1962 Norton 650SS. Chopped 376 Monoblocs. Rough idle when hot. Change pilot jet?

texasSlick

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Easiest way to check or set float level in a monobloc carb.

Make a simple manometer gauge consisting of a spare pilot jet cap which is drilled and tapped 10-32 and fitted with a miniature hose barb. Then attach a short length of transparent tubing. Attach the pilot jet cap to the right hand carb and check float level in the left by holding the open end of the tubing next to the cover of the left. Fuel level should be at the dot on the cover.

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Slick
 

Bodger

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Easiest way to check or set float level in a monobloc carb.

Make a simple manometer gauge consisting of a spare pilot jet cap which is drilled and tapped 10-32 and fitted with a miniature hose barb. Then attach a short length of transparent tubing. Attach the pilot jet cap to the right hand carb and check float level in the left by holding the open end of the tubing next to the cover of the left. Fuel level should be at the dot on the cover.

View attachment 82345

Slick
Slick, maybe (probably) I'm missing something, but as I think a previous poster pointed out, why can't you accomplish the same thing by simply push fitting some clear gas line on to the left/float carb connector barb - the barb that you would use to attach the short length of hose that connects the two carbs?
 

texasSlick

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Slick, maybe (probably) I'm missing something, but as I think a previous poster pointed out, why can't you accomplish the same thing by simply push fitting some clear gas line on to the left/float carb connector barb - the barb that you would use to attach the short length of hose that connects the two carbs?
That can be done, but I prefaced my post with "Easiest way to check or set float level in a monobloc carb." Easier to screw on a spare pilot jet cover than remove the tubng from the interconnecting hose barb and temporarily connecting another, then remove the temporary and refit the interconnecting tubing.

Slick
 
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spark plugs for 650 Manxman and atlas single crap running on e10 ethronal champion n9bcy twin carbs n7bcy
 
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Hi Anna:

Thank you for your comments.

I am running NGK B7ES plugs. Sounds like you are perhaps suggesting a hotter that standard plug will help with E10? Can't say I am very keen on Champions. I used to swear by them back in the day, (for both British cars and bikes) but ever since have become increasingly disenchanted. Nowadays I tend to like NGK's. Used to also be keen on Bosch, but they seem to have gone down hill too. That said I am happy to be proved wrong - would'nt be the first time!

I am fortunate that I have access to Ethanol free fuel and that's what I use for all my old iron.

Recently discovered that my bike has 30mm inlet ports and was originally supplied with inlet port sleeves to bring the diameter down to 28mm - to match the 28mm amal 376 monoblocs. My bike did not have the sleeves, so I have ordered some, (available from RGM in the U.K.) as well as a couple of new phenolic intake manifold gaskets. Will be interesting to see if they make any difference.

Kind Regards,

James
 
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baz

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Hi Anna:

Thank you for your comments.

I am running NGK B7ES plugs. Sounds like you are perhaps suggesting a hotter that standard plug will help with E10? Can't say I am very keen on Champions. I used to swear by them back in the day, (for both British cars and bikes) but ever since have become increasingly disenchanted. Nowadays I tend to like NGK's. Used to also be keen on Bosch, but they seem to have gone down hill too. That said I am happy to be proved wrong - would'nt be the first time!

I am fortunate that I have access to Ethanol free fuel and that's what I use for all my old iron.

Recently discovered that my bike has 30mm inlet ports and was originally supplied with inlet port sleeves to bring the diameter down to 28mm - to match the 28mm amal 376 monoblocs. My bike did not have the sleeves, so I have ordered some, (available from RGM in the U.K.) as well as a couple of new phenolic intake manifold gaskets. Will be interesting to see if they make any difference.

Kind Regards,

James
I'd be interested to hear what difference it makes when you sleeve the inlet ports
 
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I have now installed the inlet port sleeves on my bike as discussed above.

I am absolutely thrilled with the results! The motor appears to have more power, runs smoother and while the weather here is still very mild, (so I will have to wait for a few weeks to be sure)...... so far appears to get much less hot and bothered!

I've gone back to the 25cc pilot jets and stuck with the fuel level mods suggested above.

Huge improvement! I suppose it makes sense, if the sleeves were of no real importance, why would Norton have bothered adding them in the first place?

Cheers,

James
 
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First reasonably hot day up here in Vermont, (86 degrees). Hot idle is much improved! I think, for me at least, the things that made the difference were getting the fuel levels correct and adding the correct inlet port sleeves. Both changes caused significant improvements. I highly recommend both.

Thank you everyone for your help!

Kind Regards,

James
 
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seanalex

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Congrats! Your post made me second guess myself, and put the inlet sleeves onto my 650. I'm also going to start with the rocker shim under the needle seat, thats a good call.

If I could ask, would you happen to recall if both of your air screws are identical? One of mine is drilled, and has a small air hole in the side (similar to a premier carb). If its the case that one of yours is drilled, do you have it on the full carb, or the chopped carb?
 
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Hi Seanalex:

My air screws are identical. No drillings on the side. My pilot jets both have small air holes in the side / are also identical. I am not aware of any features on my twin 1 and 1/2 monobloc carbs that are in place on one side or the other to compensate for the fact that only one side has a float bowl. The air screw adjustment discrepancy from one side to another is no more than a few clicks, and certainly not big enough to make me think it is caused by the location of the float bowl; to me at least it just seems like a minor difference that one would expect to encounter between any two "identical" British carbs.

Might be helpful if one of the forum experts chimes in on this?

Cheers,

James
 
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