Extremely vexxing idle/low RPM issue

Fast Eddie said:
Well, that’s the beauty of being able to agree to disagree !

Carbs are a finely tuned instrument, and IMO the difference in flow between a 20 and a 25 jet (for example) whilst being important to carb function, would be difficult / impossible to judge via observing carb cleaner spray flow / pattern.

Ergo it would be equally difficult to observe whether or not a jet is partially obstructed.

Emphasis here on ‘partially’ of course a fully or nearly fully blocked jet would give a visible difference.
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Not talking jets.

The tiny drillings for idle passages into the throat.
 
I thought I'd update this thread. After removing the carbs, cleaning, inspecting, etc.. oh - say about 15 times.... I finally found the 6 page Bushman Guide to Amal carbs. Where was this all my life. After some very persistent tinkering I figured out the left side was VERY lean at idle. Much probing and carb cleaner later I had it getting fuel at idle again. MUCH better.

that allowed me to diagnose a small vacuum leak in the carb-intake junction.

With both these fixed, it is like a new motorcycle. All bad behavior gone. Smooth part throttle running. Easy starts. The whole ball of wax.

Now if I can just figure out how to get a title for it... (Long story, owned by my stepdad in NY, he passed. mom lives in IN, me in IL. Its complicated)
 
Using petrol has its problems. It is not a pure chemical, there can be a lot of different compounds and impurities in it. Methanol is better, but must always be drained completely after being used. In our town, one of the service stations was sued for ruining the fuel systems in some of their customers' cars, with dodgy petrol.
 
cstreit911 said:
I thought I'd update this thread. After removing the carbs, cleaning, inspecting, etc.. oh - say about 15 times.... I finally found the 6 page Bushman Guide to Amal carbs. Where was this all my life. After some very persistent tinkering I figured out the left side was VERY lean at idle. Much probing and carb cleaner later I had it getting fuel at idle again. MUCH better.

that allowed me to diagnose a small vacuum leak in the carb-intake junction.

With both these fixed, it is like a new motorcycle. All bad behavior gone. Smooth part throttle running. Easy starts. The whole ball of wax.

Now if I can just figure out how to get a title for it... (Long story, owned by my stepdad in NY, he passed. mom lives in IN, me in IL. Its complicated)
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Bushmans Guide? I attached it a few lines above your last post....8/23.
 
Bite the bullet and buy a new set of premiers. Old Amals are nothing but trouble. To really reduce problems buy a Mikuni kit. Add a few more $100 dollar bills to the pile and get a Tri Spark ignition. It gives an excellent idle, better than you can achieve with any other ignition. Beyond that I can't see much difference between the ignitions.
 
The advance factor in ignition systems is important. Tuning is about the balance between compression ratio, ignition advance and jetting. Fuel octane ratio can change the balance. Because I use methanol fuel for racing, I do not need to worry about octane ratio or fuel quality. I do not change the compression ratio and I use fixed ignition advance. So jetting the carbs is easier, and with methanol, slightly rich is good but the bike is OK. When you use petrol, it much more difficult to get the jetting right. I suggest Amal and Mikuni carbs are inadequate, however Mikunis are better, if you can afford the needle jets.
 
Tornado said:
Bushmans Guide? I attached it a few lines above your last post....8/23.
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So you did, unfortunately I went back to working on the bike instead of checking the thread. Forgot about the post, kept digging, and discovered it elsewhere. ...but thanks!
 
seattle##gs said:
Bite the bullet and buy a new set of premiers. Old Amals are nothing but trouble. To really reduce problems buy a Mikuni kit. Add a few more $100 dollar bills to the pile and get a Tri Spark ignition. It gives an excellent idle, better than you can achieve with any other ignition. Beyond that I can't see much difference between the ignitions.
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I'll do the tri-spark this winter probably. I see too much variabilty in the timing for my liking currently. The carbs are in fine shape having only 8k miles on them. The issue was more that the bike say in a shed for 45 years and I'm still finding little bits of dirt and varnish popping up. More riding will help clear it out.
 
My original amals are 48 years old and were sleeved by Ed Lund 30+ years ago and are still going strong. The problem with amals is they are complex and the knowledge needed to set them up and diagnose their issues is not common... I've had every issue, so I'm pretty good at troubleshooting them, but now that I know how to troubleshoot them, they consistently run well. They only tortured me when I was a stupid kid trying to get my bike to run for more than 20 seconds at a time without dieing. Having no one to learn from was at the root of the problem,......

...... here's something I wrote for someone else recently who was having trouble with their amals. If you use the recommended jets and settings for your model, your engine will run fine above 2,500 rpms if all the parts are good. The problems most people have with amals are at low RPM performance when the person doesn't understand how the idle air screw and Air/Fuel ratio work at idle. If you figure out that part, then you know how to find the idle air screw position where your bike idles well and also accelerates to higher rpm's smoothly. I call it the "lift and lower" technique.

o0norton0o

Post in thread 'Cuts out on hard deceleration'

Here's what I think....

When you set up your amals, the air idle screw adjustment is comfortable in usually a 3/4 turn range.... That means you get the screw in that range and your actual Air/Fuel ratio is about 12/1 at the low range screw adjustment and 13/1 at the high range. YOUR ENGINE will tolerate this range without giving you any feedback to help you find out actually where you are in the range... read this again if you are not following before you read further...

So, you have your idle air screw set and your bike idles away happily,.... But now you go to accelerate by lifting...
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o0norton0o said:
...... here's something I wrote for someone else recently who was having trouble with their amals.
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Helpful thanks. I've gotten the bike to idle pretty well now so I'm getting into the fine tuning stage. My only issue right now is that it wants to idle at about 950-1000 but in that range it occasionally stalls. If I let it idle here too long i have to blip the throttle a bit before taking off, like I'm "clearing them out". They give a little chuff when this happens. My theory is I'm still a bit rich and a couple light twists on the throttle helps clear them out.
 
cstreit911 said:
Helpful thanks. I've gotten the bike to idle pretty well now so I'm getting into the fine tuning stage. My only issue right now is that it wants to idle at about 950-1000 but in that range it occasionally stalls. If I let it idle here too long i have to blip the throttle a bit before taking off, like I'm "clearing them out". They give a little chuff when this happens. My theory is I'm still a bit rich and a couple light twists on the throttle helps clear them out.
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Well, Just the fact that you see the common sense of the post I linked for you to read, means you have your thinking cap on. When I use the lift and lower method, I go back and forth from one carb to the other readjusting and doing the lift and lower technique to see if I can get the transition from idle to 2000 rpms to be as smooth as possible. I might go back and forth from one carb to the other 3 or 4 times before I am satisfied that it's as good as it's going to be given the wear on the carburetor at it's current age. Norton got it right btw, so for any model, the recommended jets/slide/needle position is the best starting point.

Sometimes the idle screw bias that you are using to keep your acceleration as smooth as possible is also slightly rich at idle because as you begin the lift the slide it may momentarily make your A/F go lean. That sort of means you can't have both a bike that will idle all day until it runs out of fuel and a bike that seamlessly accelerates from idle to midrange. I always blip my throttle before I pull away at a stop light just to clear any quenching of the spark plug that a prolonged idle might induce.

Another part of the problem is also that as your bike idles the rotor/stator output is reduced so the generated spark weakens as time passes idling because your battery voltage is powering the bike and draining until you pull away and are above the 1800 rpm range where the R/S begins to restore proper voltage. That slightly weakened spark output can also contribute to poor idling or even stalling. The good part is that if the bike is hot, it will usually fire up on the first kick.

As far as extended idling time goes, you should fire the bike up, blip it a few times to see that it's ok, then go. The reason I do that is that I think solid lifter pushrod motors produce greater wear on the valve train parts idling during cold start up. Once you warm the engine up and get to a stop light, the oil is hot and flows much better to all the places it needs to be.

My friend had a dunstall bike that could idle down to about 6-700 rpms and sounded like a ticking clock keeping perfect time. I think it also had lightened pistons and a stock cam which may have contributed to it's steady low idle ability. At one point I hoped that I could get my bike so dialed in that it could idle steadily that low, but I think I am about 800 rpm's right now and that keeps the bike idling strong and works with my idle screw bias to make smooth take offs an every time occurrence... If you have to go to 900 or 1000 rpms, that's just fine too. That little extra crank speed helps keep the bike firing and if you need a little more it's no big deal because Nortons aren't made to sit on idling away... remember solid lifter pushrod engine...

I found a cool way to set the idle. I do it with a metronome from Youtube on my laptop and carry the laptop outside with the engine running and try to dial the idle speed screw to get the bike rhythm and the metronome rhythm to be thumping along at the same rate... bingo, idle speed adjusting without having to rely on a magnetic instrument which is least accurate in it's low rpm range. You'll be surprised how much more accurate the metronome is than the tachometer. Here's 800 rpm linked below. I bet you will be surprised at how fast it seems...

 
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o0norton0o said:
When I use the lift and lower method, I go back and forth from one carb to the other readjusting and doing the lift and lower technique
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Did I miss a post on your "lift and lower" method?

o0norton0o said:
I found a cool way to set the idle. I do it with a metronome from Youtube on my laptop and carry the laptop outside with the engine running and try to dial the idle speed screw to get the bike rhythm and the metronome rhythm to be thumping along at the same rate... bingo, idle speed adjusting without having to rely on a magnetic instrument which is least accurate in it's low rpm range. You'll be surprised how much more accurate the metronome is than the tachometer. Here's 800 rpm linked below. I bet you will be surprised at how fast it seems...

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What an outstanding idea.
 
cstreit911 said:
Thanks for all the ideas. THe bike and carbs have only 8k miles on them. Its nearly new. :) Compression and leakdown was outstanding as I checked this all before i started investing in a restore. I feel like slides probably aren't worn to the point of leakage. When I rebuilt the carbs they were tight and smooth.
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This slides are most likely no good. When good, they are in effect from 1/8 to 1/4 throttle. If they are worn they can affect higher thottle openings.

cstreit911 said:
I checked the plugs (Which have < 200 miles on them) and they are a nice medium brown color. However given the stumble I think these older machines like things a little richer so I moved the needles out a bit this evening and that seemed to help. Need to go through and fiddle some more.
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Unless you are using E0 gas, the plugs should not be brown. With E10 you look at the center insulator. Should be black half way up and white the rest.
cstreit911 said:
One other though - at certain idle speeds some gas comes out of the ticklers. Could it also be spurting into the carbs due to the vibration giving me a temporary rich condition? Seems unlikely but after many hours of fiddle-farting around with these, I'm going way out there on ideas.
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The fuel height is wrong in the bowls or the ticklers are stuck or you have the original plastic floats, and they are not empty.

So, you have a 50-year-old electrical system and 50-year-old carbs that were meant to be thrown away and replaced relatively often. Back then they were inexpensive. Today to fully rebuild them costs a lot and you still have crappy bodies and a bad pilot circuit. Life becomes much better with a set of the correct Premier carbs and there is no doubt that you have bad connections, bad condensers, and would benefit from a lot more points system knowledge on a British bike or an electronic ignition.
 
cstreit911 said:
Did I miss a post on your "lift and lower" method?
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I laid it out in this post that I linked above. (and now below) Carburetion is all about having a working Air/fuel ratio throughout the entire range of the throttle. Because amals have components that dominate certain ranges of throttle. It's not enough to set your idle (for instance) without seeing how the A/F ration changes when you lift the throttle and transition to a place where the next component begins to take over the dominance of the A/F ratio.... So you set the idle screw, but as you move it very small amounts you lift and observe the smoothness of the engine accelleration, then lower it and do it again moving the screw a tiny bit. You go back and forth from one carb to the other trying to get the smoothest acceleration possible.....

Now, if your spark is weak you won't get good ignition and a plug check will make it seem like the A/F is rich.... The carb could be fine and you'll chase that dog and never catch it because you are assuming a rich plug is a rich carb..... and sometimes it's not the carb... My point to add this is that you have to check everything.... calmly... You'll find it... shit takes some time sometimes....

I just did my second set of chevy 5.3 knock sensors in the last month.... That shit is torturing me.... but I don't give up..... Don't you give up. You'll get it right!


o0norton0o

Post in thread 'Cuts out on hard deceleration'

Here's what I think....

When you set up your amals, the air idle screw adjustment is comfortable in usually a 3/4 turn range.... That means you get the screw in that range and your actual Air/Fuel ratio is about 12/1 at the low range screw adjustment and 13/1 at the high range. YOUR ENGINE will tolerate this range without giving you any feedback to help you find out actually where you are in the range... read this again if you are not following before you read further...

So, you have your idle air screw set and your bike idles away happily,.... But now you go to accelerate by lifting...
  • Like

 
I think the idle screws on my Mk2 Amals are fuel adjusters. I make sure the slides hit bottom exactly together. Winde the idle screws right in until they just stop. Then I wind them both out 2 turns, and start the motor with the enrichers, and let it idle until it slows. Then I close the enrichers, and let the bike run, while I turn one screw in until until the motor misses then back it off until the miss is gone. Then I do the same with the other screw. The bike usually idles perfectly.
I once took it to a race circuit where it would not start. The local 'expert' helped me by immediately winding the idle screws out. After I replaced the plugs and started the bike, I just would the two screws in until I got the misses and would them out to get it right. It is not rocket science. The pilot jet, air jet, slide cutaway and idle screws all make up an assembly - the idle screws , and the throttle stops-if any, are the adjustment facility. You do not usually have to change or jets or pilot jets.
If your carburation is correct, any miss you get is usually electrical.
With experience, you will always know from your motor's sound when the jetting is too lean, or not lean enough.
 
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