Amal Carb Jetting

[Jordan]

Good to have more suggestions for tuning carbs.
I gather they are for road rather than track models, and for use with air filters?

I've had lots of bikes with Amals of various flavours.
Chokes are not worth the complication I think - tickler works well enough on an air cooled engine (quick warm up).

Mikunis generally were better finished, but Amals served well until worn.
Current versions have nice options like plated slides and removable pilot jets.

[Dave354]

Thanks Colin, I have the bushed later type… thought I was missing something… just need to get the wiring loom built and then we can see how she runs! I will be the first time in over 25 years!

[Dan C]

All good info Colin, thank you for posting.
Just as a matter of interest I think in another post you mentioned you had a Mikuni on your 250?
I was wondering what 250, what size Mikuni and what jetting? Just asking cause I might yet have to go down that route with my 250 which is a stock desmo.

Cheers
Dan

[veloduke]

Hi Dan

I am running a Mikuni on my 24 Horas, it has the following settings;

Mikuni VM28
Size 28mm
Main 150
Needle 5F21
Needle position 2nd from top
Needle jet/Atomiser 169-02
Slide 1.5
Pilot 25

I also have a 250 Road running an Amal 627;

Amal 627/424 (Premier)
Size 27mm
Main 200 (was 230)
Needle 2 grooves
Needle position Centre
Needle jet/Atomiser 106 (was 105)
Slide 3
Pilot 0.17 (2 grooves)

The Mikuni feels like it runs a little weak just off idle until it's warmed up.

Hope this is some help

Max

[Duccout]

Hi Dan,

Do a search on this forum for 'Mikuni Carb Jetting', the saga is all on there! I have never managed to get the Mikuni running correctly, it is weak when pulling away, often dying completely when cold, but the plug is always sooty. I have tried various recommendations to cure it, but nothing works, and I have just re-fitted the Amal in an effort to see if that is an answer.


Cheers,

Colin

[Dan C]

Thanks Max and Colin!

Max's settings will provide a good starting point, they have been jotted down in "the book" for future reference!!

Cheers
Dan

[Duccout]

Managed to try the bike out today with the original Amal fitted, hoping that I had cured the problems by adjusting the float level, but no. The engine stumbles on pick-up and races on tick-over, so I have to concede that the slide/body has worn, so it now means spend more on the Mikuni and try to get that running correctly, or buy a new Amal. No-one said it was easy.....

Max, btw, what led you to a 1.5 slide on the Mikuni? That is a very small cutaway, so did you start out with a 2.5 and work your way down?



Colin

[veloduke]

Colin

If I remember correctly, the carb was supplied with a 2.0 slide, and the engine would almost die when pulling away. This was mitigated by opening the cold start slightly, so I went for a richer slide, as that was about the amount of throttle I was using. That made a definite difference.

I went for a ride on the bike a couple of days ago. When cold, it is still won't pull away very well, but once warmed up it behaves acceptably. Perhaps I should have it set up on a dyno with a gas analyser - maybe in the future, but for the moment it will do.

[Duccout]

Max, I am guessing that you bought your carb from Motocarb, as you have exactly the same jetting that mine was supplied with, and exactly the same problem. Motocarb was adamant that the slide was correct and sent me a richer needle jet to try (an 06) but that made no difference, but I wonder if a bigger one might, although it would not have helped the overall rich running that I have (the plug is always sooty).

I need a 1.5 slide, which appear to be unavailable, and cost £40 if they are, so I am at the point where I may have to cut my losses and go for a new Amal........


Cheers,

Colin

[A.I.M]

To add another small piece to the jigsaw:
My Mototrans 250 SCR came with a 27mm Amal 627/419 carb
2.5 slide
200 main jet
.105” needle jet
25 pilot jet
and, I think, a V1 or U1 (? The writing on it is too small for me) needle