[coolwhi27]

Yo! Im back and I want to know what the correct jets would be that match up with dynojets "stage 1" jet power kit for the fourtrax 300 and even what the "stage 2" kit would be. There's no stage 2 kit for this atv that I can find. I know the jets would probably be from keihin but I have no idea where to start from which jets would be right for a little more power. Stage 1 is for stock atvs, stage 2 is for an aftermarket exhaust.

I think I asked this before but didn't get a specific answer on which ones. I'm on my phone and I don't feel like checking again. Any feedback would be greatly appreciated.

 

[retro]

You can't get any more power from a stock 300FW by rejetting. Leave the stock factory jets in it for best results. Dyno jet numbers and jets belong to them, so there is no perfectly accurate interchange with Keihin jets.

 

[fishfiles]

I agree with Retro , up'ing the jet size with no other mods isn't going to accomplish anything much

you can get a little more cheap power by using the camshaft from a 88-90 300 , 85-87 TRX250A or the 85-86 ATC250ES , then rejet the carb to 88-90 300 specs , unless you have a hot after market pipe , then it is going to be trail and error --------- I have read , heard and feel to me the 1st gen cam is a 2 hp gain , you can also get a genuine ( be careful with clones ) Rick's No Limit CDI , it will give you a extra 1k+ rpms on the top side

 

[coolwhi27]

I could get a UNI air filter, would that count as a mod at all? It's too bad because I had the chance of buying one of those cams when I rebuilt it- don't know if I want to do that again. This HMF slip-on here, would this count as an aftermarket pipe for a little gain? https://www.amazon.com/HMF-019243606071-Performance-Exhaust-Honda/dp/B0065T8E6M

 

[wheelsquad]

I could get a UNI air filter, would that count as a mod at all?

Nope. Going from an OEM Honda foam air filter, to a UNI brand foam air filter, is definitely not a "mod" that will increase HP.

 

[retro]

Changing the exhaust will not increase power, it will only make it loud and obnoxious. Modding a motor for more torque and RPMs requires a tailored, systematic approach. It is the entire symbiotic package that provides all gains in every motor. Any lessor (partial) efforts is generally a waste of your money and your time.

Nevermind all of the marketing hype surrounding individual aftermarket parts. They want you to be foolish... they want your money.

 

[coolwhi27]

What would it do if I put Rick's cdi box in without any mods?

 

[retro]

It might rev higher if it is an unlimited CDI, so horsepower might increase ever so slightly (simply due to more RPMs, HP is nothing but a calculation, HP cannot be measured on a motor cause it don't exist) but torque remains the same so there will be no real useful gains. An unlimited motor will scream until it reaches its designed air flow limits.

 

[coolwhi27]

One last question, Is there any scenario where a CDI box could be slightly bad and hold it back? I just feel like it doesn't rev as fast as it should.

Edit: I looked it up, and I guess not. It either works or it doesn't.

 

[retro]

There is one... if the CDI is not advancing the ignition timing as it was designed to do the motor would feel flat and be slow to build torque and RPMs. In that case it would also rev limit early due to retarded ignition timing. You can check the ignition advance using a timing light as explained in the service manual.

 

[SamUK]

You could add a small amount of power and an increase in throttle response by letting more air in and slightly more fuel. But honestly it really is a small amount and not worth the hassle.