CB350 Stock Tuning Tips

Stock CB350 Tuning Checklist

Honda CB 350 K

Honda CB 350 K

1. Check throttle cable for smooth operation and crisp return action. Throttle should snap back vigorously to full close with just a little free play through the full swing of the handle bars.
a. If it doesn’t; lube and adjust all 3 cables and ensure proper routing
2. Engine Compression should be 170+ PSI on both cylinders with a warm engine and the throttle completely open with the choke off. If it isn’t then no amount of carb or ignition adjustments will make it right
3. check and adjust valve clearance. If the valves were out of spec then redo the compression test after properly adjusted
4. adjust cam chain tensioner. If the engine has recently been apart you should also check to ensure that the cam chain and sprocket are properly indexed with the cam and crank. This is also a good to check if the engine has more than 20,000 miles or you have other reasons to suspect the cam chain or tensioner to be out of spec.
5. replace and gap the spark plugs; they are cheap
6. high tension leads and spark plug caps should be checked for cracking and replaced. I also will trim about 1/8” back from the high tension lead and re/install the spark plug cap to ensure a good clean connection.
7. spark check make sure you are getting a good spark from both plugs. If not there are lots of electrical checks that will need to be made which I won’t go into here
8. Battery check ; Make sure you have a good battery with a full charge and your stator/regulator/rectifier are charging at between 13.8 to 14.8 volts with the engine running at 3,500 rpms.
9. ignition check; time your points or your electronic ignition to spec
10. Exhaust system check; are there any leaks from your exhaust?
11. air filter check; is your air filter clean and properly installed
12. rubber intake grommets; with the engine warmed up and idling, spray some WD-40 all around the rubber intake grommets and listen to the engine idle…if the engine idle changes then you have an air intake leak.
13. fuel supply; do you have a tank full of fresh high test gas? Have you checked the petcock bowl screen for clogging? Are the fuel lines clean and unobstructed with any inline fuel filters of the proper size and clean?
14. after everything above is done, now you are ready to begin with the carbs;
15. begin by completely disassembling both carbs and I mean everything
a. remove top of carb and withdraw the slide and inspect for any holes or tears in the slide diaphragm. Clean any gunk from the slide so it’s operating room clean. Remove the needle and clean it in carb cleaner
b. remove the float bowl, float bowl gasket, 2 main jets and pilot jet, rubber passage plug, brass floats, and fuel inlet valve, inspect and replace rubber o-rings on the two main jets, fuel inlet valve, rubber passage plug and float bowl.
c. Remove the screws, butterfly, seals, and spindle for the choke
d. Remove the linkage, spring, screws and butterfly, seals and spindle for the throttle plate
e. With a wooden dowel gently tap out the two brass emulsion tubes from the main body of the carbs. You insert the dowel from the top of the carb where the slide goes and they will both pop out of the bottom from each of the main jet holes in the carb body.
f. Thoroughly clean the carb bodies and all brass parts in a carb cleaner like Berrymans, etc.
g. Wash and dry all jets and blow out all openings in the carb body and jets with compressed air. Visually inspect all holes to ensure they are all clean and clear of all debris. Pay special attention to the holes in the pilot jet and the emulsion tubes. If you cannot clean any of the holes then you’ll need to replace that piece. Keep in mind that brass is a soft metal, so anything you use to try to scrape out the holes will leave burs on the metal and likely change the opening size and fuel metering characteristics of the jet.
h. Inspect the floats to make sure they float, are not crushed, and don’t have any pin holes in them (I always hold them under water and look for bubbles)
16. Carb assembly: after complete cleaning and drying, begin assembly
a. Install the throttle and choke butterflies with a light coating of grease on the spindle. Be sure to look at the taper on the upper and lower edges of the butterfly plate to ensure you don’t install them backwards.
b. Install the two long brass emulsion tubes. Be sure to install the secondary one (smaller with a slotted end on it) with the screwdriver slot aligned with the small crossover hole from the primary tube so as not to restrict the crossover tube with the crown of the screwdriver slot.
c. Install the fuel inlet valve with new o-ring (lightly coat the o-ring in grease) and float. Float height should be set to 26mm on the 350k4s.
d. Install the pilot jet and two main jets with new o-rings (lightly coat the o-rings in grease), install he rubber passage plug
e. Install the new bowl gasket and spring jet holder.
f. Install the needle and clip into the slide then the slide into the carb.
g. Install the pilot air mixture screw with new oring and do not overtighten…set both to 1.25 turn out
17. Carb adjustment:
a. Adjust carb throttle cables with the carb mounted to the bike
b. Set both of the idle screws so that they just barely contact their stops without opening the throttle butterfly
c. Adjust cables so that the throttle butterflies begin opening at exactly the same time (you can hear it when you open and close the throttles…it sounds like one click instead of two when they are in synch)
d. Make sure there is proper throttle cable play at the throttle on the handlebar with no binding
e. Warm up the engine to full operating temperature
f. Adjust the idle screws (not the air mixture screws) in equal turns for both carbs till the engine idles properly.
g. Set the idle air mixture screws per the manual

 

Originally by Outobie at HondaTwins.net (great forum, go check them out!)