can't tach over 4500

[earlfor]

Hmmm. 4.7 ohms on the coils between the + and - terminals is fine. Anything between 3 and 5 is fine. Its commonly accepted that 3 ohm coils are used with the factory electronic ignitions and 5 ohm coils are used with points ignitions, but my 1150 has a factory electronic ignition and the factory service manual specs 2 to 5 ohm coils as being within usable range, so I think it would be the same for your bike. A 1977 750 would have been manufactured with a points ignition system, so I am guessing you probably have a Dyna S electronic system. The Dyna can use 3 to 5 ohm coils.

You can check resistance between the spark plug boots/caps on the plug wires. Set the multi meter to the 200K setting on the ohm side. Place one lead of the tester on the metal point inside the spark plug cap. Place the other lead on the metal point inside the other spark plug cap. (it doesnt matter which is which) Resistance should be between 30K-40K.
Just for the heck of it, would you check both coils this way. I am curious if they have the same values. (another piece of the puzzle maybe) :-)

On your ignition. It doesnt make sense to me that 2 and 3 are sparking and working with the ignition on and 1 and 4 only work when the starter is engaged and then only work with the kill switch. Are we describing this right? The kill switch when switched to on means the ignition circuit is in the on/continuity state. Switching the kill switch to off means continuity on the ignition circuit is lost.

The orange and white wires that attach to the coil + terminals are 12 volt + input power to the coils. Both coils orange and white wire plug into the same double connector for power supply. This single wire with the double connector is fed from the Kill switch. Turning the kill switch to the off position can only result in killing the ignition to all four cylinders (normal), or to none of them ( if not functional). I would check to see the the + lead supplying the coils is actually coming from the single orange and white wire from the kill switch as it should. The plug/connector you will be looking for will be found inside the headlight shell and measures aprox 1/2 x 1/2 x 1". It will have three leads. An orange and white (power supply to coils), a green/yellow (goes to starter relay) and an orange, comes from ignition switch.
(Let me know what you find on your wiring....if its correct or not)

What is the voltage at your coil + terminals? (Ground the neg lead of the multimeter on the engine case). What is the voltage at the battery terminals? (both test leads on the battery)

I dont have a conclusion yet as to why you would be melting a coil
Usually, running coils of lower resistance results in the coils operating at higher temepratures, but youre not doing that, so I'm puzzled for the moment.

Considering the symptoms, I am still convinced you have an electrical problem rather than a carb problem.

Earl

Okay I checked the resistance on the coils between the + and - and both coils were about 4.7 ohms. Could you explain again how to check the resistance at the caps?

I found some time to mess with it last evening and found that 1 and 4 are sparking when the starter button is initially pressed and when the kill switch is hit. As I understand it, only the orange and white wire goes from the starter button and kill switch to the coils. The fact that one coil is fireing consistently but not the other has me a bit baffled. And why would the 1-4 coil fire when I hit the kill switch? Could there be a short somewhere else?

My only consolation is that south eastern Pennsylvania has been having a very wet spring. There have been only about half a dozen days this month where there wasn't at least threat of some serious rain.

I'm hoping that I'll have this thing running right by the time the weather decides to cooperate.

[Anonymous]

Thanks for the input, Earl. I just got two more used coils on eBay and I want to get this issue worked out before I put them on so I don't end up ruining another coil. I'll check the resistance at the end caps and then check the wiring in the headlight shell.

It doesn't make any sense to me either why 1 & 4 would be firing when the starter is engaged or when the kill switch is hit. When they do fire, they only fire once. I had the plugs out on 1 & 4 when I experienced this and they had an orange spark.

Another funny thing happened Saturday. I pulled the cap off of the plug on 3 while the engine was running and it started arcing accross the engine block. You'd think that if 1 & 4 aren't firing, pulling the cap off of 3 would cause the engine to stall out completely. Instead, it sounded like 1 & 4 were firing along with 2. I got quite a jolt out of the whole situation 8O and am even more confused now then I was before :? . Anyone have any ideas?

I'm with Earl being convinced it's electrical. When I pull the plugs out of 1 & 4, they're nice and wet. I'm getting juice to those cylinders, just no spark.

[bybowtie]

grounding is the problem... try to add a ground to the mount on the coil....where the screw mounts to the frame.. make sure you are resting on the coil part not the frame side run it back to the battery

[bybowtie]

grounding is the problem... try to add a ground to the mount on the coil....where the screw mounts to the frame.. make sure you are resting on the coil part not the frame side run it back to the battery on other thing check to see if the coils are hooked up right I had an incident when I pulled them off and it was quite some time before I goot back to them.. well I had moved the wires all around and were no longer anywhere near where they started.. well to make a long story short I happened to hook 2,3 to 1,4 coil and vice versa maybe you have a similar issue ????? I dont know should probably just listen to EARL!!!

[Anonymous]

Okay, my understanding is that the coils are grounded thus completing the circuit and igniting the spark. If the coil for 1 & 4 is not connected properly to the electronic ignition system, the electronic ignition will not complete the circuit and no spark will happen. My question is, what is happening when the starter is engaged and when the kill switch is hit that completes the circuit at those times that doesn't do it any other time?

And why did having the cap off of cylinder 3, and grounded to the engine block, make 1 & 4 fire? Also, where do I start to look for the bad connection between the coil's ground and the ignition circuitry?

... Okay, wait...

I don't have the wiring diagram in front of me but if I remember correctly, the kill switch breaks the flow of current from the battery to the positive terminals of the ignition coils by grounding it? ... I don't know where my mind was going there, but perhaps someone else does and can complete my thought.

[earlfor]

My question is, what is happening when the starter is engaged and when the kill switch is hit that completes the circuit at those times that doesn't do it any other time?
******* Under the right side crankcase cover (where the ignition pickups are) Look at those pickups and tell me if you have a black,white and red wire. Do you know what type of electronic ignition was installed into the bike. They do not all wire the same.*******



Also, where do I start to look for the bad connection between the coil's ground and the ignition circuitry?
******* The coil's ground is the mounting bolts that hold the coil to the bike's frame. Unless the mount holes are thoroughly rusted or sealed in paint, its unlikely the coils are not grounded.*******


I don't have the wiring diagram in front of me but if I remember correctly, the kill switch breaks the flow of current from the battery to the positive terminals of the ignition coils by grounding it? ... I don't know where my mind was going there, but perhaps someone else does and can complete my thought.

****** The battery provides power to the fuse block. The fuse block provides power to the ignition switch. Depending on whether you turn the key to ON or Park, different outputs on the ignition switch are energized. In the on position, positive + power then flows through the kill switch.
The kill switch being in the on position completes a circuit and passes along power to the starter switch. Your coils have power if the ignition key is on and the kill switch is in the on position. I asked this question earlier and apparently an answer was overlooked. The kill switch and starter button are connected by a three pin connector that you will find in the headlight shell. (the connector could be located on the wiring harness underneath the fuel tank, but that would be unusual) The connector is a white plastic rectangle that measures aprox 1/2 x 1/2 x 1 1/2". In this connector you will find three pairs of wires.

They should be in this order:

orange | orange/white | probably green yellow
==================================
orange | orange/white | green yellow



The power supply for your ignition system should be spliced into the orange and white lead. (either side of the plastic connector will do)
this orange and white wire also powers your coils. Make sure that the orange and white wires on the + terminals of your coils are both connected to this same point. (and only this point)

(I suspect that someone has connected one of your coils to the starter lead and that is why your symptoms are so odd. Consequently, that coil would only be energized when the starter button was depressed. :-) :-) There shouldnt be anything added to the green/yellow leads on either side of the connector box.)

Earl

[Anonymous]

Update: It's alive!!!!

Well, after much studying of the wiring diagram in the Clymer manual and thinking logically through the problem (I do tech support at work as well as other more mundane programing jobs), I finally decided that the problem was either in the spark plug caps or the ignition under the right hand side cover. Since I didn't have my multi meter with me, I figured I'd at least check what I could visually to see if there was an obvious short somewhere. I pulled the right hand side cover off, pulled the ignition plate out, looked it over, and then put it back in. It went back in differently then it was before I pulled it out so I thought, "Hmm, maybe that's the problem." I screwed the ignition plate back in and fired it up.

I had cranked the idle screw the whole way open so that the bike would idle on just two cylinders. Well, when I fired her up this time, all four cylinders roared to life, a ton of smoke came out the pipe and she idled at 3k rpm. I backed the idle screw down and let her run for a bit. That was early Saturday afternoon.

I was running her around the property in the rain then Saturday evening. The smoke finally abated, though she still runs a bit rough until she's warmed up. I had her idling steady at about 1100 rpms yesterday afternoon.

Now all I need to do is get her legal. But that's a whole other story...

[bybowtie]

great job hope that takes care of it.. One more thing.. sync your caebs and you should be set