Porting a Chinese G621 Clone

[Big_Wood]

you should post a pic of the carb Chris? i got a bin i'll peak through to see if i have anything larger with minimal match up work. do you think it's a walbro or zama copy? i got a zama c3m from an 044 that might be a good candidate.

 

[nenicu]

Chinese air injection

 

[CristiRo]

Just some intake work in my Chinese 4500 chainsaw.
Advacend the timing by 1/3rd of the key. Runs great, but the transfers don't match exactly with the crankcase.

Here is how I improved my cooling on my Chinese chainsaw.
It is way better now!

And I added a dual port muffler.

 

[Chris-PA]

you should post a pic of the carb Chris? i got a bin i'll peak through to see if i have anything larger with minimal match up work. do you think it's a walbro or zama copy? i got a zama c3m from an 044 that might be a good candidate.

I believe the original G621 carb was an HDA31, and the clone is definitely an HDA-based design:


Other than the impulse port an HDA-137 or HDA-164 would almost be a bolt on with a larger venturi. I had planned on trying something like that at one point, but the saw works so well I've decided to leave it alone and use it.

I know there is more power there if I cut the jug and drop the squish down to 0.020" and add a larger carb, but sometimes it's better not to mess with success.

 

[Big_Wood]

what's the stock venturi on that thing? and when ABDC does the intake open?

 

[Chris-PA]

what's the stock venturi on that thing? and when ABDC does the intake open?

It's a 15mm venturi. The intake opens at 79.5deg (159deg duration). The HDA-137 & 164 are 16.7mm, which would be more appropriate. I could also bore one out.

 

[Chris-PA]

Just some intake work in my Chinese 4500 chainsaw.
Advacend the timing by 1/3rd of the key. Runs great, but the transfers don't match exactly with the crankcase.

Here is how I improved my cooling on my Chinese chainsaw.
It is way better now!

And I added a dual port muffler.

Nice! Did you do any work on the exhaust port?

 

[Big_Wood]

It's a 15mm venturi. The intake opens at 79.5deg (159deg duration). The HDA-137 & 164 are 16.7mm, which would be more appropriate. I could also bore one out.

i bet it would respond well to a bigger carb with that duration. that thing was 62cc? rig an HD12 to it lol

 

[CristiRo]

Nice! Did you do any work on the exhaust port?

No!
But i have in plan lowering the cylinder to set the squish.
After I took that lip of the intake and polished somehow, for better flow, it seems to run richer now.
I have the timing advanced by 1/3rd of the key.
Running the stock carb like this: L: 1 and 1/4 out and H: 3/4 and still 4-strokes in the cut sometimes.
I attached a picture with the base gasket. The grey one is cut after the case, and the green one is the stock.
I tried to measure the timing, but don't know how accurate the readings are: Intake 80, Exhaust: 103, Transfers: 123, with the gasket.
I would like to try a bigger cylinder on it, a 5200 cylinder kit. And than port that jug. I don't have specialty tools so don't mess with the transfer timing. Just intake and exhaust.
The exhaust it smallll!!!!

P.S.: I tried a friends Chinese Craft-Tec chainsaw. Man...that saw had huge compression. Brand new!
Anybody measured the stock squish on these Chinese saws?

 

[Chris-PA]

No!
But i have in plan lowering the cylinder to set the squish.
After I took that lip of the intake and polished somehow, for better flow, it seems to run richer now.
I have the timing advanced by 1/3rd of the key.
Running the stock carb like this: L: 1 and 1/4 out and H: 3/4 and still 4-strokes in the cut sometimes.
I attached a picture with the base gasket. The grey one is cut after the case, and the green one is the stock.
I tried to measure the timing, but don't know how accurate the readings are: Intake 80, Exhaust: 103, Transfers: 123, with the gasket.
I would like to try a bigger cylinder on it, a 5200 cylinder kit. And than port that jug. I don't have specialty tools so don't mess with the transfer timing. Just intake and exhaust.
The exhaust it smallll!!!!

P.S.: I tried a friends Chinese Craft-Tec chainsaw. Man...that saw had huge compression. Brand new!
Anybody measured the stock squish on these Chinese saws?

The timing numbers are decent though, so maybe widen the exhaust?

 

[CristiRo]

so maybe widen the exhaust?

Maybe! I'll have to measure width of the piston to see how far can I go.

I would try to lower the cylinder by eliminating the gasket, but i'm afraid that I could have leaks...

 

[Chris-PA]

Maybe! I'll have to measure width of the piston to see how far can I go.

I would try to lower the cylinder by eliminating the gasket, but i'm afraid that I could have leaks...

It's not a problem if you have access to any of the case sealants discussed here. Motorcycle shops should well something equivalent. Many of my saws are clamshells, but I think all of the ones that are not have had their gaskets removed.

 

[GerrySM]

Just received the new chinese clone saw, assembled it (with some difficulty because the combination brake-cover fits badly), new fuel, new oil, starts easily, but in my first big cut, with warm engine, it just dies when full throttle is applied. Have to use choke again for a single pull then then choke off and it restarts in a puff of smoke, only to die again. Cannot complete a decent sized cut. Any suggestions?

 

[TBS]

Increase the high speed adjustment a 1/4 turn and report back, also make sure everything is tight and all the lines are good. All of my saws have done that at some point.

 

[GerrySM]

Yes, I was hoping it's just a carby adjustment. My instinct is that it's running too rich, just needed that confirmed. Thanks

 

[GerrySM]

Hmm, adjusted clockwise ¼ turn, ran better (definitely) started cut well but after 5-10 seconds sounded choked up under full throttle in cut, then stalled. Had to use choke with one or two pulls to get the carb clear, then choke off and it started again with a couple of pulls. Advanced H a little more, problem still there. Should I just keep on turning H clockwise?

Brand new saw. Wonder if I should just turn L and H to their extremes and work back?

Note: running at 20:1, as advised by manual during the first 20 hours, before moving to 25:1 after 20 hours. Wonder if that is making everything too rich?

 

[TBS]

You wont have any problems running 40-1, that mix is recommended because of lower quality oils in China. Turn both screws all the way in (count the turns) then back each one out a turn. The more oil in the gas the richer the carb setting needs to be.

 

[7sleeper]

I would use1:50 fuel mix. There is absolut no reason to do anything ealse with modern 2 stroke oils. Futher I would fully adjust the carb and not only one part.

7

 

[TBS]

Bogging after 5-10 seconds could be a fuel pickup issue, needle valve may need adjustment or there is a restriction in the line.

 

[GerrySM]

Bogging after 5-10 seconds could be a fuel pickup issue, needle valve may need adjustment or there is a restriction in the line.

Does not stall out unless I get into a full throttle in cut situation. Will do little cuts all day no problem.

If I ease off on throttle in a big cut, comes back to life (aborts stall) and I can continue.