1972 Bonneville T120rv Perfomance Issue

[oldbloke]

Must be 5 months since I ordered new carbs for my Bonne, I emailed Burlen, they replied saying, that they were still having issues with the castings and they could not give a date as to when they would be available. To quote them ' it is going to be a long time' before the problems are sorted. Anyway, I have received a full refund, so will probably wait a bit longer or might fit another pair of 930/30's.

 

[grandpaul]

Hmmmmmm....

U.S. resellers got a large shipment not too long ago...

 

[oldbloke]

The only reason I was waiting is Burlen advised Pack 126 which are a pair of carbs with what they say are fitted with the correct 'Mixing Chamber Caps'. ( manufacturers original spec ). I have no idea what difference the cap makes when other carbs seem to work well. If anyone has any theories on these caps I would like to hear. I have a reasonable understanding of how the carbs but, this is way out of my depth, I cannot see what difference a cap will make. Am I missing something ?.

 

[grandpaul]

I have never heard of a "mixing chamber cap"; perhaps they are referring to the brass emulsion tubes? Triumph & Norton are different, as are 2 & 4 stroke. Now I need to google "mixing chamber cap"...

 

[grandpaul]

Apparently it is the carb top cap. These come in a variety of configurations to properly accommodate the cables, either with or without adjuster screws and/or additional abutment sleeves, per OEM configuration.

 

[oldbloke]

Cheers GP, that makes sense, the emails I have had from Burlen were from, I believe ' Administrators ' maybe not 100% up on the tech stuff

 

[oldbloke]

New carbs have arrived at last and are fitted. The bike is running very well and is a lot more responsive to the throttle, but the most impressive thing is the idle, it is now so smooth and the Tacho needle just sits there giving a reading and has no bounce, or variation in the RPM. These carbs are the Amal 'Premium' range with the redesigned pilot jet and Anodised slide. I believe they are now cast in Aluminium as opposed to the old Monkey Metal and they do look to be very good quality. I am very happy with them, seems to be money well spent to get the bike running so well.

 

[Rocky]

Great news
Several of our vintage bike club members also have those new carbs and have had the same experience with improved running and idle.
I'm toying with the idea of getting one for my BSA.

 

[oldbloke]

Personally, if you have any issues with your BSA's performance I would say go for it. I don't know all the details of the redesigned pilot circuit, but whatever it is, it seems to work remarkably well.

 

[triumph david]

These carbs seem to be the ones to have that solves a lot of problems.

 

[oldbloke]

I think a lot of people would agree with that. Amal seem to have got it right, I still can't believe how different my bike is with these 'Premiums' fitted.

 

[IKE]

Hi there, i am late into this discussion. But if it revs well with no load and not under load, I would do a compression check, it could be down a bit. All other ideas have been metioned,
cheers

 

[oldbloke]

Hi IKE, the problem has been resolved, it was the silencers/mufflers the bike was unable to breath properly, it was just pure luck that I changed them. The first pic shows the old silencer standing on the inlet, as you can see there is a 1 1/2'' pipe which stopped just short of the plate in pic 2 so most of the gas was hitting the plate with almost nowhere to go.
pic 3 shows another plate just before just before the outlet (pic 4) and there is actually yet another plate between 2 & 3 and none of the holes in the plates line-up, which to my mind would make it even worse as I presume the gas would be swirling around trying to find its way out. Now fitted are BSA Goldstar silencers, and the old girl is very happy now, and so am I as this problem dragged on for a long time and was totally frustrating.

 

[Greyfell]

well done!