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Miss when when accelerating

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N233TX

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First post. '75 Midget, 1500 engine, owned since '81. Mileage somewhere south of 50,000...odo/speedo inop. Weber carb installed less than 500 miles ago. Runs great with one exception: When I stomp down on it at less than about 3,500 RPM, it stumbles for a bit, then catches. If I accelerate slowly, no problem.

My first thought is accelerator pump but you'd think a new carb wouldn't have that problem. Thought I would check with y'all before I started tearing things apart.

The stumble is rough, sounds fuel-related rather than electrical. Filters are clean and plenty of gas is getting to carb via an electric fuel pump (got real tired of replacing mechanical ones). Plugs are the right color and heat range. Can't imagine how timing, wires or points would do this but it wouldn't be the first time I was barking up the wrong tree.

TIA,
Jim in South Texas
 
Jim,
Welcome to BCF! I only have experience with A series engines with a Weber, but the 'stumble' is fairly common. It can take trying several jets to get it right and I decided to go back to the original SUs which fixed the problem. You can go to a shop that has Weber/MG expertise or you might consider the European SU conversion.
Good luck, Rut
 
500 miles ago but how LONG ago?

Did it do that when you first put it on?

How long has it sat since you last drove it?

What's your timing set at? You should be ~12 BTDC for best results.
 
Weber installed about 2-3 years ago. Car driven bi-weekly. Since certain equipment long since removed, timing is set at the British spec...can't remember what that was. Car runs *great* except for the aforementioned miss.

I replaced the single Stromberg and got the Weber from that well-known carb shop back east and I'm already having enough fun balancing piston-driven carbs on other toys.

Thanks for the help guys; more ideas welcome!
 
If you have a spare, try replacing the coil to see if that makes a difference.
 
Did it do it when you first put that carb on? I've had two with stock jetting and never really had that problem, others complain of it constantly. Make sure your intake didn't loosen up. Mine always had a problem with the back ones.Check your pump linkage too and make sure it's working correctly. IIRC you can adjust the stroke.
 
N233TX said:
OK, sounds like I need to get into the carb. Tonite maybe tomorrow. Thanks.
Click to expand...

Ya know, if you have more money than time, they make that carb treatment for small engines that's supposed to clean it out w/o disassembly. It's $8 IIRC and made by sta-bil but it''s not their regualar treatment.
 
I'm thinking you were right about the acc pump. Upon close examination, there isn't enough cable "pull" to engage the acc pump at WOT on the footfeed and still release back to idle. Weber manual that came with the carb is pretty useless. I'll be calling tech guy to see how to adjust the acc pump linkage to engage sooner. Or some clever force-multiplier for the cable geometry. Shoulda known a one-size-fits-all retrofit wasn't going to be as easy as grinding off some of the intake manifold and cutting a hole in the hood...
 
Bad carbon core wire's can give you fit's as well.
Experience!!

I like wire and never saw much use in a radio unless you are in town all the time.

Kurt.
 
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