850 Commando - 930 or 932 Amals?

Status
Not open for further replies.
M

marctroy

Joined
Jul 27, 2008
Messages
13
It took 3 years of negotiating (and begging) to get the owner to sell me his 1 owner 1973 (or '74) Norton 850 Commando Roadster. He had packed it away in a barn years ago because the dealer he purchased it from and serviced it at, Ghost Motorcycle, told him there was a "lack of compression" (which wasn't the case...) and he bought a Honda Sabre to reduce the necessary maintenance and aggravation.

After spending a few weeks removing the "poop' and various other animal excretements; I realized there was a sub-par "fix" for stripped exhaust flanges which resulted in the fins on the front of the RH10 head being filled-in with aluminum welds, holes drilled and threaded into it and the exhaust fitted with a flange of sorts that bolted to the cylinder head.

850 Commando - 930 or 932 Amals?


I finally located an RH10 head from Phil at Fair Spares and fitted the motor with new valves, guides, springs, push-rods, tappets (expensive!) and all new gaskets and mostly new hardware.

850 Commando - 930 or 932 Amals?


Now I'm about to install the newly rebuilt 930 Amal carburettors and, when I check the factory manual (and the "Old Britts" web-site) I see the specs for the 850 call for 932 Amals.

I keep the bike at my weekend home which is about 100 miles away so it's not very convenient to get to it during the week. My plan for my next trip out is to measure the opening in the Amal base, the openings on both end of the manifolds and the openings (ports) on the head.

Does anyone have a suggestion for anything else I should be doing to insure this project goes well?

Thanks!
 
There's no chance of exchanging them?

If you know someone with a lathe you could bore them out to 32mm and re-jet.

Cash
 
Thanks, but the carburettors can't be returned since they came on the bike and were, supposedly, the originals which I'd prefer to keep IF they're the proper carbs for the application.

As I understand it, the distance between the 2 intake ports on the RH10 head was increased by reducing the diameter of the ports therefore reduced the possibility of the head cracking in that area.
 
The ports were decreased to 30mm but the manifolds were 30mm at the head end and 32mm at the carb end. You will need to see what manifolds you have by measuring the dia's at both ends. If they are 30 at both ends then stick with what you have.
 
marctroy said:
the carburettors can't be returned since they came on the bike and were, supposedly, the originals which I'd prefer to keep IF they're the proper carbs for the application.
Click to expand...


All 850 carbs were 32mm 932s. If you are able to give the build numbers stamped on the pads next to '930" then if they were removed from another motorcycle it should be possible to identify which model they were originally fitted to by those numbers?
The inlet manifolds look like the tapered 32/30 type, as used on the late 850 models, the three manifold types (30/30, 32/32, 32/30) have different external features, but the tapered manifolds could of course have been opened out to 32mm previously?


However, unless you are the type of person that rides with the throttle hard against the stop for most of the time, you may not notice much difference between 30mm and 32mm carbs? In fact the smaller carbs could increase the low to mid range performance slightly.
 
It wouldn't surprise me if Ghost switched the carbs when new. Maybe they needed them for another bike.

They always gave me the impression that they were a shady operation. When they were going out of business they showed up with a truckload of bikes and parts at the AMC Harmony NJ meet. Everything was priced out of sight and most of it was just junk.

Whoever did that exhaust port "fix" to your original head was out of his mind. :)
 
Interestingly, those 930 carbs have the late style float bowl with the drain. I guess they could have been replacement carbs or come from a later Triumph, the pre-'72 Commandos I have seen with 930's had no drain plugs.
 
batrider said:
Whoever did that exhaust port "fix" to your original head was out of his mind. :)
Click to expand...

I had almost the same 'fix' on my head when I picked up the bike. My local Norton guy sent it to a shop where they cut out the bad part, welded in a new aluminum insert, and re-cut the threads - $200.

A previous owner tapped some 1/4 - 20 holes and mounted studs to hold the 850 flanges with nuts and washers. A healthy application of Orange Permatex took care of the exhaust leaks!

My Norton guy is a big fan of canning the 850-style exhaust pipes and flanges in favor of the 750-style for two reasons - 750-style flanges have to or three more threads of holding power because there aren't collets on the pipes, and the crossover tube on the 850 pipes are susceptible to cracking.
I originally went with the 850 pipes, but changed to 750 after cracking two left side crossovers.
 
Thanks, all, for responding. After doing some additional checking I found the following:
a) the manifolds are the correct type for the 850/RH10 - 30mm at the manifold and 32mm at the carb base.
b) the current carburettors are 930/R300 and 930/R301 and I'd like to sell them on ebay. Can anyone tell me the correct application for these carbs?

I'm thinking of ordering 1 - 932/35 and 1 - 932/36 from "britparts" on ebay (http://cgi.ebay.com/ebaymotors/ws/e...arms=tab=Watching&item=300283760756&viewitem=) since the price seems reasonable and they have good "Feedback". Their auction states: "Pair of new Amal 932 carbs, one left and one right new in the boxes complete with all jets, slides, chokes and O rings. They are genuine Amals made in the UK and set specifically for 850 Norton Commando models. They are stamped R932/35 and L932/36 this is the factory code for Norton. The standard 932 carbs are stamped R932/300. They have the step or cutaway spray tube and corresponding needle part no 928.063. The current set up is 3 1/2 slides and 260 main jets."

Are these correct carburettors, should I have any concerns and has anyone had any experience with "britparts"?
 
Your bike is running Mk1 / Mk2 spec (not 'A') judging by the airbox (pretty normal for the US market per previous discussions here).

If you're not running a big plastic airbox then you don't want the cut-away spray tubes and accompanying needles. This is not a major problem - they tap out but you do need to keep the correct needle profiles with tubes.

Your 30mm carbs sound like standard replacement parts. You might get a clue by looking at the unused handed bosses for the throttle stop screws (on the inside). These were milled away for clearance ex-works. If done by an owner, they will usually simply be filed (not very nicely either if it was the same chap who worked on your head - was he a sidecar motocrosser ?)
 
marctroy said:
b) the current carburettors are 930/R300 and 930/R301 and I'd like to sell them on ebay. Can anyone tell me the correct application for these carbs?
Click to expand...

I think what Ron L said about them possibly being replacements could be correct, as 930/300 & 301 are not model-specific numbers just standard 30mm 4-stroke left and right handed carb units.

marctroy said:
I'm thinking of ordering 1 - 932/35 and 1 - 932/36 from "britparts" on ebay
Click to expand...


They should be OK, as 932/35 and 932/36 are the numbers listed for the 1974 850 MkII model.

I know 79x100 has raised the point about stepped spray tubes only being used in the 850 IA & IIA carbs (and MkIII), and we have discussed this spray tube question at some length before. I know that 79x100 has the opinion that stepped tubes were only fitted to the A model carbs, and that may or may not be completely true, as there is evidence included an early 850 model press release that appears to suggest otherwise. The spray tubes can be changed easily enough if required, and specific jet needles need to be used with each type of spray tube .
 
Status
Not open for further replies.
Back
Top