Jetting advice please

[alanscottj]

My series two rusteration has been running great, Mugello 198 with reed valve, 26mm delay, no filter, starts first kick every time. The only thing that had not been replaced when restoring it was the original petrol tank and tap which means it has been running with the original slow tap. Today I decided to fit a long range tank and a new fast flow tap. I barely made it round the block on the first run out on it tonight! Checked my plug and it was the wettest and oiliest plug I've ever seen! Obviously I was way over jetted before but that was cool due to the slow trickle of the old tap. Anyhow, I've managed to get her running relatively ok, by bringing my main jet down and by raising the needle clip to top spot on the needle.

The only thing I am struggling with is my tick over, when riding when I come off the throttle the engine goes silent like there is no fuel whatsoever getting to it, I have to blip the throttle to keep it going.

Any thoughts?

Many thanks as always

[alanscottj]

Any one?

If I have to turn the tickover screw nearly all the way in does this mean I need a bigger pilot jet???

Ta

[rosscla]

Assuming you mean by 'turning the tickover screw all the way in ' you mean raising the slide this would suggest that it's needing more air to tickover. A bigger pilot would add more fuel. Raising the slide also raises the needle though so you also get more fuel when it's on the needle but if the problem is at low revs then you need to look at the slide / pilot or mixture screw positions.

It might be worth trying a slide with a bigger cutaway. Again you don't say what your current carb settings are so it's difficult to give advice.

I would be surprised if a simple change of tank and tap could cause this unless there's an issue with the needle jet in the float bowl, this could also be worth a look.

[shocky]

Try running it with the choke on at this throttle position if its weak it will help but if its rich it wil almost die also check your choke is actually fully closed , check all your jets are clean I use thin copper wire stands from a cable to "ream" the jet and atomiser holes

[alanscottj]

Assuming you mean by 'turning the tickover screw all the way in ' you mean raising the slide this would suggest that it's needing more air to tickover. A bigger pilot would add more fuel. Raising the slide also raises the needle though so you also get more fuel when it's on the needle but if the problem is at low revs then you need to look at the slide / pilot or mixture screw positions.

It might be worth trying a slide with a bigger cutaway. Again you don't say what your current carb settings are so it's difficult to give advice.

I would be surprised if a simple change of tank and tap could cause this unless there's an issue with the needle jet in the float bowl, this could also be worth a look.

Thanks Rosscla, I'm going to have a play with the air/fuel mixture to day to see if that helps. I'll aso have a look what's in the carb and post them

[alanscottj]

Try running it with the choke on at this throttle position if its weak it will help but if its rich it wil almost die also check your choke is actually fully closed , check all your jets are clean I use thin copper wire stands from a cable to "ream" the jet and atomiser holes

Thanks Shocky, I'll give everything a clean later when I open the carb to see what jets are in there

[alanscottj]

Opened up the mixture screw one turn and she's running much better but still sounds like an airplane powering down when I close the throttle!

[rainbowrunner]

put your needle clip 2nd or 3rd notch down, try it in both positions

[alanscottj]

[quote="rainbowrunner"]put your needle clip 2nd or 3rd notch down, try it in both positions[/quote

Tried this earlier and scoot runs a bit better, but, it is still nearly completed shutting down when I come off the throttle. Going to have another play with the air mixture tomorrow

[nelson pk]

If when you rev it up and you wait for revs to come down it comes down instantly without any firing and then cuts out or really struggles to tick over and your tick over screw is more or less fully wound in and you have tried idle jets in th 48 to 55 range it is likely that your slide is too rich. Delly's normally come with a 40 slide. Check the number and if it is a 40 i would change to a 45. I have found most muggys like a 45 slide especially if running with a filter and not open mouthed. A slide will make a massive difference in the way the bike returns to tick over as a rich slide will create a higher vacuum (more fuel being pulled in) and lean slide will create less vacuum (less fuel being pulled in through jets).
In theory, when your throttle is shut off it should recieve mixture just from mixture screw circuit (first hole nearest the engine side of carb), if you have too much vacuum (slide too rich) you will get more fuel coming from pilot hole (second hole in venturi nearest engine side of carb) and main jet hole (last delivery hole) than engine can cope with.
Only when the throttle is 1/8 open the pilot hole should really start delivering and at about 1/4 or just before main jet hole starts delivering properly.

If it is taking longer than it should to return to tick over and gradually coming down on revs but "holding up" it is too weak and slide/pilot is lean.

Air screws normally run between 1 and 1/2 and 2 and 1/2 turns out.