Cota 247 Mikuni

[keychange]

Hekto

This is spraying out a lot of fuel - onto rear fender which then drips to the floor and it is doing it at say 2000 rpm + - as it won't idle.

But you could be on the money I hadn't considered the choke system being faulty - I will have a look and see if I can see any problem there .... not sure how it works. I did pull it apart and cleaned it - just a small piston as you say.

It is certainly loading up the crank with fuel but I think that is the result not the cause of the problem - I can leave the plug out overnight to let it dry out and the problems still exists from cold start.

One other maybe important point ... when I turn the fuel tap off and let it run the spraying stops and for that short period the engine runs much better.. this would appear to confirm that its not the o-ring and very likely could be choke .,... I'll let you know.

Thanks

[keychange]

I made a small rubber seal to block the choke and can now count that out of the equation.

I think this is important - once fuel is switched off and the bowl starts to empty everything runs better - is the problem is float level however there are some issues confounding me:

the fuel isn't coming out the overflow - could this be affected by the 10 degree incline - or is too high but not high enough to flood

I know how to measure the level and it is set spot on according to what I have read ie: 15-17mm from gasket indent to tang touching needle

I guess not being certain of the model number doesn't help..

Edited November 10, 2010 by keychange

[hekto]

I made a small rubber seal to block the choke and can now count that out of the equation.

I think this is important - once fuel is switched off and the bowl starts to empty everything runs better - is the problem is float level however there are some issues confounding me:

the fuel isn't coming out the overflow - could this be affected by the 10 degree incline - or is too high but not high enough to flood

I know how to measure the level and it is set spot on according to what I have read ie: 15-17mm from gasket indent to tang touching needle

I guess not being certain of the model number doesn't help..

The float level is important. Too low and it will not pick up. Too high and it will give too much fuel. It doesn't necessarily have overflow.

When you switch off the fuel and the bowl run empty it will on a certain point deliver the correct mixture - but it only indicates that the fuel mixture is too rich. Nearly all engines will rev up for a second when the bowl runs empty.

If not it's the choke and if the float level is correct you may turn to the needle valve. Maybe that is fouled up and doesn't move freely or it even may be worn out.

[keychange]

Hekto

The improved running on fuel off isn't just at the last gasp - it will run for a minute or more - then if I fuel on and off again it will start to splurt as soon as the fuel enters then runs well as the fuel runs down. To me really suggests float level but it is set right - could it be the 10% incline towards the front (engine inlet) putting the level off just enough to muck it up. Only one way to find out ... crikey these things must be finicky about fuel level!!!

Edited November 11, 2010 by keychange

[hekto]

Hekto

The improved running on fuel off isn't just at the last gasp - it will run for a minute or more - then if I fuel on and off again it will start to splurt as soon as the fuel enters then runs well as the fuel runs down. To me really suggests float level but it is set right - could it be the 10% incline towards the front (engine inlet) putting the level off just enough to muck it up. Only one way to find out ... crikey these things must be finicky about fuel level!!!

It could be the float hight. Certainly.

On my old Ducati both carburators at tilted forwards. They run with the standard float hight, and there are no recommended modifications from that.

Somewhere there must be a specification of the float hight on the Mikuni

[keychange]

Fitted a 150 main and 30 pilot and it was worse - would only run with throttle wide open and fuel spraying everywhere out the back.

I refitted the Amal - it may not be perfect but at least I can ride it with Amal. I haven't given up as I know it can run fine with a Mikuni so will keep my eye out for another one and try again one day.

Thanks for your suggestions everyone.

[keychange]

Once again reconsidering the Mikuni option - I read this in an article today "Throttle slides are quite expensive now, so if you don't have an assortment of them, you can use the "gas shut-off method" instead. With the engine running, turn off the fuel petcocks. If, as the engine gradually drains the fuel bowls, the roll-on response improves, you know the slide was too rich. Engines are often very sensitive to slide cut-away, down to 1/2 a cut-away number. If money is important, you can make a slide leaner by filling the cut-away (the raised entrance side of the slide) higher. If you try to make it richer, remember that this drops the needle by the same amount. "

The "gas shut-off method" symptoms he describes are exactly what I described in a earlier post. Does anyone have experience in re-cutting the cutaway? .... if I stuff it up - it only cost me $30 for the carbie so what the hell?

Edited January 25, 2011 by keychange

[keychange]

Well took 1mm off to 2.5 (or 3.5mm from base)and no improvement - bogs down and sprays serious fuel out the air intake then as described above bahaves nicely once fuel is turned off ie: for a few minutes. The AMAL slide is a 3.5 but is that 3.5mm from base or 4.5mm from base as in the Mikuni - or is it 3.5 x 1/16 inch which would = 5.5mm ( from base or from 1.0mm above base... too confusing)

Yet again stuck AMAL back on and went for a ride