New Amals Yield Hard Starting

After being unable to resolve erratic idle speed and other issues on my '72 Combat Commando, I decided to spring for a pair of the new, "improved" Amals.

Once warmed up, these new Amals are perfect.. stable idle, strong powerband right to redline, etc.

However, one nagging issue persists: with the old Amals, I could ALWAYS light off the Combat with a single kick and no choke, even if it had sat for a month. But my new installation seems to want 1/2 or more choke on startup, and then after tickling, will still fire on first kick, but then runs 2-3 seconds then dies. Back to a second tickle, same trick.. runs a few seconds and dies. Usually the 3rd attempt is a charm and I am able to keep the bike running. Still, it runs rough for a minute or so, whereas before I could literally launch off immediately if I should so choose.

For some reason, it just seems as though initially the carbs aren't getting enough fuel. In conjunction with the new Amals, I also purchased a nice one-piece swaged-fitting transparent fuel line and I can clearly see plenty of fuel in both lines.

After a short ride, the Norton is back to its old health, and even after a 2-3 hour rest, will fire right up on first kick, no choke, just like always.

I am baffled as to what might be the problem.

Any help?

Phil
Austin, TX

Hello!

Not sure what you mean by 1/2 choke, when starting?

My opinion is that the choke only kicks in at the far end of the levermovment.
The poor running when started may have many reasons. Floatlevel, idlemixscrewsetting etc.
When I renewed my Amals they accidently came with bigger cut 3 1/2 on the slides.
That made them run leaner initially, on a cold engine.

I compensated on the idlemixscrews and used the choke a little longer after starting the Engine!

All of this on my -72 750 Interstate w.32mm Amals


Benton

Use full choke, if half choke isn't enough.

Or am I missing something?

Half choke would only restrict air flow at more than half throttle opening! So as others have already said, you need full choke for it to act as a cold start aid. Full on / full off is the only way to use these chokes.

I think it's worth noting that a correctly set up engine SHOULD need a choke / cold start device of some kind. If it doesn't, it is too rich.

Nevertheless, I would check you have the correct slide cutaway, the correct size pilot jets, also check the pilot circuits for blockage, Amals have been known to suffer from machining swarf causing partial blockages. You could also check the float height, but the fact it's OK when warm leads me to suspect this least of all.

Don't forget that a low battery can cause running issues, especially with a Boyer.

The fact that it's 'ok when warm' could actually be 'it's ok after the alternator has charged the battery'...

pauldridge said:

After being unable to resolve erratic idle speed and other issues on my '72 Combat Commando, I decided to spring for a pair of the new, "improved" Amals.

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Great idea.

Once warmed up, these new Amals are perfect.. stable idle, strong powerband right to redline, etc.

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Good, settings are clearly correct/ close enough.

However, one nagging issue persists:

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I think you mean a "new dynamic exists".

with the old Amals, I could ALWAYS light off the Combat with a single kick

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That's good.

and no choke,

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That is bad.

But my new installation seems to want 1/2 or more choke on startup,

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That is good.

and then after tickling, will still fire on first kick, but then runs 2-3 seconds then dies.

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Insufficient tickling/insufficient choke, or pilots too small (possibly).

Back to a second tickle, same trick..

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Same answer.

runs a few seconds and dies. Usually the 3rd attempt is a charm and I am able to keep the bike running.

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A little heat from the first couple of attempts has warmed the intake manifolds sufficiently to reduce Condensational Losses to a point where the bike will now run. More choke if possible, and keep throttle as closed as possible.

Still, it runs rough for a minute or so,

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That is ok, add some more choke if possible, the engine is currently lean due to the fuel falling out of suspension after contact with the cold manifold walls(aka Condensational Losses).

whereas before I could literally launch off immediately

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That is bad. Too rich.

For some reason, it just seems as though initially the carbs aren't getting enough fuel.

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No, the engine is not getting enough fuel. Your new carbs are not running stupidly rich like your old flogged out ones were, and you need to compensate for the condensational losses appropriately.
Very unlikely that the fuel flow to the carbs themselves is in any way varying hot or cold.

In conjunction with the new Amals, I also purchased a nice one-piece swaged-fitting transparent fuel line and I can clearly see plenty of fuel in both lines.

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Of course, fuel flow almost certainly has nothing to with it.

After a short ride, the Norton is back to its old health,

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That is good, carb settings (outside of choke/enrichner) are only relevant to fully hot running, and yours sound close.

and even after a 2-3 hour rest, will fire right up on first kick, no choke, just like always.

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Residual manifold heat, not some "extra special engine or carbs" ( I say that jokingly as over the years so many people have tried to tell me their engine is a "really good one", as it doesn't need choke from cold. Apparently it never occurred to them their vehicle was simply too rich on the low speed).

I am baffled as to what might be the problem.

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There is no problem, as such.

Any help?

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If the bike really exhibits extreme symptoms of the ticklers and choke being unable to overcome the COMPLETELY NORMAL dynamic of Condensational Losses (which your old carbs were masking, as they were running far too rich, and which is exactly why we have enrichers and chokes, not because cold engines need more fuel, but rather because, in simple terms, they need the same fuel and are simply not getting it), then the next size pilot is for you, as you may be slightly too lean.

Hope that helps.

Perhaps take a look at the plugs and ensure that the rich mixture choke levels haven't fouled the plugs. I wouldn't mess around with the float levels; the factory settings should be spot on. But look to see if the needle setting is the same as told Amals. Mine is set to the middle groove and starts on first kick.
My start up procedure is as follows:

Tickle carbs.
Kick through with throttle 1/2 on, with ignition OFF (I've got Boyer).
Ignition ON (I also have a cutoff/anti sump valve but that's irrelevant here), 1/2 throttle, no choke, full kick and away it goes.
It always starts.

BC

It sounds like the carbs are really close to being right. If you still have your old carbs compare the fuel level in the bowl with the new ones.

Greg

gjr said:

It sounds like the carbs are really close to being right. If you still have your old carbs compare the fuel level in the bowl with the new ones.

Greg

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I'd second that, do your new carbs have the stay up floats with the bendable tab to set float level? Makes is much easier to do.

This forum is great. Thanks for all the helpful and knowledgeable advice and education. This morning, after a 2-day layup, I went out to the bike.. tickled the carbs until overflow, fully closed the choke, left the throttle fully closed, and, amazingly, the old gal fired right up on first kick and settled down into a nice tick over with little coaxing from me.

without this forum, I would likely have been using the wrong (and unsuccessful) technique for months, maybe years.

Many thanks

pauldridge said:

After being unable to resolve erratic idle speed and other issues on my '72 Combat Commando, I decided to spring for a pair of the new, "improved" Amals.

Once warmed up, these new Amals are perfect.. stable idle, strong powerband right to redline, etc.

However, one nagging issue persists: with the old Amals, I could ALWAYS light off the Combat with a single kick and no choke, even if it had sat for a month. But my new installation seems to want 1/2 or more choke on startup, and then after tickling, will still fire on first kick, but then runs 2-3 seconds then dies. Back to a second tickle, same trick.. runs a few seconds and dies. Usually the 3rd attempt is a charm and I am able to keep the bike running. Still, it runs rough for a minute or so, whereas before I could literally launch off immediately if I should so choose.

For some reason, it just seems as though initially the carbs aren't getting enough fuel. In conjunction with the new Amals, I also purchased a nice one-piece swaged-fitting transparent fuel line and I can clearly see plenty of fuel in both lines.

After a short ride, the Norton is back to its old health, and even after a 2-3 hour rest, will fire right up on first kick, no choke, just like always.

I am baffled as to what might be the problem.

Any help?

Phil
Austin, TX

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Working as designed

Glad it's sorted. Just for reference, I've never had a problem starting my Norton unless there's been a problem and I consider a problem 3 tries and no poot. My original carbs were worn after 10K miles and wouldn't hold an idle, so I rebuilt them to very little betterment. Then instead of paying for a whole new set, I got them sleeved by Lund's and after that, they're just about perfect. Cost me about the same in the long run. Now it takes about 5 minutes of warmup to have them great and idle perfectly, I can even take my hand off the throttle which I've hardly ever been able to do. The Amals are dead simple carbs and most of the problems are usually dirt or float level. Shoot, I've had mine sit in the garage for over a year and start it up with 1 or 2 hits, but then I'm using avgas which seems to keep the system clean, everything evaporates in about 2 hours after a run and no junk in the fuel. It's going to be in the 50'sF tomorrow, so I may just see if it will start, if the battery is not dead. I'll put the charger on it.

50's Dogt? Hmm sounds like good ridding weather. I like it a bit on the cool side so that I can wear a good jacket.