BritBike Forum logo
BritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorThe Bonneville ShopBritBike Sponsor
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
ShoutChat Box
Comment Guidelines: Do post respectful and insightful comments.
Buy BritBike staff a coffee
Buy BritBike's staff a coffeeStill here since 1996 serving BritBike enthusiasts..
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Random Gallery photo
Member Spotlight
Posts: 134
Joined: October 2012
Show All Member Profiles 
Newest Members
rudi, Derek, Psychorider, Shedengineering, Shayne Brown
10860 Registered Users
Top Posters(30 Days)
franko 180
reverb 64
DavidP 63
NickL 58
Popular Topics(Views)
1,006,064 mail-order LSR
a word from..
Forum Statistics
Forums34
Topics67,756
Posts680,007
Members10,860
Most Online14,755
May 5th, 2019
Who's Online Now
56 registered members (Al Eckstadt), 490 guests, and 649 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Amal 928 to 930 #757220 11/26/18 9:13 pm
Joined: Feb 2018
Posts: 110
T
Tracey Spear Offline OP
BritBike Forum member
OP Offline
BritBike Forum member
T
Joined: Feb 2018
Posts: 110
For a '69 Thunderbolt. What are the pros/cons of increasing the carburetor from 928 to 930?


Support Your #1 BritBike Forum!

Check out British motorcycles for sale:
British Motorcycles on e-Bay UK
British motorcycles on e-Bay North America
Re: Amal 928 to 930 [Re: Tracey Spear] #757221 11/26/18 9:17 pm
Joined: Aug 2001
Posts: 4,682
gavin eisler Online Content
BritBike Forum member
Online Content
BritBike Forum member
Joined: Aug 2001
Posts: 4,682
The low speed performance will be worsened, correct jetting will be difficult and the fuel economy will drop ,there arent any pros.

Last edited by gavin eisler; 11/26/18 9:18 pm.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Amal 928 to 930 [Re: Tracey Spear] #757223 11/26/18 9:38 pm
Joined: Aug 2001
Posts: 7,903
triton thrasher Online Content
BritBike Forum member
Online Content
BritBike Forum member
Joined: Aug 2001
Posts: 7,903
It’s been tried by a few people (not me) on here, over the years and reports have been bad.


Amateur Loctite enthusiast.
Re: Amal 928 to 930 [Re: Tracey Spear] #757225 11/26/18 10:10 pm
Joined: Feb 2018
Posts: 110
T
Tracey Spear Offline OP
BritBike Forum member
OP Offline
BritBike Forum member
T
Joined: Feb 2018
Posts: 110
THAT is why this forum is such a great place. Thank you for the advice.

I ordered a bunch of parts today from The Bonneville Shop to take advantage of their 10% off sale. They have the 930 premier set up for single carb bikes with proper slide. The salesman had me convinced I could get away with the 930. Since your advice was so unambiguous. I called to cancel the 930 from the order and explained the advice y'all shared. He called his supplier. His cost was close enough that he will honor the discount on a 928 Premier, even though he has to order it. In my book that more than makes up for misleading me in the first place. The whole transaction this morning was great. I called in the order because I had a few questions about the fork parts. They made suggestions that saved me a few bucks and carefully reviewed the order for accuracy. And I made a point to thank them for supporting the forum.


Re: Amal 928 to 930 [Re: Tracey Spear] #757233 11/26/18 11:40 pm
Joined: Dec 2013
Posts: 4,741
kevin roberts Offline
DOPE
Offline
DOPE
Joined: Dec 2013
Posts: 4,741
my 65/70 bitsa cyclo-thunder-light runs one. seems to work okay. i did mess with the main jet to get it to run right.


every day you do not take a chance is a day of your life that you will never get back.
Re: Amal 928 to 930 [Re: Tracey Spear] #757256 11/27/18 2:24 am
Joined: Sep 2014
Posts: 567
J
Jeff K. Offline
BritBike Forum member
Offline
BritBike Forum member
J
Joined: Sep 2014
Posts: 567
The first year Triumph TR5T used a 630, the next year they went to a 928. Most people that I know who are running the T100c like the 626. Plenty of torque and and others have pointed out great gas milage.
Jeff

Re: Amal 928 to 930 [Re: Tracey Spear] #757265 11/27/18 4:46 am
Joined: Apr 2011
Posts: 875
D
Deadstiffcatt Offline
BritBike Forum member
Offline
BritBike Forum member
D
Joined: Apr 2011
Posts: 875
Although you have made your choice, here is food for thought:
What is the diameter of the intake manifold versus the 930 carb? For example only and illustrative purposes: If the carb bore were 30mm and the intake manifold bore was 28mm, this would appear to create a "step" of about 1mm all the way around. It would appear to me that this step would cause turbulence at certain flows as the mixture hits the difference height of the step. It would seem that an internally angled spacer would be needed to smooth out the flow from larger carb diameter to smaller intake diameter. Even so, it would also make sense that rejetting, changing the slide, and changing the needle position would all have to be messed with to obtain good results.

I mention the above as I deal with a 1965 Triumph TR6SR fitted with a 389 1 1/8" Monobloc. When fitting, I had the luxury of playing with several different intake manifolds which permitted me to find one that had the same bore at the carb, as well as matching bores from the intake manifold to head side. (And yes, I also found a couple that would cause that stepped effect.) The above food for thought is what I was thinking when setting it up. Runs fine, but many other Triumph 650's I have played with averaged 60 MPG- this one is a constant 50 MPG. I'm not a power freak, so cannot state whether it improved anything or is just eating more gas. But since I now have a collection of 1 1/8" carbs and matching manifolds- looks like I'm stuck with it...…….

What? Spend money on a new carb when I got 5 or 6 old ones to last me a lifetime that all operate smoothly? (Many, many thanks, Bonzo!)

Re: Amal 928 to 930 [Re: Deadstiffcatt] #757287 11/27/18 1:04 pm
Joined: Sep 2014
Posts: 567
J
Jeff K. Offline
BritBike Forum member
Offline
BritBike Forum member
J
Joined: Sep 2014
Posts: 567
Deadstiffcatt
Has a good point and something that I did not put in my reply. The TR5T manifolds fit the Carburetor. So you nee to match up 26mm to 26mm, 28 to 28 and 30 to 30.
Jeff

Re: Amal 928 to 930 [Re: Deadstiffcatt] #757295 11/27/18 2:49 pm
Joined: Feb 2018
Posts: 110
T
Tracey Spear Offline OP
BritBike Forum member
OP Offline
BritBike Forum member
T
Joined: Feb 2018
Posts: 110
Originally Posted by Deadstiffcatt
Although you have made your choice, here is food for thought:
If the carb bore were 30mm and the intake manifold bore was 28mm, this would appear to create a "step" of about 1mm all the way around. It would appear to me that this step would cause turbulence at certain flows as the mixture hits the difference height of the step.


I picked up on that too. The salesman's answer was to port the manifold. All workarounds. I'm thankful to the members on the forum who provided sound advice, and happy that The Bonneville Shop made it right by ordering the proper carb and still honoring the sale.

Unfortunately, the only carb I have is so corroded from being stored for 40 years in Oklahoma humidity that I'm not even going to try to salvage it.

Re: Amal 928 to 930 [Re: Tracey Spear] #757299 11/27/18 3:37 pm
Joined: Mar 2006
Posts: 1,496
htown Online Content
BritBike Forum member
Online Content
BritBike Forum member
Joined: Mar 2006
Posts: 1,496
Some 850 Nortons run a 32mm carb on a 30mm head port via a tapered manifold and it apparently works okay. Good move on buying a new carb instead of pouring money into an junk one. Best thing you can do to get an old Brit bike running right.


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
2018 Kawasaki Z900RS


Everything will be alright in the end. If its not alright, its not the end.
Re: Amal 928 to 930 [Re: NickL] #757302 11/27/18 3:50 pm
Joined: May 2013
Posts: 5,876
Allan Gill Offline
BritBike Forum member
Offline
BritBike Forum member
Joined: May 2013
Posts: 5,876
Originally Posted by Tracey Spear
Originally Posted by Deadstiffcatt
Although you have made your choice, here is food for thought:
If the carb bore were 30mm and the intake manifold bore was 28mm, this would appear to create a "step" of about 1mm all the way around. It would appear to me that this step would cause turbulence at certain flows as the mixture hits the difference height of the step.


I picked up on that too. The salesman's answer was to port the manifold. All workarounds. I'm thankful to the members on the forum who provided sound advice, and happy that The Bonneville Shop made it right by ordering the proper carb and still honoring the sale.

Unfortunately, the only carb I have is so corroded from being stored for 40 years in Oklahoma humidity that I'm not even going to try to salvage it.



Worst advice ever would be to port the manifold, if your going to fit a 30mm either use a tapered spacer as Tracey states or keep the step, I machine stepped spacers when I increase carb sizes, I find it better than a smooth taper TBH, it also emulates what goes on with a port on a modern vehicle. Increasing the port size will loose all the bottom end which is where the Thunderbolt is King!

However as mentioned above, I prefer to use a smaller carb where possible, Im using a 32mm carb on a 28mm port lightning head, but this is a case of jetting reasons rather than bigger is better, I simply can't get a 928 or 930 to jet lean enough!

Originally Posted by NickL

My own t'bolt runs out of breath at around 90mph but it's quiet quick up to that.
Thats becasue those magaphone silencers sap a lot of power, my old T-bolt was the same, however with some triumph silencers it went quite a bit better.


beerchug
Re: Amal 928 to 930 [Re: Tracey Spear] #757320 11/27/18 5:27 pm
Joined: Apr 2005
Posts: 1,797
A
Adam M. Offline
BritBike Forum member
Offline
BritBike Forum member
A
Joined: Apr 2005
Posts: 1,797
Had 2x 32 carbs on my small port head ( 30 mm port going down to 27 ) with stock mufflers without any ill effects.
Bike was very fast for A65.

Re: Amal 928 to 930 [Re: NickL] #757618 11/30/18 1:39 pm
Joined: May 2013
Posts: 5,876
Allan Gill Offline
BritBike Forum member
Offline
BritBike Forum member
Joined: May 2013
Posts: 5,876
Originally Posted by NickL
Originally Posted by Allan Gill


Originally Posted by NickL

My own t'bolt runs out of breath at around 90mph but it's quiet quick up to that.
Thats becasue those magaphone silencers sap a lot of power, my old T-bolt was the same, however with some triumph silencers it went quite a bit better.


Limiting me to 90mph is not such a bad thing these days Allan.



To be honest its more than fast enough for anyone wanting to keep their licence and stay shiny side up


beerchug

Moderated by  Allan Gill, Jon W. Whitley 

Home | Sponsors | Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons | DVD- Manuals & Parts books
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Powered by UBB.threads™ PHP Forum Software 7.7.3