carbtune

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blacklav

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Just balanced my commando amals with a morgan carbtune. Did as the manual said, balanced them to a high tickover rate of 1500-1800rpm on the throttle not the throttle stops.Lowered the left to equal the right. All set up fine until I blipped the throttle. This saw the level on the left decrease slightly but the right side increase!
Is this normal , or should both increase in proportion to the throttle position.
Other than that everything runs ok.
All the connections were correct and free from kinks.
It does have a slightly less compression ratio on the left, but nothing drastic.
Not used these before, always done it by wire under the slide which works ok if all else is fine.

any tips welcome
thanks
chris r
 
I'm not that familiar with the carbtune but I've used an electronic version (Harmonizer Vacuum Multi-tool) to accomplish the same thing and I think it would be similar.

http://www.youtube.com/watch?v=CCDLUktfB6c
http://www.advrider.com/forums/showthread.php?t=701625

I balanced it while idling by adjusting the stops as you did. Then revved to maybe 2-3000 RPM steady and it was slightly out of balance so I adjusted the cables (top of carbs) to balance. It was already close doing it with the drill bit method. It is sweet when you get it right. The Harmonizer makes it really easy.

Russ
 
blacklav said:
Just balanced my commando amals with a morgan carbtune. Did as the manual said, balanced them to a high tickover rate of 1500-1800rpm on the throttle not the throttle stops.
Click to expand...

Which "manual", and whereabouts in it does it give those instructions?

http://www.carbtune.co.uk/inst.html
The Carbtune instructions say this:

Step 2:

Set the engine to slightly above idle by adjusting the master idle screw, then read the gauges.
Click to expand...

Obviously it isn't possible to set the engine with the "master idle screw" because there isn't one, so both throttle stop screws must be used.

blacklav said:
All set up fine until I blipped the throttle. This saw the level on the left decrease slightly but the right side increase!
Click to expand...

For whatever reason, it sounds as if the R/H carb slide is not lifting in unison with the left. If the L/H slide lifts more than the right, then the L/H vacuum reading will drop as the engine speed increases, if the R/H slide does not open as much as the left then the R/H vacuum reading will increase due to the higher engine RPM.

Worn Amals often give inconsistent readings can that alter between one blip of the throttle and the next, so it may be a case of setting them as near as possible.
 
I have always adjusted idle the way it is described in the owners book - ground one spark plug cable to ground and adjust the idle stop on the other carb - I adjust the stop/idle jet for an idle at 700 RPM. Then disconnect that cable and ground it, reconnect the other, and adjust the other carb to produce 700. Re connect both cables and check idle - it will probably be a bit high but adjust both stops the same amount up or down to produce the specific idle speed you want. I tried using a carb stix but frankly, the Norton method produced a better transition from idle to power than the carb stix did. So now I just stick with the "old method."

Of course, if the throttle cables aren't properly adjusted to pull both slides exactly evenly, you still won't get a good transition, regardless of how precisely the idle is set.
 
blacklav said:
Just balanced my commando amals with a morgan carbtune.
Click to expand...

Anywhere in this procedure did you adjust the idle mixture screws, to give a smooth even slow idle tickover ?

Amals are different in that the idle mixture screws adjust the AIR SUPPLY at idle.
If these are not correctly set, it will influence how each carb runs at higher throttle pulls.

Although it does sound like your throttle cables are not lifting the slides evenly.
 
Thanks for the replies but I must be missing something .
I thought the idea is to get both slides in unison sucking equal amounts of air in. If you set the throttle stop screws higher ( for tickover) and one happens to be higher than the other, then surely when you adjust the lower of the two slides up to match the air flow of the higher slide- by the throttle cable adjuster- it is not going to close fully when the throttle stops are lowered for the tickover rate. This Is why I adjusted the slides with the throttle slightly open, to give me the faster tickover.
Hope you can understand what I`m saying I confude myelf quiet esilly.
Please explain It just seems odd to me.
Thanks
chris r
 
blacklav said:
If you set the throttle stop screws higher ( for tickover) and one happens to be higher than the other
Click to expand...

If one throttle stop screw is set higher than the other, then the vacuum readings will be unequal.

I suggest you synchronise the throttle stops so the vacuum readings are equal at normal idle speed, then hold the throttles open slightly (so they are clear of the throttle stop screws) and use the cable adjusters to synchronise the slides.
 
OK. lets look at the problems here.
Balancing your carbs, you are trying to get the same amount of air/fuel in each side, BUT thats only a volume adjustment, consider you have got the depression right ,but the mixture may be wrong on one side..basicly you have the carbs "in balance" but one side can be richer than the other. getting the correct air /fuel flow is tricky. old colour tunes are good, co meter up the pea shooters better. So correct the mix, then hang the slides on there wires ,just pulling the slides off the throttle stops. adjust the wires to get the guages correct, then drop onto the adjusters and set them again on the meter....jobs a gudin!
 
Remember that idle setting - "balance" - for the slides/mixture and proper adjustment to ensure the slides are synched and move in unison are two entirely different adjustments. You can set the AMAL idle mixture/slide stops for a perfectly smooth idle at whatever RPM you like and still have terrible transition and throttle response if the slides/cables aren't synchronized. So first the cables/slides must be checked and adjusted as necessary. THEN set the idle using your preferred method.
 
Hi, whats your method of correct mixture?

mike996 said:
Remember that idle setting - "balance" - for the slides/mixture and proper adjustment to ensure the slides are synched and move in unison are two entirely different adjustments. You can set the AMAL idle mixture/slide stops for a perfectly smooth idle at whatever RPM you like and still have terrible transition and throttle response if the slides/cables aren't synchronized. So first the cables/slides must be checked and adjusted as necessary. THEN set the idle using your preferred method.
Click to expand...
 
First you want to make sure the slides are opening evenly, or synched. First check is to open the throttle with the air cleaner off and pull the slides up until one is just about to disappear in the body, you should just be able to catch it with your thumb nail. Now using the cable adjuster on the top of the other carb to set it to match. You can check the synch now by sliding 3/16 drill bits under the cut away (for a #3, !/8" for a 3.5) on each slide adjust the idle stop screws until they are a sliding fit. They should dip at the exact same time when you open the throttle. If not use the carb top adjusters to fine tune.
Now you can check with the carb tune.
First check is for the slides opening together. Obviously you don't want the slides on the stop screws for this so use the set screw on the throttle twist grip to hold them open just a bit. Then start it up and take a reading. Each side should read about the same, if not do a fine adjustment on the carb top adjusters. You can check the synch as you open the throttle further but in my experience with the carbtune is you are not likely to see a great match. I've also read that the most important place to synch is coming right off idle. After getting the synch dialed in with the cable top adjuster now you can let it back down onto the stop screws and take a reading and set them to match.
 
Well , simple aint it, I think.
Mixture correct by colourtune.
I will check it again tomorrow and the balance.
Basically I was doing it right but the error in the readings when revved up caused some concern. I`ll look for other causes i.e. worn out slides etc.
Many thanks all, will update asap.
ps
Anyone going to Donnington Friday for the Norton day. I`ll be there on a balanced, or not, Commando.
Chris r
 
Yep that sums up air/fuel volume....BUT thats not going to make the ALL and more important MIXTURE correct :!: I have pissed about with carbs ,fuel injector's for 45 years ,and i donot use gauges. A length of rubber pipe placed in my ear and against the carb inlet when the engine is ticking over is very ,very close . The pitch differance of the inlet hiss is easly heard, Screwing in and out of the airscrew has no effect on volume, but a massive differance on how the engine responds, a lasor heat gun aimed at the headers shows a considerable differace in temp..which is mixture...but the vacume gauge shows equal balance. Balance alone is not good enough!


htown16 said:
First you want to make sure the slides are opening evenly, or synched. First check is to open the throttle with the air cleaner off and pull the slides up until one is just about to disappear in the body, you should just be able to catch it with your thumb nail. Now using the cable adjuster on the top of the other carb to set it to match. You can check the synch now by sliding 3/16 drill bits under the cut away (for a #3, !/8" for a 3.5) on each slide adjust the idle stop screws until they are a sliding fit. They should dip at the exact same time when you open the throttle. If not use the carb top adjusters to fine tune.
Now you can check with the carb tune.
First check is for the slides opening together. Obviously you don't want the slides on the stop screws for this so use the set screw on the throttle twist grip to hold them open just a bit. Then start it up and take a reading. Each side should read about the same, if not do a fine adjustment on the carb top adjusters. You can check the synch as you open the throttle further but in my experience with the carbtune is you are not likely to see a great match. I've also read that the most important place to synch is coming right off idle. After getting the synch dialed in with the cable top adjuster now you can let it back down onto the stop screws and take a reading and set them to match.
Click to expand...
 
I've got a mechanics stethoscope for this but I most go by feeling the intensity of the exhaust puffs after getting each side doing its thing nicely on its own with very little on no help from other side temporary backed off so not helping rotate very much. Diddle so each sides' puff balls sounds and feels similar. Works best if float level allows ~1.5 pilot screws out for good idle but not at all necessary to be barely detectable refinement even if screw turned out rather less or more to get nice idle. i have such a low opinion of my skills if I can't get nice runner so often enough in mood of depressing opinion of taking on more than I can digest.
 
JR Bould,
I couldn't agree with you more, mixture has to be set correctly.
But in my experience if you get the volume part dialed in first, setting the mixture is a lot easier. Maybe I have just been lucky, but once I get the synch and idle stop screws set right (and yes float level, Hobot) I rarely have to adjust the mixture screw more than a quarter turn from one and half out, if at all.
Mitch
 
Sorry to appear so forthright, but why not get yourself a Gunson Colortune Kit and set the pilot air screws to the exact instructions in the book.
One word of advice use it outside!( away from your neighbours on a deserted road) on a dark night-you’ll see it much better :!: :shock:
 
All done. Got it set just right at tickover and on the throttle. Carbtune floats even, through all revs.
Now I have the annoying vibration at 2750 rpm that I used to have. I`ll try adjusting the iso`s a bit.
Serves me right, if it aint broke don't fix it!.
Thanks again for the help
Chris r
 
Good bit of kit . in the right hands :roll: ..or should i say eyes :?:

Bernhard said:
Sorry to appear so forthright, but why not get yourself a Gunson Colortune Kit and set the pilot air screws to the exact instructions in the book.
One word of advice use it outside!( away from your neighbours on a deserted road) on a dark night-you’ll see it much better :!: :shock:
Click to expand...
 
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