carb issues, excessive backfiring thru mufflers, and more....

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EstuaryBoy said:
Am I right in thinking the thicker ones were perhaps from the pre Commando 750's??
Sure my P11 used them, what 'manifolds' there were sat on three studs and one allen screw, unless my memory has screwed up (not totally out of the question!)
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Unsure but the two types I have were the correct opening for the 850 inlet ports, I think 32mm? Not sure if other bikes have that size.

Edit: here is the thick insulator , 32mm port, on Eurojambalya
www.eurojamb.com

Phenolic Amal Carburetor Insulator 32mm Triumph Norton BSA thick

Norton part number 06-3458, also suitable for Triumph/BSA with 32mm ports/carbs. Typically used between carb and manifold for racing 500 BSA and large-carbed 650/750 twin, standard for 850 Commando. American made, GUARANTEED to fit, but Commando will require slight relieving at inner edges as...
www.eurojamb.com www.eurojamb.com
 
update - back on the road, and running great (knock on wood). backfiring's gone and pulls strong thru the gears - i'm a happy camper. ended up pulling the pilot needles and checking the circuit with a home made .016" wire probe. followed up with a blast of choke and carb cleaner. also pulled the float bowels and checked the levels. one seemed fairly low - (from the plug reading - the lean side). re-adjusted both to about 1/16" below the edge of the bowl. reassemble and road test- all is good. big thanks for all the help and suggestions.
 
joe czech said:
update - back on the road, and running great (knock on wood). backfiring's gone and pulls strong thru the gears - i'm a happy camper. ended up pulling the pilot needles and checking the circuit with a home made .016" wire probe. followed up with a blast of choke and carb cleaner. also pulled the float bowels and checked the levels. one seemed fairly low - (from the plug reading - the lean side). re-adjusted both to about 1/16" below the edge of the bowl. reassemble and road test- all is good. big thanks for all the help and suggestions.
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Do you have the 'stay-up' floats or the original type. The reason I'm asking is because I have the stay-ups installed and when the fuel level in the bowl is set correctly (around 5mm below top) the float sits proud of the bowl top, no way it's below the edge as you have. Same as shown in:

Setting AMAL Fuel Level - GME

Setting AMAL concentric Carb Fuel Level
www.gregmarsh.com
 
NickZ said:
Do you have the 'stay-up' floats or the original type. The reason I'm asking is because I have the stay-ups installed and when the fuel level in the bowl is set correctly (around 5mm below top) the float sits proud of the bowl top, no way it's below the edge as you have. Same as shown in:

Setting AMAL Fuel Level - GME

Setting AMAL concentric Carb Fuel Level
www.gregmarsh.com
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stay up floats. my adjustment is approximately 1/16" below the edge of the bowl. don't recall having any protrusions on the top of the floats. again, my 1/16" is an approximate setting - for all i know, it may be 3/32". whatever it is, it may fall in the +/- .040 level window. in any event, bike seems to be running okay.
 
joe czech said:
stay up floats. my adjustment is approximately 1/16" below the edge of the bowl. don't recall having any protrusions on the top of the floats. again, my 1/16" is an approximate setting - for all i know, it may be 3/32". whatever it is, it may fall in the +/- .040 level window. in any event, bike seems to be running okay.
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Yeah, the proof is in the running. If it's running good that's great. Do you attribute the improvement ("back on the road, and running great (knock on wood). backfiring's gone and pulls strong thru the gears") to the adjustment of the float level?
 
As per Amal web page, quoted in Greg Marsh's linked post above, it is the fuel level that should be 5mm below top surface of bowl. Float level is not relevant as long as not excessive high above top surface (so as not to interfere with carb body). If float is too high, then the needle valve seat needs knocking higher in the bore, like was done on older type Amal MKI's.
 
NickZ said:
Yeah, the proof is in the running. If it's running good that's great. Do you attribute the improvement ("back on the road, and running great (knock on wood). backfiring's gone and pulls strong thru the gears") to the adjustment of the float level?
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well, i also did the pilot circuit, but my money and best guess is, it the floats all along. thinking i may have had one cylinder running a tad too lean. not sure how they got out of adjustment from the previous rebuild. proof in the pudding is to put some serious miles on the bike and read the plugs. hopefully, i won't run into anymore hiccups for a while.
 
My curiosity comes from the fact that I was wrestling with very similar symptoms on my '71 Roadster. It is resolved now, but I too made several adjustments at once and not certain which one fixed it. I did the pilot jet cleaning, static carb synch (wasn't off much), but most notable, when I took float bowls off to check the levels, I noticed that both jet holders were loose and down 2 or 3 threads from tight, so I tightened them up. Not sure, but it was probably this last item that was my issue.
 
well whether it was the floats, pilot circuit, or a combination of both, just thankful i didn't have to pull those carbs!
 
Seems to me that the moral of the story is, ensure they’re put together properly (with no blocked jets) and they’ll probably work properly.

S’all about checking the basic things first before moving on to the more dramatic. Often we do the opposite.

An‘ I ain’t preachin‘. We all does it!

I once had to coast in to the paddocks when a race bike cut out. I’d been fighting the carbs so had a clear hypothesis of what was wrong by the time I got to the van. I had one carb off and stripped before I noticed I’d not turned the fuel tap off... yet there was no fuel pouring out... because there was none in the tank... I had simply run out of petrol. We live and learn !
 
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Fast Eddie said:
Seems to me that the moral of the story is, ensure they’re put together properly (with no blocked jets) and they’ll probably work properly.

S’all about checking the basic things first before moving on to the more dramatic. Often we do the opposite.

An‘ I ain’t preachin‘. We all does it!

I once had to coast in to the paddocks when a race bike cut out. I’d been fighting the carbs so had a clear hypothesis of what was wrong by the time I got to the van. I had one carb off and stripped before I noticed I’d not turned the fuel tap off... yet there was no fuel pouring out... because there was none in the tank... I had simply run out of petrol. We live and learn !
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42.
 
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