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FJ 1200 rebuilt carbs.. works for a few miles then stops...

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BristolFJ1200...
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Joined: 27 Aug 2018
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PostPosted: 17:36 - 02 Dec 2018    Post subject: picture says it all Reply with quote
So these jets were new, only had a few miles on them (see pic)

I have a theory which is useful to share....

The previous owner had the tank sealed after pinholes had appeared. And had no issues. Neither did I until I added some redex carb cleaner to the tank. It was very soon after this that i started having problems.

Now the gunk that was all over the jets has a glueish type quality. My guess is that the addititive I put in has affected the sealant causinng it to disolve...

Anyway. Whilst I had the tank reversed on the seat i managed to knock it off causing a good sized dent. Since its full of random gunk anyway, I think it is time for a good clean second hand tank - if anyone has one please pm me!

I have taken the carb apart completely now, everything off needle valves, mixture screws the lot and will run compressed air through it...

ill post an update when I get a new tank on it!
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FJ1200 3CV
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WD Forte
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Joined: 17 Jun 2010
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PostPosted: 17:42 - 02 Dec 2018    Post subject: Re: update! Reply with quote
BristolFJ1200Russ wrote:
Just as an update - i checked the fuel line for kinks and its fine. I used a petrol can as a temporary fuel tank - direct to the fuel pump - by passing the fuel filter (fuel filter is transparent and looks clean)

I also checked the reserve solenoid and it is working.

starts up easily and idles, sounds healthy - no popping, even idle - all cylinders but at 3k rpm hunts and dies out again.


Forum fault finding is best guess at best and can be like pulling teeth
but that 'sounds' like fuel starvation.
Just because you hear a pump run doesn't mean it's developing and
holding the pressure needed to feed 4 carbs
Have you tried by passing the pump and gravity feeding them to see if there's any improvement?
OR
It may be over fuelling for all we know but it would usually be stinky with black smoke if it was and plugs would be sooty
what colour are the plugs?
OR
if it aint fuel the electronics in the igniter box may be breaking down
dry caps sort of thing
or the trigger pulsers playing up as they heat up

Some K series beemers could have that problem with hall effect pulsers that started fine but as they warmed up, they'd break down

Talking electricules....
have you checked the charging system is giving an nice steady 13.8V?
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Fizzer Thou
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Joined: 06 Aug 2011
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PostPosted: 18:12 - 02 Dec 2018    Post subject: Reply with quote
It sounds more as though there is a weak mixture and at low revs it is okay as FJ's tend to run rich at small throttle openings.

On several bikes that I have worked on there have been similar instances of the engine cutting out above certain revs and having investigated found that the inlet manifold 'O' rings seals have shrunk and split,causing an intake air leak,part number 6 on the fiche.Easy to check and I would suggest replace anyway,as they are in a very high heat area and may well cause a problem now or even in a not too distant situation Confused

https://www.fowlersparts.co.uk/parts/4057023/fj1200-3cv2-1988-999-a/intake

If you are on farcebook then check in on the FJ1100/1200 page.Lots of advice and access to spares Thumbs Up Wink Thumbs Up
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