Britbike forum Forums British Motorcycle specific Brands Norton bulletin board Carbs and Starting Difficulty

I am having a very difficult time getting my 1970 Commando running. I have a Rita fitted and I get a "good" spark upon turning the key off and on, so I don't think spark is the problem. The slides in the carbs are a bit of a sloppy fit at the bottom but a little snug at the top, so I am guessing that the bodies are a little warped. Could that cause me not to be able to get the bike started? I have cleaned out the idle jet with a cleaning tool, so that is most likely not the problem. I can kick it over a dozen or more times and if I am lucky, I can get a cough or two. I have, on occaision, actually got it to catch for a few seconds, but no consistancy at all.

I see on Ebay, new English made AMAL Concentrics for sale. How is the quality of these? I also see Keihin 30 carbs for sale that are supposed to be a direct fit. Is this a "preferred" set-up?

Oh, I forgot to say - the battery is new and strong.

The trick is to crack the throttle part way through the kick.
Keihin carbs are good. I should have this type carb available in a couple months for cheap.

Jim Schmidt
http://users.gotsky.com/jimschmidt/nortonrods.html

Thanks, Jim. I have tried cracking the throttle, I have tried with choke, without choke. I have, though rarely, gotten some response with the choke closed.

One thing that you may have overlooked (I did) is that the timing is set with the pistons on the up stroke. If you set static timing with the wrong rotor mark she ain't gonna go.

Thanks, Dave, but it has run since I last touched the timing, just that I have a very difficult time getting it to start.

I have gotten a response from the bike on occaision - but a rare occaision. I actually got it started a few times, but the next time I tried, or after it died, still very difficult.

You have Amals?
Tickle and choke when cold?
Try a squirt of starting ether in the air box?

Yes, Amals, choke and tickle when cold. Haven't tried the ether yet.

In my experience it is very easy to flood a Commando because of the down draft carburation. When it happens I can usually get mine to fire with a throttle about 1/4 to 1/2 open. (It does, however, startle the neigbors when I do that.) I tickle mine until the first sign of fuel, then stop. That's enough. One prime kick, then down hard. Starts every time. If it doesn't then its time to pay attention to points (which may have closed up)or pilot jet settings. That is assuming everything else is OK including the valve lash, right spark plugs, good electrical connections from the points and to the coils etc. etc.
Bill

Is this a new problem? how long have you had the bike?
Have you taken it for a ride?
11 kicks is WAY to much. Not to mention challenging.
How does it start warm or hot?

Tickle to the fuel runs out around the plunger.
Choke full on. (cable released)
Kick with out holding throttle open.
At the very end of the down stroke, thats when you should crack the throttle. And just a little bit, not a big handful, otherwise you negate the choke and the tickle with too much air.

If still no fire, check to see if holding the throttle open 1/2 to full gets you a responce. If that does, than its too much fule. (flooded)

I used Autolite direct replacement for Champion N7y plugs for my Atlas. The Champions were unavailable at the time I finished rebuilding the bike. The bike would not start. I checked everything over and over. Tore apart the carbs, checked timming etc, etc. As a last resort I ordered the Champions. When I put them in the bike it started 1st kick. The Autolites had what appeared to be a good spark. That assumption by me sent me down the long road of shooting baloons. Its usually the simplest things that cause big problems.

If you haven't already done it, I'd suggest you drain the tank & get some fresh gas, especially if the bike has been standing for a while. This probably isn't the cause, but it's an easy one to eliminate.....

I think I may have Autolytes in there. Could it be as simple as that? I will try to find the time to get different plugs today.

Sore legs and dead plugs! I have had problems where a plug would fire good when grounded to the block but when installed would not fire at all while under compression. This will cause you to get grease on your scalp while scratching your hesd. I used to spray the plugs wth gunk carb cleaner to remove the carbon after wire brushing them but some how it seems to ruin the plugs???(maybe it disolves the the seal between the porciline and body)who knows. Since I have been wire brushing them and blowing out with compressed air.

Hard to believe that changing the brand of spark plugs, assuming all were of the appropriate reach and electrode type and all were clean, not fouled, made ANY difference in starting. I'd suspect something else was the problem.

Nothing about a plug has anything to do with starting except electrode design and reach. The heat range, though VITAL for an engine's operation is irrelevant for starting purposes. Did you have those multi-electrode plugs in there by any chance? They are known for shrouding the electrode and are ONLY useful to put money in the pockets of the makers - they are worthless as actual spark plugs.

Just to prove my point I put the Autolite plugs back in. Will absolutely not start. The Autolites are #63's, supposedly direct replacements for Champion N7y. I put the Champions back in, 1 kick starts.

Sounds like your Autolites are fouled. Take a blow torch to the insulators until they're not black anymore and try again.

The Autolites are not fouled. Their brand new and have never fired up.

They're defective then. I've used Autolites in many different vehicles with good success. Much better than NGK in my experience.

I guess I should re-phrase my origional post.

"I used plugs that were direct replacements for Champion N7y plugs for my Atlas. The Champions were unavailable at the time I finished rebuilding the bike. The bike would not start. I checked everything over and over. Tore apart the carbs, checked timming etc, etc. As a last resort I ordered the Champions. When I put them in the bike it started 1st kick. The replacement plugs had what appeared to be a good spark. That assumption by me sent me down the long road of shooting baloons. Its usually the simplest things that cause big problems"

Hi,

Have to agree with hh...there is no way that a plug won't work in an engine due to it's brand..If it is the correct heat range and reach, and is not defective, then your bike will start as easily on them as on any other brand.

It is not uncommon for brand new plugs to be defective, and show a spark when shorted on the head, but fail to spark under load in the cylinder.

Dave.

Even the heat range is irrelevant to starting. The heat range won't come in to play until the bike has at least started warming up and the plug is approaching operating temperature. It most certainly couldn't be responsible for causing it to cough and die immediately upon kicking.