Mikuni Carbs

[Biker Biggles]

I know one or two peeps on here have experience of fuelling and carbs so I thought I'd pick some brains.I'm doing up a 1977 Rickman with a Kwak Z1000 (1015cc) engine and I'm having a carb problem in that the right (as you sit on the bike)carb does not get any fuel.It was running rough and the relevant exhaust wasn't getting hot so I drained the float bowls and this one was totally dry.
Now I am familiar with the usual problem on these carbs where a float sinks and the carb overfills,but why might it not fill up at all?The other three carbs seem to run OK.Any simple suggestions or do I need to take the whole lot off rip them apart?

Originally Posted by Biker Biggles

I know one or two peeps on here have experience of fuelling and carbs so I thought I'd pick some brains.I'm doing up a 1977 Rickman with a Kwak Z1000 (1015cc) engine and I'm having a carb problem in that the right (as you sit on the bike)carb does not get any fuel.It was running rough and the relevant exhaust wasn't getting hot so I drained the float bowls and this one was totally dry.
Now I am familiar with the usual problem on these carbs where a float sinks and the carb overfills,but why might it not fill up at all?The other three carbs seem to run OK.Any simple suggestions or do I need to take the whole lot off rip them apart?

If the float chamber is empty then it seems that either the float is sticking up (and blocking the petrol feed) or the feed pipe assembly is blocked,
John

[Biker Biggles]

Not sure how the float can stick in the up position as gravity should let it drop down with the bowl empty,but a blockage is a possibility.Either between carbs 1 and 2 or in the float valve bit.Looks like it will have to cme apart.

[northwind]

Any chance there's a pinched or damaged hose? I've seen it happen with fuel hoses where they happily stay in a curve until they get older, then they fold.

[Sid Squid]

If it's been unused for a while it's not unknown for the float to move fine but the needle to stick in the seat, if it's the earlier kind with the chrome point and it's a bit worn it's more common, but the rubber nosed needles stick too. Also if I remember those carbs right they have two supply hoses and internal cross feeds between each pair of carbs - a short push fit tube with 'O' rings either end - those can only be accesssed effectively by removing the carbs from the brackets and splitting the carbs apart, as I remember the tubes are quite narrow and could possibly block.

HTH, memory of those carbs is hazy at best.

[Biker Biggles]

Cheers for that.The fuel feed is by twin pipes which join at a Y piece just before it enters the carbs.There is then a set of horizontal short pipes between each carb,which look like the carbs would need to come off their mounting bracket to replace.I'm tending towards the stuck valve in seat though,as it has been standing for some time.Should be obvious with the float bowl off.

Disconnect the fuel feed hose to that carb and try to blow through it. Should indicate if the needle is stuck or there is a blockage in that piece of pipe.

Pete

[Biker Biggles]

Took the carbs off,removed the float bowl and had a look.There was nothing obviously wrong,so I sprayed some carb cleaner around and through the feed pipes,took out the float and valve,and cleaned it all up.Put it all back together and checked that petrol flowed right through the system before putting it all back on the bike.It did,so I put the carbs back on and tried it out.Ran fine.I think it must have been a sticking valae which esponded to being moved about and cleaned up.
Cheers BB.