No spark on number 1 and 2. Two half bad coils? GSX750F 1986

[calypso]

Hello guys,

I have recently bought a GSX750F that is running rough as anything. While riding it home it appeared to be running mostly on two and three cilinders but ocasionaly on four. Today I took the carbs appart and they look nice and clean ( the last owner told me they had just been cleaned). I decided to test for spark and got a good spark on number 3 and 4 but nothing at all on 1 and 2. I am a little bemused as this means that both coils have failed on one plug but not the other. Changing the low voltage wires around makes no difference always no spark on 1-2 and good spark on 3-4. I have taken the coils out and tested them the low voltage side gives me 3 Omhs on both coils but testing the high voltage side I get nothing (I am testing the omhs between the two sparkplug leads).

What do you think? a trip to the breakers for new coils?

The last owner told me the bike was running poorly because the carbs need balancing. Will this make the bike run on two or three cilinders? In any case no spark no fire I guess.

One las thing... any sugestion for a cost effective but reliable way to get a set of coils for not much cash.

I have done a search and it has helped but there is nothng on a failure like this. Thanks for any help.

[blackraven]

Mine did the same thing after ridding it for about 1,000 miles. You could feel that it was only running on two cyclinder. So instead of checking everything i just got new spark plugs. I figured if its not the spark plugs at least i have new ones.

[blackraven]

O yea afterward it ran perfect.

[calypso]

I have checked the coils all with the same spark plug. 1-2 no spark 3-4 good spark. I am going to get new plugs but I fear the problem runs deeper

[Black_peter]

Unless your coils are running to the wrong plugs.
IE:
1 and 2 are firing from the same coil..
Then:
You don't have a good ground for your testing.

You don't have two grounded plugs hooked to the coil at all times.

There is too much light. Believe it or not one spark of the coil is "weaker" than the other.

You have two bad wires.

It really isn't possible to have half a coil go bad.
Both plugs hooked to the coil fire at the same time.
One fires on the fuel charged cylinder, the other on the exhausting one.

[loudnlow7484]

It really isn't possible to have half a coil go bad.
Both plugs hooked to the coil fire at the same time.
One fires on the fuel charged cylinder, the other on the exhausting one.

You know, I never knew that! In all the toying I've done with my bikes, I never came across that bit of knowledge. My day has a meaning now, thank you!

[Black_peter]

It really isn't possible to have half a coil go bad.
Both plugs hooked to the coil fire at the same time.
One fires on the fuel charged cylinder, the other on the exhausting one.

You know, I never knew that! In all the toying I've done with my bikes, I never came across that bit of knowledge. My day has a meaning now, thank you!

What, are you making fun of me??

[calypso]

Thanks guys for the help, the light may be starting to shine into my small brain...


Ok, so I cannot halve only half a coil working. Spark plugs are ruled out as all the testing has been done with the same spark plug. the left coil fires 1 and 3 and the right 2 and 4 so that is as installed and tested. Switching the low tension wires makes no diference to the results (ie 1and 2 still don't fire). The resistance on the low tension side is correct at 3ohms but on the High tension side the result is 1 (ie no continuity). This may be because I cannot get a good earth.

It all seems to point towards the high tension leads then. Can I change them without changing the whole coil? If so what is the best method to go about it? what is the best cable to use?

The fact that I am getting no resistance between both high tension leads is still bugging me. What can I do to get them tested efectively?

Cheers

[Black_peter]

Ahhh good!
The resistance between the high tension leads (are you in the UK??) should be the coil spec (40K ohm?) + the wire. So no more than say 50K ohm. You cannot read one high tension lead to ground, one end goes to one plug the other to another plug. Follow? You have to read between wires or between points on the coil.

The coil to wire connection is very tricky!
It involves a gland connection where a split collar squeezes the wire insulation as it's fitted into the "tube" at the coil then a clip to hold it in place. I suggest removing the coil. warming the clip area with a blow dryer and then ever so gently easing the clips and wires free. Then you can measure the coil and or wires.
However while Suzuki made the coil end a royal pain in the butt, they made the plug end easy.
The spark plug connector comes apart very easily and I suggest you try that first. After all this end gets more stress during plug changes etc. If necessary trim a bit from the end then reattach. The boot slides back and the wire unscrews from the base. The wire basically connects to like a wood screw inside the connector.

[calypso]

I have taken all the leads off the coils and tested them for continuity. They tested OK. Unfortunately the clips have broken as they where very brittle. I have recut all the leads and retested them. One coil was dead so I have replaced it with a new one (two good sparks now) the other one tested OK with the multimeter so I reattached the leads with silicone and I get.... one spark one dead. I tried the one with no spark directly form the cable to the engine block (ie take off the spark plug anbd the cap) and I get a very weak spark. Back with the multimeter I have checked the spark plug caps and I get either no continuity at all or very high resistance. I guess I have a combination of bad conection to the coil + high resistance from the caps. I am wondering how the thing run at all... mind you it was rough as a badgers a##. Specially takiing into account that the carbs are not balanced.

So I have seen a set of coils including caps on ebay form a Bandit 1200. Do you think I can use them? externally they look the same. I have to replace the spark plug caps as they may all be internally corroded. Amazing thing is that even with high resistance they still create a spark on the good coil, even when I sawp the around. I guess with newer ones I get better spark wich cant be bad.

[Black_peter]

Those coils are a bear!
I warned you!!!!
I advise against silicone. Sorry I didn't get that out.
IMO the crimping effect of forcing the clam shell part onto a new section of wire is tight enough. Now thats another thing I didn't mention:
If you trim say 1/4 inch off the wire at the coil end you have to move the clam shell bit 1/4 as well. Too bad that there is just the spike inside the coil. It would have been great if they used the same screw type deal like on the boot end..

[calypso]

Cheers BP,

what do you think about using a set of Suzuki Bandit 1200 coils and caps?. I have just bought a set from ebay. Can I damage another part of the ignition system?

[Black_peter]

I'm gonna say that if the primary resistance is the same or with in spec the load on the CDI is the same or similar. I'm also going to guess that the bandit uses a very similar coil. After all the if the Japanese know one thing.. It's how to same money on parts.

Someone who has done a Bandit 1200 conversion might know. Search some of the forums for engine replacements. I know Special K did a whole write up on the changing engines

[kwebbel]

Never looked into it, used a new harness from a B1200 motor, so didn't have to, but one thing i remember is that the bandit's electrics are not the same as the Kat-electrics (there's a built-in resistor in the ignition-switch) so be carefull before blowing the new coils or overloading the CDI.

[calypso]

Cheers guys, Iwill report further