QD-14 backfiring, won't crank ???

[jbjennings]

I've got a QD-13 powerhead to put on my QD-14. Finally got it mounted, all the bracketry changed over, used my QD-14 carb, magneto plate, coils, points, etc. Now I'm trying to crank it and all it will do is backfire--Pow! I changed the coils and condensors--not the points with no change. The coil wires are on correctly, the carb is working o.k. (working fine before). I tried to crank it with the bottom wire off---pow! same way as before. I put the bottom wire on and took the top wire off --pow! same as before. I'm thinking it's obviously out of time somehow but the point gap is right, coils good. The only thing I can think of is the cam on the crankshaft that operates the points is somehow not right. I looked at it and it was sitting on the key on the shaft. Can anybody think of what could be wrong?? I'm sure it's something simple but I can't figure it out yet.....by the way, the compression is about 65 lbs. on both cylinders.
THanks,
JBJ

 

[guy74]

Re: QD-14 backfiring, won't crank ???

Have you tried switching the plug wires?

 

[jbjennings]

Re: QD-14 backfiring, won't crank ???

Tried that, nearly jerked my arm off!
JBJ

 

[guy74]

Re: QD-14 backfiring, won't crank ???

do you have any of the old ingition pieces off the new QD 13 powerhead to compare with the ones off the QD 14? Could be that the pieces are not compatable, even though they will bolt up.

 

[tashasdaddy]

Re: QD-14 backfiring, won't crank ???

did you put the key in the flywheel, and torque it down to specs. sounds like a sheared woodruff key.

 

[jay_merrill]

Re: QD-14 backfiring, won't crank ???

Issues that can cause a backfire:

Air leaks at manifold gaskets
Warped manifold
Broken leaf valves
Carburetor adjustment too lean

Also, the flywheel key on that motor may have an "upset mark" on one end - make sure the key is oriented with that mark on the bottom end when installing in the groove at the crankshaft taper. I don't know why but apparently putting it in with the mark on the upper side affects timing. Whether it would affect it enough to cause backfiring is also something that I don't know but it is worth making sure that it is right.

 

[HighTrim]

Re: QD-14 backfiring, won't crank ???

Firing (backfiring) out the exhaust port can be caused only by having the ignition system fire a particular cylinder when the exhaust port is open (piston down). This would sound like a shotgun going off..... is this the condition that you're experiencing?

It does sound like a sheared flywheel key like Tash said, or a flywheel with melted (moved) center sensor magnets if they exist, or having the timer base leads routed incorrectly to the powerpack, or having the leads from the powerpack to the coils reversed to mention a few. Not real familiar with the older outboards though,and their magneto systems, so most of this would not apply to you. perhaps PM FR.

 

[jay_merrill]

Re: QD-14 backfiring, won't crank ???

His is an older motor with a simple flywheel/magneto system. He doesn't have a timer base or power pack.

 

[guy74]

Re: QD-14 backfiring, won't crank ???

Well here are the very few things I know about that kind of ignition system. If he has spark at all, the points and the pickup coils on the stator are timed together. Thats why they are all mounted on the same assembly that rotates around under the flywheel in order to advance the timing. that the flywheel and points cam must not be in the right orientation to the crank throughs, or the points/coil assembly, or linkage that turns it is not put on right. I would figure out where TDC is on the motor and see how cose that is to where it fires. Just reach though a sparkplug hole with something like a pencil and feel for when the piston is at its highest point, if its poping out the exhaust, but not kicking back, the timing must be really late.

 

[R.Johnson]

Re: QD-14 backfiring, won't crank ???

There is a up, and down to the magneto breaker point cam, it is stamped up, do you have it in correctly?

 

[JB]

Re: QD-14 backfiring, won't crank ???

Have you tried going back to the QD-13 mag stator, cam, points, etc.?

 

[guy74]

Re: QD-14 backfiring, won't crank ???

I had the thought of the points cam being upside down too, but I don't think it would have anyspark at all if it was.

 

[MikDee]

Re: QD-14 backfiring, won't crank ???

I guess I'm out of the loop, have no idea what a QD-13, or QD-14 is??? it must be code of some type?

 

[HighTrim]

Re: QD-14 backfiring, won't crank ???

QD 13 is a 1951-1952, QD14 is a 1953, both 10 hp Johnsons. Model numbers.

"http://home.earthlink.net/~brixent/Johnson1979.htm"

 

[jbjennings]

Re: QD-14 backfiring, won't crank ???

Thanks for all the info. men.
I rechecked the compression and it's 85 on the top and 80 on the bottom. THe ad said 65 lbs., and I got 60 on both by just turning the flywheel with a socket. Tried with recoil today and got 80 and 85. The '52 powerhead didn't have any ignition stuff on it, so I have no way of comparing the two. I do know the '52 had a throttle lever instead of a twist grip throttle on the tiller. I checked the pistons and top cylinder is TDC with the flywheel key facing straight toward the spark plug, and the bottom piston is TDC with the flywheel key facing straight toward carb. 180* opp. as expected. I checked the '53 powerhead and it seems(the pistons have a LOT of slack in the wristpin on the top cylinder) that it is TDC when the flywheel key is 90 degrees from the spark plug. (different from the '52)
How can I correct this? Or is it even possible? I don't even understand how the stroke of the piston and the flywheel key could be different unless something's broken.....
Now..... What is a woodruff key? I thought it was the key the flywheel fits on? Am I correct? The timing cam on top of the crankshaft does say "Top" on top of it just like my '53 does so I'm certain it's not upside down. I checked the reed valves and they look fine from out front. I'm pretty darned sure there's no leaks on the manifold, definitely not enough to cause this.
It is sounding like a shotgun, not a lean sneeze. It has to be incorrect timing. Where is this woodruff key if it is not the key the flywheel sits on? Could this key be broken but not look like it from above--in other words, what do I need to take off to check that key? Could the key have snapped off and let the cam spin on the shaft a little and binded up again so it seems o.k. but actually be 90 degrees wrong? THis would make sense on what it is doing. Do you just pry up on the cam on two sides with a screwdriver or need a special tool so you don't break it?
Anyway, sorry for the long post but I felt like you guys could figure it out if I just gave you enough info.
THanks again,
JBJ

 

[guy74]

Re: QD-14 backfiring, won't crank ???

It sounds like you found your problem, its firing at 90 degrees ATDC, that would make a big bang as the exaust ports would be open by then. If you can't get the right parts to fix it, I guess you could have another keyway cut into the flywheel and points cam so you can move it 90 degrees.
I think that would fix the timing issue.

Brian

 

[jay_merrill]

Re: QD-14 backfiring, won't crank ???

Just a minor point but one that can be usefull in these discussions - a backfire is when ignited gases move back through the induction system and an afterfire is when they exit via the exhaust system. To me, the terms are a little fuzzy when the problem is in a 2-stroke because they were really meant to describe such problems in a 4-stroke engine with valves in it. That said, it helps to know which one we are talking about.

 

[HighTrim]

Re: QD-14 backfiring, won't crank ???

I agree with guy, as said earlier, Firing (backfiring) out the exhaust port can be caused only by having the ignition system fire a particular cylinder when the exhaust port is open (piston down). This would sound like a shotgun going off..... and this is exactly what you are experiencing I believe.

 

[JB]

Re: QD-14 backfiring, won't crank ???

Is there a way that you could have actually mounted the magneto stator 90* off? Aside from switched plug wires, incompatible parts or a broken flywheel key that is the most likely thing I can thkink of.

 

[samo_ott]

Re: QD-14 backfiring, won't crank ???

So somehow they changed the firing timing from the 13 to the 14. Interesting. You might need the plate and ignition parts from the 13 then so that it is the same... this is assuming the key is not busted...

The loose wrist pins are another issue of course...