Cranks over SLOW

[CUMMINSPOWER121]

Hi i just got a 04 yfz last week now it cranks over then gets real slow on compression i thought it was the battery so i put a cbr battery in and still same thing but if i put a jumper box on with the battery it will start and run fine i was reading some ware about a decompression spring? its really starting to bother me. any help would be appreciated thanks alot!

[Ride1Rob]

The spring on the cam could be the issue as it would leave the decomp notch on the cam closed or flush with the cam walls. Once the motor/cams spool up the spring keeps the lever on the cam from opening. This controls a notch on the cam to run across the exhaust valves so that they open to relieve some of the pressure on initial startup. Once the motor starts and the revs get faster the spring opens all the way up causing the notch to sink in flush with the cam. This is done so you won't have a premature opening from the notch as well as the lobes on the cam. Bearings seizing will also cause this.

[CUMMINSPOWER121]

How can i see if thats working correctly? because soon as it starts it runs fine no noise or anything

[Ride1Rob]

Just take the cam cover off of the head(2 bolts) and the cams will be sitting right there with timing chain going around the cam sprockets. Look at the cam sprocket on the cam in the front. You should see a little spring there. If you need a pic posted let me know.