Mikuni -Amal tuning

Ok , so you want a single Mikuni? Instead of those worn amals, single Mikuni will be less trouble when set up correctly?
The differance between the two set ups is ,firslty the amals have much simpler pilot slow running , Mikuni VM 34 as 25 differant sizes of Pilot jets from 10-120
One is correct for you bike, it's no use twiddling with the screw if the jets not right,
So this is my way, after fitting screw out the idle screw two turns and stick in a colour tune, these are real handy things ,start the bike and observe the colour ,if the nice blue colour cannot be seen ie Whiteish jet up , yellow jet down ...Now i know what you are thinking..adjust the screw ..if you have a Very near correct jet this may just do the job...Remember Mikunis are not designed to be a one jet wonder,,that why there is 27 sizes !
change the jet and leave the mixture screw alone ! only when the the blue flame appears is it right [two turns out] .
Now its crange time!
I order a jet on the small side , then with a micro drill set drill out in steps of .05mm until i start to get the "blue" . these drills are dirt cheap and start at .3 then increase by .05 ..eg .5 ,5.5, .6, 6,5 etc... i would'nt attempt drilling steel, but carefull brass hole enlargement is OK .
Air raid hat on!

Your drill procedure is what I do for the Lotus with dual side draft webers and other removeable jet carbs.
You also can solder them shut and redrill them to go back down in size. Once your have your size, you buy a set of the real thing. Otherwise buying multiple sets of 4 of every thing gets expensive real fast....
One of these days I want to try a single CV Keihin on one of my commandos, kind of like a SU or stromberg. I think it is 34 or 36mm. This might require a custom needle,... which I'm prepared to do.

added: I'm not a fan of the color tune things since they are "advertised" for idle adjustment only. They state they will be damaged if used under real power.
That's why I now use a brake dyno to test EGT and get the mixture right, and run equal on both sides while doing a steady 55-70 MPH. How often do you drive at idle? How do you adjust the carbs (cables) at 55 MPH? :mrgreen:

I'm about to use an Innovate LM2 meter and O2 sensors to do just that, though on the road rather than on a dyno. I suspect that on the road measuring the air/fuel ratio in all sorts of different conditions , rpms,gears, pulling hills etc. will be a great way to do precise Carb tuning. The device has Data Logging so it stores the information which can be viewed after the ride via connecting cable and laptop computer.

Glen

Any method for deciding if the carbs are synced? vacuum guages sensors? or can you tell a lazy cylinder from the pulling cylinder by the devices?
What are your desired readings to not seize/melt an engine at WOT. The dyno EGT is around 1325deg F. You can always make more power :twisted: but then you can turn the piston into aluminum mush

A down/dirty method is to feel the exhaust puffs each side and diddle so both evenly puffing by all the means and factors known to man and beast.

Look at Morgan Carbtune Pro

With twin carbs what I do is stick my fingers in a feel that both slide cutaways are together as they disappear from the venturis at the top, by adjusting the cables. Then I allow the throttles to drop and listen to see that they hit the stops at the same time, and adjust the stops if necessary. If you've bought the carbs new and specified which fuel you will be using, the air jets, idle jets and slide cutaway should be correct. With methanol, I use a rich petrol needle and make the needle jets. The essential thing is that if you lower the needle one notch beyond the centre position you should cause a cough when you ride the bike, at 3/4 throttle as the needle goes in beyond the parallel part. If you don't get it, make another set of needle jets one thousandth inch smaller . With petrol, I would do similar however it is much more difficult, I would buy the jets in a range of sizes. Once the bike is running on both cylinders, I screw in the idle screws (screw out if its an air control) until I get a spit out of the bell mouth, then I richen the mixture until the motor stops spitting. If you do it to both carbs you will be very close to the right idle mixture. I then trim both the stops and the idle screws. If you wind a stop up the motor will quicken slightly, I then bring the other side up until the sound of the exhausts are even. If you turn the idle screw in 1/4 turn you should get the spit even when the motor is hot.
From memory the thread on the needle jets is zeroBA, I use brass hex, and number and metric drills to achieve the sizes. The correct way is to match the jets using a bottle of gas and a flow meter. I get it good enough using methanol not to need to do that. Petrol is much more critical, if it is even slightly too rich the motor will be sluggish.
I set the main jets with a plug chop.

This is working great for me ..... 73 MKV 750 stock engine with Emgo peashooter pipes ,no crossover tube. NGK #6 plug.I live at sea level. Carb is a single Mikuni 32 mm VM. 2.5 Slide,159 P-5 Needle Jet,F5 needle with clip 2nd notch from bottom,35 pilot jet,main jet 250 ,air screw 1 1/2 turns. Easy starting hot or cold, perfect throttle response from idle to full song,great gas milage 60+mpg at cruise speed. I'm not racing anyone and don't need a hot rod Norton. Reliability and consistency count more for me......Skip

dynodave said:

Any method for deciding if the carbs are synced? vacuum guages sensors? or can you tell a lazy cylinder from the pulling cylinder by the devices?
What are your desired readings to not seize/melt an engine at WOT. The dyno EGT is around 1325deg F. You can always make more power :twisted: but then you can turn the piston into aluminum mush

Click to expand...

Here is a bit on the Innovate. This is to avoid melted pistons firstly, but also to get a good tune. Looking for around 14.3 cruising, 13 to 13.5 hard on the throttle.

http://www.innovatemotorsports.com/products/lm2.php

Glen

I've never used colourtune, however as an industrial chemist I believe you must always relate the observed measurement response to the actual performance result. If the test unit has been calibrated against performance using the same fuel you will be using, you can probably use it with confidence. If your idea of the colour blue doesn't give the same outcome that the test unit manufacturer predicted, you might have a problem. I'm old fashioned, I rarely trust black boxes without verifying their performance.
When you tune a bike there are about four main things which are variables - comp.ratio, mixture, ignition advance, gearing. The first three of those are adjusted through tuning to get the best efficiency out of the fuel which suits the application. However the main influencing factor is the combustion conditions, which are the result of changing the variables to get power without detonation or burning the mechanicals.

In other words be careful you don't burn the shitter out of it.

"Here is a bit on the Innovate. This is to avoid melted pistons firstly, but also to get a good tune. Looking for around 14.3 cruising, 13 to 13.5 hard on the throttle."

http://www.innovatemotorsports.com/products/lm2.php

Noticed the pix of the guy in a liquid cooled car not anything to do with an antique air cooled motorcycle.
You can run around for weeks at parade speed and not hurt the engine, but one blast trying to do the "ton" on the highway to get data and your bike may end up going home on the "hook"...or you might go home in a pine box.
Of course on the dyno you always start rich to be cool (temperature) then work EGT up.
I wouldn't mind seeing what an O2 sensor and the F/A would say but unless I learn more... I would say it would be secondary to EGT.
I will admit this type of device would be of benefit to evaluate slide cutaway and needle progression. To me these are more important than garden tractor smooth idle while at a stop light. The $669 dual kit is the only thing that would be useful...IMO

Deets55 said:

Look at Morgan Carbtune Pro

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Looked this up.
Tool OK and basically the same as mercury carb stix I use.
Watched video of syncing at idle only. The guy never put it under load...AKA brake dyno.
Cool techie music. Marketing at it's finest.
Otherwise not impressed at all.

Dave, same as you do on the dyno, I am starting rich and gradually leaning it out, the AFR numbers tell me what to do. The EGTs you are measuring are the result of whatever AFR exists in that particular situation you create on the dyno, so really these are just two different methods of getting at the same thing.
I do like the on road ,real conditions data logging feature of the Innovate setup. Certainly if one does not have a Dyno and egt measuring equipment on hand, then here is another method of getting the AFR correct at various throttle positions,speeds and engine loads without accidentally venturing into a too lean piston burning condition.

Glen

I'd lean off the mid-range until I got best performance up through the gears and then measure the air to fuel ratio, then work backwards the next time you tune the bike -try different tapered needles. Always check the main jets with a plug chop. There is a situation where the mixture can be metered off the tip of the needle instead of the main jet. You need to check for that by fitting a larger size pair of main jets and making sure the mixture richens. If you have that problem through the needle being too fat at the end, you need to recess the needle jets and meter at a lower point in the jet so the tip of the needle is still captured at full throttle, otherwise you might get a quick trip into the boonies. The leaner the midrange jetting is without the motor coughing, the better.

Yes i agree tuning the pilot first seams odd, but i have to start the bike before any thing can be done? thinking about how big/small the main should be ain't any use if the bike will not start :roll: or tick over :?:

acotrel said:

I'd lean off the mid-range until I got best performance up through the gears and then measure the air to fuel ratio, then work backwards the next time you tune the bike -try different tapered needles. Always check the main jets with a plug chop. There is a situation where the mixture can be metered off the tip of the needle instead of the main jet. You need to check for that by fitting a larger size pair of main jets and making sure the mixture richens. If you have that problem through the needle being too fat at the end, you need to recess the needle jets and meter at a lower point in the jet so the tip of the needle is still captured at full throttle, otherwise you might get a quick trip into the boonies. The leaner the midrange jetting is without the motor coughing, the better.

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Has anyone tried the color tune on JS flatslide carbs? If so I'd like to know how it worked. The flatslide carbs are similar to the Mikunis in the sense that the adjustments are more refined than with Amals. For those who have an ear and know how to tune carbs, its easy. But others need help and the color tune would at least help with the idle mixture.

john robert bould said:

Yes i agree tuning the pilot first seams odd, but i have to start the bike before any thing can be done? thinking about how big/small the main should be ain't any use if the bike will not start :roll: or tick over :?:

acotrel said:

I'd lean off the mid-range until I got best performance up through the gears and then measure the air to fuel ratio, then work backwards the next time you tune the bike -try different tapered needles. Always check the main jets with a plug chop. There is a situation where the mixture can be metered off the tip of the needle instead of the main jet. You need to check for that by fitting a larger size pair of main jets and making sure the mixture richens. If you have that problem through the needle being too fat at the end, you need to recess the needle jets and meter at a lower point in the jet so the tip of the needle is still captured at full throttle, otherwise you might get a quick trip into the boonies. The leaner the midrange jetting is without the motor coughing, the better.

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John, the Sudco tuning guide says start at the bottom and work up, so pilot first as you are doing is normal.

Glen

As long as the mains are rich enough, they are irrelevant when you are adjusting the pilots and midrange jets. In my own case, after I got the midrange throttle response really good I did a plug chop a bit later just to check that I wasn't going to burn a piston, however on most race circuits it is not a big concern, you are not usually at wide open full noise for long enough. If you intend blasting down tens of miles of freeway with the throttle wide open, the main jet size would be important. I never check midrange jetting with a plug chop, however in your case, riding on public roads, it might be worth doing if you sit for miles on half throttle. Always tune with your hotter plugs. If you change the exhaust system, ignition timing or comp. ratio - always re-tune. If you are running lean in the midrange to get performance fuel quality can be an issue. That is one of the beauties of using methanol for racing .

I've never had the situation where I've had to change a pilot jet or air jet to get the carburation within range for the idle screw adjustment. Even when I've used methanol in a carb previously used for petrol, the slide cutaway and low running system have been OK. My brother has that problem with the 34mm Mk2 Amals on the 880 JAP on methanol - it is simply a matter of persistence when you encounter it. When I bought my own Mk2 Amals, I bought the methanol kitted ones from Mick Hemmings and didn't have the idle circuit air jet/pilot jet problem, however everything else was completely wrong. If you do this stuff with a two stroke, it would drive you insane. That low running problem means the bike won't even start.

Ludwig.
Those plugs sure look clean, indication the engine is in good shape...no oil trace.

ludwig said:

worntorn said:

I'm about to use an Innovate LM2 meter and O2 sensors to do just that, though on the road rather than on a dyno. I suspect that on the road measuring the air/fuel ratio in all sorts of different conditions , rpms,gears, pulling hills etc. will be a great way to do precise Carb tuning..Glen

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I also used an onboard AF meter to tune the carbs . I set them to the lean side , because I ride a lot in the mountains .
This his how my plugs look like after a 4000 km trip :

]

Bosch WR7DC plugs , Twin Amals , Pazon shurefire , 33°total advance , Blue Streak 4.8 ohm coil .
Fuel consumtion is 4.5 l/ 100 km , or 60 mpg (imp) .

This video is with the camera right in line with the exhaust .
Elevation well over 8000 ft .
There is not the slightest puff of black or blue smoke :
https://www.youtube.com/watch?v=f8EaNVzNXxc
( ringing noise is clutch pressure plate ..)

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From that photo, you cannot see the right place to read the plugs. You need a light and a magnifying glass and look right down inside to where the porcelain joins the metal. There should be a 2mm black ring there on the porcelain, if the mixture, plug heat range, timing and comp. ratio are correct during a high speed wide open throttle run with the motor slightly under load. What you are seeing from that photo are also the effects from when you are slowing down. It looks as though the bike was idling before you took the plugs out. Personally I only use plug chops to check that the mains are in the safe range while racing. For road use your considerations might be a bit different. The porcelain in the photo is very white, so I'd be checking the ring is still there.