Wierd carb problem on 394

[fourfivefour]

Finally got a chance today to swap the carbs, and yes, it was the carb?? Runs fine with the other carb. Anything to look for in the old carb? I did just rebuild it. I've taken it apart 3 times checking it over to make sure I didn't do it wrong. Everything is in the correct order. I haven't checked the needles yet though for damage.

Is it possible you have the pump on first then the gasket? The gasket goes against the carb and then the pump diaphragm. Did you compare the old needle to the new one?
Welsh plug leaking?
Broken mixture screw? Compare them to your good carb.
Review your carbs exploded view, you may be missing something.

 

[parrisw]

Is it possible you have the pump on first then the gasket? The gasket goes against the carb and then the pump diaphragm. Did you compare the old needle to the new one?
Welsh plug leaking?
Broken mixture screw? Compare them to your good carb.
Review your carbs exploded view, you may be missing something.

Ya, that's what I thought at first, I've checked and rechecked the order of things. Its all correct, something has got to be leaking, like a plug, needle & seat, mixture screw. I'll take it apart again, and have a look around.

 

[parrisw]

I know a stock saw when I hear and run it and this one is definitely not, a tear down will tell the story.
Pioneerguy600

Ya, I didn't mean yours wasn't gone through, I meant that just stock they run real well. I have a nice ported cylinder for a 394 on my shelf, but the sucker is toast, major lean run.

 

[Ghillie]

Ya, that's what I thought at first, I've checked and rechecked the order of things. Its all correct, something has got to be leaking, like a plug, needle & seat, mixture screw. I'll take it apart again, and have a look around.

Have you been able to rig up a pressure test on it?

 

[parrisw]

Have you been able to rig up a pressure test on it?

on the carb?? I blew into it with my mouth, and it seemed to hold, but who knows how accurate that is.

 

[Ghillie]

on the carb?? I blew into it with my mouth, and it seemed to hold, but who knows how accurate that is.

Put constant pressure on it and dunk it in water. Look for bubbles.

I'll try to find the exact psi if you want.

 

[parrisw]

Put constant pressure on it and dunk it in water. Look for bubbles.

I'll try to find the exact psi if you want.

sure, I'll check tomorrow, I'll pump it up.

 

[Ghillie]

Here is a page out of the manual.

50kPa = about 7 psi

I used a mity-vac pump on the pressure side to test my 372 carb. Tee in a pressure gauge to get the pressure right. I used a automotive fuel pressure gauge.

 

[parrisw]

Here is a page out of the manual.

50kPa = about 7 psi

I used a mity-vac pump on the pressure side to test my 372 carb. Tee in a pressure gauge to get the pressure right. I used a automotive fuel pressure gauge.

Thanks, ya, I got a whole rig setup for pressure testing. I'm just lazy.

 

[Ghillie]

I hear what your screamin'... LOL... Good luck.

 

[Brmorgan]

This sounds like exactly the same problem I had a month ago after porting my 181SE - no matter what I did with the H jet it was running way too rich. I narrowed it down to my carb having a governor circuit. There's a big ~1/4" brass screw plug on the right-hand side of the carb near the choke lever. I removed it, and following Brad Snelling's advice punched a 1/4" round piece out of an aluminum can. I put this at the bottom of the hole to cover the inlet to the carb's venturi, and replaced the brass screw. This effectively blocked the governor circuit so the saw could only pull gas thru the H jet. Runs like a bat out of hell now!

I don't know if a 394 could have a governed carb like my 181SE, as my 395XP doesn't, but the symptoms sound exactly the same. I had also tried everything else, replacing the diaphragm, gaskets, metering lever, valve, and eventually the entire carb which fixed the problem.

 

[parrisw]

This sounds like exactly the same problem I had a month ago after porting my 181SE - no matter what I did with the H jet it was running way too rich. I narrowed it down to my carb having a governor circuit. There's a big ~1/4" brass screw plug on the right-hand side of the carb near the choke lever. I removed it, and following Brad Snelling's advice punched a 1/4" round piece out of an aluminum can. I put this at the bottom of the hole to cover the inlet to the carb's venturi, and replaced the brass screw. This effectively blocked the governor circuit so the saw could only pull gas thru the H jet. Runs like a bat out of hell now!

I don't know if a 394 could have a governed carb like my 181SE, as my 395XP doesn't, but the symptoms sound exactly the same. I had also tried everything else, replacing the diaphragm, gaskets, metering lever, valve, and eventually the entire carb which fixed the problem.

I'll have a look, but don't think 394's have governor circuit's.

 

[parrisw]

Well I think I got it licked today. I took the carb apart and put it through the Ultrasonic cleaner for 30mins(don't know why I didn't do that the first time), put it back together and it runs great, tuned it to 12,800rpm, idled good at 2700. Time will tell when I get it into some wood though.

 

[JT78]

Where is some video I want to see that bad boy run.

 

[parrisw]

Ya, didn't make one. Here is one I did the other day with my other 394xp, after I ported it. Will that do?

<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/SVD4-7Xw1hI&hl=en&fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/SVD4-7Xw1hI&hl=en&fs=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>

 

[JT78]

I guess that will have to suffice for now I want to see how that ported 394 stacks up against my ported 395. Awesome sounding saw by the way.

 

[parrisw]

I guess that will have to suffice for now I want to see how that ported 394 stacks up against my ported 395. Awesome sounding saw by the way.

Ya, I saw your vid, it was pretty cool. Just bring it out here, and I'll find some wood to put them in. LOL.

I got a 395xp project that I got big plans for. I got a full circle 2101 piston that needs to get some lathe work, to make a popup piston, then a full port job. Should be a screamer.

 

[JT78]

That sounds awesome that saw should be flat nasty. Yeah that vid with the 42 inch bar kinda sucked because the rakers were set too deep.

 

[parrisw]

That sounds awesome that saw should be flat nasty. Yeah that vid with the 42 inch bar kinda sucked because the rakers were set too deep.

ya, but it still pulled that bar no prob by the looks of it.

 

[Ghillie]

Well I think I got it licked today. I took the carb apart and put it through the Ultrasonic cleaner for 30mins(don't know why I didn't do that the first time), put it back together and it runs great, tuned it to 12,800rpm, idled good at 2700. Time will tell when I get it into some wood though.

Awesome!! I've never used an ultrasonic cleaner. What info do you have on them?