I have a 2002 crf 450, it has a new top end. it is hard to start and when it does run it pops a little. if i let it run at idle for about 5-10 minutes it gets hot and starts leaking coolant out of the overflow tube. could this be a timing issue?

Is it modified? Does it sputter only at low throttle or any position of the throttle? Does it start and idle ok?

If you need further help, I’m available over the phone at https://www.6ya.com/expert/oscar_403cc49e0f00cda7

Check your pilot jet is not blocked or try adjusting your idle screw for the idle issue and it sounds like its runing lean which can also make it idle low and rough and will cause it to pop and backfire. Dont think it has anything to do with your hot start cable that will make it run it run better if its running rich but your is doing the opposite

Hi from Spain,

coul be related to lean mixture during deceleration that makes the exhaust hotter that make the blow-by gas to "explote". Check all carburator spec. are under standar, especially slow jet and slow screw adjustament.

br,

Emilio.

Many of those CRF have problems with the valves, check the valve clearances, as well as all the general maintenance items, clean carb, clean air filter, new plug.
If the clearances need more than one number smaller on the shims, it may be the start of valve regression.

1. First thing is when was the last time you had your valves adjusted
2. On cold start up twist about 15 times on your throttle, as you do that the accelerator pump in carb will shot gas in cylinder, I have a 2003 yx426 & 2005 yz450 have to do to both of them when cold out to get started

Hi Smit,

here are some thread that will really be helpful for you and your bike.

http://www.thumpertalk.com/forum/archive/index.php/t-589583.html

http://www.supermotojunkie.com/showthread.php?p=862289

http://www.mototips.com/general-bike-repair/21014-crf450-04-hard-start-cuts-out.html

happy trails,

regards,

voodoo

Back to shop and have them do their job righthtis time.

Think about the valves. If they are to tight (Valve clearance) with the heat added when warm, they (Or one) might not close. I'd check there first.

Back firing usually indicates a timing problem.

Classic valve train issues. Sounds like the valves are tight. One thing that concerns me is the "sudden onset". Valves usually tighten over time.
Make sure you also tighten the cam chain as well.