Novice question on the rectifier in my ST300/D circuit

[Papa]

Folks, I'm very new to this 6x6 world having bought a 1970-72 (?) Attex ST300/D with a JLO 300 cc engine recently. The wiring was mostly disconnected so I've identified a diagram from this site that pretty much matches my ATV. But, I don't know what purpose the rectifier serves. Is it critical for the engine to operate, or is it used for the headlamps or some other purpose???

I'm in the process of cleaning up the engine and want to crank it over (w/o fuel) to see if I've got a good ignition coil, but I don't know if I need to have the rectifier in the circuit for this test.

Any advice would be much appreciated. thank you.

Papa.

[racerone3]

before you crank the engine over w/o fuel, pull the spark plug and spray some oil down the plug hole and turn it over by hand a few times. the piston, rings and cylinder walls are probably dry from sitting, and may be gumed up from old fuel/oil drying out.
the charge coil on the engine puts out AC current, the Rectifer converts it to DC and usually serves as your voltage regulator as well. you can crank/ run the engine without it hooked up, just make sure the 2 charge wires coming from behind the flywheel (usually yellow on a JLO i think) aren't touching anything/ each other.

[Papa]

To Racerone3; thank you for the advice

Racerone3 - thanks so much for the advice on getting my JLO engine running. Yes, two wires coming from behind the flywheel are yellow. So, taping them up and cranking over the engine should show me a blue spark across my spark plug, eh ?

Do you recommend squirting any type of cleaner down the spark plug hole before oiling it up for a crank over? I saw a 'plug' on the bottom of the "crank case" and unscrewed it. A small "glob" of what appeared to be dried fuel/oil (approx. 1/8" dia) fell out of the hole. It started me thinking that maybe I should run some sort of cleaner thru the block to clear out any more 'stuff' left in there ???

Again, any advice would be much appreciated. Thank you.

P.S. my spark plug wire from the coil to the plug is broke. I'm planning on taking the coil with me to a small engine repair shop to see if I can get a new wire with the correct 'boot' on both ends. Any advice on getting the correct wire???

[Papa]

Novice question on starting my JLO 300

Hi, guys - I'm feeling my way thru the clean up and start up of my JLO 300 engine. I have it out of the ATV and on my bench. I've rigged up a temporary fuel tank. I've got a DC power pack hooked up to simulate the battery to the coil for starting. I can't get it to fire yet.

Question: does the muffler need to be connected to the exhaust pipe to generate some back pressure for the engine to run on my bench???

Any tips on starting a JLO on the bench would be much appreciated. Thanks.

P.S. I have a new plug and it is sparking.

[Don]

You won't need the battery pack for the JLO- it's a magneto with no exciter circuit. I'd hook up a temporary switch to kill the ignition just in case....

Just to run the engine you won't need a muffler. It should start fine without one. If you open up the carburetor and squirt a little gas/oil mix down the throat, it should crank right up. Make sure the engine's secured to the bench!

Good luck & be careful!

[thebuggyman1]

"Any tips on starting a JLO on the bench would be much appreciated. Thanks"
First tip: No muffler, wear ear plugs AND ear muffs.
Second tip: Bolt it down, they vibrate alot. I doubt you want a broken foot and/or engine when it falls off the bench.
Is the plug getting wet when you try to start it?

[Papa]

Thanks, buggyman1 and Don - just read your replies. I'm OK with bolted down engine to the bench, and have the ear plugs/muffs (and a fire extinguisher just in case!). But I don't understand the "don't need a battery pack" comment. There is a black wire that comes off of the coil and (the wiring diagram shows) runs to the ignition switch where, I assume, it is picking up 12 v during the 'key turned to start' position. So, I thought it is giving the coil/spark plug extra "juice" until the magneto gets up to speed/output ?????

Also, the wiring diagram I picked up from this forum shows 'negative ground' for this engine, and that's what I've set up. But, I also read (late last night) that this engine is 'positive' ground. But, I can't find that statement again (mabe it was too late when I read it and I was already dreaming!). Anyhow, I'm going to leave it 'negative' ground and try the tips you guys just gave me as soon as I send this reply. I'll let you all know how I made out.

[Papa]

Hi, guys - it's novice Papa trying to start his JLO 300 engine on the bench. Well, I just tried again with and w/o th 12 v power pack in the circuit to no avail. I checked for spark while cranking the engine with a rope. No spark (I did have some yesterday). So,I checked the voltage coming off the magneto to the coil; approx 12 volts from the few revolutions from the rope. Then I checked the voltage coming off of the coil; approx 100 volts. Is this not enough to spark the plug??

Do you know what the coil is supposed to put out; 100 volts or 1000 volts (or more?). Is there a bench test for a coil to see if it's bad (or weak) ????

BTW I checkd my compression (again pulling with the rope) and it looks to be 70 to 90 psi (or more). That sounds good ???

Thanks for any more comments.

[Don]

Hey, Papa;

The black wire to the ignition switch will be the "kill" wire and go to ground when the ignition is in the off position. You shouldn't need a 12V source for ignition unless someone has drastically changed the stock system. I'm not sure what the secondary coil voltage should be, but my guess it's lots more than 100v. The external coils do go bad from time to time, but it's not the usual suspect when you have an ignition problem. More likely it's points, condenser, or adjustment problems. A rule of thumb is 100psi bare minimum for compression on a two-stroke. If the engine's not been run in a long time, shoot a little light oil (WD40) down the plug hole and try it again.

Good luck.

[thebuggyman1]

Coil voltage depends on RPM, thats actually the job of the condenser. It is a capacitor (think of as a battery) it absorbs the high and gives back during the low. Oversimplification, but it should get the point across. I would guess you need about 10,000 volts for a decent spark, but it really should either be there or not be there.
Depending.....it may take more than a couple pulls on the rope to build the compression up on the gauge. Watch the gauge build up as you pull. When it stops building thats your compression pounds. If my memory is correct the JLO's were 10 or 11:1 that means
roughly 14psi atmospheric pressure times 10= 140 psi. 11x14=154psi

[racerone3]

usually you can clean off the points with an emery board (stolen from the wife) through an access hole in the flywheel. with the pull start removed, you can put a socket on the flywheel nut. remove the spark plug, oil the cylinder and use a drill with the socket on the flywheel nut to spin the engine over faster than you can with the drill. this will give you a better chance of getting/ seeing the spark. if you put 12v+ to the black kill wire on the coil, you might have fried it that will usually kill a coil pack on a Briggs

[Papa]

Don/buggyman - thanks again for feedback. I had another buddy tell me that I can't read the voltage off the coil with a mult-meter 'cause it happens too fast (milli-seconds). So, I need an ociliscope. I'll try that compression check again; hard to hold the gauge in the plug hole and yank on the rope at the same time ! I might have the plug gap set to wide at .030". I was just reading one of the JLO manuals on line and it says .016" to .020". But, I don't think that would prevent spark. I'll have to check that the plug is making good ground when I'm checking it for spark. Will try again tomorrow. Goodnight for now.

[Papa]

racerone3/Don/buggyman - wow, things happen fast here on 6x6world. I didn't see racerone3's reply last night about touching up the points. But, had another buddy tell me the same thing this AM. So, I tried that, and wola; the ol' JLO fired right up (after a lot of pulling on the rope). Yep, it vibrates a lot; glad it was really secured to the bench, but the bench started "walking away" ! Anyhow, you guys have really helped me. I tried adjusting the carb and got it to smooth out quite a bit. But, when trying to restart it really doesn't want to start again with the "smoothed out" carb settings. Also, am getting a lot of dripping from around the diaphram/bowl area of the carb. Took it off to inspect; didn't find anything unusual looking. Added a light film of grease around all the mating surfaces before reinstalling the pieces (to help seal it up). Still gets some leaking; more when it's just sitting there trying to start it than when it's actually running. I was surprised how good the diaphram(s) looked. I'm going to look up the carb settings in the manual here on line. I think it's 1 1/2 turn for the main jet and 1 3/4 turn for the idle jet. Thanks again; I'm sure I'll have more challenges for you guys again (soon).