[Fot] Weber help and/or advice

[fubog1]

 Excellent write-up Tony!
 Glen
 
-----Original Message-----
From: Tony Drews via Fot <fot at autox.team.net>
To: Alec Buchan <agb at compsnw.com>; fot at autox.team.net <fot at autox.team.net>
Sent: Mon, Jan 18, 2021 5:20 pm
Subject: Re: [Fot] Weber help and/or advice

Alec, in my experience (also a TR-4), you can make just as much power 
with a well tuned set of SU's as with Webers.  My dad (Jack) ran SU's, I 
have Weber 42's (came with the car).  We were virtually the same speed / 
power.  Took us both a while to get there and required running on the 
Dyno to dial them in.

 From what I understand, the "Cannon" intake manifolds are considered 
the best.  I discovered that the 42's (which are rare as hen's teeth) 
take the same internal bits as the 40's, so I think the advantage is 
more psychological than anything over the 40's.  I ended up with the 
biggest chokes (venturi) that would fit - I think 36 mm was as big as I 
could go.  I do have a set of 45's that I keep threatening to spiff up 
and try.  I suspect that going to a 38 mm choke would be the hot ticket 
for my engine.  Depending on the build, 40's work pretty well.  Big 
bore, billet crank, hairy cam, high RPM would probably benefit from 45's.

What I found on the Dyno is that there's a ton of power in just getting 
the mixture right across the rev range.  I ended up with pretty small 
air correction jets to keep it from going lean at high RPM's.  I 
probably gained around 20 HP just by tuning the carbs.

 From what I understand, comparing jetting from one engine build to 
another is pretty haphazard, it's best to tune it to the specific engine 
rather than just copy someone else's jetting. Also, I believe the 
emulsion tube can make quite a bit of difference, so just comparing main 
/ air jet sizes if you're not running the same emulsion tube kinda 
invalidates the comparison. In my case I just used the emulsion tubes 
that came in the carb's and didn't try alternates.  I believe the big 
differences in those is more for part-throttle driveability which I 
generally ignore. If I can drive it to the grid it's fine, otherwise 
it's pretty much just wide open or closed, not a lot of part throttle.  
But other drivers may use more part throttle and so the emulsion tubes 
would be of greater importance.

I love the looks of the webers, but Jack was able to get decent mixture 
control with SU's and some slighly custom needles - I think he took RB's 
and skinnied down the tips to be more of the RA needle profile there.  
He also ran 0.104" jets to get enough fuel out (stock is 0.100").  We 
would draft each other at Road America, so were pretty close in overall 
power.

I'm not quite sure what kind of advice you're looking for - should I do 
it or not?  What specific setup should I get?  What carb settings should 
I start with?  None of these have cut and dried answers in my opinion.

Should I do it?  Maybe, but you can also get similar results with good 
well tuned SU's.  The webers look awesome though.

Which setup to get?  Partially depends on the engine build.  I suspect 
you'd be happier with 40's on a decent manifold with a decent linkage.  
If you have a monster motor you'll want 45's.

Starting setup?  If 40's, 36 mm chokes, possibly 150 mains with about 
130 airs is roughly where I ended up (need to dig through the expensive 
box of brass bits to verify).  No idea what emulsion tube or accelerator 
pumps I'm running.

One advantage of the webers is that they DO have accel pumps, so getting 
the engine started on a cold day without the choke is easier than with 
the SU's.

I found the tuning of SU's to be more obvious than the Webers.  I used a 
couple of books and Teri Ann's website to get a good understanding of 
what I was doing with the Webers.  The big aha for me was understanding 
that the main jet affects the mixture across the entire rev range while 
the air correction affects high RPM mixture more than low RPM mixture.  
Changing the air correction does also affect lower RPM mixture so they 
need to be tweaked in combination with each other.  Getting the air 
correction small enough that it didn't lean out at high RPM but big 
enough so it didn't richen at high RPM was my key, then I tweaked the 
main jets for max power and maybe went a step richer to keep the pistons 
un-molten.

Regards, Tony Drews

On 1/18/2021 2:54 PM, Alec Buchan via Fot wrote:
> It looks like I am moving up a group and in order to not maintain my 
> 'blue caboose' moniker, I am looking at converting to Webers. Moss and 
> Pierce sell a 2 x 40 DCOE kit but I've also located a 2 x 45 DCOE kit 
> (not from Moss or Pierce). looking for recommendations, if you might 
> be so kind.
>
> On a side note, the few of us here in the PNW are looking forward to 
> seeing all you 'front of the packers' in Portland this summer.
>
> Kindly,
>
> Alec Buchan
> Bellingham, WA
> '62 TR4 #5 (aka the Blue Caboose)
> _______________________________________________
> fot at autox.team.net
>
> http://www.fot-racing.com
>
> Donate: http://www.team.net/donate.html
> Archive: http://autox.team.net/archive http://www.team.net/pipermail/fot
> Unsubscribe/Manage: 
> http://autox.team.net/mailman/options/fot/tony@tonydrews.com
>
>
_______________________________________________
fot at autox.team.net

http://www.fot-racing.com

Donate: http://www.team.net/donate.html
Archive: http://autox.team.net/archive http://www.team.net/pipermail/fot
Unsubscribe/Manage: http://autox.team.net/mailman/options/fot/fubog1@aol.com


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://autox.team.net/pipermail/fot/attachments/20210119/f70d4117/attachment-0003.htm>