OT- Small engine problem

The unit under test is a Troy-Bilt chipper made in the late 80's. Engine is an 8 HP Briggs. It appears to have very low hours. The engine starts easily, runs well for about 20 minutes, then begins to drop RPM and return to normal operation. Loading appears to have no effect. Eventually the engine will come to a halt. The engine will start again, like a hit or miss engine, coughing puffs of smoke, and ramp up to full operational speed.

So far: Fresh gas with a healthy dose of Sea Foam. Plug is new, dry, and a gray-cream color, no carbon. New synthetic oil in the crankcase.

Any suggestions?

Kevin Gallimore

Reply to
axolotl
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axolotl fired this volley in news:jt2df9$q09 $ snipped-for-privacy@dont-email.me:

If it's an updraft carb, they're easy to take apart and clean. It might just be a sticking float valve. But it sounds like the magneto is giving up after it gets hot.

I equipped an 8HP Briggs with an external coil for that reason, since the

12V charger portion of the maggy was still working.

LLoyd

Reply to
Lloyd E. Sponenburgh

axolotl fired this volley in news:jt2df9$q09$1 @dont-email.me:

Should have said, too... put in a new capacitor, and check the points gap before you do anything else. Caps can fail hot, and the points may be worn to where it's barely running right, anyway.

LLoyd

Reply to
Lloyd E. Sponenburgh

I'd want to check for bad ignition coil, or inadequate valve clearance.

Other things to check, try running with gas cap about 1/2 turn open, so it's able to breathe in air.

Christopher A. Young Learn more about Jesus

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So far: Fresh gas with a healthy dose of Sea Foam. Plug is new, dry, and a gray-cream color, no carbon. New synthetic oil in the crankcase.

Any suggestions?

Kevin Gallimore

Reply to
Stormin Mormon

Thanks, Lloyd. Further research shows it has a "Magnetron" transistor ignition. Heat and silicon being what they are, the module may be the best place to look.

Kevin Gallimore

Reply to
axolotl

Bingo

Exhaust valve seat insert may be loose.

Reply to
bw

Does it help to wash out an oil-soaked coil with solvent?

jsw

Reply to
Jim Wilkins

"Jim Wilkins" fired this volley in news:jt2lrn$9qn $ snipped-for-privacy@dont-email.me:

Not usually.

Oil, by itself, won't necessarily hurt a coil that's made properly, unless it's one of the old tar-potted versions, and it has soaked for a LONG time. Not likely to be tar, though, unless it's a pre-60's machine.

Solvents may harm it. If anything compromises the enamel on the magnet wire they wound it from, it will kill the coil ASAP.

Besides, if the coil is potted - and most were since the 1940's - then the oil didn't really get into the coil, just on it.

LLoyd

Reply to
Lloyd E. Sponenburgh

I've heard of that. and, also, exhaust valve seat may be burnt, and the exhaust valve heats and lengthens.

Christopher A. Young Learn more about Jesus

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Bingo

Exhaust valve seat insert may be loose.

Reply to
Stormin Mormon

I doubt it. Oil is non conductive, which is fine for this situation.

Christopher A. Young Learn more about Jesus

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Does it help to wash out an oil-soaked coil with solvent?

jsw

Reply to
Stormin Mormon

Try using Premium gas that with octane in it. The older and newer machines can't hack the Bio-gas they make now with alcohol in it - as the former absorbs moisture out of the air and puts water in the gas.

The neighbor just go back his lawn tractor - new everything and tuned up. He began to mow and after several hours put it up and went in for night. He refilled the tank the next day (tank cooled and sucked in water) and the engine acted like yours. Water in the lines, carb and just in the gas.

Mine was like that - I parked it in the hot sun and while it was hot ran it with some stp in the tank - the anti-Alcohol stuff - and it now runs.

Good Luck. And on small engines - never to much oil. It flood the engine.

Mart> The unit under test is a Troy-Bilt chipper made in the late 80's. Engine

Reply to
Martin Eastburn

Sounds like it is flooding. Since it takes 20 minutes to show up, I would check the air filter, choke and fuel mixture adjustment

-jim

Reply to
jim

Martin Eastburn fired this volley in news:Hb7Jr.182130$ snipped-for-privacy@en-nntp-16.dc.easynews.com:

Phooey. The only thing my 1962 Upright Briggs on my genset needed to be alcohol compatible was re-adjusting the needle valve settings. At worst, it might have needed a new needle valve, since it did have a cushioned seat -- but it didn't.

Martin, do you actually WANT them to destroy their engine? Over-filling a recip is a bad way to end a good day. You don't "flood" the engine, you fill it to the recommended fill height, and no higher.

LLoyd

Reply to
Lloyd E. Sponenburgh

I made an old flea-market Powermate 3.5KW generator run smoothly by swapping the jet from 166 to a 162 that the repair shop thought might work better. The hole in the 166 is between 0.033" (#66 drill) and 0.036" (#64). I don't have odd numbered sizes of tiny drills.

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The 1950's 6BS engine on my lawnmower needed only a richer needle setting.

jsw

Reply to
Jim Wilkins

I understood him to mean don't put too much oil in them ... I sold a really nice mower to a neighbor , idiot did just that . What started out as a low-hours self propelled mower was in the junk pile before fall . I shoulda kept that one and sold him the one I still have ...

Reply to
Snag

"Snag" fired this volley in news:fSgJr.38426$ snipped-for-privacy@newsfe05.iad:

Yeah, upon re-reading, I can see he might have meant that. It read sort of like pidgeon English, and I thought he was meaning you could never HAVE "to much oil".

In the re-interpreted case, I agree -- never add too much oil.

Lloyd

Reply to
Lloyd E. Sponenburgh

"the oil was low, so I put in a quart...."

Christopher A. Young Learn more about Jesus

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I understood him to mean don't put too much oil in them ... I sold a really nice mower to a neighbor , idiot did just that . What started out as a low-hours self propelled mower was in the junk pile before fall . I shoulda kept that one and sold him the one I still have ...

Reply to
Stormin Mormon

My old Case backhoe was acting the same way. After running it a while it would start to miss and act like it was running rich. After cooling for a day it would start and run fine then start running crappy after about 20 minutes. After checking the points and plugs I put in a new coil and the problem went away. It now starts easily just like before and runs for hours without any problems. Eric

Reply to
etpm

But it sounds like the magneto is giving

If the run time is less when you restart it, then the magneto is likely. I had a 5 Hp Briggs give this symptom, it would start from cold and run fine for about 10 minutes, run rough and then quit. If you waited a minute, it would restart, but only run a minute or two before quitting. I pulled it up next to my car and put a timing light on it, and it was clear the spark was dying when hot. The guy at the mower shop tried to dissuade me from buying the part, wanted me to bring it in for testing, but I just bought it and it fixed the problem.

It was a plain coil and breaker ignition on that one.

Jon

Reply to
Jon Elson

Had a Snapper lawnmower I rescued from a dumpster with the same problem. Got about 10 minutes of running, then it stopped and no amount of messing would get it going again until it cooled off. Replaced the magneto module and it's been running for 8 years. Was $50, but a new mower of that type is over 1000. No points/capacitor, it's an all-electronic sealed module. It works or it doesn't, all there is for tweaking is the gap between the poles and the flywheel. Tear off a flap of the shipping box and that's the gap gauge.

The other thing I've found is that the early '80s engines really want premium gas, with the low end cheap stuff, it just stalls on tall grass and weeds. Since this year is looking to be a 4-5 mow job one, I can afford a gallon or two of 91 octane for the increase in performance.

Stan

Reply to
Stanley Schaefer

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