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MG MGB Technical - Manual Choke Conversion Installation

Does anyone have a good writeup for installing a manual choke conversion kit?

My car is a US non-california 1980 MGB with a single SU carb.
JG Grant

Do you mean a 175 Zenith Stromberg? I don't think single SU's were used in the US. There are now replacement single SU's for the troublesome Zenith sold by Moss and VB. I think they are 44HIF. The 44 being mm throat. These carbs are manual choke.

Below is a web site that doesn't recommend the manual choke conversion. Moss and John Twist have writeups on how to set up the auto choke. It likely takes regular maintenance. http://www.motorheadltd.com/bad_parts.htm

I'm sure you'll hear good input from others.
Robert McCoy

Sorry Robert, I thought SU and Zenith Stromberg were interchangable terms. I've been out of the MG scene for many years now but have recently gotten my '80 B started again.

I purchased a manual choke conversion kit years ago and never installed it.

Your link states the following with regards to the manual choke conversion...

"We do not recommend these as we feel that a properly maintained auto choke works best. If the choke is serviced as per workshop manual recommendations, it will work correctly."

I do not know what the workshop manual recommends for maintenance on the automatic choke.

This being said and seeing as the link did not say the manual choke conversion was a bad thing in it of itself, assuming it's more than just adding oil to the carb regularly, I feel it's simplest to go with the old fashioned manual choke conversion so I can simply control it myself.

In the short term, the manual choke conversion is likely to take longer than a single service of the automatic choke. In the long term, I hope for this to be a single time investment which will net me many years of troubleless starting/idling.

More feedback is greatly appreciated, from you Robert and everyone else.
Jeff Grant

I had a 74 VW camper van with a single Solex downdraft carb with auto choke. I hated the auto choke and always wanted rid if it but never got around to it. People were always prattling on at me about making sure it works properly, but I wanted rid of it for the same reason I bought the electronic ignition kit for it and the electronic distributor for my MG. Its one less thing to worry about. Its just fit it and forget it. I like that.
Ross Kelly

I don't know anything about the Solex-Stromberg except what I've ready. Luckily I have good old SU HS-4's.

Hopefully someone who's done the conversion will chime in. I can understand your desire to go manual choke. A 67 Mustang I had lots of auto choke problems.
Robert McCoy

JG,
I have a '77 MGB with the original single carb. About five years ago, I had major problems with the original automatic choke and had a manual choke installed. No problems! And, no worries about making ajustments. Starts the car every time.
Donald Elliott
Noblesville, Indiana
DonaldElliott

Thanks Donald for your response.

I'm glad to hear that everyone is not just "if you maintain it properly, there is no reason to change it" and instead understands where I'm coming from with my request.

How much did it cost to have someone do your conversion kit for you? (Sounds like you paid someone to do it)
Jeff Grant

Many years ago I had a Scimitar GTE with a dual choke down-draft Weber with water choke. A manual conversion for that was a popular option, and mine definitely wasn't right when I got it. But I persevered tweaking both amount of enrichment and amount of fast idle until I got it right, thereafter it was fine.
Paul Hunt 2

I have to agree, just fit it. It should be very straight forward and you can give your full attention to something else on the car which im sure is duly needed. Of course a well serviced auto choke will still work the way it should, but I ask this question.... If the HS4 SU's had an auto choke option would you all be wiping out your credit cards and calling moss right away ?
James

Can anyone comment on installing a manual choke conversion on their own and it's difficulty?

I tried to look for the one I had purchased many years ago (after I last parked it), but couldn't find it. I fear I'll need to order another.

You can rest assured I will do a detailed pictorial when I install it if I end up ever getting some info on it! =)
Jeff Grant

http://www.sterlingbritishmotoringsociety.org/files/choke.pdf describes the water choke and how to get the best out of it. It doesn't describe fitting a manual kit, but as I understand it is not much more than removing the water jacket and substituting a housing containing the cable quadrant. You will probably spend more time running the cable than modifying the carb.
Paul Hunt 2

I installed a manual choke in my 1980 mgb a couple of days ago. Pic shows how it looks now.

There was way more stuff attached to that choke cable than I imagined.

Stu Rodger

I've just noticed the original poster has a single SU, which always had manual chokes when used on the MGB anyway. If you *do* have a single SU with water choke, it is a PO mod, and I don't think you are going to find many (any?) who have done the same thing and then converted it to manual. I.e. you are on your own. Unless, of course, what you actually have the single Zenith and not an SU.

Stu - your photo shows an engine bay! Not much help in determining how the choke is installed.
Paul Hunt 2

Just a lighthearted post after much hard work converting my ZS carburetor. Sorry to intrude Paul! I suppose I should have posted something about my Scimitar GTE with a dual choke down-draft Weber with water choke.

Jeff it appears to be a very simple change to manual choke. Purchase the kit, and you can see how the manual choke housing replaces the water choke on the ZS. I have heard many differing positions on auto choke on ZS, but if I had not replaced mine with HS4s that auto choke would be gone.

Take the rheostat out, connect the wires together. Your dash lights will be on bright whenever your lights are on, but this is the easiest location for choke handle. There is a rectangle rubber cover on the firewall, drill a hole through the rubber just large enough to squeeze the choke cable through.
Stu Rodger

I feel so ignorant when I ask about these cars!

The first reply questioned if I really meant SU or Zenith Stromberg. I honestly don't know which is which. As far as I know, it's the stock carb for a 1980 MGB LE 1.8L I4 motor.

Here's a picture I found on the web.

http://www.chicagolandmgclub.com/photos/zs_rebuild/32.jpg

Paul, your PDF doesn't give a full blown picture of the carb, is that the one we're talking about?

Considering you said the SU never had an auto choke, it's probably safe to assume I really have Zenith Stromberg.
Jeff Grant

Another note Paul. That PDF did a good job at explaining the parts of the auto choke setup.

But it did not explain what could be a cause of my idle never being in a "high idle" mode. My car starts and stalls. I hold the idle with my foot until it's warmed up at which point it idles fine again.
Jeff Grant

Jeff,

Your picture is the Zenith Stromberg. It is similar in operation to an SU, but uses a rubber diaphram in the dash pot instead of a metal piston/metal cylinder.

Can't help you with the high idle. It's been too long since I had my Saab with the Stromberg.

Charley
C R Huff

Jeff - pages 2 and 3 show the fast-idle pin (item 3) and fast-idle cam (4), the cam has to move this pin to open the throttle slightly to prevent stalling when cold (p6). P13 and 14 show the idle and fast idle screws and the correct clearances. However Haynes shows the clearance at 4 as being .025" not .035" as in the PDF. Haynes says to set by "turning the throttle stop screw as required. Tighten the locknut to retain the screw and recheck the clearance." You need to check that moving the pin opens the throttle, and that the cam can turn and moves the pin.

Rotating the heat mass control the amount of enrichment required, and adjusting the screws controls the amount of idle and fast idle. I think the idle needs to be set first when the engine is hot, then you fiddle with the heat mass and fast-idle screw to get the cold running right. In theory the correct clearance should result in the correct fast-idle (if the cam and pin are working correctly), but in practice you may well need to experiment. I know I did on the Scimitar, and also on the HIFs even though the latter had a manual choke anyway
Paul Hunt 2

Thanks Paul for your response. I wasn't sure if there was more to it than that.

I guess I'll actually need to let it idle up to temp so I can set the warm idle so I can try and adjust the cold start idle.

This will at least let me run the auto choke until I find the manual one.
Jeff Grant

This thread was discussed between 02/04/2008 and 07/04/2008

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