394xp compression question

[Trent Curtis]

Been a long time arboristsite fan- always googles and searched threads for info

I currently run an MS 460 and a 372xp.... Just found a 394xp-

Before I did anything I tore it down and cleaned it.

Here are my questions:

Cylinder and piston look good, compression test came out to 155psi. This seems low. I can pull the saw no problem even without using the decompression valve. I'm thinking I might need to slap on a new set of rings.... Thoughts?

Secondly..... I set the tune to 2500 rpm at idle, and 10,700 at wot.
I run 11,500 on my 372, but I'm Leary of heating up these big saws.
Running a 36" bar, What is a good tune for this saw? Is 11,500 ok on these big jugs? Or is it better to keep them a little fat?

Thanks in advance! Hopefully this video will load ok...... This is after the tune up.

 

[HuskStihl]

155 is fine. Mine is ported, and was 13,800. The bottom end is stout, and can easily take more RPM's. Just tune it to 4 stroke as soon as you ease out of the cut, and it'll pull that 36" no problem. 11,500 is really low on a 372 BTW

 

[Trent Curtis]

Thank you for the reply! Ok I'll give her some more air then- 13,800 and your still 4 stoking? I have never pushed the envelope when tuning... And I know that specs say 12,500 max.

I haven't put the saw to work yet, I wanted to see what kind of RPMs it holds through the cut (I'm assuming 8800 is a good target while under load?).

 

[HuskStihl]

Here's mine with an 8pin. If you want to tune it with a tach, I'd set it to 12.5 and make sure it 4 strokes nicely.

 

[Trent Curtis]

Ok so I went to try to get some more oompffff out of the 394 and in stumped.

I'm getting 10,800 max rpm at WOT.

In an attempt to liven it up I started turning In my H jet.

I got it ALL THE WAY TURNED IN and it's still 10,800!?

Still 4 stroking hard (loaded up). But there's no more adjustment.
Pulled the plug and it's more black than brown/ rich.

Has anybody seen this? Carb rebuild, new jets, or new carb?

Thanks!

 

[blsnelling]

11,500 is WAY too low for even a stock 372. You're losing TONS of power and only carboning it up.

 

[Trent Curtis]

Brad-

372 has been tuned up, I appreciate the reply.

Any ideas on above problem w the 394?

 

[blsnelling]

Thank you for the reply! Ok I'll give her some more air then- 13,800 and your still 4 stoking? I have never pushed the envelope when tuning... And I know that specs say 12,500 max.

I haven't put the saw to work yet, I wanted to see what kind of RPMs it holds through the cut (I'm assuming 8800 is a good target while under load?).

13,800 would only apply to his ported saw. Forget any specific RPM under load. That's way too variable.

 

[blsnelling]

Brad-

372 has been tuned up, I appreciate the reply.

Any ideas on above problem w the 394?

You should definitely be able to lean it out farther. Are there limiter caps on a 394? I have little of any experience with them.

 

[Trent Curtis]

Nope it's an older saw. No EPA garbage.

 

[Trent Curtis]

Just springs behind the screws (between jet and carb body)

 

[decableguy2000]

Screen clogged in the carburetor. I have a 394 that had a bad coil and put an aftermarket on and wouldn't turn over 11k. I thought bad aftermarket spent some coin and got Oem same thing. Cleaned the carb and all was happy. Also make sure the spark arrestor is clean as well.

 

[blsnelling]

Screen clogged in the carburetor. I have a 394 that had a bad coil and put an aftermarket on and wouldn't turn over 11k. I thought bad aftermarket spent some coin and got Oem same thing. Cleaned the carb and all was happy. Also make sure the spark arrestor is clean as well.

This saw is getting too much fuel, not starving.

 

[Big_Wood]

I run stock 372's at 14k, a 372 4 strokes something fierce even at 13k. Must be pretty well unusable at 11.5. Your metering diaphragm is likely not hooked properly onto the metering lever. Or you metering lever height is set to high. Metering lever should be set level with the dish in the chamber. Not level with the gasket sealing surface of the carb body like many others.

 

[Trent Curtis]

I run stock 372's at 14k, a 372 4 strokes something fierce even at 13k. Must be pretty well unusable at 11.5. Your metering diaphragm is likely not hooked properly onto the metering lever. Or you metering lever height is set to high. Metering lever should be set level with the dish in the chamber. Not level with the gasket sealing surface of the carb body like many others.

Hmmmm.... Good info.

so the 372 is running perfectly- I didn't adjust it. I must have pulled a bad reading first time. Tested again and it's showing between 12,600-12,900. Still a slight four stroke, sounds good. Plug=nice chocolate color when killed at WOT in the cut.

Regarding the 394 Metering lever..... It's a good thought. But I still don't understand how a closed jet is allowing fuel through the carb? It's blubbering hard at WOT, as expected with a 10,500 tac reading.

I think I'll purchase a carb rebuild kit- including new H and L needles.

 

[Trent Curtis]

Does anyone know where I can purchase the carb jets for this saw? Really all I need is the H jet.
Can't seem to find online-

 

[HuskStihl]

Mine had a coil go bad, and it would run, but wouldn't rev, and was weak.

 

[Trent Curtis]

It revs just fine- just loaded up/rich.

I'm not at home..... Won't be for another week. Ordered a carb rebuild kit- looking for the jet screws. Under the assumption that the jet/screw itself could be washed or otherwise damaged.

Killing me to not be at home wrenching on that thing. A

 

[Trent Curtis]

If that fails I can buy an OEM carb replacement for 80 big ones.

 

[Trent Curtis]

Ok so I tore the carb apart and rebuilt it.... But couldn't find new h/l needles.
Made sure the metering lever was set flush to the bowl using a straight edge. Saw still not turning more than 10,800-11,100 rpm. even with high screw turned all the way in.

So- I'll be ordering a new carburetor tomorrow.

In the meantime I decided to tear the saw down. And check it out. Here is what I found...... I WELCOME any ideas or advice to make this thing perform better!

1. I was surprised to find that it already had a gasket delete done.... As it was only pulling 155 psi. But it had no liquid gasket either, which explains why there was all kinds of soot build up on the base of the cylinder/fins. What kind of liquid gasket do you guys recommend?

2. Top of the piston and a fair amount of carbon build up..... Hit it with some 120g sandpaper and finished w 600g.

3. Low end looks good..... Clean and tight.

4. Cylinder and piston look good..... Some very fine wear lines on exhaust side, but nothing I wouldn't expect on an old saw.

5. Rings..... Looked ok, no obvious flat spots. But I can see that the exhaust side of the rings are a little thinner than the rest of the ring.
- I'll be ordering a new set of rings to give it some extra oompffff.

I thank you in advance and look forward to any suggestions!