Bimota Forum

[luciousesox]

I have an issue with the idle circuit on number 4 carb, can not get it to fire on idle but it is fine when the throttle is turned. It’s been in the ultra sonic cleaner twice now and did get marginally better but still is not right.
If I put my hand over the carb air inlet on number 1,2 or 3 the engine speed decreases but if I do it on number 4 the engine revs higher, this is obviously not correct, does anyone one have any idea on what might be wrong please.

[Bud977]

If the carbs are clean, then I'd be looking at the spark plugs. Try swapping them around and see if the problem follows the plug.

It is unlikely to be the coil as #1 is firing, and both #1 and #4 are fed from the same coil.

[Jonny B Bad]

You don’t say which YB? Sounds like too much air is getting into the idle circuit. I would replace all mixture screw O rings. Where are your mixture screw settings at the moment?
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What, Jonny's gone!

[luciousesox]

Most of the air screws are between 1 1/4 to 1 1/2 turns out. It does not change at all when I turn the screw we in or out on number 4 but as I mention if I open the throttle up it kicks in.
YB9

[Jonny B Bad]

OK, the idle circuit has a small jetting downstream of the throttle butterfly and this is what should keep the engine idling whilst the throttle is closed. A second jetting on the idle circuit is masked by the bottom of the throttle butterfly and feeds extra mixture as the throttle opens but before the needle starts to rise.

It is important that all of the throttle butterflies mask their respective secondary idle jettings at idle. This is done by balancing the carbs, which is effectively moving each butterfly so that it masks the secondary jetting. Have yours been balanced? The mixture screws govern the amount of mixture coming out of the primary idle jetting. So it is important that all of the secondary jettings are masked at idle by balancing the carbs, before setting the mixture screws at the same number of turns out. Otherwise you might be disguising mis-set mixture screws by partly open secondary jettings.

I think it is likely that the throttle butterfly on pot 4 is slightly open and therefore allowing mixture out of the secondary jetting making that pot too rich to run at idle. When you open the throttle it allows more air in, leaning the mixture enough to get it firing. When you put your hand over the inlet you are reducing the negative pressure that is drawing fuel up the pilot jet which is also leaning off the mixture sufficiently to get it to fire.

Hope that's helpful.
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What, Jonny's gone!

[brian]

Even though the carbs have been through an ultrasonic cleaner, you could still have a blockage in the pilot circuit for #4. Double check that the pilot jet is clear. The pilot jets have a VERY small orifice. Also ensure that the galleries in the carb body are clear by blowing compressed air through them
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'99 DB4 #104, '96 SB6 #1165, '94 DB2 J #652, '99 DB4 #088, '08 VTX1800, '93 ZXR750R M1, '95 ZXR750, '95 ZXR750 Race Bike, '94 CBR400rr NC29 Race Bike, '94 CB250, '49 BSA C10 250, '61 BSA A10 650, '89 ZXR750, '91 Ducati 851

[luciousesox]

Thank you for all the help, bike is running nice now, just need to re fit the air box and do a fine tune.
Another 30 mins in the ultra sonic cleaner sorted it out, must have been a small blockage.
On wards and up wards. Still need to sort the brakes out, fit a new speedo and a general good clean and polish. I bought it as a rolling chassis with a big box of bits. MOT and get it registered.

[brian]

[luciousesox]

I’ll get some taken tomorrow, I have the bars and clock mounting off at the moment for a re-spray. The bike is bright Yelliw, not to everyone’s taste but I quite like it.

[luciousesox]

Hi
Stupid question time. I have taken some pictures but have no idea how to get them loaded on this site, any clues would be greatly appreciated
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Bimota YB9, RD500,Z1 1974,Z1 1975, Benelli 750sei, 900sei, GPZ 750 turbo, Rudge super sport, S.O.S, BSA Rkt 3 1969, 1966 Bonnie, Egli Vincent 1954,Guzzi 850T, Commando fastback, Commando Interstate, Enfield Interceptor 69, 72 H2, 69 H1, Suzy Gt750 J

[phil-short]

Sign up to an image hosting site like https://postimages.org/ and upload there. Then copy the *hotlink for forums* that will be under your pics and copy and paste here. Simples... and nice big pics when posted

[luciousesox]

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Bimota YB9, RD500,Z1 1974,Z1 1975, Benelli 750sei, 900sei, GPZ 750 turbo, Rudge super sport, S.O.S, BSA Rkt 3 1969, 1966 Bonnie, Egli Vincent 1954,Guzzi 850T, Commando fastback, Commando Interstate, Enfield Interceptor 69, 72 H2, 69 H1, Suzy Gt750 J

[luciousesox]

https://postimg.cc/4KK2zK1f
https://i.postimg.cc/g049b8XZ/57-BAA578-7-DE1-4297-B45-D-6-A5-EED22-A3-DE.jpg
[57-BAA578-7-DE1-4297-B45-D-6-A5-EED22-A3-DE.jpg](https://postimg.cc/4KK2zK1f)
[](https://postimg.cc/4KK2zK1f)

<a href="https://postimg.cc/4KK2zK1f" target="_blank"><img src="https://i.postimg.cc/4KK2zK1f/57-BAA578-7-DE1-4297-B45-D-6-A5-EED22-A3-DE.jpg" alt="57-BAA578-7-DE1-4297-B45-D-6-A5-EED22-A3-DE"/></a>


<a href="https://postimg.cc/4KK2zK1f" target="_blank"><img src="https://i.postimg.cc/g049b8XZ/57-BAA578-7-DE1-4297-B45-D-6-A5-EED22-A3-DE.jpg" alt="57-BAA578-7-DE1-4297-B45-D-6-A5-EED22-A3-DE"/></a>
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Bimota YB9, RD500,Z1 1974,Z1 1975, Benelli 750sei, 900sei, GPZ 750 turbo, Rudge super sport, S.O.S, BSA Rkt 3 1969, 1966 Bonnie, Egli Vincent 1954,Guzzi 850T, Commando fastback, Commando Interstate, Enfield Interceptor 69, 72 H2, 69 H1, Suzy Gt750 J

[luciousesox]

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Bimota YB9, RD500,Z1 1974,Z1 1975, Benelli 750sei, 900sei, GPZ 750 turbo, Rudge super sport, S.O.S, BSA Rkt 3 1969, 1966 Bonnie, Egli Vincent 1954,Guzzi 850T, Commando fastback, Commando Interstate, Enfield Interceptor 69, 72 H2, 69 H1, Suzy Gt750 J

[luciousesox]

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Bimota YB9, RD500,Z1 1974,Z1 1975, Benelli 750sei, 900sei, GPZ 750 turbo, Rudge super sport, S.O.S, BSA Rkt 3 1969, 1966 Bonnie, Egli Vincent 1954,Guzzi 850T, Commando fastback, Commando Interstate, Enfield Interceptor 69, 72 H2, 69 H1, Suzy Gt750 J