2010 YZ450F Starting problem with new RS4

Hi Guys I'm new to this forum and would like some advice on a small problem.

I have a 2010 YZ450F and have just put a full Yoshi RS4 system on it, now I have problems starting it? it used to start fine, two or three kicks and it was into life. Once I fitted the pipe it now takes a good 10mins of kicking to get it fired up!!! I have a GYTR power tuner and have being looking for a solution(MAP) on here but no one seems to have reported or had this problem yet. I have had a small play with it and got it to start a bit better by going +2 on the FI in the first box and -2 on the IG in the first box and leaving the rest of the map all 0s (stock).

Thanks for your help.

P.S. once started it runs fine.

You giving it a little throttle at the end of your kick kind of like a two stroke? That is what works for my bike contrary to most four strokes I have ridden. I still have stock exhaust however and running the jay marmot map, getting a muffler soon, but doubt my issues would be same as yours, might have to experiment with how you start the thing to find out what works.

I have the same bike, same exhaust and it is the worst starting 450 I've ever had when it's hot! When cold it's not bad, usually 3 kicks no problem. I agree with Seoinage a little throttle at the end of your kick helps, but too much and you will be kicking 20 extra times. What this tells me is that the bike is a little lean which makes sense with the pipe. I remember when I got the Yosh pipe I called Yosh tech to talk to them about tuning and they recommended going up 5% on FI at low to mid throttle and RPM's. A +1 on the tuner is 7% I believe...close enough. So that would be the lower left 4 blocks on the tuner map. I never tried it! lol. That was along time ago I called Yosh, it was a new bike then, so they may have even better info. Their tech line is good, they are very helpful. If you mess with it and get some improvement in starting please post your comments!

Just a bit of info, but I had to add approx 10% more fuel to the starting circuit to get my bike to start easier. This was with the stock pipe and muffler.

I use a PCV and you can adjust it to add more fuel for the first 30 seconds of run time. With the cold start on, I don't have to play with the throttle or anything if the engine is cold, just kick about 3-4 times and that's it.

The setting was recommended to me by dynojet after I emailed them about starting issues with my bike after buying their unit. (still had issues even before the PCV install btw. )

What brentn says about hot starts makes sense to me, as well. Unfortunatly it is not possible to do with the power tuner. I have tried different procedures. So far my best one is to crack the throttle a few millimeters open (fix it by pulling the front brake) and kick. It starts second kick latest - even when in gear!

Thanks for the replies much appreciated. It looks like I'm not alone in this one, will try the above suggestions and post my results.

On a side note has anyone changed the fuel filter in the tank?


i have the same bike, same sytem etc but have none of these problems, the bike fires up 3rd kick when cold, the only difference is i have not touched the setting using the gytr power tuner, sorry cant be of much help

This is my 3rd fuel injected bike. Every one of them needed a bit of fine tuning in kick and procedure...nothing bad, just some getting used to.

Hi guys, thanks for your replys. Just a quick up-date, I seem to have it sorted now, I tried the Jay Marmont map and all seems to be fixed. It's not starting as good as stock but not far off.

I like the Marmont mapping, so all good.


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