New amal premiers wont stay idling

normally when a carb is running out of fuel at idle it will speed up as it gets leaner till it starts to misfire than stop running.

lwmcd1 said:

It sounds more like a fuel supply problem. Friend had a similar problem and I found that ethanol have deteriorated the rubber inside the petcocks to the point that they were clogging up.adjustments.

Click to expand...

Just to be clear, you adjust the pilot (air) screws with the engine warm and running. The screws are turned in 1/4 turn increments until the highest rpm is achieved (running, watching tach and listening to the engine as you adjust the screws). Each carb should be adjusted separately. Once the highest rpm is achieved on each carb the idle stop screws are adjusted to get the proper idle rpm and opening. Then the cables are adjusted and sync set (be sure the cables are not tight and interfering with idle prior to this).

The 1 1/2 turn setting is the "static" starting point with a new or rebuilt carb(s). It's a common mistake to think this is the setting. It is only to get the bike started and running.

The new pilot jet number 17 makes it the same as the old 25, the 17 is the thou diameter.

When I screwed the pilot air screws out from 1 1/2 turns it made the engine die instead of rev up like I thought it should. I ended up with the screws 1 turn out to get the best idle. Even with the air leak I decided to take it out for a short ride, and the idle was much worse in real world riding conditions. So I need to pull the carbs again and try to seal the carb to manifold air leak, then do adjustments again from scratch. This time I will do the carb adjustments before I take out the slack in the cables. I may order a color tune while I'm at it, and maybe a real sync tool if I can scrounge up some dough. Thanks again for all the input and for not getting frustrated with me. This forum is way more helpful and polite than some of the other auto specific forums I have been on.
Josh

Forgot to mention that the bike came with a 2 into 1 exhaust, a K&N air filter, and my elevation is ~3200 ft. I have the needle set in the middle position. I now realize that a stock combat has 230 main jets and I have 220s. I didn't think these conditions would affect the issues I'm having, but thought I should post them.
Josh

Just to mention, any tuning on these carb should be done when the motor is warmed up completely and hot.

Bowtoy70 said:

When I screwed the pilot air screws out from 1 1/2 turns it made the engine die instead of rev up like I thought it should. I ended up with the screws 1 turn out to get the best idle. Even with the air leak I decided to take it out for a short ride, and the idle was much worse in real world riding conditions. So I need to pull the carbs again and try to seal the carb to manifold air leak, then do adjustments again from scratch. This time I will do the carb adjustments before I take out the slack in the cables. I may order a color tune while I'm at it, and maybe a real sync tool if I can scrounge up some dough. Thanks again for all the input and for not getting frustrated with me. This forum is way more helpful and polite than some of the other auto specific forums I have been on.
Josh

Click to expand...

Josh,

I thought you checked for air leaks by spraying earlier...a little confused here. If you have an air leak you will need to fix that before doing any adjustments. Idle adjustments should be done without any tension on the cables...the idle setting is based on the slide stop screw (idle) position once the pilot (air) screws are set. There should be a slight amount of slack in the cables even after everything is set to insure that the cables don't hold the slides up and not allow them to contact the slide stop screws (idle). Cables have nothing to do with idle adjustment. They are for throttle after idle. The slide movement needs to be synchronized with the cables but this should be done after the idle is set.

Based on your other response you may need a larger pilot jet also.

Dennis

Thought I would give an update. Pulled the carbs again and got the air leaks fixed with a little bit of high temp sealant. Got the bike started and warm, then adjusted the idle with the throttle cables slack. Got it to idle great for about 5 minutes. After the bike had ran for awhile, it idled down to the point it would die. Also began to run rough and thumpy like it was suddenly way too rich, and had a bad dead spot off idle. At this point, adjustment of the air screw made no difference. This rough, thumpy running was something it had never done before. Thought that a spark plug may have been loose because occasionally a spray of carb cleaner around that area would cause it to die. Tightened the plug and it made no difference. This may have been a coincidence, because it didnt die everytime I sprayed there. I am thinking it is something other than ignition or carbs at this point. I am going to pull and clean the pilot jet again and check the valve clearances next. I have put multiple subaru engines in VWs and rebuilt many Toyota Land Cruisers through the years. I have never been stumped like this. I guess the old Norton is a completely different animal and requires much patience and respect.
Josh

Patience respect and new spark plugs

Bowtoy70 said:

Thought I would give an update. Pulled the carbs again and got the air leaks fixed with a little bit of high temp sealant. Got the bike started and warm, then adjusted the idle with the throttle cables slack. Got it to idle great for about 5 minutes. After the bike had ran for awhile, it idled down to the point it would die. Also began to run rough and thumpy like it was suddenly way too rich, and had a bad dead spot off idle. At this point, adjustment of the air screw made no difference. This rough, thumpy running was something it had never done before. Thought that a spark plug may have been loose because occasionally a spray of carb cleaner around that area would cause it to die. Tightened the plug and it made no difference. This may have been a coincidence, because it didnt die everytime I sprayed there. I am thinking it is something other than ignition or carbs at this point. I am going to pull and clean the pilot jet again and check the valve clearances next. I have put multiple subaru engines in VWs and rebuilt many Toyota Land Cruisers through the years. I have never been stumped like this. I guess the old Norton is a completely different animal and requires much patience and respect.
Josh

Click to expand...

This is my method to adjusting idle air screw position, and it's hard to explain... but I'll give it a shot...

When you set the idle air screw, usually there's a range of positions for it where the bike idles ok, but turning the screw in that range seems to do very little to the idle. In actuality, what I believe happens, is that the bike will idle similarly as the mixture changes when you turn the screw either way, up to a certain point when turned in the lean or rich direction. Then, once it's out of that workable mixture range the bike will begin to stumble.

The fine tuning of that idle screw position can't be set only using the bike's idle speed because the idle circuit also is in play during the early stages of lifting the throttle as well. SO,...

First, At an idle only, I try to find the idle screw position where the bike stumbles as I turn the air screw in. Then I do the same thing to find the position where the bike stumbles when I turn the idle air screw out. The position half way between them is the "starting position" for finer adjustment. I do this on both carbs. I was surprised at how little turning the idle air screw effected the engine when it was only idling, but how much turning the screw a tiny bits either way effected the way the bike transitioned from the idle circuit only to needle jet & idle circuit.

Then, I gentley lift and lower the throttle slightly as I micro-adjust the air screw positions to obtain the smoothest transition from the bike's idle speed to about 1800 rpms. This method of adjustment takes into account that the mixture is changing due to the needle jet interaction as you lift the throttle off of the idle stop screws where it's primarily running on only the idle circuit.

If you can't get a smooth transition from idle ~900 - 1000 rpms to 1800 rpms using this method, You may have more than a single issue besides carburation effecting your bike's performance. One of the things guys sometimes brag about is that they have a "One kick bike". Well if you retard a bike's timing it will start a lot easier and idle a lot better too,... (but it won't have the same top end power), so maybe retard your timing a few degrees and see if that helps you work out your carburation.

This is just my method. I'm sure someone will say I am either crazy, wrong, or both...

What state are the K&N air filters in? I've had dreadful problems with them in the past, so it might be worth removing them until you've got the problem nailed.

I like your method of carb tuning. I will give it a try. I will also throw in some new plugs even though the plugs im using are basically new. I have been tuning without the k&n filter on, although I wonder if things would change after I put the filter back on. I am worries there is something else at play, like a crack in the head that opens up when it gets warm. I will keep plugging away, trying all these suggestions. Thanks
Josh

Bowtoy70 said:

Pulled the carbs again and got the air leaks fixed with a little bit of high temp sealant.

Click to expand...

Not sure what you mean by "high temp sealant", and also not sure where or why you would need this.

Sealant in the fuel system is problematic, because it can break loose and get into the carbs...very few sealants are impervious to fuel.

Your description sounds just like that might have happened...

On that same note, are you sure your fuel system is clean? Clean gas tank?

Consider trying your old Carb. I had a FCR flat slide that would start idle accelerate fine, slow down front end dive and the motor would die. After having the thing apart more times than I can remember, adjusting the float height, I took it back. The speciality shop that sold it tried it on one of their bikes ,and couldn't get it to work. They gave me a new Carb. Problem solved.

As usual you are down to substitution. Swap for a known good part ( in this case carbs ) and try again. Silicone is bad news around fuel or fuel related joins for sure.

I understand that silicone is a no-no in the fuel tract. I am usually anti-sealant, but i could not get the carb/manifold o ring to seal. I only used a very small amount and cleaned the excess after torquing down the bolts. It did fix the air leak. I could try the old carbs, but I had similar issues with the old carbs. It would still be worth a try. Maybe I should try new coils also. Maybe after the coils get hot they start to act up.

Check the manifold for a flat surface...that is the only thing that could cause the o rings not to seal except for a warped carb or the wrong size o ring...Since the new and old carbs have the same problem, it has to be something that hasn't been changed out...

Cleaned up the excess? If you cleaned up the excess from the outside imagine what the inside looks like.

I've seen this many times, someone describes what they are doing but unless you can show someone in pictures or videos, inevitably you leave out some crucial detail that you may not think is relevant.

Cleaned up the very little excess from the inside and outside. It was very easy to clean as i bolted the manifold to the carb off the bike.

Has anyone mentioned the possibility of bad gas?
About a month ago, my Combat refused to rev over 4K.
Sputtering and missing really badly.
Ran well below that RPM and had revved to 6K just a few weeks before that.
Changed plugs, swapped leads, checked carbs and timing... no help.
Was running low of fuel, so decided to try another brand (had been running e-free stuff) of high octane.
As soon as the new stuff hit the carbs the problem went away.