Pocket Bike Engine Project II

[lowracer]

WOW...The Stage 7 kit I ordered from China on Saturday is here today Tuesday (2 days)..
Now I gotta find some time to get back into the garage...
-Lowracer-

 

[lowracer]

I installed the new cylinder, rings, piston, needle bearings, wrist pin, head & gaskets. I had to cut away about an inch of the the pull starter cover to fit the larger head due to the cooling fins. Came out real nice. I hooked it up to my new DIY friction drive experiment & took it for a few test spins. Wow, its nice & simple & a bit quieter back behind me. These pocket bike engines with expansion chambers can be a bit noisy, but worth it (huge power)...
http://motorbicycling.com/f6/diy-friction-drive-experiment-34337.html
-Lowracer-

 

[gera229]

Hey, the kit you ordered was ported with a larger boost and exhaust port.

How was your experience.

I predict that you have a sacrificed low end (So acceleration would be slower), but a better top end (more power, acceleration, and speed at the higher RPMs).

This is because the large boost port does not give as much velocity for the fuel to go from boost port to expansion chamber so at lower RPMs it may be a little slow. But at higher RPMs the piston is able to suck in more fuel due to the larger boost port which causes the boost.
I imagine that jetting MAY be necessary due to this change. Do not fall for it however, just do what you think is right.

 

[lowracer]

Gera,
I only am able to do limited power test-drives since the drivetrain isn't completed yet & I'm still using vice-grips in those last 2 pics to hold the friction roller arm down against the tire. The new cylinder & rings need to get broken in too. I can tell from what little I rode it today that its got great low end power. I really like the Stage 7 head with the added cooling fins. It is also more heavy duty than the cheapo Stage 2 heads. The kit also came with lots of extra parts. I got a spare set of rings, gaskets, carbon reeds, fully polished full circle crank etc. The best part was the totally polished & machined cylinder. The Stage 2 looked like it came right off the casting with some exhaust burrs & all. The Stage 7 is shiny & well polished. I coated all the innards with a thin coat of 2 stroke oil using before assembly. I re-used my old needle bearing & wrist pin, keeping the new ones as spares. For under $70 shipped, received in 2 days & fixing my serious self-inflicted problem, I feel very fortunate to have found this kit.
-Lowracer-

 

[gera229]

Yeah lowracer, I want one too. But I'm waiting till my stage 2 blows lol.
If you replaced the carbon reed with the reed that was in the engine. Can you tell me what kind of reed was previously in the engine? Was it Carbon reed?

 

[lowracer]

Gera,
I didnt replace the old reed so I dont know what is in there?
I am keeping all the spare parts for the one day I'll need them.
I wouldn't have gone thru the trouble & expense of purchasing the Stage 7 kit to repair my blown engine if I didnt admire that little monster of an engine. I also dont think it was the engines fault...just its stupid owner...lol (me)
-Lowracer-

 

[gera229]

For the boost port, was it 3 boost ports or was it 1 large boost port in your cylinder?
The boost port is one that is on the opposite side of the exhaust port.

I forgot to ask: what color was the spark plug when you took the engine apart?

 

[gera229]

Hey I also wanted to ask:
Do you have this pipe:
pocket bike Exhaust - Cag, Pro Jet Pipe

Or do you have this exhaust pipe:
Exhaust - Performance, Cag

Please compare yours based on pictures rather than price.

Thanks.

 

[lowracer]

The ports opposite the exhaust port are 3.
I dont have either pipe. Look on my other thread for pics of the two I bought.
The good one says REV on the canister.
-Lowracer-

 

[gera229]

I hope the $40 performance pipe is good and as good as yours or even the pro jet pipe and fits because I bought it.

Hey how did you install the throttle cable in the Carburetor?
If you can take any pictures that will be appreciated.

 

[lowracer]

Throttle cable comes attached already. If it didn't, you just remove the two top screws & pull the slide out. The cable end fits in the slot, then you put the slide back in & tilt it to allow the choke arm to get under the choke lever assembly. Dax has a video on You Tube on how to do this on the same exact carb (his You Tube name is Grabir01).
-Lowracer-

 

[gera229]

From big motor sport the cable was not attached for me, I don't get why it was attached for you and not from me since you bought from the same seller.

One thing I noticed is the cable tip that slides in seems a little large. It will go in horizontally, but not vertically. Maybe I should take some pictures.

 

[lowracer]

Look for the video
(Thats Dax RT Carb)

 

[gera229]

I already saw it. I repeat, the cable does not fit in like his cable did.

How long is your cable, can you measure it? Mines is 31-32 inches.

(I am just making sure you got the same cable as me from big motor sport which is the same seller you got your engine from).

 

[lowracer]

Gera,
Both my pocket bike engine cable housings are 42" long (the black part).
Thinking back now, they came with the kit, but weren't attached at the carb. I had to remove the two screws myself & install the cable end thru the slide slot. The small barrell end should fit into the hole part of the slot & the cable lays in the slot, then you pull it up slightly before re-installing the slide.
-Lowracer-

 

[gera229]

Here are some pictures.

Good thing the throttle set came with a cable because that one fits, just the draw is too small.
If I can trim the black part I will use that other cable.

Here is a picture of the cable that came with the pocket bike engine.
Is that how you fit yours?
Because if it is, I think that it is incorrect and these cables were not made to fit these carbs, but the stock carbs. But that's what I think.

 

[lowracer]

Gera,
That is the correct cable, you just havent figured out how to place it into the slot. In the 1st pic, you need to put the cable into the slot by pivoting it downward. Then the barrel end is inside the slot.
-Lowracer-

 

[gera229]

In the second pic, is that how it should sit?

By the way I have DAXs cable, so I might use that instead.

The rest of my stuff came today and I can say I am disappointed with the exhaust because it does not fit due to the gearbox in the way.

 

[lowracer]

Gera,
In the 2nd picture, you got it all backwards. The hole you have the barrell sticking out isn't used.
These exhausts only fit the pocketbikes they were designed to fit.
We as bicycle builders need to cut & either weld or clamp sleeves onto the pipes to fit our intended purpose. I use some nice flex pipe I bought online to connect the exhaust header to the cut down exhaust pipe. I then use some ceiling fan drop pipe to connect & clamp the connections (I dont weld).
-Lowracer-

 

[gera229]

See my thread.