still problems with rear cylinder carb ?????

[Darren69]

if the bike will not idle but otherwise runs ok, then the problem is most likely to be in the idle circuit or something related to that like floats or the actual fuel supply, which I think you've checked both and is ok?

[Mr Gazza]

Jerry just because the floats and valves are new doesn't guarantee they are going to work perfectly. Since the float bowls are not transparent there is no way (that I know of) to check that you have a steady flow of fuel and a consistent fuel level.
I would swap all the float assemblies over into opposite carbs and see if the problem swapped sides or even disappeared. Rather than put a completely different set of carbs on.
A Norfolk member who's name escapes me atm had similar problems to yourself on a 750, it was down to a sticky float or valve in the end, even though all the parts looked good and the float heights were correct.
It's only going to take a little interruption to supply on idle to mess up the pilot circuit.

I have known for gaskets to snag the float on some carbs, but those plastic floats are quite complicated mouldings, so a little bit of plastic flash could rub enough to fek things up.

That's the area I would be looking anyway. If it draws another blank then I might send you a packet of straws to clutch.

[utopia]

Originally Posted by jerry

I rechecked the valves and shims also ran compression test both cylinders 115psi

A bit of a red herring here from me because I don't think it has any logical connection to your current problem, but ...
I happened to be reading an old thread of yours where you previously did a compression test on one of your 750s.
After initially getting low readings due to a leaky o-ring seal, you ended up recording 148psi on both cylinders.
Your recent readings of 115psi seem rather low in comparison.

However, since the readings from both cylinders are the same then it probably throws no light on your current problem.
Sorry that's not very helpful.

A couple of other thoughts ....
1) It seems unlikely that it would only affect running at low revs but is it worth checking for a leaky diaphragm ? I only mention it because it seems to be one of the few remaining areas that you haven't either checked or replaced.
2) Is there any chance that this is a problem of fuel delivery TO the carbs .. eg a faulty fuel pump ? I can't rationalise why this might affect only one cylinder though. But if you have one of those temporary fuel "tanks" which you hang above the bike, you could try running the bike from this (ie eliminate the fuel pump from the system) and see whether it makes any difference. As said earlier, I can't see why it should but if you've already tested the most obvious areas then maybe its worth investigating the less likely ones.

[Darren69]

It would appear to be a fuel supply issue but since it runs ok except tickover it would appear to be in the idle circuit. Pilot and main jet work ok from what I can tell. From 4k on it runs ok?

Have you tried winding the idle adjuster for that carb out incrementally (say half a turn each time) while the bike is running to see if that has any affect? Could be blocked or partially blocked with crud because due to the cleaning process it could still be blocked as even ultrasonic cleaning isn't guaranteed to clear everything. It can for example cause sedimentation.

[350TSS]

^^^^ I agree with Darren69 above

[Darren69]

It's got to be something along those lines. When i built my Laverda I had found some schematic cutaway diagrams for the Dell Orto carbs that showed the internal passage ways and how it all worked, fuel/air flow etc, complicated in that case by the accelerator pumps that they have, but CV's are usually more straightforward i think as there is a lot less stuff to adjust.

[ibduke]

If your not sorted, I have a pair of mikuni off a 600 you could try. if you want to pick them up from Preston

[jerry]

Originally Posted by Darren69

It would appear to be a fuel supply issue but since it runs ok except tickover it would appear to be in the idle circuit. Pilot and main jet work ok from what I can tell. From 4k on it runs ok?

Have you tried winding the idle adjuster for that carb out incrementally (say half a turn each time) while the bike is running to see if that has any affect? Could be blocked or partially blocked with crud because due to the cleaning process it could still be blocked as even ultrasonic cleaning isn't guaranteed to clear everything. It can for example cause sedimentation.

Having had this one carb apart so many times I have put fuel and carb cleaner in every hole of the pilot circuit including the ones under the internal bung the fluid always dissapears down the holes and comes out the other end of the circuit and same with pilot screw so no blockages anywhere ... but in action the pilot screw does bugger all in or 6 turns out no change ? and that is with new parts

[motomartin11]

Not directly relevant but 12 months ago I was having similar issues with my '95 MY CBR600 Keihans .My mate who is a very experienced bike mechanic totally stripped rebuilt them several times. I even collected the bike and on the way home it began to run badly again. So it went back and in the end despite all the work he had done (and believe me it was loads- photos emailed on a regular basis) which included ultrasonically cleaning he had to approach a trade contact (NRP Diaphrams) who owed him a favour and they supplied a tried and tested used set which once bolted on were fine. I was told no amount of cleaning would get rid of the PLASTIC based connectors which joined the set of 4 individual carbs as a unit.Not sure if this would translate to the Mikunis used on our bikes but I thought I would post just in case it helps.

[Pedro]

You’ve changed most of the electrical elements but could it be the flywheel pick ups misbehaving?

[ibduke]

on idle slowly put you fingers across the air inlet, it should induce fuel. if it speeds up and starts running on two cylinders there's still a problem on fuel delivery. restrict the air flow like your pulling the choke with a strangler flap on it............maybe you never know.

[Darren69]

I've run out of ideas.Maybe you've tried compressed air already?

[jerry]

Maybe i should try fire or a shotgun to clean the carb out ...kill or cure

[Darren69]

some dynamite? Maybe you could try a more aggressive solvent, if you have access to something industrial strength?

[jerry]

Originally Posted by Darren69

some dynamite? Maybe you could try a more aggressive solvent, if you have access to something industrial strength?

Sulphuric acid available when I get rid of local councillors