Engine/tuning/mikuni carburetor tips

Engine/tuning/mikuni carburetor tips

These Tips were originally posted on the Cope Racing website, which no longer exist. They were authored by engine guru Greg Cope. Greg is the current crew chief on Geno Scali's NHRA pro stock Suzuki. Many people missed these tips when Greg shut the site down, so the fact that I do not know him at all I thought it was OK to rip off his page and repost it for everyone to enjoy. The page will stay up until we receive the "cease and desist" letter from Greg's attorneys. Most of this stuff applies to the older Kawasaki KS and Suzuki GS style motors. Technical tips are given as a courtesy to the racer. Results achieved by these tips are the sole responsibility of the racer.

Airbox
When running a full body and fairing combination on your drag bike it is essential that you install an air box. The air is streamlined around your fairing causing a dead air space in the area of your carburetors. This starves your carbs of air and performance is dramatically decreased as much as three tenths or more. Lining your airbox with a heat reflecting material will keep engine heat out so that you have clean cool air.
CAMS Cam Timing
If you want more bottom-end torque, advance your intake cam by 2 degrees. Camshafts
Anyone building a CBR 600 F2/F3 motor for formula car autocross competition with a turbo charger may benefit by using a set of California EPA cams for these engines. With added boost from a turbo you don't need as much lift and duration in the cam. The EPA California cams are .220 duration compared to the .235 duration 49 state cams of the regular CBR 600F2/F3 models. These are factory OEM camshafts. NOTE: California cams only have .263 lift compared to .325 lift for the 49 state cams. Camshaft Lift
A simple method of determining the lift of your camshaft. With a vernier caliper measure from heel of cam to nose, then subtract the base circle. This gives total valve lift. Cam Timing:
KZ 900/1000, GS1100/1150 naturally aspirated motors 110 both intake and exhaust. GSXR (stock cam) - 105 both intake and exhaust GSXR (G21X cam) - 106 intake, 108 exhaust. Turbo Engine Timing
Turbo bikes under boost create a tremendous intake charge. In order to release this charge the exhaust must stay open longer than usual. Suzuki and Kawasaki engines benefit greatly when exhaust cams are set at 112 degrees lobe centers. Set ignition timing at 28 degrees. To Degree Cams:
Install degree wheel and find TDC with a positive stop. Setup dial indicator on valve and zero indicator with valve closed. Rotate engine until valve is .050" off seat and write down reading on degree wheel. Continue to rotate engine until valve is .050" from closing. Note the number. To figure lobe center for intake cam subtract opening number from closing number, divide difference by two and add that number to 90. For the exhaust subtract the closing number from the opening number and follow the same formula.
CARBURETORS Carburetors
For those of you running 29 smoothbores on a mildly modified street machine, here are some suggestions for carb modifications to give better mid-range performance:
# 20 Pilot Jets # 0-4 Needle Jet # 1.0 Air Jets # 2.5 Needle & Set * Float level heights, base of gasket to top of float 23.5 - 24.5mm Mikuni 33mm Smoothbores
For those of you who still own these carburetors a little jetting trick. In order to get better throttle response install 0.6 air correction jets. This allows you to run a smaller main jet while still giving you approximately the same air fuel ratio as before. Good starting point is 4 main jet sizes smaller than you previously had. Also installing a O-6 needle jet will help lean out the mid range. Fuel Pressure
If you're having trouble figuring out correct fuel pressure on your turbo bike buy yourself a 16oz ratio-rite cup like the one moto-crossers use for pre-mixing fuel. Disconnect fuel line going to carb and place in ratio-rite cup. Turn on fuel pump switch and spin motor over with ignition off. Cup should fill in Approx. 15 seconds. If not, adjust fuel pressure regulator in either direction until result is obtained. Lectron carbs
set needle height adjustment at 1.825 - 1.835. Intake Manifolds
For those of you who are planning on running 40mm Mikuni Radial Slide carbs on your '91-92' GSXR-1100 motors, use the intake manifolds from a 1988-89 GSXR-750 and match these to your intake ports. Anyone planning on building a 1978 GS 1000 2V Suzuki and doing a semi-pro ported head with 38 mm Lectron carbs, use Mikuni manifolds Part #VM 36 -200. When mounting Lectrons on your Suzuki GS1100/1150 use Dayco Radiator hose cut to 1-5/8" length. For 40mm Lectrons use 1-5/8" I.D. hose, for 44mm Lectrons use 1-3/4" I.D. hose. Use Kaw "J" model manifolds for mounting Lectrons or Mikuni RS carbs on your KZ/Z1.
CLUTCHES Clutch Plates
If you are having problems with busted clutch plates in your motor, Check the steel plates to see if they are warped. Clutch plates need to be mated properly in order to get a proper grip and not distort. Standard lock-up clutch
use O.E.M. Clutch Springs For those of you setting up your Kawasaki lock up clutch: spring pressure should be checked at .930" in a spring checker. You should look for around 40lbs per spring.
Connecting Rods
When installing Carillo rods on most late model sportbikes, you need around .002 clearance on the big end of the rod. You need to use Plasti-Gauge to determine how much clearance you have, then contact a dealer about bearing sizes needed. Cooling
Use a portable fan hooked up to your generator to cool your motor down between rounds. Crankshaft
When using a GPZ crankshaft in your drag motor you should replace the thrust bearing which is susceptible to failure with a needle bearing. Crank will have to be disassembled. At this time it is a good idea to also have your crank index trued and welded. Cylinder Head
When installing a GPZ head on a KZ-1000 Kawasaki bottom end you must install a cam conversion tower. If the crank has a 15 tooth sprocket use a 122 link cam chain and KZ 900/1000 cam sprockets (30 teeth). If the crank has a 16 tooth sprocket use a 124 link cam chain and Kawasaki MK II cam sprockets (32 teeth). Piston to valve clearance ( minimum ):
KZ / Z1 - 0.050 Int., 0.075 Ex.
GS 1100/1150 - 0.050 Int., 0.075 Ex. Valve to valve clearance ( measured on the seat ):
KZ / Z1 - .200
GS 1100/1150 - .100 Largest valves on a stock seat:
GS 1100/1150 - 28.5mm Int, 24mm Ex
GSXR 1100 (oil cooled) - 30mm Int, 26mm Ex
KZ 900/1000 - 37.5 Int, 31mm Ex
KZ 1000J/GPZ - 38.6 Int, 33mm Ex Exhaust Pipes
Tired of that new chrome exhaust system turning blue after a couple of passes? Paint the inside of megaphone and head pipes with header paint like VHT, etc. The heat is reflected off the coating and out of the exhaust system. Heat does not get absorbed as quickly through the pipe wall. Front End Stiffness
Don't run too high an air pressure in your front tire. 30-35 lbs is satisfactory. Keep front end springs on medium stiffness. Not following these steps can cause the rear tire to lose traction at high end due to unloading of chassis.
HEAD GASKETS On motors using 10.5 to 1 compression ratio pistons, a fiber head gasket will work fine. For racing applications; where 13.5 to 1 compression ratio pistons ar used, a copper head gasket is required. Also, when using a copper gasket, the cylinder block must be o-ringed to help the copper gasket seal. Cutting a groove around the sleeve and using a copper wire thickness of .039 is common place. Leave about .009 height of wire above the block surface. *A Note Of Caution:
When using fiber head gaskets, put them on dry; no sealers or coatings. For copper head gaskets, a spraying of copper coat on both sides is sufficient. Allow it to dry and tack-up for 2 hours before installing. Make sure both the head and cylinder surfaces have been machined flat and are clean before installing the gaskets. Do not use a Copper Head Gasket on a watercooled motor. If the cylinder has been o-ringed, the gasket will not seal enough by biting into the wire and the water will leak by causing overheating problems. Use a spring steel headgasket and do not o-ring the cylinder. Head Gasket Sealing
Proper sealing of head gasket can be accomplished following these three steps. 1. Have your cylinder o-ringed 2. Treat both sides of copper head gasket with a light film of Copper Coat, let dry for 2-3 hours 3. Torque stock cylinder studs to 36 ft lb., heavy duty cylinder studs to 42 ft lb.. Note: both head and cylinder surfaces must be parallel. Horsepower
The formula for figuring correct horsepower is RPM x Tourque divided by 5250
IGNITIONS Ignition System
For those of you who plan to purchase the new Dyna-2000 ignition for a GPZ 1100 motor (1981-85), you must use the ignition housing with seal from a KZ1000J motor. When using a Vance & Hines Powerpak Ignition on your sportbike, use 3 OHM coils with graphite suppression wires. With a Dyna-2000 Ignition, use 2.2 OHM coils with the same type of wire. Air Kill / Rev Limiter
When wiring a two-step with an air shifter on your bike you need to wire the air kill to wherever the tach source is (i.e. Dyna-4000 MSD box) so as not to interrupt the two-step. Ignition Timing
When running a motor at high altitude you must advance the ignition timing.
Example: a Suzuki GS 1100/1150 motor running at 4000 feet above sea level would advance the ignition timing approximately 3-4 degrees. Ignition Timing:
Kaw KZ 900 / 1000 / GPZ
Single plug head - 38 degrees
Dual plug Head - 32 - 34 degrees
NOS motors - 26 - 28 degrees Suz GS 1100 / 1150
Single plug head - 34degrees Dual plug (2-valve) - 32 - 34degrees NOS motors - 26 - 28degrees Battery Charging
When using a total loss ignition system where the charging system has been removed the battery only takes 1-2 runs to lose its peak voltage. Re-charging battery between rounds with a 5 amp charger will cure this problem. Spark Plug Gaps
When running a Suzuki or Kawasaki with a Dyna-S and high performance coils set plug gap at .026. When running an MSD or Dyna-4000 Ignition system set plug gap at .018. Spark Plugs
Racing motors usually require a heat range one colder than stock. We recommend NGK plugs. For a Suzuki GS1100-1150 use a D9EA. For a Kawasaki KZ 900-1000 use a B9ES. With a Dyna-S ignition and aftermarket coils run a gap of .028. If your vehicle has a MSD box or Dyna 4000 ignition run a plug gap of .018 - .020. Ignitions
If you are having problems with your ignition or rev-limiter check your ground. Make sure that you are grounding to bare metal, not a painted surface. Dyna Ignitions, rev-limiters, two steps and Dyna 4000 Ignitions require the use of Dyna wires to work properly These wires have a wire spiral core center which doesn't interfere with the electronics on your bike.
Nitrous Oxide
When running NOS on your bike use a gasoline with an octane rating of 116-120. The higher the octane the slower the fuel burns. This allows you to run a high compression without fear of pre-ignition and detonation. The higher the compression the smaller you go on NOS and gas jet sizes. If you have a low compression motor the bigger you can go on NOS and gas jet sizes. Ignition timing must be set at 28° on Kawasaki KZ and Suzuki GS motors. A rule of thumb in jetting is to allow a spread of 4 jet sizes between gas and NOS, with gas being the larger of the two sizes.
NOS
Before filling that NOS bottle make sure it's good and cold. Place bottle for several hours in your freezer at home. NOS is under pressure at about 200 degrees below zero. Getting the bottle cold allows it to pack more tightly by creating a denser atmosphere. MAKE SURE BOTTLE STAYS COLD UNTIL YOU GET IT FILLED. Oil Level
When changing oil in your drag racing motor never exceed 2-1/2 - 3 quarts. This amount allows adequate lubrication while allowing minimum crank windage. Break in new motors with good grade petroleum base 30w motor oil. We recommend a 5w-30 synthetic motor oil either Mobil 1 or Torco at oil changes.
PISTONS Pistons
When cutting the domes of blank pistons cores you must leave a minimum of .150 piston dome thickness for aspirated motors and .300 for turbo charged applications. Rings
When breaking in a new motor DO NOT use synthetic motor oil as rings will not seal properly. Only use petroleum based motor oil.
Kaw Lock Up Piston To Valve ClearanceFor those of you with a GSXR 1100, this is the easiest method:
Put a degree wheel on crank, get exhaust at 8 degrees BTDC. Set dial indicator on valve tip and put screwdriver between the rocker arm and cam. Pull down read indicator in thousandths to check clearance. With intake set at 8 degrees ATDC, do same as above. Wristpin Buttons
A method for determining what size teflon wristpin button you need is to subtract the length of the wristpin from the bore size. Subtract .020 from this figure, then divide by 2. Racing Gas
Most racing engine applications use an octane rating of 108-114 when compression ratios of 12 to 1 or higher are used.
On turbo/nitrous applications where compression ratios of 8 or 9 to 1 are common, an octane rating of 120 should be used. The higher the octane rating, the slower the fuel is burned. This helps overcome detonation and pre-ignition when large amounts of turbo-boost increase cylinder pressures causing heat build-up.
STUDS Heavy Duty Cylinder Studs
When installing studs in cases put a drop of red Lock Tite on threads and torque to 10-12 ft lbs. Heavy-duty cylinder studs
torque to 40-42 ft lb. Heavy duty main studs
torque to 20 ft lb.
TIRES Slicks
Worn and dried drag slicks can come back to life with a paint brush and a can of VHT traction compound available at your local speed shop. Apply a few coats and let dry. Tire Temperature/Pressure
A little trick that will keep your tires at a constant temperature and pressure. Keep a nitrogen bottle with adapter and filler hose hook-up in your van. Filling tires to recommended pressure with nitrogen keeps tires from growing on hot days. Better foot-print maintained means consistent times while keeping chassis from unloading due to traction loss.
Transmission
If you are using a car tire chassis with your Kawasaki motor, it is a good idea to have a heavy-duty 2nd gear input installed in your transmission. In a high-horsepower motor there is a tremendous load put on this gear when going into 2nd gear, because of the traction the tire gives you. Suzuki 750 Straight Cut Gears
Anyone installing these gears in their motor will need to take approximately 7 teeth off the rear wheel sprocket. Valve Springs
For those of you running high-lift cams, .485-.507 lift Kawasaki and .410-.420 lift Suzuki, we recommend changing your complete set of valve springs every 15 passes for maximum performance. Valve Spring Pressure
When checking valve spring pressure on your Kawasaki KZ900/1000 or Suzuki GS1100/1150, measure the seat pressure at 1.400" in a valve spring checker. Kawasaki 90-100 lb, Suzuki 55-60 lb. Valve Spring Pressure (seat)
GS1100/1150 48-50 LB Street GS110/1150 55-60+ LB Race Valves
When doing a street/strip port job on a GSXR-1100 water cooled head we have found it very beneficial to go to a 1mm oversize intake valve. Valve Seals
Finding it hard to install seals on late model GSXR heads with valve tappets? Applying a little white lithium grease to an 8mm socket will hold seal on socket, then press firmly and evenly into place. Wheelie Bars
In setting up your wheelie bars we recommend painting your wheels with white shoe polish. After making a run check wheels to see if both are having weight applied equally. Adjust wheelie bar heim joints to compensate. Oiling
To get maximum lubrication to your GS1100/1150 motor, remove stock oil pump gears and replace with gears from a GS 750 4 valve model. Valve to valve clearance ( measured on the seat ):
KZ / Z1 - .200
Jan 18th 2023 Cope Racing

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