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Carb question

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jaybird

jaybird

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Brian (my son) has a 75 Midget. He wants to convert the carb to either SUs or a Weber downdraft.

Got this email from him:

Would you mind asking around on the forum and find out which set up would be best for a 1975 Midget 1500? And how much people would spend for used twin SUs for an 1500 midget. This would be a good start for trying to convert my
car back to British specs...Thanks.

https://cgi.ebay.com/ebaymotors/MG-Midget...1QQcmdZViewItem
 
We'd have to hear from someone who tried it, but I heard that the dual SU setup doesn't fit on the 1500 midget due to frame clearance issues. However, a single 1.5" SU would be a good replacement (direct fit, too) for the ZS carb. Or, as an alternative, I would recommend the single sidedraft (45DCOE) weber. I would not recommend the DGV and other variants of the downdraft variety. I think they're only marginally better than the ZS in terms of potential flow. The single 45 DCOE may be a bit more difficult to tune (mariginally so), but it will be a blast if he's looking for a bigger carb setup (and it's a single carb setup, so no balancing of carbs ... a big plus in my opinion). Dual 40 mm DCOE's is overkill for a stock engine.
 
I've seen pictures where people cut the corner of the foot box for clearance for the dual SU's. They said it was no big deal. I'll look for reference on it. I see alot of 1500's with the down draft weber.
 
I've heard of someone that trimmed the inner fender and used pancake filters as well.
 
[ QUOTE ]
However, a single 1.5" SU would be a good replacement (direct fit, too) for the ZS carb.

[/ QUOTE ]

I'm going to do this eventually, but it's unfortunately not a direct fit. The studs on the intake for the ZS do not match up with the 1.5" SU I have. To mate my existing intake to the carb, I'll have to weld up the stud holes and redrill them (the bolt pattern overlaps) How the linkage will work isn't immediately aparent to me either, and will require some fabrication.

After messing with my ZS at some length I'm convinced it's not that bad of a carb once you plug all its emissions related ports. He should try this first IMO.
 
I think mebbe (and as always, feel free to tell me I am crazy) that a single HS4 or HIF4 is an excercise in futility. What would be the objective? You are not going to get any significant power out of that swap. You may get a little less fuss out of that carb, but I would think it would have to be a LOT less fuss to make it worth welding anything. Rebuilding the stock ZS and replacing the needle makes much more sense to me.

BTW, the biggest problem most people have with the ZS is with the choke I think. And those problems can usually be fixed with a little cleaning and adjusting.

Finally, there are three emmissions related ports (on my carb anyway) and I would not reccomend plugging any of them. One goes to the ELC cannister. If that one is giving you greif (unplug it while running, if your idle changes, you got problems) you can easily and inexpensively (@$10) rebuild the canister. Another goes to the crank case ventalation system. Plugging that one can lead to all your oil being blown out the dipstick (trust me!). The final one leads to spark advance and EGR. If you are disabling your EGR, just remove the tee from the line and voila!

Just my $.02.
 
Twin SU's on the third hand... well.... /ubbthreads/images/graemlins/wink.gif
 
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