1979 Special with Unknown MNS Motor Questions

[79xs1100s]

Hi All!

I am pleased to say I have finally installed a running motor to my '79 Special after I blew the original engine last July. I aquired the motor from a guy who thought a running Midnight Special was a great candidate for an OCC style custom chopper, which was ultimately never finished.

My problem is that I do not know the year of the motor and I think this is causing me timing woes.

The ICM is standard to the '79 Special,
The Coils are new 3ohm Dynatek with the resistor bypass
Vacuum advance is original to the MNS motor
Carbs were rebuilt for the '79 with Kerker and K&N round ovals

Could someone cue me in on how to identify the year of the motor without any of the other parts to the bike?

in closing, it does start and run, but has no strong pull through the RPM range like it did prior to the motor swap. It feels like a timing issue so I and trying to start with what year the engine is and make my next moves based off of that.


Thanks for the help everyone, I'm happy to be back in the XS11 Saddle!

-Mark

[Ranger_xs1100]

Vin

The first 3 digits of the VIN number on the motor will tell you what year it is.

4H3 = 1980

4W1 = 1981

[BA80]

If the engine is a 4R0 there's no mechanical advance under pick up coil plate. It's easily changed, just put the advance unit off an 80 engine on there.

Your 79 has different cams therefore a different timing curve and won't work with the MNS engine because it will be either an 80 or an 81.

[79xs1100s]

Thanks for the replies so fast!

Would it behoove me to "convert" this motor to a '79 spec? I still have the '79 engine and only removed it because of a compression issue, the cams would be fine from that engine.

[BA80]

It would take some experimenting and research to know because I'm not certain anyone has ever tried it.

The thing that I would be worried about is the valves hitting each other. The 79 cams have a much longer duration and the 80 - 81 heads have larger intake valves and the angle towards each other in the combustion chamber. They may not be able to get out of each others way.

[79xs1100s]

Ahh,

So the actual head itself is different too, Damn. I suppose since the Vac and Mechanical advance is likely from an 80, If I just install the corresponding TCI to my harness, it should get me to at least an '80 Spec system as far as I understand it.

I believe I have TCI (3) boxes for a 79, 80, and 81 so I can just plug the correct on in later and see the result.

[BA80]

79 and 80 are the same TCI, the 81 is all by itself. There has been some discussion about that exact thing just recently here........ http://www.xs11.com/forum/showthread.php?t=45878

[79xs1100s]

Thanks Again,

I was reading that thread which helped a lot.

I'm starting to think the Motor is an 81 if the 79 & 80 tci's are the same and the timing is still off. I will determine this when I get home and go from there.

[BA80]

I'm starting to think the Motor is an 81

What are the first 3 characters of the number stamped in the case above the clutch cover on the right side?

[79xs1100s]

I'll check that as soon as I get home. Thanks Greg!

[79xs1100s]

4W1 so that makes it an "81" MNS motor. Thankfully I still have a 4RO tci. Should that get it back to square?

[BA80]

4W1 so that makes it an "81" MNS motor. Thankfully I still have a 4RO tci. Should that get it back to square?

It theory.

[Dbshea]

4W1 so that makes it an "81" MNS motor. Thankfully I still have a 4RO tci. Should that get it back to square?

You do it first! I'm not ready to install mine yet, so let me know how it works out.

[79xs1100s]

You do it first! I'm not ready to install mine yet, so let me know how it works out.

Plugged in the 4RO and it's a raped ape again! I figure if the Z4RO ever craps out, I have a mecanical Tim Adv from an '80 Parts moto I can convert in to run the (2) 2H7 I have on the shelf now.

Thanks for all the guidance everyone

[Dbshea]

Plugged in the 4RO and it's a raped ape again! I figure if the Z4RO ever craps out, I have a mecanical Tim Adv from an '80 Parts moto I can convert in to run the (2) 2H7 I have on the shelf now.

Thanks for all the guidance everyone

Good to hear! I know you're running 3ohm dyna coils, but did you do anything different to accommodate the 4R0? I've bypassed the ballast resistor (which may or may not actually be necessary as I don't believe the 4r0 harness has any provision for it) and swapped to 81 coils.