Amal MkII carb - running Really rich

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Zunspec
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Amal MkII carb - running Really rich

Unread post by Zunspec » Sat Jul 12, 2014 12:32 pm

Good day all,

The MkII carbs fitted to my recently acquired T140 are running really rich at low speed, black smoke from exhaust as you blip the throttle etc. I have replaced the small rubber faced whotsits in the choke mechanism as I suspected the old ones were not closing off the enrichening circuit completely. I still think I may still have issues in this area but wondered if there might be any other obvious problems which would cause the same symptoms. Pilot jets are Std and I have tried various settings with the pilot air screw etc and using NGK B8ES plugs. The richness is causing the plugs to foul and eventually stops the engine, particularly on the left cylinder.

Cheers for any insight.

Cheers Geoff

DAVE M2
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Re: Amal MkII carb - running Really rich

Unread post by DAVE M2 » Mon Jul 14, 2014 11:24 am

try a B6ES

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Hooli
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Re: Amal MkII carb - running Really rich

Unread post by Hooli » Mon Jul 14, 2014 6:19 pm

Mine used to smoke at idle when hot & be worse on the left. In my bike's case it's worn valve guides oiling the plugs, being worse on the left I think was due to often leaning that way on the sidestand so more oil as in the head to leak down.

I do agree about the different plugs, it helped a lot on mine.
Classics ain't built in Metric

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Zunspec
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Re: Amal MkII carb - running Really rich

Unread post by Zunspec » Tue Jul 15, 2014 1:46 am

Thanks guys,

The symptom are not, I believe, due to any sort of oiling issues. When blipping the throttle the "black" hint of smoke, particularly from the left side, indicates a rich as heck mixture. You should see the removed plugs, pure black sooty appearance and not a hint of oil. If it was oil the smoke would be grey/whitish etc. I am reluctant just bung in a hotter/softer plug such as the B6ES as you suggest Dave, when using fresh/cleaned plugs it goes a very well at larger throttle openings (i.e. when thrashing it :D ). A hotter plug may cause other issues, like melting a hole through the piston.

I think that despite renewing the rubber capped "enrichment" piston it must still not be sealing and therefore running as if the choke is still on. Is there any way you can bypass or eliminate the choke action on a MkII Amal?

Thanks for the feedback.

Cheers Geoff

Hoole - I hesitate to mention but it also uses a Boyer ignition system, but I have ensured the new battery is fully charged etc.

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Hooli
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Re: Amal MkII carb - running Really rich

Unread post by Hooli » Tue Jul 15, 2014 2:19 pm

Zunspec wrote:
Hoole - I hesitate to mention but it also uses a Boyer ignition system, but I have ensured the new battery is fully charged etc.
I don't think I can blame boyer for this, I just got misfires all the damn time due to them.
Classics ain't built in Metric

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Zunspec
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Re: Amal MkII carb - running Really rich

Unread post by Zunspec » Tue Jul 15, 2014 2:30 pm

I have just done a bit more web searching on the subject. It seems float height is pretty significant in producing a rich mixture at low speed running. Then I looked for "how to adjust the float height" and was taken aback at the sh1t needed to do the adjusting, involving hitting the needle valve eating face up and down apparently. Oh well, I can always fit a set of Mikunis :lol:

Cheers Geoff (I think I'll crack open a cold one and enjoy the sunshine in the garden for the rest of the day lol)

Looper
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Re: Amal MkII carb - running Really rich

Unread post by Looper » Tue Jul 29, 2014 9:39 am

They might need a good clean. The mark2 amals are over complicated, a simple strip wasn't enough for mine. I couldn't get carb cleaner so I soaked them in coke, rinsed them off and blew them out with an air line. They were fine for years but I left the bike sitting for too long and they seem to have blocked up again. If I could I'd replace them with the good old mark1.

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Zunspec
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Re: Amal MkII carb - running Really rich

Unread post by Zunspec » Tue Jul 29, 2014 2:13 pm

Hello Looper,

Problem now seems to be solved. It did involve another cleaning session and some tweaking of the choke cables. I believe the basic problem was the choke plungers not seating fully.

Cheers Geoff

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