Amal MK2 Single Carb on a 850 need specs

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MS850

MS850

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Hello, I have a 75 850 stock engine with Amal MK2 carb
It has new jet needle and needle jet, float needle. (kit from http://amalcarb.co.uk/)

here's the setup now.

Basically runs good except at full throttle. It accelerates good up to 3/4 throttle then, at full throttle its flat, no power. When rolling
throttle back to 3/4 continues to accelerate.
Im going to try a larger main jet and go from there.
If anyone have this setup, whats the carb specs.
I don't have carb off at the moment and don't remember the clip position, think its in the middle.

Amal carb, L2036 301,
Slide, 2036 #3 cutaway
Throttle Needle, 2A1
Needle Jet - Size 106
Pilot Jet - 30
Main 300
 
Sounds to me as if you require a smaller main jet. Start with a 270 & take it from there.

Martyn.
 
Matchless said:
Sounds to me as if you require a smaller main jet. Start with a 270 & take it from there.

Martyn.
Click to expand...
+1 I scratch-built a pair of 34mm's for a 650 twin, and erred on the safe side with the mains. Same thing; it would pull good up to about 3/4 throttle, then flatten out. First instinct was too lean, but going up another step on the mains caused it to start loping at wide open as if the choke was on!

Nathan
 
I think Ill do WOT, kill the engine and check the plugs. plus try using the choke.
 
Does anyone know what the chrome slide (as spec'ed in the RGM pdf) does in comparison to a normal slide? I have a single 34mm Amal MKII on my '74 850 and am currently trying to suss out the carbs as well. I'm having trouble with the slide getting stuck open when the engine is on (works fine with engine off). I've read that perhaps the venturi effect of both cylinders sucking in might cause the slide to pull against the carb body and get stuck? I'm guessing the chrome slide is slicker? I'd like to confirm this could likely solve my problem before I purchase as it looks likely that I'll have to import from UK...
 
I too had a sticking slide on a Mk2, didn't do it when not running, I never tried a chrome slide though Just moved on to a single Mikuni and then twin PWK
 
marinatlas said:
http://www.rgmnorton.co.uk/csi/1245184/f/pdf/single_carb.pdf

hope this help.......!
Click to expand...

Yeah great thanks, acually thanks for all responces.
I guess Im close, except for the pilot, plus I have a 36mm carb.
 
Does anyone know what the chrome slide (as spec'ed in the RGM pdf) does in comparison to a normal slide?
Click to expand...

In a std Amal Concentric MK1 the body and slide are made from the same material, as a bearing design it is a total no no to use the same metals as they bond on a molecular level and this causes galling and rapid wear.

https://en.wikipedia.org/wiki/Galling

The Chrome slide changes this bearing to 2 dissimilar metals so much less likelyhood of galling and wear, the Premier Amals do this a different way and anodise the slide as their earler attempts at chroming Concentric MK1 slides the chrome flaked and sent them back to square one. Surrey Cycles had some slides chromed and this was not a problem.

I do not know if the MK2 has the same slide and body materials, if it does the chrome slide will help (as long as it does not flake) , if they changed the materials then chrome slide will not change much. There are anodised MK2 slides available which would sound like the best option.

http://amalcarb.co.uk/mk-ii-concentric- ... alves.html
 
MS850 said:
Hello, I have a 75 850 stock engine with Amal MK2 carb
It has new jet needle and needle jet, float needle. (kit from http://amalcarb.co.uk/)

here's the setup now.

Basically runs good except at full throttle. It accelerates good up to 3/4 throttle then, at full throttle its flat, no power. When rolling
throttle back to 3/4 continues to accelerate.
Im going to try a larger main jet and go from there.
If anyone have this setup, whats the carb specs.
I don't have carb off at the moment and don't remember the clip position, think its in the middle.

Amal carb, L2036 301,
Slide, 2036 #3 cutaway
Throttle Needle, 2A1
Needle Jet - Size 106
Pilot Jet - 30
Main 300
Click to expand...

Update,
I went up one size on the main jet, 300 to 310.
Flat spot at full throttle is gone, now that I fixed it I'll probably never go to full throttle again.
 
MS850 said:
Hello, I have a 75 850 stock engine with Amal MK2 carb
It has new jet needle and needle jet, float needle. (kit from http://amalcarb.co.uk/)

here's the setup now.

Basically runs good except at full throttle. It accelerates good up to 3/4 throttle then, at full throttle its flat, no power. When rolling
throttle back to 3/4 continues to accelerate.
Im going to try a larger main jet and go from there.
If anyone have this setup, whats the carb specs.
I don't have carb off at the moment and don't remember the clip position, think its in the middle.

Amal carb, L2036 301,
Slide, 2036 #3 cutaway
Throttle Needle, 2A1
Needle Jet - Size 106
Pilot Jet - 30
Main 300
Click to expand...

Changes in the jetting
Bought new 3.0 slide, old was worn
main 320
pilot 35
needle position, 2nd from bottom.

Runs really great through all throttle positions, very happy.
 
MS850 said:
Update,
I went up one size on the main jet, 300 to 310.
Flat spot at full throttle is gone, now that I fixed it I'll probably never go to full throttle again.
Click to expand...
After all our sage advice, I'm thankful you didn't have a melt-down! Thanks for the follow-up, as it's always nice to know what ultimately fixes these things.

Nathan
 
Nater_Potater said:
MS850 said:
Update,
I went up one size on the main jet, 300 to 310.
Flat spot at full throttle is gone, now that I fixed it I'll probably never go to full throttle again.
Click to expand...
After all our sage advice, I'm thankful you didn't have a melt-down! Thanks for the follow-up, as it's always nice to know what ultimately fixes these things.

Nathan
Click to expand...

Thanks,
I always appreciate the info on this site, maybe it will someday help someone with the same carb set up.
 
I'd like to give my experineces for people who start with MKII Carb
Needle 2A1
Main 300
Slide 3
Pilot 20
Needle Jet 106
This setup was MUCH too rich.
Sparks are sooted.
Will change the Slide to 3.5 and Needle to 280
Regards Lorenz
 
Lorenz said:
I'd like to give my experineces for people who start with MKII Carb
Needle 2A1
Main 300
Slide 3
Pilot 20
Needle Jet 106
This setup was MUCH too rich.
Sparks are sooted.
Will change the Slide to 3.5 and Needle to 280
Regards Lorenz
Click to expand...
Is this 1 or 2 carb setup?
 
NickZ said:
Is this 1 or 2 carb setup?
Click to expand...
1 carb setup!

Before I change to Amal Single Carb I was sick over the start bahavior of the all time vowed mikuni vm34. :mad:

Cold start by Mik OK, hot start by Mik OK. But betwenn this both situations it was really disgusting to start my Commando.o_O

Really, taht was not funny at all!!

And to all Mikuni Fans: I have checked EVERYTHING .
From A= A new set of Sparks to Z = 100 Zetup's of Carburator.
My MKII A Motor HATES defenetly the Mikuni
Regards Lorenz
 
Lorenz said:
I'd like to give my experineces for people who start with MKII Carb
Needle 2A1
Main 300
Slide 3
Pilot 20
Needle Jet 106
This setup was MUCH too rich.
Sparks are sooted.
Will change the Slide to 3.5 and Needle to 280
Regards Lorenz
Click to expand...

Hello. I found my setup after a weekend of test:

850 MK2 motor with fresh Cylindes and new valves, 1 single Amal MK2,34mm, NGK Sparks, Trident ignition, Single Coil.

Needle Jet 106 (107 was too lean, motor pops up)
Bought a new Needle 2A1
Main 300
Slide 3.5 a huge different in my case compare to Slide 3
Pilot Jet from 15 back to 20.
Sparks brown! Not sooted anymore
Start behavior:
cold: Ignition of, full open chocke, 1 kick, ignition on, a bit of throttle 1 Kick, fires up.
Approx 1 km of drive, chocke complete closed, motor works fine.
Hot start: Throttle a bit open, 1 kick.
Frankly speaking: I NEVER had such uncomplicated start behavior with the sophisticated VM34 carb.
If the motor runs better with Mikuni VM34? No idea, feels as there is no big difference in torque and accelaration.
I just like to share my experiences. Maybe it helps other members in Setup the MKII.
Regards Lorenz
 
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