Puch Maxi top end

Crisis--Cincinnati /

I have a 1977 Puch Maxi-Luxe. Recently I upgraded to a new 14mm carb, and a biturbo exhaust. The bike definately has more pickup, and more hill climbing ability, since the upgrade, but the top end is the same, at 27ish. Is there anything that I can do other than rejetting the carb to get a faster moped? I have already messed around with the airbox restriction, with no results. Also, the exhaust is tightened and sealed. I checked the throttle cable too, to make sure the slide was comming all of the way up. I would like to get up around 30-33mph. Any suggestions would be sweet!

chris

Re: Puch Maxi top end

XBrandon EdgeX /

Get a bigger front sproket. If you have a 15 tooth, go to a 16. If you have a 16 tooth, go to an 18 tooth. You'll lose a little acceleration and climbing ability, but nothing too horrible.

Re: Puch Maxi top end

brian away /

Will one or two teeth on the front spocket really give you 5 mph, or just a couple? But I am in the same situation with Chris, as far as Puch Maxis going 27 mph, and no faster.

5 mph is all I ask!

Re: Puch Maxi top end

XBrandon EdgeX /

Well, I know someone with 15 tooth sprocket and he goes 30, and I've got a 16 tooth sprocket and I go about 35-37 with a biturbo.

Re: Puch Maxi top end

brian away /

Awesome, man, thanks.

Re: Puch Maxi top end

Listen to the motor, if its already wound out, you need to check into other things like the sprocket. Yes, the increase of 1 or 2 teeth can make a fairly large differance depending on the size of the rear sprocket. You can use basic geometry to figure out the increase once you get the measurements of all of the sprockets and the tire. You are only wanting to increase your speed by a few mph so the increase doesn't have to be too large.

Imagine spokes extending from the teeth of the sprocket, now imagine the added distance of tire travel created by the addition of the extra tooth. It is a small differance in the circumference of the sprocket but then when you extend the radius to the size of your tire, you can see the change in tire rotation. This would assume that the front and rear sprocket are the same size which they are not. The differance is going to be greater or smaller depending on the number of teeth on the rear sprocket. Each revolution of the front sprocket translates into a number of revolutions of the rear sprocket. Because the two circles have teeth, this is easy to figure out. ie front tooth has 10 teeth, rear has 20. for every revolution of the front sprocket, the rear will make half of a revolution. If this is reversed (20 front, 10 rear) for every revolution of the front sprocket, the rear will make 2 revolutions. Because the rear sprokets revolutions are extended to the tire, the rear = the turns of the tire. If both were =, then increasing 1 tooth will translate into (16 to 17teeth for the front) an increase of about 6% (6.25%)

when you throw the rear sprocket in, you can get an increase that will be greater.

Even assuming that the two sprockets are the same size, you will see an increase in top speed of about 2mph. This doesn't take into acount the differance that the change in gearing will make on the motor. If you are topping out fairly quickly, you shouldn't see much of a reduction in performance. If you went from 16 to 18 teeth your increase would be about double. ie 27mph to 30mph. Keep in mind that this doesn't take into consideration the rear sprocket being a differant size. If the rear sprocket has fewer teeth, the amount of increase will be greater.

Jamie

Using 27mph as the base, count the number of rear teeth, then count the front. Check to see how many more revolutions will be made by the increase. This increase can be turned into a percentage and you can use that to figure out the increase in speed from 27mph. This increase will assume that you will be able to obtain the same number of RPM's on the motor at full throttle. ie 15% more revs = 27X1.15 = 31.05mph

Re: Puch Maxi top end

Crisis--Cincinnat /

Look, we got Isaac freakin Newton up in here! :) Just kidding. Jamie, thanks for the thorough explanation. Now I uderstand completely. You are the man!!

chris

Re: Puch Maxi top end

Hey,Crisis! I don't suppose you could have the 1.5 HP model?Probably not,but in my Puch repair manual it lists the 1.0,1.5 and 2HP models of Puch bikes.I don't know if it would apply to your model,though.Just a thought.Also,when you put on your Bi-turbo,did you check the exhaust port for restriction and is your timing right on or a little advanced for RPM enhancement?Also,better do a `plug chop' tro make sure you're jetted right.Just some thoughts.

Re: Puch Maxi top end

Chris,

There is something much more fundamentally wrong with your bike in my opinion. All 50cc two strokes should be able to do around 30-35mph no problem. True, the engines are restricted, but are also designed very specifically to do this range of speeds.

Mopeds in general are inexpensive products (compared to a motorcycle, etc), and are not "performance" machines. This means the manufacturer can get away with making less precise, poorer quality parts. Therefore, most likely, things inside your engine are "out of spec." Hell, even expensive performance two-stroke bikes have these problems. I would recommend taking the engine apart and blue-printing it. Meaning make sure the engine is to design spec. I know you don't have "design specs" (well, if you do kudos) but all you need to do is match up the intake manifold to the cylinder or crankcase (depending on piston ported or rotary), smooth out all the transfer ports and boost ports (if you have one), and match these to the crankcase also. Just mark one side of a mating part with a non permanent magic marker, reassemble the parts, and then look at where the overlap lies (now marked on the opposite part in magic marker). Just line 'em up now.

Worst case you don't have to do this but you could go through all the ports and clean them up with varying grits of sandpaper. I've found various two-stroke engines that are so mismatched it's rediculous, or the ports are so rough the engine runs o.k. all the time, even when new. Fluid dynamics are so very important in two-strokes that smoothing out everything just makes it easier for your engine to do it's work.

Of course, there are a ton of other problems that could be wrong like worn rings, clogged exhaust, etc. Sounds like you have checked all this? As usual, the How To Fix Your Ped should be referenced here right? Hehe! But cleaning up manufacturing flaws is a great way to get you bike tip top without really messing with dangerous modifications. Sorry if that was too much garble, but hope it helps a little.

Crisis--Cincinnat wrote:

>

> Look, we got Isaac freakin Newton up in here! :) Just

> kidding. Jamie, thanks for the thorough explanation. Now I

> uderstand completely. You are the man!!

>

> chris

Re: Puch Maxi top end

Chris,

Sorry, didn't want that to sound like "this IS what's wrong." But going through an engine and smoothing out manuf. flaws is oe the first thing I do with all my new bikes and it hadn't been mentioned yet. If the manufacturer says it's supposed to do Xmph, damn it, it better right! Hehe! Later.

Re: Puch Maxi top end

Ron Brown /

Chris,

Before you take Roberto's advice and get out the wrenches and sandpaper, keep in mind that the manufacturer never said it would go that fast.

What Roberto is describing, is the kind of thing you do to win races by getting a slight edge over the competition.

Bet your carb jetted right first and see how it runs. Btw, how is that coming?

Ron

Re: Puch Maxi top end

brian away /

As far as horsepower, my 1.5HP Newport can't climb hills to save its life, but my 1HP Maxi can zoom right up any hill. Both are Puchs, of course.

I just started messing with the Newport (haven't even had it a week), it needs work in a lot of areas, but one would think a 50% increase in HP over the Maxi would be a lot stronger. Rear sprockets are a good point. And I already have the muffler off, it's disghusting. But yeah, have to check out the carb, of course, but it was allegedlly just cleaned.

By springtime, we'll own the hills, Crisis.

Re: Puch Maxi top end

Ron, I agree. I don't really want to take my engine apart just yet. I am waiting on the jets to come in. Can you do a plug chop after the engine is cooled down a little. That bad boy is hot! Too hot for my supple fingers. :)

chris

Re: Puch Maxi top end

Ron Brown /

Chris,

A plug chop is a plug chop, if you have done it right, you can read the plug next spring and nothing will have changed its color.

Ron

Re: biturbo restriction???

don, is there really a restrictor on the biturbo, and how do you remove it??????? thanks..........

Re: Sprocket Ratios

Don't make it so complicated. The change in speed, assuming you have the power, is directly proportional to the ratio of the increase in the number of teeth in the front sprocket and inversly proportional to the decrease in the number of teeth in the rear sprocket.

25 mph goes to 28.6 mph with front sprocket change from 14 to 16 or

25 x 16/14 = 28.6

25 mph goes to 30 mph with rear sprocket change from 48 to 40 or

25 x 48/40 = 30 mph

If you change both 25 x 16/14 x 48/40 = 34.28 mph WOW.

I changed mine from 14 to 18 front and 48 to 40 rear. I went from 26 mph to 31 mph and lost considerable pick-up. There are no hills at all where I live so I enjoy the quiet ride at the low RPM.

I am suprised that "Crisis" did not get a better result from the 14 mm carb. That was my next step. but now I wonder.

Re: biturbo restriction???

No,sorry Paul! I didn't mean a manufactured restriction,although there probably is some mod you could do.I meant a restriction caused by carbon blockage that some people don't check for right AT THE PORT where it enters the exhaust piping.I'd say,in general,a Bi-turbo pipe needs no enhancement;,just maybe lengthening or shortening to tune it.

Re: Puch Maxi top end

did you change the inlet pipe to 14mm?

Re: Puch Maxi top end

Crisis--Cincinnati /

Everyone, I figured out my problem! I was using the choke to start my bike, when it was cold. When I pulled the throttle, the choke plate wasn't sliding all of the way up. I was being choked :) Now, I just check it to make sure that it is up when I take off. If not, I just pull the stick up and I am cruising. I am getting around 33-35mph now! That is with the 14mm carb, and intake manifold, along with a biturbo. So Ken, get the 14mm carb and intake manifold. It makes a huge difference. I wish that I would have checked the choke in the beginning. It is always best to check the simple shit first. Next time I will.

chris

Re: Puch Maxi top end

Great! Way to go,Crisis! Now fix it right so it doesn't stick when you sell it to some unsuspecting poor schmuck down the road.Just kidding! Enjoy it and `Swarm and Destroy' scooters.

Re: Puch Maxi top end

Crisis--Cincinnati /

Don, I will never sell my Puch. I love it, and I am just going to keep replacing stuff until it is pricless! I still haven't taken my carb apart to check out the sticking, but I am sure it will be a simple little fix. I haven't felt like doing it, because the weather has been super nice and I want to ride as much as I can before the long cold winter comes.

chris

Re: Puch Maxi top end

I hear THAT Chris! This weather has kept me from all kinds of work and not just on mopeds.Enjoy it! It's turning sour Tuesday.

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