Puch E50 – bogging down

Joseph Ferguson /

I bought my first moped this past August (a 1977 Puch Newport), and I've been slowing working my way through its various quirks and issues. At this point, it starts pretty consistently and runs all right; the only issue is that, if I give it too much throttle too quickly while riding, it starts to bog down quite a bit. The engine's sound becomes more muffled, and the pitch of it goes down. The power decreases dramatically. I've tried moving the needle to all of the positions offered by the needle clip, but the issue still remains. I've found that taking the air filter off appears to improve the situation, and when I took a look at the spark plug, it was very dark – essentially black.

Now I'm new to mopeds and working on engines in general, but to me it seems that the engine is running quite a bit too rich. It doesn't four-stroke, but I figure the air filter experiment and the condition of the spark plug still point to this conclusion. Does this seem correct? And if so, what's the proper remedy? Down-jetting so that the fuel-air ratio is leaner? I know the first goal when fixing up a moped is to get it running well with a stock setup, so I want to ensure I evaluate any other possible contributors to this issue prior to changing out the jet in the hopes of resolving it.

In case it's of any help, here's a summary of the work I've done so far:

Cleaned the gas tank

Disassembled, cleaned, and reassembled the petcock

Replaced the fuel line and in-line fuel filter

Disassembled, cleaned, and reassembled the carburetor

Added a stock air filter (it had no air filter when purchased)

Replaced the throttle cable

Disassembled the top end, cleaned the piston and cylinder, and reassembled

Replaced the spark plug

Replaced the clutch, and replaced the transmission fluid

Cleaned the points and adjusted the timing to stock

Disassembled, cleaned, and reassembled the exhaust

Replaced all gaskets

Any thoughts?

Re: Puch E50 – bogging down

Richard Eberline /

you gave the engine more unrestricted air, by removing the AF. down jet and double check timing. use a ngk b6hs and gap to .020

Re: Puch E50 – bogging down

Nice fully understandable and detailed post. PO probably drilled out stock jet when they removed the air box thinking the bigger the better. Look up stock jetting on myrons, im thinking depending on what motor/carb maybe a 54 -64 would be close.

A quick simple test would be, start it up normally, put on stand, turn off petcock and listen while u rev.

There will be a long chug chug chug while its overly rich, then a nice clean pop pop pop shorter moment when the A/F mixture is perfect then it will uncontrollably go lean and rev till it dies.

if you get a micro drill bit set, you can solder and drill to any size you want.

Re: Puch E50 – bogging down

Joseph Ferguson /

Great, thanks so much for all the input. I'll definitely try out that test with the petcock.

Also, in case it's helpful to anyone who comes across this in the future, another thing which made the cause of the bogging down clear was the increased severity of the issue upon fixing an air leak between the carb and the intake (using an o-ring).

Re: Puch E50 – bogging down


> if you get a micro drill bit set, you can solder and drill to any size

> you want.

You can also sort of smash the opening of the jet with a large rounded nail, causing it to get smaller, then drill out to your liking.

Although I'd just order a party pack of jets from treats in the range you need and call it a day.


Re: Puch E50 – bogging down

> Chris Straub Wrote:

> -------------------------------------------------------

> Although I'd just order a party pack of jets from treats in the range

> you need and call it a day.


> https://cdn3.volusion.com/vod3d.s9orw/v/vspfiles/photos/bing-jet-range-5pk-2.jpg


> https://www.treatland.tv/range-of-5-bing-jets-pick-a-size-p/bing-jet-range-5pk.htm

Even after you figure out that the cost of that 5 pack would get you close to 900 miles down the road . And , that's only figuring 85 miles to the gallon .

Of course if you happen to order the wrong pack ... ;)

Re: Puch E50 – bogging down

roots to wings /

I like Rich Eberline's recommendation. You could bog if you weren't getting enough air, or were getting too much for the fuel. If you want to run the stock airbox, you'll likely have to down jet, but before doing any of that, you should see what the stock specs are for your carb and bike year on myrons mopeds.com. if the previous owner ran it without an airbox, they may have changed the jet, atomizer, or needle, or all three, possibly even the carb itself.

Re: Puch E50 – bogging down

Joseph Ferguson /

I recently got my order of jets (50s, even) from treats and had a chance to try a few out. The carb on my moped is stock, and the jet that was in it was a size 64 Bing jet (that is, Bing brand – not generic). From what I’ve read on Myron’s Mopeds, this is the stock size, and – due to what are essentially inaccuracies in Bing’s original jet sizing – it is roughly equivalent to a size 60 generic replacement jet. I’ve tried the size 58, 56, and 54 generic replacement jets I ordered, and things seem to be getting a bit better. If I keep the air filter off and move the needle clip to the leanest position, things seem to improve a little as well. However, the issue still isn’t resolved. I’m going to try out the two remaining jets when I have the chance, but I’m just wondering if anyone thinks there may be other contributing factors I should consider. I’m pretty new to mopeds and working on engines in general, but it just seems unusual that the stock setup would require this much downjetting. Perhaps this is just a symptom of general wear That comes with age and usage? (The moped has about 5,000 miles on it.)

Here’s a quick video demonstrating the issue. This is with the size 54 generic jet in and the air filter attached. If I ever give it more throttle without really slowly working it up, it bogs down like this:

Re: Puch E50 – bogging down

That sounds like lean bog.

If you creep the throttle open, the increasing rpm sucks harder through the carb and lets you get revved up a bit more by drawing up fuel.

If you upjet, it should get better.

Make sure your float level is right. If it is too low, the carb can act lean even with the right jet (I’m repeating that from somewhere). Sounds true to me.

I always always keep upjetting until I have a rich four stroking at wide open throttle and full speed. Then back down just until the four stroking stops. Fine tune with needle after that to get cleanest mid throttle behavior.

Re: Puch E50 – bogging down

Joseph Ferguson /

Thanks for the input!

I had a few spare minutes, so I skipped ahead and tried out the size 50 jet. It was the worst out of all of them; I could barely move the throttle before it started bogging down. This makes sense with what you've said (that it's running too lean), but I'm still a bit confused.

After this test, I noticed a little bit of liquid dripping from the end of the exhaust and where the exhaust meets the engine. Could this indicate that it's running rich and is therefore unable to combust as much of the fuel as it is supposed to?

Also, as I described in my initial post, the spark plug – at least when I inspected it after using the Bing 64 jet – has been very dark (nearly black), and even a bit wet. Additionally, when I recently fixed an air leak (where the carb meets the intake), the bogging down became noticeably worse. It seems like this would suggest that the moped is running too rich; after all, by resolving the air leak, the mixture became richer, and if that caused it to bog down more, then it seems like I should be looking to make the mixture leaner.

At this point, the only one of the jets I haven't tried is the size 52. I'll give that a shot tomorrow, just in case. Otherwise, I'm a little bit stumped. I know people say to try jets that cause four-stroking and work your way down, but so many of the clues suggest that it's running rich. Might I be missing some other issue?

Re: Puch E50 – bogging down

roots to wings /

I think you are pretty far from shore man and need to back up. Go back to the stock carb specs for your bike and figure out from there why it is not running right. If your bike is stock and you have a 1.5 hp you should have a 60 jet. If 2hp, 64. If you have everything on spec with the carb then you can start dicking around with air leaks, which if you took some things apart I am sure you have. If oil is dripping from your exhaust manifold, you have a leak there at a minimum. You won't find much help on this forum if you are obviously not following the advice of the guys who really know their shit like a Rich Eberline or Ken Roff for example. I am not one of those guys, but many have helped me here. Beginners Mind. If you keep posting the way you are posting you will either get trolled or not responded to at all. Be specific about your setup when asking a question and stick to the facts. There are many guys here who can tell you what is going on with your bike in 2 seconds, but you've got to do what they tell you if you want results. Good luck.

Re: Puch E50 – bogging down

hold on roots, take it easy i have faith that newbie joe is not a hack and has a brain, hes just excited, Joe gi back like roots suggested to the top and take one step at a time.

1. sit on toilet and read thru freds guide, there is a link on the top post. There is an order to repairs for a reason.

Post what you have done w picts or if you get stuck, everyone likes picts.

2. Follow the order. compression, spark, timing, fuel

3. two things to check "AFTER" you have followed the order above. This leads us to where your at now... check for air leaks causing lean condition, float height as mentioned above, take back to stock as a reference point as mentioned above, check that you actually have a filter on inside your tank/petcock(these usually break and dissappear)

Ok, if you wanna richen the mix take off air bix and partially cover the carb with your thumb thus increasing richness while feathering throttle.

Or get a spray bottle full of premix and squirt into carb while you open up the throttle, if it runs better with extra gas then now you know you have an air leak or its a fuel issue.

Another possibility is tickling the tickler on your carb while constantly repeatung outloud , "run better mofo". (edited)

Re: Puch E50 – bogging down

Swish and flick

it’s: “run better mOh-fo”

not: “run better mo-FAH”

Re: Puch E50 – bogging down

The unburned fuel in the pipe makes me think you set the timing wrong? How are your plugs looking. Try putting in a fresh plug and running for awhile with the 54 jet, it should stay stark white. If it starts to get dark you need to consider the timing and double check. I like to check it with the micrometer to initially set it and check it with the timing light after it's been running awhile to adjust.

The other thing to consider would be a bad trans side case seal, the goo in your exhaust could be oil getting sucked out of your transmission. TBH, this is probably it, the air leak is making you lean.

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