Been a while since I haunted this forum... got great advice and had my old girl running well until yesterday. After a great start and quick warm up I took off... after about ten yards, it began backfiring loudly. Gave it some throttle and it did it even more ferociously and then quit. Pushed it back and let it sit a few hours while I worked. Came back... Figured maybe water contamination.. drained the tank. Got it running again, but still rough. Had a moment when it ran fine, but then rough again... backfiring and quit. At one point, the electric start switch got bumped and the starter began turning! Electric start has never worked, only "clicked" since I have had the machine. After a while, it went back to a click sound.

Tried starting fluid, and even that would not start it after a while. Had intermittent success getting it started, but only to keep backfiring and sputtering.

Wondering if the electric start issue and the sudden backfiring are related...? Am I chasing a cracked circuit board or bad ground or connection perhaps? Or is this symptomatic of a component failure...CDI or something?

Way back when my neighbor got this machine, it had been rewired to repair where a dog had chewed threw the harness around the master switch area. Since it always worked (Except the intermittent starter), I never bothered to unwrap and check everything. I have replaced the switch in the past couple months and it ran fine.

Well, I need this thing for work around my place! Any ideas would be appreciated. Not sure if the starter issue is related or not, but I figured worth mentioning in case there is a common area to that and the sudden backfiring... maybe electrical related since I did clean out the tank and fuel runs freely through the fuel filter. No, I haven' taken the carb off, but I did rebuild it a while back and it has run fine for months.

For anyone unfamiliar with the machine, it is a 1989 Big Boss, 2-cycle... maybe a similar problem with another 250 2-cycle?

MANY thanks! - Doug

 

First off I would check compression and if its at least 100 psi or more, while you're at check spark with a new plug. Just ground the plug to head and check for a good spark(backfiring can also happen from a partially fouled plug) Starter circuit won't affect the way its running!
As far as the starter sounds like it tried to work,but probably crapped out on the inside(brushes, dirty armature not allowing it to operate properly) If you want to replace it its 69 bucks at DB Electric.Plus you could check the starter and the solenoid to make sure connections are tight.
If continues to back fire and compression is good could be stator related,especially the exciter coil.
Any 89 250 manual on the engine can give you the elec specs to check the stator out (Trail boss,Big boss)
OPT
.

 

Sorry for delayed gratitude... was offline for a few days. Don't own a compression gauge; might bite the bullet and buy one. Will check into the stator and exciter coil.

Use Polaris only on stator and/or coil? Replace the whole assy.? Manual says drain the oil... the only oil I know of is trans on that unit.

Can't change the starter from the same side, can I?

Also, manual describes using sealant around the wires... Any preferred kind?

Started it again the other morning just for grins. Cranked up and ran for a minute, then started to backfire and sputterred out and quit. Consistent with Stator?

 

Manual should give you the stator resistance specs along with the coil primary and secondary specs.
Check these out before throwing parts at it! (Ricks Stators,Ricky stators are a couple of aftermarket sources. Could be just the pick up coil or the complete stator you may need if it is an electrical problem??
Get a compression tester!100 psi MINIMUM! Backfiring could be a compression problem, worn piston,etc. If starting fluid won't help then probably one or the other,electrical or compression!
Any good rtv sealant except RED,stands out like a sore thumb!
There's NO oil in the engine,just in the oil tank and transmission!
Recoil has to be removed to remove two starter bolts along with bolts on the starter bracket behind the front clutch! ONE thing at a time! Check compression FIRST,then electrical specs! Then go from there. OPT

 

I'll get a tester and check the compression. Just pull the plug and then pull the starter? Saw something listed about having the throttle wide open or something for full compression.... does that matter a lot? Guess I can do that also, but I want o be sure I do it the best way for diagnosis.

By the way, do I need a flywheel puller from Polaris (Same question for aclutch puller)? Or is there a parts store brand that will work? My local Polaris dealer is less than humble on their pricing.... Can travel 40 miles or mail order....??

Thanks, as always for your time and help. - Doug

 

I always have the throttle wide open when checking compression,two or four stroke! It actually doesn't matter that much on a two stroke whether you do or not,BUT it really matters more on a four stroke to have a wide open throttle to accurately measure compression!
Just use a multi position round puller gear puller OR a universal 3 position puller(steering wheel puller) with 8mm OR 6mm long bolts(can't remember size on the older flywheels?) available at any auto supply. Just use heat around the flywheel while under pressure and the flywheel will usually pop off or just tap around it or on the puller bolt head to free it. Plus the older flywheels were notorious for the magnets separating from the flywheel(just check it out when you remove it) OPT

 

Thanks very much for your input. Will advise how it goes... Need to get some tools.

 

The puller I got has 8mm bolts... the ones that came out of the flywheel have a "7" stamped on them, so I'll take one with me to the hardware store to see if I can match them up or find another puller.

When the cover came off, looks like no gasket was there, just some sealant. On the bottom, puddled a little around the starter is some dirty, almost watery looking oil. Brown... ALSO was VERY skinny little spring about 3-1/2 inches long, with a much shorter little piece next to it... maybe a half inch or so. Can't be good; but I don't have the flywheel off yet.

Question: How in the world do you hold the flywheel while trying to back off the nut??!!

What is the little spring and is there supposed to be any oil in the bottom of that area? Not a lot, but there is some nonetheless.

 

The little spring is what holds the ratchet lever in place and allows the ratchet to engage the flywheel when pull starting! Look on the inside of the recoil and you will see the small hole in the ratchet lever and the other mounting hole. Hopefully spring isn't broken to where it got in under the flywheel and stator. There is no recoil gasket,just use rtv sealant on the cover! You will usually find a little watery/ oil residue,hard to seal the recoil completely! Also after the recoil is repaired,you can put a little rtv under the rope handle on the cover to stop water from coming in. Its best to have an electric or air impact to remove the flywheel nut. Handy to have on the flywheel puller too! Its tough to remove flywheel with just hand tools! OPT

 

OK. Impact got the flywheel off. The spring is not the ratchet spring.... that one is still there. Can't find it identified in the manual. It is a continuous wind.... like a little snake made out of a coil of wire....??

Manual says check the resistance at the wires outside actually. The book says no continuity means trouble. Range is .25 to .35 and I have .*!! no idea what that means. Also, when examining the top of the exciter coils, (where they touch or get close to the flywheel) each of the three coils has a green, plastic type end cap with what looks like impregnted wires or contacts that run the length of the cap or contacting area. What seems bad there is that each one is coated heavily with a thin film of greasy,almost sticky grime that can't possibly let much current go between that cap and the magnets under the flywheel..? Does that mean the stator should be replaced, or can you/should you clean the ends of those things somehow? Super fine sandpaper or maybe wipe with some chemical...?