Cross Pop-up Piston in MS390 topend

[94BULLITT]

I got an old rough looking 029. When I shook it I could hear stuff rattling in the muffler. It had low compression so I thought it had a busted piston. I did not care enough to pull the muffler since it needed a top end. The saw was missing the recoil assembly and spur sprocket.

I tore the saw down and found that muffler was broke and the saw had ingested pieces of the muffler. I rebuilt it with a Cross Performance cylinder and the Cross Performance pop-up piston from H L supply. The Cross cylinder looked really nice. I was concerned about the weight of the pop-up piston. I thought if it weighed more, the weight might offset the bump in compression. My pop-up weighed 10 grams less than the flat top piston that came with the cylinder!

After I got into the saw I realized that the crankcase was busted on it. It was usable but I had bought a parts saw or part of a saw when I bought my 039. Luckily I had a good crank case. It is a late model with flippy caps which I like.

Everything went together without a problem. It started right up. I left it stock, other than the pop-up. The sounded. It had better throttle response than my 039 and 290/390.

I made videos of the tear down and rebuild. Then I did some testing of the muffler mod and some other things. I have videos of all of that as well.

 

[94BULLITT]

 

[94BULLITT]

 

[94BULLITT]

 

[94BULLITT]

 

[94BULLITT]

I'm uploading the air filter video now.

 

[Clemsonfor]

Cool project.

I need to go back into my 390 and re seal it up at the 2 halves and then re mod the muffler, I didn't touch that area right in front of the exhaust port. I don't think k it's too loud as is and want to take that spot out.

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[Warped5]

Nice thread!

(I sure as hell never thought a 390 would ever get this much attention ... )

 

[Frank bierce]

Well done!! Great job documenting the steps!!

 

[David Young]

I just sold a very clean 390 on the bay. I always wanted to see if I could tune one into something. I think a little tweak to a 026 is light years ahead of the 290-390 class.
maybe with the compression bump. ignition muffler mod they come around . they just never seem snappy.
I think it is the carb. The walbro carbs supposedly have a mid jet that may affect the way they rev. I suggest trying to put the meter lever a little lower or finding a stiffer spring.

this one is stawk
must be someone had a large boat and needed this saw...

 

[Fruecrue]

I just sold a very clean 390 on the bay. I always wanted to see if I could tune one into something. I think a little tweak to a 026 is light years ahead of the 290-390 class.
maybe with the compression bump. ignition muffler mod they come around . they just never seem snappy.
I think it is the carb. The walbro carbs supposedly have a mid jet that may affect the way they rev. I suggest trying to put the meter lever a little lower or finding a stiffer spring.

this one is stawk
must be someone had a large boat and needed this saw...

They can be turnt up a bit.

 

[Clemsonfor]

Anyone ever seen the 390 that Adirondackstihl makes?? That thing is nasty

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[94BULLITT]

Cool project.

I need to go back into my 390 and re seal it up at the 2 halves and then re mod the muffler, I didn't touch that area right in front of the exhaust port. I don't think k it's too loud as is and want to take that spot out.

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Thanks, you should try one of these new pistons in it while you have it tore apart.

Nice thread!

(I sure as hell never thought a 390 would ever get this much attention ... )

Thanks, I kinda like these saw because they can be made into a good runner.

Well done!! Great job documenting the steps!!

Thanks!

I just sold a very clean 390 on the bay. I always wanted to see if I could tune one into something. I think a little tweak to a 026 is light years ahead of the 290-390 class.
maybe with the compression bump. ignition muffler mod they come around . they just never seem snappy.
I think it is the carb. The walbro carbs supposedly have a mid jet that may affect the way they rev. I suggest trying to put the meter lever a little lower or finding a stiffer spring.

this one is stawk
must be someone had a large boat and needed this saw...

I have addressed the carb issue.I only have time to edit one video a night. It is not boggy anymore.

 

[94BULLITT]

Air filter testing

 

[David Young]

They can be turnt up a bit.

great hair cut btw

 

[David Young]

Thanks, you should try one of these new pistons in it while you have it tore apart.



Thanks, I kinda like these saw because they can be made into a good runner.



Thanks!



I have addressed the carb issue.I only have time to edit one video a night. It is not boggy anymore.

looking forward to seeing what you found in the carb.

 

[Clemsonfor]

Good call I may just order one and shelf it for when I go back into it!

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[Frank bierce]

Have generally steered away from these...but after seeing some of these threads...I’m gonna have to give one a go!!

 

[Terry Syd]

Looks like the nylon mesh filter can substitute for a custom handmade filter (I like mine better because it does FILTER). So how much did that 'high performance' air filter cost?

Look at the difference in performance between the filters - how much work would it take to get that much difference by 'porting'?

Crikey, by the time we finish messing with these POSs we may have a cheap and easy formula to make a respectable saw.

Well done on the mesh filter!

 

[94BULLITT]

Carb testing

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