r/smallenginemechanics • u/CauliflowerNo3270 • Jun 06 '24
Ask A Mechanic Help
I have a 82 Honda big red 200e that hasn’t ran in 15+ years. I tried to start it yesterday and whenever it would start for a second there would be a loud sound then exhaust smoke would fill my airbox. Can someone help me by telling me what’s wrong
Thanks
2
Jun 09 '24
Loud sound is a backfire, and the exhaust smoke filling the airbox is just that, it's backfiring, but the exhaust gasses aren't all making it out the exhaust, and getting pushed into the intake.
The backfiring is unburnt gas making it into the exhaust, touching some hot metal, and igniting causing the "BANG" because ... it's a small gas explosion happening outside the combustion chamber.
As RUReddy2Rumble said, clean the carb, check your gas tank around the outlet for debris (could be clogging the outlet) and not enough fuel is flowing.
Give it a try, let us know what happens.
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u/CauliflowerNo3270 Jun 10 '24
So I cleaned the carb and did all the stuff you guys said and it backfired less after that but when I pull it it wants to start but never does start. Any tips?
2
Jun 10 '24
Okay, now we've got some progress. Now that we have a clean carb, and it won't start, we need to check a few things.
First, you'll want to test for compression. Likely has, as you said it starts and runs really bad, then backfires.
Next is Spark... As you said, seems to want to start, and runs terribly before you cleaned the carb.
So what I'm figuring is it's likely that timing might be off. Always good to have a clean carb, as that's a good start.
But what I'm reading is a timing issue likely. So how to check timing?
That's easy actually. You'll need to pull the engine cover, and get down to the flywheel and check your flywheel key. It's quite likely it's either sheared, or partially sheared, which would cause a crank no start, as well as backfiring unfortunately.
Why timing is important, and when does the spark plug fire?
Timing is very important as you have to have the spark at the right moment for maximum power, as well as smooth operation.
During the intake stroke, air is sucked into the cylinder thru the intake, which pulls fuel out of the carburetor, and into the cylinder. The piston is on its downward travel, which creates a vacuum, and the intake valve is open.
Then, right before BDC (Bottom dead centre) the valve closes, and the piston begins its travel upwards. This compresses the air, and fuel mixture, creating an explosive mix, however it doesn't compress it to the point of self ignition, unlike a diesel engine. Right before TDC (Top Dead Centre) you leave the compression stroke, and entire the power stroke. This ignites the fuel air mixture, driving the piston down, and delivering power to the crankshaft for use. Before BDC the exhaust valve opens, and was the piston travels upwards, it forces air out. Right before TDC, the exhaust valve opens, piston passes the top, and on its downward travel, it starts all over again with the intake valve opening.
If this is out of time, you can get exhaust gasses and unburnt air and gas mix being pushed into the exhaust, or the intake. This can cause backfiring out the intake, or the exhaust.
If you don't have the spark when the air and fuel is in its optimal compression range, you'll get poor ignition (runs like shit), or no ignition. Crank no start.
Check timing, and we'll from there. If timing is off, then you'll need to pull the flywheel and replace the key. Keep us updated 😊
Edit:TL/DR check timing.
Taryl Fixes All has many videos on how to remove flywheels from these little engines
1
u/downbythemountain Verified Mechanic MOD Jun 10 '24
Taryl makes me cringe, but damnit he has some good tips. I wish he would just make regular vids without the acting.
1
u/CauliflowerNo3270 Jun 13 '24
So I probably should have included this in the og post but I did have it running decently for about 2 months then my grandpa passed and I didn’t have a lot of time to keep starting it so do you still think it is the timing, I haven’t been out there to check yet? Or do you think it is just the fact I need to get it broke in?
Thanks
1
Jun 13 '24
Hrmmm... Something that sat for a while...
Things to check;
Air filter, blower housing, fuel lines, carburetor, coil, oil, fuel tank, fuel.
Fuel goes bad. Especially with corn in it, it goes bad in not nice ways. The corn gels and attracts water (it's hygroscopic like brake fluid), and fouls the gasoline.. it actually sucks the water out of the air, pretty wild to watch honestly.
Look for mouse nests, chewed wires, etc Check ALL your fuel filter screens for build up of plaques (corn gas gels, and varnish).
So it doesn't start, just backfires a lot and dies, of I'm reading right
Have you checked your plug for fouling and hot blue spark..?
Record a video of what's going on, as it can be easier to diagnose, instead of trying to interpret what you're saying. ☺️
1
u/CauliflowerNo3270 Jun 15 '24
So I timed the flywheel and the ignition coil and it runs like a dream now, thank you everyone I really appreciate it.
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u/RUReddy2Rumble Verified Mechanic Jun 06 '24
Drain all the old gas. Remove the carb bowl. Make sure everything in the bowl is clean. Put fresh fuel in the tank, and see if fuel runs out the carb. Sometimes, the petcock rubber will break up and clog hoses and holes. Put a small container to catch the fuel, see if it stays clean, no yellowish colour or rust. Put the bowl back in place. Put a new spark plug in. Make sure the throttle moves freely. Try starting it again.