630 to 670 Jonsered build

[huskihl]

OK I am a little confused, the 630 and 272 both have the impulse circut to the carb in the intake block. Only the 625 and 670 use an external pulse line and have a port on the cylinder for pulse. Your first picture shows an external pulse line on the carb, where are you getting vacuum from?

Joe

Good eye. The 272 impulse system has always been a pain to seal up for me. Again, I'm sure it's aftermarket gaskets leaking, not that it's poorly engineered. I drilled the transfer duct and plugged the intake impulse hole because I could not get it to seal originally.

 

[BigDee]

Rich and burbling for a second or 2, then just like you turned the high speed jet in 1/2 turn it gains about 2000 rpm

Thanks. Don

 

[huskihl]

I ended up opting for a 268xp full circle piston like this While I like the standard windowed piston, I like the added stability in the bore that a full skirt piston provides as well.
I did a muffler mod on the 670 as well. I used a double cut carbide burr to create a 5/8"×7/8" hole in the front of the muffler and wire welded on a piece of 3/4" tubing cut on an angle. Finished it off with a few coats of Rustoleum 2000° high temp paint. I like how it runs.

I got new intake gaskets in for the 630/272xp build today. Installed them and she's good to go with no more air leaks.
Comparison videos coming...

 

[huskihl]

1st up is the 625/670


Next is the 630/272xp


Both saws are wearing the same 20" bar and round filed chain. Both have a muffler mod and timing advance.

And for comparison, here's my muffler modded 7900 with 24" bar and square filed chain

 

[67L36Driver]

Was this as simple as it looks?

Just pay attention to the throttle blade chamfered edge. Hold it up to a strong light source to make sure you have it clocked correctly.

 

[huskihl]

Just pay attention to the throttle blade chamfered edge. Hold it up to a strong light source to make sure you have it clocked correctly.

Yep. Sometimes they'll go in either way. Sometimes only one way. And snap the linkage a couple times to center the plates in the bore before you tighten them