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Discussion Starter #1
I've almost got my 86 /88 750 back in one piece but I can't see where to mount the one coil for cylinders 1 and 4.I see the studs behind the head tube for one coil. The bike was totally dissasembled when I got it so I don't know where it was mounted before. Any input?

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They both mount the same way, beside each other, up where you are describing. There should be two places, on left and right of frame, behind headstock.

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1990 GSXR750, reasonably modded
 

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if i remember correctly, the threaded holes for each top coil mount bolt are on the frame spars behind the steering head.

if you look at that triangularized section of the frame (on both sides), there should be a threaded hole on each forwards spar - that's the top coil mount. the lower coil mounts are further in and towards the bike's centerline, they're raised towers cast into the bracing behind the steering head, fairly close to the valve cover.

stock, there were metal spacers for all of the mounts, so the mounting bolts are fairly long.


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Discussion Starter #4
This frame is an 86, there is one pair of bosses cast into the back of the steering head. Those are the only two. I've been all over this bike and can't find any holes or provision for the second coil. The way the wires are bent from time looks like it goes near the other coil. This frame has had extensive mods done to it especially up in the front. I'm thinkin someone cut out the bosses. #1 cylinder is on the clutch side of the motor right ?

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[This message has been edited by OldSchoolGixxer (edited 04-05-2001).]
 

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Discussion Starter #5
Nevermind I just found em. They've been cut off to make room for some bracing and a tube for a front race stand. Thanx Jeff you were close. Both sets of bosses are cast into the back of the steering head and the coils bolt in pointing diagonally down toward each other. The nubs that were my uppper mounts are behind that tube that I mentioned. A little more fabrication , no prob!

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you're right.

it's funny, cuz when i got a set of dyna coils, they wouldn't go in the stock locations (because they're much bigger than the stock coils and the mounting holes on the dynas didn't line up with the mounts on the bike).

so i looked around for a suitable location to mount the coils, and i ended up mounting them sideways, with the top mount of each dyna bolted to a threaded hole in the left and right front frame spars as i mentioned.

that's why i thought the stock top mounts were on the frame spar - my memory got a bit corrupted cuz i THOUGHT (wrongly of course) that i had mounted the top of those dynas to the stock top coil mount locations.

now i'm just trying to remember exactly what was originally bolted to those front frame spars.



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Discussion Starter #7
What wires did you use with the Dyna's? If I relocate these coils the facory wires are gonna be too short and they aren't removable. I may be gettin the Dyna's myself and I was also considering that Dyna 2000 sportbike ignition.

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the dynas take regular off the shelf automotive spark plug wires. the factory wires are removable - if you pull up the clips that are holding them to the coil bodies, you can pull them out. but they won't go into the dynas cuz the dynas use a different connection method on the coil end.

if you go for the dynas, what you can do is buy a set of automotive spark plug wires (you can go for straight copper core wires, since the emi suppressors are in the spark plug boots, assuming you're using the 86-87 coils and not later model ones which relied on resistor type spark plugs to suppress electromagnetic interference), then use the spark plug boots from the original coils. you need to kinda 'screw' the boots off the old wires, and screw them into the new ones.

the other end of the automotive wires should have a metal connector (that would normally go into the distributor cap of a car - if you can picture the kind of connector i'm talking about), that you insert into the dyna coils, and they click right in.


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If you are removing the stock airbox for KN's like I have you can mount 4 RG RD 350 individual coils in a horizontal flat pack above the KN's and they will fit between the frame rails, which is what I have done and run copper core non suppression silicone wire . Just wire two coils in series and the stock ign box is happy.

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86 totally non stock
 

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not to argue with your results, but i'm just surprised that wiring the coils in series would work - you'd essentially be halving the voltage going into the primary winding of each coil.

of course, hooking two coils up in parallel would draw twice the current from the ecu, and that would likely be a lot worse.


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Jeff I had the same problems when I put some dyna coils on my 921100,they wouldn't bolt straight in,we got a 1/2 inch piece of aluminium put that between the 2 top holes,put 2 new holes in that to mount the top then used the 2 original bottom holes.
it was a bit of a mission.

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Discussion Starter #12
Will they fit under the AirTech Yoshimura Tornado Sprint Tank and will they be compatible with the Dyna Ignition that I plan to use. It's probably been 10 years since this bikes seen an air box. Also when you wire them in series does that still supply both coils with the 12 volts that they require to create 35,000 volts like the Dyna's do?

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[This message has been edited by OldSchoolGixxer (edited 04-08-2001).]
 

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well, that's what i was kinda getting at - wiring two coils (for example, 1 for cylinder 1 and the other for cylinder 4) in series WILL drop the voltage to each primary down to 6 volts each. wiring them up in parallel is the only way to maintain the full voltage through both - but it draws twice the current from the ecu through the primary (signal) lines.

if doug's setup runs fine, then i guess running the coils at half voltage works, at least on his particular bike.

i'd probably stick with the dual output coils.


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the coils are wired in series so that the primary resistance is not less than 3.5 ohms which is what the stock ecu wants to see as a load, if you wire the coils in parrallel then the reistance drops to half of 1.75 ohms which is about .9 ohms then what happens is the current draw doubles and that is what blows the ecu as far as the voltage it does NOT change it still remains at 13.5 volts and I can asure you it puts out a lot of juice I would not recommend grabbing the ignition lead. The main advantages are the coil saturation is better, there is less heat buildup in the coils, aftermarket leads are easy to install and they are a lot cheaper than dyna coils etc. As for how they mount I will try for a pic soon.

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86 totally non stock
 

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just to be shure put a fluke volt meter on the primary side of the coils and there is no voltage drop between the plus supply side and the negative side or at least it is less than a tenth of a volt difference. I believe the reason is because the coil is not a dc resistnce it is an impedance.

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86 totally non stock
 

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i did a little more research (my prior knowledge of how coils worked was very fuzzy at best), and what i found corroborates with the results you've obtained.

while wiring two coils in series does halve the voltage that goes to the primary windings in each coil, this has no effect on the actual spark voltage induced by the secondary windings - as this induced voltage only depends on the ratio of secondary winding turns to primary winding turns.

i had previously thought (incorrectly), that perhaps the reduced input voltage to the primaries may have a detrimental effect on the secondary spark voltage, but this isn't the case.


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consulted my electronics genius buddy who says that the drop in voltage should be there but only under dynamic load not under static load so that means that I should be able to get a better spark than I currently have which is pretty good the way it is. That leaves me two choices I could try wiring the coils in parrallel which would probably smoke the drive transisters in the ecu or go to 6volt coils in series or to 12 volt coils in parrallel but with a higher primary side resistance so that in parrallel the load would be around 3 to 3 1/2 ohms seems to me that when I was seaching through the box of coils there where 12 volt coils with the higher resistanceI will let you know how it turns out in the mean time it does work significatly better than the stock crap. The other thought I had was n MSD box which if it the same as the MSD 6 for cars gives you switched 450 volts on the primary side but it is high frequncey so that it does not smoke the coils this is also how they get the spark to last for 20 degrees of crank rotation. Ah more mods. doug


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86 totally non stock
 

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what did he mean by 'dynamic load' and 'static load'?

the 6 volt coils would be a neat idea - forgot that they had even existed.


the higher resistance 12's in parallel would also work without frying the ecu, but are there 12 volters with 6 ohm primaries?


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static load would be with ign on but the bike not running dynamic load would be with the engine running as the ecu is under load then.

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86 totally non stock
 

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jeff something else that you might find interesting is by wiring the 2 coils in series one of the coils is referenced 6volts above ground on the high voltage side as 1 of the primary terminals is also the return for the high voltage. Thinking for me the hot setup is parrallel wire the coils and then put a load resister in series?

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86 totally non stock
 
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