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Re: [TR] fast idle problem

To: Bob Leaver <>, "" <>
Subject: Re: [TR] fast idle problem
From: Michael Marr <>
Date: Wed, 13 May 2020 01:40:50 +0000
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Thread-topic: [TR] fast idle problem
The Moss reamer cuts a hole that is 10 thousands (nominal) oversize, and 
requires you to use ten thousandths oversize throttle shafts.  The reamer has 
an extended pilot, so that, even when reaming by hand, the alignment between 
the holes on each side of the throttle body is maintained.  To that extent, it 
is a special reamer, which accounts for its price.  I found other piloted 
reamers, but they are chucking reamers and the pilot is quite short, so you 
would have to set the carb body up on a good drill press (or vertical mill, 
preferably) with the axis of the throttle bushing holes perfectly vertical.  
The body would have to be clamped to an angle plate in some manner.  Such a 
reamer, of the right size, can be found here...

Part number 99-703 is what you would want.  But, unless you've done this kind 
of set-up before, I wouldn't recommend doing this.  I think sending the bodies 
out to have new oversized shafts fitted might be the most expedient thing.


Michael J Marr, P.E., CEng.
Albion Technical Services
W5918 Hackbarth Rd
Fort Atkinson, WI 53538

Cell:  630-202-0065

-----Original Message-----
From: Triumphs <> On Behalf Of Bob Leaver
Sent: Tuesday, May 12, 2020 4:58 PM
Subject: [TR] fast idle problem

I have a 1965 Triumph TR4a that I rebuilt the SU carbs and now I can't get the 
idle below about 1500. I've tried all the screws and checked all gaskets and 
nothing. The only possibility I can come up with is air getting around the 
shafts. When rebuilding the cars I didn't replace the shafts because I didn't 
have a reamer. Moss has a reamer for $290.00. I looked on line and can't find a 
less expensive replacement. The book states the size of the reamer is 5/16" + 
0.0105". What kind of measurement is this? Can you use a 5/16" reamer?
Does anyone have ideas how I can get the idle down? Does anyone know of a 
cheaper reamer to use? Thanks, Bob
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