GS450 Issue fitting New Coils

[David450]

Hi All What have I done wrong?
My GS450S is used frequently and has not had any major issues. The other day I was riding along at 55mph kicked down a gear and it just died. When trying to re start got a big backfire and nothing else. The existing coils were original but the HT leads had been spliced and very short so I decided to upgrade to new coils as an easy fix.
The new coils have a + and - spade connector
I connected the orange wire to the + and checked this wire was getting power when the ignition switch was turned on.
The white wire is fitted to the - on the left side coil and the black wire to the - on the right side coil
So far so good, I thought, so I went to start it and the bike only just managed to turn over with a very rough idle not getting above 1100RPM then a backfire.
I thought maybe one of the new coils was corrupt so I took the HT leads off both cylinders and swapped the left HT lead to the right side plug. Strangely the bike ran quite well, all be it on one cylinder. I then fitted the right HT lead to the left cylinder and the bike runs great. How can that be?
When I switch the HT leads back to the correct side the bike runs rough and only just starts.
My 450 is a 1981 electronic ignitor system not points.
I'm a bit reluctant to just switch the HT leads and forget it in case it screws another component after riding the bike for a bit.
There may be an obvious solution but I do not have enough electrical experience to see it, so over to you clever people.

Thanks

David

 

[zed1015]

Switching the plug leads won't do any harm if it runs as it should.
Sounds like you may have got the lt wires mixed up from left to right coils and swapping the leads corrected it.
A 180 twin shouldn't have run with the ht leads swapped over though as the spark would occur at the bottom of the stroke.

 

[David450]

Hi zed1015
It only just ran but I needed full choke to get it to fire so I suppose there was enough residual fuel to make a combustion when the piston got to the top. It was only just running and very rough.
Yes I thought that I may have the wires mixed up too. so I checked the manual against the wire colours. Not sure if other bikes are like this but the GS450 has a male connector on one coil and a female on the other so you cant really mix them up.
The previous owner had marked left and right on the connection so I checked against the manual in case that was wrong. I'm kicking myself at this point I didn't take a photo before making the changes.
Nice to know It won't do any harm but I'm a bit stumped as to why it seems to be the reverse of the manual.

 

[Gorminrider]

How strange! That diagram suits your 81 450 S diagram is for US models but it shouldn't make any difference*...a coil is a coil...however possibly the sensor wires at the advance ("signal generators") are swapped? The coils you bought are a question per correct wiring internally? but i doubt it.

*I looked it up in the 450 shop manual and I haven't yet seen anything specific that pertains.there were some differences visavis headlights and "parking" lamps I know about... But if you don't have the manual,
GS450 Official Service Manual PDF

 

[David450]

Thanks Gormanrider
I do have a manual but it is a first edition that only shows the points system so I was a bit in the dark re the signal generator. The pdf download is just what I need. I'll have a look at that and check against what I have.
Just thinking aloud, and this might be a complete herring. Is it possible the magnet in the signal generator has changed polarity somehow. The only reason I say this is the bike was running ok then all of a sudden not. I did check the old coils and the primary wire ohms were as per the manual but the secondary coils were only around 12k^, this (and the spliced HT leads) is the reason I thought they might be faulty. I tested the new coils and got the same reading as the existing coils so I have to assume (I know, dangerous to assume) this must be correct and maybe the old coils were ok. Is it unusual that both coils may have failed at exactly the same time. and by simply swapping the HT leads the bike now runs fine.
Anyway I'm off to check the signal generator against your pdf I'll come back with any news.

 

[rphillips]

I've had a bunch of bikes, both old & new. I've never had a coil problem. Changed out a set once before I found the coils weren't the problem. I just couldn't imagine 2 going bad at once.

 

[Gorminrider]

Thanks Gormanrider
I do have a manual but it is a first edition that only shows the points system so I was a bit in the dark re the signal generator. The pdf download is just what I need. I'll have a look at that and check against what I have.
Just thinking aloud, and this might be a complete herring. Is it possible the magnet in the signal generator has changed polarity somehow. The only reason I say this is the bike was running ok then all of a sudden not. I did check the old coils and the primary wire ohms were as per the manual but the secondary coils were only around 12k^, this (and the spliced HT leads) is the reason I thought they might be faulty. I tested the new coils and got the same reading as the existing coils so I have to assume (I know, dangerous to assume) this must be correct and maybe the old coils were ok. Is it unusual that both coils may have failed at exactly the same time. and by simply swapping the HT leads the bike now runs fine.
Anyway I'm off to check the signal generator against your pdf I'll come back with any news.

ah, good. It's the manual to have! ...per

Is it possible the magnet in the signal generator has changed polarity somehow

No*. The "signal generators" are just that-generators! they make a lttle pulse of current when the little magnet on the shaft goes by each one at just the right time...The pulse tells the Black Box "TCI" to "interrupt" the primary coil's circuit so the magnetic field that was around the winding collapses through the secondary winding ... This collapse creates the spark...and it's the same way your phone charger works from house sockets, it's a "transformer". But instead of having Alternating Current like your house, the bike makes the transformation happen when the piston wants a spark.

rphillips,and I agree. I haven't had a coil fail on a Suzuki but where the leads come out of the coils can be iffy or the insulation on the wire.. if mistreated. Also the "resistor" plug caps"( about 5-7 kiloohm each) If you "found" a problem with the old coils secondary resistance, it can be these caps, not the coil. Most people jam a prod into the cap to test the coil and that's perfectly fine if both coils are the same and seem good. but a "wrong" reading is more likely to be the cap, not the coil. Caps are ok to take off the high tension lead if you want to know only about the coil...the wire can be pushed back on.

* I say "no" but actually their's a residual field built up in the steel laminations the tiny coils are wound on...if you're super curious you can look up the effect of "reversing coil polarity" which is pretty arcane and usually just makes sparks weaker for awhile (I think) but there's really no way on these signal coils.

 

[David450]

Thank you all for your replies and the link to the manual.
I'll close this out now. When I swap the HT leads the bike runs fine (just don't quite understand why).
Just for your info the pic below show the wires from the signal sender (first time I have looked in here) and the ones going to the coil. As far as I can tell they are as per the manual.
The final one is my bike on the Devils staircase Just north of the Llyn Brianne reservoir, Mid Wales, UK

​​

 

[David450]

Coil connection showing White and orange to the left and Black and orange to the right. Male and female connections reversed so you cant mix them up

 

[David450]

Devils staircase Just north of the Llyn Brianne reservoir, Mid Wales, UK

 

[Gorminrider]

Cool! I have a GSX (8valve) 400E (same but no fairing) so I know you're having fun!-I love mine...The narrow 18" tires go round curves with less effort than the -aah- "croozer-style" T's and L's with their differing wheel sizes...the seat can be a pain on inner thighs on longer rides though...a chafe point there somewhere?

it's still incredibly odd. You might try swapping the signal generators' leads...

 

[David450]

Thanks
Yes I have looked at the 400 and they are exactly the same to look at with the exception of the motor. Did the 8 valve head keep the performance the same as the 450 4 valve?
I'm in the UK and just fitted Avon road rider2 tyres, they are great. I would recommend them if you can get hold of them.
When I bought the bike it had been sitting along time so I have been slowly replacing rubber seals as and when it develops a new leak.
It had pod filters but the jetting was standard so I installed a stock airbox, this improved the running but I still had a flat spot when rolling on the throttle at around 4000rpm. I must have spent 3 years off and on messing around with the carb settings but making very little progress.
Then a cheap 450L parts bike came on the market, it had carbs and a stock exhaust so I grabbed it. The exhausts needed a hanger plate making up, the S fixes above and the L fixes below.
Long storey short the flat spot has gone I was gobsmacked. I shouldn't have been really there is a stamp on the exhaust stating that it has been designed specifically for the bike and should not be tampered with. Just goes to show those 1980's Japanese engineers knew what they were doing.
Its just a looks thing but the originals follow the shape of the motor and fit in a lot more snugly than the Motad 2 into 1 that was on it. Pic with new exhaust below.
When I bought it the screen wasn't on it, I was loaded up and just about to leave when the owner said "oh by the way there is a goofy looking screen but I doubt you will want it" lucky or what?

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[Gorminrider]

That fairing is what member pete might call 'Unobtainium"- you should look pete up here. Many posts and pix.. he was much into the 450E..https://www.thegsresources.com/_foru...-gs450-refresh
I'm not sure how the 450 and Gsx400 compare to ride..but I expect yours is as smooth...one of the few twins i can mount a camera on and it isn't at jerky and vibrating- but I can say it's got a little more on the go than my Honda 450, though I'm not a tuner and my bikes are probably all a little soggy...Your valve-train is simpler with shims and more likeable than my doubled screw tappets..it's easy to make a bit too much "tippy-tappy" with 8 valve settings on 2 cylinders!

Tip-the manual will having you removing the exhaust to remove the rear axle. it's much easier to remove the shocks and lift the swing arm up with a plank to get at the axle...by the way, looks like you have the original shocks? They are ok. If they seem harsh, adjust one notch tighter not softer.

 

[Gorminrider]

you may have the cool fairing, but I have the cool rear rack! I've never seen another like it, except member pete made one..

 

[David450]

That rack looks handy I have to bungie my bag on the seat and it gets a bit tight if the bag is too full.
Yes when I was fitting it I thought it was a bit odd the centre of the exhaust is right in line with the axle, thanks for the tip.
I find this bike is plenty fast enough, put it this way I would be upgrading the brakes before I upgraded the power. Do you find it is very easy to lock up the back drum?
It is just a personal thing but I prefer to accept the bike for what is and just enjoy riding it. if I wanted more power and better handling I think I would just buy a SV650. it would probably work out cheaper, give a better result and keep this bike intact. Not saying anyone shouldn't modify bikes it's just not what I would do.
Yours is red so probably quicker anyway ;-)

 

[Gorminrider]

No, it's not easy to lock the rear but it's good enough to hold the bike on a hill etc. Of course it's worth going over all of it, even to painting the bits that rust-that brake-plate strut and the swing-arm itself (plus the insides of the steel fenders!) are places unseen that get beat by the road dirt and rust quickly.

 

[grcamna2]

Thanks
Yes I have looked at the 400 and they are exactly the same to look at with the exception of the motor. Did the 8 valve head keep the performance the same as the 450 4 valve?
I'm in the UK and just fitted Avon road rider2 tyres, they are great. I would recommend them if you can get hold of them.
When I bought the bike it had been sitting along time so I have been slowly replacing rubber seals as and when it develops a new leak.
It had pod filters but the jetting was standard so I installed a stock airbox, this improved the running but I still had a flat spot when rolling on the throttle at around 4000rpm. I must have spent 3 years off and on messing around with the carb settings but making very little progress.
Then a cheap 450L parts bike came on the market, it had carbs and a stock exhaust so I grabbed it. The exhausts needed a hanger plate making up, the S fixes above and the L fixes below.
Long storey short the flat spot has gone I was gobsmacked. I shouldn't have been really there is a stamp on the exhaust stating that it has been designed specifically for the bike and should not be tampered with. Just goes to show those 1980's Japanese engineers knew what they were doing.
Its just a looks thing but the originals follow the shape of the motor and fit in a lot more snugly than the Motad 2 into 1 that was on it. Pic with new exhaust below.
When I bought it the screen wasn't on it, I was loaded up and just about to leave when the owner said "oh by the way there is a goofy looking screen but I doubt you will want it" lucky or what?

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I Like your 'S' model !!
I have a 1981' GS450E silver with blue stripes.
I purchased it in very poor cosmetic condition,missing parts.. although the fuel tank and tail section are very nice; it's slowly coming together quite well.
The bike was purchased from a man who purchased it at a charity auction in the Bay Area which has a heavy salt-air environment;the orig. owner had it there 43 years and it has lots of rust.
I want to spray some 2K clear coat on the front fender which I fully prepped/painted;I park it w/ a light cover in my parking space at my apartment building and the weather has been cold and stormy all Winter/Spring so far here and as soon as it warms-up I will finish it.