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luciousesox
Joined: 31 Jan 2018 Posts: 42 Location: WORCESTER, ENGLAND
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Posted: Tue Nov 24, 2020 7:44 pm Post subject: YB Carb issue |
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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. |
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Bud977
Joined: 03 Mar 2013 Posts: 525 Location: Sydney
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Posted: Tue Nov 24, 2020 8:45 pm Post subject: |
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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. |
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Jonny B Bad
Joined: 05 Dec 2009 Posts: 555 Location: NE London
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Posted: Tue Nov 24, 2020 11:56 pm Post subject: YB carb issue |
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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? _________________ What, Jonny's gone! |
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luciousesox
Joined: 31 Jan 2018 Posts: 42 Location: WORCESTER, ENGLAND
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Posted: Wed Nov 25, 2020 9:57 am Post subject: |
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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 |
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Jonny B Bad
Joined: 05 Dec 2009 Posts: 555 Location: NE London
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Posted: Wed Nov 25, 2020 8:09 pm Post subject: YB carb issue |
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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. _________________ What, Jonny's gone! |
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brian
Joined: 22 Aug 2011 Posts: 3769 Location: Australia
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Posted: Thu Nov 26, 2020 12:44 am Post subject: |
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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 _________________ '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 |
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luciousesox
Joined: 31 Jan 2018 Posts: 42 Location: WORCESTER, ENGLAND
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Posted: Thu Nov 26, 2020 10:39 pm Post subject: |
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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. |
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brian
Joined: 22 Aug 2011 Posts: 3769 Location: Australia
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Posted: Thu Nov 26, 2020 10:43 pm Post subject: |
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luciousesox wrote: |
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. |
Good news! Pilot circuits are notorious for blockages and can be hard to clear sometimes. Glad you got it sorted. Would like to see some pics of the bike _________________ '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 |
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luciousesox
Joined: 31 Jan 2018 Posts: 42 Location: WORCESTER, ENGLAND
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Posted: Thu Nov 26, 2020 10:53 pm Post subject: |
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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. |
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luciousesox
Joined: 31 Jan 2018 Posts: 42 Location: WORCESTER, ENGLAND
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Posted: Fri Nov 27, 2020 8:26 pm Post subject: |
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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 _________________ 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 |
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phil-short
Joined: 30 Jul 2012 Posts: 197 Location: Dublin,Ireland
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Posted: Fri Nov 27, 2020 11:35 pm Post subject: |
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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 |
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luciousesox
Joined: 31 Jan 2018 Posts: 42 Location: WORCESTER, ENGLAND
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Posted: Fri Nov 27, 2020 11:59 pm Post subject: |
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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 |
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luciousesox
Joined: 31 Jan 2018 Posts: 42 Location: WORCESTER, ENGLAND
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Posted: Sat Nov 28, 2020 12:03 am Post subject: |
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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)
[![57-BAA578-7-DE1-4297-B45-D-6-A5-EED22-A3-DE.jpg](https://i.postimg.cc/g049b8XZ/57-BAA578-7-DE1-4297-B45-D-6-A5-EED22-A3-DE.jpg)](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> _________________ 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
Last edited by luciousesox on Sat Nov 28, 2020 12:13 am; edited 1 time in total |
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luciousesox
Joined: 31 Jan 2018 Posts: 42 Location: WORCESTER, ENGLAND
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Posted: Sat Nov 28, 2020 12:07 am Post subject: |
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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 |
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luciousesox
Joined: 31 Jan 2018 Posts: 42 Location: WORCESTER, ENGLAND
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Posted: Sat Nov 28, 2020 12:14 am Post subject: |
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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 |
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