Video Credit Red Beard's Garage

The Tillotson 225RS stands out as a 4-cycle TAG(Touch-and-Go) engine, a unique feature it shares with the Briggs LO206, World Formula Engines, and Harbor Freight with the Ghost 212. 

EC and Tillotson collaborated on developing the 196R, 212R, and Tillotson 225RS. EC contributed the 225RS block, head, rod, piston, flywheel, and blower housing, while Tillotson handled the carburetor and, with RLV's assistance, the exhaust. PVL, now under Tillotson's ownership, produces the coil.

The 225RS is a 'spec engine, 'meaning it is a Race Spec engine with the bottom end sealed, rev limited coil, and strict rules. Tillotson's T4 Series extends this concept with the spec T4 kart made by IPK, which produces Praga, Formula K, and OK1. Additionally, Maxxis has developed a spec tire. Tillotson offers a complete turn-key package for novice and experienced racers at an entry-level price. The T4 Series has achieved international success, and Tillotson hosts their World Championship in Valencia, Spain. 

While initially designed for karting, the Tillotson 225RS has gained popularity beyond its spec class and karting in general, thanks to its robust block. The 225RS can be purchased as a long block, providing a versatile base for engine modifications. Some retailers even use the long block to create a complete engine known as the 225R. This flexibility allows you to either complete a short block or upgrade your Tillotson 225RS with parts from EC, empowering you to tailor your engine to your specific needs.

Like many of the previous videos, we are examining overall performance and the cost of performance to find the best value in the context of modified engines. 

The Tillotson 225RS, priced at around $950-$1000 for the spec version, offers a competitive cost-performance ratio. If you're not running the 225RS in a specific class, consider using it as a turn-key mini bike engine or a base platform for modifications. In such cases, start with a Short Block 225R, EC's 228R, or one of EC's 236cc kits. 

The Tillotson 225RS Long Block costs approximately $520 and needs a flywheel, coil, carburetor, and header to be completed. Depending on the parts, these parts cost around $300-$350 extra. Some places will sell complete versions for around $850. It is unusual but not uncommon for the 225RS Spec Engine to be upgraded.

What carburetors will be tested?

One significant difference between these engines will be the carburetor and intake. While the Tillotson FM22, GPS22(Knock-off VM22), and Wildcat WC22 are similar carburetors in appearance, they will be tuned and perform differently. Another contributing component is the intake manifold. Tillotson has a curved intake manifold initially designed for an HW diaphragm carburetor. To adapt the FM22, they made a billet adaptor, so the intake is technically two pieces. Recently, Tillotson has produced new intakes that are one solid casting. 

EC uses a short straight intake but also has curved intakes, one for flat-mounted engines like on mini bikes and one for 8° angled engine mounts, typically used on sprint-style racing go-karts. The intake has a nice gradual taper to improve airflow and velocity. 

Knock-off VM22 Carburetors have a billet intake manifold that angles the carburetor, which can sometimes cause misalignment. The intake is straight but longer than the EC intake, which can cause fitment or clearance problems. The intake doesn't gradually taper but chokes down right before the port's inlet, which can result in turbulence and poor carburetor signal.

Tillotson 225RS Specs

Bore x Stroke: 72mm x 55mm 

Compression: 9.3:1

Cam: 265 lift/235 Duration

Carb: 26mm Round Slide

Flywheel/Ignition: Billet Aluminum Flywheel with PVL CDI Ignition Rev Limited to 6500rpms

Head: 27/25mm, 5mm Stem, 22cc Combustion Chamber

Rod: Billet Aluminum w/Bearing

Piston: 72mm hypereutectic casting, 13mm wrist pin, .767 compression height

We are embarking on a comprehensive testing process for the Tillotson 225RS, examining its performance in various stages and comparing the effects of different components. This thorough approach ensures that the results we present are reliable and can be trusted by our audience of engine enthusiasts and karting racers.

What components or configurations will be tested?

1. Exhaust Testing—The Tillotson 225RS uses three different exhausts: a Euro Spec and two USA specs. In the video, we will test the US specs back-to-back. The short header is pre-2024, and the long header is new for 2024. The new exhaust should improve performance both in power and engine longevity.

2. FM22 vs. WC22 – The Tillotson 225RS is very restricted on engine and carburetor blueprinting. We want to see if more power is left on the table for a blueprinted carburetor. Does this help the engine start and perform better?

3. Tillotson 225R—Tillotson 225R is the Tillotson 225RS long block with an ARC Racing Flywheel, Stock Tillotson Ignition Coil, and GPS22 slide carburetor.

4. GPS22 vs. WC22—Which carburetors start and run the best? In this test, we're not only answering which is better but also want to take a closer look at both carburetors' air-fuel ratio and jetting. There is a little bit of misunderstanding regarding carburetor tuning and blueprinting, and we want to show why people have difficulty tuning these knock-off "VM22" carburetors.


1. Exhaust Testing – The longer exhaust helps to make a little more power and moves peak power closer to the max rpm. But that's not the only benefit. The short exhaust restricts exhaust gases, which trap more heat inside the engine and increase back pressure, which makes the engine less efficient. Heat is one of the worst things to an engine. Not only doesn't ambient temperature play a role in an engine's performance, but so does the cylinder and exhaust temperature. If the carburetor is running too rich, unburnt fuel can trap itself in the header and muffler, and exposure to high heat or ignition and fresh air can cause explosions. The exhaust valve is more prone to warpage because of the high exhaust temperature, whereas the intake valve is cooled by fresh intake charge and fuel. We're glad to see Tillotson change this for those racing in higher ambient temperatures and endurance racing formats. Not only will the engine perform better, but it will also last longer. 

2. FM22 vs. WC22 – The FM22 is the spec carburetor and can only be run in its unmodified state. So, if you are watching this video looking for an upgrade to your Tillotson 225RS, the WC22 is not a legal carburetor.

There is very little difference in the power made by each carburetor. The FM22 made .3ft-lbs more torque but ran much richer. 

Tuning for a richer low speed was common when we ran flatheads to increase compression without compromising flow from decking the head or block. The fuel occupies space in the cylinder, and unburned essential makes the combustion chamber smaller. There are a few drawbacks. The unburned fuel can pass the rings, especially at idle and low speed or when the ignition coil is bouncing off the rev limiter. That fuel will dilute the oil, leading to lubrication problems at the bottom end. You'll need to change your oil more frequently to prevent any problems. The other issue is carbon buildup on the plug, which can cause misfires or entirely extinguish the spark. Over time, this makes the engine harder to start and causes a loss of power. 

From another technical aspect, the WC22 has better Brake Mean Fuel Consumption(BMFC) than the FM22. It produces approximately the same power while using less fuel. In an endurance race, you're trading a small amount of torque for better longevity and better mpg. 

3. Tillotson 225R – The Tillotson 225RS is advertised to be around 15hp, and it's very close now that it uses the longer pipe. On the same dyno, the Tillotson 225R claims to make 17hp. We've said before that all dynos will measure differently. However, the Red Beard's dyno is recalibrated with guidance from the manufacturer to give closer to real accurate numbers than most. Nether engine makes what it claims, but that's not our point. We wanted all these combinations to be compared using the same dyno to compare better the performance and value of each engine and part. 

4. GPS22 vs WC22 – Both carburetors are versions of what many call knock-off Mikuni vm22, even though they are closer to a PZ26 in design. Both have far different calibrations and jets. The GPS22 has a 130-main jet with a 16-pilot jet. EC's WC22 has a 105 main and 12 pilot. However, the WC22 air-fuel ratio is more consistent and has more top end than the GPS22. Why is that? 

EC has a better understanding and many more years of experience. The jetting is only one part of a carburetor's tuning. The carburetor has a float, nozzle, emulsion tube, air bleeds, slide, and metering rod that all play a role. So, if you get an EC WC22, don't immediately go to changing jets under the assumption it needs to be tuned like another VM22 knock-off. The WC22 has been used on the Stage 3 tested so far, and both the Tillotson 225RS and Tillotson 225R have been used without any jetting changes. 

The Knock-off VM22 carburetors and jets are very cheap on Amazon and eBay. One of the most popular questions is how to get these carburetors to run, and most land is between 125-135 for the main and around 15-20 for the pilot. 

The Knock-Off VM22 is highly hit or miss because of its high volume production and broad application use. Typically, with eBay and Amazon carburetors we've tested years ago, even with a 130-135 main jet, there isn't enough fuel for high rpms pulls, and the main jets tend to enrich the low-speed fuel circuit, which leads to a misinformed spark plug reading with a very dark wet plug. These problems are all over the internet, social media, and forums. Rarely is there an answer but never a resolution. Those carburetors are not calibrated for these engines, so you'll always have a compromised tune. Now, with the GPS22, it seems the carburetor is too rich for high rpms. 

The great thing about the EC carburetor is that it is far better tuned out of the box and more responsive to changes. Since the carburetor flows close to 90cfm and starts with a 105 jet, the carburetor can continue to be tuned for more heavily modified engines. 

Comparing advertised dyno numbers with Red Beard's Garage

Road to Horsepower aims to provide comparable results for different brands and engines. It's easily one of the most frequent questions we get, and it's usually difficult to answer because of each dyno's setup and test procedure. We've already covered the difference in the Tillotson 212E, advertised as about 30-45% higher (9-10hp) than Red Beard's dyno (7hp). The Tillotson 225RS and Tillotson 225R are no different. The Tillotson 225RS with the original short header was advertised to make 15hp, whereas it made 13.83hp on Red Beard's dyno, which is a difference of about 9%. The long pipe now makes it even closer to 15hp by making 14.29hp for a difference of 5%. 

The Tillotson 225R is advertised to make 17hp, about 13%(2hp) more than the Tillotson 225RS. However, the real-world test results show the engine made less power than the RS model, even with the short pipe, making 13.62 for a difference of about .21hp for the short pipe and .67hp for the long pipe. The difference between the real world and advertising is about 25%(3.38hp). Again, dynos can read differently, making it hard to compare the engines. Luckily, GPS has a graph of their dyno results, which we can use for comparison. 

Here are the dyno results for each engine as they have been displayed. However, the output of the results is on a different scale, so overlapping the results will require some manipulation to match them to scale. Here are the unmanipulated results:

Tillotson 225R Unaltered Tests

Here, the manipulated rpm scale means we didn't change the horsepower between the two graphs, just matching the rpms.

Tillotson 225R Test 1

Here, the manipulated to full scale means the rpm and power curves are adjusted to the same scale in height and width. The curves themselves are not changed. You can interpret the information from the original dyno graph, but it is easier to explain by matching the scales of the dyno results. 

Tillotson 225R Test 2

We've added the Tillotson 225R with EC's WC22 carburetor to compare all three tests. 

Tillotson 225R Test 3

Since there is about a 25% discrepancy in numbers, we have to match the graphs by lining up the charts and where the horsepower and torque cross over at 5252rpms. However, it appears to be a different location on the three GPS tests, so we will use test 2 since that is the best run. Remember, horsepower is a calculation of torque x rpms divided by 5252, so that is where the power and torque will cross over. The rpms where the Tillotson 225R makes peak torque and peak horsepower are basically the same. Where the engine falls off is the same, too. While the information is presented differently from the GPS test to the Red Beard test, the results are the same even with the different scaling. 

If you have followed the Road of Horsepower Series, Red Beard has tested the Predator 212 Hemi, Wildcat 223, and a stroked version of the Ghost 212 to make it 223cc. The components and specs of these engines are nearly identical, especially regarding the carburetor, camshaft, flywheels, and coils that come in the stage 3 kits. The peak numbers and general power curves are very similar. The Ghost 223 and Wildcat 223 also had their heads ported, which was a significant gain in performance. However, none of them have reached the 17hp claim of the 225R. The point is that nothing substantial can be tuned, or modified to meet those numbers. Instead, Red Beard's tests on all these engines were the most accurate comparisons. We will test our 228R MKII in the following video with a breakdown comparison of all the "stage 3" builds at this point. 

How significant is the difference in performance in the context of a kart or mini bike racing? 

The WC22 carburetor makes more power and torque and can turn more rpms. The engine was still pulling past 8000rpms, but Red Beard ended the run as the wheel speed had exceeded the manufacturer's recommended limit. In the context of racing, this can be just as significant as making more power. For example, the Maxxis Sprint tires have a circumference of 33.25", and if we are running 19/68 gears, it gives you a 3.579 ratio. Using our gearing calculator at 7200rpms, that is 63.34mph. Suppose we use the same ratio but turn 8500rpms produces 74.87mph. Realistically, the air resistance/drag and required track length would make that difficult. However, we can use the extra rpms to improve torque and acceleration.

The Tillotson 225RS with the GPS carburetor achieves 63.34mph with a 3.579 ratio. If we multiply the torque and power numbers by the ratio, we get 48.75hp and 46.09ft-lbs at the tire minus resistance and losses. With the EC WC22 carburetor and turning 8500rpms, we can change to 16/67 gears for a 4.188 ratio to achieve 63.91mph, which is a little more but very close to the other setup if we multiply the 14.6hp/13.45ft-lbs by 4.188 for 61.14hp and 56.32ft-lbs. That's a difference of 12.39hp(25%) and 10.23ft-lbs(22%) between the difference in power at the crank, the rpm range, and the gear ratio for both engines to have a max speed of 63mph. Even if you used the 17hp claim, if the max 7200rpms and gear ratio of 3.579 is used, that's 60.85hp to the tire. An engine turning more rpms with less hp can be quicker to the same mph. 

We want to make the case that relatively small changes in engine performance can be much more significant when applied in context. This means your setup, such as your gear ratio, is also critical to the performance of your kart or mini bike. 

The 228R MKII is up next with more dyno testing videos in the near future.

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