3rd transfer port plz help

[Adam E]

I am adding a reed valve to my engine and want to use a windowed piston and 3rd transfer port with it. I made my own window piston but I need some clarification on how to make a third transfer. So I know it’s on the intake side but how far up do I go? Anyone who’s done it before plz feel free to chime in. Thanks In advance

Adam

 

[indian22]

Hi Adam, I've included photos of some things that help a reed work in the 66cc GT 4 type motors with the RSE type reed.. This is a place to start. Window piston and reed valve normally boost the power the combination with third port is normally better, but tuning is necessary to really make mods work well. Jetting, pipe, combustion ratio etc. have to be right or power suffers despite the added modifications.

If your a gear head and have machine skills and a well equipped shop photos are all you will need, if not I'd buy a cylinder with the work completed. The work shown wasn't done with a Dremel tool!

X-pipe, head and carb are suggestions to help setting up a tuned engine, what I've used to build engines that I'd call well modified but not nearly the highest tune possible. Nice running street bikes not high strung race tune for sure, but get into the 5hp range which is quite noticeable improvement from stock!

Rick C.

 

[Venice Motor Bikes]

If you're going to cut the 3rd port yourself, don't make it any higher than the two side ports!

Also... One of the first things I learned (the hard way) about adding a reed valve to one of these engines is that you need to 'throw gas at it"!!! Jet the carb a lot bigger.

 

[indian22]

Absolutely correct!!

 

[FOG]

I concur with Rick's advice on using a dremel. I tried it on a scrap cylinder and won't be doing that again anytime soon! It jumped and bucked and landed in the bore where I didn't want it. A light and extremely accurate touch doesn't seem to be in my particular toolbox.

There are guys that do, but they must be brain surgeons in their spare time.

FWIW, a 3/16" carbide barrel cutter is the 1st weapon of choice and the 1st barrier is getting thru the chrome.

You may already know this but making sure your ring gaps never cross a port is of vital importance. They can snag. Cylinders do get broken.

As far as how high. I'm using a pocket bike motor and the experts are telling me my boost ports should open 1mm "before" the main transfers. This seems strange to me but these guys have a vast amount of experience blowin' 'em up so I'm listening.

I did these on my little mill. No dremel.

 

[indian22]

Nicely done FOG.

Chrome bores serve a purpose but I really like steel liners when modifying and rebuilding engines, but most of these little pecker woods are chromed.

Rick C.

 

[Adam E]

Thank you guys! That helped a lot and cleared up my confusion! The reed valve I’m going to be using is a 4 petal box type with a Keihin knockoff. I think it’s the same set up seen in the gt80. Anything I should do specifically with this setup?

 

[Adam E]

Hi Adam, I've included photos of some things that help a reed work in the 66cc GT 4 type motors with the RSE type reed.. This is a place to start. Window piston and reed valve normally boost the power the combination with third port is normally better, but tuning is necessary to really make mods work well. Jetting, pipe, combustion ratio etc. have to be right or power suffers despite the added modifications.

If your a gear head and have machine skills and a well equipped shop photos are all you will need, if not I'd buy a cylinder with the work completed. The work shown wasn't done with a Dremel tool!

X-pipe, head and carb are suggestions to help setting up a tuned engine, what I've used to build engines that I'd call well modified but not nearly the highest tune possible. Nice running street bikes not high strung race tune for sure, but get into the 5hp range which is quite noticeable improvement from stock!

Rick C.

View attachment 103981 View attachment 103982 View attachment 103983 View attachment 103984 View attachment 103985 View attachment 103986

I’m using this setup without the ported cylinder
https://batchsports.com/gt80-reed-v...4&utm_source=google&utm_medium=smart_campaign

 

[indian22]

Adam are you running the window piston that you fabricated? If so are you seeing a performance boost with the Keihin carb & 4 petal reed compared to before?

Rick C.

 

[Adam E]

Adam are you running the window piston that you fabricated? If so are you seeing a performance boost with the Keihin carb & 4 petal reed compared to before?

Rick C.

I haven’t ran it yet but will let you know when I do. I just need to order some piston rings then I’ll try running it.

 

[Jerdoggiedog]

If you're going to cut the 3rd port yourself, don't make it any higher than the two side ports!

Also... One of the first things I learned (the hard way) about adding a reed valve to one of these engines is that you need to 'throw gas at it"!!! Jet the carb a lot bigger.

What jet size bigger, than what the gt80 khien carb has

 

[Venice Motor Bikes]

What jet size bigger, than what the gt80 khien carb has

All engines are a little different & need different jet sizes to run perfectly... I suggest buying a cheap jet kit off eBay & start off with a jet several sizes bigger than what's in it now; then keep testing bigger jets until it starts feeling 'sputtery' , then drop down a size (or two)

Another thing to remember is that your carb probably also has a pilot jet which controls the low speed mixture... that will also need to be changed... So buy a pilot jet set too.

 

[Jerdoggiedog]

All engines are a little different & need different jet sizes to run perfectly... I suggest buying a cheap jet kit off eBay & start off with a jet several sizes bigger than what's in it now; then keep testing bigger jets until it starts feeling 'sputtery' , then drop down a size (or two)

Another thing to remember is that your carb probably also has a pilot jet which controls the low speed mixture... that will also need to be changed... So buy a pilot jet set too.

OK another dam problem, I too purchased the GT7 Kiehn Reed valve motor, I thought the cylinder had the 3rd transfer port in it. I don't think it does. Why dafuc would kingsmotorbikes sell a product without a window piston and without a 3rd transfer ported cylinder for the Reed valve. So I have put a windowed piston in, I will probably have to make the 3rd transfer port