Tillotson 225RS Carb Problems

So, six of us bought new 225RS motors to run in 2024 for our Orlando Cup heavy class. So far 3 of us have had nothing but issues with the FM-22 carb that comes with the motor. Tillotson switched to this cheap carb from the diaphragm style they first introduced the 225 with. As many owners know, these motors have notoriously been very hard to start. Many times requiring starter fluid to get them to fire. Not ideal on a starting grid when multiple classes run and you literally have minutes to get there as soon as the previous class finishes their qualifying, heat or final.

Our issue is the motor dies in the turns. Runs good down the straight which leads us to believe it’s a float level problem being too high. If it was too low, it would run out of fuel down our pretty long straight at OKC. I’ve tried lowering the float level to no avail to completely eliminate the stalling issues. The factory level was much higher and initially it was bogging and stalling all over the track. Lowering it has now isolated it to the corners only.

Out of frustration, I decided to see if my Briggs 206 carb would line up with the mounting holes on the Tilly manifold. It did so I installed it and took it out on track. It started extremely easy and ran flawlessly like our 206’s tend to do. 1 or 2 pulls at most to start and no bogging or stalling the 3 sessions I ran with about 10 laps each. Our track owner was interested in my experiment and they had given me a new FM-22 under warranty last weekend. That was the first time taking the kart out with the new motor. Same issues with the warranty carb.

We purchased all 6 motors from them and he mentioned he’s had 8 carbs come back to him over the last couple of months all with running issues. Anyone else here experiencing the same problem? There’s literally no information on the web regarding float height settings for the FM-22 and their emails to Tillotson have so far gone unanswered.

OKC told me I may have solved everyone’s problems with the Tilly carb and may notify tech to allow us to use the Briggs carb as an alternative. I suggested that or an actual Mikuni VM-22 which I’m going to order and try next. These knockoff FM-22’s seem to be absolute garbage and the parts guys at OKC agree. They’re just as frustrated as I am with the problems and giving us new carbs under warranty all out of their pocket so far.

I had one of the very first 225 RS engines that came into the states. Also had same issue, that was before carb change.

Anyway, I ran a 225 a few months ago with the new carb at an endurance race. 4 hour race and we had challenges getting it started. It mainly came down to priming it beforehand as you say and then pulling like a ‘real’ man every time to start it. It’s annoying and unnecessary. The Briggs carb helping it does not surprise me at all.

The only thing I can suggest is potentially checking the float drop height on the Tilly carb. On a Briggs carb if that is not set correctly (1” drop) that will cause the same issue on the Briggs.

I spoke with a guy who was the president of Tillotson USA about a month ago at PRI. I’ve been in karting quite a while but had never heard of him, and he seemed a little annoyed when I kept asking for clarification of Tillotson USA vs Tillotson MFG vs Tillotson Ireland vs EC….but I digress.

It’s a cr@pshoot at this point because there’s no information whatsoever on height and drop settings for this newer style carb. It just pours fuel out of the filter at times after shutting it off indicating a stuck float need. I tried my Mighty Vac on the fuel inlet and it held vacuum so when seated, the needle is sealing.

In the end, I was amazed how well it started and ran with the 206 carb without changing a thing. I simply took it off my motor, put it on the Tilly and once fuel was in the bowl it started on the first or second pull repeatedly. Andre the owner at OKC and his parts guys/mechanics were shocked when they saw my experiment worked and how easy it started every time.

EC sells a blueprinted FM-22 so I think they’re all aware of the problem and are offering a tweaked carb to help but to me that’s a money grab in my opinion and owners shouldn’t have to fork over money to replace a bad design.

You could try a restriction in the line such as a jet at the inlet… that might help with over fuelling.

Sounds like a frustrating experience though.

This is going to be a long story, but the starting problems have been an issue since the engine was released. We have felt like we’ve been caught in the middle of this program since we started it at the end of 2015.

I’ll first address the difference between Tillotson MFG, Ireland, USA, and EC.

Tillotson was bought by Borg Warner in the late '60s and sold in the early to mid-80s. I believe Borg Warner built the factory in Ireland, which became the location where Tillotson carburetors were manufactured. It’s an Irish company owned by Americans.

Tillotson-USA was EC. EC was advertised as EC Tillotson USA in all the kart magazines or online publications for decades. EC became the primary importer of carburetors for kart racing around the time Borg Warner sold the company. EC designed and developed many of its carburetors. Part of the problem is so many people believe EC was Tillotson. That’s not the case. However, EC developed the carburetors, wrote the technical articles, blueprinted the carburetors, and built the reputation for decades. We even helped develop the Tillotson 196R, 212R, and 225RS engines, with some exceptions regarding the carburetor and exhaust systems.

First, the carburetors. Tillotson started with an HW diaphragm carburetor. There isn’t a greater authority with Tillotson carburetors on 4-cycle engines than we are, having designed many of the ones sold by Tillotson. We told them you would have a problem getting the diaphragm carburetor to idle on any 4-cycle engine, and it’s not something you want to use for a spec class. They tried to reassure us they could get it to work.

To get the carburetor to idle, you can try setting a high pop-off pressure or leaning out the low side circuit, but the engine becomes difficult to start, and it isn’t going to perform very well. Tillotson had both issues. The engine wouldn’t start, so they came up with a starting procedure they posted on YouTube that included removing the air filter and choking the engine by hand to get it to start, but it would still take many pulls to start. The other problem is a very narrow tuning window and the sensitivity of the high and low-speed needles.

We were able to fix the starting issues and improve the carburetor, but Tillotson decided to switch to their TCT, which I don’t believe made it state-side but was covered in an article with Vroom or Tkart. Then, they switched to a knock-off “VM22” from one of their other distributors before rebranding a version of the FM22.

We had already worked on these knock-offs, which are not knock-offs of the Mikunii VM22 but more similar to a PZ26, like what comes on the World Formula.

We made our own casting and brand with the Wildcat WC22. We fixed the starting and tuning issues.

Tillotson has refused to believe they have a carburetor problem. They have reworked the ignition coil and gone through several different spark plugs, trying to blame the problem on something else. We’re glad this post made the point that switching to(of all the carburetors) a Briggs carburetor. Insult to injury.

The other part that we disagreed on is the exhaust. The exhaust is too short and too restrictive. It contributes to some of the starting issues and, we believe, the main problem with the engine’s durability. The header keeps a lot of back pressure and heat in the cylinder head. The carburetor also runs too rich, and any unburnt fuel is caught and burned in the exhaust. We have any one racer send us pictures of an exhaust that has blown apart.

Finally, after years of battling this issue, RLV has created a new exhaust more like the traditional ones used on the Briggs or the oval racing Clones. We haven’t tested one yet, but we believe this should help.

That said, we don’t support the Tillotson 225RS class to protest how the program has been handled. Outside the engine issues, we have had issues because the distribution of this engine doesn’t come through us. Had the engine come through us, we could have forced the right changes, and this wouldn’t have been an issue. However, the other distributors lacked the knowledge and experience and decided to sell the engines anyway. Those companies are ones you may never have heard of or have never been associated with 4-cycle karting or Tillotson carburetors. For them, it’s of no consequence because they’re not the ones mentioned in this post, but we are.

That is why we have been fairly silent for the last four years on this program.

So, how do we fix the issue?

Many of our customers have thrown the rule book away or created their own and started using one of our carburetors and exhausts. While they are not rev-limited and not a spec engine, we have even sold them our 228cc version or components to build 236cc versions.

We will not blueprint FM22 carburetors. We cannot support that carburetor because it’s not something we designed, and it’s too accessible to other distributors; we will not support their mistakes so they can sell engines, especially when the factory should have never sold the engine with a poorly functioning carburetor.

Our Wildcat WC22 is based on the same carburetor, so it’s dimensionally the same as the FM22. Our carb works, and most importantly, you have someone that can support it. We have a better version of the curved intake or, if you prefer, our short intake manifold. We recommend using our ETC5011 header with the 4106 muffler.

If you think it’s wrong for us to sell you parts for your engine, we agree. Tillotson should have had the engine right from the start.


Thank you for informing me and the rest of us about the Tillotson company and various divisions. I stand corrected on the carb you folks offer. I was misinformed that it was a blueprinted FM22.

I apologize if I worded my post to appear as if you folks were profiting off of a bad design Tillotson should have remedied. If anything, your team deserves kudos for caring about us end users and offering a product that eliminates the headaches and problems we’re facing.

Local spec rules can be difficult to see change in, especially if another competitor feels there’s an advantage using anything other than what the manufacturer intended or supplied.

For now, I have a workaround that I can at least practice with. Time will tell if OKC takes action and allows a rule change regarding the carburetor. One thing we have in our favor is the 6 of us that bought these motors are coming over from the 206 Heavy class which has a very small entry list at OKC. We’re all pretty close and we can petition to allow an alternative carburetor if it comes to that.

News will spread quickly around the grid to the handful of other Tillotson Heavy entries that we may have found a solution to the starting and drivability issues and get them onboard regarding a rule change. That’s my hope for now, otherwise I can’t see myself committing my season to the new engine. Especially after such a trouble free experience with 206 program in the past.

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No offense taken.

We share everyone’s frustration because the engine has a lot of potential. We put a lot of energy into these products, and it’s disappointing to be so close but fall short over one or two components that have easy resolution. Even with our relationship with Tillotson, we can’t get them to fix this issue. Unfortunately, the racers and tracks have to do as you have done and come up with an alternative.

Outside the 225RS classes, the engine has been very successful for us in the oval kart market with stock appearing and modified classes. There is no reason for it to have the problems in these spec classes.

If we have the opportunity we may make a trip to race with you guys and see if there is any way we can help.


Mark really appreciate your insight and commentary on this.

Before that race I did with the 225 I did a lot of calling around to sprint kart contacts I knew that had a longer history with the engine to get an idea of what wears out on them, what can be changed, etc etc. Surprisingly, I was met with a lot of “we don’t know,” when it came to what can be adjusted on them: even those that have 1-2 years of running with them aren’t really familiar with what it actually takes to squeeze all they can out of them.

I’m curious what other markets often tweak or play with? Just curious on generic areas, any areas that are weaker or are known areas for focus from a maintenance standpoint.

Similar to Briggs, the company answer will always be “there’s no issues,” and “so and so ran their engine for 5 years without replacing anything,” but we know that just isn’t true. For the 206 the head is the biggest area of fatigue and a maintenance center.

So, just curious on what you’ve seen other markets focus on.

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Our use of the engine is anything from recreational builds on mini bikes to 10,000rpm methanol race engines for dirt ovals. I’m unsure how much that information will help since we mostly use the Tillotson block and piston, and nearly everything else is aftermarket.

Regarding the 225RS, ongoing changes with the engine have made it difficult to gain consistent data, but here are a few things we know.

  1. Exhaust – RLV has the replacement header and muffler on their site. We haven’t tested it, but we have used similar headers from the dirt market. You should gain power across the board but mostly on the top end since we’re reducing back pressure. It should help some with starting and the overly rich problem with the tune. Most importantly, you are reducing the heat on the exhaust side of the head. Aluminum expands when heated and shrinks as it cools, contributing to head gasket failure when it’s exposed to extreme temperatures. It also means the valves are not going to last long. We have had issues with leak-down on the exhaust valve because of the extra heat from the exhaust, but with the change, I expect the maintenance to be similar to the Briggs head.

  2. Cylinder Head Bolts - Another contributing problem to head gasket failure is the tread depth of the block; the cylinder head bolts may bottom out before it clamps down on the cylinder head. Between the heat and the bolts blowing, head gaskets were fairly common. Tillotson’s solution was to use thread locker on the bolts, which helps some, but removing the cylinder heads is a pain. You could use shorter bolts, or we use a Nord-lock washer, which helps the bolt to clamp on the head more and prevents the bolts from backing out.

  3. Carburetor Tuning – The carburetor is very rich. Part of our problem is the rules have had tech for the jetting. I can’t remember which exhaust and how much other work we did to the carburetor, but I believe we were using a 95 jet, and the rules spec a 120. The rules need to eliminate the tech on the fuel side of the carburetor so it can legally be fixed, and so the carburetor can be adjusted for atmospheric conditions.

Between the exhaust and the carburetor tuning, the engine has rod failure. From what we are told, most of them have happened at OKC because of how long they stay on the rev limiter. Tillotson has reworked the PVL coil to be “softer” to resolve this issue, and it seems it has helped, but we believe it has a lot to do with the carburetor tuning and exhaust. The carburetor is running rich, so the fuel isn’t completely burned, and the rev limiter is making the problem worse because it’s either not firing or retarding the timing. The exhaust isn’t flowing or allowing that unburnt fuel to escape, so we believe there must be a hydro-locking effect, which puts stress on the piston and rod and raises compression to cause detonation. It doesn’t make sense that a billet rod with a rod bearing fails when a cast rod without a bearing is holding up.

Hopefully, the exhaust helps with starting, but we use a plastic bag over the air filter for cold starts to choke the carburetor. The enrichment valve/choke on the carburetor seems to struggle to work, so all of the guys pull the air filter off and choke it by hand. We use a plastic bag to seal the carburetor to save the hassle of putting the air filter back on. Then give the carburetor about ¼ throttle, and that helps.

  1. Spark Plug – The rules have changed from plug to plug, and the current rules allow three different plugs. The AR3910X may show a little more power on the dyno because it fills the combustion chamber a little more to increase compression, but it’s an extremely cold plug throughout a race it’s going to foul out, especially with the rich running carburetor. I would use the BPR6ES and gap it between .028-.032, We tested a few other plugs, and the NGK BPR6EIX was one of the best.

  2. Engine Oil – We had one racer using the Tillotson 225RS as close to Tillotson’s recommendations, including using their oil. He had a couple of engine failures and had the engine oil sent to be analyzed. The oil itself doesn’t seem to contribute to the engine failures. However, looking over the report, it seems to be a 10w-40 oil. I don’t like it when some of the most basic information, such as the oil weight, isn’t included with engine oil.

Even though Briggs doesn’t tell you it’s a 10w-30, they provide a data sheet with the kinematic viscosity. The oil analysis report on the Tillotson oil does show ppm of the anti-wear and detergents, and it’s high in both, which is very similar to diesel oil. It’s not something I would want to run when we’re running a class where oil can provide a performance advantage. I’ve written a blog on engine oils on our website that covers a lot of information on oils. EC’s Engine Oil Blog

First, I would break in the engine with good break-in oil and ensure the engine is running under a load. The easiest way is to run it in a 10-15min practice session. Don’t let it sit idle or free-rev it on the stand. Zinc is going to activate with heat and pressure. Without a load, the break-in oil will have a hard time doing its job. The engine will seal better and have less wear.

I recommend a 0w-20 racing oil for engine oil, specifically Maxima Racing Oil RS 0w-20. We sell this oil, but not to be biased, I would recommend Driven KRT 0w-20 as well. Both oils have high viscosity indexes, which give me hints about their chemistry, and the high viscosity index means the oil’s operating viscosity isn’t going to change as much with high or low temperatures. The lower viscosity weight should free up power. The Tillotson rules have gone from 450mL to 500ml or 17oz; this is going to add to windage and resistance, especially with a 40-weight oil. You’ll lose about 2-3oz of oil to your catch-can, especially if you gain a couple of oz from fuel dilution from the rich carburetor. We only run 14oz and have had no issues.


@KartingIsLife how do you “super” like something???

Mark, the amount of information you shared there is staggering and was very insightful. Thank you! I’ve bookmarked this comment for future reference.

Sounds like the 225RS is a work in progress for everyone involved. I’ll read your oil article to learn more!

I just use love for that :laughing:

Agreed….Mark, outstanding information about the 225RS. We appreciate your knowledge and expertise regarding this motor and what we can do to increase longevity and reliability. I kept the first couple of inches of the header unwrapped since that seemed to be a concern on the 206 as well retaining heat at the head.

I used Amsoil break in oil with high zinc in the manner you described out on track putting a good load on the motor, braking and repeating the process during my first two sessions keeping it below 5k rpms. I had installed a magnetic drain plug prior to starting the new motor to capture any fine metal particles during the initial break in as an extra precaution. Break in oil came out a bit dirty but no visible metal on the drain plug. I attribute that to the initial carbon blow by and the extremely rich conditions I was already experiencing with the FM22 until the rings seated and not something I’m particularly surprised by. I replaced it with fresh regular 4T and I’ll see how it looks at the 3 hour mark.

On the subject of oils, there’s been mention of engine failures due to folks switching between pag or compressor style oils to esterol based where the two do not like to mix well leading rod bearing galling and or failure. I’m no oil expert but I take that reputable builders word regarding that issue and will stick to using a single type and brand as in the 4T. It’s engineered specifically for air cooled splash systems and has served me well in my Briggs.

My motor was shipped with an E3 plug so it’s interesting that you had mentioned earlier that they had changed the plug a couple of times attributing some of the running issues to that or the coil. The rule book lists a couple of different plugs allowed with the AR3910X being one of them. I have several of those in my toolbox for the Briggs.

I received a text from a fellow racer that someone from Tillotson was going to be at OKC today and asked me to drop off my carburetor for them to look at. Not sure what they’re going to find or if they intend on running it on a kart there but we’ll see. Luckily OKC is just around the corner from my job. The Briggs carb is still on my kart and it’s staying there for the foreseeable future so I can at least get out on track and practice.

The oil blog is fairly long, but it talks a little about the problem of mixing PAO and PAG oils. PAG oils were frequently used in kart racing, especially before modern engine oil chemistry. PAG oils have their advantages, but they are expensive, do not mix with hydrocarbon base oils in most cases, and are not as accessible.

The AR3910X is designed for endurance automotive racing or power adder applications. Guys racing clones started using them to reduce the combustion chamber’s size to raise the engine’s compression since it wasn’t part of the cc check. It started when the class had fixed jets, but once the jetting opened up and the carburetors were running richer to make more power, they had more issues fouling plugs. Horsepower sells, and it would make a little more power on the dyno. But no one is simulating a race or idling them on the grid, waiting for their class to get on track with their dynos. It’s a known problem, and it is handled by keeping spare plugs and changing them out for qualifying or the race.

In my experience, I’ve found fine-wire iridium, and it has to be the fine wire that was the best plug. It wasn’t a miracle plug that made more power, but the read-out on the air-fuel ratio was more consistent. We believe the tuning of the engine would be more consistent since atmospheric conditions affect the carburetor, it is one less variable impacting the engine’s performance. We could also get them it heat ranges that kept the plug clean during a race.


My son and I each have one we bought from OKC, one had the needle and seat sticking and died in a race. The trick to getting them to start easily is to open the idle fuel screw (bottom, engine side of carb) to 3.5 turns. Ours start first or second pull every time, and run great. My son won the season 3 pro league championship and I got 3rd. The first Tilly engine I bought (I have 3) last year (blue tag) was under powered. The white tag I got a few month ago is on par the all the other engines. We run the Tilly oil and follow their maintenance sheet rigidly.

I dropped off my carb to Chris at the parts counter about an hour ago. A Tillotson distributor was arriving around the same time I got there that was going to take a look at my carb. He mentioned a couple of other racers worked on the float needle seat area by using a q tip and polishing agent like Mothers to clean it up and supposedly it cured their flooding problem. I’ve used that trick before on other carbs in the past. We’ll see what, if anything they do with my carb. Chris mentioned they’d give me yet another one if they had to.

We also discussed my Odenthal mount and whether the angle may be causing an issue. It’s my same one I ran my 206 on and we need the angle due to the air filter clearance over the tire. With the Tilliotson, it puts the carb at about an 8 degree angle which should be within tolerance but perhaps the fuel transfer to the front of the bowl under hard braking could be causing the issue where it nearly dies coming off the apex and accelerating out of the corner. Considering all possibilities at this point.

Some really great insights Mark - you need to do a tech column in whoever reinvents the print magazine from the other thread! :smiley: Very good stuff whether someone runs the Tillotson package or not.

I have to be that guy though and just ask why we are even doing this still at this stage? Seems like they tried to bring a product to market too soon, that was untested and did so for the wrong reasons (for the sport, not for a business). Just have trouble seeing any upside to dragging this experiment out, particularly as the 206 has addressed most of their problems and the supply chain issues (real and manufactured) have relented.

Not trying to be an ass, just asking a serious question.

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Mark has a TON of knowledge and could probably start his own forum :laughing:

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For me and everyone we race with, the tillotson is way more fun to drive. I drove a 206 around orlando a few times and I can hold it flat in areas where you have to actually brake and use partial throttle to be fast in the tilly. It comes down to driving enjoyment for me. That said, we have yet to have any serious problems. My tune may change if we toast a couple rods.

This is where the World Formula used to slot in above the 206, or blueprinted animal before the time of 206. In our region the World Formula has more or less died, though one track still continues to run it. Nowadays, the 100cc stuff has kinda filled that slot for most people however for those that prefer 4 stroke the lack of WF has left a bit of a hole that the 225 is trying to fill. Depending on your area depends on whether the numbers can support this.

Rob, What gear are you running? I tried 15/58 and it was just kissing the rev limiter at the start finish line which I think is ideal….but with the extra hp, it might be able to pull a 57. I typically ran a 59 on the 206.