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#494689 - 06/19/13 6:40 pm Poor idle on '73 750 Tiger  
Joined: Jul 2011
Posts: 122
fried okra Online content
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fried okra  Online Content
BritBike Forum member

Joined: Jul 2011
Posts: 122
TN/VA/FL USA
I picked up a nice original single carb 750cc '73 Tiger today. The bike starts easily and runs great at all throttle openings but won't idle well. The bike runs ragged and uneven at idle. Idle speed is roughly 1000 rpm.

The 930 AMAL was replaced about 10 years ago and maybe has a couple thousand miles on it. It idles best with the mix screw turned out about one quarter (1/4) turn from seated.

Any thoughts on where to start looking??

thanks,
fried okra

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#494691 - 06/19/13 6:47 pm Re: Poor idle on '73 750 Tiger [Re: fried okra]  
Joined: Dec 2004
Posts: 8,890
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,890
Scotland
#78 drill through the pilot jet followed by a good spray of carb cleaner through the passageways making sure they are clear. Modern fuels do not like small jets and try to block them.

#494693 - 06/19/13 6:53 pm Re: Poor idle on '73 750 Tiger [Re: kommando]  
Joined: Jul 2011
Posts: 122
fried okra Online content
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fried okra  Online Content
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Joined: Jul 2011
Posts: 122
TN/VA/FL USA
Thanks....I've got some #78 drill bits ordered, can hardly wait for them to get here in about a week!!!!!

fried okra

#494732 - 06/20/13 12:33 am Re: Poor idle on '73 750 Tiger [Re: fried okra]  
Joined: Sep 2011
Posts: 933
Excalibur Offline
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Excalibur  Offline
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Joined: Sep 2011
Posts: 933
New Zealand
With needing to be 1/4turn from seated for best idle, it sounds like blockage to me too. Turning the mixture screw inward cuts the air supply off to the idle circuit, so either the fuel is restricted or there's an air leak elsewhere (manifold, etc).

I hear the US gasoline has an alcohol content. That won't be good news for carburetors, especially zinc based ones. I speculate that even the small amount of alcohol in the fuel will be attracting moisture. I run alky in the dragbike so I see the damage it can do. The carbs get drained EVERY time on that bike.
So I just wonder how the Amals are they holding up to the US fuel?

#494740 - 06/20/13 1:21 am Re: Poor idle on '73 750 Tiger [Re: Excalibur]  
Joined: Nov 2008
Posts: 2,672
desco Online content
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desco  Online Content
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Joined: Nov 2008
Posts: 2,672
Bishop, Calif.
@ Excalibur
They are holding up just fine. Bored and sleeved to correct wear problems, an annual PROPER cleaning and a bit of spring time general maintenance works miracles. I have access to aviation gas and I quit using it as it plugged up the idle jet all the time. I don't know how planes run on it.
PS Bless you for keeping Triumph in the records book.


1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.

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