mikuni carbs

I am new to the site and looking to solve a few unanswered questions. A couple summers ago I resurrected my dad's Norton commando. It is a 71' 750 drive train with most components being 71' too. Who knows what year the frame is, there was no id badge anywhere on it. The tank is from the 71' "S" type I think. Its the one year Norton attempted to make an off road bike that seemed to have failed miserably. I have made a few custom parts for it and some cosmetic alterations.

As it set when I took on the project it had a single 34mm mikuni carb conversion. It is what I have been running since it first came back to life. It cranks on the first kick just about every time (as long as I set the idle right and choke it) unless it hasn't wet sumped. Anyway, it runs strong and is reliable. But I have heard other people talking about having 36mm mikunis and I was wondering if a 34mm would affect the performance at all? Also, not that my goal is to a wheelie, but I have heard of it done and mine sure wouldn't with the current setup. It just isn't that strong when you first roll on the throttle. Could this be due to the carb setup, or is it a matter of compression and the right cam?
I am also running a battery eliminator, I love the simplicity.

My hunch is that the original amals would preform better. Is that the case? I am not so worried about ease of tuning either, I like a good challenge thats why I chose a Norton for my first bike/ project.

I am new to this, but learn quickly. Any advice is appreciated.

There has been a recent post on the very subject.

mikuni-t4868.html

Normally a 34 would pull just a bit better than a 36 down low. A smaller opening moving air faster. So yes, you like simple but you have made a compromise with your electrical system that makes it weaker down low dependent on the alternator to spin up, just add a good battery for a short run and see how the grunt comes back.

The tank is from the 71' "S" type I think.

Click to expand...

The 'S' was not available in 1971. Besides, the tank is the same for the 'S' and later Roadsters. If it is the small 2 3/4 gallon tank it could have come trom the 'SS' , a relatively rare model only offered in 1971. The 'SS' tank is the same as that on the Hi-rider.

Both the 'S' and 'SS' models were never meant for off-road use and were cosmetic exercises only. They didn't even come with an offroad tread tire! The closest thing to an offroad 750 that Norton built was a P11.

I have to agree with Norbsa48503, the Norton charging system was marginal with a battery. Without it is asking a lot. A battery does not add much complexity to the system, and a sealed battery needs little maintenance.

Another item to check is the auto advance mechanism. Since you are not running a battery you must still be using points and the AA could be stuck and not allowing the ignition to advance properly.

thanks for the advice. I will try the battery and see how that works out. As far as the AA unit, I timed it with a stobe when I first got it running. I know for a fact that it is working correctly.

As for the tank, it is the same as the high rider. Thanks for the clarification on the use of the "SS" model, it being cosmetic makes more sense.

does anyone know how much advance the 750 can take with premium fuel with a octane addative simulating 99 octane fuel? Currently its set to the factory specs outlined in the manual

you can try to advance the timing just a twitch, if you get any "popping" on deceleration then you are too advanced
also, if you any significant kicking back on the kick starter, another sign you are a little too advanced

in time, and with a little more money to spend, get an electronic ignition like a boyer or rita or tri spark
and forget about points wearing and mechanical advance "issues", just set it and forget it, bulletproof