4-stroking just before pipe hits

Setup:

Puch e50

AJH clone large reed kit (basically a 70cc Gila) ported.

190* exhaust timing

3rd transfer

bridged exhaust

gila size stock 2 petal with .030 cf reeds

Low comp head

mikuni tm24 flatslide

24mm intake

geared at 16x40 at the moment

derestricted shortened (3") estoril

timed at 17*

carb settings:

22.5 idle

4j13 needle (also tried 5n13 and 4f10) on multiple settings

170 main

It wants to 4 stroke just before it hits pipe (around 30mph) no matter what needle/setting I've tried. If I tuck on flat ground it'll clear out and blast on the main jet. This thread has some good info, but it's not working for me. Maybe I need a leaner main and a powerjet setup or a lower hitting pipe? Ports stalling? Paging Mr. CWayne?

Re: 4-stroking just before pipe hits

Port for more intake duration

Re: 4-stroking just before pipe hits

It's got 360* intake duration right now.

Re: 4-stroking just before pipe hits

Overpriced Parts /

I ran a treats pipe on different setups and it did the same thing

So I sold the pipe and I'm running a derestricted Estroil

Re: 4-stroking just before pipe hits

Yeah, I'm thinking that with a lower hitting pipe it would solve the issue. I may try to borrow a friends pipe with a longer tuned length.

Right now this pipe is almost identical to the doppler pipe for peugeot (overall angles and lengths).

Re: 4-stroking just before pipe hits

Important question .

Where is your throttle position at the time of the four stroking ?

That is the key .

If your wot , then downjet the main .

If your 1/2 throttle then keep adjusting the needle/settings and or slide.

Less then 1/2 throttle , downjet the idle .

Make cents ?

Maybe mark your grip to double check your throttle position so you can see whats metering gas flow atm .

Re: 4-stroking just before pipe hits

Isn't that a good thing?

If you have a hard hitting pipe, then it's good to 4 stroke a little before the powerband.

Or are you saying it's extreme 4 stroking where you can't even clear it sometimes? (edited)

Re: 4-stroking just before pipe hits

Once I get to the point in the rpm where it wants to 4 stroke, it doesn't matter if I'm at wot or 3/4.

I stole a needle out of another mikuni that's a lot thicker at the end and it seemed to nearly eliminate the problem.

Re: 4-stroking just before pipe hits

Are you still cool everywhere else ?

Running a temp sensor ? Temps ?

I knew it was a needle issue . What needle did you go to ?

Re: 4-stroking just before pipe hits

i have had that happen on a gila/tm24/destroyer setup. i could usually coax it thru that into p.band. it kinda made me feel safe.

Re: 4-stroking just before pipe hits

back pressure, you may have too much. That pipe is meant for 50cc right? You can also try a hotter plug and indexing the open side towards the exhaust port, both those things will make a bike four stroke less. But it also could be this weird thing that happens with hard hitting pipes and cdi's that fire at tdc and bdc. So cdi or points?

Re: 4-stroking just before pipe hits

Points

Re: 4-stroking just before pipe hits

yeah its probably just a misfire where the timing goes from needing to be super advanced to when the pipe starts flowing and needs to retard. At that point the piston is moving very fast and the flame isn't spreading through the whole chamber before the exhaust port opens, but the pipe hasn't kicked in to boost the heat/pressure in the cylinder.

you can advance the timing to see if that is the problem, but you'll detonate like crazy when you hit the pipe so be careful. i would be super hesitant to do any down jetting because its probably an ignition misfire and not too-rich misfire.

Re: 4-stroking just before pipe hits

Overpriced Parts /

Points and big/higher rpm pipes don't mix

Cause you need hi timing to carry over to the pipe hit then retarded during hi rpm to run cool .

Most of my point bikes have Derestricted Estroils and got good take off, no

Gaps in powerband even with high gears and run cool at speed but at least 5 mph slower then with a destroyer/bk100 type pipe.

A Hpi setup with regulator, new 12v bulbs, shipping etc is like 450.00 + the time to install, wire lights and tune That's just nuts I could buy a clean stock bike and time to work on it for the same.

I do want that 5+ miles I'm missing that's why I'm keeping the few big pipes

I got and I hope Hpi's come down in price

Re: 4-stroking just before pipe hits

not a Baron Asshole /

Boy there are lots of vairables here! do you know what compression PSI you are at with that combo? I have heard big presure can blow out the points spark. which base gasekt?

thanks

pete

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account