Still won't run...

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Apr 15, 2004
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...for more than a couple of minutes. I put my cleaned-out, un-stuck amals back on the bike tonight and tried it out. Tickled the carbs and it started 2nd kick. Ran well for a couple of mins then stalled. Wouldn't start without tickling again. So I re-tickled and it started right up and did the same thing.

It certainly seems like it's starving for gas. So I disconnected the fuel line and measured the flow from my nice new BAP petcocks. They seem to be clogging up just like the cheap chinese ones did. I collected 100cc of gas in 15 secs from one and about 80cc in 15 secs from the other. That's not much, the gas just trickles out, but it seems like it should be enough to keep the engine running at low rpm with no load. Could it be the low flow doesn't produce enough fuel pressure to make the float valves open? I'm just guessing but that's about all I can think of. The float assemblies are squeaky clean now and I really don't think they're sticking. But I suppose that's possible too. Opinions welcome!

Debby, ready to put a parts bike for sale on ebay


You don't mention the choke. Even with tickling (flooding) the choke should be about half-way on a cold engine.
Are the screens on your petcocks picking up any debris? If, they are clean, you should be getting plenty of gas. Pull the plug on the bottom of the float bowl, you should get a good idea of how much gas is actually in the carb.
Don't give up yet!
Well, just another possibility.

You say it runs if you give it a tickle at the carbs again so.....
Is there any chance that the floats are getting caught on the edge of the fuel bowl gasket & only filling up when you force them down by tickling ?

As others have said before, things like this can be difficult to diagnose from afar.

Keep at it, you will sort it out, otherwise I am chasing some 750 barrells. :D
Won't run

Hi Debbie,

When a Commando is causing an unsolvable problem, they can be a real pain. It happens to all of us. Just walk away and come back much later.

Low pressure from the fuel lines won't effect the carb float bowls, they work off gravity. It really sounds like the floats are hanging up. The floats can get trapped by the bowl gasket. I would take one carb off and shake it up and down. If it doesn't rattle the float probably is stuck.

Before you do this, you might try tapping lightly on the bowl with a screw driver handle...just might free up the float.

My '72 has been running for 7 years after a complete restoration with very few problems. The Boyer caused some grief, but I took Dave Commeau's advise and replaced it with a Lucas RITA...much better.
Tank full of dried varnish?

I just restarted a '72 that had sat for years. It probably had a 1/3
of tank in it that slowly evaporated. Every time I cleaned the carbs
and it would run for a few seconds. Each time I checked the
carbs they had varnish deposits. I took the tank off , filled it with a combo
of carb cleaner and gasoline, and shook ithe heck out of it.
I then dumped the contents out by turning the tank upside down.
Lots of varnish debris. Cleaned the carbs AGAIN and it now runs fine.
Hope this helps.
Hi Debbie,

Before you sell your bike on e-bay, try the following:

Make sure your gas cap is vented!

If your gas cap is vented and you continue to have the same symptoms, check to see if you have a fuel delivery problem by removing the carb drain plugs imediately after the bike stalls. If scant fuel comes out of each bowl, you have either a float problem or plugged petcock filters.

Remove the petcocks and inspect the filter socks. If they are plugged with gunk, clean the tank and petcocks.

If the petcocks are OK, check your float height.

With the float bowl upside down with foat and needle installed, the top edge of the float should be level with the top edge of the float bowl.

Let us know what happens.

with the float bowl upside down and my thumbs holding the spindle in place, the top of the floats do hang down a bit - I'd say 2mm or so - below the top of the float bowl. Could that contribute to the problem? They've been like that since day one though and I haven't had this problem until just a few weeks ago when it suddenly developed. I installed some new brake shoes in the pathetic front brake and thought I'd try a test ride to see if they helped. The bike had other ideas though and hasn't run since. Hmm, maybe I should put the old brake shoes back in...


Good to see you still have your sense of humour :D

Remember the basics that an engine needs,
compression, fuel & spark.

You did mention earlier that you did some drilling into your carbys ????
Is this area of your "fuel" requirement all OK ?

Just another thought to throw in the ring.

Sometimes I just threaten to sell mine & they behave properly :D

Your float level, if anything, sounds a bit on the rich side, so it does not appear to be your problem.

Did you check the gas cap vent? Start the bike and run it with the cap open slighlty and if it doesn't stall, you have a plugged gas cap vent.

What about the petcock filters, are they clear?

I went over to the Very Detached Garage after work today to try a few things. I removed a petcock - fuel screen was fine. Couldn't get it apart so I just put it back in. Fuel level in the tank was pretty low so I bought some more gas. That helped the fuel flow through the petcock but had no effect on the stalling problem. Neither did running with the gas cap open.

The next time it stalled out I quickly shut off the gas and removed a float bowl (these don't have drain plugs). Was full of gas just like normal. So I dumped the gas, hooked up the fuel line and turned on the tap holding the float bowl in my hand. It filled up and shut off just like it's supposed to.

So I don't know, it's the unsolvable problem. The last time the bike ran normally was July 5 (I've been keeping a maintenance log). Maybe it will never run again. Years ago I had a Ducati 250 single that died a similar death. One day it decided it wasn't going to start. My dad, my brother and I checked everything we could think of. Everything seemed normal yet the bike never ran again. This seems very similar. Anyone wanna buy a parts bike?


Most things are usually simple & u curse yourself after u find the problem.

I suggest you get some one with some years of norton experience.

My bet is they will find the fault within 30 minutes.

Let em find it for you, then buy em a beer or 3........

U will probably learn a new thing about nortons also.


Are you sure you're not making this whole thing up in order to give us something to think about and discuss on the forum? If not, you've really stumped the panel.

Can you keep the engine running at higher RPMs? What do your spark plugs look like? If they are sooty (great name for a black cat) perhaps you have a peculiar electrical problem. Condensors can act strangely when they are faulty, but I assume you've replaced these.

Are the carburetors set up with the slides, needle position, jets, etc. as per factory recommendations for a 750 Commando.

How much do you want for this bike with mystery ailments?


The plugs do look rather black and sooty. Funny you should mention that as a cat name, the local shelter has a black smoke Persian up for adoption and that's his name! Cute kitty.

I've thought about replacing the condensers but haven't tried it yet. It looks like the hunt has turned back to the electrical side after ruling out all the fuel issues.

I guess the last resort will be to haul it down to denver, hand it over with a blank check to the brit bike shop, and let them have a go at it.

Or I could just sell it. Would be a great bike to put on display, looks very nice. Lots of good parts too. PM me if interested!

Debby, How did you fill in the blank off holes you drilled out? As I told you earlyer I have seen some very strange problems come from the blocking of these holes. The simtoms seem to indicate that your piliot curcit is running out of gas If you used old cut off air screws, are they blocking the pathway? New carb bodies and brass slides could be in your future. norbsa
I plugged the holes with old air screws, cut down to remove all the threaded portion. I used some nice tight-fitting orings from the local NAPA car parts place. I wouldn't think they'd be plugging the passageway because that's much deeper, down at the end of what would be the threaded area.

It does seem like a fuel related issue. If it's an electrical problem why would the bike restart so easily when I flood the carbs? It's very strange.


What does PM (private mail) mean?

Yes, I too believe it's still a fuel problem. It's as if the enigne is stalling because it has run out of fuel. That's why I thought the vent in the gas cap may have been plugged. And it's also why I suggested to check the fuel level in the carburetors imediately after the bike stalls. I was positive you would find near-dry bowls, but you proved these two hypothesis' wrong.

Also, I thought momentarily that you had a too-rich condition and once the bike was warm it would stall from excess fuel. But this logic is counter to your restarting process of tickling the carburetors.

Your riding season is about gone, I would suppose. So, perhaps you can hunker down during those long cold winter months and get to really know your Norton; it helps to have a pal around for consultation, how about Sooty?



PM = private message. You can send one by clicking on the PM button at the bottom of my post.

Our riding season probably has a couple of months left. This summer has been much cooler and wetter than the past few years so who knows? We might be getting snow in September this year. The snow generally doesn't last long though, so you can ride year round if you choose the right days. I doubt if I'll get the Norton running reliably this season though. Guess I'll have to go back to riding my Ducati :)

Sooty is a cutie! Maybe he could help me work on the bike. I'm moving next weekend so I have to wait until that's done but I thought I'd go have a visit with him if he's still available. Persians are such sweet, loving little creatures.

Debby, Start at the floats everything else will go easy. This is off Old Brits: Several articles have been published about setting the float level on Concentric Carburetors and this is a summary of the important points from people in the know:

The actual specification, from the engineer who designed the Concentric Barry Johnston, gives a gas level of between .170" to .240" below the top edge of the float bow, 170” being rich and .240" being lean. This level has a dramatic effect on the running of a properly tuned motorcycle. It pays testaments to the design of this carburetor that the range of miss-adjustment it can tolerate and still have the motorcycle run, if only poorly. It is suggested that you set the float level first before doing any carb adjustment.

The level can be estimated by placing the round edge of the plastic float between .060" and .090" below the edge of the bowl when the needle is depressed by a slight force on one of the float's needle tangs. You can turn the bowl upside down to establish this. With the float above the top of the bowl, as described in the Norton Tech manual, the float can contact the bottom of the body and not allow the float needle to seat firmly. It also makes the carb rich through the jetting range. With the float, level with the top of the bowl, although not as rich as when it is above the top, it is still out of the specified range.
The Norton News says set them 3/32 above the float bowl edge while holding them upside down. The only way to realy know for sure is to build a service tool that replaces the drain plugs and allows you to run plastic tubes to atmosphere to check where they are durring a run. Dyno Dave on this site has a set of these and they takes away all the mysteries. Allen Goldwater has wrote an article on Amal jet sets for all years I can help you find that but I think you have float problems. No sence in adjusting anything till this is just right. norbsa
Wow, I reckon I will have to get a degree in engineering to continue working on my Nortons after reading that last chapter.
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