Engine Surges/Falters Under Load
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bertsmobile1
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This may help to easy your mind about the key
So after slight struggle I managed to get the flywheel off this afternoon. They key didn't look perfect, but it also didn't look all that damaged either... I replaced it anyway and still have the ripping the handle out of my hand thing when starting. There's not a whole lot to this it looks like right? The magnet on the flywheel crosses the transformer, jacks the voltage, and creates the spark right? In theory this happens at top dead center so the piston drives back down and continues the clockwise motion of the crank shaft when looking at the flywheel end. If the spark fires too soon, OR the piston does not reach top dead center when it should, the spark happens, fires and knocks the crankshaft counter clockwise ripping the chord out of my hand. Interestingly enough, once I get it started, it runs fine. Still not perfect at no choke with the junk carb with the surging, but it runs and sounds smooth.
So given that the flywheel does not look damaged and they key is new, what else can I chase? Is there something I can adjust with the position of the flywheel magnet, or the magneto/transformer itself? Or should I be chasing a mechanical problem with the crankshaft/arm/piston? Am I right when I think if the crankshaft to piston arm joint was loose, it would be really rough/knocking and sound terrible? (cause it doesnt). What about if the joint between the arm and the head of the piston had play? Would that make noise? Cause if either of these joints are loose, the piston wouldn't reach TDC in time and have this trouble, but once there was some inertia, it would work fine right?
Sorry for all the thoughts/questions. Hope I'm making sense.
So given that the flywheel does not look damaged and they key is new, what else can I chase? Is there something I can adjust with the position of the flywheel magnet, or the magneto/transformer itself? Or should I be chasing a mechanical problem with the crankshaft/arm/piston? Am I right when I think if the crankshaft to piston arm joint was loose, it would be really rough/knocking and sound terrible? (cause it doesnt). What about if the joint between the arm and the head of the piston had play? Would that make noise? Cause if either of these joints are loose, the piston wouldn't reach TDC in time and have this trouble, but once there was some inertia, it would work fine right?
Sorry for all the thoughts/questions. Hope I'm making sense.
Just reread the entire thread and a few things popped out. First you are over thinking many things in your last post. I never seen any of those possibilities. I'm going to sound like a smart a-/(&, but please bear with me. Remember I am not there to see, hear or feel your problem. First, are you sure that you torqued the flywheel nut correctly. If it was a bit loose the key may have sheared again. If you feel you did it properly, do not got back and check. Second, I still think it may be a carb problem, so I would like you to try this procedure in adjusting the carb. If the carb is allowing too much fuel in at startup, a kick back could result.
Adjusting a carb
Ok, the first thing I would suggest is to reset the armature air gap with the single thickness of a business card, unless you are sure you have a gap of .010 inches. *I don't normally recommend doing it this way, but in your case it may be best. *Second, this is the procedure I always taught my students to adjust a carb with two fuel controlling needles.
1. *Start the engine and move the throttle control to top speed.
2. *Adjust the high speed needle (this is the one under the float bowl) clockwise very slowly until the engine starts * * *
** * to bog down.
3. *Back the needle out 1/8 turn, the engine should now run smoothly.
4. *Now move the throttle control down to idle. *If the engine stalls out turn the idle speed screw in one full turn,
** * restart the engine and bring the throttle control down to idle. *If the engine is running to fast, turn the speed*
** * screw slowly out until the engine seem to want to die and then in 1/8 turn.
5. *Now with the engine running, adjust the idle needle out until the either gains in RPM's or starts to bog down. *If
** * the engine gains in RPM's, continue to adjust out until the engine starts to bog down. *At this time turn the*
** * screw in 1/4 turn. *Now the engine may be running to fast, so turn the idle speed screw out until you get an*
** * RPM you like.
6. *Now you must repeat step 5. *If the engine bogs down right away turn idle needle back in to your starting point*
** * and go to step 7. *If it speeds up, repeat step 5 again.
7. *Turn idle needle in until the engine bogs down and then out 1/8 turn.
8. *Now the engine should run smoothly at all speeds.
9. *To check, set the engine to idle, then quickly push the throttle control tohigh speed. *If it dogs and does not*
** * come to speed, open the idle needle 1/8 turn and repeat.
10. Set to go.
There are 2 *reasons I have it done this way is, first the high speed needle controls the fuel going to the low speed circuit and second is that the idle needle controls how much fuel is used when going from idle to high speed. *You should also review the section in the manual I posted before starting this procedure.
Now if this does not solve the problem we will have to look at the valves. If the exhaust valve is sticking or not seating properly, hot gases may be igniting fresh fuel entering the cylinder causing kickback. This will mean that the head will need to be removed, so pickup a new head gasket before disaasembly. I don't know how far into this you want to go, just giving my thoughts. Will trade snow for our cold in payment for this advise. Let us know if you need more help.
Adjusting a carb
Ok, the first thing I would suggest is to reset the armature air gap with the single thickness of a business card, unless you are sure you have a gap of .010 inches. *I don't normally recommend doing it this way, but in your case it may be best. *Second, this is the procedure I always taught my students to adjust a carb with two fuel controlling needles.
1. *Start the engine and move the throttle control to top speed.
2. *Adjust the high speed needle (this is the one under the float bowl) clockwise very slowly until the engine starts * * *
** * to bog down.
3. *Back the needle out 1/8 turn, the engine should now run smoothly.
4. *Now move the throttle control down to idle. *If the engine stalls out turn the idle speed screw in one full turn,
** * restart the engine and bring the throttle control down to idle. *If the engine is running to fast, turn the speed*
** * screw slowly out until the engine seem to want to die and then in 1/8 turn.
5. *Now with the engine running, adjust the idle needle out until the either gains in RPM's or starts to bog down. *If
** * the engine gains in RPM's, continue to adjust out until the engine starts to bog down. *At this time turn the*
** * screw in 1/4 turn. *Now the engine may be running to fast, so turn the idle speed screw out until you get an*
** * RPM you like.
6. *Now you must repeat step 5. *If the engine bogs down right away turn idle needle back in to your starting point*
** * and go to step 7. *If it speeds up, repeat step 5 again.
7. *Turn idle needle in until the engine bogs down and then out 1/8 turn.
8. *Now the engine should run smoothly at all speeds.
9. *To check, set the engine to idle, then quickly push the throttle control tohigh speed. *If it dogs and does not*
** * come to speed, open the idle needle 1/8 turn and repeat.
10. Set to go.
There are 2 *reasons I have it done this way is, first the high speed needle controls the fuel going to the low speed circuit and second is that the idle needle controls how much fuel is used when going from idle to high speed. *You should also review the section in the manual I posted before starting this procedure.
Now if this does not solve the problem we will have to look at the valves. If the exhaust valve is sticking or not seating properly, hot gases may be igniting fresh fuel entering the cylinder causing kickback. This will mean that the head will need to be removed, so pickup a new head gasket before disaasembly. I don't know how far into this you want to go, just giving my thoughts. Will trade snow for our cold in payment for this advise. Let us know if you need more help.
Guilty as charged for over thinking things. As for the flywheel, I torqued the piss out of it with my impact wrench, so I'm pretty sure it's seated hard. I've got a new real OEM carb on the way on tuesday instead of this junky cheap POS with the rubber tipped needle. Will try your carb procedure with the new one.
As for the possible valve problem, I get how a sticking valve would cause hot gasses to auto ignite, but it does the ripping the handle out of my hand thing usually on the first pull when the engine is cold and hasn't turned over more than once. That's why I was more thinking timing issues as opposed to sticking exhaust valve.
And for the armature gap, I have gap measuring tools to check it. Not going to mess with it till later in the week cause it's going to snow, AGAIN tonight/tomorrow and it's running atm.
As for the possible valve problem, I get how a sticking valve would cause hot gasses to auto ignite, but it does the ripping the handle out of my hand thing usually on the first pull when the engine is cold and hasn't turned over more than once. That's why I was more thinking timing issues as opposed to sticking exhaust valve.
And for the armature gap, I have gap measuring tools to check it. Not going to mess with it till later in the week cause it's going to snow, AGAIN tonight/tomorrow and it's running atm.
bertsmobile1
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A lot of OEM is made in China but most of it is made to OEM specs.
The stuff that fails QC gets sold to evilbay discounters through middle men.
Then there are the copiers who get one, make something that looks similar and sell them into the distribution networks.
Big difference in quality.
bertsmobile1
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Now as for the air gap pn the ignition coil.
The closer it is to the flywheel the earlier it will spark,
The further away it is from the flywheel, the latter it will spark.
Now we are not talking massive differences but it has been a tuning trick to tweak the beast out of these engines for a long time.
The other thing to "over think " about is the electronic ignition trigger.
A lot of these will revert to full advance when they are on the way out.
They are not replaceable in most engines being an inergral part of the coil.
You might like to try swapping the one from the 90 with yours.
The magnets should start to cross over the first leg of the coil before TDC and should be past the last leg as the piston starts to drop.
Contry to popular belief & terminology the advance unit does not advance at all. The coil is set in the full advance position & the "advance unit" retards the spark so they fail either completely or fail to the fully advancd position.
When in your position , just before I run the Gillette across my wrists I put a dollop of white paint on the flywheel where I can see it at the TDC position.
I then start & run the engine with a timing light on the plug lead ( you will need an external battery to power the lamp because of interference ).
At idle the spark should be on or slightly past your mark.
At full speed the spark should be before your mark.
Worth while doing if for no other reason than eliminating timing problems.
Also if it is inconsistant or flickering then you do have a coil problem
The closer it is to the flywheel the earlier it will spark,
The further away it is from the flywheel, the latter it will spark.
Now we are not talking massive differences but it has been a tuning trick to tweak the beast out of these engines for a long time.
The other thing to "over think " about is the electronic ignition trigger.
A lot of these will revert to full advance when they are on the way out.
They are not replaceable in most engines being an inergral part of the coil.
You might like to try swapping the one from the 90 with yours.
The magnets should start to cross over the first leg of the coil before TDC and should be past the last leg as the piston starts to drop.
Contry to popular belief & terminology the advance unit does not advance at all. The coil is set in the full advance position & the "advance unit" retards the spark so they fail either completely or fail to the fully advancd position.
When in your position , just before I run the Gillette across my wrists I put a dollop of white paint on the flywheel where I can see it at the TDC position.
I then start & run the engine with a timing light on the plug lead ( you will need an external battery to power the lamp because of interference ).
At idle the spark should be on or slightly past your mark.
At full speed the spark should be before your mark.
Worth while doing if for no other reason than eliminating timing problems.
Also if it is inconsistant or flickering then you do have a coil problem
Thanks for the extra thoughts Berts. Still haven't had a chance to even look at the gap cause I'm not ripping it apart while it's still snowing. And since I continue to reside on the surface of Hoth, it may not be till late this week that I get a chance to dig into this. "They" were thinking rain on tuesday... Now 6" of snow 