dissecting an earthquake chainsaw

[nenicu]

Cmi bks45 :45 cc on modified GZ 400[4000?] case. Left 37 cc clone case and right 45 cc case. Left 40 cc clone crank and right 45cc crank.

 

[nenicu]

More pics. The piston has from the factory a strange shape on the intake side. 42,5 mm diameter versus 41,5 GZ 4500.

 

[nenicu]

More

 

[nenicu]

This mutt is sold as CMI bks 45 by OBI . Is 45cc on a little bigger case than GZ 400. Front to back the bolts spacing is 4-5 mm bigger. Side to side the same as GZ 400. Impulse port on the case. The crank is diferent than that on the 37cc clones. Bigger counter weights and diferent rod . No thrust whashers on the rod. The case has diferent shape on the transfer port entry. The cylinder has a rubber intake bolted to it. First picture is a Ryobi oil pump and a chinese worm gear. The pump is non adjustable, the chinese pumps are all adjustable.

 

[nenicu]

Clone

 

[Chris-PA]

Clone

Interesting - I can see how the rear cylinder bolts are moved back. Is the crank centerline moved rearward too?

Did the GZ4500 use this sane approach? I didn't think so but I never had one.

 

[nenicu]

GZ 4500 has the same bolt spacing like G3800 and clones, GZ 400 and clones. Just the hole for the cylinder is a little bigger.

 

[Chris-PA]

GZ 4500 has the same bolt spacing like G3800 and clones, GZ 400 and clones. Just the hole for the cylinder is a little bigger.

It's a strange mashup. I wonder if the cylinder was from something else? Still, it's not that different from the kinds of adaptations the Chinese have done on other Zenoah designs.

 

[nenicu]

I'v seen on Ebay some time ago a Tanaka cylinder. On the outside close to this one, inside closed transfers. 45 cc Tanaka.

 

[psjwi]

So, I've got two of the 45 cc saws and though they seem to be a bit lacking in power, (even with the muffler mods) they are super easy to start and they both run great. I've also got two of the 41 cc saws and they are great performers (again with the muff mods). However, they both have the same problem... They start very easily and run great until you shut them off... then if you wait more than maybe a minute, they will not start until you let them cool completely - like say 1/2 hour.

It's a fuel delivery problem - even if you choke them and pull till your arm falls off - the plug is dry. I replaced the fuel lines and it made no difference at all. The carbs are tight to the cylinders so no air leak there.

Since there are so many of these in use among the members I thought sure this would be something that has been addressed but I'm not finding anything (unless I just missed it). This couldn't have something to do with those check valves could it?

Thanks,

Paul

 

[Chris-PA]

So, I've got two of the 45 cc saws and though they seem to be a bit lacking in power, (even with the muffler mods) they are super easy to start and they both run great. I've also got two of the 41 cc saws and they are great performers (again with the muff mods). However, they both have the same problem... They start very easily and run great until you shut them off... then if you wait more than maybe a minute, they will not start until you let them cool completely - like say 1/2 hour.

It's a fuel delivery problem - even if you choke them and pull till your arm falls off - the plug is dry. I replaced the fuel lines and it made no difference at all. The carbs are tight to the cylinders so no air leak there.

Since there are so many of these in use among the members I thought sure this would be something that has been addressed but I'm not finding anything (unless I just missed it). This couldn't have something to do with those check valves could it?

Thanks,

Paul

Sounds like the typical vapor lock issue I deal with all the time on various saws. I use E10 which makes it worse. I doubt there is anything wrong with the lines or carb, it's just the fuel boiling during heat soak. If you still have a cat muffler that might contribute a lot to the heat.

 

[psjwi]

Hi Chris,

No, the cat elements were removed along with muff mods. No ethanol and full synthetic Amsoil 40:1.

Those 41 cc saws are real screamers but it's pretty hard to deal with this issue... I've pretty much stopped using them. Bought a little Echo 352 to use for the times I was using the 41 EQ. That's a real sweet saw for only 34cc and it does start - any time you want! lol

 

[leecopland]

Hi Chris,

No, the cat elements were removed along with muff mods. No ethanol and full synthetic Amsoil 40:1.

Those 41 cc saws are real screamers but it's pretty hard to deal with this issue... I've pretty much stopped using them. Bought a little Echo 352 to use for the times I was using the 41 EQ. That's a real sweet saw for only 34cc and it does start - any time you want! lol

I have to agree that the little Echos are fine saws. The larger ones are pretty good too. I use a 520 on a regular basis and it's strong even without a muff mod.

 

[Chris-PA]

Hi Chris,

No, the cat elements were removed along with muff mods. No ethanol and full synthetic Amsoil 40:1.

Those 41 cc saws are real screamers but it's pretty hard to deal with this issue... I've pretty much stopped using them. Bought a little Echo 352 to use for the times I was using the 41 EQ. That's a real sweet saw for only 34cc and it does start - any time you want! lol

My 38cc Earthquake is basically the same saw as the 41cc. It has vapor locked a few times on hot days, but no worse than other saws I have. I think it is a combination of how much heat energy is built up in the cylinder and case while running and how the fuel system is packaged/located - how easily that heat can get into the carb and lines. In my experience plastic-cased clamshells are less prone to vapor lock.

Note that if yours are doing this at this time of year it might be something other than vapor lock. I have this issue only on hot days.

 

[psjwi]

My 38cc Earthquake is basically the same saw as the 41cc. It has vapor locked a few times on hot days, but no worse than other saws I have. I think it is a combination of how much heat energy is built up in the cylinder and case while running and how the fuel system is packaged/located - how easily that heat can get into the carb and lines. In my experience plastic-cased clamshells are less prone to vapor lock.

Note that if yours are doing this at this time of year it might be something other than vapor lock. I have this issue only on hot days.

It doesn't matter if it's a hot day or 30° same thing... It just seems odd that I have two of these with the same problem and yet nobody else seems to be mentioning it.

 

[Chris-PA]

It doesn't matter if it's a hot day or 30° same thing... It just seems odd that I have two of these with the same problem and yet nobody else seems to be mentioning it.

Ok, then I withdraw the vapor lock theory, as I don't experience that at low temps. My 38cc is easy to start and dead solid reliable otherwise, even with all the mods. Squish reduction, porting, muffler mod, timing increase. Stock carb though.

EDIT: The muffler on mine is not the original with the cat, it's an opened up non-cat muffler from a different saw.

 

[Chris-PA]

It doesn't matter if it's a hot day or 30° same thing... It just seems odd that I have two of these with the same problem and yet nobody else seems to be mentioning it.

I remembered that I did replace the check valve in the original carb - but that effected starting at all times.

 

[psjwi]

I remembered that I did replace the check valve in the original carb - but that effected starting at all times.

Yes, I saw that. I've been coming back to this thread every so often thinking that eventually someone would have run into this. I guess I'll pull the carb off one of them and maybe try replacing all the tubing again and make sure everything is tight.

 

[nenicu]

For enyone interested: i got my hands on a carburator of a 62 cc Zenoah clone built on the G 5000 case. They come as 58 cc and 62 cc with 34 stroke x 45 bore and 34 stroke x 48 bore. The carb on these has hy idle on the choke lever ,the 45 cc and 52 cc on the handle. The 62 cc clone carb has 15 mm venturi vs 12,5 on the 45cc and 52 cc.So for enyone who still plays with these a bigger carb is available. The 45cc is 32x43bore, the 52 cc is 32x 45 bore.

 

[Chris-PA]

For enyone interested: i got my hands on a carburator of a 62 cc Zenoah clone built on the G 5000 case. They come as 58 cc and 62 cc with 34 stroke x 45 bore and 34 stroke x 48 bore. The carb on these has hy idle on the choke lever ,the 45 cc and 52 cc on the handle. The 62 cc clone carb has 15 mm venturi vs 12,5 on the 45cc and 52 cc.So for enyone who still plays with these a bigger carb is available. The 45cc is 32x43bore, the 52 cc is 32x 45 bore.

That would be a big help - carb size is one reason I've stayed away from the 58 and 62cc versions of this saw.

Do you think the larger carb is still based on the WT type carb, or did they fit on something based on the HDA series?

I'm looking but have not found any loose carbs like this on eBay yet.