carburation

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ducati2242
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Joined: Sat Jul 15, 2017 6:50 pm
Location: Durham

carburation

Post by ducati2242 »

s-l1600.jpg
Well I got my newly assembled 55 G9 started for the first time today . I have built it out of a box of bits I purchased it started quite well after about 6 kicks but to be honest its not very keen to respond to the throttle . It ticks over lovely but revving is either on or off would I be better off with a concentric carburetor as opposed to the monobloc and if so which one . Heres a before picture . Seat looks great but its the wrong one .
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Andy51
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Re: carburation

Post by Andy51 »

Hi, I don't know if Concentrics are better than monoblocs but I replaced the carb on my 18S with a new concentric mk 1 and there was a big improvement. A new, unworn carb is nearly always better than a worn old one even if it is later, unoriginal model. Choose size nearest to imperial original, increase main jet size by approx 20%, other settings as for monobloc, and experiment from there. Andy
SPRIDDLER
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Re: carburation

Post by SPRIDDLER »

ducati2242 wrote: its not very keen to respond to the throttle . It ticks over lovely but revving is either on or off would I be better off with a concentric carburetor as opposed to the monobloc
Well done, it looks great!

I wouldn't be so hasty in condemning the monobloc. Monoblocs rarely fail/wear to the extent that a bike becomes unusable (unless some major fault exists, like the main jet dropping out, float punctured, pilot jet blocked, or the needle clip failing etc.).
A bit more detail on what you mean by 'on or off' might help.
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ducati2242
Posts: 69
Joined: Sat Jul 15, 2017 6:50 pm
Location: Durham

Re: carburation

Post by ducati2242 »

SPRIDDLER wrote:
ducati2242 wrote: its not very keen to respond to the throttle . It ticks over lovely but revving is either on or off would I be better off with a concentric carburetor as opposed to the monobloc
Well done, it looks great!

I wouldn't be so hasty in condemning the monobloc. Monoblocs rarely fail/wear to the extent that a bike becomes unusable (unless some major fault exists, like the main jet dropping out, float punctured, pilot jet blocked, or the needle clip failing etc.).
A bit more detail on what you mean by 'on or off' might help.
Ive rebuilt the carb with new jets etc and it is the correct one for the 55 g9 . Like i say it started and ticked over great I was trying to work out the best position for the advance retard lever and then gave it a little throttle it seems to rev quickly but when closing the throttle it doesn't drop the revs so quickly it returns to a decent tickover slowly . The one thing I didn't replace in the carb was the slide . I have purchased one now and will fit it to see if it responds better . I dont even know if the one i have is the correct cutaway . I have new 220 jet and needle/clip in no. 3 notch with a new float installed . Thinking about it I believe it could be the slide . I'm pretty sure the float height is good .
SPRIDDLER
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Re: carburation

Post by SPRIDDLER »

It's worth a go with a new slide before writing off the whole carb.
A worn slide may not drop cleanly due to 'suction' when th'engine's running faster than tickover - another possibility is that the carb body may be distorted through the nuts at the mounting flange being over-tightened at some time.
Does the slide drop smartly with a click with th'engine stopped? If not, cable friction may be holding back the slide.
Were the new jets etc. genuine AMAL with the AMAL logo on sealed packets? I have heard of poor quality and out-of-spec'n carb parts from online sites that are claimed to be genuine AMAL.

(I'll be away from internet access now for a week or so).
Last edited by SPRIDDLER on Sun Sep 24, 2017 8:27 am, edited 2 times in total.
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shifter
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Re: carburation

Post by shifter »

Hello Ducati2242
Looks like you have made a grand job of the bike it and looks like the one I was going to bid on a while ago from just north of Morpeth. I have a Model 20 (kept the monobloc, as like you I was contemplating with a concentric), I also had a little bother with the carb internals in the beginning on my bike but got fantastic advice from the lads in the forum its been champion ever since
shifter
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ducati2242
Posts: 69
Joined: Sat Jul 15, 2017 6:50 pm
Location: Durham

Re: carburation

Post by ducati2242 »

shifter wrote:Hello Ducati2242
Looks like you have made a grand job of the bike it and looks like the one I was going to bid on a while ago from just north of Morpeth. I have a Model 20 (kept the monobloc, as like you I was contemplating with a concentric), I also had a little bother with the carb internals in the beginning on my bike but got fantastic advice from the lads in the forum its been champion ever since
shifter
It is that bike . To be honest though there were more parts missing or incorrect that were right . But all is good now .
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clanger9
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Re: carburation

Post by clanger9 »

If the throttle is "holding up", then it's probably a worn slide. The fit is critical here (on both Monoblocs and Concentrics). Unfortunately, fitting a new slide won't necessarily cure it as the carb body may be slightly oval.

For a 100% cure, either buy a new carb (stick with the Monobloc, there's nowt wrong with 'em...), or send your carb off to Martyn Bratby (see the Recommendations section for his contact details) and he'll overhaul the carb and fit a brass sleeve to the slider. This is a permanent fix for the "worn slider" problem - my bike runs perfectly since having this mod.
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ksj_LAPSED
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Re: carburation

Post by ksj_LAPSED »

don't mess about buy a mikuni
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