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Engine Setup Guide (Stomp)

Read Fully Before Continuing

Congratulations on your purchase! You have chosen wisely; the engine you have bought is one of the best available. We put every conceivable effort into the specification and sourcing to ensure that you enjoy your machine to the fullest. We usually get asked the same questions repeatedly. So we have put this page together to answer some of the most frequently asked questions. Hope it helps you out. If not, we are still always on the other end of the phone or email if you are still stuck: [email protected]

TAPPETS​

Set valve clearances on ALL engines. This must be checked on all new engines and during your regular service periods. This will help you get the most out of your engine's performance, so it is good practice to keep on top of this. Out-of-spec tappets can give the symptoms of many faults, and spending a good 20 minutes will keep you on track longer and result in less time in the pits.

Symptoms of a tight tappet can be:

  • Cutting out when hot.
  • Backfiring through the carb while idling.
  • Difficult to start.
  • Low compression.

We recommend setting the valve clearance to 0.004" (0.15mm) for the inlet and 0.006" (0.20mm) for the exhaust for optimal range.

  • Remove generator cover, valve caps, and spark plug.
  • Turn the engine to the T mark, watching the rockers. If they are rocking on the T mark, turn the engine another 360 degrees to the T mark. This is the firing stroke.
  • Undo the locknut on the inlet rocker. Wind out the adjuster.
  • Put the feeler gauge in between the adjuster and valve. Wind down the adjuster to the point of contact, back off a quarter turn, and tighten the locknut.
  • Check resistance on the feeler gauge and repeat the process for the exhaust.

The CDI Unit​

The CDI itself is really just an amplifying switch with time delay. It stores up electricity in a capacitor (i.e., the "C" in "CDI"), then the pulse sensor spikes the input. The CDI waits a small amount of time and then puts the burst of electricity it stored into the coil. That small amount of time represents the advance curve of an engine. For example, at idle, an engine may need 10 degrees advance, but at full revs, it may need 40 degrees advance. By delaying the signal and having the pulse sensor in the right place, the CDI can ensure the engine gets the correct advance curve.

Pulse Coil (Pick-up Coil)​

Another coil, but only a small one. It also has a magnet spinning near it, but the magnet only passes by the coil once per revolution, and it's a really small magnet. This means that most of the time there is no electricity flowing in the pulse sensor, but when the magnet passes by the coil, you get a tiny spike of electricity. This tells the CDI to make a spark as the magnet is positioned so the spike hits the CDI at just the right time. Make sure you have a 0.015” or 0.40mm air gap.

YX 150/160 Oil Coolers​

An oil cooler on these high-performance engines is very important. Keeping the oil temperature lower on these engines will help not only with performance but also with the engine's lifespan. On the YX range of engines, there is a small link pipe on the oil cooler outlets on the bottom of the engine. To run a cooler, you must remove this and screw in the oil cooler fittings supplied in the engine kit. These must be plumbed correctly via the external oil filter. If you fail to do this, you will stop the oil feed and cause serious damage to your race engine, voiding your 28-day manufacturer's warranty.

Caution! If you choose not to run a cooler, please leave the link pipe in place. Failure to do so will restrict oil flow and cause serious engine damage!

Oil Cooler Z155​

Warning! These engines come WITHOUT link pipes fitted! Running the engine without an oil cooler or a link pipe will cause major engine damage, voiding any warranty! You have been warned!

Fitting an oil cooler to the Z155 race engine is the same as the YX150/160. The only difference is there is no external oil filter (the Z155 has an internal oil filter that should be changed with every oil change at a max 5 hours riding time). So simply remove the two bungs on the bottom of the engine, screw in the two oil pipe fittings, and then connect the oil cooler pipes.

Engine Break-In All Engines​

Run the bike at no more than 2/3's throttle and do not allow the engine to rev to a high speed. Engine break-in should be no less than 2 hours.

2 Hour Service​

After 2 hours, carry out the following checks and procedures:

  • Drain oil & replace with Putoline DX4 semi-synthetic 10w 40 4-stroke engine oil.
  • Check all nuts & bolts, and tighten where necessary (use PDI data as a reference).
  • Check the flywheel nut.
  • Check spark plug gap: ~0.6mm-0.7mm.
  • Check Tappets: INLET 0.15MM EX 0.20MM.

Riding Tips For Long Engine Life - IMPORTANT​

  • Do not over-rev your engine as you may cause damage to the valves. Under load, the engine can rev into major valve bounce, causing permanent damage. If you feel the power dropping off or start to hear valve bounce, change up a gear or ease off.
  • It is good practice to carry out these checks regularly, ideally each time you ride your machine. We advise an oil change after every 5 hours of use.
  • Do not stamp through the gears—always use the clutch.
  • If you miss a gear, do NOT stamp into gear from high engine revs.
  • Avoid dropping your clutch heavily or slipping it unnecessarily.
  • Do not allow your air filter to fill with fuel.
  • If the engine backfires while the air filter is filled with fuel, it may ignite—check air filter regularly while riding.

Problem Solving​

  • Exhaust Glows Red (fast tickover): Carburetion too lean, richen mixture via raising needle.
  • Engine misfires at mid to high engine speed, open throttle: Mixture too rich, drop needle.
  • Engine Pops & bangs on over-run: Mixture too rich, drop needle.
  • Engine kicks back hard whilst starting: Ignition too advanced, or mixture too lean.
  • Engine difficult to start: Engine flooding or mixture too rich—check float height.
  • Weak Spark: Pick-up coils too far from rotor (where inner rotor kit fitted) or bad earth.
  • No spark: Either poor earth or faulty Rotor Coils/CDI/Coil/Lead/Cap/Plug—use a multimeter to diagnose.
  • Fuel leaks from overflow: Floats set incorrectly or blocked by debris or sticking.
  • Engine runs fine, but then starts to misfire: Faulty rotor coils/CDI/Coil/Plug.
  • Rattles from engine: Tappets set incorrectly.
  • Engine will not tick over when warm: Tappets set incorrectly.
  • Engine will not return to idle & races: Sticking throttle cable.

Correct Jetting​

Remove the spark plug and check the electrode; the color should be golden brown. If it is white, the engine is running too lean (not enough fuel). If it is black (sooty color), it is too rich (too much fuel). If it is white & black, the engine is VERY lean and causing misfire, which should be noticeable when riding. Since your jets are close to what they should be for the UK, minor alterations can be made by adjusting the needle height on your carb without the need for different-sized jets.

To add more fuel, raise the needle one notch. This is achieved by removing the carb from the engine, removing the throttle slide, removing the needle, and adjusting the position of the circlip. Conversely, if you need to reduce the amount of fuel, drop the needle one notch. Reassemble the carb and continue testing, remembering to check the color of your spark plug.

Once you have achieved the correct full-load fueling, you can set the idle mixture screw. The 140 engines like to run very rich at idle, ensuring a clean progression from idle jet to main jet. To achieve a richer mixture, turn the air screw (next to filter) clockwise. Idle speed may need adjusting at the same time to keep the engine running.

Stomp engine set up guide

The document 'Engine setup guide (Stomp)' is available for download below

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