My 72' 750 commando

andrew hester · May 23, 2011

Hey guys, this is my first big project. I'm 17 and got my '72 750 from my Grandma when Grandpa died. It had just sat in their garage for over 30 years. I have basically restored everything (hopefully) but I'm still having a bit of trouble. I've gotten a couple of good starts and few minute runs out of it, but after a while it will start to go in and out, no matter where I hold the throttle, and then eventually die. There is a small leak in the right banjo joint on the carb. The floats aren't punctured and i re-jettted both carbs and gave them a good cleaning before i got the whole bike running. I've also messed with the pilot screw and throttle stop screw while it's running to try and "tune" it in. I'm stumped because it could be a number of things but what i guessed most likely was the carbs flooding... but if the floats are working properly then it really shouldn't. Not really sure what to do next. Any idea's and tips would be great! Thanks

bluto · May 23, 2011

go through everything in this Amal rebuild and tuning guide and the carbs will be right... http://www.jba.bc.ca/Bushmans Carb Tuning.html
also fix the leak and make SURE to have a fire extinguisher handy while tuning, my own bike had sticky floats (FWIW they were new but slightly too wide...fixed that with a file) when I bought it and caught fire when a bowl overflowed while starting

DogT · May 23, 2011

Hey, 17, cool, you're only 50 years younger than I am.

You need to check out the carbs thoroughly. Here. http://www.jba.bc.ca/Bushmans%20Carb%20 ... html#FLOAT There's a couple of pages there check them out. Make sure your petcocks are not leaking (risk of fire and leaking fuel into the engine), you can check the float levels with the float bowls off the bike on a flat piece of metal. Here leaky-float-bowl-seat-t8025.html?hilit=float%20bowls Make sure the needle valves are sealing and not flooding the carbs. The carbs are very simple and 1 1/2 turn out on the pilot should get you in the ball park. Adjusting the float height will make a difference in how rich/lean it is, but not extremely critical. If you have a fiberglass tank, make sure it is not melting and putting crap in the carbs and engine from the ethanol. Avgas is an option on the f/g tanks. Do a search on the carbs on forum, plenty of info here. Let us know how it's going.'

Dave
69S

andrew hester · May 23, 2011

I was also wondering about the amal stay up float. Do they help/ do anything different at all?? and yes the tank is fiberglass but i use ethanol-free and have fuel filters in the fuel lines :mrgreen: and I realize that the stock setting is 1 1/2 turns but my engine is bored out and jetted slightly larger so would that effect where the setting would be put?

swooshdave · May 23, 2011

andrew hester said:
I was also wondering about the amal stay up float. Do they help/ do anything different at all?? and yes the tank is fiberglass but i use ethanol-free and have fuel filters in the fuel lines :mrgreen: and I realize that the stock setting is 1 1/2 turns but my engine is bored out and jetted slightly larger so would that effect where the setting would be put?

Stay up floats are great.

How much is "bored out" and why the bigger jets?

DogT · May 23, 2011

The stay up floats don't do anything different if the old ones are working. Fuel filters will not help with the f/g dissolving in the tank. There's a lot to jetting, if you have a non-stock setup. We may need lots more info, like everything about the carbs through the exhaust. I'm not the expert, I'm sure many will be here to help, I just know about the basic settings for stock bikes. Are you sure you are not starving the fuel supply somehow, check the flow of the petcocks. There are many issues and you will have to go through them all by the time you're done.

Is fuel dripping out the bowls as you try to keep it going? What do the plugs look like after running?

Don't start a fire.

Dave
69S

caddy chris · May 23, 2011

Clean or replace your spark plugs. Run it till it dies and pull the plugs immediatly. Snap photos and post them, or tell us what they look like. Sounds to me like you're really rich. Starts good when cold, but dies after it warms up.

AltaNorton · May 23, 2011

Hey Andrew,
Welcome to the forum. Great to hear that there is another young guy with a Norton. I'm 16 and am restoring a '72 750 as well. Unfortunately since this is my first taste of motorcycling I can't help you too much with your question. I do know that those links that DogT and bluto posted are very helpful. I'm not quite at the stage in my restoration to get her fired up yet...hopefully by the time I'm 17

I'll tell you this much though; there is no way I'd be as far along as I am without this forum, it's a great asset and I'm sure you'll find it very helpful.

Matt

andrew hester · May 24, 2011

I have pulled the plugs after a run and I knew i was running rich because they were black on top. but even after tweaking it, it still happened.

Hobot · May 24, 2011

You yongsters don't yet know the ancient accepted wisdom's of British Iron codified in motto's, like
Clean The Sludge Trap... or
If it smells like a fuel issue, sounds like a fuel issue, acts like fuel issue go straight to the electrics first!

Sure sounds like low voltage issue if it has electro brain ignition or a bad sticking over advanced mechanical advance unit if its got contact breakers. Its also possible as engine warms and softens a power or earth wire insulation, the broken copper stands inside can separate enough to cause harsh running onset.

Another motto - always suspect zinc oxide crust in the pilot jet and stick a wire in there to ream out or #16 drill bit. No solvent will touch that crust. Bath and title cleaners can but also eats carb metal if used more than a few minutes w/o flushing away.

Crank it up in the dark and see if anything illuminates the problem.

Carbonfibre · May 24, 2011

Almost certainly blockages in one or both carbs............you can find out for sure if this is the problem by removing the air filter, and spraying fuel into the intakes while the bikes running. If it keeps running when you spray the fuel in then you can be sure your problem is carb related. In some cases its possible to clean out blockages, but sometimes this is impossible and the carbs will need to be replaced.

Seeley920 · May 24, 2011

Are you sure the chokes are off?? they work the opposite to how you might think.....slack in the cable means they are on, you will foul your plugs after a couple of minutes.

rvich · May 24, 2011

Check the kill switch, check for air leaks at the manifolds, check the kill switch again...and yes make sure those chokes are open when you tighten the cable!

Post some photos too! Did your grandfather buy the bike new? Tell us more!

Russ

Hungry J0e · May 24, 2011

andrew hester said:
Hey guys, this is my first big project. I'm 17 and got my '72 750 from my Grandma when Grandpa died. It had just sat in their garage for over 30 years. I have basically restored everything (hopefully) but I'm still having a bit of trouble. I've gotten a couple of good starts and few minute runs out of it, but after a while it will start to go in and out, no matter where I hold the throttle, and then eventually die. There is a small leak in the right banjo joint on the carb. The floats aren't punctured and i re-jettted both carbs and gave them a good cleaning before i got the whole bike running. I've also messed with the pilot screw and throttle stop screw while it's running to try and "tune" it in. I'm stumped because it could be a number of things but what i guessed most likely was the carbs flooding... but if the floats are working properly then it really shouldn't. Not really sure what to do next. Any idea's and tips would be great! Thanks

Andrew -

Regarding leak from the banjo bolt: I also had this issue. I fitted an O ring around the base of each banjo and it cured the leak. Snug it up and you'll be good to go. Don't overtighten or you'll comprimise the O ring and be back where you started. O ring will prevent the banjo from loosening up as well.

Not sure where you live, but if you're stateside Harbor Freight sells O-ring kits that have a zillion O rings of varying sizes for around $8. You can also buy similar Viton O ring kits for $15-$20 if that's you're style.

http://www.harborfreight.com/catalogsea ... t?q=o+ring

Cheers,

- HJ

rvich · May 24, 2011

Speaking of where you live, you should include it in your profile. You never know you might have a Norton expert right down the street that would be willing to help puzzle things out.

If you live in Alaska, let me know, I will be right over. I'm not an expert but you gotta take what you can get when you live around here.

Russ

gtsun · May 24, 2011

Wow 17! I think I was a little older when I got my first bike, a Norton P11/G15 hodge podge parts bike but it ran! You seem light years ahead of what I knew at that age. (still don't know much more) are you sure your plugs and wires & caps are good? Clean ALL ground connections etc. Sometimes just fiddling with it you'll find the problem. Good luck and be greatful you found this forum. We had nothing like it years ago & it was a lot harder to learn all the little tricks back then.

andrew hester · May 24, 2011

Thanks guys for all the feedback. I know it's not the contacts i replaced it with the electrical boyer triple spark. also is the choke what that little lever thing is up on the handlebars? cause i've never figured out what it is! I will also try and figure out my profile deal

caddy chris · May 24, 2011

Yes the lever thingie.... take off the air cleaner and look in the Carbs and hold open the throttle. Now move the lever the opposite it is now. Look in there again. See the rectangular thing that moves up and down? Those work to cut down airflow and richen the mix for cold starts. Closed when cold then open when warmed up. I never use mine and alot of ppl get rid of them.

DogT · May 24, 2011

The choke (air control) might look like this or it may be separate from the brake lever. On the Amal carbs, tight cable means choke off, loose cable means choke on, kind of counter intuitive.

Dave
69S

My 72' 750 commando

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