I've read up a bunch on the '85 and hotter cams and since I have 2 1985s built three months apart, might be in a position to help settle the debate.
Bike 1 is new to me, service records up to 1992 (10k miles on odometer since), originally bought in California and built in August 1984. It has the engine fuel vent opening at the front of the top of the engine that has been capped in the past. 49 state emission sticker. It's not yet up and running again.

Bike 2 I have been riding for 2 years, unknown history and also purchased in California. Also 49 state sticker. It has no vent opening (a flat spot where the opening protrudes on the other bike but was built later, November 1984.

I understand that the vent is supposed to be a way to tell if the bike has the hotter cams but it's interesting that the later bike is the one without a vent. Maybe this all means nothing, but I figured some here would be interested.

I'm hoping the cams are marked somehow, but if not what's the best way to measure? Is it the size of lobes or their orientation?
Also wondering if it's ok that the vent is capped on the one with it, and if so what can I use to replace the old cap on it now?

Does one of your motos have a camshaft cover with this screw (red arrow) in it?

My 84 RT has engine date 32/84 [August 1984], has no engineering screws on the cam cover and has a vacuum sensor, bought at 36,000 mils.

Nt 83 RS has engine date 48/83, has the engineering screws on the cam cover and has a vacuum sensor, bought at 29,000 mils.

No comparison, the 83 RS is miles quicker than any of the others including my K1100LT. It also consistently uses less fuel.

All tip top in terms of injectors etc etc.

Negative, Laitch. Are those also identifiers?
Olaf, are the engineering screws the same as what’s in the picture?

clappy wrote:Negative, Laitch. Are those also identifiers?
Olaf, are the engineering screws the same as what’s in the picture?

Thats them, one for each cam.

The concensus here is that the vacuum sensor does nothing, it's supposed to advance the ignition by I think 6 degrees. My 92 K100LT did not have a vacuum sensor and the RT the day I got it impressed me, much more lively but I put that to the LT having 105,000 miles and the RT having the hot cams..then along came the RS.

The strange thing though, couple of weeks ago I paid a visit to BSK Speedworks. Ben Kingham there builds race K engines and I asked him about it. He figured the cams are the same, no change in overlap or valve timing. I had learnt the profile changed but no change in part no. Sadly the man that gave me all that info, ex main dealer service tech for Ks, passed on November 9th.

In case anyone asks, I have spares so the RT did get the vacuum sensor replaced, changed FICU and ICU, made no difference.

So you agree that vacuum sensor has little or no effect?
I guess BSK would have a good idea since they alter cams.

92KK 84WW Olaf wrote:Ben Kingham there builds race K engines and I asked him about it. He figured the cams are the same, no change in overlap or valve timing. I had learnt the profile changed but no change in part no.

Here's is an extract from Max BMW's parts fiche.

clappy wrote:So you agree that vacuum sensor has little or no effect?
I guess BSK would have a good idea since they alter cams.

Not quit.

The difference is substantial and has to be attributed to

a: Vacuum sensor having an effect [as far as I can see this is the only difference between the 84RT and the 92K100LT]
b: Different camshaft profiles [as far as I can see this is the only difference between the 83K100RS and the 84 K100RT]
c: Combination of both.

Mine are all european spec.

Laitch I hadn’t come across those screws before so if that’s the marker then chances are they both have the CA cams. I’ll figure out how to measure them and check the earlier built in in the coming week.

I thought I might be in a spot to shed some light but I guess there’s more to the story I wasn’t aware of.

The cams that were used from when the K100s were sold in North America had only one difference and that was that the inlet cam opened 20° later than the European cams. In effect what this does is slightly reduce low end torque (I doubt that most riders wouls even notice the difference) and effectively lower the compression ratio at low speeds and idle so the combustion temperature is not quite as hot and therefore the pollutant nitrogen oxides are a bit lower so as to get past the CA emission regs.

Well then it might be time to start looking into BSK cams or have a local shop do some work to one set. I want the 2nd bike to be faster!

There's a cheaper way than that, depending on your definition of 'faster'. Fit a set of K1100 throttlebodies and advance the timing by six degrees (4mm). Doesn't do too much for the top end but adds a big chunk of get-up-and-go in the middle where you really need it. At one point I had two RS'; one modded and one not. The unmodded one was a lot slower off the line.

Just read up on that and will be doing the TB mod asap. Thanks, Dai.
One thing isn't clear yet, but I'm hoping the k1100 TBs work with the k100 manifolds and boots, since I already have new ones. Do you remember?

Yes they do.

Well I bought some euro cams with parts numbers matching the screenshot from Laitch. Will see how they compare to my other bike when I get everything back together!