T: Fuel Tank Amal 229/289 Carburation frustrations finally resolved

Chris S

Well Known and Active Forum User
Non-VOC Member
I have posted previously about problems with the carburation on my twin. Early in the year, after the bike was running a bit erratic (posted as "twin with fast idle when hot") I went back to basics and set the carbs from scratch, successfully making the bike run as it had last year, but when used a bit it kept fouling the front plug after 50 to 80 miles.
After seeking advice from my local section, I checked the metering wire on the front cylinder inlet valve oil feed, this was fitted, but dislodged, so I replaced it but no improvement. I then started to look at the front carb again. I had already replaced the float and float needle. The new float lowered the fuel height in the float bowl by 1.4 mm and had made an improvement, but it still fouled the front plug as described above, particularly at lower speeds.
I tried running a hotter plug (NGK Bp5EVX) which again improved things but not much and the front plug fouled again. On inspection the plug was fouled with dry powdery soot that would fall off the ceramic core like dust if the plug was tapped against the bench.
Thinking this still pointed to richness, particularly at lower revs, I recalled some postings on the forum about 229/289 needles being sourced that were out of spec. So I decided to replace the needle and needle jet on the front carb. On removal and inspection the old needle has some minor differences in the taper measurements and also about 30mm from the point end there was a score about 4 mm long around the needle.
Eureka, the bike runs perfectly, cold start is ok, idle is spot on, it will sit there as long as I leave it without missing a beat and hot start is easy. It will start when hot without touching the throttle, going straight to a steady tickover on its own.
Smoother riding, better gear changes, better economy and a bigger grin when riding it! I fitted a pair of NGK BP6EV plugs after replacing the needle and needle jet and have now done 400 miles of mixed riding without missing a beat.
229/289 carbs seems to be a bit of a common problem on the forum, but keep at it and they can be sorted and possibly / hopefully the info above may help someone sort their bike out.
Chris Smart
 

A_HRD

Well Known and Active Forum User
VOC Member
Chris,

Well done for the careful, one-thing-at-a-time, approach to problem-solving.
And congrats on the 'Highly Commended' award that your Rapide received at the recent 'Cheltenham Festival of Bikes'.

Peter B
Bristol, UK.
 

JohnA

Forum User
VOC Member
I am to start an investigation on why my recently acquired BS is running rough and fouling plugs on the front as well. So far I have checked the float and needle which seem to be fine. The plug is different to yours as it seems to be wetting and the carbon is bad. The rear is perfect which leads me to believe I may be more to do with a fault developing rather than wear. I'm not sure what the oil metering wire is as yet? I am always open to ideas on what might be the cause, I keep reading about float height which seems to be set but maybe a new float will help. Being a bit green to this bike, it could take me a while.
 

Bill Thomas

Well Known and Active Forum User
VOC Member
I would try a slide with a bigger cutaway, Weaker, You could also twist the carb' a bit, To alter the float height
On standard carb's. Some of us have had trouble with NGK plugs, I only use Champion N5c. Cheers Bill.
 

JohnA

Forum User
VOC Member
Thanks Bill, I will try to twist the carb a little - seems an easy way to start. I will probably start a new thread detailing the problem to learn what I can from other experience.
 

James B

Forum User
VOC Member
Very interested in this thread - I’ve been trying to track down similar symptoms on a comet.
It performs faultlessly when cold, but once fully warmed up it develops a racing idle. If I pull the revs back down with the clutch, it will then idle normally.
Current thoughts are that the auto advance might be binding in an advanced position once hot. Since I’m chasing ignition at the moment, it will of course turn out to be a carburation issue ;)
James
 

JohnA

Forum User
VOC Member
I'm now convinced it's oil fouling, in the picture you can see the plug looks like it's painted satin and it's wet always. I have the same plug reading no matter what I do to the carburation and I've made many adjustments. I have six plugs that look the same. Again the rear is always perfect. I have checked for wet sumping, if this has any influence but fear now I may have to begin a strip down - in the summer :/ I was thinking maybe after the lead free conversion done some time ago, someone may have used valve seal and one popped off? Ir a retaining screw come loose? If any one has any suggestions before I get seriously spannering I'll take anything!
 

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Black Flash

Well Known and Active Forum User
VOC Member
It may sound stupid as it is so obvious, but have you tried a hotter plug on that cylinder only?
My friends comet and my brother's comet had the same cr. same timing, same carb yet still needed different spark plugs.
Just an idea
Bernd
 
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