New (old) stuff

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Agreen

Member
Feb 10, 2013
792
11
18
Southeastern GA
Long story short, I acquired a Huffy "good vibrations" bike and a USED 66cc kit that was missing parts. The engine is in good shape, and upon inspection shows that the engine is well broken-in. Strong compression, starts without choke, and strong exhaust pulses too. The cylinder is shiny and the rings have worn the black coating off, so I'm calling them seated.

Anyway, I get the bike assembled after ordering some parts (which includes a 41t sprocket) and I went for a ride. It starts up good, runs quiet, and pulls well without misfires. The only thing is that it's just incredibly slow! I thought for sure a 66cc with a 41t would outperform a 48cc with a 44t?

I'm going to compare the ports on the 2 engine's and see what I come up with. Here's what I'm thinking:
-put a degree wheel on the crankshaft
-find TDC and make it 0*
-note the angle at which the exhaust port opens
-note the angle at which the exhaust port is fully open
-same for intake opening and closing

I also want to see if there's a difference between the two as far as magneto positioning.

If everything check out, then I'll probably port the transfers where the cylinder meets the base.

I kind of want to get to the bottom of why everyone is having different results with these engines. My 48 should not be powering past the 66 with a taller sprocket. Something's got to be amiss here.

...

Something else I noticed is that this engine is a center-fire head. I haven't seen one of those in a long time. Then again, so is my 48 (but it's a freakin beast!)

Maybe this is a much older model with bushings instead of roller bearings? I guess we'll see.
 

crassius

Well-Known Member
Sep 30, 2012
4,032
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USA
on flat ground, the 48 should gradually build up to a faster speed than a 66 (not much diff tho)

I've seen cheap 66s that take quite a while to run in to get full speed.
 

Agreen

Member
Feb 10, 2013
792
11
18
Southeastern GA
The 48 is ridiculous. Out of the box it made an excellent rival in stock trim. But the Enfield bike it's on is significantly heavier than the bare bones Huffy. While I agree it should be able to rev higher, the 66 should come somewhat close.

I've seen that there are several differences between manufacturers. Some have very clean castings, some are ... worse. I had a kit once that the exhaust flange covered up 50% of the port area because the port was square and the flange inlet was a tiny round hole.

I know engines pretty well. I may not know every minor detail about the 66 and 48cc 2 stroke bike engines, but I've been around engines long enough to know that it's holding itself back.
 

YesImLDS

Member
Jun 29, 2013
960
12
18
Columbia, Missouri
A 66cc should always have more torque than a 48cc so theoretically it should always accelerate faster. Given the compression ratio would be the same and the ports be in good condition on both. I have seen extra casting on the inside of the ports before that partially blocked so I could see the performance being slower on one engine due to that. In the very top end the 48cc theoretically could go faster than the 66cc due to being more balanced, but wind becomes a huge factor in that and being able to have enough power to maintain acceleration to the point where the 66cc is unbalanced and having a hard time accelerating due to that and wind factor.

I'd love to see a 48cc keep up with a 66cc, but I think if it does the 66cc has a couple things that need adjusted on it or the 48cc is modified.
 

Agreen

Member
Feb 10, 2013
792
11
18
Southeastern GA
So the 48 was completely disassembled before I put it on the bike because I didn't want to risk what happened to my first HT. The cylinder walls got scored badly because of leftover china trash inside from manufacturing. While I had it apart, I noticed that the transfers didn't match at the base, so I smoothed it out a little and matched the base to the cylinder. Not much metal got removed, just enough to clean it out and smooth the transition.

I also developed a small head gasket leak, so I lapped the head a little, raising compression just a touch.

The last 2 things I did was I fabbed a ghetto poopoo pipe because I got tired of smelling like 2stroke all the time. I think the poopoo pipe did something for performance because after that it ran terrible and I had to open the jet up a little bit to get rid of the high rpm WOT lean surges.

So overall, I don't really consider that much modification. So far though, the top speed has been clocked at 43 MPH. And that's on a 44t rag joint sprocket. It's got plenty of pickup too. It gets my 190 lb butt (plus 40-ish lb bike) up go speed in no time. I will put it against almost any modified 66 any day.

I may get some time tomorrow to do the degree wheel idea. I'll be sure to post results.
 

YesImLDS

Member
Jun 29, 2013
960
12
18
Columbia, Missouri
I don't know. Seems like 43mph with a 44t on a 49cc is wishful thinking. Especially with the simple modifications you have going on. Anyways we are taking about an engine that has 4/3 the displacement. It's going to have more power in stock form when set up properly any day of the week. No replacement for displacement. I'll race ya with my 66cc!
 

Agreen

Member
Feb 10, 2013
792
11
18
Southeastern GA
This is the 2nd 66 I've had, and neither could hold a candle to the 48cc bike.

I have a neat little secret I'm about to reveal with the 48. I have to install it first :)

Anyway, today I swapped the spark plug and did a plug chop. Everything's in order, so once I get back home again I'm probably going to hit both with a degree wheel and a set of calipers.
 

ZipTie

Active Member
Jan 8, 2016
750
82
28
Mpls Mn
I've read over and over the 48ccs vibrate way less also? Do you still have your john deer 4 stroke Gt2 build?
 

ZipTie

Active Member
Jan 8, 2016
750
82
28
Mpls Mn
Oh yea, I love your bike. I got your build confused... Very cool build. You need to get a album up on it.
 

Agreen

Member
Feb 10, 2013
792
11
18
Southeastern GA
My dad came by yesterday, so we went for a ride.

He started out on the 66cc huffy, I was on the skyhawk. The huffy is several pounds lighter, but he weighs 300+. I am under 190, so I figured him on the bigger engine bike with the lighter frame would be more fair.

I would rip past him without a sweat.

So after a mile or so, we swapped. He's now on the heavier bike with the smaller motor, and I'm on the lighter bike with the bigger engine. I'm able to pull away at first, but once we get going up around 20, the skyhawk bike flys by me.

It's official, the 48 is better for now.

Next steps:
-do all the port timing measurements that I said I was going to do but haven't.
-tear the 66 apart and balance that shaky rotating assembly
-port the 66 to equal that of the 48
-rematch
 

ZipTie

Active Member
Jan 8, 2016
750
82
28
Mpls Mn
It will be interesting when you get the 66 torn apart and balanced up and ported. Maybe you will find out the 48 is just one of those dragon blessed engines.
 

Agreen

Member
Feb 10, 2013
792
11
18
Southeastern GA
Numbers from the 48 are in

I'm referring to zero degrees as TDC

Exhaust port begins to open at 110*

Transfers begin opening at 120*

The intake port begins uncovering at 50* before TDC, and (duh, shouldn't have to say this) closes at 50* after TDC.

Both the exhaust and transfers seem to extend a little below the top of the piston when at BDC.

I also checked the piston/cylinder deck height clearance. It measures in at 0.085" (at the crown of the piston.

I should have checked the cylinder head volume while I had it off, but I was too busy polishing the inside of the head. Then it got below 40 and I took my southern self inside.
 

Agreen

Member
Feb 10, 2013
792
11
18
Southeastern GA
Something's weird. I installed a centrifugal clutch on the Enfield bike a few days ago. From a stop, I would pull back on the throttle and start going. If I gave it full throttle though, it would just die. I figured it had to be a jetting issue, so I pulled the jet out and resized it to a 68 jet. Much better.

The weird part is that the 66 likes a 72 jet better. (Smaller)
 

ZipTie

Active Member
Jan 8, 2016
750
82
28
Mpls Mn
Glad you quickly remedied the bogging fast. I saw the pull starter in your last photo installed and figured you swapped to a centrifugal clutch. How do you like the pull starter and cent clutch? Your take on the pros and cons of the new set up would be cool to hear.
 

Agreen

Member
Feb 10, 2013
792
11
18
Southeastern GA
The pull start is awesome. I read some bad reviews about them, but figured why not. It seems the cord ripping issue has been fixed. They installed a plastic bushing where it goes through the case. It's also easy to install.

The centrifugal clutch... I love having it. It's installing it that sucks. I still don't have the cover on it yet. I'm working on a clever fix for that.

My newest venture is installing a pz19 carb. I think it's comparable to a Mikuni 19mm? Anyway, I fabbed the manifold up today, but now I need a new throttle cable and also a choke cable as well. So far I've only fired it up and let it idle. The best part about this carb (aside from the size jump from 14mm to 19mm) is that it has an actual TUNABLE idle circuit!! You can adjust the idle speed AND mixture! It idles like butter now, and I'm all about those creature comforts like that.

I wonder how much faster it'll be with this monster carb now:D

I think sometime soon I'll be pulling the 66 and doing some work. Port work on the transfers and lapping of the head is in order, plus some balancing.

(at 35F here, some churches open their doors as homeless shelters)
 
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