MGB & GT Forum

Greetings, All! I have a 1976 MGB with a Weber 32/36 conversion. I find that the car is incredibly hard to start when it's hot and has been sitting for a few minutes. I've also noted that it sometimes runs on after switching the ignition off (not continuously running, just hitting on a cylinder or two or three as it spins down). I suspected an overly rich mixture, however when I pulled the plugs they were only a little on the grey side of tan, indicating an acceptable mixture. There was some carbon build up on the flat ring at the bottom of the threaded section, but that's a much cooler area of the plug, and I'm not concerned about that at all. The electrode and ground strap both looked perfectly fine. I'm not very familiar with the Weber carburetors, and so thus I'm very unimpressed. The car doesn't seem to make much power, and I also notice an occasional backfire if I give it too much throttle before it's fully warmed up. I'm very mechanically inclined, however I don't want to just go tearing into this thing without understanding how it works, and how it's supposed to be set up. Alternatively, if someone has a decent set of HS4's with a manifold and everything that they'd be willing to part with, I would much rather do a complete replacement to SU's (even though this year would have come with a Zenith-Stromburg). Any advice on where to start looking, and what tools and reference manuals would be helpful would be gratefully received! Cheers!

I've run the Weber and SU (HS4s) on my B and I MUCH prefer the SUs. I don't have any hot starting issues, but I did have them with the Weber. Can't remember if I had the run on as well. I always thought that was a lean issue, but I'm probably wrong. I did something similar to this on my Weber - https://www.mgexp.com/forum/mgb-and-gt-forum.1/weber-carb-heat-shield.452701.3722513/page-2 I probably still have the shield if you want and if I can find it. I know I didn't put anything heat resistive material on the bottom, but I should have. And it's been so long that I can't really remember if it worked. I want to say what worked on the Weber with a hot start was putting the accelerator all the way to the floor when starting.

Here's another form of the heat shield - https://www.mgexp.com/forum/mgb-and-gt-forum.1/weber-carb-heat-shield-installed-and.1494140/

Sorry, I'm not much help, but I thought the link would at least help.



Edited 2 time(s). Last edit at 2024-04-17 12:43 PM by 19911976.

Contact Harry Singleton in the Piney Woods of East Texas if you want perfectly rebuilt SU carbs. He goes by "Rufus" here on the forum.

I run a Holley 5200 near about the same as a Weber. Non problems and my car runs much beter than the old wore out SU's. YRMV

Thank you all for the replies. I think I'll fiddle with the Weber for a bit to try to get something a little better out of it while I'm on the hunt for new SU's and all the bits that go with them. I automatically assumed that it was a rich condition, but as I'm doing more research, and as mentioned here, it might be a lean condition. I'll play with everything this weekend and see what I can sort out. I'm also hoping to get the last of the issues sorted with the Midget and get that back on the road. Thanks again, everyone!

Have you tried fine tuning the timing to see if that reduces the running on ? I was convinced I had a carb problem when i experienced this but it was resolved by adjusting the timing

When I bought my Weber 32/36, I bought it from Brit-Tek b/c they supposedly said that all Webers were not created equally for the B and their setup was jetted correctly for the B. Whether that is true or not, I don't know, but it certainly sounded good to me! I will occasionally get a run-on condition in my '70 B, but since lowering the idle a bit, that too has all but disappeared. Many guys, as you've read above, like the Weber. I ran mine for many miles, but after having both on the car, I think my car liked the SUs better. Not trying to start a carb war...to each his or her own. Run what you can, like, afford, etc.

And if you're new to the MG world, you might want to learn the name, John Twist.

What type of choke? Manual? Electric? Water?

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Chip Long
Charlotte, NC

Retarded timing causes extra heat and lethargic performance. Try 14 BTDC at idle and richen your idle mixture a little bit as fuel cools the cylinders to prevent hotspots.

Also learn to set the float height. That'll prevent a lean condition via the emulsion tubes as well.

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jeff@advanceddistributors.com

Chris, I set the timing to 10* BTDC with a timing light. Somewhere in the last 50 years or so the distributor has been replaced. I have no idea what it is. I have three white wires coming out of the bottom (near the engine block), and three multi-coloured wires that are hooked up coming from the top (just below the rotor cap). There's no vacuum advance on the unit, and so far ignition seems to be pretty strong.

Bill;

Thanks for the reply. I know of John Twist; He puts out some fantastic videos. I'm also not interested in getting in the middle of the carb camps. I have SU's on my Midget and love them. I would like to simply put a pair on the 'B because I'm familiar with them, and I think they look fantastic. If this Weber wasn't giving me such a hard time, I would just leave well enough alone, and run it until it didn't run any more. Since I'm having trouble with it, and the Weber isn't even close to the original equipment, I think I'd rather go with something that I like if I'm going to go through the trouble of replacing the carb and manifold. Thanks again for your insight!

Chip, thanks for asking about the choke. I hadn't thought to mention that. The choke looks like it might have been a manual at some point, but the pull-knob is completely seized inside the car, and all the bits for the choke are loose/not hooked up on the side of the carb. I was giving some thought to getting a replacement manual setup from Amazon. That would at least solve that part of the puzzle.

Jeff, thanks for the info! I set the timing to 10* BTDC with a timing light. As I mentioned, the distributor has been replaced some time in the past. It was at about 15*, and I notice a pronounced drop off in performance after setting it to factory specs. I'm holding off on buying the manual for the Weber until I see if I can scare up a pair of SU's and a manifold. I think I'm leaning much more towards just chucking the Weber and going with the SU's if I can find a setup at a reasonable price. Have a great day!