Dies at half throttle

My Puch goes 30-35 at half throttle, but as soon as i open it up any more, it cuts back and almost dies. It's been suggested it might be the exhaust which is clogged that would cause that. I took the exhaust off and ran it at half, it worked fine, then opened it up and it died down just like normal. It has also been suggested i need to jet up, I have the Puch High Performance Air Filter shown below. Right now my jet is a 64. Any suggestions on how high I should try? I also gave a pic of my bike, it's a Puch Maxi N (or NS, I'm not sure)

Re: Dies at half throttle

30-35 at half throttle is pretty fast for a stock puch? that doesnt seem right

i am running a 64 with the standard airbox, does your plug look like coffee with cream in it? If it dies at full thottle that sounds like its getting to much or not enought of any part of the fuel mixture, probably to much air

i would suggest going through all the standard moped procedures, clean exhuast port and pipe, set and clean all points, throughly clean carb, ect.

then get a variety of bing jets and start small and run through the numbers untill it starts to feel right, if you get to a jet that allows the bike to run and feels all right, then ride it around and do some plug chops, make sure you have the correct ratio, once you have a general idea of the plug area you may have to move up or down to fine tune it,

and remember, a really big jet doesnt always mean the bike will work fine,

Re: Dies at half throttle

Jason Luther /

maybe its that gigundous rear wheel. it bogs and almost _dies_? have you checked the timing? not only that, perhaps your points are worn and 'flapping'. try covering your intake with tape (about 1/4 of the way) and see if that helps. then you know which direction to go in. -jason

Re: Dies at half throttle

the rear wheel isn't as big as it looks. it's trick photography. unfortunately, jason, i am kind of new, so some of the suggestions you made are, right now, beyond my ability to do alone. but i do have a decent group of people around me (mosquito fleet and all) that can help me with those issues. we're just all busy with the christmas season upon us.

brett, i took the exhaust all the way off, then started it to see if it was due to that needing cleaning. but the problem persisted and and my assumption then was that wasn't the problem. I'm going to get some jets that are larger and work from there. I just need to find time to spend with Tim P, who is busy trying to put an 80cc kit on his Sachs (http://www.livejournal.com/users/georgeitems/24303.html), so he's kind of busy.

Re: Dies at half throttle

Jason Luther /

im telling you, try the tape. itll let in less air, which (kind of) is like putting a bigger jet. at least that will give you a clue to whats wrong.-jason

Re: Dies at half throttle

i'll do that tonight. you say 1/4 of the way? do you think it matters where the tape is? my idea is from the end further out.

Re: Dies at half throttle

Jason Luther /

yes, tape about 1/4 on the intake part of the carb, underneith the boot to your filter, just make sure the tape wont get sucked in.

Re: Dies at half throttle

yeah calebs told me of this big ass reed valve kit for the sachs engines, thats crazy, almost twice as many cc's as what a stock moped is, same with the minarelli kit

the exhuast probably isn't the problem or the sole contributor of the problem, but if its dirty or there is a ring of carbon in the port it definately isn't doing any good, plus removing the pipe entirely may not help you to troubleshoot anything, as the engine needs a certain amount of back pressure to run properly

i would suggest putting tape on the outside of the cone if your going to go that way,

infact if i remember right thats how josh dahl in boston has his magnum set up, theres a nice peice of duct tape around the wider part of the cone, on my standard air box i have a bunch of holes drilled in it and i usually ride around with some tape on some of the holes when i am trying to find the correct jet,

in terms of checking and cleaning your points, its real simple, get an automotive feeler gauge from napa for about 5 bucks, i believe .016 is the correct measurement off the top of my head, when you look inside the magneto, the stator plate should have 2 coils, a larger and a smaller, a condensor and a set of points. the points look like 2 little discs and they open and close when you turn the magneto, next to the points is a screw, loosen it up a little and then insert your screwdriver into the lever in the same area, the lever will manually open and close the points, stick the feeler gauge in and close the points on the feeler and then tighten the screw back up, then take a small emery board and stick that between the points and quickly pull it out, this will clean off any worn surface area, then take a little piece of card stock or something and spray some carb cleaner on it, stick that in the points to clean any gunk or what not that you my have loosened by sanding and adjusting, just make sure you dont loose anything in the magneto and you should be all set

in terms of your timing, i would have someone show you or read the manual on how to do it, as it would probably take me forever to tell you on here, plus if your bikes running at all the timing is probably set close enough to run fine, however have someone show you how to properly set the timing

i would suggest reading the puch manual as well, you can find one on the moped riders website,

and maybe buy a few jets under the 64 you currently have, say a 60, 62, 66, 68,70, 72, 74,

give yourself a good carb cleaning while your at it, the smallest piece of junk could clog everything up, in fact i could almost bet that half of your problem lies in the carb being dirty, did this problem just happen with the same set up that you have always run, or did you put on that filter and jet and it suddenly started cutting out at half throttle? Because if you have always run the same set up and the bike suddenly started cutting out, it could very well be a dirty carb,

and make sure your tires are inflated properly and your chain in at the proper tension

man i've typed a lot, hope that helps,

Re: Dies at half throttle

30-35 MPH at half throttle doesn's sound right and could be a clue.. some kinda carb or cable adjustment problem or something.

Or maybe an RPM related problem..maybe the points start floating at some high RPM, due to a weak spring? Maybe something else in the ignition/magneto is loose or somehow causing troubles when it spins real fast.

Of course the carb could be part of it too. Half throttle is right in the middle of critical needle range.. maybe drop or raise the needle a notch and see if there's a difference.

Re: Dies at half throttle

I agree with JoeW.

Try moving the clip to the bottom notch on the throttle needle. Take it for a test drive and see how it does. Then try moving the notch to the thrid or next to last from the bottom and repeat test run.

Standard stock setting is 2nd notch from top.

If you've put a bigger filter on your Puch it is sucking too much air in relation to the amount of gas it's getting when you go past half throttle.

Re: Dies at half throttle


When i got the bike, it had no air filter, so i purchased the one i have now. Before it arrived though, i cleaned out the carb completely, and throughly. Once the filter arrived i put it on and this was the problem. so what we (Tim P and I) did was play with the needle like joe and zippy are suggesting. We found that no matter where the needle was, the same thing happened. So, Tim wanted to do a test and we took the needle all the way out to see what would come of that. Well, after the initial test drive, I realized that I could open up a tad bit more, so we left it out.

Once things start settling down a bit with the holidays and accidents, I'm going to go over to Tim's or the Barrens' house and see if they can help me with all these ideas.

Re: Dies at half throttle

okay, so it probably just needs to be jetted properly, easy enough,

i ve never really had any luck adjusting the needle setting, it never seems to make enough difference for me, so i usually just leave it be,

well get a bunch of jets and tune that carb right!!!

merry christmas

Re: Dies at half throttle

".. so we left it out."

If i read this right, you are now running with a carb that has the needle removed?

Re: Dies at half throttle

It's always the question you don't ask that gets you.

Re: Dies at half throttle

James Foster /

Yea my bike does the exact same thing with the same air filter. But my prob is that I'm running too rich, because when I put a bigger jet in, it made it worse. And even with my 82 in there, it still dies if you put on more that half throttle. I'll have to get an 76 and a 78 so I can make sure it's lean enough. What's odd is that it used to run just fine with an 86, until i fixed some air leaks...


Re: Dies at half throttle

The Keihin on my PA50 is a butterfly throttle.. no needle. But the "needle" orifice is sized and shaped appropriately. The carb's tapered throat might have something to do with it too.

If he's running without a needle, i can see where the slide might let it run OK until it was opened up wide.

Re: Dies at half throttle

yeah it does seem odd to run without a needle

but have you ever tried riding without a jet

doesn't work so well

Re: Dies at half throttle

running without a main jet (as an experiment) can tell you a something.. like whether or not your needle jet is large enough.. but you must have a needle installed during the test.

If it runs at half throttle but dies (floods) further on, the needle jet is big enough.. but if the engine still runs near full throttle the needle jet may be too small.

Re: Dies at half throttle

you are right, no needle, no need.

Re: Dies at half throttle

Jason Luther /

you didnt try the tape, did you.

Re: Dies at half throttle

here's what i get.. but i'm not at all sure about it.. and if someone has a better theory, jump right in.. the water's fine.

Originally, the carb had no airbox and no filter. Instead of installing a box with a tiny intake hole like a stock one, just a wide open filter was installed. So, the bike was running real lean and died at half throttle.

Next, the needle was removed. Although there is some metering below half-throttle, anywhere above that and the engine floods and dies.

So it went from dying due to leaness to dying due to richness.

Taping over the intake may have helped before the needle was removed, but at this point it needs more air than can be provided by any means..

The best that can happen without a needle (assuming enough air were somehow provided) is it might be made to run near full throttle but not below.. kinda like a model airplane engine.. but I wouldn't know how to accomplish that.

Re: Dies at half throttle

I haven't tried the tape yet, but i will soon.

Joe, I'm not sure what you're telling me here, but I have no idea how it preformed before with a regular airbox or filter. Although, when we put the new one on, no matter where the needle was placed, the same thing would happen, just at a lower throttle, and could never get up much speed.

Re: Dies at half throttle


I got the idea that the engine died at half throttle both before and after you put on the air filter and took out the needle... from the above message.

I was thinking that although the symptom (engine dying) was the same, the cause of it dying did change.

If you can try reinstalling the needle and then also restricting the air intake i think maybe you might have some luck.

If you already tried this and i'm mistaken about the sequence of events, maybe you could lay them out clearly..

Right now it seems like you corrected for way too much air intake by removing the needle.. (you had too much air coming in so you added some gasoline). A better thing to do seems to be restricting the air intake, not adding fuel to the mix.

Re: Dies at half throttle

Jason Luther /

yeah, dont do the tape without the needle, your probably way rich now. your problem is like my golf game, you keep chipping back and forth over the green.-jason

Re: Dies at half throttle

my hypothesis;

i put the needle back in, same thing happens that happened before (which was dying before i get to half). Put the tape on and it will go back to dying at half throttle like it does now.

i'm not sure if this is true, i'm still going to try it and find out. what i'm wondering is, how can i get my engine to accept the amount of gas i'm giving it to bring my speed up. or, maybe i should just get a longer throttle cable and call it good. it's all a mystery and i'm about to enjoy a nice hot dog from cyber dog, so i need to go.

Re: Dies at half throttle

well.. this is getting ugly.. and it's all because of that air filter. I assume, since i see nothing to the contrary, that you have a bone stock bike except for the filter.

Mopedwarehouse notes that rejetting will be required when using that air filter. But without upgrades and modifications elsewhere in the engine / exhaust you aren't likely to see any performance improvement. Modifying your bike to accomodate that filter is a waste of money and a needless headache, imo.

I suggest you find a stock air box and filter.

Re: Dies at half throttle

Thanks Jason,

I'm not sure what I'm going to do. Once I get time and people in the MF stop crashing, I'm gonna get some hands on help.

Re: Dies at half throttle

although theres always the possiblity of an rpm related issue with the points or something i highly doubt thats the problem,

infact i am almost 100 percent certain its a problem with jetting and carb tuning

further more theres nothing wrong with that air filter, its no different than a stock filter except it lets in more air, and in the end you will most likely see a little more power using that air filter than with an un modified stock filter

what needs to happen is that the carb needs to be jetted properly, when you bought that filter you should have also gotten some jets, almost anything you do to a moped has some sort of other reaction that will need to be addressed, for example,

a new exhuast pipe will require re jetting,

increasing or de creasing the # of teeth in a sprocket will increase or decrease your low or high power band

a larger carb or a performance air filter re quires re jetting

what i suggest is to put the needle back in and set up the carb as it should be, order a range of jets, then use some tape and try find the correct ratio using that method for the time being, its most likely an issue of to much air, so restricting that air intact should help you for the time being,

when you get some jets, start at the smallest you have and run through all of them, from small to large, this is sort of a pain in the ass and takes some time, but its usually the best way to find the correct jet, once you fine a jet that seems to be working fine, do some plug chops and really fine tune it,

my phone number should be in the members info if you want to call me for help

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