Okay, what could I have done?

[81xsproject]

Well, I uninstalled the MSD and hooked up the original coils and iggy and to my mild surprise I am still not getting the performance I had before I took this MSD project on. So somewhere in the process, I screwed something up. My mid range is really lacking, although overall running seems fine. So, here is what I did.

Initially I thought I would be able to run with just the MSD iggy and loose the stock box so long as I went to a mech advance. So, by the time I figured out that I had to use the MSD with the stock iggy, I had already pulled the stock timing mechanism and replaced it with the older mechanical unit. When I re-installed the timing rotor, I gapped the PUC's to .006". The stock unit on the 81 also has no adjustability for timing, so I am pretty sure I didn't screw that up. I didn't make any other changes during the swap. Timing light test show that the timing does advance as the rpm goes up and it still hauls A above 5k, so I imagine the timing advance is indeed working fine.

So, what the hell!?

One thing I did notice is that the timing rotor on the non-mech advance has a MUCH wider (~5-6mm wide vs. the ~2mm wide piece on the older mech units) piece that passes by and triggers the PUC. I can't find it in the Clymer, did the 81 perhaps require a different PUC gap...? I am at a total loss.....

[Dragon Tamer]

To be perfectly honest with you, I do not have a lot of experience with the '81s. It does seem to me that it still would have to be a timing problem of some sort. Been searching my mind (instead of the search function) and cannot remember how the stock iggy box read the engine rpm to figure the advance. Is it possible that you still have one wire that is not hooked properly???

[TopCatGr58]

Hey Jessie,

Okay, you put the older Mech. Adv. parts on which has the cent. adv. AND the Vac. adv parts.! Now, you're still using the later model 81 TCI which has the Cent. Adv. timing curve programmed into it! SO..now with mech. cent. adv, AND the 81TCI, you are getting way too much timing advance down in the lower rpm!

Once you get to 5K range, you have reached the max adv, and so it runs just about as strong as before.

IF you have the 81 Timing parts, put them back on IF you are going to keep the 81 TCI, and you should then be back to the proper combination of vac. adv. with the electronically programmed cent. adv. of the TCI!
T.C.

[81xsproject]

no no no, TC. You misread the post. I put on the old mech assembly on and then removed it when I realized that I had to run the MSD WITH a stock box. I didn't have a 2H7 box, so I pulled the mech adv unit and put everything back to stock.

[TopCatGr58]

Okay, my bad!

Hmmmm, are you sure the vacuum advance mech is working properly? You say you checked the timing with the timing light, but was this at the lower rpms, or above 3K?

That's about all I can think of regarding the ig. system! Ohhh, just thought, did you REGAP your spark plugs closer together after removing the MSD ??

IS the timing plate rotating freely/easily?

T.C.

[81xsproject]

Yes, and yes. I put the plugs back to .035". I also tested that the diaphragm held suction and that everything moved nicely. That is what is crazy! All the equipment is the same, but it runs different.

[mro]

Don't think it is a timing problem but...
Did you check that the stationary pointer is set correctly?


mro

[81xsproject]

I didn't move it during the swaps, and the timing housing for the 81 doesn't allow for any timing adjustment anyway. Does anyone have a factory manual that would have the PUC gap for the 81?

[mro]

Does not say in the 81SH Supplementary Service Manual
5 degrees at 1,100 rpm
6 degrees at 1800 rpm +- 100
35 degrees at 3900 rpm +- 300

pick up coil resistance 720 ohm +- 20% at 68 degrees temp.
(the little "U" on timing plate is the firing range for @1 cylinder)


mro
BTW,
most likely pointer is good, but
did find one off several degrees on a standard I was working on

[randy]

PUC gap is .7mm

That's point seven millimeters.

[81xsproject]

.7mm...? Wow, that is .027". BIG difference. Maybe that is my issue. Not that I doubt it, but where did you get that number from, Randy. Maybe I should start looking for a factory manual to have for rare occasions like this.

[randy]

I got that from the Yamaha microfiche, in one of the more obscure pages entitled service data.It's on the Yamaha website.

Yeah, the TCI is just an amplifier. If the signal from the pickups is not strong (ie gap too wide), you may get misfires or no fire!

[81xsproject]

Well, that was it. THANK GOD!! I was out of ideas. Thanks to Randy for the tech data. My midrange is back and I am super stoked.

So, as an addendum to Driver Ray's tip about decreasing the PUC gap to .004, DO NOT DO IT ON 81's and later.

On the plus side now I get to re-try the MSD

[DiverRay]

Sorry Jesse, I guess I need to stick with the '78-'79 models. Those I DO know, as I ride mine ALL the time.

[81xsproject]

No prob at all, Ray. It was a really good learn and now we can cross one more thing off of the list of the few actual NEW question that get asked around here. So, what oil and tires should I run?