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Re: carb question

To: TeachJP@aol.com
Subject: Re: carb question
Date: Tue, 05 Feb 2002 14:22:32 -0500
Cc: spridgets@autox.team.net
John,

There are three schools of thought on carbs for the later 1500 Midgets (which, 
btw, are from '75 to '79).  Earlier CB cars used HS2's and H1's, I believe.  

The 1st school of thought is that the car should remain as originally designed 
with a single ZS CD150.  There are two major issues with this setup and one 
small one.  The major issues are a) the manifold has several design flaws which 
seriously impede performance and b) the carbs have the nasty tendency to fill 
the piston chamber with gas if not kept in tune (which contaminates the oil).  
The minor issue is that the auto choke stinks.  This is fixed by installing a 
manual choke conversion kit.

The 2nd school of thought is to install a Weber cause "you gotta have a Weber 
on that thing."  I hate this reason.  1st off, most people say this because 
they assume that installing a Weber will give you a performance boost.  What 
they dont realize is that there are two Webers.  A DCOE which is a true side 
draft twin barrel carburetor, and a DGV which is a single barrel downdraft with 
a second barrel for when you stomp on the gas (great for mileage, sucks for 
performance).  The DCOE will give a great performance boost, but are real 
expensive and difficult to locate for the 1500 (with manifold).  But they do 
exist, and can even be set up with two carbs i.e. 4 barrels).  Be prepared to 
spend mega bucks.  The DGV gives about the same performance (maybe a little 
better) as the ZS, but has the added features of 1) set and forget, 2) no 
emissions functionality, and 3) a small attractive bump in the bonnet where the 
air filter usually hits.  Once set up, the DGV will run forever wi!
thout need for adjustment.  They get good mileage, and perform consistently.  
"Adjustment" leads me into the 3rd school of thought, SUs.

The 1500 Midget and Spitfire came equipped in the US with the ZS CD150 as 
stock.  But the UK versions came stock with SU HS4s, which are 1 1/2 carbs.  
Locating these carbs was once difficult, but as more people chose this route 
they are becoming more common.  John Esposito (Quantum Mechanics in CT) has 
been importing and selling them for years, but only the last 2 have shown a 
significant increase in sales.  As with anything else, there are benefits and 
detriments to the SUs.  Benefits:  1) more power and the potential for better 
performance (why potential, b/c most people install them, but dont take the 
time to experiment with the hundreds of needle profiles available for SUs.  Me 
included (no time).  2) more air and gas available at high velocity for the 
engine (high rpm).  Made better with K&Ns and velocity stacks (are these 
available for DGVs?).  Detriments:  1) difficult to set up for the uninitiated 
(novice) SU user.  But a little practice, a bunch of questions, and!
 a bit of reading later and you move along the learning curve rather quickly.  
2)  Balancing the carbs?  Easy.  Just takes a little time and some reading.  
You dont even need the SU air measurement tool for $25.  3) Requires regular 
maintenance, i.e. topping up the damper, and checking the plugs once a month to 
see if youre running rich or lean.  

I chose the SU route.  And once my wife lets me in the garage, I plan to 
install the Fuel/Air ratio gauge I bought last year.  This way I can really 
learn to play with the needles.  I have a program for selecting needles will be 
helpful when the time comes.  I hope this helped.

Just my 2 cents.

Mike

TeachJP@aol.com wrote:
>What is the advantage of the dual unit over a carb like the weber?  Aren't you 
>introducing the calibration problems with the duals as opposed to setting up 
the weber?

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