8Ball's winter project
This is a discussion on 8Ball's winter project within the Project Builds forums, part of the Caferacer.net Forums category; Originally Posted by Mackey
this is Lukas from Germany. I also wrote you an private message, but I Think you did not see it ...
12-10-2019, 07:31 AM
I will be amazed if the response is anything other then the stock jets just adjusted properly. If your K&N felt filters are properly oiled you haven't really changed anything that will alter the fuel to air ratio appreciably.
Originally Posted by Mackey
If you also made huge exhaust system changes at the same time possibly, but you have not indicated that.
K&N air filters don't actually pound 50% more air into your carburetor then a brand new clean OEM paper filter, their claim to fame is that they trap and hold dirt more efficiently and while doing so their ability to allow air flow is less affected. Properly serviced, they hold more dirt, are impervious to the affects of water and still pass air where a dirty paper filter would clog up and starve your motor for air.
Last edited by TrialsRider; 12-10-2019 at 08:03 AM.
12-11-2019, 10:32 AM
Honestly, it has been so long, I don't recall exactly. My latest notes indicate 100 and 102.5 mains in (up from OEM 80's), stock pilots (with adjustments made on the air and fuel screws) for idle, and the needles raised 1 or two notches.. But the carbs have been off several times since then, and I don't remember if I made any adjustments.
Originally Posted by Mackey
What I will say is that there is NO MAGIC number, or formula for tuning carbs. There are too many variables. The filters are just a small part. The exhaust system is a large factor. Variations in the engine, temperature, elevation, humidity all play a role. And here in the US, our government has determined that it is a good idea for the corn farmers to sell surplus corn to the oil companies instead of exporting it to places that have more need. Consequently the gas we get has 10-15% ethanol in it, wich not only wreaks havoc on rubber seals in old carbs, but I have found it also requires a slight bump in jet settings to compensate.
Tuning carbs is a process!
First step is to make sure all your boots are good and the o-rings sealing them to the cylinder head are good.
Second step, and THIS IS IMPORTANT, is a valve lash adjustment. Particularly on this bike because the valve lash adjustment interval is every 3000 miles and the lash spec is stupid small (like .03 - .08 mm).
Third step, if you have points is to adjust them and be sure you have good and equal spark on all four cylinders. (I installed electronic ignition, higher ohm coils, and a relay to feed the coils directly from the battery to ensure good spark)
Fourth is to do a compression test.
Don't even think about your carbs before the first 4 steps are done and any issues are resolved.
5. Remove and clean the carbs, all passages and all the brass need to be cleaned thoroughly. Clean out all the holes on the emulsion tubes.
6. These bikes are really sensitive to carb synchronization. Do a bench sync when you have the carbs off. (The manual tells you how to do it) You will need a good set of syncro gauges or mercury sticks later to perform a running sync
7. Get the idle right. Start with 1 turn out on the fuel screws (the ones closer to the engine, and 2 turns on the air screws. There is a procedure to get the idles right, and it does involve a bit of "feel" and know-how. But basically you set the idle speed to about 1100, and adjust the air screw on the first carb to get the highest idle speed. If this happens with the air screw less than 1 turn out, you need to bump the fuel screw out a bit. Reset the idle speed and repeat on the next carb. Once you have a good even idle you can move on.
8. I set the main jets next. This requires a long empty road and do a crap ton of "plug chops". Run the bike at wide open throttle down the road through the first few gears and shut off the ignition with the bike in the upper RPM range and the throttle open. Coast to the side of the road and pull the spark plugs and read them. White means you need a larger jet, black means you need a smaller jet and tan is pretty close. Look for variations between the cylinders.
9. Once you have the main jet sorted out you can adjust the needle height. I do this with a combination of setting the height so I can roll the throttle on without bogging or stumbling, and doing a few partial throttle plug chops to verify the needle setting.
10. Once all this is done, it is time to do a running synchronization of the carbs.
You need to go into this with the realization that you will be removing the carbs many times during the process. This is the old school way.....without a dyno.
Last edited by 8ball; 12-12-2019 at 08:46 AM.
I always find a soap box useful to get on my high horse.
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