Modern Enhancements to 750 Combat

Status
Not open for further replies.
so what does identify this as a combat i was just saying what a combat spec should be , its obviously been modified with single carb and 850 style breather but as we know by the serial no they cant be 850 cases
 
chris plant said:
so what does identify this as a combat
Click to expand...

37 years after it left the factory....nothing can positively identify it as originally being built to Combat spec. as far as I know?

As any identifiable Combat parts including the cylinder head, carbs, etc. could have been fitted to a standard engine or vice versa?
 
Whipped the tank and head steady off and found the 'C'. So it's a Combat. Not sure if that's good or bad ;)

d
 
RedEvo said:
Whipped the tank and head steady off and found the 'C'. So it's a Combat. Not sure if that's good or bad
Click to expand...


Not necessarily a bad thing, but the Combats in their original 65 BHP :shock: form were rather overtuned and low geared, so tended to have short lives of they were ridden enthusiastically! Any that survive should at least have had FAG 'Superblend' main bearings fitted by now?

The Combat head gasket face was skimmed by .040" to increase the compression ratio up to 10:1, and Combats were supposed to be run on 100 (RON) octane fuel, however the factory in their wisdom didn't bother shortening the pushrods to match, which altered the rocker geometry slightly. Later on in 1972, the factory started to detune their stocks od Combat models because of all the warranty claims, thicker head gaskets were fitted to reduce the compression ratio back to more a sensible level, and with modern lower octane fuels available these days, reducing the compression ratio could be worth considering?

And how is Aboyne these days? As I haven't been there since the early '70s.
 
I've run my Combat both with and without the cylinder base decompression spacer. No problems either way. Used 93 octane fuel and Boyer MK III ignition.
 
JimC said:
I've run my Combat both with and without the cylinder base decompression spacer. No problems either way. Used 93 octane fuel and Boyer MK III ignition.
Click to expand...

But as you live in the US, then that "93 octane fuel" would be 93 MON or 93 PON octane, which is higher octane than 93 RON, as 100 octane RON = 91.5 MON = 95.8 PON (all approximate).

[Broken Link Removed]
 
That's as clear as mud, to me. I quit trying to figure out octane ratings when we went from ethyl and regular to the numerical ratings. I use the pump that says 93 on it. Yes, that's in the US.
 
L.A.B. said:
And how is Aboyne these days? As I haven't been there since the early '70s.
Click to expand...

Gods own country in my view. I'm from Barrow in Furness originally but I've been up here for almost 20 years. Can't wait to get the Command fettled, it's perfect Commando country (apart from the deer :shock: ).

Thanks for all the great advice. I've been 'degreasing' the bike today and sussing out a few things. I've discovered it's got MkIII Micro Digital ignition and I'm going to add a Boyer powerbox to this. Once I'd degreased several years of 'shed life' off it it's looking pretty good. Cosmetically I want to sort some stuff (chainguard, wheels, grab rail) and then over the winter I may take a look inside.

I've got another "did he really say that" question. What fuel should I use with the bike and should I be using some sort of additive?

cheers

d
 
RedEvo said:
I've discovered it's got MkIII Micro Digital ignition
Click to expand...

I think you have either got a Boyer "Micro Mk3" analogue (Black box) ignition, or a Boyer "Micro Digital" ignition (Red box) as I've never heard of a Boyer "MkIII Micro Digital"?

http://www.boyerbransden.com/products.html

RedEvo said:
What fuel should I use with the bike and should I be using some sort of additive?
Click to expand...

Lead replacement additives aren't really needed as the Norton valve seat material is quite hard enough to cope already apparently.
If your Commando is still running the Combat 10:1 compression ratio then you may need octane booster with regular unleaded petrol, or try to use higher octane if you can find it in your area?


RedEvo said:
it's perfect Commando country (apart from the deer :shock: ).
Click to expand...

And we have plenty of them in NE Norfolk as well!
 
L.A.B. said:
RedEvo said:
I've discovered it's got MkIII Micro Digital ignition
Click to expand...

I think you have either got a Boyer "Micro Mk3" analogue (Black box) ignition, or a Boyer "Micro Digital" ignition (Red box) as I've never heard of a Boyer "MkIII Micro Digital"?

http://www.boyerbransden.com/products.html
Click to expand...

OOps yes, Micro MkIII, black box. Someone was saying the Micro Digital would provide a closer match to the auto advance retard that came as standard as the Combat is sensitive to not having the right settings. I'm wondering about this because the last time I rode the bike I was very aware of pinking.

d
 
Hi Dave,

Your photo is definitely a combat engine - narrow space between the head lowest fin and cylinder top fin. It already has the breather modification that I did. That fixture on the back of the timing cover is the "combat breather", just moved from low on the left crankcase. Scratch my comment about not doing that mod...you already have it.

Combat heads have a "C" stamped in the center of the head under the head steady if at all (some had no stamp). Also nearly all 750 Commandos coming to the US with 201xxx were combats as we Americans had a need for speed. You Brits didn't get the good stuff right away as it was shipped to the where the money was. :D

David
 
RedEvo said:
I'm wondering about this because the last time I rode the bike I was very aware of pinking.
Click to expand...

That's probably a lot to do with running high (10:1?) compression with low octane fuel?

The Micro Digital advance could suit it better, but it's difficult to say. There are also more modern ignition systems available these days, such the digital Tri-Spark 'Classic Twin' and Pazon Sure Fire (analogue) and Smart Fire) digital systems, plus the new Boyer MkIV which I know nothing about so far.
 
illf8ed said:
Hi Dave,

Your photo is definitely a combat engine - narrow space between the head lowest fin and cylinder top fin. It already has the breather modification that I did. That fixture on the back of the timing cover is the "combat breather", just moved from low on the left crankcase. Scratch my comment about not doing that mod...you already have it.

Combat heads have a "C" stamped in the center of the head under the head steady if at all (some had no stamp). Also nearly all 750 Commandos coming to the US with 201xxx were combats as we Americans had a need for speed. You Brits didn't get the good stuff right away as it was shipped to the where the money was. :D

David
Click to expand...

Thanks for this. I found the 'C' today. Apparently the bike lived in California. It was brought back as a basket case and rebuilt a few years ago so that ties in with your thoughts about the 201xxx stuff. I bought the bike in 2003 but have hardly used it and it's been stored in a garage (with a short spell living outside!).

The grand fettling is now under way thanks in no small part to the great advice and expertise in this forum. I only hope over time I'll be able to contribute back!

d
 
L.A.B. said:
RedEvo said:
I'm wondering about this because the last time I rode the bike I was very aware of pinking.
Click to expand...

That's probably a lot to do with running high (10:1?) compression with low octane fuel?

The Micro Digital advance could suit it better, but it's difficult to say. There are also more modern ignition systems available these days, such the digital Tri-Spark 'Classic Twin' and Pazon Sure Fire (analogue) and Smart Fire) digital systems, plus the new Boyer MkIV which I know nothing about so far.
Click to expand...

Thanks again. Perhaps I'll get something to boost the fuel although it would make more sense to detune it to behave itself on normal fuel.

d
 
illf8ed said:
That fixture on the back of the timing cover is the "combat breather", just moved from low on the left crankcase.
Click to expand...

Although commonly refered to as the "Combat" breather, all '72-'73 750s had that breather, regardless of them being built to Combat specification,-or not.
 
Status
Not open for further replies.
Back
Top