Jetting (Ron?)

Matt Wilson /

I've been working on my 1977 puch maxi these past few days. Yesterday I cleaned out the gas tank with Muriatic Acid (I couldn't get phosphuric acid anywhere). It worked well, but it took me forever to flush out all of the rust. I was running water through the tank for hours before it was running clear. Finally all the rust had washed out, so I filled the tank with 1 bottle of dry gas and a gallon of gas and oil. I let it sit for a little and then flushed this out. Then I filled it up with regular gas oil. It worked great! When I look into the tank with a flashlight, it is perfectly clean. For everyones information I let it sit with straight muriatic acid for 2 hours. I also left my petcock in, because I couldn't plug the hole any other way. The acid completely ate through the plastic mesh filter in the petcock...so I installed an inline fuel filter, no big deal.

Now the real question. Again 1977 puch maxi with a biturbo. My top speed with airbox and filter is 27. Without the filter or the box my top speed is probably 34.

The airbox and filter are very clean, as is the carb. I don't feel like taking the carb apart to find the jet size because I just took a shower and finally I don't smell like gas any more! I'll do it later. Does anyone have any ways that they get rid of the gas smell on their hands? It takes me two showers before its gone.

Obviously the bike is running rich and I should decrease the main jet size. But I had some thoughts....

If I decrease the jet size will the bike run as fast as it does with the airbox and filter removed?

And I was thinking about taking a dremel and enlarging the air intake port a little. Do you think this would help at all?

Their is a guy a town away who has a bunch of puch parts. I'm gonna stop by his house and try and pick up a few smaller ones

Re: Jetting (Ron?)

Matt, Just because you go faster without the airbox, doesn't mean you are running rich...A lean moped will go very fast, until you seize your engine. Have you done a plug chop? What color is it. If it isn't really black, then you aren't running rich. First things first... do a plug chop...Get a new plug in there, and get your ped warmed up. Then ride it about a quarter mile at full throttle. Once you are at top speed for a little while, hit the kill switch with your thumb. It is important that you hit the kill switch while your bike is at full throttle. Park it, then take out the plug and check the color of the ceramic part underneath the contact. You can let it cool off if you want to, but I never do. Once you do a chop; If the color is really dark, first you should check to see if your airfilter, inside the box is really dirty. You can tell because it will look black on the side that faces the hole in the airbox. This happens a lot. At any rate, take it out and clean it with brake cleaner, and then see if the ped runs any faster. You may have to cut along the edge of your airbox with a razor to get it to pop open, because they are usually sealed...but don't worry, because they are hinged at the bottom and close right back up, even after you have broken the rubber seal....they were meant to be opened. Do a plug chop after that and post back. I bet this is your problem. If you still aren't satisfyed, that is when you start modifying the airbox and buying bigger jets.

Chris

Re: Jetting (Ron?)

By the way, I know that you said your airfilter is clean, but did you actually take it out of the airbox and look at it?

Re: Jetting (Ron?)

Matt Wilson /

Ok I went to my moped guy, Larry's house ..he's an old retired car mechanic that tunes up peds for fun. A really great guy and quite a character.

Before I went over I took my carb apart. The jet in my carb was a 60. We poked through a pile of stuff and found a 58. When I got home I put it in. The bike runs great and plug chops are tan. Top speed is ~34. And Chris I had taken the airbox apart and cleaned it and the metal mesh filter.

The main point that I was trying to get at is:

Will a moped theorhetically go faster with a larger jet and no airbox, than a ped with an airbox and a propererly jetted carb? In the first case the engine is getting the maximum amound of air and fuel, and in the second case it is getting the same ratio but less mixture. Is it the ratio that counts or the ratio and the amount?

Also when I swapped my jet from a 60 to a 58, I noticed something wierd. The jet in my carb was very small, about the size of a pencil tip. It threaded out with a screw. The jet I got at moped guys house was really big, and long. I had to remove the lower piece of the jet with a ground down socket wrench.

Whats the difference between a two and one piece bing carb jets?

Also does anyone think that enlarging the air port of the carb would allow me to put in a larger main jet or would this be a waste of time.

Thanks for reading all this. I tried to make sense but if you've got some questions let me know.

Matt

Re: Jetting (Ron?)

Matt Wilson /

With a given motor and carburator will a motor with a fairly restrictive airbox and proper jetting give the same performance as a motor with a racing airfilter and larger main jet?

I think this best sums up what my question. I was trying to think of a better way to say it

Thanks

Matt

Re: Jetting (Ron?)

Ron Brown /

Matt,

All else being equal, the more mixture you burn per unit of time, the more power you generate.

I like to pick the correct jet without the air box and filter, by doing plug chops, then do whatever I have to to the air box and filter, to allow the ped to breathe easily. Others have posted about air box mods to various brands of peds.

Ron

Re: Jetting (Ron?)

I'm with Ron! If you take the hose and the restrictor plug off of your airbox, and get a bigger jet, it will be faster.

Re: Jetting (Ron?)

Matt Wilson /

I already took the hose off, and I've taken apart and cleaned the airbox and steel mesh filter.

I'm pretty happy with the way its going now...34mph and good accelleration

I may try the size 60 jet and the performance airfilter that I use on my Zuma scooter and see if I get an improvement.

The only bad thing about this ped is it vibrates so much when its going 34mph my butt practically goes numb... I have to stand every now and then.

Has anyone tried enlarging the air intake port?

Thanks

Matt

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