17-6810 XS Performance 3 ohm Dual Coil to XR700 on RD350

[holypiston]

I'm crossing my fingers. I have a Crane Cams XR700 ignition on a 1975 RD350. The ignition is basically a points to electronic trigger ignition requiring a 3 ohm coil, which this is #17-6810 (PAMCO /XS Performance 3 ohm Dual Coil).

I'm wondering if i screwed the pooch. I've connected the positive and negative to the coil, but had to creatively tie wrap the coil to the frame. The tank won't go on w/ the coil bolted in place..

I started and ran the bike for about 5 minutes. Since i did not bolt the coil to ground by the holes in the bar running through the center, I am going to run a ground wire through one of the holes and locate the other to the frame.

I am hoping I didn't fry this coil, since i have run a dual spark CB750 coil not hard mounted to the frame for quite awhile.

So, is the coil ok and all I have to do is ground the coil or did i fry it?

The bike seems to be running ok, and i think if i truly fried it, it would stop working right?

 

[Travis]

I no expert on these things, but I've read that you can damage coils and they don't always just completely fry. Something about them working for a little while until they get hot.

 

[holypiston]

I no expert on these things, but I've read that you can damage coils and they don't always just completely fry. Something about them working for a little while until they get hot.

Thanks Travis.

I'm hoping Pamco Pete? comes on and tells me, no problem, you ran it on a cold bike for 5 minutes at idle...just make sure you run that wire to ground.

So, I'm holding out to see what Pete has to say. It's freshly mounted and only ran it on the stand for about 3-5 minutes to make sure it was running, BUT the coil bar through the center of the coil was not grounded to frame...didn't think this would be a problem, but I've heard on the 2strokeworld forum that both terminals on the Pamco are (+) and the ground bar is the ground.

I just want to get positive confirmation that I didn't do irreparable damage (yet)..

 

[holypiston]

ok, did some searching and found out that Pamco Pete said the center bar is mainly for heat dissipation and the reasoning for hard mounting firmly...heat xfer, I'm guessing.

so it looks like i didn't fry the coil. I've run a CB750 coil for about a year w/o hard mounting it to frame and haven't had any adverse problems.

It's just that the spacing is so tight in there, that i had no choice BUT to soft mount it in a particular position (coil holes facing right cylinder under main spine running down to the seat.

I'm thinking i shouldn't have any problems since it is very similar to the CB750 stock Dual spark coil.

What do you think Pete? any creative solutions...I'm not quite sure the ground clamps would work on an RD350...i know these are for XS650, but just saying...

 

[pamcopete]

holypiston,

Right. There is no need to ground the coil core for electrical purposes. The coil is "floating" and has no internal reference to ground.

However, it is advisable to mount the coil firmly to the frame in some way for heat dissipation. I'm assuming that your points / electronic setup has a 90 degree dwell angle, that's the portion of the rotation of the cam or crank, whichever has the points, that the coil is turned on.

I am not familiar with the bike in question, but if it is a four cylinder with two coils and two sets of points, like a CB750, then a 90 degree Dwell angle means the coil is only on for 25% of the time and there should not be a problem with overheating.

If the bike is a 2 cylinder, using just one coil in wasted spark system for both cylinders, then the coil will be on for 2 X 90 degrees = 180 degree = 180/360 = 50% of the time, and that will be a problem if you do not mount the coil firmly to the frame for heat dissipation.

But, you say that you have done this with a coil from a CB750 and had no problem. The CB750 coil is 4.5 Ohms whereas the 17-6810 coil is 3.5 Ohms, so it is going to run a little hotter. It all depends on how you ride the bike. If you typically ride for less than an hour at a time, then I think you will be fine.

 

[holypiston]

Thanks Pete,

It is a twin cylinder 2 stroke. I just measured the coil I pulled out (not your coil!) w/ my Fluke 16 multi-meter. It measures 2.5 ohms. Now i'm wondering if it is a mikesxs coil replacement (it's covered in all black with pos/neg spade terminals and the bars plastic coated at each end). I'm sure that your coil at 3.5 ohms can easily handle it, since this one has been working well for 3 to 4 hour rides..maybe i get some kind of good airflow under the tank.

here's a pic of the XR700 iggy converted to the 1975 RD350 yamaha.

Should I back cut the plate and make the pie hole bigger? I got this mod from Mark H. in S.C? N.C.? he's done it to his two strokes...when the leading edge sees the other trigger it fires. HE did recommend making the pie hole bigger, maybe i need to do this? This one is mated to an OLD Allison /Crane optical triggerr (XR700) and holes tapped to original points plate (pictured and looks the same as the current trigger before Crane went out of business) and mounted, the control box (in front of the airbox loosely mounted under the tank rear) is the newer Crane Cams brain w/ LED for timing on the side.

The XR700 requires a minimum of 3 ohms, so it looks like i'll be better off w/ your coil vice the 2.5 ohm coil i was running. It is wasted spark, so both cylinders fire at the same time like a banshee motor. So if i read your statement correctly, the 2.5 ohm coil i was running would run hotter than your 3.5 ohm coil. That is good to hear.. I think I'll be alright. Should keep the control box cooler too, if I read the instructions to the car iggy correctly.


The control box looks like this (this picture taken off my RD400 two stroke)

 

[Tz250racer]

Kevin?.The holed piston you mean.

 

[holypiston]

Ciao! Luciano. Unfortunately, yes.

Looks Like i should be ok. you can tell it fires stronger at idle. that 2.5 ohm coil was pretty pathetic with pro-x pistons and rings, but it was ok with the dykes rings and OEM pistons (probably because the dykes rings seal better at low rpm than any other)...until seized it playing w/ the needles.

 

[Tz250racer]

Kev this a 4 stroke forum.It is propably a good idea to post where we usualy do.Don't you think so?.

 

[XSLeo]

Can you make an aluminum plate to mount the coil to. Then mount the plate to the frame, zip ties even. The plate will help dissipate The heat.

 

[holypiston]

Well it looks like the clamps i bought won't work...the space is not there like the XS. But it will mount w/ tie wraps and the tank will fit on nice (as pictured). I'll run it like this and I am pretty confident that if a 2.5 ohm coil can survive, this 3.5 should survive nicely.

 

[holypiston]

Hi Leo,

This is the easiest and coolest (literally) way to mount it. Working great and no problems.

This is taken from the top of the bike w/ the tank off...it's mounted on the left downtube in front of the cylinder. i had to richen the needles one clip and turn the airscrews on the carb in 1/8th turn.