[Fot] Weber DCOE 45's on TR4

[Bill Babcock]

the additional holes can probably be drilled and will likely solve the  
stumbling problem. I haven't done anything like that yet, my weber- 
equipped TR experience consists mostly of "will it run at some kind of  
idle" and "does it pull cleanly with full throttle", but the  
modifications you're considering were done commonly with the over- 
large carbs fitted on motorcycles. You can probably reduce the problem  
across the range by fitting a substantially smaller choke. The big  
benefit of drilling progression holes is that once the butterfly or  
slide is open they don't do anything, so they don't screw up the rest  
of the range.

If I were going to do such a thing I'd go about it the same way we did  
on motorcycles--make a drilling jig. This is simply a piece of steel  
with a properly sized hole in it, a stop on the other end to locate  
the drill hole, and a jobber length drill of the appropriate size.  
Long skinny drills require a very light pressure and a steady hand.  
Don't make the jig thick expecting that it will help guide the drill-- 
thick walls will make it very hard to keep from binding the drill. As  
I dimly recall, the semi-official jig for adding another progression  
hole to the carbs on the Yamaha 500 twins (I think they were called  
XS500) was a piece of cad-plated sheet metal--probably 16 gauge.

You can also make the existing holes larger or make them more trench- 
like. For that we used a foredom flex shaft tool with a dental  
handpiece. You might be able to fake it with a dremel and flex shaft.

All these kinds of mods are cut and try. You can screw up some  
expensive carbs and render them unusable for street use, but then they  
are race car parts where progression isn't anything to worry about.

Really, the problem is best solved with injector bodies and a laptop  
with fuel mapping software. There used to be lots of guys who could  
make carbs do everything but speak, I suspect there are a lot fewer now.

On Jan 1, 2009, at 3:38 PM, Peter Vucinic wrote:

> Dear Lister's,
>
>
>
> I am seeking those people who have had experience with 45mm WEBER  
> DCOE's
> fitted to TR3/4 engines.
>
>
>
> Specifically those that have modified the progression circuit holes to
> remove problems such as 'stumbling/hesitation' and having to run  
> excessively
> RICH idle jets to overcome 'stumbling/hesitation'. I suspect this  
> issue will
> more relevant to those of us who run road cars, rather than race.  
> But it is
> as equally relevant to those who race. It appears that the problem  
> is found
> with those of us running modern DCOE 152's with 78 Degree throttle  
> plates.
> But not limited to this model. DCOE 152's have three progression  
> holes that
> are all position FORWARD of the throttle plate.
>
>
>
> When you look at the throttle plate position (remove progression  
> hole plug
> in top of carb), it is behind the first progression hole and NOT  
> directly
> over the plate. This means that when acceleration begins, the top of  
> the
> throttle plate, moves forward towards the ram tube/air cleaner side.  
> The
> throttle plate then covers the first progression hole as the  
> throttle plate
> moves forward.
>
>
>
> My question is, has anyone drilled other progression hole(s) so that  
> it/they
> are positioned directly above the throttle plate?
>
> I suspect the 'period' DCOE9's will have different progression holes  
> and or
> positions.
>
>
>
>
>
> Kind Regards
>
> Peter Vucinic
>
> TR-4
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Bill Babcock
Babcock & Jenkins
Billb at bnj.com
503.936.7660
www.bnj.com

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