there will be natural contaminants in fuel that I can't do anything about, but I'm not going to put a filter in at this stage, as the bike as standard didn't have one. Might be a different story when I get to the Tank.

OK, back to bench syncing and sticking them on the bike.

[McCabe-Thiele (Ted)]

It's ironic, when I first started my 500 it ran great, I had treated myself to a new auxillary petrol tank that came with a T piece and pipe.

A few days later just before I was going to fit the tank I started it up again, iirc the pipe had swollen and was a bit sticky to the touch. When I started the engine it ran like a camel and started flooding.

There were black bits off the inside of the pipe in all the bowls. I was so gutted I walked away for a few weeks before I could find the motivation to take the carbs off to strip & clean them again.

That's why I added the Aeroline filters, yes they are not original, they are pretty well hidden under the carbs, you have to look to notice them. I just figured an old bike needs some extra help, probably ott, peace of mind.

When you eventually fix the problem anf post the cause/fix it will be satisfying, sharing here helps us all.

[badger_eng]

From my experience of using the auxiliary tanks that are cheap as chips from all the usual places, the tubing that comes with them is very poor quality. I have my doubts that the tubing is even fuel compatible.

After using the cheap aux tank for my first resto 5 years ago, the tubing had perished within a year.

I replaced with cheap clear polyflo style tubing. Whilst this quickly goes hard / brittle, it does not shed its guts into the carbs like the ‘’rubber’’ variants do.

[deltarider]

It's another advantage of my simple method for checking the fuel levels: by draining the bowls you'll detect any contaminants rightaway. http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647.

[scottly]

Could the rubber bits be coming from the rubber sealing washer inside the petcock?

On the auxiliary tank fuel supply ?

I don't know what config is there, but running some fuel i to clear container should show anything not desirable.

I'm using a clear auxiliary tank with a clear pipe.

Sorry, I missed that an auxiliary tank was being used. I was thinking of the petcock in the stock tank.

[Oddjob]

I think it was a good suggestion either way. We seem to forget the tap uses not only the doughnut seal but orings as well. All could be failing after this amount of time. I’ve already upgraded my 500 petrol tap to all Viton fittings.

Whose to say the next failure could well be the fuel tank cap seal.

[deltarider]

[...]
Whose to say the next failure could well be the fuel tank cap seal.

Mine has been failing for the last 46 years. I don't mind and do not worry about blocked ventilation holes. During hibernation I put some plastic foil in between cap and tank to prevent evaporation.

[Neilw]

Back to tuning, and here's where I need help!

Carbs are back in, connected and good to go. Have the air box carb side fitted, but not connected to the air filter, etc., so air is just passing through unhindered. I have the air screw at 1.5 turns, and the carbs are synced using Bryan's method with the smallest drill bit i had. Less than 1/16th.

Starts on choke and revs up to about 4000rpm.

I start decreasing the choke and revs come down; when I put the choke off, the bike dies on its own.

I repeat the sequence and hold the throttle open as I turn the choke off, and the bike continues to rev at where I'm holding it (but not below about 2000 rpm). The smoke is white for a while, then becomes black when I'm holding it with the choke off.

So in terms of moving forward i can presently keep the bike running by holding the throttle open. I tried adjusting the throttle stop and it wont keep the bike running

Tappets were set, and I have dynamically set the points using a strobe light, so i know that side is as good as it gets.

What are the next steps?

[deltarider]

Just to make sure: when the little chokelever is horizontal the chokeflaps are down (to facilitate cold start), when the lever is vertical the chokeflaps are up (engine warmed up).

[Neilw]

Just to make sure: when the little chokelever is horizontal the chokeflaps are down (to facilitate cold start), when the lever is vertical the chokeflaps are up (engine warmed up).

Good point - i'm calling the choke off when the lever is horizontal ( in this position the butterflies in the carbs are closed) and when it's pressed down i'm calling that on/engaged ( and the butterflies are open/vertical). Kehlin 069a Carbs.

Hmmm sounds like i may have my words back to front - so the bike starts when the choke lever is down i.e off, and dies when it's horizontal i.e on?

Guess that makes a huge difference!