HELP! Need help with a Holzfforma G366

[mrhack]

Don't know where to post it, so dropping it here.
Hello, first time poster.
I recently got the clone saw. Mechanically inclined and willing to work on it, so it wouldn't bother me if it had problems.
I've been chasing a bottom end air leak for a few months and it's been driving me crazy. Saw picks up idle rpm with tilted clutch-down, a throttle blip brings it back down for a second or two then it picks up again. Changed both seals carefully and to spec depth, with oil on both the crankshaft and the seal, clean of debris. Idled fine for a few minutes, called it a day. Next day I started it up again, air leak's back. Pulled the clutch side seal out, bone dry. No oil's getting to it and there was a fine dust around the inner bearing race. The bearing itself had plenty of oil, as well as the whole bottom and top ends. Carb's set ever so slightly rich on both jets. Four strokes nicely at WOT, cleans up in the cut. Saw has a lean bog at certain rpm ranges and can even die if I wiggle the throttle in them. Also, lacking high rpm range torque. Muffler's gutted, didn't like how it ran. Changed it to an Ironhorse style pipe. Made the fuel/air mix richer, adjusted accordingly and it had the same problem. Can't max rev as high with the pipe, compared to the can. Reinstalled the can and tuned accordingly. Air horn is opened, lower transfers are opened up, exhaust port is widened, secondary uppers are raised ever so slightly, intake floor is flattened without changing the duration, lower piston ring is out, to allow for the wider exhaust. Running with base gasket and 0,6mm/23 thou of squish. No changes to timing, spark plug gap's 0,45mm/18 thou. Could the cylinder have an intake port that's too high, resulting in a lot of case vacuum being pulled on it, resulting in the seals letting air through? It's the only explanation I could come up so far. On a phone call with a Stihl tech the guy said the bearing could be too fat, which would rub the seals lip off and make it fail. Could also be that, considering all the fines I found. Any and all help/suggestions/ideas would be appreciated.

 

[hacskaroly]

Welcome to the forum!! Not sure I can offer much in recommendations, but I know that chainsaws typically say to gap the spark plug at 20 thousands (0.5mm) but I typically increase mine to 25 thousands (0.635mm) and have better results. Sounds like your cylinder has had some modifications so that may change where the sweet spot will be for your spark plug gap.

Have you split the case yet? If not, I am guessing that will be the next step to do a through inspection of the case and bearings?

 

[mrhack]

Welcome to the forum!! Not sure I can offer much in recommendations, but I know that chainsaws typically say to gap the spark plug at 20 thousands (0.5mm) but I typically increase mine to 25 thousands (0.635mm) and have better results. Sounds like your cylinder has had some modifications so that may change where the sweet spot will be for your spark plug gap.

Have you split the case yet? If not, I am guessing that will be the next step to do a through inspection of the case and bearings?

Haven't split the case. Bearings look fine, no slop in them, but they may need to be replaced, if they have thicker than specified inner races.

 

[GMB74]

Let's get back to basics.
Have you done a vacuum/pressure test on the engine to determine if you really have a leak?
What about fuel starvation?
Have you checked the fuel filter and line for kinks, leaks, sucking flat, partially plugged filter, filter not sitting on the bottom of the tank, etc.?
Gas tank vents have been known to be a little funky on this model clone saw.

 

[mrhack]

No means to do a vacuum/pressure test on the engine, that is going to be the next purchase. Fuel filter's changed with OEM, lines are soft and pliable, no kinks, squishes or leaks, filter's always resting at the lowest point, fully submerged in gas. It uses up almost all the gas in the tank without an issue, but I will have a look-see over the vent. What pointed me towards crank seals is that when I replace them, the problem goes away for a short while and then pops back out.
Edit: on a second thought, it could be the fuel tank vent.

 

[DillonBuck]

Don't know where to post it, so dropping it here.
Hello, first time poster.
I recently got the clone saw. Mechanically inclined and willing to work on it, so it wouldn't bother me if it had problems.
I've been chasing a bottom end air leak for a few months and it's been driving me crazy. Saw picks up idle rpm with tilted clutch-down, a throttle blip brings it back down for a second or two then it picks up again. Changed both seals carefully and to spec depth, with oil on both the crankshaft and the seal, clean of debris. Idled fine for a few minutes, called it a day. Next day I started it up again, air leak's back. Pulled the clutch side seal out, bone dry. No oil's getting to it and there was a fine dust around the inner bearing race. The bearing itself had plenty of oil, as well as the whole bottom and top ends. Carb's set ever so slightly rich on both jets. Four strokes nicely at WOT, cleans up in the cut. Saw has a lean bog at certain rpm ranges and can even die if I wiggle the throttle in them. Also, lacking high rpm range torque. Muffler's gutted, didn't like how it ran. Changed it to an Ironhorse style pipe. Made the fuel/air mix richer, adjusted accordingly and it had the same problem. Can't max rev as high with the pipe, compared to the can. Reinstalled the can and tuned accordingly. Air horn is opened, lower transfers are opened up, exhaust port is widened, secondary uppers are raised ever so slightly, intake floor is flattened without changing the duration, lower piston ring is out, to allow for the wider exhaust. Running with base gasket and 0,6mm/23 thou of squish. No changes to timing, spark plug gap's 0,45mm/18 thou. Could the cylinder have an intake port that's too high, resulting in a lot of case vacuum being pulled on it, resulting in the seals letting air through? It's the only explanation I could come up so far. On a phone call with a Stihl tech the guy said the bearing could be too fat, which would rub the seals lip off and make it fail. Could also be that, considering all the fines I found. Any and all help/suggestions/ideas would be appreciated.

My first thought on a phantom air leak is the retarded impulse system. Everything I’d depending on that hole in the boot lining up and sealing. I swap the pitiful little carb for a 460 carb. Swap the throttle rods, swap and modify your throttle rod to fit the 460 carb.
Then either tweak the 460 impulse tube to be clear of the throttle rod, or make a new throttle rod. Now you unhook the impulse line from the mounting plate, and plug it into the carb.

This is well worth trying. With your mods the stock carb can’t supply the air your motor can pull. It just might fix your problem and find you the missing top end.

 

[mrhack]

Today I checked the gas tank breather. It had pulled a hard vacuum inside. Drilled a tiny hole in the outer vent cover and that sorted it out. Started the saw, it got pig rich, so the vent was definitely problematic. It still picks up idle rpm when tilted, but now it does it to the flywheel side, too. Could the carb be responsible in any way? If I fatten the low jet, when the saw is tilted, so as to bring the rpm down and then I set it back up, it bogs down as if tuned rich. I still think the seals leak under vacuum. Any ideas?

 

[EFSM]

To find air leaks, you can use some kind of flammable cleaner or ether with a straw to check for leaks by spraying it on the suspected components. When the engine dies you’ve found the problem.

 

[mrhack]

Pulled the clutch off, started the saw, sprayed brake cleaner around the seal, absolutely no change in rpm. It's probably an issue with fuel lines/carb/intake boot. Thanks everyone for the input.

 

[Outback]

If it went pig rich when you got the tank to vent you tuned around a clogged vent. Fix the vent. Then fix the tune...

1.Turn the low jet in until you get the highest rpm possible. Then turn it out 1/8th of a turn. Turn out the idle screw until the chain stops moving.

2. Rev the saw. If it bogs when you rev it, add a little low speed fuel until it doesn't bog.

3.Set the high speed needle where you can just hear it 4 stroke.

...........

Sometimes you have to repeat the steps twice because you had so much idle air going in that the high and low circuits were both in play at the same time or the saw wasn't warm and you had to tune it to get it to run long enough to tune properly.

When you have it tuned right then check for air leaks. Fuel puddling from too much fuel will act a lot like a air leak causing weird bogging and rpm changes when you move the saw around.

This assumes that you don't have a crunchy diaphragm in your carb.