bigger carburetor for chinese chainsaw / Komatsu Zenoah clone

[Stefanseiner]

meanwhile I did some modifications on a cheap chinese 52cc saw I bought on eBay before christmas

works done so far:
1. changed the orig. dual port cylinder to the better quad port version (higher agility, higher rpm at stock possible, higher torque)
2. Muffler mod (drilled the internal diffusor with bigger 16mm hole, bigger outlet ports with 15mm)
3. thinner gasket seal 0,15mm (original is 0,50mm)
4. paper air filter with ported intake
5. bigger carburator from an 372XP (with 3d-printed manifold to fit it)


left the dualport version, right the quad port

muffler mod, here without the paint

widened air filter intake

I made the base gasket out of 0,15mm gasket paper

modified 372xp carb. It's a little hard to tune at the chinese chainsaw, I have to raise the idle screw at maximum so the engine will not die when letting the throttle go after full speed

side-gapped spark plug

just for fun: adapting some 372XP felling hounds to the chinese saw

and I will try to have the look of the Holzfforma Pro for my cheap chinese saw by foiling some parts with carbon look foil

but honestly I am not happy with this work and maybe I will try to do this again with hydro dipping but this is new for me too.





I did some cuts at the same wood and stopped the time. The timings are for:
1. stock
2. cylinder change + muffler + base gasket + paper air filter
3. carburator + spark plug

actually I am working on porting the cylinder.
Because this is my very first try I used the "old" dual port cylinder, What I've done:
-widened the intake (just left and right, no timing changes in high / depth)
- widened the exhaust outlet (just left and right, no timing changes in high / depth)
- widened the transfers
- polishing the exhaust outlet

yesterday I tried the cylinder in the wood but the cutting times are getting worse (38sec instead of 35sec before).
I guess it's because I did some mistakes while porting by slipping away with the dremel and hitting the cylinder coating.

Or because I was not able to do a better carb tuning. The cutting felt like the saw wanted more fuel and I tried to adjust the carb more rich but then the engine will die after full power.
What do you think?


Next try will be to port the good quadport cylinder and be more careful with the dremel in particular when working with the rotating direction,
but I would also like to figure out what's the problem with my first porting job at the dual port cylinder

 

[Leafy]

I could never get the dual port jugs to perform as well as the quad port one do stock. It’s pretty crazy how what stone pellet think would be too big of a carb for this saw makes a way bigger difference than anything else.

 

[Stefanseiner]

you have ported the dual ports as well?
There is a guy on Youtube at UK which is porting these chinese saws very high and he swears on the dual ports but I am not sure he ever tested out the quad ports. But I think what he saying is right: the transfers of the quad are significant smaller then the dualport because of the devidier. Thats the reasson why I tried very hard to widen the transfers at the quadport top end.

If the weather will be good I maybe can test the ported quad cylinder later this day.

And yes the bigger carb makes a huge difference, even at the small 49,3cc cylinder which is as big as the original and therefor the original carb should be right.
But I guess the difference of more power will increase with the bigger 62cc engine.

This will be my next step when I have done all of my testings and mistakes on this saw, I will go further to my good saw, a Greencut GS680X which comes with the 48mm piston / 34mm crank shaft. And a very rare dualport cylinder (which is already very strong at stock, just 0.27.56 seconds at the same tree as above, but with 3/8" full chisel).
At Aliexpress, eBay and Amazon I only can find the 62cc cylinder with quad ports but I will give it a try

 

[Roschdworschd]

I'm just thinking about this topic. I have a 5800 clone with a 372 carburetor. The manifold I built is a horrible construction made from a piece of plastic pipe and lots of epoxy. But it runs very well.
I recently saw that Zenoah model engines have a G620. Judging by the pictures, the engine has the same cylinder cast as the one from the 6200 chainsaw. There is even an attachment for the decompression valve. The inlet connection also looks like the cylinder for the chainsaw.
And there is a manifold from Zenoah for this G620 engine.
Unfortunately I don't have everything there, but does anyone have the opportunity to measure how wide the mounting holes are on the 6200 cylinder? Are they the same as 5800? The Zenoah G620 manifold is attached together with the carburettor with long screws. if the distance is the same as the 372 carburetor we could make a combination 6200 cylinder, manifold G620, carburetor 372. Or with the carb used by the G620…but at the moment i have no idea wich carb that is.

 

[el33t]

I'm just thinking about this topic. I have a 5800 clone with a 372 carburetor. The manifold I built is a horrible construction made from a piece of plastic pipe and lots of epoxy. But it runs very well.
I recently saw that Zenoah model engines have a G620. Judging by the pictures, the engine has the same cylinder cast as the one from the 6200 chainsaw. There is even an attachment for the decompression valve. The inlet connection also looks like the cylinder for the chainsaw.
And there is a manifold from Zenoah for this G620 engine.
Unfortunately I don't have everything there, but does anyone have the opportunity to measure how wide the mounting holes are on the 6200 cylinder? Are they the same as 5800? The Zenoah G620 manifold is attached together with the carburettor with long screws. if the distance is the same as the 372 carburetor we could make a combination 6200 cylinder, manifold G620, carburetor 372. Or with the carb used by the G620…but at the moment i have no idea wich carb that is.

The Chinese “62(00)” cylinders (48 mm bore, 34 mm stroke) can be used with a crankcase and connecting rod designed for “58” cylinders (45.2 mm bore, 34 mm stroke). The hole spacing is the same and is approximately 46x46 mm. On the other hand, the cylinder for Zenoah G620(x) (47.5 mm bore) has a different hole spacing and is approximately 46x52 mm.
The holes for attaching the intake manifold in Chinese 58/62 cylinders also have a different hole spacing (~41 mm) than in the cylinder for Zenoah G620(x) (~31 mm).

 

[Stefanseiner]

at the meantime a had a lot of port jobs on G5000 series chainsaws, 50cc, 58cc and 62cc
Actually I do a little work on a 62cc model with 372XP carb I can't get to run propperly. The carb is not adjustable well, at this point I haven't figuered out the problem. Maybe an air leak somewhere, maybe at the 3d printed manifold, I have to do a closer look

 

[Roschdworschd]

The Chinese “62(00)” cylinders (48 mm bore, 34 mm stroke) can be used with a crankcase and connecting rod designed for “58” cylinders (45.2 mm bore, 34 mm stroke). The hole spacing is the same and is approximately 46x46 mm. On the other hand, the cylinder for Zenoah G620(x) (47.5 mm bore) has a different hole spacing and is approximately 46x52 mm.
The holes for attaching the intake manifold in Chinese 58/62 cylinders also have a different hole spacing (~41 mm) than in the cylinder for Zenoah G620(x) (~31 mm).

Do you know the difference of the hole spacing ? ?

The Chinese “62(00)” cylinders (48 mm bore, 34 mm stroke) can be used with a crankcase and connecting rod designed for “58” cylinders (45.2 mm bore, 34 mm stroke). The hole spacing is the same and is approximately 46x46 mm. On the other hand, the cylinder for Zenoah G620(x) (47.5 mm bore) has a different hole spacing and is approximately 46x52 mm.
The holes for attaching the intake manifold in Chinese 58/62 cylinders also have a different hole spacing (~41 mm) than in the cylinder for Zenoah G620(x) (~31 mm).

Thanks for the information. That would be too complicated.

 

[Stefanseiner]

I see youre from Germany too. You can buy the parts for using an 372XP carb on the chinese G5000 chainsaw here on eBay