wcorey
Pinnacle OPE Member
- Local time
- 7:21 AM
- User ID
- 29
- Joined
- Dec 11, 2015
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- 1,078
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- Location
- ma usa
I have a 394 that I did a fairly hot woods port on maybe 4 years ago, more or less a gtg toy, though it's not really too hot for a work saw.
Typical port widths/timing numbers, cut chamber and base, exhaust just has biggest hole possible under the stock deflector, stock wj39 and low top air filter, blows around 215 cold.
First year ran really well with no issues, mostly just gtg duty and the occasional large takedown, maybe ran a half dozen tanks through it.
The next gtg 'season', I noticed it was sometimes leaning out toward the end on extended cuts. Would run fine for a maybe a few long cuts then lean out again unpredictability, always a good way into the cut, very sneaky.
Could tune it out but then would suddenly run pig rich and I'd have to lean it back out to where it was originally.
Tried the usual obvious fixes with no success.
I have other big saws to use and always way too many waiting their turn on the bench, got frustrated and just shelved it till the next year.
Brought it to the next years gtg with the intent of figuring it out as I went, even though I had already checked misc everything probable including multiple passed press/vac tests, checked tank venting, int manifold integrity and changed out fuel line/filter. Swapped to still another known good carb, then did seals just to rule that out completely, no change, if anything was getting worse.
Tried still another carb, coil, ign timing..., stuff that shouldn't even matter but what hell at that point.
Shortly after that got used as a test mule for a bunch of 3-5 second dyno runs, software filter testing, initially they were short enough so it wouldn't go lean. (One interesting aside there is that the decomp was sticking open and it had no noticable effect on the peak hp #'s.)
The repeatability gave me a good idea of just how quickly and progressively worse it was getting.
Tried more fixes, likely many I'd done previously, don't even remember what.
After dozens of runs, it wouldn't even make the 3 seconds..., burble, burble... screeeeam...
Now totally consistent and repeatable. Could tune it so rich as to blow serious smoke on the spool up... for a second...
Shelved for yet another year.
Fast forward to present, gtg season right around the corner.
I miss the beast, just feel inadequate without it and an annoying reminder of my troubleshooting shortcomings, lol.
This time I'm fixing it come hell or high water, even if i have to swap every part but the p&c.
Have so much time into it by now, could have just built another one or three.
Pull it down, dust it off, still idles and tunes fine on the low side but can go out multiple turns on the H to no further effect and will burble for a second then runs away, over and over.
Have a good running stock saw that I've resisted canabalizing up to this point, decided to stop chasing my tail and just swap the cylinders on 'em.
Would have/should have done it sooner but in a way that was finally conceding to defeat. I hate that...
Guess what?
Problem now followed the cylinder.
Original modded problem saw now with stock muffler/cylinder runs fine.
Stock saw now with modded muff/cyl same old crazy rich>lean... Wtf...
Well..., I finally, finally figured it out, both saws now running great.
In retrospect of course it seems like something simple I should've figured out much sooner, actually a known issue pretty much specific to modded saws (hint hint).
Figured early on it's got to be an air leak or the fuel circuit/carb not delivering enough fuel... but...
What really messed with my reasoning was that it originally ran fine and the problem showed up later as a gradually deteriorating condition so I was focusing on finding something that could gradually go bad.
It wasn't, not directly anyway...
Any guesses on the what and why?
Typical port widths/timing numbers, cut chamber and base, exhaust just has biggest hole possible under the stock deflector, stock wj39 and low top air filter, blows around 215 cold.
First year ran really well with no issues, mostly just gtg duty and the occasional large takedown, maybe ran a half dozen tanks through it.
The next gtg 'season', I noticed it was sometimes leaning out toward the end on extended cuts. Would run fine for a maybe a few long cuts then lean out again unpredictability, always a good way into the cut, very sneaky.
Could tune it out but then would suddenly run pig rich and I'd have to lean it back out to where it was originally.
Tried the usual obvious fixes with no success.
I have other big saws to use and always way too many waiting their turn on the bench, got frustrated and just shelved it till the next year.
Brought it to the next years gtg with the intent of figuring it out as I went, even though I had already checked misc everything probable including multiple passed press/vac tests, checked tank venting, int manifold integrity and changed out fuel line/filter. Swapped to still another known good carb, then did seals just to rule that out completely, no change, if anything was getting worse.
Tried still another carb, coil, ign timing..., stuff that shouldn't even matter but what hell at that point.
Shortly after that got used as a test mule for a bunch of 3-5 second dyno runs, software filter testing, initially they were short enough so it wouldn't go lean. (One interesting aside there is that the decomp was sticking open and it had no noticable effect on the peak hp #'s.)
The repeatability gave me a good idea of just how quickly and progressively worse it was getting.
Tried more fixes, likely many I'd done previously, don't even remember what.
After dozens of runs, it wouldn't even make the 3 seconds..., burble, burble... screeeeam...
Now totally consistent and repeatable. Could tune it so rich as to blow serious smoke on the spool up... for a second...
Shelved for yet another year.
Fast forward to present, gtg season right around the corner.
I miss the beast, just feel inadequate without it and an annoying reminder of my troubleshooting shortcomings, lol.
This time I'm fixing it come hell or high water, even if i have to swap every part but the p&c.
Have so much time into it by now, could have just built another one or three.
Pull it down, dust it off, still idles and tunes fine on the low side but can go out multiple turns on the H to no further effect and will burble for a second then runs away, over and over.
Have a good running stock saw that I've resisted canabalizing up to this point, decided to stop chasing my tail and just swap the cylinders on 'em.
Would have/should have done it sooner but in a way that was finally conceding to defeat. I hate that...
Guess what?
Problem now followed the cylinder.
Original modded problem saw now with stock muffler/cylinder runs fine.
Stock saw now with modded muff/cyl same old crazy rich>lean... Wtf...
Well..., I finally, finally figured it out, both saws now running great.
In retrospect of course it seems like something simple I should've figured out much sooner, actually a known issue pretty much specific to modded saws (hint hint).
Figured early on it's got to be an air leak or the fuel circuit/carb not delivering enough fuel... but...
What really messed with my reasoning was that it originally ran fine and the problem showed up later as a gradually deteriorating condition so I was focusing on finding something that could gradually go bad.
It wasn't, not directly anyway...
Any guesses on the what and why?
