394XP low on max rpm after port work

[Timbco84]

I just finished porting a 394 and now at full throttle with the high speed needle all the way in, the best i can get is 11,000 rpm. At 1 1/4 turns out it is pig rich and like 7,ooo. Low speed needle and idle screw adjusted with tach and in spec. I thought I found the problem when I pulled the carb and the metering lever was way high, but set it with the walbro guage to spec and same problem. Was a good known running saw before port work and original owner saw.

Walbro Kit in the carb
New fuel filter
New air filter
New spark plug
Passes vac/pressure tests

I didn't widen the ports at all
I didn't raise the intake roof at all
I didn't lower the exhaust floor at all
I port matched the exhaust-muffler and added a port to the muffler
I cut the jug in my lathe and took the squish down to .024
I advanced the timing 1/4 of the key
I set it at 20 degrees blowdown
I increased the intake duration 8 degrees (156 Total)
Took exhaust back to stock height after lowering the jug
Compression is up 20 psi after lowering the jug and is good
Throttle is reaching full throw and cable is not stretched

I can't imagine that the extra 8 degrees of duration on the intake would cause this problem... but I am still learning porting, and this is the first saw I have adjusted the port timing on.

Please help, if the added intake duration is not of concern, I think I need to consider trying a new carb next.

 

[Adirondackstihl]

Leaking Welch plug?

 

[huskihl]

Throttle cable is stretched out or not mated with the trigger. Take the cover off and see if the throttle is opening all the way

 

[Moparmyway]

If the throttle is opening 100% ......... mayhaps you retarded the timing instead of advancing it ?

 

[drf256]

Pressure check the carb. I'm not familiar with the saw or the carb. I did have a similar problem myself on a Zama that had both a fixed and an adjustable H side circuit in the carb. Apparently many do.

Confirm you did advance and not retard. Also confirm the key didn't shear on the flywheel.

Confirm WOT operation.

Try a run without an air filter.

I can't see your mods causing any issues themselves. Looks like you executed your plan well and exercised proper restraint.

Interested in knowing what the solution was.

 

[srcarr52]

If it's still rich with the high side needle closed off the fuel inlet needle isn't seating correctly or it has too little spring pressure.

 

[Adirondackstihl]

POP was my next suggestion

 

[Termitebuffet]

How was it before the port work ....rpm wise ?

 

[paragonbuilder]

How was it before the port work ....rpm wise ?

This^^^^^

 

[Timbco84]

If the throttle is opening 100% ......... mayhaps you retarded the timing instead of advancing it ?

I just checked that, timing is advanced and the key hasn't sheered.

 

[Timbco84]

Pressure check the carb. I'm not familiar with the saw or the carb. I did have a similar problem myself on a Zama that had both a fixed and an adjustable H side circuit in the carb. Apparently many do.

Confirm you did advance and not retard. Also confirm the key didn't shear on the flywheel.

Confirm WOT operation.

Try a run without an air filter.

I can't see your mods causing any issues themselves. Looks like you executed your plan well and exercised proper restraint.

Interested in knowing what the solution was.

Tried running without the air filter, same symptoms, confirmed WOT operation, confirmed advance...thanks for the many suggestions. Will pressure test carb tonight.

 

[Timbco84]

How was it before the port work ....rpm wise ?

This^^^^^

Here in lies the problem, my uncle bought this saw new in '99, he is a logger and uses it for falling oversize, has always been a known good running saw, I didn't run the saw or check rpm before taking it down for port work. I seem to be a full time student at the college of learning things the hard way. Not going to make that mistake again.

 

[Timbco84]

I just pressure checked the carb and it passed just fine, took the high/low needles out and cleaned the orifices and examined. Can't see any debris in the holes or cracks, needles are straight and tips look nice (no gouges etc). Re-installed, re tuned, backed the high side out to make sure I wasn't just way lean before and the saw just went way rich...blubbered smoked dropped to 6000 rpm. Screwed the High side all the way in and back to 11,000 with heavy 4 stroking. I tried leaning out the low side and re adjusted the idle and that just causes it to have a lean bog when you floor it from idle. I can't get how it is getting so much fuel from the high side? The fixed High speed jet doesn't look like it has been bored out. I am stumped.

 

[Adirondackstihl]

Case sucking bar oil?

 

[Outback]

How many turns out is your low. Your not compensating for a minor air leak are you?

 

[drf256]

Sounds like you need to just try a replacement carb and see what happens. Maybe someone here can help you out with one.

Again, not that familiar with the model. Even though the carb pressure tested OK, it's somehow getting excessive fuel into the carb bore. Not sure if this model ever came with a governed carb.

Are you sure the kit was correct for the carb? I've seen discrepancies in the metering button/lever/needle before.

Did you install the metering side gasket to carb, then metering diaphragm, then metering plate?

 

[MattG]

I experienced similar behaviour with a 200T.

I'd adjusted the L side with the tach and got a nice juicy response and idle.

But the L side was so rich that the H side couldn't lean the mixture enough. So I reset the L to the manual spec....and then I could get better control (i.e. it would go full rich then full lean) with the H.

Perhaps try that..... and if it works, carefully set up the L side, without making this too rich.

 

[Mastermind]

You.need a new carb.

 

[Termitebuffet]

I'd try a known good ,or new carb ...help narrow down what's up

 

[Termitebuffet]

Case sucking bar oil?

Good thought Jer [emoji106]