Commando 850 weird issue with carbs possibly ?

Hi all its my first time writing on your forum, but i have been following for quite a while now on many issues and it seems i have taken the turn to ask myself.
I restored my 74’ 850 fully by myself and enjoyed every part of it. I have rebuilt the whole engine with quality parts and had it machined by specialists for Nortons in the UK. Now the problems started when i bought a brand new pair of Wassell Amal 932 carbs. Unstable idle also sometimes it rises itself out of nowhere, and always have the left cylinder kind of running weaker than the right i can tell by sound and by having my hand over the left exhaust the pulse is noticeably weaker (note: compression checked cold both are 150 psi). I have checked the carbs today again and they do seem a little loose in the carb body but not terrible. Carbs are synced i have done everything by the book as they say. Playing with the mixture screw does change the rpm but doesnt change the running of the left cylinder.
What am i missing or is the problem that i didnt buy the proper Premier Amals ?
Iginition is a boyer the latest one with their single coil. Timing is correct.

Thanks

Welcome to the site.

Sometimes an idle will go up and down if the fuel feed is erratic. Check the taps and all your lines filters etc are clear. Maybe even the tank breather. Cable runs and leaks in the inlet manifold can also do it.

When it comes to the Wassell carb however I cannot help sorry. I don't think I have ever seen one.

johnm said:

Welcome to the site.

Sometimes an idle will go up and down if the fuel feed is erratic. Check the taps and all your lines filters etc are clear. Maybe even the tank breather. Cable runs and leaks in the inlet manifold can also do it.

When it comes to the Wassell carb however I cannot help sorry. I don't think I have ever seen one.

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Thanks for the reply, i have checked the tank breather and fuel lines are clear i even took the bowls off to check for dirt and its all clean and fuel flows perfectly. Also the bike goes great when im riding its just the idle thats annoying and the sound of the left weaker exhaust sound.

johnm said:

Welcome to the site.

Sometimes an idle will go up and down if the fuel feed is erratic. Check the taps and all your lines filters etc are clear. Maybe even the tank breather. Cable runs and leaks in the inlet manifold can also do it.

When it comes to the Wassell carb however I cannot help sorry. I don't think I have ever seen one.

Click to expand...

I also noticed that the carb slides on my carbs are different colours dont know if that means anything at all. One is a lot darker than the other.

Are the float levels equal and correct?

seattle##gs said:

Are the float levels equal and correct?

Click to expand...

Yep both checked

Have you got slack in the throttle cables when the slides are at bottom together ?

NortonNik96 said:

I also noticed that the carb slides on my carbs are different colours dont know if that means anything at all. One is a lot darker than the other.

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With Amals that could mean you had one of the newer anodised slides perhaps.

Wassell's are copies of the Amal carb...even use the same size jets, floats and throttle sliders. The darker slide should be the hard anodized type and should be same in both wassell carbs...so soinds like you've got a standard one on one side.

Check for air leaks at carb flange and inlet manifold joints...and check the inlet mani cross over hose for cracks and poor fitting. Spray wd40 or brake cleaner on the joints while idling to see if rpm varies if spray gets drawn in.

Do you have a good, thick insulator "gasket" at the kanifold ro head joint? The idle rising could be to heat build up in the carbs making for a lean mixture as fuel heats up.

Check if both silencers warm up from cold at about same rate and to same running temp. I recall an old thread where someone chased the weak left side exhaust pulse and turned out the silencer innards had collapsed on that side.

NortonNik96 said:

I also noticed that the carb slides on my carbs are different colours dont know if that means anything at all. One is a lot darker than the other.

Click to expand...

Take the slides out and look underneath. Each should be stamped 3.5 or 3-1/2. The almost black anodized slides wear better but that's unlikely to be the problem.

Also, look at the sides of the carbs. One should be marked R932 with 2-3 more numbers and the other L932 with two or three more numbers. Report back with those sub-numbers.

Set the air screw exactly 1-1/2 turns out from seated. Adjust the throttle stop screws to make them even, if possible.

If all that turns out to be good, then the pilot circuit is partly blocked.

More here: https://gregmarsh.com/MC/CarbSync.aspx#gsc.tab=0

marshg246 said:

Take the slides out and look underneath. Each should be stamped 3.5 or 3-1/2. The almost black anodized slides wear better but that's unlikely to be the problem.

Also, look at the sides of the carbs. One should be marked R932 with 2-3 more numbers and the other L932 with two or three more numbers. Report back with those sub-numbers.

Set the air screw exactly 1-1/2 turns out from seated. Adjust the throttle stop screws to make them even, if possible.

If all that turns out to be good, then the pilot circuit is partly blocked.

More here: https://gregmarsh.com/MC/CarbSync.aspx#gsc.tab=0

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I have checked the slides both are 3.5 i will come back with the carb numbers in the afternoon. Thing is the left mixture screw is already out at 2 turns and it does react to opening or closing it, but the pulse is still weakish well weaker than the right. The right pulse is fabulous.
Thanks for that link i will follow the steps once again and see what i get.

NortonNik96 said:

I have checked the slides both are 3.5 i will come back with the carb numbers in the afternoon. Thing is the left mixture screw is already out at 2 turns and it does react to opening or closing it, but the pulse is still weakish well weaker than the right. The right pulse is fabulous.
Thanks for that link i will follow the steps once again and see what i get.

Click to expand...

Two turns out? that's weak.

Sounds like you have a partially blocked pilot circuit on the left side, enough to let some fuel through but not enough to get the correct mixture if you are 2 turns out. New Amal's can come not cleaned out properly so the cheaper Wassells could have the same issue. You need to check the full circuit not just the pilot jet, for the pilot jet carb cleaner fluid is not enough, you need a 16 thou drill to clean it out properly.

This will help, the Wassell carb is a direct copy.

NortonNik96 said:

I have checked the slides both are 3.5 i will come back with the carb numbers in the afternoon. Thing is the left mixture screw is already out at 2 turns and it does react to opening or closing it, but the pulse is still weakish well weaker than the right. The right pulse is fabulous.
Thanks for that link i will follow the steps once again and see what i get.

Click to expand...

Keep in mind that the "mixture screw" is an air screw. The fuel is metered by the pilot jet (non-Premier=hidden in the pilot circuit, Premier = removable opposite the air screw). I have never had an air screw out more than 1-1/2 turns - they usually end up between 1-1/4 and 1-1/2 turns out. Makes me wonder if someone "cleaned" the pilot jet using a drill bit and made it too big.

Throttle:
0-1/8 Pilot Circuit
1/8-1/4 Slide cutaway - yours is correct
1/4-3/4 Needle position and possibly needle jet - if you have a 106 it is correct
2.4-WOT Main Jet

I think you said that the fuel level in the bowls is correct - if not, it's important to get it correct and most importantly the same in both bowls.

If you only have a problem at 0-1/8 throttle, then it's the pilot circuit. There is very little overlap - almost like four carbs in one.

marshg246 said:

Keep in mind that the "mixture screw" is an air screw. The fuel is metered by the pilot jet (non-Premier=hidden in the pilot circuit, Premier = removable opposite the air screw). I have never had an air screw out more than 1-1/2 turns - they usually end up between 1-1/4 and 1-1/2 turns out. Makes me wonder if someone "cleaned" the pilot jet using a drill bit and made it too big.

Throttle:
0-1/8 Pilot Circuit
1/8-1/4 Slide cutaway - yours is correct
1/4-3/4 Needle position and possibly needle jet - if you have a 106 it is correct
2.4-WOT Main Jet

I think you said that the fuel level in the bowls is correct - if not, it's important to get it correct and most importantly the same in both bowls.

If you only have a problem at 0-1/8 throttle, then it's the pilot circuit. There is very little overlap - almost like four carbs in one.

Click to expand...

So i have just re-set the carbs and started it and its running perfectly both cylinders i will have to see if it changes after its properly warmed up and also need to do some plug chops at different throttle positions. I also sprayed the manifolds to check for air leaks and nothing changed when i sprayed so thats all ok.

Thanks for the advice !