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Poor idle on '73 750 Tiger #494689
06/19/13 6:40 pm
06/19/13 6:40 pm
Joined: Jul 2011
Posts: 129
TN/VA/FL USA
F
fried okra Offline OP
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fried okra  Offline OP
BritBike Forum member
F
Joined: Jul 2011
Posts: 129
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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Re: Poor idle on '73 750 Tiger [Re: fried okra] #494691
06/19/13 6:47 pm
06/19/13 6:47 pm
Joined: Dec 2004
Posts: 9,149
Scotland
kommando Online content
BritBike Forum member
kommando  Online Content
BritBike Forum member
Joined: Dec 2004
Posts: 9,149
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.

Re: Poor idle on '73 750 Tiger [Re: kommando] #494693
06/19/13 6:53 pm
06/19/13 6:53 pm
Joined: Jul 2011
Posts: 129
TN/VA/FL USA
F
fried okra Offline OP
BritBike Forum member
fried okra  Offline OP
BritBike Forum member
F
Joined: Jul 2011
Posts: 129
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

Re: Poor idle on '73 750 Tiger [Re: fried okra] #494732
06/20/13 12:33 am
06/20/13 12:33 am
Joined: Sep 2011
Posts: 947
New Zealand
Excalibur Online content
BritBike Forum member
Excalibur  Online Content
BritBike Forum member
Joined: Sep 2011
Posts: 947
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?

Re: Poor idle on '73 750 Tiger [Re: Excalibur] #494740
06/20/13 1:21 am
06/20/13 1:21 am
Joined: Nov 2008
Posts: 2,721
Bishop, Calif.
D
desco Online content
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desco  Online Content
BritBike Forum member
D
Joined: Nov 2008
Posts: 2,721
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.

Moderated by  John Healy 


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