Sawmill engine problems

maple flats · October 22, 2018, 07:49:55 PM

I ran my Peterson several times during the last 10 days without an issue, until today. I have a 20 HP Honda on it and it ran perfectly until today. The last time I ran it 3 days ago I ran out of gas, and I went and bought 2.5 gal of premium gas, in the same gas can I had used the previous 2 refills during the previous week.
# days ago, I then added just about half of the gas, started the engine and finished sawing the log I had on the mill. It ran perfectly. Then today I put a new log on and added the rest of that can of gas to the tank. It started fine, but when I turned it to full RPM and began to saw the engine kept back firing. I just made one cut and shut it down.
What trouble shooting should I do? This Peterson and the Honda have never fail me in the last 14 years. Might it be spark plugs, plug wires, stuck valve, or a carb issue? Or something else? Your ideas please.

craazyhoss · October 22, 2018, 09:38:22 PM

Does the engine have any kickback on starting?

I had a honda 20 on a concrete saw do that and would about break your hand on the crank rope it had a cracked rocker arm on one of the valves.

barbender · October 22, 2018, 09:39:17 PM

It's hard saying, my buddy's 24hp Honda started acting up like that and something had gotten plugged up in the carb. I can't remember what. I'd check fuel flow to the carb first, then pull the carb and check for debris or gumming.

Southside · October 22, 2018, 09:41:30 PM

When you said it ran out of fuel my first though was that you sucked up some junk from the tank. Try a new filter and cleaning the carb bowl out, perhaps even some sea foam or other fuel cleaner additive to help clean up the system.

StimW · October 22, 2018, 11:21:25 PM

If it has a Honda fuel tank you probably have water in the tank.
The Honda tanks have a very fine screen in the bottom of the tank that will stop most water. If water gets above that screen it will shut off. Some water can get through from vibration.
I had a customer bring a machine in that "just quit". I found the tank half full of water. I ask him if anyone was asking to go home early? He said now that you mention it!
I have a HF blow gun with a pick up hose with a copper tube on end and I always sucked out the bottom 1" of gas into a clear container to check for water when doing a service.

maple flats · October 23, 2018, 08:29:08 AM

I'll check the tank, but it is not a Honda tank, Peterson makes the tank out of aluminum, it's a rectangle and it welded right to the frame. I can check that and will put a new filter on. If it persists I'll check the carb.
Thanks for the ideas thus far. All sounded good except I did not like reply about a cracked rocker arm. I sure hope it's not that. It does not kick back when I pull to start it, but most of the time I use the electric start. I only pull it to start it if I've run out of gas which has happened a few times over the years but not very often, or if the battery is low.

mike_belben · October 23, 2018, 09:20:44 AM

You ran out of gas, refilled and continued sawing. That is likely unrelated to this issue and just coincident in time frame.

Backfiring is usually valvetrain or ignition related. Since you didnt have engine apart it is less likely valve related than ignition. They do get weak.

Pull the plug, put on a alligator clip to ground jumper the strap and crank it.. See how strong the spark looks. If it looks weak or dim flare the gap open fairly wide and see if you can get a good hot blue spark. If not, the ignition module or plug or wire may be getting tired. The gap from coil to flywheel magnet may be rusty or misadjusted, the ground path may be getting corroded or the shutoff switch may be crusty inside and shorting the coil. (Pull the one wire off the coil's spade terminal and try again. It is the shutoff and the kill switch merely grounds it)

Remove coil, sand up the flywheel perimeter, the magnet and the pickup legs, sand or file the faces where the coil sits on the bosses and reset the air gap to MFR spec. You can ohm out a primary and secondary coil but i just toss em on and crank again. Never hurts to grab a known good plug from something else to verify spark intensity. Under high rpm and heavy load the pressure in the cylinder makes for a high resistance across the plug gap that a weak coil wont jump. If you are at the point of buying a coil just to try it or have a dead one.., put yours in the oven at 300F for 10 mins. It wont melt but it will get very hot and pretty often come back to life. Same with CDI boxes. This bakes out moisture and juuust starts to reflow crusty internal solder joints. Jolts the capacitors too so they start charging better/more/whatever.

If this engine uses a CDI box to fire the coil and a crank trigger to tell the cdi when, check then crank trigger for proper gap off the magnet and proper resistance to the mfr spec. Check all wiring for faults. I dont think this has a stator but if so you could have an issue there and a meter is how youd have to verify the coils.

If the ignition service doesnt give a bright spark, or if you have good spark already, then you either have a mixture ratio pretty lean (clog in the main jet, i dont think that has an adjustable main circuit) or the valves are out of adjustment. Pull the cover and roll it around with spark plug out to check valve lash with a feeler gauge and adjust as needed. I doubt its out of time but valve seats do wear in. I guess if that doesnt cure it its time for a compressiom test to consider a melted or pitted or chunked out valve seat.

Hands down ignitions give me more backfiring than any other component on a "ran then quit" condition if no prior fiddling was done from the last time it performed correctly.

Hilltop366 · October 23, 2018, 05:22:10 PM

If the carb has a drain on it I would drain it and try to catch the contents to see if there is anything in it.

I worked on motorcycles that would run fine at lower rpms but as soon as you accelerated above a certain rpm it would start to skip a sputter. It had just enough water in the carbs that when running hard it would start picking up a bit of the water.

Which reminds me of another bike that ran much the same way but it turned out to be the side stand safety switch, (the spring used in the switch was not strong enough) it would cut in at a higher rpm that produced a vibration in the switch and caused the engine to skip and sputter and then return normal at lower rpms, that was a bugger to find the first time around.

There is no side stand safety switch on you mill but there is probably a low oil switch, may be a fuel shutoff switch on the bottom of the carb and a ignition switch.

esteadle · October 23, 2018, 06:25:48 PM

Quote from: maple flats on October 22, 2018, 07:49:55 PMI then added just about half of the gas, started the engine and finished sawing the log I had on the mill. It ran perfectly. Then today I put a new log on and added the rest of that can of gas to the tank. It started fine, but when I turned it to full RPM and began to saw the engine kept back firing. I just made one cut and shut it down.

I think you have water mixed into this fuel. Where was the fuel can stored?
I'd drain the fuel tank into a transparent container and let it settle to see if there may be some water that settles out.

Gasoline is lighter than water, so water should sink to the bottom of the tank.
If the fuel line pulls from the bottom of the tank then you will get water in the fuel line sometime - now may be that first time.
But then again, when water is in the fuel, the engine runs rough or not at all, but doesn't really backfire.
Do you have a sediment bowl under the fuel tank for sawdust and water to sink into?
If not, you might want to add one to make it easier to avoid this problem in the future.

Best of luck...

maple flats · October 24, 2018, 09:06:24 AM

I'll check the gas, but it came fresh from the gas station and it is kept in a "no spill" gas can. Never got water in the gas before from this gas station but it certainly is possible, especially if I pumped the gas shortly after a delivery while it had not yet settled down.

mike_belben · October 24, 2018, 09:36:12 AM

It should be a half hour or less to get the center bolt off the bowl, drop it down and look whats accumulated.. then find the fuel pump if it has one, pull the cover and inspect the diaphragm and any relief valving inside it for straw or grass or wood fiber. Seen that a bunch. Lean under load will backfire so it is a high priority if the spark is hot and bright with large gap (indicating strong coil)

maple flats · October 25, 2018, 07:14:06 PM

It appears it was an easy fix. I just changed the spark plugs and it seems to be good. One old plug showed a black streak on the porcelain that the electrode comes out of. That plug may have caused the issue. A second thought is that as I finished the one cut I made the other day when it acted up the final back fire might have blown some carbon out off one of the exhaust valves. Either way, with no load on it I got no backfiring. If the weather is OK tomorrow I'll pull out another log and put it on the mill. Then I just need 3 more floorboards, so as I cut them I'll see if a load on it makes a difference.
Then after I fasten down those last floor boards, I can then cut some 2x's for a lean-to shed to be build next year, and also a blacksmith shop, just to finish off the log.

esteadle · October 25, 2018, 07:39:41 PM

I think you got it.

If that plug is bad, then you would be blowing uncombusted fuel out of that cylinder and into the exhaust manifold where it would mix with the hot gases from the working cylinder. that would of course combust in the exhaust system and cause the backfire, exactly as you described it. Boom!

And with that, your smithing plans shall be realized, and shall not be thwarted.
Good luck, my liege.

maple flats · October 26, 2018, 05:00:12 PM

I got another log pulled out, which was not very easy. It seems when I cut the trees in a hurry last year in order to have open space to drop two large trees with significant rot in them, I dropped them so the tree I had to extract was under a pile of whole tree mess, limbs and all. Once I got to where my excavator could extract it, I was almost done for the day. I then set it on the mill and went home.
Thus, I have not yet tested the engine under a full load. Tomorrow the forecast calls for heavy rain all day. maybe Sunday or Monday.

fishfighter · October 26, 2018, 06:05:57 PM

Quote from: StimW on October 22, 2018, 11:21:25 PM
If it has a Honda fuel tank you probably have water in the tank.
The Honda tanks have a very fine screen in the bottom of the tank that will stop most water. If water gets above that screen it will shut off. Some water can get through from vibration.
I had a customer bring a machine in that "just quit". I found the tank half full of water. I ask him if anyone was asking to go home early? He said now that you mention it!
I have a HF blow gun with a pick up hose with a copper tube on end and I always sucked out the bottom 1" of gas into a clear container to check for water when doing a service.

I use a piece of 1/2" PVC piping. Stick one end in, put your finger over the other and lift.

Stephen · October 29, 2018, 12:34:23 PM

"One old plug showed a black streak on the porcelain that the electrode comes out of."
Hope that fixes it.
If it happens again, you may need to replace the wire, or at least the boot, at the same time. The spark may jump to this carbon streak again, boot ruins new plug, old plug ruins new boot, etc.