Pulled over for 5 mins, engine won't start, good spark gas and compression???

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rudyauction509

New Member
May 8, 2012
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Spokane, WA
My friend and I stopped at a hardware store on our ride. Went in for 5 mins to get a pair of hose clamps. Came back out and my friend's bike wouldn't start. Gas is good, spark is strong, compression is great. Cleaned crankcase with carb cleaner and drained, it came out heavily colored by 2 stroke oil. Sprayed starter fluid in spark plug hole, tried to start. No luck. Towed my friend 3 miles home, friends clutch out and engine spinning. Never got a single pop. Spark plug appeared dry, dark brown.

Any ideas? I'm going to heat the crankcase with a hair dryer after pulling cylinder to try to evaporate the rest of the carb cleaner. Also changed CDI and magneto and spark plug to mine, his works on mine and no change in his engine.
 

2door

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Staff member
Sep 15, 2008
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Littleton, Colorado
When you say, "gas is good", what does that mean? Is fuel flowing to the carburetor from the tank?
Have you checked head bolts for tightness?

If above is good, check the magneto magnet (rotor) to make sure the keyway in the rotor and the crankshaft are aligned.

Tom
 

rudyauction509

New Member
May 8, 2012
160
1
0
Spokane, WA
Gas gets to the carb. Checked rotor and it's aligned. Also won't start on starter fluid or carb cleaner. Head bolts were a bit loose but no sign of leak on gasket. Compression feels good, enough to lock up rear wheel for a couple seconds. pulled cylinder, there's a couple scratches but nothing serious. Stuck lighter down crankcase opening, the vapor inside burned slowly at the opening for 10 mins. Heated up crankcase with hairdryer, burned another 10 mins. Going to put cylinder back on and give it a try.
 

Davezilla

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Mar 15, 2014
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San Antonio Texas
Have you pulled the float bowl off the carb to see if there's anything blocking the main jet? these fuel tanks come with all kinds of leftovers from china and the smaller stuff can get in there and block off the needle and seat valve in the carb, and can also block the main jet from getting enough fuel thru it. if you got fire, fuel, and compression and it's still not starting, the next thing to check is the ignition to make sure the timing didn't slip from a broken or missing key, and then the carb for debris blocking off the jets.
 

Davezilla

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Mar 15, 2014
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Ok... this may be a dumb question but have you tried some fresh fuel in the tank? Bad gas or old gas won't burn that well can can make it impossible to start, and very unlikely but these things are easy to sabotage by pouring something other than gas into the gas tank when the owner isn't paying attention.
 

brown

Member
Feb 1, 2013
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Bloomington IL
I don't know how many times I had people riding my bikes and they have the same problem only to find out some how they moved the choke lever. Always the first think I check. Just saying.
 

Davezilla

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Mar 15, 2014
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Well hopefully he figures it out and gets it running... We can only help so far from behind the desk. The good thing tho is that these things are very simple and there's not a whole lot that can go wrong.

Since this was a sudden death where it was running just fine then now it won't start I'd look at the ignition system very closely, then pull the carb and check that the main jet isn't obstructed,Next I'd pull the plug and run a compression check with a comp gauge.

Other possible reasons... Air leaks at the carb to manifold connection, same for the manifold to jug, and finally at the crank seals. Air leaks can also happen at teh base gasket and the case it's self. If the engine refuses to start after the basics have been checked and passed it's time to look for air leaks either by pluging the intake and exhaust and pressurizing the case to about 5 to 10 psi and seeing how long it'll hold pressure, if it leaks down in just a few seconds it's time to find the source, this can be done with soapy water from the outside of the case (keep that mag dry at all costs tho) paying extra special attention to the manifold flange, the base of the jug, and the case split line. Also pressurize thru the spark plug hole and spray soapy water on the jug it's self to rule out a cracked jug or head, or porosity in the casting.

Most case leaks won't be enough to keep one from starting unless it's really bad, but we've already checked all the basics and we're working our way up, doing the easiest checks first. It could also be something as simple as a shorted out kill switch or cdi wir shorting out to ground, you'll get a spark when testing the plug, but under compression it won't fire in the cylinder. Also, as uncommon as it is, a broken magnet key or a missing key could throw off the ignition timing enough to prevent a start.

Just gotta look at everything, but don't overlook the obvious, look at ALL the easiest reasons first... Even pulling the head to make sure there isn't a melted piston is easier than a full pressurized leak check so obviously, do this check before going up to a higher difficulty level check.

Hopefully there are a few hints in there for ya to get it running.
 

rudyauction509

New Member
May 8, 2012
160
1
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Spokane, WA
Thanks guys, no luck yet, gas was put in tank 15 minutes earlier and spark plug wire and boot replaced on the first day. I noticed the spark is really weak now (odd, was fine earlier) so I'm going to replace the entire electrical system and see if it starts. Choke was down - first thing I checked. Piston and cylinder were OK, one decent scratch, but not enough to be a problem. The rest was smooth.
 

rudyauction509

New Member
May 8, 2012
160
1
0
Spokane, WA
No luck. As a last ditch effort we're going to pull the engine, pull the cylinder, pressure wash it and dry it in the oven for 2 hours at 200 degrees, as this whole problem was started when the engine flooded (fuel valve and carb drip a bit, first repair attempt we rinsed out the engine and got 1/4 cup of gas from crankcase)
 

Davezilla

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Mar 15, 2014
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San Antonio Texas
A weak spark can prevent it from starting, do you know where the spark plug gap is set? Try reducing the gap to .025" or even .020" and see if it'll fire... Sometimes if the spark is weak enough, you can see the spark, but it may not be able to jump the gap under pressure. We used to close the gaps on our turbo cars back in the day whenever we cranked up the boost because there would be a point where they worked just fine but would begin to start miss firing above a certain boost level and taking the plugs out and closing the gap by another ,005" would fix the problem and let us run a few more psi boost pressure.
 

rudyauction509

New Member
May 8, 2012
160
1
0
Spokane, WA
Got it put together, my friend took it for a test ride, it started, ran 30 feet, made a loud pop and died. Removed cylinder head and that scratch is now a 1/4" wide gouge in the cylinder wall. Looks like I'm going to have to order a new cylinder kit.
 

Davezilla

New Member
Mar 15, 2014
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San Antonio Texas
Ouch!!
Sounds like maybe got a cylinder with bad plating in it... at least the parts are cheap and easy to replace, get new rings and also a new piston if the piston is scratched as badly. But the rings should be replaced anytime a cylinder is because the rings may not seat in the new jug, and if there's any scratches or damage to the rings they can mess up the plating in the new jug. Another preventive measure is to chamfer the port openings, any plating that protrudes past the ports can lead to the plating separating and causing a similar failure. This can be done with emery cloth or a dremel with a carbide burr and a steady hand. If you need more info on chamfering the ports ask and ill explain, it'll help the engine last a lot longer.
 

rudyauction509

New Member
May 8, 2012
160
1
0
Spokane, WA
Ouch!!
Sounds like maybe got a cylinder with bad plating in it... at least the parts are cheap and easy to replace, get new rings and also a new piston if the piston is scratched as badly. But the rings should be replaced anytime a cylinder is because the rings may not seat in the new jug, and if there's any scratches or damage to the rings they can mess up the plating in the new jug. Another preventive measure is to chamfer the port openings, any plating that protrudes past the ports can lead to the plating separating and causing a similar failure. This can be done with emery cloth or a dremel with a carbide burr and a steady hand. If you need more info on chamfering the ports ask and ill explain, it'll help the engine last a lot longer.
Found a piston kit with piston, cylinder, piston pin, clips, all gaskets and rings for $30 shipped. Going to jump on it.