idle adjustment

I've been having some recent problems with my hot idle on my 73 850 and wanted to get some feedback on the best way to set it.

I've got new 32mm Amal Concentrics that have the correct jetting and spray tubes for the 850 (I found that originally the new carbs came jetted for a 750 and this did cause a lot of driveability problems). The bike starts on the first kick hot or cold and has plenty of power througout the rev range. It also has a Boyer ignition and a Norris SS cam.

The problem is that it tends to stall at idle when hot, especially coming to a standing stop immediately after running at freeway speeds.

I set up the idle to around 2K by adjusting the throttle stop screws on the carbs and then adjusted the air pilot screws inward by a quarter turn and got a smoother idle, then backed off the throttle stop screws to lower the idle to around 800 rpm. Seems like it's better now, but I wanted to check to see how others do this adjustment.

Does anyone follow the Norton manual instructions by setting the idle high, pulling one plug lead and setting the idle for that cylinder, then repeat for the other cylinder? Then according to the manual you should drop the idle speed with both cylinders running, then adjust the pilot screws, then the throttle stop screws again.

As always, I appreciate any inputs.

Mike

mgrant said:

(I found that originally the new carbs came jetted for a 750 and this did cause a lot of driveability problems).

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If the carbs were jetted for a 750 what slide cutaways were fitted? As 750s would normally have a 3 cutaway and 850s would have a 3-1/2.

mgrant said:

Does anyone follow the Norton manual instructions by setting the idle high, pulling one plug lead and setting the idle for that cylinder, then repeat for the other cylinder?

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Pulling the leads off the plugs while the engine is running isn't really recommended for electronic ignition systems.

Mike never pull the plug off a running bike no matter were you read it. The power will find ground it has to and it's the inside of the coil that pays for this bad behavior. Getting some balance gages will help always switch the hoses when you done one way the the opposite way to double check the gages themselves. Before you do anything have you changed your balance hose this year? Or checked the float level to see that they are exactly the same level about 2MM below the rim of the bowl?

Mike, what (if any) air filtration are you running ? It sounds as if it's a bit lean at idle to me. perhaps try the pilot screws a little further in.

I'm not sure that the rev counters are always that accurate at the lower end so I wouldn't spend too long worrying about achieving a particular figure for the tick-over - set it so it feels comfortable.

I do the single-sided tick-over set up thing by starting it on one cylinder with the detached lead fitted to a spare plug resting on the head. It has never caused me any problems (unless that's what makes the Boyer pick-up wire fracture ! :shock

Hello Mike

it seems definitly that your bike runs to lean ( for that reason your enginge stalls, rich mixture will drop the rpm's after stopping ) I would adjust the mixture by rpm or vacuum method. Warm up the engine by driving ( no freeway highspeed excess !) adjust the idle to 800 rpm ( or what u like ) put a digtal tach with 10rpm increments to the coils and adjust the mixture screws to the highest rpm u can get ! ( with correct mixture, the enginge will build the most power, so the rpm's raise ) Then drive the bike and control low response of the bike, if it stalls hard richen the mixture, if it stalls soft lean the mixture ! This adjustment require a enginge in good condition, so good breaker's and setting, correct valve adjustment and timing. Also intake manifold hasn't to be leaky.

Good luck
Marco

Norbsa,

I haven't changed the balance hose this year. I've inspected it and it looks okay but I can pull it and put some compressed air on it to verify its integrity. Is a yearly changeout of this hose recommended?

I had the float bowls off yesterday and trimmed the float gaskets to ensure that the float movement was not fouled by excess gasket material. It looks like there might have been an issue with the right carb. The movement of the float needles appeared the same for both. I've looked for information on setting the float height but found nothing in any of the manuals that I have.

You mention that the float height should be set about 2mm below the top of the float bowl. What is measurement point to look for the 2mm? Is it the float top itself with the needle fully open or fully closed?

I used to use a 4 stick mercury gauge for balancing the carbs on a 4 cylinder bike I had long ago and it worked great, but the gauge is long gone along with the bike. For the Norton I've tried a single air gauge, like the Unisyn of long ago. The problem with it is that you only read one carb at a time and changing the setting on one will impact the other. What kind of gauge do you recommend for the Norton so you can get a reading on both carbs at the same time? Do you use the balance tube ports to attach the hoses?

Sorry for all the questions. I've worked on cars and bikes most of my life but I'm relatively new to fine-tuning a Commando.

Mike

mgrant said:

You mention that the float height should be set about 2mm below the top of the float bowl. What is measurement point to look for the 2mm? Is it the float top itself with the needle fully open or fully closed?

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Info: http://www.jba.bc.ca/Bushmans%20Carb%20 ... html#FLOAT

mgrant said:

What kind of gauge do you recommend for the Norton so you can get a reading on both carbs at the same time? Do you use the balance tube ports to attach the hoses?

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I use a Morgan Carbtune connected to the balance stubs:
http://www.carbtune.com/

L.A.B.

Thanks for the information on float setting. As I've gotten pretty adept at pulling the float bowls recently, I'll do it once more and make sure that the height is set right. I'll have to be extra careful about using a drift to raise and lower the jet seat in the bowl.

From the information in this link and the comments from 79X100 and 4onthefloor, the indication is that my bike is running lean. Both carbs take a long time to tickle, the right one especially. This is consistent with a low float level and lean running. Also, I found as I screwed in the pilot air screw, the idle improved which also says that its running lean. BTW, I'm running a stock air box and a stock paper filter. The engine was completely rebuilt about 1K miles ago and the valves were just adjusted a few hundred miles ago.

Mike

Your inputs are really helpful to me. This stalling problem causes me big issues because I'm 5'6" and I have to start the bike on the center stand. When it stalls, I need to push it to the side of the road, put it on the center stand and thump it through...big problem in traffic. Based on these inputs I'm confident that I can get this thing nailed.

Amal basic settings
A pair of vacuum gages can be had at JC Whitney see this link about 80.00
http://tinyurl.com/2zevzo
It will do a four cylinder or any other combination.
Just remember always check the gages after you think you have it right. Yes just use the balance spigots. The hose is cheap going mad is not good for you. Holding a vacuum is harder than holding fuel.
Setting floats is about getting consistent readings before moving anything. You are trying to make a pair of carbs just the same. Now the only way I can get a consistent reading is by turning the float bowl upside down. It's best if you have thumb nails they are used to keep the hinge pin pushed hard into its groove while taking the reading. You must be sure at any rate that no part of the flesh at the ends of your thumbs touches anything but the hinge pin.
You hold the bowl upside down hinge pin nearest your body just above eye level. The needle is seated because gravity is acting on it. The gaskets are still on the carb bodies or set aside for this. You are reading the distance between the top of the float and the top edge of the float bowl. Some where between one and two MM 's works well but get them just alike as well as you can.
Adjustment is a bit of a pain you have to do very light taps with an 1/8 pin punch from below to lower the float increasing distance and very light taps from above with a 3/8 punch from above to raise the float height. You are moving a brass seat in a press fit just a little adjustment is a lot at the opposite end of the float. You must rest the bowl on a very strong flat surface while doing the tapping, if you feel it move it may have gone too far. A soak in hot water is sometimes needed. Use good clean punches with flat dressed ends. Get them both the same not less than one mm and no more than two. You can scribe a line inside the bowl for reference but make sure you get them just right (the same).
Always check the idle jet with a drill bit. No not a music wire a #78 drill bit that is checked with a gage to be sure it's .016. You have to epoxy it in the end of a plastic tube that comes on brake clean cans. A pin vise won't let it reach deep enough to do the job. Turn the drill between your fingers all the time never just shove it in. The jet your after is behind the air screw. The hole in that jet was drilled with a bit like this you should feel it enter the hole a tightish fit.
Setting the float height and cleaning the idle jets are the first steps before any other adjustments with gages. The gages can be used to even the idle using both the idle screws and the air screws . The gages can also be used to check that the carbs are pulling the same vacuum readings as you rev the motor up from idle. But before you even hook them up you need to do some mechanical reference work.
Now you need to set the cables up so that with the idle screws backed right off the slides there is just perceptible slack. Then you need to use a pair of 3/16 drill bits to set the idle screws. The bits are put in the carbs tip outward trapped under the slide. Now run the idle screws up till you get a slip fit on the drill bit on both slides. Now you must check the cable adjustment side to side. With a drill bit in both slides move the throttle just as little as you can. The bits will move you will have to tweak the cable adjustments so both bits move together at the same time. I have found that the 3/16 size sets a pretty good idle off the bat. But don't miss the point here you are trying to create reference points at the adjusting screws and cables and using a gage on the carbs without doing the ground work is silly. From this point on you need to note where the screws are always referring back to these settings as you make adjustments. These adjustments may be very tiny indeed.
As you said a little part of a turn on an air screw inward to the rich side off the fastest idle settings will sometimes cure a stumble off idle and help the motor recover from being shut down. That's just some basics there's much more to learn and do. Good luck.

"Both carbs take a long time to tickle, the right one especially. "

Sounds like new Amals to me - the cheepo split dowel tickling pins are just that bit too short - I screwed a couple of short M2.5 pan heads into the ends to give an extra mm travel.

Also had the same problem that on arriving home I would cruise up the driveway in perfect silence on acount of the fire having gone out. 8) Scrapping the boyer & going to tri-spark ignition & replacing one coil did the trick - but I'm not sure which bit it was :? - the coil is my favourite.

good luck!
Chris

F_Magna said:

the cheepo split dowel tickling pins are just that bit too short - I screwed a couple of short M2.5 pan heads into the ends to give an extra mm travel.

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Normally it's possible to gain more length on the pins by pulling them out of the tickler buttons sightly, as the pins are only a push fit in the buttons.

http://www.trialsbits.co.uk/product_inf ... ucts_id=65

Quick update:

Based on advice from L.A.B. and others, I went back to basics and checked the float levels on both carbs. Both are set very low, the right one especially so. This would probably explain why the carbs take a long time to tickle, with the right one being worse.

It would also explain why the bike is exhibiting the symptoms of lean running. In order to use the air pilot jet to achieve the best and smoothest warm idle, I have to set the screw at only 3/4 turn out from the full in position. According to the manual, the nominal setting should start around 1.5 turns out from full stop, but the bike won't come close to running smoothly (or at all) at that setting.

So, I'll get a 3/8" flat tip drift and very gently tap in the float needle base to obtain the correct float setting on both carbs. Then I'll check the air pilot jets with a #78 drill bit as described in some of the posts on this thread. I'll check the other static settings for the carb synching and tune in the idle with the throttle stop screws and air pilot jet. I have the feeling that this will make a big impact on the idle problem.

It seems to have been a real bad assumption on my part that because these carbs were new, the float settings would be correct. They are both pretty far off and they're noticeably off from each other. Once I learned what to look for this was very clear.

This is a great forum and I'm learning a lot very quickly. Thanks to all of you for your inputs.

A heat gun on the float bowl will make an easy job of moving the seat. Once the bowl is warm the seat can easily be moved.

Nobody has mentioned leaky slides. Is it possible that you can't get a decent idle because one or other or both of your slides are worn? I could never get my Commando to idle well with the twin Amals. I converted to a single Mikuni a few years ago and it idles great now. I am thinking of going back to the Amals but will not consider it without first getting them sleeved. I have 5 other bikes with Amal Concentrics and Monoblocs and all are sleeved and all idle beautifully. Sleeving these carbs is a required mod in my opinion.

tpeever, It was not talked about because this man has brand new carbs. However you are right about this if I had new bodies I would fit the new chromed slides ...$$$$ ouch.

norbsa48503 said:

tpeever, It was not talked about because this man has brand new carbs. However you are right about this if I had new bodies I would fit the new chromed slides ...$$$$ ouch.

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Oooooops!! I guess I should have read the message more carefully before replying!! I wonder if people have experienced poor idle even with new ones??