ATVmechanic

Check out this kit: Yamaha YFZ450 - Twist Throttle Kit - ATV Parts - Yamaha YFZ450 | R

I agree with DirtDemon, take the cover off and see what it's doing.

There is a sensor that is referred to as the angle sensor, which could be your issue. If you are not confident, you should have someone troubleshoot it for you at a shop/dealer. Once you locate the sensor, look at the condition of the wires, connector, and sensor iteself. Make sure no trail debris hit it. Look at #10 below: If it turns out bad, go to Bike Bandit where you can get it for @ $70 Part# 5904359-001

Is that a semi-auto tranny? Make sure you don't need oil with additives that Mobil1 may not have. I would double check with the dealer. Check out this link about using Mobil1 synthetic in your atv: Using Mobil 1 in ATV Deploying One Oil Supply for Transmission and Engine

Glad to hear she's runing better!

Hey Matt, any update? How did you make out?

Yes, I believe stock is: Compression Ratio 9.2x1 Compression 834 kPa (121 psi)

Glad it helped! Good luck!

I attached a diagram for you... If you search these forums, you will find the Artic Cat parts finder....http://www.quadcrazy.com/atvforum/arctic-cat-atv-technical-help/3289-arctic-cat-e-parts-catalogs.html Maybe someone should STICKY that thread. I'm also attaching carb disassembly procedure for you out of a manual.

There's no links here for info...

I have to agree also, that carb may have issues. Fresh gas also when you are done. I attached a carb breakdown and some specs for your machine...

Well said. Hard time starting, does it eventually start? If it does, how does it run once it starts. If it never starts, pull that spark plug out and check it. Check your spark.

Did you get this going? What's the status on this machine?

That's good to hear!!!

What's the status on this thread? Still having issues?

Thank you for the concideration, but I am not interested in being a moderator right now. I will continue helping when I can. I just cannot commit to being here all the time.

Unfortunately it sounds like you may have shorted the CDI box or the starter relay. I'm attaching a Raptor Wiring diagram, but I believe it is for the 350. It may be similar if not the same. I do not have a 700 diagram.

Turned out he had a loose ground...

Glad to help.

Since it's modified, it may take more cranking power to get it started. That is my guess since you said you put a new battery in it and it's difficult to turn over. It does however turn over when hooked up to a 12V source. Even though it is a new battery, it could be defective and not taking a full charge. You may want to have it tested at the place where you bought it. I believe that atv takes a battery #YTX9-BS which is a Yuasa number if I'm not mistaken. If it tests good, you could try finding the same group size battery but with more CCA. (Cold Cranking Amps) Have a look at these Honda batteries, notice the CCA: Honda ATV Batteries You may also want to doublecheck your charging system..as a second possibility.. "The Honda TRX400EX uses a full wave permanent magnet type of charging system. To test the charging system the battery must be fully charged. To accurately check the charging system and its components you will need a digital multimeter. A set of alligator clips for the meter leads will make some jobs much easier. To test the charging system as a whole, leave the multimeter set to VDC, touch the red meter lead to the positive post of the battery and the black meter lead to the negative post. Start the engine with the meter leads still connected to the battery posts. Rev the engine up to approximately 4,000 rpm and compare your reading with specification. (Specification for battery charging voltage with the engine at 4,000 rpm is 13 to 15.5 VDC) If battery charging voltage does not reach 13 VDC, the charging system is not working and the components must be checked. If the battery charging voltage goes over 15.5 VDC, the regulator is defective and the regulator/rectifier must be replaced."

I'm not sure what that model has, but usually there is a positive wire for power, and another wire sending the voltage back to adjust air fuel mixture, based on throttle position. Check the signal wire voltage for fluctuation while you move the throttle. This should give you an idea if it's working. If it's not and is shorted, it may be signaling for closed throttle. That has an electric fuel pump. You may want to check fuel pressure or see if the pump is delivering fuel and not just making noise.

TBI Assembly. Look at the parts diagram: World of Powersports' Honda ATV Parts Finder

You should test that TPS with a volt meter....when you're not disgusted anymore.

Is yours also an 800? Or is it a 450, 500, or 700... Sounds like it could be the TPS sensor but as you get higher in CC's you may have some other possible stuff going on.

I know this is an old thread, but was it the jetting?