What size jet?

Hey guys,

What size jet should you use? It's my understanding that it all depends on weather and such... but is there a general range that should work for summer riding?

Thanks

Mark

Re: What size jet?

oh, and what does it mean to "upjet". Is an example of upjetting going from a size 60 to a size 70? What size is stock?

Re: What size jet?

I.R.E. Mike Pee /

Upjetting is going up in jet size. So yes, 60 to 70 is upjetting, but that's a pretty big leap.

For us to tell you about what jet you will need, you need to give us more details. What kind of bike/engine, what size and type of carb, kind of air filter, kind of exhaust.

Re: What size jet?

hey, you need to let people know what kind of bike you have, then they may be able to help you.

Re: What size jet?

Thanks, sorry I'm a bit new to this but I'll get the hang of it.

I have a Puch Newport 1978. It's real beat up but its comin back baby! I don't know what size jet is in there now, but I've cleaned it about 6 times. What jet comes stock with that bike (assuming it _is_ stock).

I also did a search and apparently what I want to do is buy a couple jets and do plug chops to see what kind works best in my given area.

Only problem there is I need to have a running moped to do a plug chop, I'm trying to order parts (chains, fuel filter, probably some gaskets) might as well get jets too. What sizes are pretty standard for a Puch Newport 1978 in the new england (vermont) summer? Oh, its a one speed engine (e50 i think) with your stock exhaust (the one on themopedjunkyard.com)

Thanks

Re: What size jet?

Oh and its a stock bing carb. Stock air filter.

Re: What size jet?

The size of the jet is stamped into the side of the jet, it's real tiny, you'll have to look real close to see it.

What size Bing carb? There should be some numbers stamped into the carb, let us know what those are. It's probably a 12mm or 14mm carb.

You're probably looking at jets in the 50-60 range, but if you get it all cleaned up and running and it's all stock parts, the stock jet that's already there should work fine.

Oh, when you're cleaning out the carb, cleaning the main jet, make sure to not poke anything that's remotely hard into it, if you change the size of that hole in the main jet even the tinyest bit it will change things. Liberal use of carb cleaner, maybe poke at it with a pointy toothpick if it looks blocked.

Re: What size jet?

Yeah, if everything else is stock, the jet should be stock too. The only other variable is altitude, if you live near sea level, the stock jet should be fine. If you live at 10,000 feet, you will actually need to go down in jet size to avoid being to rich. The best way I found to clean a jet without damaging it, is to strip the insulation off some stranded wire, like an extension cord, and then just stick one or two strands through the hole, and wiggle it around, and spray plenty of carb cleaner through it. Be careful not to get the carb cleaner in your eyes. It hurts like hell. The soft copper wire will not damage the jet. If you have never worked on a Bing carb before, I'm sure you will have some other questions. Ask first, before using a sledge hammer on it. Also, if it runs, but runs really rough, before deciding the carb is the problem, check the point gap. I don't remember the numbers right now, but I set mine according to the manual on MRA, and could not get a consistant spark. I readjusted the gap to about 1/2 what the manual called for, and it ran fine, with a good spark. This happened with 2 different Puchs, both a ZA50 and an E50, so there must be a mistake in the manual. And no, I didn't get in. and mm mixed up. Good luck and have fun with it. And stock is the way to go, especially for a beginner.

Re: What size jet?

if its stock stock will work

Re: What size jet?

Good input you guys, thanks. That helps a lot.

So the 14mm socket works on the carb bowl, I'm assuming I've got the 14. The main jet was already cleaned out with lootttss of carb cleaner and a thin thin sewing needle. I'll have to check the number on the side tomorrow when I've got some sunlight.

As for the point gaps, I have no idea what I'm doing. Are you talking about the point gap on the spark plug? I usually just leave the spark plug as it is when I buy it.. seems to work fine. Any advice on that would be great, I've never worked with any of this stuff before and I'm loving it, anymore advice would be greatly appreciated.

The other points I know of are under the flywheel, but those are supposed to be touching until they 'break' and trigger the spark. So no gap there, right?

Cheers

Mark

Re: What size jet?

Actually, if it's stock, you should have a 12mm Bing. The nut on the bottom of the float bowl has nothing to do with it, the measurement is of the inside of the carburetor body, where the air goes through. And yes, I'm talking about the points behind the flywheel. There should be a specified gap between the points when they are fully open. If the gap is to big, the points won't close, and if it's to small they won't open far enough, or stay open long enough. Point gap also affects dwell (the time the points remain open), and therefore ignition timing. Puchs in general seem to be really sensitive to points gap. The spark plug gap on the other hand, can be off a bit, and the engine will run fine, for a while. If the gap is to small, the plug will foul easily, and if it's to big, the ignition system may not generate enough voltage to make a spark jump the gap properly, especially after the plug has worn a bit. It's better to gap them properly, with a gauge, although I admit I just do it by sight.

Re: What size jet?

Thanks JJW, I just got my hands on a service manual (as opposed to the other manual which basically tells you to send it to a puch dealer when anything happens and how to take a left/right turn properly). So thanks to all of your help and this service manual I should be asking smarter questions soon.

Mark

Re: What size jet?

check out the repair section of the wiki too, fred's guide is a good place to get started

http://www.mopedarmy.com/wiki/Category:Repair_tutorials

« Go to Topic — end of thread

Want to reply to this thread?

We'd love to have you join the discussion, but first you'll need to login (or create an account).