066 RPM's creep up at WOT, ? about fuel filter

[komatsuvarna]

No doubt the higher compression runs hotter. Though why that would make the revs creep up is beyond me. Maybe it is detonating ? I don't hear any funny noises, but then I'm not sure that one would be able to hear detonation on a chainsaw.

Could be maybe, I dont think you could hear detonation either, but you might could. Detonation will make the cylinder pressure alot higher(temporarly), but I dont know if it would make it the rpms creep up or not..... If it is detonating, looks like you could tell by looking at the piston crown and the spark plug as many times as its done it.....just thinking out loud here lol.

 

[mtngun]

I'm not seeing anything unusual on the head, piston crown, or spark plug.

 

[komatsuvarna]

Im still thinking its making more heat than it can disapate. The hotter the combustion temperatures get, the leaner it goes. Just a guess though, probably wrong.

 

[albert]

Detonation usually reduces rpms. A regular cylinder set up is your best choice in this case.

 

[tdi-rick]

Possibly worth checking the height of the needle arm and the condition of the diaphragm, it is possible there isn't enough fuel in the metering section of the carb on a long run of WOT. It may be worth increasing the height a little to get more fuel in to this part of the carb and retune the carb.

I remember 'relieving' the metering chamber on HL Tillo's when I was a whipper snapper to give a greater fuel reserve when racing 100cc karts.

Might be worth considering chopping a few winds off the metering lever spring too.

The old rule of thumb when racing was that if the engine didn't chop off clean when lifting the throttle at the end of a straight, (all else being equal) the pop off pressure was too high, and Terrysyd's checked a few saw carbs now and their pop off has been very, very high compared to what I was used to.

 

[tdi-rick]

This thread is great for getting the grey matter going, but I bet you wish you didn't have to post about it

Mate, which main jet are you using ?

Remember John/Tzed250's thread on swapping the main if you need more than 1 turn out on the HS screw ?

Re detonation, if you had a cylinder head temp gauge and an EGT gauge you'd actually see a drop in EGT's but a rise in CHT's.
Heading towards a lean seize scenario you see a distinct rise in CHT.

Karters all use CHT thermometers these days, but I don't think they are cheap.

Just a thought, have you tried going down a heat range or two with the plug ?
Might be worth a shot, particularly with a separate head that may not have the fin area of the original and very long cut times.
Maybe try backing the timing off a bee's #### ?

 

[angelo c]

Mtngun,

As the RPM's are creeping up can you check the compressions and see if there is/are variations. I can't think of any ways to check for leaks while the engine is hot and it seems as though the "leak" or weakness is showing up with heat and therefor expansion cycle of something...

we used to clean cylinders off real good and spray talcum powder around to id some leaks in aircraft. any chance of a bad case gasket that is showing up during a "heat cycle" .

hoping you find this one so we can all rest....

 

[mtngun]

Mate, which main jet are you using ?

Don't remember the number off the top of my head but believe it is the smaller one.

Remember John/Tzed250's thread on swapping the main if you need more than 1 turn out on the HS screw ?

That thought crossed my mind. After the needle gets so far out of the orifice, adjustment becomes too sensitive.

Just a thought, have you tried going down a heat range or two with the plug ?

Would have to order, so that's prolly not going to happen.

Maybe try backing the timing off a bee's #### ?

Could be, but I've never messed with timing on a saw and and think that would just add another variable to an already confusing situation. Bearing in mind that it's a challenge to make a single cut without frying the top end.

The old rule of thumb when racing was that if the engine didn't chop off clean when lifting the throttle at the end of a straight, (all else being equal) the pop off pressure was too high, and Terrysyd's checked a few saw carbs now and their pop off has been very, very high compared to what I was used to.

There doesn't seem to be any agreement on the best way to set that up.

This saga began with very weak pop-off pressure that was prone to flooding. The RPM creep was present then -- has been present since I installed the 2-piece top end earlier this year.

Since then, I stretched the spring a bit. That solved the flooding problem. No change in RPM creep.

Currently it pops around 18 psi and re-seats around 10 - 12 psi. Walbro claims the re-seat is the critical one and that is their spec. Not that I claim to know a lot about that, other than I definitely run into flooding in hot weather if it's much less than 10 psi.

In any event, I am putting the 2-piece aside since that was the constant since the RPM creep began. Dunno why the 2-piece would cause unstable WOT but......

It's now wearing an NWP BB. If it works out, I'll post more details on the BB later, but first I gotta fix the ghost problem.

If the conventional top end doesn't fix it, then I'm sure running out of ideas. Things left to try:

-- bigger main, which should improve H screw sensitivity

-- different coil. Dunno why coil would cause RPM creep, but heck, other than the cases and the top end, all the other parts have been changed at least once.

Yes, this is a bad time to have a saw down because my other 2 milling saws are down, too, and I don't even have time to work on them. A guy just can't have enough saws. :biggrin:

 

[mtngun]

Another discouraging update on the ghost problem(s). Now it has a NWP BB top end.

I wasn't able to get a good seal at the base. Generous permatex #2 on both sides of gaskets, but still tiny leaks, this time at several spots on at least 3 sides. Vacuum leak 7 - 8 inHg per hour. That's within spec, but disappointing.

Dunno what to do about the base leaks other than to keep trying different sealants.

Original WJ69, except I bent the lever up a hair. Didn't retest pop-off.

Idle wouldn't tune well. Seemed like idle speed screw had to be maxed out and L screw leaner than normal -- about 3/4 turn out. In fact, I could turn the L screw all the way in and it would still run. That doesn't seem right.

Remember, I experienced a similar idle problem with the new-to-me carb a few days ago. I assumed it was that particular carb, but now it's happened with both carbs.

Tuned to 11,500. Made a 12' cut, at end of cut it would spin 13,000 - 13,200. However, after retuning the H it seemed to hold steady while not in wood. Since this was a virgin piston and rings, I'm not sure if the WOT creep was the ghost problem or just normal breaking in.

But by then the idle had deteriorated even more, had a hard time getting it to idle at all, even with idle speed maxed out.

Something is definitely not right.

I will leak test again for the zillionth time, to see if a new leak erupted, but otherwise, I'm out of ideas and will go work on another saw for a while until I regain my sanity. :bang:

Other random, crazy ideas:

-- something wrong with coil or wire. Doesn't act like coil or wire, but that's the only part that hasn't been swapped.

-- something wrong with BOTH carbs that I'm not seeing. Idle circuit plugged ?

-- the itsy bitsy base leaks, though I wouldn't think they'd cause problems.

What else is there ? Yes, plug was swapped somewhere along the way.

 

[komatsuvarna]

Well darn!

7 to 8 inches in an hour is not very much. I wouldnt think that would make it creep up at 12 thousand revolutions per second.

I just dont know gun, I hope you get it straightened out though.

 

[Mastermind]

Are you using a metal base gasket this go around?

What would squish be at without a gasket?

 

[blsnelling]

I would definately be trying a different, known good carb!

 

[mtngun]

Randy, in order to get my squish, I had to combine a metal gasket with a manila folder gasket. Both had a thin film of permatex #2.

Without a gasket, squish would be near zero.

Brad, short of buying a new carb, I don't know what else I can do there. Hard to believe 2 carbs would have identical problems. But ..... this is a weird situation.

 

[Mastermind]

Randy, in order to get my squish, I had to combine a metal gasket with a manila folder gasket. Both had a thin film of permatex #2.

Without a gasket, squish would be near zero.

Brad, short of buying a new carb, I don't know what else I can do there. Hard to believe 2 carbs would have identical problems. But ..... this is a weird situation.

I'm sure I've missed something here. Is the BB top end in stock form?

I've been using threebond and have had zero issues so far. I've not tried permatex #2. It seems like by stacking gaskets you're asking for trouble. Is there any way to machine the piston to eliminate the gaskets?

 

[mtngun]

Is the BB top end in stock form?

Ported. Widened ports, transfers raised to 26 blowdown, intake & exhaust timing stock.

I've been using threebond and have had zero issues so far.

I used hondabond (same as threebond) for a while and switched to permatex because of leaks with hondabond. They are both very tenacious sealants, have not had this problem on other saws, so I'm puzzled by the leaks.

It seems like by stacking gaskets you're asking for trouble.

Maybe, maybe not. I also experienced leaks when using a single metal gasket on the previous top end.

Is there any way to machine the piston to eliminate the gaskets?

Very narrow top land on piston, and "black ring of death" at top of jug, so a pop-up is not a good idea here. Though maybe it would be possible to take a few thou off. Would only require 5 - 7 thou to eliminate 2nd gasket. Will look at it closely if top comes off again.

Getting back to the idle problem. It was idling slow, had to max out the idle speed screw. It was probably drawing from the main jet, explaining why L screw made little difference.

Why the slow idle ? I don't think the tiny base gasket leaks are a significant problem, but even if they were, they'd cause a fast idle, not a slow idle.

-- idle circuit plugged ? On BOTH carbs ? After several ultrasonic baths, etc.. ?

-- ignition timing off. Will try to verify timing with a degree wheel, otherwise I'm at a dead end on this saw and need to go do something else for a while to regain my sanity.

 

[Mastermind]

Ported. Widened ports, transfers raised to 26 blowdown, intake & exhaust timing stock.

I used hondabond (same as threebond) for a while and switched to permatex because of leaks with hondabond. They are both very tenacious sealants, have not had this problem on other saws, so I'm puzzled by the leaks.

Maybe, maybe not. I also experienced leaks when using a single metal gasket on the previous top end.

Very narrow top land on piston, and "black ring of death" at top of jug, so a pop-up is not a good idea here. Though maybe it would be possible to take a few thou off. Would only require 5 - 7 thou to eliminate 2nd gasket. Will look at it closely if top comes off again.

Getting back to the idle problem. It was idling slow, had to max out the idle speed screw. It was probably drawing from the main jet, explaining why L screw made little difference.

Why the slow idle ? I don't think the tiny base gasket leaks are a significant problem, but even if they were, they'd cause a fast idle, not a slow idle.

-- idle circuit plugged ? On BOTH carbs ? After several ultrasonic baths, etc.. ?

-- ignition timing off. Will try to verify timing with a degree wheel, otherwise I'm at a dead end on this saw and need to go do something else for a while to regain my sanity.

Yeah you are right about a leak causing a faster idle, so????

I'm with you on the carbs, no way both could have a plugged up idle circuit. Both could have issues though.

I doubt the timing is off unless a key has been sheared.

I'll have to agree with Brad this time, a known good carb would be a blessing at this point.

As for your sanity. You are most likely in short supply after all this so yeah a break is definitely in order.

 

[albert]

IIRC permatex 2 is non-hardening, and not for fuel, #1 hardens and is fuel compatible. I would try dirko or yamabond ect.

 

[mtngun]

IIRC permatex 2 is non-hardening, and not for fuel, #1 hardens and is fuel compatible. I would try dirko or yamabond ect.

Hondabond, 3 bond, dirko, and yamabond are the same product, or close.

Permatex #2 is called non-hardening, but it does cure and become very stiff -- tough to scrape off.

Permatex  Form-A-Gasket  No. 2 Sealant once applied,
develops a hard, semi-flexible sealant by solvent evaporation.

Chemical / Solvent Resistance
The product retains effective properties in contact with water,
ethylene glycol, gasoline, motor oil, transmission fluid and sea
water.

Be that as it may, it wasn't doing the job on this saw. It's possible that I should have let it dry longer before testing. It does take a long time to dry.

 

[albert]

I just remembered, when I was a kid, a guy mixed permatex#2 with alcohol to make a thin paste to seal a oil tank. Maybe the methonol in gas is affecting the #2.

 

[72thing]

mtngun, did you ever find out anything else with the RPM creeping?

Will