Don’t take your SU HS4 carburetor apart


Why would anyone in their right mind take apart a well running SU HS4 carb that came off their MGB? Because you can!

I started out with the thought of just cleaning my carburetors and polishing them so they look nice. I would hate to have dirty carbs installed on my freshly painted engine in my freshly painted engine compartment, that just wouldn’t cut it. Here’s the problem. I decided to take the carburetors apart and of course they show 135,000 miles worth of wear and tear. There is lots of wear and play on the throttle shafts as can be seen below. These are relatively inexpensive to replace but how far do you go? If you replace the shaft you should likely replace the bushings. And if you do that you should… Get the idea?

Wear on SU HS4 throttle shaft
Wear on SU HS4 throttle shaft

The fuel floats are pretty ugly as well although when I last ran the car they weren’t leaking. One of them was sticking a little causing the occasional flow of gas to land on the hot exhaust manifold. There are solutions to this exciting car bursting into flames scenario with the proper installation of the always missing fuel overflow pipes.

SU HS4 Fuel Bowl Float
SU HS4 Fuel Bowl Float

So, do I just put the old SU’s back together and hope for the best or do I spend a few hundred dollars to rebuild them completely? Does the cost of restoring a 50 year old MGB ever come to an end?


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  1. Have you gotten these put back together and running? I am at this stage on the 1970 MGB GT I sold to my niece. Had to take them apart to clean them as fuel wasn’t getting through. Also, I wonder if you could post an extreme closeup of the throttle and choke linkage so I can see how they’re put together. I had a brain fart and didn’t take a picture before I started, now my 2 brain cells can’t remember how they went.

    • Thanks! I’m thinking I’m getting closer to divorce at this stage. Fortunately it’s only an MG, not a Porsche or Ferrari!


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