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Old 04-25-2012, 11:11 PM   #1 (permalink)
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How To Rebuild The Top End on a 400EX or Fourtrax

PART 1



This is mainly for the 1999 2002 400EX and Fourtrax. Newer years will be similar with maybe a few differences. Check manual for torque and specs on newer years just to make sure theyre correct.

TOOLS NEEDED:
Metric Socket Set
6 and 10mm Hex Sockets
Needle Nose Pliers
Standard and Phillip Screwdrivers
Feeler Gauges
Micrometer or Caliper
A Good Straight Edge
Valve Spring Compressor
Hydraulic Press (for servicing the camshaft)
Engine Oil
Molybdenum Oil (Molybdenum Grease mixed with engine oil in a 1:1 ratio)
Locktite
Anti Seize

NOTE: There are some special tool that you may need too, but you can take the parts to a machine or motorcycle repair shop to have checked or serviced if needed


REMOVING THE HEAD COVER:

The first thing you need to do is remove the front and rear fenders and give your quad a good bath so you dont have any dirt or debris falling in the engine while its apart. Then the Air Box, Gas Tank and Heat Shield. Dont forget turn off the gas and disconnect the cable at the front of the heat shield. I usually like to close the choke (on position) on the Carburetor and put it in a clean plastic bag to help keep debris from getting into. You dont need to disconnect the throttle cable from the carb either. Just route it around to the front and set it onto the frame.

Remove the Spark Plug Wire and disconnect the Breather Hose from the top of the head cover. Next remove the upper Engine Hanger Bolt and Spacers that go through the top of the Head Cover.

On the left side of the crankcase, remove the Timing Hole Cap, Crankcase Hole Cap, and at least one of the Valve Adjusting Hole Caps. Using a 17mm socket, rotate the Crankshaft counterclockwise to align the T mark on the Flywheel with the Notch on the inside the timing hole. (The T mark will be sideways with a straight line above it.) The Piston should be at TDC (Top Dead Center) of the compression stroke. To make sure that it is, try to wiggle the Rocker Arms; they should be loose. If they arent then rotate the Crankshaft one more time and re-align the T mark.
Click the image to open in full size.

NOTE: Always rotate the crankshaft counterclockwise. If you pass up the mark then rotate the crankshaft one more time and try again.

TIP: To help know when it coming up on TDC of the compression stroke, watch the rocker arms to start moving down then start watching for the T mark. The Camshaft will rotate twice for ever rotation of the Crankshaft so the mark may not always be right there. There is also an F mark (Fire) a little before the T mark (TDC), so look closely at which one it is. Removing the Spark Plug can make it a little easier too.


After you get it at TDC of the compression stroke then remove the (12) 6mm bolts and the (1) 8mm bolt to the Head Cover. Do this in a crisscross pattern in 2-3 steps. For the first step I usually like to turn them just till you hear the pop of them breaking loose. Then go through them again with about a half to full turn, and the final of fully removing them. Then remove the Head Cover.

TIP: Some of the bolts are longer then the other so heres a tip to remind you were they all go a little easier. Here we have three different length bolts so for all the longest ones I put a green mark on the head of the bolt and a green mark next to the hole it goes in. Then for the second longest bolts I put a black mark on the bolt head and the hole they go in. For the short ones I just left them alone. This is good for when youre not sure how long it will be apart for and dont have to go through dropping the bolts in the holes trying to remember which one went where.
Click the image to open in full size.

Also with the cylinder being at a slant some oil tends to hang out in the left front corner, which will run down the front of the engine when the cover I is removed. To avoid this I usually lift the front of the quad up to where the cylinder is vertical or close to vertical.


Next remove the gasket and then using a pair of needle nose pliers remove the (2) Dowel Pins. Sometimes the Dowel Pins will stay in the Head Cover.

On the back right side of the cylinder, loosen the Cam Chain Tensioner Plug and remove the (2) bolts to the Cam Chain Tensioner and remove it and the gasket.

Back up top, note the position of the Cam Sprocket to the Camshaft, the index mark next to the bolt is pointing up while the lobes are all pointing downwards. There are no marks on the Camshaft or the Cam Sprocket to line it up to and the Cam Sprocket can be bolted on in either direction, but should only go one way. Remove the bolt from the Cam Sprocket and then rotate the Crankshaft counterclockwise to reveal and remove the other bolt and remove it. Pull the Cam Sprocket off of the Camshaft Flange and then while holding the Cam Sprocket and Cam Chain remove the Camshaft with the Bearings and then remove the Cam Sprocket. Attach the wire to hold the Cam Chain from falling into the crankcase.

NOTE: The Bearings on the Camshaft are not pressed on and can side off so be careful not to catch the one Bearing on the Cam Sprocket while pulling it through.

Remove the small Plunger and Spring on the right side and the (2) Bearing Setting Pins. The Plunger and the Bearing Setting Pins should just pull right out loosely. The Spring usually gets held in the hole from the oil. It could be removed after pulling the Head by turning the Head upside down. Just dont forget about it if you leave it in there.
Click the image to open in full size.


REMOVING THE CYLINDER HEAD:

Remove the Exhaust System and the Carburetor. You can leave the Throttle Cable on the Carburetor and just route around to the front of the quad to rest on the frame inside of a good clean plastic bag or rag.

Next remove the (4) nuts and washers. Be careful with the one next to the Cam Chain so that you dont drop it down into the crankcase.

Tip: A small magnet usually works real good for removing the washers. The one large washer in the front can sometimes be pain, but it could stay and removed after pulling the Head.

Remove the Cylinder Head and remove the washer(s) and the spring if you didnt get them before hand. Then remove the gasket and the (2) Dowel Pins.


REMOVING THE CYLINDER AND PISTON:

Remove the front Cam Chain Guide and then remove the (2) 6mm bolts on the lower right side of the Cylinder. Then remove the (4) 10mm bolts and washers on top and remove the Cylinder.
Click the image to open in full size.

Remove the (2) Dowel Pins and place a clean rag around the Connecting Rod and down inside the crankcase.
Click the image to open in full size.

Then with a pair of needle nose pliers remove the Piston Pin Clip from each side of the Piston and then push the Piston Pin out from the Piston and Connecting Rod.

Clean the gasket off using a gasket scrapper being careful not to get any pieces inside the crankcase. I like to use an angle grinder with a light scrub pad on it for the final cleaning.

NOTE: A razor blade can also be used to clean the gasket off, but you half to careful not to dig the blade into the metal and mar it up.
Click the image to open in full size.
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Old 04-25-2012, 11:12 PM   #2 (permalink)
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PART 2



INSPECTING AND INSTALLING THE PISTON:

With the Piston removed, if there’s no abnormal wear, cracks, or damage, then measure the diameter of it at 90 from the pin hole and at about 15mm (.6 in) from the bottom of the piston skirt. The Piston should be replaced it is or less then 84.88 mm (3.3417 in). Compare this measurement with the measurement of the Cylinder to get the Piston to Cylinder clearance.
Click the image to open in full size.

If the Piston is good and will be reused then spread each Ring at the gap and remove them by lifting the other side of the ring up and over the top of the Piston and clean the ring grooves in the Piston with the end of one of the old rings.

Insert the new top and second Piston Rings (one at a time) in the bottom of the Cylinder and square it up using the Piston and measure the gap between the ends of the Piston Ring. The Top Ring should be no more then .50 mm (.02 in) and the Second Ring should be no more then .65 mm (.026 in) and the Oil Side Rails should be no more then .9 mm (.04 in)
Click the image to open in full size.

Next insert the new Rings onto the Piston by starting with the Oil Ring Spacer making sure not to overlap the ends and then the (2) Oil Side Rails (one at the top and one at the bottom of the spacer). Then the Second Ring and then the Top Ring with the mark at the gap facing up. (Look carefully at the rings case there is a difference between the two of them. See pic for an idea of the difference in them). Starting with spreading the gap in the ring and inserting into the grove and sliding the other side down over the side of the Piston. Then check that the rings move freely around in the groove without catching.
Click the image to open in full size.

With new rings you shouldn’t have to worry about this, but it doesn’t hurt to check the ring to groove clearance. While pushing the ring in until the outer surface is flush to the side of the Piston, measure the clearance between the ring and the top of the groove. The top ring should be no more then .14 mm (.006 in) and the second ring should be no more then .12 mm (.005 in).
Click the image to open in full size.

NOTE: Sometime with the Second Ring it’s easier to go to the top ring groove then move it down to the second.

Next stagger the rings as shown here.
Click the image to open in full size.

I usually like to space the ring gaps like this.
Click the image to open in full size.

To install the Piston:
Apply molybdenum oil solution to the Piston Pin and the Connecting Rod and install the Piston with the “IN” mark toward the intake side and insert the Piston Pin through the Piston and the Connecting Rod. Then install new Piston Clips in the grooves of the Piston and make sure they are fully seated. Don’t align the gap in the Piston Clips with the small cutout in the Piston.


INSPECTING AND INSTALLING THE CYLINDER:

Start by checking the inside of the Cylinder for any cracks or scratches. Then the top of the Cylinder for warpage with a good straight edge and a feeler gauge. Lay the straight edge across the machined surface and up against the studs, checking in all four directions. If there’s more then .1 mm .004 in() of space anywhere along the straight edge then it will need to be resurfaced.
Click the image to open in full size.

You’ll need a Dial Indicator to do this next step, but most machine or bike shop should be able to check it for you too if you don’t have one.

Measure the inside diameter of the Cylinder at the top, middle, and the bottom and use the maximum reading to determine the wear. This should be less then 85.1 mm (13.35 in). If exceeding this measurement you’ll need a New Piston and have the Cylinder re-bored.

NOTE: Never have the Cylinder re-bored without having the piston first. If a machine shop says they can do it without the piston, go to another machine shop.

The Cylinder to Piston clearance should not exceed .1 mm (.004 in). This can be determined by subtracting the Piston’s diameter from the Cylinder’s diameter

To install the Cylinder:
If you haven’t already clean up the gasket surfaces of the Crankcase and the Cylinder as mentioned above and install the Dowel Pins and a new gasket. Coat a new O-ring with oil and install it in the groove on the bottom of the Cylinder.

Apply oil to the Cylinder wall, Piston, and Rings and double check the Ring spacing. Route the Cam Chain through the Cylinder and slide the Cylinder over the Piston while compressing the Piston Rings with your fingers. Don’t force the Cylinder down over the Piston Rings.

With the Cylinder fully seated, apply a light coat of oil or anti-seize to the threads of the 10mm Cylinder Head Bolts and install them with the washers. Tighten them down in a crisscross pattern in 2-3 steps to a final torque of 33 ft lbs.

Install the (2) 6mm bolt to bottom right side of the Cylinder and tighten them securely (about 10 ft lbs).

Install the Cam Chain Guide into the Cylinder and Crankcase aligning the knobs on the guide with the grooves on the Cylinder.
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How To Rebuild The Top End On A 400EX Or Fourtrax
How To Clean A Carb
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Dail-A-Jet
142 Main Jet
And homemade air scoops

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Old 04-25-2012, 11:13 PM   #3 (permalink)
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PART 3


INSPECTING AND INSTALLING THE CYLINDER HEAD:

Clean off the carbon deposits from the valve area, and clean off the gasket surface. Check for cracks, especially in the spark plug and the valve area. Then check the Bottom of the Head for warpage with a good straight edge and a feeler gauge. Lay the straight edge across the machined surface along the bolt holes, checking in all four directions. If there’s more then .1 mm .004 in() of space anywhere along the straight edge then it will need to be resurfaced.
Click the image to open in full size.

Using a spring compressor, remove the (2) Valve Spring Cotters, Spring Retainer, inner and outer Valve Springs, and Valve Seat with each of the Valves. Mark all the parts so that they can go back into their original locations. Then remove all the Valve Seals.
Click the image to open in full size.

NOTE: Set the spring compressor up to compress the spring just enough to get the Spring Cotters out.

If you don’t have a Spring Compressor, but have a drill press then you can try this idea of a Drill Press Valve Spring Compressor by Helmut (scroll down to post #8 to view pics of it in use).


Here you can see all the valve parts and the order they go in. For keeping each valve set together I like to stack all the part onto the Valve that they go with and mark the bottom of the Valve with an “L” or “R” for what side of the Head they go on.
Click the image to open in full size.

Measure the height of the Valve Spring and replace them if they become or are shorter then 36.3 mm (1.43 in) for the Inner Valve Spring and 43.1 mm (1.7 in) for the Outer Valve Spring.

Check that the stem of the Valves move smoothly through the Valve guide. Check for bending, burning, or abnormal wear. Measure the diameter of the stems and replace them if they become or are less then 5.46 mm (.215 in) for Intake Valves and 5.44 mm (.214 in) for Exhaust Valves.

You’ll need a Dial Indicator to do this next step, but most machine or bike shop should be able to check it for you too if you don’t have one.

Ream the Valve Guides to remove any carbon from them before measuring the guides. Insert the 5.5mm reamer from the Combustion Chamber side and always rotate it clockwise. Measure the inside diameter of the Valve Guides and replace them if they become or are more then 5.52 mm (.217 in)

Subtract diameter of each Valve from the measurement of the corresponding Valve Guide to determine the stem to guide clearance. Replace the Valve and/or the Valve Guide if the clearance is or more then .12 mm (.005 in) for the Intake Valves and .14 mm (.006 in) for the Exhaust Valves.

NOTE: Inspect and reface the valve seats whenever the Valve Guides are replaced

Use compressed air to blow through the oil passage and the intake and exhaust port to make sure they’re clear of any dust or debris in the Cylinder Head, and install new Valve Guides (if replacing), and lubricate new Valve Seals and install them.

Lubricate the stems of each Valve with molybdenum oil solution and insert them into the guide while turning it slowly to avoid damage to the seal. Install the Spring Seat, inner and Outer Valve Spring (with the tightly wound coils downward) and the Spring Retainer. Compress the Valve Spring and insert the (2) Spring Cotters with a little bit of grease on the inside of them to help hold them into place. Then release the spring compressor slowly.

After all the Valves are reinstalled support the Cylinder Head so that the Valves will not contact anything and tap the end of the Valves gently with two plastic hammers to make sure the Spring Cotters are fully seated. With one hammer resting on the top of the Valve tap it a few time with the other hammer.

To install the Cylinder Head:
Remove the Carburetor Insulator if you haven’t already and install a new O-ring coated with oil and install it back onto the Cylinder and tighten the (3) bolts securely.

Install the Dowel Pins and new gasket onto the Cylinder. Then route the Cam Chain through the Cylinder Head and install the Head onto the Cylinder. Apply a little oil to the threads of the Cylinder Head Nuts and install them and the washers by tightening them down in a crisscross pattern in 2-3 steps to a final torque of 33 ft lbs.

NOTE: Make sure that the larger washer goes to the front cylinder stud by the Spark Plug. Could use anti seize on the nut next to the Spark Plug.
Click the image to open in full size.

Install the Spark Plug by just a few threads to keep any debris from falling through hole.
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How To Rebuild The Top End On A 400EX Or Fourtrax
How To Clean A Carb
Download Free Service Manual

2001 TRX400EX
Dail-A-Jet
142 Main Jet
And homemade air scoops

Like rabid monkeys in a washing machine.
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Old 04-25-2012, 11:13 PM   #4 (permalink)
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PART 4


INSPECTING AND INSTALLING THE CAMSHAFT:

Check the cam journal surface for any scoring, scratches, or signs of not getting enough lubrication. Check the holes in the Camshaft to make sure they are clean and not clogged up. [i]The Camshaft is hollow so that the oil will run through it and out the holes to lubricate it.[/ i]

Check the bearings by spinning the outer race to make sure that it turn smoothly and replace if needed.

Measure the runout of the Camshaft with a dial indicator and replace the Camshaft if it is or more then .03 mm (.001 in)

Measure the height of the cam lobes and replace the Camshaft if they are or less then 30.57 mm (1.204 in) for the intake and 30.37 mm (1.196 in) for the exhaust.

Next set the Camshaft in a hydraulic press by supporting the Reverse Decompressor Cam Flange and press the Camshaft out of the Sprocket Flange.
Click the image to open in full size.

NOTE: Do not support the assembly by the Sprocket Flange cuz it will crack or break. When setting the assembly, take care not to contact the support blocks with the cam lobes or the Decompressor Cam to avoid damaging them.

Remove the following parts from the Camshaft and inspect them for wear or damage. Then lubricate all the parts with oil for reassembly.
Thrust Washer
One Way Clutch (Clutch Outer, Rollers and Spring)
Reverse Decompressor Cam
Stopper Pin
Decompressor Cam
Spring
Click the image to open in full size.

Install the spring into the Camshaft hole and install the Decompessor Cam while holding the spring down inside the hole.
Click the image to open in full size.

Next assemble the Reverse Decompessor Cam and Clutch Outer with the Stopper Pin and install the assembly onto the Camshaft.
Click the image to open in full size.

Install the Springs and Rollers into the Clutch Outer grooves as shown in the pic. Then install the Thrust Washer.
Click the image to open in full size.

Using a suitable tool (collar with 19mm ID) press the Sprocket Flange onto the Camshaft making sure to align the wide groove with the wide tooth.
Click the image to open in full size.

To install the Camshaft:
Making sure that the “T” mark on the Flywheel is lined up with the notch on the inside the timing hole, start off with installing the Bearing Setting Pins and the Spring and Plunger. Then lubricate the Camshaft Bearings with oil and installing them on the ends of the Camshaft making sure that the sealed side is facing out on the one that goes on the sprocket end. This is so that the oil can fill up into the side pocket area of the head and flow into the camshaft to lubricate it.

Next apply molybdenum oil to the cam lobes and journal and set it to the side where you can get to it easy like the top of the Cylinder Head. Install the Cam Sprocket onto the Cam Chain so that two of the index lines on the sprocket are inline with the upper surface of the Cylinder Head and the third one is pointing upward.

Install the Camshaft onto the Cylinder Head through the Cam Sprocket and slide the sprocket onto the Camshaft. Check that all the slack in the chain is on the backside of the engine while the index marks are still inline with the head surface. If it not, slide the sprocket outward and you’ll have enough slack in the chain to adjust it on the sprocket. Make sure that the lobes on the Camshaft are facing downward and bolt the sprocket to the Camshaft Flange with some locktite on the bolt threads and toque down to 14 ft lbs.

NOTE: You will need to rotate the Crankshaft (counter clockwise) in order to get to the second sprocket bolt.
Click the image to open in full size.

Click the image to open in full size.

Remove the plug from the Cam Chain Tensioner Lifter and check it for proper operation. The Tensioner Shaft should not go into the body when pushed. With a small screwdriver rotate the screw inside the body clockwise and the shaft should be pulled into the body as the screw is turned. Pull the screwdriver out and the shaft should immediately spring right back out.

You’ll need to make a Tensioner Shaft Stopper Tool out of a thin piece of metal about 0.8mm thick. See pic for dimensions.
Click the image to open in full size.

After you got you’re new little tool made, use it to turn the Tensioner Shaft clockwise until it is fully retracted then push the stopper tool into the slots on the tensioner to lock the shaft in the retracted poison.
Click the image to open in full size.

Install a new gasket and install the tensioner onto the Cylinder and tighten the (2) bolts down securely and remove the stopper tool. Look down the Cylinder to double check that the shaft sprung back out and is pushing up against the Chain Guide. Then coat and/or replace the o-ring on tensioner with a little oil and reinstall the plug.
__________________
How To Rebuild The Top End On A 400EX Or Fourtrax
How To Clean A Carb
Download Free Service Manual

2001 TRX400EX
Dail-A-Jet
142 Main Jet
And homemade air scoops

Like rabid monkeys in a washing machine.
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Old 04-25-2012, 11:14 PM   #5 (permalink)
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PART 5


INSPECTING AND INSTALLING THE HEAD COVER:

The Head Cover doesn’t really need to be torn down unless the one or more of the Rocker Arms is damaged or worn.

If this is the case then with the mating surface of the Head Cover face down on a bench with thick rag underneath it, loosen the Sub-Rocker Arm Shafts and remove them along with the Sealing Washers, Sub-Rockers Arms, and Wave Washers.
Click the image to open in full size.

Then the same thing for the Rocker Arm Shafts, Sealing Washers, and Rocker Arms.
Click the image to open in full size.

Clean all the parts thoroughly and apply oil to the Rocker Arm Shafts and Rocker Arms sliding surfaces. Install the Rocker Arms into the Head Cover followed by the Rocker Arm Shafts with new Sealing Washers. Apply locktite to the threads of the shafts and torque down to 20 ft lbs.

Then again the same thing with the Sub-Rocker Arms, Sealing Washers, Sub-Rockers Arms, and Wave Washers.
Click the image to open in full size.

Note each identification marks on the Sub-Rocker Arms.
Click the image to open in full size.

Here’s a closer look at the identification marks.
Click the image to open in full size.

To install the Head Cover:
One thing I always like to do just before installing the Head Cover is to pour little oil over the Camshaft and Cam Chain. Also put oil in the pocket on the side of the Cylinder Head.

Install the Dowel Pins and new gasket and rotate the Crankshaft counter clockwise and realign the “T” mark on the Flywheel to the notch and the Index Lines on the Camshaft to the head surface (camshaft lobes should be facing downward).

Clean the mating surfaces of the Head Cover and the Cylinder Head and then apply molybdenum oil to the ends of all the Rocker Arms where they slide against each other or the Camshaft. Then install the Head Cover onto the Cylinder Head and bolt it down using a crisscross pattern in 2-3 steps to a final torque of about 10 ft lbs on the (12) 6 mm bolts and 17 ft lbs for the 8 mm bolt.

This is the bolt tightening order I usually use.
Click the image to open in full size.

Check and adjust the Valves as needed. 0.10 mm (.004 in) for the intake and 0.12 mm (.005 in) for the exhaust.

Connect the Crankcase Breather Hose to the Head Cover and make sure that the engine rotates freely by manually rotating the Crankshaft counter clockwise a few rotations. It would also be good to do a Compression Test at this time. Then you can fully install the Spark Plug and torque down to 13 ft lbs.

This would also be a good time to install the Carburetor and just set the Gas Tank and Front Fender (to hook up ignition) on and lightly seat the Exhaust Header and muffler against the new gaskets. Start it up and run it just long enough to make sure all is good. Just want to make sure there are no noises that shouldn’t be there.

If it’s still in one piece and/or not screaming tear me back apart then you can finish it up and install the Spacers and Upper Engine Mounting Bolt and torque to 40 ft lbs. Then fully install the Exhaust System, Air Box, Heat Plate, Gas Tank, and Fenders

BREAKING IN THE ENGINE:

There are many different ways that people like to break-in their engine, but this is the way I usually like to do it. After starting up the engine, immediately turn off the choke (along with any time you start the engine even after break in), keep it revving slightly above 2,000 RPM in order to get sufficient lubrication. Vary the load on the engine up a little at a time as it warms up until 70% of redline. When it gets up to about 120 or where your hand is uncomfortable against the side of the cylinder, take it for a good semi-aggressive ride varying the load and avoiding long full throttle operation or bogging the engine for about 30min with a few good thumps on the throttle in 2nd-4th gears then ride it like you stole it (or however you like to ride).

Here are a couple other ways.
How to "Break-In" Your Newly Rebuilt Engine (By: Saber6)

The Motto Man Way



THAT”S IT!!! NOW GO RIDE AND ENJOY THE FRESH AIR AGAIN….




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How To Rebuild The Top End On A 400EX Or Fourtrax
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2001 TRX400EX
Dail-A-Jet
142 Main Jet
And homemade air scoops

Like rabid monkeys in a washing machine.
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Old 04-26-2012, 09:43 AM   #6 (permalink)
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Great write up. That should be of great use to people who have no exp. with engine work. good detail, props to you for this.
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Old 04-26-2012, 09:59 AM   #7 (permalink)
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great write up i thank this should be a sticky im gonna add it to my sig for people who need help
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Old 04-26-2012, 10:29 AM   #8 (permalink)
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Thank for the comps guys. I agree on the sticky "Hint, Hint" Moderators.
Also a great idea with putting your sig. I think I'll do the same along with a few others.
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Old 04-26-2012, 04:22 PM   #9 (permalink)
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This is awesome!

Great job, will help many many people.

Agreed on the sticky!



Oh400ex
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Old 04-26-2012, 07:38 PM   #10 (permalink)
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Great job any information like this should be a sticky
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