Ask Curtis Sparks Racing
- Updated: August 22, 2000
By Curtis Sparks Racing
Dear Sparks Racing,
What kind of jetting should I run with my modified cylinder? I have a carb off a 1998 Kawasaki KX250 I think that is a PWK 38. I need to know what slide, needle,
pilot and main jets to use as well.
Thank you for your time. Any hints would be a big help.
Timx2
Tim
We have found that a 185 main, 50 pilot, CEL needle and 1 turn out on the air screw works well with our motors. We use a 38mm PWK air striker carb.
Sparks Racing
Hi. I have a question about my 400ex. I am in the process of ordering some aftermarket performance products, but before I install them I want to get my stock machine running in top form. I know that Honda is jetting the 400EX lean from the factory. What I can’t understand is why I can’t get a straightforward answer on how to fix the condition. Some say to raise the needle; others say to increase pilot jet size to a size 40. I don’t know. If at all possible could you please help?
Thanks for your time.
Brian Marsh
Brian,
We have found that the 40 pilot jet works well with the stock set up on the 400EX. It is not necessary to have your bike 100% jetted correctly if you are about to bolt on some aftermarket performance products. Usually you will receive jetting recommendations with the products that require jetting changes. If you don’t just give them a call and ask.
Sparks Racing
Dear Curtis Sparks,
If a certain brand name of oil says to run at 32:1, how many ounces is that to (1) gallon
of gas? Also, do you go by the oil manufacturer or do you use your own ratios?
If you mix your gas at a 32:1 ratio, you will be putting adding 5 ounces of oil to each gallon of gas. We recommend 6 ounces oil to each gallon of gas. We also use a specific brand of oil that we have found to work very well.
Sparks Racing
Hello Sparks Racing Team.
I want to hop up my wolverine, but not to the point of sacrificing the longevity of the motor, I have a aftermarket pipe but what else should I do, your opinion is greatly appreciated.
JMW
The first step in determining what you can do to your Wolverine is to know that most of the modifications from the Warrior will fit on the Wolverine. From there your have to evaluate where the performance is lacking, (throttle response, top end, etc.). From that point, you need to establish your budget. Power is normally related to the amount of money that can be spent. It also takes some smarts to figure the best way to spend your hard-earned money. Now you just start contacting performance companies that you trust and ask them what they would recommend. Ask any question that you might have before you spend your money. You should feel comfortable with the company and the people that you talk to about your ATV.
Sparks Racing
What’s Up,
My name is Kevin. I live in Fairfax VA. I own a 1986 Honda TRX 250R. I turn 16 on June 21st and plan to start racing as soon as possible. What nerfbars would you recommend I get also what steering stabilizer? My friends and people I meet race me, but no one has been able to beat me! I hope to get sponsored by the middle of this summer. I hope to meet you all some day.
Thank you for your help!
Kevin
Kevin
The best thing that we can recommend for you is to take a look at what the top pros use. They rely on their quads to be the absolute best, so they choose their aftermarket parts carefully. Take a look at what the top racers use at the Nationals. You will learn a great deal from them.
Sparks Racing
Dear Sparks Racing,
I have an 86 TRX 250R, stock except .020 Wiseco, aftermarket torque reeds, Uni air
filter, and an aftermarket pipe/silencer. A friend recommends running an 86 CR head gasket and two TRX base gaskets to change the port timing to gain bottom end. He also said to cut 1 to 2 inches off the stinger end of my pipe. I’m trying to increase the bottom for the woods/trails. Also may try some cross-county amateur racing next year. Any advice would be appreciated.
Your friends were right on one of the points. The CR head gasket would be fine to run on your bike. Two base gaskets will raise your port timing, which will make more top end power and less bottom end power. If you seek more bottom end you might try eliminating the base gaskets and you a thin coat of Three-Bond 1211 instead. That will lower your port timing and increase bottom end. Aftermarket performance companies spend a great deal of time developing their products that they sell to you. Generally, it is not wise to modify their product after they have spent so much finding what they found works well.
Sparks Racing
Hello Curtis and teammates,
I have a ‘99 400EX. It has a K&N filter, aftermarket pipe and silencer, a 162 main jet (a 157, and stock were also tried) I race at sea level. The air-screw is 1 turn out, and an aftermarket CDI is used. The quad has an intermittent power loss. Perhaps, once or twice per race event/motocross, it acts like the plug starts to foul or someone hits the kill switch, which has been removed. It normally only lasts a couple of seconds and
then clears up and runs cleanly. It normally only happens under extreme race conditions on rough tracks. I replaced the CDI, checked for electrical shorts, and cleaned the carb. Still, this didn’t help. What do you suggest?
We have found that at sea level a 152 main and a 45 pilot are the best combination for the 400EX with the bolt-on performance modifications that you list. You are over-jetted and the problem you describe should be cleared with the jetting changes.
Sparks Racing
What’s up Curtis?
This is Tommy from Texas. I have an Arctic Cat 300 4×4 that I want to get a little more out of. Does any one make any mods for this kind of quad? Exhaust, filter, or Jets maybe? I really want a new pipe but no one seems to have one. I have found a universal silencer; will it do me any good?
Thanks for your help.
Tommy,
We regret that we are not familiar with any mods for you quad. It would be nice if there were more available for the 4×4 quads but it doesn’t seem that there is enough demand for the products.
Sparks Racing
Yo, Curtis what’s up?.
I bought a used bike and it has an aftermarket 300 cylinder on it. It doesn’t have any bark whatsoever. I like a motor with a lot of bottom. What are my options? I go to MMI here in Phoenix and have access to machining equipment and was wondering if I should throw a 330 sleeve in it to get more grunt. I know I would have to match up the ports, but am I just asking for trouble? Your advice would be greatly appreciated.
Thanks,
M.J.
MJ
To get your motor to a 330cc displacement we would recommend a different cylinder to get you there. Your cases would require machining to accept the larger cylinder. You would get more grunt with a good 330 cylinder. I would warn against having a cylinder sleeved by someone other than a company or person that a great deal of experience in sleeving cylinders. There are many potential problems with a cylinder that is not sleeved correctly.
Sparks Racing
Dear Curtis,
I am currently racing an ‘87 250R. The motor is stock but everything else isn’t:
(aftermarket shocks, aftermarket swing arm, stem, clamp, aftermarket pipe, aftermarket bars, aftermarket A-arms, aftermarket axle — everything that you need to race except motor work). The people that we ride with have all kinds of ideas, but what do you suggest? I’m 16yrs old and big for a racer — 6’2″ 240 lbs, so I can handle plenty of power. I clear all the jumps but not by much (4th gear wide open).
Thanks for any help!
Eric Sealander
Eric
What are you waiting for? Do some research on aftermarket performance companies and send your motor to them. You are heavier than most ATV racers. Most ATV racers already have a modified engine. That puts you at a huge disadvantage. The only place on the track that you pass 19 riders at once is on the start. Hole shots crucial and it takes horsepower to get them.
Sparks Racing
Hey Sparks Racing,
This is Kevin here. I’m 16 and have a 1986 Honda TRX 250R. All of the frame mounts around my engine have cracked because of vibration, age and one of the previous owners left it out in the rain a lot! My Uncle is repairing my quad now and should have it back to me in a couple weeks. I really need to know what to do. Should I keep mine and save up the money to get a new frame? Should I sell mine and get a TRX 400EX? Or should I sell mine and get a Raptor 660 when they come out? Do you have any other suggestions? I could really use your professional opinion on this problem. I don’t have any extra money saved towards a new quad right now and plan to race a lot with whatever I end up with.
Thank you for your time.
Kevin
The decision rests with you. How much do you like your current setup? The aftermarket companies are producing some great chassis combos for all of the ATVs. The Honda TRX 400EX is a great quad, there are plenty of aftermarket goodies available for them. Curtis raced an EX at the Legends 2000 event in Ashtabula, and got 6th place on one. The new Yamaha Raptor promises to be a great ATV as well. I am certain that all of the aftermarket companies will be quick to produce a long list of goodies for the 660 as well. You just need to do a little thinking which quad best suits you.
Sparks Racing
Curtis…
I have heard of you and your engines and you have built yourself quite a reputation! That is why I am interested in having you turn my 250R motor into the ultimate MX engine! I am interested in your National 265 kit. On you site it says it is “AMA LEGAL”, is it AMA 250 class legal. If my memory serves me right, you are permitted a .060 bore in the 250 class and that brings you to 262cc. So is your engine 250 class legal? It is very important because that is the class that I race.
Thank you
Matt Ruszkiewicz
Matt,
The AMA rules allow for a .080 bore from stock, which would put it to a 265cc engine. All of our National riders use our 265 kit and we have been found legal in previous engine protests before and we will continue to be found legal in the future.
Sparks Racing
Hello Curtis.
What makes a better 400 four stroke a YZ or WR
Kadillac Karl
Karl,
The YZ400F and WR400F are essentially the same motor for 1999. The differences are in the cam timing, carburetor and internal gear ratios. The first two items can easily be modified. The WR is set up to be a tamer version of the YZ. The WR (wide ratio) would probably be our choice because of the transmission. However, both engines have the same potential for horsepower and usability.
Sparks Racing
Dear Curtis;
I run a full-race Polaris Sport 400 two-stroke. I’m on the original bore since 1997. I’ve always used Power Plus oil at the recommended ratio of 50:1 with no burn downs or appreciable cylinder wear. I just dropped in a new set of rings recently and recorded 185 lbs. of compression. My bike has been dynoed at the rear wheels for a reading of 72.3 horse power. Why should I run 24:1 oil ratio on my bike as suggested on your web site? I know that this has been an ongoing issue for years and have noticed that Go-Carts use 20:1 religiously.
Thanks!
Eric Bellinger
Eric,
We have found through our experience that 6 ounces to a gallon works well in the high demand motors than we race week in and week out. Everybody has their own opinion and experience with oils and ratios.
Sparks Racing
Dear Sparks Racing,
I have a problem with my 2000 Bombardier. It backfires and blows the carburetor out of the rubber boot it mounts to. I have taken it to my dealer several times but they haven’t been able to repair it. It is completely stock. Also the front chain roller comes apart after about 30 minutes of riding. And one last question the headlight burns out on every night. If you have any idea of a possible cure it would be appreciated.
Thanks!
Don
Don
We would suspect that your pilot might be too lean. Your local Bombardier dealer best address the other problems on your new ride.
Sparks Racing