Crap! Is my carb hosed? (50V)

So, I was taking apart my carburetor ('78 50V, stock Gurtner carb) to clean it, when I noticed something odd about this throttle piece:

The throttle cable lowers/raises this piece inside a cylindrical chamber, and that meters the flow of air. The odd thing was that this piece seems like it should definitely face a particular way, since one side has a wedge-shaped cutout, but it was free to spin inside the chamber. The chamber has a keyway down one side, as if to prevent this piece from spinning around in there, but nothing on this piece goes in the keyway. Part of the top of this piece looks chipped off-- was there a nub here that fit in the keyway? If not, what mechanism keeps this thing in the right orientation?

Then, I started taking out a brass screw on the bottom. That fell out, revealing a threaded brass collar. I took that out, and there was another, smaller brass thing under that... but when I tried to unscrew that, I stripped the slot right off of it. I think it was my main jet, or it holds it in. So much for getting it out... should I just put the other brass pieces back in? Or will it not work now that its surface is, err, "modified". Should I just get a Dellorto carb?

If you read all that, thanks! If you know anything about these carbs, I'd love to hear it.

Re: Crap! Is my carb hosed? (50V)

Found this drawing in the photo section:


It's _just_ low enough resolution that I can't tell for sure, but it looks like I was right about this piece being keyed.

Can someone confirm that? Does anyone have one of these carbs that's broken for another reason, and could send me this throttle piece (intact)?

Re: Crap! Is my carb hosed? (50V)


The part you are picturing is the Throttle Slide.

Yes, it is damaged. Some clever person didn't install it correctly, and when they tightened on the top cap, they broke the little key off of the slide. If you look carefully on the upper surface of the throttle slide bore on the carburetor, you may be able to see the a small indent where the key got pinched and broke.

In any event, you need a new throttle slide.

The parts you removed from the bottom of the carb are, in order - the main jet, and the diffuser (atomizer) cap. The part you damaged is the diffuser (atomizer) itself. You're in kind of a tough spot.

If all you did was strip the screwdriver slot in the bottom of the atomizer, and it didn't swage any of the metal over the atomizer inlet, then you might be able to just reassemble it and run. I've never had any reason to remove the atomizer from a Gurtner, so I wasn't even aware that it was threaded - I assumed the cap held it in place.

If it's actually threaded in there, about the only wat to get it out is some careful drilling and use of a screw extractor. Let some penetrant work on it first, and then heat up the area before trying to use the extractor.

If it's not threaded, then remove the cap, and use a plastic or hardwood dowel down through the slide bore. Give it a couple good taps, and see if you can knock out the damaged atomizer.

In the future, be careful with those little brass parts. They're just too easy to break.

Thanks again!

Legendre, you are on a roll today. I will look for markings to see how that key broke off. The "clever person" might have been me, I loosened that cap where the throttle and choke cables connect a while ago, and didn't realize that I couldn't just tighten back down on it.

Although, I haven't run the engine since then, so the broken key should have still been in the carb, and I didn't see it. Maybe it broke off a while ago and ended up in my crankcase. I hope it doesn't cause trouble in there.

Re: Thanks again!

Just so you know all throttle valves from gurtners are not the same. I had a gurtner from a model 50. it looked the same it all respects, but the throttle valve was too small to fit a gurtner from a 50v.

So if you are looking for a replacement gurtner valve or whole carb, insist that it came from a 50v.

they show up on ebay frequently, and since people do install delortos on motobecanes you may have luck finding a gurtner in the buy sell section of this site.

People have had trouble mounting the delortos on the moby intakes, so I would do some research before trying to do it yourself.

good luck


Love the illustration

Re: p.s.

Yeah, about that illustration.. it's not exactly what I'd call an accurate mechanical drawing, but whomever did it has some real artistic ability. Good eye for form, perspective, light & shadow.

Has the look of being done on some kind of digitizer, like a Wacom (wack'em!) tablet or something.

If the key made it into the crankcase, it's probably not much of an issue. It's vey small, and made from cheap, soft potmetal. As long as it didn't snag in a port, or get directly into a main/rod bearing, it will be fine down there forever.

Thanks, guys

Glad you guys liked the artwork... I was just going to make the outline, but then I started using the fill tool, then went a little nuts with the airbrush. I'm sure it's not accurate, since I was working from memory, but I had shoved my moped back into the garage in disgust and didn't feel like going back out there to photograph any parts.

Since the keyway is supposed to be (nearly) aligned with the cable slot on the slide anyway, I'm thinking of putting a strip of metal in there that would fit into both the keyway and the throttle slide cable slot... do you think that'd work?

Re: Thanks, guys

There are a couple of problems with that..

First, the slide would not be in the correct position, and it would have some effect on how the bike ran. The profile of that cutaway on the slide is critical to operation.

Second, I'm not sure how you'd ever be able to replace the throttle cable.

Re: Thanks again!

Mike Scouty McScoutington /

i have a 15:15 on my 50v. i wouldnt trade that for anything. true it can be a pain to get the carb mounted to the intake but the solution their is simple. get a new intake. i got my hands on a 15 mm intake for like $8. everythign fits nice and snug. whats more i know a guy who is looking into getting some 15 mm intakes made up that will fit in the space even better. if you want any info in getting your hands on a dellorto and or a new intake drop me an email and i can get a hold of the shop.

Re: Thanks again!

Cool. drop another post on this thread if this guy makes some better intakes, with how much he would charge

Re: Thanks again!

Mike Scouty McScoutington /

you got it.

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