My Hawg

Year: 1997

Model: FATBOY

Carburetor: Mikuni 42

Pipes: Samsons, With samson AR cones

Ignition: Crane HI4 E, Single Fire

Cam: Vthunder 3020

Brakes: Chrome Performance Machine, 6 Piston front, 4 piston rear

Additionally: K&N Airfilter,Nacelle headlight assembly,White brothers Lowering kit,Chrome lower fork legs, Polished Rotors, Goodridge Stainless Lines, Nology Plug leads, Crane coils and some other additional bolt on items.

CARBURETOR TUNING

Mikuni 42 mm

Along with increasing the breathing abilities via aircleaner and exhaust modifications the Mikuni can offer quicker throttle response and years of realiable service. I recommend this upgrade after a cam and ignition change, simply because the stock CV can be modified to perform until you reach this stage.

When installing the Mikuni be sure to route the cables correctly and insure that the choke cable has proper end play (About the thickness of a dime), Failure to do this will cause a rich condition that will affect your baseline tuning.

These carbs are typically jetted correctly 90% of the time from the factory so a bolt on is all that is needed. Your first stage in tuning is to turn the mixture screw in to the seated position then back it out 1-2 turns, from there turn it in (slowly) until it faulters then back it out till it faulters, now split the difference. If the best idle is is achieved with the mixture screw less that 3/4 turn out,the pilot is too small and will need to be change to a larger size. On the other hand if the mixture screw must be more than 2 turns out for the best idle, the pilot jet is too large and will need to be changed.

With the K &N THUNDERSLIDE installed

One of the best modifications you can do to the twin is to increase the breathing abilities. View this in the big picture, that is starting at the air filter and ending at the exhaust baffle. Any changes in these items affect your final jetting. Start with a high flow air filter, lightly oiled to prevent even the smallest particles from entering the combustion chamber. From there I would look at your exhaust baffles. The GENERAL RULE here is back pressure increases low end and little back pressure increases top end. Remember this is a general rule, in extreme cases this can be detrimental to performance and the life of your engine. I drilled out my baffles (Removed the screen). This gave if a nice throaty rumble and increased my top end.

Now install your THUNDERSLIDE according to the directions. If you've increased the breathing you'll need more fuel. so start with the 185 main jet, needle clip: 3rd from the top, mixture screw: 3 out from the seated position. ( This may have a plug installed from the manurfacurer, metal or silicone, its located on the inside bottom towards the intake manifold, if its metal, drill a small hole then visually verify that the screw is under the plug. If its silicone use a drill bit approximately the same size but use your hand to remove it NOT a drill) Care should be taken not to damage the threads.

After installation your ready for a test run. Try to do this with a fresh set of plugs when the weather (temperature,humidity)is average for your area. After warm up run it hard with no idle. Noting any flat spots or surging (cruising speed,throttle steady about 3K to 4k the RPMS will seem to audibly fluctuate). Now check the plugs, they should be a light tan not white (lean condition) or black (rich condition) Now record and your findings and your base line settings on a piece of paper, note the tempeture as well. Follow the troubleshooting guide included with your kit. Recording these items will enable you to view your findings in the event you don't get it right the first time. Noting any changes, what worked and what didn't. you can then go back to one of your original settings and change something else to fine tune you machine. This can save alot of time and aggravation.

Flat spots can usually be corrected by adjusting the needle height. Raising the CLIP will lean it out (worsening the problem), Lowering the CLIP (resolving the problem).

For instance, I started with the Mainjet:185, Pilot Jet:Stick, Needle:3rd position, Mixture Screw:3 turds out. This reflected in a lean condition via plug check, although I detected no surging commonly associated with this condition.

Next I installed the 195 Main Jet and left the same settings on the needle, pilot, and mixture screw. This showed a vast improvement in my top end performance as well as altering the sound of the machine during idle. However I now had a barely noticeable flat spot around 2K-3K. To correct this I dropped the clip one position (4th Down) to try to richin this area up. And turned my mixture screw in 1/2 turn (2-1/2 turns out from seated position). Great low end and a force to be reckoned with up top.

I hope this little insight will help you resolve any THUNDERSLIDE tuning problems you may have.

FOR RICHER OR LEANER?

LEAN CONDITION:	RICH CONDITION:
Engine won't respond when throttle is snapped open, but picks up speed as throttle is closed.	Engine acceleratuion is flat, uneven, loses that "crisp feel"
Engine runs hot, knocks, pings, and overheats	The engine will "8 stroke" as it loads up and skips combustion cycles.
Popping thru the carb when throttle is opened, or popping and spitting thru the pipe on deceleration with a closed throttle. ( Classic lean pilot circuit)	The throttle needs to be opened continuously to maintain acceleration.
Engine runs better in warm weather, worse in cool.	Engine works better when cold, falls off when warmed up.
Performance gets worse when air filter is removed.	Black smoke from tailpipe, Sooty plugs & exhaust.
Poor acceleration, engine feels flat.	Poor fuel economy.
	Engine performance improves when air cleaner is removed.
	If the pilot circuit is overly rich, the engines idle is rough or "lumpy" and the engine won't return to idle without blipping the throttle.

CLICK THE CHIK TO

RETURN TO MAIN PAGE