Timing difference between 79SF & 81H

[willwatsonfl]

Hello everyone,

I'm rather new to this forum, but so far it looks better than other bike forums I've been on. Great Job!

I just bought a 79 XS1100SF to replace my 84 Honda VF700C. The serial # on the engine makes me believe that the motor is from a 81 XS1100H. This bike didnt run to well so I'm going completely through it.

My question is about the timing. I know the timing settings are different between the standard 79 models and the Special, but are they much different from the 81H? Also, am I going to run into more problems with the charging system, the ignition system, or any other oddball thing?

I have searched most of this site and come up with a few things to check, but if anyone knows more detailed information, the help would be greatful.

[John]

What is the S/N of the frame, and engine? If the engine is an 81, and the frame is a 79, then the ignition pieces will need to be swapped, as the 79 uses a different ignition module than the 81. Charging systems are the same. I don't have my manual with me, so I can't comment on the timing. I'm sure that somebody will chime in with the timing specs. I have a 78 engine in my 81 SH right now. I had to swap the pick up coils from the old 81 engine onto the 78 engine, but that was easy. I just set the timing by ear, only cuz I don't have a working timing light.

[willwatsonfl]

Frame # 3H3-012233 and Motor # 4R1-001328. If the Ignition module needs to be changed, would it still be able to plug into the 79 wiring harness?

[willwatsonfl]

Looking into this more, I found other threads that help. Lets see if I can get this straight. 78-80 had both centrifical and vacuum advance and used an ignition box 2H7-10. In 81 they got rid of the centrifical portion but kept the vacuum and used a ignition box 4R0-10.

Looking at mine, the ignition box does say 2H7-10, but on the timing plate in says 4R0-10. So in other words, I'm not getting the proper timing advancement.

Thanks John for pointing me in the right direction.

Can anyone confirm if this sounds correct?

[mro]

TCI part number for 1981 H, 4R0-82305-10-00
TCI part number for 1979 SF, 2H7-82305-10-00

Could cause "issues"

cool site for Yamaha part brake down and part numbers
http://www.yamaha-motor.com/sport/parts/home.aspx



mro

[willwatsonfl]

Has anyone seen a 81 TCI on ebay lately or know any options to get one?

TCI part number for 1981 H, 4R0-82305-10-00

[andreashweiss]

Your other option might be to buy the 78/79 pickup coil assembly to replace the 81 stuff. Then the tci and pickup coils are correct, I have 78e coils and pickup coils used decent price andreashweiss@yahoo.com

[TopCatGr58]

Hey Will,

I meant to reply to your thread yesterday, but brainfarted!!

Your research was correct. You've got the 2H7 TCI and frame, but the 81 4RO/1(SH/H) engine and timing plate/vacuum advance on your engine.

The 4R0/1 TCI's are rather rare since they were only made during 1 year's production. The 2h7's are plentiful, and also easier to repair. Because the 2H7 engines are also more plentiful, it would be better to get the timing mechanisms for the 2H7 engine....the centrifugal advance, vacuum advance and appropriate timing plate.

Believe it or not, the PICKUP COILS are the same 2H7 series, it's just the other stuff that was changed!!!!

So...it'll probably be cheaper to get the Cent. Advance and complete timing assembly from Andreas....don't know if he would want to separate the PU Coils from it, or you might want to have them as a nice backup!?
T.C.

[willwatsonfl]

That is a good idea...I will send Andreas an email. Now it looks pretty simple to swap the ignition advance assembly, but do you know of any issues that might get in the way.

Also, If the TCI is the same for 78-80 and the pickup coil assemblies are the same too....Then why is the timing different for the 79 E & F (36deg) than the 79SF (31deg)? Is it because of cam profile or something else that differs on the Engines.... and if I put the 78E Assembly (that Andreas might have) wouldnt I still have to use the 81H timing settings?

Thanks for everyones help!!!

[TopCatGr58]

Hey Will,

Well, a quick review of the Clymer's shows that the 78 E &79 F used the same model carb, but the 79SF was a different model, even though all of the jets and needles are the same? In the 80-81 series, again there are different model carbs for the Standards vs. the Specials, AND the jet needles ARE different as well.

If you read the Cycle Mag review on this site, one of the things it talks about is the vacuum advance/retard unit, and how it makes the throttle response smoother cause under low throttle input, the timing is advanced a lot which provides for better fuel economy, but under load, the vacuum device actually retards the timing to the less advanced more powerful timing degree mark to better use the extra fuel during that function.

The STANDARDS are/were more intended for highway cruising, not that much throttle twisting, and so perhaps the more advanced timing to take advantage for better fuel economy? Whereas the Specials were more In Town sport cruisers with lots more stop and go type activity expected, and so the lesser advanced setting to provide a bit more overall power in the rpm range?

The engines for the same years are the same, so other than this speculation and conjecture, I can't find a reason why the timing differences?!

Finally, since you'll be using the 2H7 TCI and timing components, you'll want to use the 79 timing settings. The Different timing settings for the 81 were because the TCI controlled the cent. adv. portion electronically, and only used the vacuum advance/retard unit for that function.
T.C.

[willwatsonfl]

I feel like I just won the Lottery. After reading about the parts that needed to be changed...I started looking through the boxes of MISC parts I got with the bike. I found the Mechanical advance, the timing plate, and another vacuum advance. I looked through the Yamaha site to see if I was missing anything else...and I dont think I am. The shaft (that replaced the mechanical advance) had a wider pickup on it, but it almost looks like it was rubbing on the pickup coils. So I might need the pickup coils anyway.

So...If thats all there I hope I only have one more question...The "fixed" pointer isnt totally fixed. It is locked down with a screw and looks like it still has the "tamper proof glue" on it. If someone loosened and moved that pointer, Is there a way to set it back to the factory spot.

I think I explained that right.

[willwatsonfl]

Sorry...brain went to sleep about the pointer....TDC...Line up with T....All is good

[TopCatGr58]

Hey Will,

Great find! As for the timing pointer, you were right, they can get bent! So...use a long straw or pencil, piece of wood, and put it into the spark plug hole when you are closed to TDC, and then slowly rotate crank backwards and forwards until you "SEE" the straw stop rising and going back down, find the highest point in the rotation, and that is TRUE TDC, and then align your pointer with the "T" mark on the timing plate!!
T.C.