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


Chris S

Well Known and Active Website User
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 Website 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

Website 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 Website 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

Website 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

Website 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
 

Bill Thomas

Well Known and Active Website User
VOC Member
James, I would have thought yours was a worn slide, These Bikes do drive you MAD !!. Cheers Bill.
 

JohnA

Website 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!
 

Attachments

Black Flash

Well Known and Active Website 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
 

JohnA

Website 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
Thank you for your input Bernd, The rear cylinder is working perfect with the same plug and I feel reluctant to go down this route thinking it just hides the problem by hotter plugs burning up the oil. if all else fails....
 

erik

Well Known and Active Website User
VOC Member
sometimes the resistor in the spark plug connector makes Problems.especially NGK ones.The resistance grows over the years.
 

JohnA

Website User
VOC Member
It's not the plug as I have changed it every time I test. I will likely have to take the head off. :/ ty
 

erik

Well Known and Active Website User
VOC Member
I don`t mean the plug ! i mean the connector or may be the high Tension cable has a fault making the spark weak when warm.
 

Texas John

Well Known and Active Website User
Non-VOC Member
Those (NGK BP6EV and Champion N5C) are non-resistor plugs, so resistance really should not change over time. Resistor plugs do not play well with Magnetos, from what I understand. Those NGKs are supposed to be really great plugs, but perhaps someone has had a bad experience?
 

davidd

Well Known and Active Website User
VOC Member
I have never had a bad NGK. I use B9's in the racer also. Others have reported problems. It may be the supply countries are different for the UK and the US.

David
 

Cyborg

Well Known and Active Website User
VOC Member
Same here, NGK is the go to plug. There are lots of knockoffs, so if buying from EBay, I buy the NOS ones that come in Honda or Yamaha boxes. Probably safe to assume that the folks at Itsaknockoff don’t bother putting individual plugs in old dusty Honda branded boxes.

The NGK site has a link that shows how to identify some of the fakes, although they are always evolving.

Oil filters are also a big issue.

Ps. NGK factory in France. I always try and source Japanese manufacture although not sure if it really matters.
 

Mike 40M

Well Known and Active Website User
VOC Member
I've heard that there is different ceramics in the France ones compared to those made in Japan.
Don't know if true, but I use Japanese NGK without problems on most bikes.
 

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