Proma Circuit Pipe problem

I put a proma circuit pipe on my 1986 Puch Maxi sport 1.5hp.

The stock jet was a 56, I have #62 jet in it now with the new pipe. I did a plug chop and I get a nice even tan brown color on the plug. The bike runs great with the pipe (three times louder!).

My problem is though at high rpms and full throttle the engine starts to break up and lose a little power (sounds terrible). The bike runs nice and smooth everywhere less than full throttle. What do you think I can do to fix this?


Re: Proma Circuit Pipe problem

Oh I forgot to mention, the pipe is wet with gas where the pipe meets the silencer...not dripping wet, but wet to the touch

Re: Proma Circuit Pipe problem

well i would say check your fuel mixster or it sound like your not getting enough gas or getting a little to much cause it sound like it bogging down

hey load pipes save lives lol

Re: Proma Circuit Pipe problem

Ron Brown /


Test it without the air box and filter to see if the problem is worse or better. Do a plug chop while the air box is off.


Proma Circuit Pipe problem solved


Well it was bothering me so much that I went home during lunch to tinker with it.

I took the air box off and rode the bike. It ran terribly. It bogged down, wouldn't accelerate etc..

So I figured it must be getting way too much air. I took off the little elbow that branches off of the air box and goes into a hole in the frame and put the air box back on. Well it ran fabulously, in the entire throttle range. It was a little hard to start but I think that was because the engine was still cold. I then did a plug chop with the air box change and I got the same nice tan color.

So I think I'm golden now. Thanks for you help.

Btw..just taking that little elbow off made the bike noticably louder..I was surprised

Re: Proma Circuit Pipe problem solved

Yeah, sounds like you were running too rich before, hence the bogging.

Re: Proma Circuit Pipe problem solved

Yeah by just a little..the plug looked good

77 maxi sport II with proma

Mine's on the way, but I'm not looking forward to messing around with testing this jet and that. I know it's just a plug chop, but if someone had a maxi sport with a 1HP engine and could tell me what jet they use on their Circuit, that'd be sweet. : )

But I'll probably just plug chop it.

Re: 77 maxi sport II with proma

I had a 56 (on a stock 1.5 hp engine), before the pipe and I'm using a 62 now with the pipe (and that little air box mod above). People here and where I bought the pipe said that the jet will probably need to be 2-3 sizes bigger, once I put the pipe on. So I ordered a 60, 62, 64 & a 66 (just to be safe..hey for $3 each)

So how fast is it now ?

What did it do before ?

And now ?

As far as the jets and the airbox elbow... I would put the elbow back on... (for noise reasons) and then try one size richer (just to be safe)... then try one size leaner (if it got worse with the one size richer).

Re: So how fast is it now ?

before I topped out at 27 mph on a level ground with no wind.

I don't know exactly how fast I am going now yet because the aftermarket speedo cable that I installed snapped up at the speedo (just like the original did a few weeks back), as soon as I started to go fast. The speedo turns freely so I think the cables are crap.

I know I did get some good speed with the pipe. On a 30 mph road that people usually go 40 as the norm, I am not that far behind. I wouldn't guess I gained 5-7 mph on my little 1.5 hp.

I'll try the 60 and the 64 jet when I get the chance. The noise kinda reminds me when I was 12 and my next door neighbor tore the muffler off of his YZ80 in a crash. He stuck a 20 ounce beer can in it's place. No, was pretty funny and loud as all hell. Mine ped is actually not THAT loud.

Re: 77 maxi sport II with proma

cool, that's what I'll do.


Re: 77 maxi sport II with proma

Matt Wilson /

I have a 2hp maxi and a biturbo. I've been playing a little bit with the jetting lately and with a 58 jet the bike is spot on.

It tops out at 34 with great accelleration from 20-30mph

0-25 in 11-12 seconds

Hope this helps.

Also anyone know why some puch have two piece jets and some have only one piece? Whats the difference? Is there any?


Re: 77 maxi sport II with proma

That does help, thanks.

I've never seen a 2-piece jet.

Re: 77 maxi sport II with proma

Matt Wilson /

The two piece is the standard.... one piece is the wierd one

In a two piece jet the top screws off...its a small little brass piece the size of an insect. The other piece is still in the carb...its a long brass piece with 3/16" hex flats. You need to grind down a socket to remove this part.

Has anyone else noticed this?


Re: So how fast is it now ?

Ron Brown /


I don't do this very often, but I am going to disagree with Fred.

In my humble opinion, your original problem was caused by an over rich mixture as a result of restricted intake air flow.

The fact that you experienced poor running with the air box removed and improved it by putting most of the air box back on, shows that your intake is still restricted. Without the air box, you leaned out too far. If you can install a larger jet which will take advantage of the increased air flow, you will go faster. Keep in mind that you must get enough gas to maintain the tan color of your plug.

After you achive the correct mix, figure out how to derestrict the air box and filter so that the do not affect how the ped runs.


Re: So how fast is it now ?


so I should size the jet w/o the airbox on? Won't I end up with a very rich mixture when I put the airbox back on, no matter how I derestrict the airbox?

I had a nice tan color on the plug with the airbox untouched, but the bike ran bad at full rpm (& full throttle). When I took off the little elbow piece from the airbox the problem disappeared and I still had the same tan color on the plug. The bike is running good now although it got a bit louder without the elbow (the inside of the frame must really dampen the noise, when the airbox elbows into it)

If I jet up, I'll have to make further mods to the airbox in order to get a tan plug. The bike will probably get faster...but louder as well.

I'm a serious novice here, so my opinion is extremely humble:)

Re: So how fast is it now ?

Ron Brown /


As they say, if you want to make an omelette, you have to break some eggs.

I am not familiar with your exact ped. Why don't you start a new thread called Puch air box mods, or something similar and see if you get any help from others who may have done it.

Normally, if you can figure out a way to expose enough area of filter foam, you can get essentially unrestricted flow. It mostly depends on how ambitious you want to be. The result does not have to be a lot more intake noise, it all depends on how you mod the box/filter.

You may want to just see how fast you go without an airbox and decide if you want to go further with the airbox mods.

Good look.



Re: Proma Circuit Pipe problem solved

You can get even more power, if you take that restrictor plug off of the airbox, right where the hose was connected. Then get an even bigger jet.

Re: Proma Circuit Pipe problem solved

on the end where the airbox goes into the frame I took the s shaped elbow piece off entirely. There is just a hole in the airbox. I can see the wire mesh/paper filter through the hole.

What does the restrictor plug look like?

Re: So how fast is it now ?

yeah... but we're really not disagreeing... you are probably saving time by going with what he's going to have to do in the end... I am just making the progression step by step.

For one reason....

... From repetetive experiences... I know that motorcycles retain broader more useful powerbands with their airboxes intact... and stay much quieter.. much.

Despite the fact that I am a hotrod... I have learned to never discount the benefits of either of those factors for a street ride.

So... from my side... I would TRY to save as much of the original airbox and flow characteristics.

But this being a Euro ped... my plan may be a waste of time.

One example... A friend who in the old days was talked into the old ... "K&N pods" (whoop-de-doo!) on his GT750 Suzuki.

After much fiddling (jetting)... he pronounced it 'good'.

Bah!... that thing had lost ALL the low end it was tuned for with the stock airbox... and he was forever accompanied by this flat bleating weak .... waaaaaak!... noise from the carbs.

He was insulted when I suggested he try changing back.... Oh well... his loss.


hey Ron... there is a University engineering competition being held this weekend in the parking lot of the Silverdome.

Their assignment was to build "Formula race cars" with only one stipulation.... 600cc limit to the motor displacement.

Teams from all over the world I guess.

I going to ped over and check it out ... (7 miles)

Friday and Saturday as far as I know.

Re: So how fast is it now ?

I think I'm going to to stay with how I have it set up now. I haven't seemed to have lost any low may even accelerate faster now since I've added the pipe. The top end is nice and smooth. I'm guesstimating I'm doing maybe 35mph. The bike did get maybe 15-20% louder by taking off the box elbow..but seeing how just adding the proma pipe made the ped 4x louder..I think I'm ok there. It's still 100x quieter than any Harley in my neighborhood.

And hey I have no need for a loud horn anymore!:)

Thanks for your comments and help!

Re: Proma Circuit Pipe problem solved

How big is the hole? if it is small, look a little closer, that is a plug with a hole in it. If you don't have the restrictor plug, the hole will be the same diameter as the tube.

Re: So how fast is it now ?

Ron Brown /


No argument from me on the street bike mods. However, peds have notoriously restrictive intakes and exhausts, presumably for speed limitations. Having installed a performance exhaust, the chances of the stock air box configuration providing enough air are slim to none.

Having said that, if Phil is happy with the performance after removing the inlet tube and his mixture is good, he has avoided a lot more testing and modifications.


Formula Cars

Matt Wilson /


My school (RPI) will be there! A couple of my friends are in the SAE club at my school. Last year they finished 49th.

Its actually a restricted 600cc engine, but the thing flies! They race it behind my dorm during hte school year.

Let me know how they do!


Re: Formula Cars

Hey cool... I saw RPI there too ... And many many others...

Couldn't tell you how they did.

Saw teams from Japan and Britain... in addition to mostly US teams.

Most of the cars use 600cc 4 cyl Jap motorcycle motors... the wheelbases look too short for the rest of the car.

They share one thing with US peds... they force the cars to breathe through a single tiny 20mm opening... so they are restricted from making max HP.

Dyno runs... drag runs... skidpad runs... and the main course.. an Autocross event.

Not a bad diversion... hard to enjoy with the cold.

... man what a miserable day weather wise... 40 degrees and blustering wind... and I got SNOWED (or hailed) on on the way over there ! ... My L hand is freezing.

speed gain

I asked my wife to drive beside me and tell me how fast we were going while on a flat staright.

she said 32 mph, before the pipe I topped out at 27. Now I wish my engine was the 2 hp and not the 1.5 hp because 35 or 36 mph would be great. Has anyone upgraded their 1.5 HP to a 2 hp?

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