MCCULLOCH The official McCulloch thread

[Mac131]

This is a 7-10 but the principle of the De Stroking Port or DSP is the same.

With the muffler off you can see the working parts as well as the port from the DSP valve to the muffler where the compression is redirected when the valve is open.

View attachment 286755

With the tank off you can see the top of the valve.

View attachment 286756

And the valve removed.

View attachment 286757

You will need to make some careful measurements down the bore of the DSP valve in order to come up with a suitable plug. If I make it to the other shop today and remember, I will try to get some photos of a plus someone else made for a similar saw.

Mark

Ahhh this is starting to make sense now. Thanks for showing, I was still trying to wrap my brain around how it worked. Yeah I think the best option is to plug it.

 

[PogoInTheWoods]

I would love to have a SP125! that's awesome you are collecting all these parts. Post pictures when you get started on it. It would be fun to see.

Just go here instead. (I'm sure Dave won't mind the slight re-direct.)

https://opeforum.com/threads/mcculloch-super-pro-125c-build-thread.16112/

 

[heimannm]

Here is one example of the DSP valve and the modified socket head cap screw to block it. As long as the tapered end bottoms out in the valve seat the head of the screw does not necessarily have to abut the boss on the cylinder.



Of course you will have to tap the port to allow the screw to install.

Mark

 

[Mac131]

Finished the port work and assembly on the power mac 6. Hoping to have it running in a day or two. Final numbers appear to compare with stock macs. Polished the exhaust ports and did extensive transfer porting. Port timing is:

Exhaust - 103 deg ATDC
Blowdown - 121 deg ATDC
Intake - 61 deg BTDC
Squish - 39 thousandths

I will compare it to my stock power mac 6 to see how it does.

Jeff

 

[Maintenance Chief]

Finished the port work and assembly on the power mac 6. Hoping to have it running in a day or two. Final numbers appear to compare with stock macs. Polished the exhaust ports and did extensive transfer porting. Port timing is:

Exhaust - 103 deg ATDC
Blowdown - 121 deg ATDC
Intake - 61 deg BTDC
Squish - 39 thousandths

I will compare it to my stock power mac 6 to see how it does.

Jeff

Id really like to see a comparison video.

 

[Al Smith]

The good thing is if the DSP valve gets inoperative on the 70 cc saws,6-10 ,7-10 they don't pull over that hard only being 70 cc's .Now it might be another story on a 125 ,they won't pull over easy .On the 82's,850 etc they would be tad hard to pull over but they are a different style than the poppit style used on the 7-10 .I managed to flood an sp-81 and attempted a drop start except the DSP closed early and knocked me off of my balance and down I went and just barely missed falling on the chain .Had it started I could have cut my arm off .BTW that was and will be the last time ever do that again .

 

[Mac131]

The good thing is if the DSP valve gets inoperative on the 70 cc saws,6-10 ,7-10 they don't pull over that hard only being 70 cc's .Now it might be another story on a 125 ,they won't pull over easy .On the 82's,850 etc they would be tad hard to pull over but they are a different style than the poppit style used on the 7-10 .I managed to flood an sp-81 and attempted a drop start except the DSP closed early and knocked me off of my balance and down I went and just barely missed falling on the chain .Had it started I could have cut my arm off .BTW that was and will be the last time ever do that again .

Good grief! Yeah I bet that freaked you out a bit...

 

[Al Smith]

Yes it did .Then I hear these tough guys dropping say an 084 or Husky 2100 ,3120 and think they are out of their minds .

 

[PogoInTheWoods]

Polished the exhaust ports and did extensive transfer porting.

I just hope the tank doesn't leak!

 

[heimannm]

This week, I'll only show the "after" photos.









Mark

 

[heimannm]

Mark

 

[Mac131]

So one with dsp and one with the later decomp valve? Interesting....

 

[heimannm]

There is also a model with the pop up compression release and no throttle release. This particular saw is one of my favorites to run.



Mark

 

[northwest saws]

View attachment 286963

View attachment 286964

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View attachment 286966

Mark

That is slick looking 7-10 you have Mark. Can't wait to get one of my own.

Sent from my SM-N970U using Tapatalk

 

[heimannm]

Not just anyone can make a Super 797 with a 36" bar look small.



Mark

 

[Bigmac]

This got drop off on the porch this morning

 

[jacob j.]

This got drop off on the porch this morning View attachment 287216View attachment 287218

Someone must have known that it's tree-trimming season for you?

 

[Bigmac]

Someone must have known that it's tree-trimming season for you?

Guy said he had an old Mac he didn’t want, so he said he would drop it off, didn’t know what it was, kind figured it would be this or a macsinder block

 

[Maintenance Chief]

This got drop off on the porch this morning View attachment 287216View attachment 287218

I figured it was swaddled in an old afghan with a note.

 

[heimannm]

The 300 Series saws are not bad performance wise, but the ergonomics on the top handle version is not great. The rear handle models (330, 340) are about as ugly as a chainsaw every could be, but they are quite comfortable to operate. Best wishes to you if you have to work on the carburetor side, there is quite a lot going on there with the carburetor & boot, impulse line, fuel line, and throttle cable all arriving in the compact little air box.

Mark