394XP low on max rpm after port work

[huskyboy]

Well I tried the brand spankin new Walbro carburetor out and it runs exactly the same.

Can someone tell me if it is a possibility that I gave the saw to much intake area/duration...I measured the saw stock @74* (148*duration), I lowered the jug to adjust squish and I took a little out of the floor of the intake and ended up @79*(158* duration). I originally measured 78* after port work, but think I got a bad measurement cuz of assembly oil film, rechecked and got 79*.

Is it possible that the intake is flat open to long and its drawing in too much air/fuel per rotation?

Is it possible for a coil to be weak and thus the week spark won't burn the mix well enough to get max RPM?

Is there any other reason why I can't get over the 11,000 rpm wall I am hitting?

I had one that coil was going out on and it caused hot restart issues, but revved past 11k no problem. Maybe the timing key sheared?

 

[CR888]

Ya coil, ignition system, flywheel are good guesses at this point. However does this saw have a spark arrestor screen in muffler outlet & is it clean???

 

[Timbco84]

Ya coil, ignition system, flywheel are good guesses at this point. However does this saw have a spark arrestor screen in muffler outlet & is it clean???

Has spark arrestor screens, I added a a 288 style deflector and screen so muffler is now dual port, both screens new/clean. Good idea for stuff to check under normal circumstances though, thank you

 

[Chainsaw Jim]

Did you give it a run with the timing back in its original location? I've seen several saws start to act like that when the timing goes too far.

 

[Moparmyway]

Did you give it a run with the timing back in its original location? I've seen several saws start to act like that when the timing goes too far.

I've seen it do this with retarded timing

 

[beaglebriar]

I've seen low RPM with a aftermarket coil on a 395. Was testing a coil out for Jamey and his aftermarket was about 2000 rpms lower than my oem with the same carb setting.

Just somewhere else to look haven't read the entire thread so this might be completely irrelevant.

 

[Timbco84]

Did you give it a run with the timing back in its original location? I've seen several saws start to act like that when the timing goes too far.

Well I finally got back to this project. I swapped the coil with a brand new oem one...no change. I then removed the new spark plug and tried the original plug...no change. I then pulled the flywheel and returned the saw to original timing...no change.

So I have a good known source of fuel with both the original carb and new carb. I know I have good airflow because of the port work, a new air filter and dual porting the muffler. I have good ignition with the original coil/plug and new oem coil/plug. I have known good compression that increased the expected amount after lowing the cylinder via cutting the base. The saw passes both vac and pressure tests without a hiccup.

At this point, all I can deduce is that maybe when I lowered the jug about .030" to get the squish where I wanted it, and shaved about .020" out of the floor of the intake to get intake opening/duration where I thought I wanted it... is that the intake has too much area/duration for the given setup and the saw is flat drawing too much air/fuel ratio in during each engine cycle. I never gave that too much thought before this whole problem arose, but from all the symptoms this saw exhibits, and from all the checks I've made and parts I've swapped I literally cannot for the life of me come up with any other possible cause.

Open to any ideas, I've tossed around clutching possible causing problems, just seems unlikely since when I screw the h speed adjuster all the way in it's still 4 stroking hard and no hint of even trying to lean out or 2 stroke wide open. Hitting a wall at 11,000 RPM still. Also double checked the tachometer is performing correctly.

 

[Chainsaw Jim]

I think it's time to put a degree wheel on it to see exactly where you're at.

 

[Moparmyway]

Can you video what’s happening to your saw so we can see ?

 

[beaglebriar]

What was your timing numbers? You want the intake around 80.

 

[mdavlee]

Intake will make it spool up slow once it gets close to 90. Other than that it shouldn't hold back the rpm unless it's widened past the skirt

 

[peter92]

Following this with interest

Peter

 

[Timbco84]

What was your timing numbers? You want the intake around 80.

Intake will make it spool up slow once it gets close to 90. Other than that it shouldn't hold back the rpm unless it's widened past the skirt

Intake was at 74 Degrees before the port work, it's now at 79 degrees. I didn't widen any of the ports. Exhaust is at 101, transfers at 121...20 degrees blowdown. I was all set to go epoxy the floor of the intake back in up to 74 degrees and try it until I read Mike's post, I'm still 2 new at this game to know the outcomes of screwing up the timing. Idea's/Help Please!

 

[Moparmyway]

Can you video what’s happening to your saw so we can see ?

I was all set to go epoxy the floor of the intake back in up to 74 degrees and try it until I read Mike's post, I'm still 2 new at this game to know the outcomes of screwing up the timing. Idea's/Help Please!

The idea is for you to video whats happening so we can help

Can you video what’s happening to your saw so we can see ?

 

[Chainsaw Jim]

My offer still stands if you want to bring it on by my shop.

 

[Moparmyway]

101 / 121 / 79 now, The timing numbers that you have now are fine


You took 0.030 off the base, correct ?
Are you running a gasket, did you cut the chamber, and what is squish now ?
This 11,000 RPM's is WOT no load, correct ?
And its still 4 stroking hard, correct ?
New carb and coil yields the same results, correct ?

 

[Redfin]

Did you verify pop off as Shaun suggested? May be the new carb has the same setting.

 

[srcarr52]

Well I finally got back to this project. I swapped the coil with a brand new oem one...no change. I then removed the new spark plug and tried the original plug...no change. I then pulled the flywheel and returned the saw to original timing...no change.

So I have a good known source of fuel with both the original carb and new carb. I know I have good airflow because of the port work, a new air filter and dual porting the muffler. I have good ignition with the original coil/plug and new oem coil/plug. I have known good compression that increased the expected amount after lowing the cylinder via cutting the base. The saw passes both vac and pressure tests without a hiccup.

At this point, all I can deduce is that maybe when I lowered the jug about .030" to get the squish where I wanted it, and shaved about .020" out of the floor of the intake to get intake opening/duration where I thought I wanted it... is that the intake has too much area/duration for the given setup and the saw is flat drawing too much air/fuel ratio in during each engine cycle. I never gave that too much thought before this whole problem arose, but from all the symptoms this saw exhibits, and from all the checks I've made and parts I've swapped I literally cannot for the life of me come up with any other possible cause.

Open to any ideas, I've tossed around clutching possible causing problems, just seems unlikely since when I screw the h speed adjuster all the way in it's still 4 stroking hard and no hint of even trying to lean out or 2 stroke wide open. Hitting a wall at 11,000 RPM still. Also double checked the tachometer is performing correctly.

You have the metering lever too high or you don't have enough pop off pressure from a weak or incorrect spring.

 

[Greenerpastures]

It would be easy to strengthen your metering spring,
stretch it or shim it somehow.
I would expect a new carb and a good old carb not
being able to lean out properly should indicate something.
Is the plug wet or getting there during your tests.
Is there any chance something is getting grounded,
a vibrating / loose kill wire.
Put in a tiny bit of fuel in the tank and run her, see if this helps
to lean her out before altering the metering valve spring.
Instead of running with muffler off, block one of the outlets and run
a little.

Just some thoughts.

 

[Chainsaw Jim]

How does it run without the air filter and cover in place? Maybe remove the ground wire when you try it.