JRed 670 Impulse quandry

[SuperII]

Ok, I am either going to learn something here of slap my forehead and say” I knew that”! 670 sn#7100252 black tag. Mahle PC. TILLOTSON HS230A 73 carb. Rubber boot intake. I have not been into a 670 before. My question is two fold. 1) Cylinder has an internal impulse port at base of cyl that continues all of the way and through the boot to carb. It also has an external pulse fitting and hose to the top of the carb. Do they run both on these saws? I have only seen one or the other. I must have missed something along the way. 2) Is the top of the piston supposed to be flat to the edge? This one is beveled at the edge about 3/16” toward the center. I ask because the bevel does not look exactly right. Go ahead, roll your eyes or just humor me. Thanks to all of the experts in advance.

 

[SuperII]

I forgot to mention that this saw has the two piece ignition.

 

[fossil]

Ok, I am either going to learn something here of slap my forehead and say” I knew that”! 670 sn#7100252 black tag. Mahle PC. TILLOTSON HS230A 73 carb. Rubber boot intake. I have not been into a 670 before. My question is two fold. 1) Cylinder has an internal impulse port at base of cyl that continues all of the way and through the boot to carb. It also has an external pulse fitting and hose to the top of the carb. Do they run both on these saws? I have only seen one or the other. I must have missed something along the way. 2) Is the top of the piston supposed to be flat to the edge? This one is beveled at the edge about 3/16” toward the center. I ask because the bevel does not look exactly right. Go ahead, roll your eyes or just humor me. Thanks to all of the experts in advance.

Run your impulse line from the barb on the cylinder to the fitting on the carb.

I would guess that the impulse passage that would be coming through the block ahead of the carb would be blocked on the carb.

Easy tell by taking the pump side cover off and running a wire through the passage.

 

[huskihl]

You have a Frankensaw. You have an early 670 cylinder with the pulse in the intake flange and someone retrofitted it with the later external pulse. Or someone drilled the intake flange and created a new internal pulse. Does your rubber boot have a pulse port in it? I’m not certain which way the 230 carburetor is but the later 250 carburetor requires an external pulse

 

[Cantdog]

Can't imagine why they would have used both or gone to the trouble to tap in an external line. But it would set you up to use the later boot without the impulse. The older internal type must be near impossible to find now. How does it run?

 

[SuperII]

It does have the pulse port built into the boot and the drilled port in the bottom cyl does not look to be an addition. I should add that when I tore it down that whoever had it apart last, used silicone to base gasket. Consequently t port was semi plugged and it almost appears that silicone was clear through the passage through the boot. I it all came out with minor probing and air. The saw ran good although i was suspecting an air leak and compression was getting a bit under 140, hence teardown. I was searching last night and ran across a post mentioning something about some of these early saws came with ported boots and were showing up at dealers with both types of pulse ports. It seems odd that the would produce a cyl with an external and internal port.

 

[SuperII]

The carb has the pulse nipple for pulse line,which is hooked up, and the carb does not have a blind hole for the internal pulse port. Somehow all of this stuff looks to be intentional from factory. The internal pulse hole in bottom of cyl sure looks factory. And the external ported cyl cannot be mistaken. Hmmm.

 

[SuperII]

Run your impulse line from the barb on the cylinder to the fitting on the carb.

I would guess that the impulse passage that would be coming through the block ahead of the carb would be blocked on the carb.

Easy tell by taking the pump side cover off and running a wire through the passage.

It has always had the pulse line hooked up. The impulse passage is moulded into the rubber boot and is open to the cylinder, although it had some silicone in it which leads me to believe that there was some attempt to block this internal passage. I just don’t understand why both systems are there. Might never know. Just not sure how to proceed.

 

[SuperII]

Do any of you guys know the born on date from this saw, I don’t know the magic calculations.

 

[SuperII]

Her you go.

 

[SuperII]

Carb.

 

[82f100swb]

I have an early boot impulse 670 jug that came to me with the pulse nipple added at an odd angle, and a non impulse boot. I suspect there may have been an update kit at one point. I will have to poke through the service bulletins one of these days.

 

[SuperII]

I have an early boot impulse 670 jug that came to me with the pulse nipple added at an odd angle, and a non impulse boot. I suspect there may have been an update kit at one point. I will have to poke through the service bulletins one of these days.

Thanks. And to be clear, I am not necessarily trying to solve the riddle, although it would be interesting, I am merely trying to find a path forward. Thank you all for the help.

 

[SuperII]

And here is the top of the piston in question, thoughts?

 

[Woodwackr]

And here is the top of the piston in question, thoughts?

Well, that ain’t factory

 

[SuperII]

Well, that ain’t factory

Ya think? That one will be on the wall of shame. Why would someone do that. Did someone just think that up, or is there some reason in a land far away to do this?

 

[huskihl]

Ya think? That one will be on the wall of shame. Why would someone do that. Did someone just think that up, or is there some reason in a land far away to do this?

Is it a pop-up or a dome? I noticed earlier but couldn’t really tell for certain what was going on.

 

[Cantdog]

Somebody was full of bright ideas!!! Did the cyl base gasket look stock? They are fairly thick. Like in the 0.030" range compressed. I've never seen a piston or cyl like that. As Bob (Spike60) would say....."You've got a puzzler right there!"

 

[SuperII]

Is it a pop-up or a dome? I noticed earlier but couldn’t really tell for certain what was going on.

It doesn’t look like any pop up i have ever seen. It looks homemade.

 

[Cantdog]

Ya think? That one will be on the wall of shame. Why would someone do that. Did someone just think that up, or is there some reason in a land far away to do this?

The only thing I can think of and this is just a thought, can you tell if the cyl base has been cut down? They may have cut it to far and did not have the ability to cut the squish band so trimed the piston top instead.