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Modifying a compression release

Terry Syd

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I had set up my 029 with a 390 jug with a compression release. To make it a simple 'pull and go', I added a 066 coil with the 4 degree retard on starting. Everything worked just great, until I put in the new pop-up piston. Now the compression release will close too early. I have now ruined two of the plastic pawls on the starter mechanism.

Has anyone ever modified a compression release?

I thought if I reduced the size of the vent holes on the release it might close at a higher compression. Anyone else have any ideas?
 

Larry B

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I had set up my 029 with a 390 jug with a compression release. To make it a simple 'pull and go', I added a 066 coil with the 4 degree retard on starting. Everything worked just great, until I put in the new pop-up piston. Now the compression release will close too early. I have now ruined two of the plastic pawls on the starter mechanism.

Has anyone ever modified a compression release?

I thought if I reduced the size of the vent holes on the release it might close at a higher compression. Anyone else have any ideas?
My 660 with a big bore kit and advanced timing had same prob. I drilled out the vent in the side of the decomp valve about a 32nd larger. Starts like a normal saw now
 

drf256

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Terry, are you sure that the coil didn’t advance timing too much?

I’m not familiar with the differences in the coils, but an oem starter mechanism shouldn’t break on a saw from the small comp increase the popup adds. And that’s with or without the sissy button being pressed (I’m older an like them too).

I bet it’s firing early. Perhaps the old 039 coil had built in starter retard and the 66 coil doesn’t?
 

Terry Syd

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Naw, it worked fine before I put in the pop-up. The pop-up didn't add that much compression, but it was enough to trigger the de-comp after I put the piston in.

I may have a bit too much advance, I'll have to play with it (I have an adjustable coil). It is like the carburetion, I just keep fiddling with it until I don't think I can get it any better.

As far as the carburetion, I gave up on the HD and went back to the Zama twin jet. I tried the Zama after messing with the HD for a while - OOPS - I decided I wanted to just get on with cutting wood.

EDIT: The 066 coil had the 4 degrees of retard on starting. I put it on and noticed the difference. It is a good mod ($20 Chinese coil) to one of these saws - especially if you advance the timing.
 

CR888

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This ain't useful to your problem but when I send some chain & stuffs your way I'll put in a couple of decomp plugs with washers should you need them. The dozen I bought are not really needed.
 

Terry Syd

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Thanks for the message, I was going to start drilling out the de-comp tomorrow. I'll wait and try to get a feel for what is going to work with your de-comps.

Aussies don't need any Vegemite. I was wondering what to send the Aussie blokes that send a chain. Tim Tams, Minties, etc. are all so common over here. Maybe I can come up with something that is out of the box. I learned to love 'Nuoc Mam' over in 'Nam. Maybe I can send the Aussie blokes some fish sauce (fermented fish), but they can get that at the market. Hmmm, gonna have to think about this...
 

67L36Driver

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You will need some letter & number drill bits in the tiny range.

I ended up at 1/16” on a MS880 I rebuilt.

Standard hole was too small for this 130# geezer. [emoji849]
 

zero_sum

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I need to try this on my 2260 I suspect. I pops every pull (pop up) & is hell on the recoil guts as a result. I was under the impression that the decomp was the same (same part #?) for all saws. Is this not the case?
 
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