Sudden KT17 issues: starting/backfiring/red hot muffler

brdfrd · #1 11-22-2015, 09:12 PM

So, I searched this forum before I started this thread. I saw some these problems, but not necessarily all together.

I've got a 1712 Hydro with the KT17, series II--which a replaced with an identical good unit at the beginning of summer. Did everything right, rebuilt the carb, new plugs, the whole 9 yards.

It ran great all summer--it sat while I waited for the leaves to fall. I used it 2 weeks ago and it was a little hard starting, and then it ran on a little and backfired out the muffler when I shut it down. I didnt think too much about that, the old one did that occasionally.

I went out to start it to haul leaves and firewood today and it didn't want to start at all. It ran the battery down, so I hooked it up the the charger and put it on quick charge, got the starting fluid and finally got it going. It seemed to run okay, but when I shut it down it ran on quite a bit and then backfired again. When I walked around front the muffler was bright red--which is not normal.

So, seems like it is leaning out somehow. I took the filter off to see if that made a difference--if it was too plugged up, no. Sprayed ether or gas in the carb, it doesn't start any easier, so I don't think it's just running lean.

I saw a post where someone had a backfire that kicked back and sheared the flywheel key, retarding the timing--is this something that really happens? Could this be my issue? I've never heard of anything like that happening.

Thanks, Brad

MWShaw · #2 11-23-2015, 05:35 AM

Sure sounds like a very lean condition. I've had a couple of KT II 17s and currently have a M18 I never never sheared the flywheel key.

I would get a can of carb cleaner and start spraying areas of the intake / carb while the engine is running, checking for air leaks.

Could be some crap in the main jet as well, restricting fuel flow.

But I'm no expert.

twoton · #3 11-23-2015, 07:18 AM

Just wondering, what does the whole 9 yards mean? (I know that part, yeah a full truck load) but in your case? Decarbonize the head?, pull the valves? replace the guides/seals? Just wondering, think you have a stuck valve? Regarding the starting fluid. Washes the lubricating oil from the cylinder walls. Like trying to start your engine with no oil in it. Bad stuff! (Just my opinion)

Good luck.

finsruskw · #4 11-23-2015, 08:53 AM

9 yards was the length of the 50 cal ammo belts on the B-17's in WWII.
That's where the saying originated.
After a tough mission, when the ships made it back w/no ammo left and the crew was debriefed, the gunners would say when asked, "Yeah, we gave 'em the whole 9 yards!"

brdfrd · #5 11-23-2015, 09:02 AM

Twoton, points, condenser, reset governor, adjusted carb per manual, new filters--full tune up type service. The new unit installed was in pretty good shape, not a whole lot of use--both cylinders had about 110psi when I checked them. Compression is still good.

Regarding the starting fluid--I don't drown it, just enough to see if it'll start or not, if it's a fuel issue or not.

ol'George · #6 11-23-2015, 09:17 AM

First off, KT 17 Series 1 and 2 are timed off the camshaft lobe with a pushrod activating the points. not flywheel timed.
The magnum's do pick up impulses from the flywheel, and yes some engines can be affected by a sheared key in the flywheel, happens all the time to the 3-5 hp.
vertical lawnmowers when hitting a large obstruction in the grass, usually bends the crank and blade.
I would suggest you check your timing (points) first, if No cigar, then check fuel delivery.( carb/Fuel flow) as it sounds real lean, and or advanced too much.

Yosemite Sam · #7 11-23-2015, 09:18 AM

Unless you have a serious internal problem, there are really only three things that will make an air cooled engine run hot.

A lean condition, including sucking air in the carburetor/intake system, possibly a leaking head gasket.

Out of time.

A lack of airflow over the cooling fins.

Since there are no magnets on the flywheel that control when the spark plugs fire, unless you timed the engine after the flywheel key sheared, a bad key will have no consequence on timing.

A "whole 9 yards" will mean something different to each person who reads the phrase.