Ignition Module

[skids]

I would like to know how you pulled that one off! Didn't the 81 engine have later type advancer behind the timing plate (ie not centrifugal thing)? Did your 80 have the 4RO box?

Originally posted by Crazcnuk
If you are asking whether the 79 pickup will work with the 80 TCI box, I think it depends on which one each of these had. As long as you have both the same seires, ie; 2H7 or 4R0 then your all set.

I am running an 81 engine in my 80, and I didn't have to change anything.

[sailor202]

Driver Ray, thanks,
Brother named Max is sending a known good pick-up coil and matching ignition module from a 79 to my mechanic friend Jim. I hope this solves the problem.

Sailor

[sailor202]

t3rmin -- Good question, when I was test riding the bike I really didn't pay attention to the rpm/mph question. Can you elaborate on the vent tube situation? Where,how,what is the "correct" or "ideal"?

[DiverRay]

sailor202,
I did think about one more thing yesterday. I ride a STANDARD, and yours is a SPECIAL. The fuel delivery is DIFFERENT on the two bikes. Have Jim try it with the fuel set to PRIME, NOT ON or RESERVE. IF you can run it with no problem, then the octy probably has problems. There are tips on dumping the octy, and shutting the fuel off after every ride. The other thing it could be is a pinched fuel line. have him look at the line routing with the tank on, and watch as he lifts or lowers the tank.

[t3rmin]

Originally posted by sailor202
t3rmin -- Good question, when I was test riding the bike I really didn't pay attention to the rpm/mph question. Can you elaborate on the vent tube situation? Where,how,what is the "correct" or "ideal"?

I'd have another ride ASAP and pay attention a little more closely. It's fairly important whether this is correlated with MPH or throttle/RPM.

Air turbulence around the bowl vent tubes causes (I think) negative or positive pressure into the bowls which either floods or starves the motor. It can be fairly dramatic and will be most noticeable at speeds of 50+mph or any time there's a strong crosswind. The symptom I usually see is an intermittent drop-out while cruising in a high gear, which you can generally "power past" with more throttle. Won't usually show up scooting around town, just on the highway.

I'm not sure what the factory routing is for these bikes, but you want those tubes up under the seat or sidecovers so they're protected from wind. And no kinks!

[DiverRay]

The vent tubes SHOULD be plugged into the stock airbox! The '78 and '79 had fittings on the airbox for the vent tubes. the '80 and up vented the carbs through the intake bell on the carb itself, so the fittings on the airbox did NOT have the holes in them.

[jurgenkoppen]

Timing advance unit

Thanks to all for the input.
AlanB yes, they do look the same , except for the silly bolts in the 80, which I will positively replace with regular bolts should I need to remove that unit. I just did buy the 79 timing advance unit, to keep both engines complete.

sailor202 You might want to check in the tech tips regarding the pick up wiring wearing out where the vaccum advancer keeps moving them,
if you did not already. It describes a fix for a problem similar to yours.

One more question:
I read in another thread that there is such a thing as installing the advance mechanism upside down, or 180 degree out. A mistake one can make easily, according to the tread writer. Anybody understand what that is about, and how to make sure it is installed right?
Thanks, Jürgen

[Jerry]

Yes, there are only the two types.

Actually, there are 3.

The '81 models went to a TCI system that does not use a mechanical advance, so their black box will not work on earlier 11s. Then in '82 Yamaha came out with the XJ version using YICS, TCI box starts with 10M, which is different than the '81 TCI.

So, as I understand it, there are 3 TCI boxes

2H7 - '78, '79, '80 models
4RO - '81 models
10M - '82 XJ

2H7 for mechanical advance models, 4RO for '81 models, 10M for the XJ. Both the 4RO and 10M units use a "boost sensor" module that takes vacuum from the engine and converts it to an electrical signal that the TCI uses to compute the timing.

It may be possible to adapt a 4RO or 10M to an earlier 11 but it would be a lot of work and, becuase there are differences in the built-in timing curve of the 2 later TCI boxes, the results may be disappointing. I would stick with the correct TCI for the year of your engine.

By the way, I would not recommend swapping the 4RO and 10M boxes with each other. The different timing curves seem to lead to poor performance although the engines will start and run. Comes up mostly with XJ folks looking for a replacement TCI and they end up trying the 4RO. Results are not satisfactory.

[Crazcnuk]

I have no idea, but since mine runs fine, I assume they have matched series of p/u and TCI.

The engine I put in came from an 81 Special, and mine is an 80 standard. I changed nothing in the ignition system except spark plugs and boots.

One of these days, I'll get around to checking

[Jerry]

I could be wrong; do all of the '81s have solid state pickups? If not then the TCI boxes could interchange. However I was under the distinct impression that at least some of the '81s had no mechanical advance and the TCI box would not interchange without the use of the 'pressure sensor' also found in the XJ.


Wouldn't be the first time I've stuck my foot in my mouth...

[TopCatGr58]

Hey Cnuck and Jerry,

The 81's(4RO) don't have mech. advance parts, that timing curve is built into the TCI. But the 81 does use the mechanical vacuum advance/retard unit. ONLY the XJ uses an electronic boost vacuum sensor to signal the TCI.

As the FAQ's point out, the vacuum advance is also a retarding unit. The extra timing advance is used during cruising low load rpms where the fuel is a bit leaner, and the extra advance allows better fuel mileage. However, the cent. timing curve that is built into the 81 TCI is quite adequate for the power range of running, and a recent member installed one on his XJ and it's working just fine without any input from the vacuum boost sensor!

Cnuck, did you swap the timing components on the side of the engine when you put the 81 ENGINE into your machine, or did you keep the pickup/vacuum advance assembly, and just plug them into your TCI system? IF so, then you are missing/loosing out on the power band due to NO cent. Advance, however you are getting vacuum advancing from the vacuum module which is probably why you are able to still drive it!

Just checked the Cycle Mag stats, idle advance is 10 degrees, then should be 26 degrees from full CENT. advance(standard) for total of 36 degrees=max POWER advance amount! But the vacuum advance provides another 16 degrees for total of 52 degrees during cruising low load amount, but when you crack the throttle, the vacuum drops, timing retards back to the powerful 36 degrees when at 5200 rpm or above!

So...IF using 81 engine with just vacuum advance, you are getting 10 degrees static, plus 16 degrees max vacuum advance=26 degrees total, 10 degrees LESS than optimal power amount of 36 degrees, and will be LESS when you are getting on the throttle. So..Cnuck.....you may be able to find some more POWER in your machine IF you put the 80 timing components onto your 81 engine!

Hey Jurgen,

I don't remember it being the ADVANCE unit being installed 180 degrees out, but putting the pickup coils onto the timing plate 180 degrees out, yes!
T.C.

[Crazcnuk]

Kewl, I will have to check it out.

Andreas also mentioned this as I had a few problems when I first got it started.

It may explain why the bike is a little more sluggish than I think it should be, and why my fuel economy is lower than others are reporting.

As for performance, rolling start, full throttle Derwat's 79SF just barely beats my fully decked standard. You're telling me I should be able to kick his butt? :^)

[andreashweiss]

I am pretty sure I pulled that motor out of a 81 special. I remember it because it was strange to me that it had a 2h7 TCI unit. The owner I got the bike from said it was the stock box. Bike was made in Jan 81 and Yamaha must have used the 2h7 units they had leftover from 80.I would bet the pickup coil assembly in that motor is 2h7 not 4ro. That is why your 2h7 tci box works on that motor.I agree most 81 bikes had the 4ro.andreas

[Jerry]

.

a recent member installed one on his XJ and it's working just fine without any input from the vacuum boost sensor!

Well, I'm still a bit confused. Running the 4RO box on an XJ eliminates any advance/retard adjustment to the timing curve. This has to have an effect on performance up to the 5200RPM mark.

The XJ spec for the timing curve is:

15 degree Mark
5 degree at 1100 RPM
36 degree at 5500 RPM

But the vacuum advance provides another 16 degrees for total of 52 degrees during cruising low load amount, but when you crack the throttle, the vacuum drops, timing retards back to the powerful 36 degrees when at 5200 rpm or above!

At lower RPM running the the 4RO on the XJ would retard the timing by 16 degrees. Are you saying this 16 degree difference has no effect?

It appears to me that for anything under 5200RPM the 4RO box on the XJ with no vacuum sensor or mechanical advance would cause the ignition to be running in a retarded condition, resulting in a loss of power. This loss would be more noticable in the lower RPM ranges where the effect of an advance/retard mechanism is greatest.

My conclusion is that the 4RO box would make a good spare for the XJ, but I would run one only until I could find an OEM 10M replacement.

[TopCatGr58]

Originally posted by Jerry .
Well, I'm still a bit confused. Running the 4RO box on an XJ eliminates any advance/retard adjustment to the timing curve. This has to have an effect on performance up to the 5200RPM mark.

The XJ spec for the timing curve is:

15 degree Mark
5 degree at 1100 RPM
36 degree at 5500 RPM


At lower RPM running the the 4RO on the XJ would retard the timing by 16 degrees. Are you saying this 16 degree difference has no effect?

It appears to me that for anything under 5200RPM the 4RO box on the XJ with no vacuum sensor or mechanical advance would cause the ignition to be running in a retarded condition, resulting in a loss of power. This loss would be more noticable in the lower RPM ranges where the effect of an advance/retard mechanism is greatest.

My conclusion is that the 4RO box would make a good spare for the XJ, but I would run one only until I could find an OEM 10M replacement.

Hey Jerry,
The 4RO box does have a built in timing curve, the centrifugal curve since those parts are not on the timing plate, so it does calculate the 26 degrees of cent. advance(incrementally dependent on engine rpm)added to the initial 10degrees up to the 5200 rpm point.

The vacuum advance adds the additional 16 degrees when not under heavy engine load/lean operation, but when the throttle is cracked open the vacuum pot retards it back to the more powerful ~36 degrees IF at 5200 rpm, or slightly less if less than 5200 rpm.

SO...using the 4RO box without the vacuum advance/boost sensor,used on the XJ DOES provide the Cent. Adv. curve and most of the power curve, just not the extreme advanced vacuum timing advance of the low load/throttle cruising rpm range.

What's interesting is the amount of advance that the XJ specs you stated provide...only max 36 degrees, or perhaps that also doesn't account for any additional advance due to the vacuum boost sensor??

Now the above advance values I'm basing on the specs provided from the Cycle Mag article which was about the 78E's mechanical advances. I have not actually measured the 4RO's advance amounts, I'm "assuming" that they are similar to the mechanical units values since it's still the same engine, although Yamaha may have changed them due to EPA requirements?? But I do know that the 4RO box incorporated the Cent. Adv. Curve into it since that engine doesn't have Cent. Adv. parts on the timing plate/assembly, just vacuum advance.

It would be nice to be able to put the bike on a DYNO type machine to provide controlled resistance for the rear wheel to measure the amount of advance that is provided under lesser rpms and modest throttle input vs. WOT!?

Hey CrazCnuck, IF what Andreas says is true, then your engine may be alright, can only tell IF you take the timing cover off and check for the existence of the mech. adv. parts! IF they are there, then it's either an 80 engine using the 2H7 system. BUT if it says 4RO on the engine cases, but has the cent. adv. parts, then the PO must have swapped them from the 2H7 frame/engine that the 4RO engine was put into!

But if it doesn't have the cent. adv. parts, then YES you are not getting much timing advance since the vacuum advance only provides a max of 16 degrees, so your missing 20 degrees worth of adv. at 5200 rpm!
T.C.