Different gurtner carbs on Mobys

I've got two bikes here, both 1977 models. One is a 50V and the other a 40TL. Both have the larger style gurtner carb.

The carb on the 50V has a 6mm stud to attach the air filter, and a choke cable than enters from the bottom.

The carb on the 40TL has a 5mm stud, and the choke cable enters from the top, next to the throttle.

There are a couple other minor differences, like the design of the mounting clamp. Other than the obvious differences, are there any actual functional differences between the two carbs? Can they be interchanged? What's the point of the variations?


Re: Different gurtner carbs on Mobys


The difference in these Gurtner Carbs is the end speed is different. These carbs are junk, though. You probably would get a better performance out of a Bing.


Re: Different gurtner carbs on Mobys

Thanks for the info, EK. So I take it then that the carb with the 5mm stud is for a 20mph model?

In my brief experience with them, the gurtner has not overly impressed me. I have seen much worse, though.. like the Amal concentric. All I can say is "Lowest bidder". And then there is the Amal monobloc - what were they thinking with that float bowl cover?

Thing is, I'm one of those folks who either keeps it as completely original as possible, or just modifies at will. I'd like to be able to make the gurtners work.

If I had to modify it, I'd probably go for a dellorto. I'm quite fond of those carbs.

Re: Different gurtner carbs on Mobys

See Ya Moped Army /

The carb body itself is the same with the exception of the size of the intake on the carb. The speed rating is correlated to the intake size (10mm or 12mm) and the size of the jet. It is also determined by the size of the ports in the jug.

Re: Different gurtner carbs on Mobys


Dellortos are good too. I'm the same way, I like mopeds 100% original.

I had a 72 Moby-X and it was next to impossible to find a decent Gurtner for it that would fit properly due to the small engine configuration as well as limited space for the carb. I purchased 3 or 4 of these and after finally getting the right one, I cleaned it up and put it on. In 2 weeks, the Gurtner was already gummed up- even if I had an inline lawnmower filter.

That drove me nuts. I love to work on mopeds, and the such. But when it comes down to cleaning the same carb over and over, it can get old fast.

Gurtner also needs to be airtight in order for it to work properly. Other carbs can deal with a little bit of an air leak. But not Gurtners.

Best of luck on your project.


Re: Different gurtner carbs on Mobys


In most cases, the Gurtner carb bodies are the same. But there are some varying smaller sizes available for older mopeds that are pre- 1974. (To fit on the Motobecane Moby-X mini's as well as the Motobecane Cady with the smaller engine head.)

The intake size and the ports do make a big difference in the end speed.

I find it interesting, because on my Columbia Open Road with the Solo engine, for instance, the speed was changed via the clutch flange nut. On these when you grind off about 1/8 of an inch off the flange nut, the clutch engages "smaller" so the front belt is running smaller, giving the Columbia more speed. I've already done that and my Columbia goes around 35 stock with the flange grinded down. I've got a rear wheel in the garage with a 42 tooth sprocket. That ought to give me a little more end speed. Can't wait to install that. ;o)

On others, it's either the rear sprocket size, front sprocket, or the variator. But with the Gurtners on Motobecanes its the carb size/jet/port. Hmm..


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