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MG MGB Technical - Sidedraft MCHH Weber Carb Conversion

Has Anyone tried this conversion. I found the an ad for the complete conversion with filter for about $350. Here is the link

http://www.racetep.com/mgbmcch.html

Steve Sletta
Stephen Sletta

I've had no personal experience, but the word I get is that the mixture is not right out of the box. Also, you are best to leave the choke disconnected and be very careful of vacuum leaks.

You might want to talk to a weber specialist like Mike Pierce (Pierce Manifolds) and see if he has some experience with them.

Sean
Sean Brown

And don't expect miracles, since your engine is still going to be strangled by the standard inlet/exhaust manifold.
Derek Nicholson

Three cautions:

1. Before replacing a Zenith Stromberg carb, talk to John Twist. He knows how to make these carbs work well and he's very positive about them.

2. My only experience with Weber carbs is with a '76 B I bought back in the '90s that came with a DCOE side draft. It had spun a bearing due to fuel in the crankcase which I was told was due to over-carburation. I rebuilt the engine using HS4s. No doubt the Weber was just poorly set up and it could have been made to run right, but I had neither the interest nor the patience.

3. I don't know anybody who has switched to the DGV downdraft that didn't eventually convert back to SUs due to disappointment with performance of the Weber.

Having said all this, I know nothing of the new MCHH. It might be very good. My question is: "Why?"

FWIW,
Allen
Allen Bachelder

Allen,
I changed my 74 BGT to a Weber downdraft in the late 80's. It is now on the third engine. Firtst engine 135000. Second engine 95000. Still works great.

Steve
Steve

What do all think about this set up from Brit-tek

http://www.brittek.com/webersuperkit.html

thanks again for you advice
Steve Sletta

Steve-
You just had to ask, didn't you? The downdraft Weber DGV 32/36 makes the engine look as though it was pirated from a Russian tractor. Its usually-included adapter manifold has the airflow characteristics of a bathtub with a hole in each side. This is due to Pierce Manifolds, its distributor, bundling their own poorly designed intake manifold with the carburettor and selling the resulting package as a kit. As a result, virtually every example of this combination that I have encountered or ever heard of had a “flat spot” in the powerband from 1,500 to 2,500 RPM where throttle response was poor due to a weak fuel-air mixture. This “flat spot” can be eliminated by instead using a Cannon intake manifold that incorporates a pair of fittings to cycle the hot coolant from the radiator heater hose (flexible pipe) to the front of the manifold and from the rear of the manifold to the heater box. The result is smoother running and elimination of the infamous “Flat Spot”. However, this will not eliminate the problems imposed by the restrictive airfilter that Pierce Manifolds supplies with it in its kit. The Weber DGV 32/36 is a progressive-type carburettor. This means that the 32mm primary bore is opening with the throttle first, but the 36mm secondary bore (hence the 32/36 designation) does not open until the accelerator pedal is about 2/3rds of the way to the floor. Since 1˝” equals about 38mm (1.496”), there are two considerations. First, due to the smaller bores of the Weber design, the two bores of a Weber DGV 32/36 series carburettor together cannot possibly flow as much fuel/air mixture as twin 1˝” SU carburettors can at full throttle. Second, when at less than full throttle, the progressive opening of the 32mm and the 36mm bores of the Weber design do not flow as efficiently as the constant-velocity airflow of the 1˝” SUs. It is simply impossible for a Weber DGV 32/36 to perform as well as twin 1˝” SU HS4 or 1˝” SU HIF4 carburettors.
Steve S.

Steve S,

"The downdraft Weber DGV 32/36 makes the engine look as though it was pirated from a Russian tractor. Its usually-included adapter manifold has the airflow characteristics of a bathtub with a hole in each side."

Thanks for my chuckle for the day. And of course, you are right about the SU carb. I'm an amature, and I've never had one that I couldn't make work really well (admittedly, sometimes changing out several parts) just by using a color-tune and some careful test drives. If a person doesn't like their single Zenith Stromberg, their best choice is a pair of HS4 or HIF4.

And don't get me started on the standard sauce-pan air cleaners. I've never had any aftermarket device work better than the original set up on an MGB.

Warm regards,
dave
Dave Braun

Steve S & Dave B,

Amen!

Allen
Allen Bachelder

This thread was discussed between 04/03/2008 and 08/03/2008

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