#1 no spark coil to sparkplug

[mason79]

here i go again, in my euphoria in getting the beast to run, i didn't notice #1 cylinider was not getting spark; man it's fast on 3 cylinders.

i looked at tech tips more thoroughly this time, but found nothing, and i need help again thanks in advance.

apparently i found a new invoice from a yamaha dealer that the previous owner bought and had installed a new coil and caps, $140.00 for parts alone, sad indeed.

and in this invoice it states coil 1&4 and i guess for you Xsessive Techicians, i can guess this mean one coil runs 1 and 4 and the other runs 2 and 3, correct me if i am wrong.

i first notice a cold header pipe and pulled the plug no spark, all others has them, can i eliminate the coil as the culprit?

i'm sure you will know the diagnostic procedure, i'm a better with wrenches than electrons, so where do i start, i would be indebted.

thanks again.

[TopCatGr58]

3 outa 4 ain't too bad!

Hey Mason,

Yes one coil fires both 1 and 4, the other 2 and 3. IF #4 is warm, then most likely the coil is working. Could be as simple as removing the cap, check the wire end for corrosion, clip back 1/4" from it, ALSO check the cap with ohmeter, should be about 5K, if much more than that, then it could be bad and should be replaced, otherwise stick cap back on.

How did you check #1 for spark? IF it was with the #1 plug, it could have gotten gas fouled, and might not show a true spark. Try a new plug. ALso you can swap plug wires 1 with 4, they both fire at the same time, and run it and see if #1 warms up and if #4 stays cool!? IF so, then plug lead/cap for #1 that is NOW on #4 is bad. IF 4 gets warm, and 1 stays cool, check plug for presence of gas, wet=no spark, dry=no fuel!?

That should get you further along!
T.C.

[mason79]

thanks topcat,

i was polishing the chrome today and the sensation of vintage era shape and design and the top qualty material felt through my fingers was awesome, i'm keeping this baby forever, my first bike was a 78 rd 400 maxed out by gary from spec II, this bike is the motherlode of all thing2 yamaha, the first 4 clylinder, not too shabby.

so polishing was for today and the daylight is gone, the mechanical stuff maybe tue,

btw, i didn't pull the plug, i pulled the plug wire, thanks i;ll look at the plug, can i get them at autozone?

[TopCatGr58]

I've not had much luck finding plug caps(NGK) at local auto store, NAPA might be better, but MikesXS, Dennis Kirk I know have them, might be other places as well?

Yeah, if you thought 3 cylinders was awesome, just wait till it's truly hitting on all fours....SHAZAAAM!!! It'll be love/lust at first throttle twist!

IF you were talking about getting a new spark plug, there's a tech tip on spark plugs and what other brands and models you can use!
T.C.

[mason79]

i haven't been able to get to the bike to try anything, but i want to find out since looking at some of the secondary wiring, 2 and 3 the insulation is cracking and that can't be good.

i will need new wires or a coil if i don't want to attemped it myself, forget the coils, on the other hand if i'm going through the trouble, i like the accel 140403 remedie.

so to better round out my knowledge:

1) why is a 3 ohm impedance from accel not optimal for the 79f as a 1.5 ohm would be? is it because it would overload the ignition unit? with this put at risk the longevity of the ignition unit?

2) on stock plug caps, why is it we need it to show any resistance, is this used to filter noise?

3) do all caps have resistance?

4) if i decice to put in wires instead of coils, and i leave resistor caps off and use rubber boots instead and get resister plugs as i have read in the tech tips, is this a viable alternative?

5)what is the function of solid core vs. other types, am i retsricted to one type?

any comment would help?

thanks

[DiverRay]

Here are some answers for you:
1) why is a 3 ohm impedance from accel not optimal for the 79f as a 1.5 ohm would be? is it because it would overload the ignition unit? with this put at risk the longevity of the ignition unit?
1) the ignition system is set up with a "balast resistor", so the 1.5 Ohm will work, and the 3 Ohm won't, unless you bypass the resistor.
2) on stock plug caps, why is it we need it to show any resistance, is this used to filter noise?
2) Yes, the 5K ohm caps are for reducing noise.
3) do all caps have resistance?
3) No, but you should use the resistance caps.
4) if i decice to put in wires instead of coils, and i leave resistor caps off and use rubber boots instead and get resister plugs as i have read in the tech tips, is this a viable alternative?
4) It helps, but I run the caps and resistance plugs, with no problems.
5)what is the function of solid core vs. other types, am i retsricted to one type?
The solid core wire is noisy, the "carbon core" wires act like the resistance caps. The solid core will stand up to the vibrations from the engine much better than a carbon core wire.

Just my $0.02
Ray

[mason79]

that's worth 200 bucks. thanks

come on now, only our bikes are cheap, but xsive wisedom to keep it alive.

do you have any, comments on the aftermarket coils?

[TopCatGr58]

Accel Shockingly overpriced!?

Hey Mason,

Check out this thread:Replacement Coil alternative

Should be worth $144 worth of savings on those $200.00 coils! Also, MikesXs has the solid core wires, and plug caps, both resistor and NON resistor!!
T.C.

[mason79]

thanks tiger

[mason79]

okay back to the spark thing and thanks in advance for any help

swapped plug wires 1 to 4 and 4 to 1, ONE still not firing, but 4 is, when i pull the wire off the spark plug , there is sometimes an intermitent weak spark i can feel in my hand, but the engine rpm does not go down and the pipe is cold, plug is wet from gas, swap #4 spark plug and it gets fouled the same.

coils:
measured impedance on primary side, my vom reads only a 1k setting so the 15 ohms requirement for the primary side shows zero, so far not clear

secondary side measures 20,000 ohms with caps and 15k without

all cap in tolerance at 5k good.

could this be pick up coil wires? please assist and thanks again

[DiverRay]

mason79
You have a carb problem with #1!!
The coil isn't firing because it's easier to go through the #4 plug.
I would check the float level on all carbs, and "bench test" the valve and seat for the fuel inlet. The "Tech Tips" on the left, or a search of the threads will give you plenty of information on this.
You may also want to do a compression test, if you have a gauge. Just to make sure you don't have any "hidden" problems.
Ray

[mason79]

i checked the compression cold, i can't warm up the bike, # 1 does not run

#1 150
#2 175
#3 175
#4 132

i didnt put oil in to see if it's rings, maybe this weekend

looks ugly

4 runs 1 does not

i pulled out the plug for one and there is a weak spark when it's out of the cylinder.

is it because maybe ( i will check) the float for 1 is set too high or leaking and rendering a boarderline clylinder no to run?

any help would be appriciated.thanks in advance

[turbopete]

i checked the compression cold, i can't warm up the bike, # 1 does not run

#1 150
#2 175
#3 175
#4 132

i didnt put oil in to see if it's rings, maybe this weekend

looks ugly

Those figures aren't enough to stop it firing on one cylinder. I'd say they were pretty good for a bike of that age.

[mason79]

so turbopete,

what do those compression numbers mean?

how far off can they be and do you think i have to deal with internals anytime soon if i can get it running right at all?

[John]

Did you hold the throttle open when you were cranking it over? A couple of the numbers seemed kinda high. The norm for these engines is around 140 and the cylinders should be within 10% of each other.