2001 Kodiak 400 4x4 Will Not Crank - I'm Puzzled - Need Help

[Attala]

I bought a used 2001 Kodiak 400 4x4 Camo recently and my plans were to make this ATV into a Prescribe Burning ATV Unit...it cranked and ran great when I got it.... I knew it had a brake problem and a speedometer/odometer problem....I used the bike for three weeks off and on and then I did some work around Perry Florida and on the next to last day the ATV started to act funny about cranking and switching off...after cutting the bike off to do some work, I returned twenty to thirty minutes later and it would not crank....it would try to start but then it would back fire....well I loaded it up and took it to a local ATV repair shop and left it for repair....its now been two months and the problem has not been solved...put a new (rebuilt Yamaha) carburetor in, new coil, new battery, drained fuel tank and put new fuel in, new spark plug, checked timing, checked compression, etc...still try's to start but backfires.....need some help here at     [email protected]

[Ajmboy]

Sounds like a timing issue or possible a faulty CDI. Before that, I would start checking all wiring. When you say speedometer odometer, is it digital and not working or is it an analog display? Do you have a speed sensor? 

[Attala]

The speedometer/odometer is not digital...it was a cable issue and that & the brake problem have been fixed, or I think so....hasnt moved to see if they work or not....i have questioned mechanic about it possibly jumping timing, he says it has not....he is gonna put in a new voltage regulator now....

[Vertigo]

Despite report from your tech, I suspect timing.
Recent work on three Bears of that era, the cam guides/chain do seem to  experience some slack, and wear.
Jumping time is easy on one with some miles, but there may still be enough slack that one might
visually mistakenly believe the marks are accurate. I fear just tossing external parts at it will get expensive,
not to mention possibly futile. May be time to do head/rings/chain and guides-it's gonna be more expensive,
but the long term benefits will keep giving return in power and fuel consumption.
Are the guides worn down badly? Adjuster working correctly? I am assuming he has pulled the left
sidecover off and pulled flywheel/starter clutch to see chain and lower sprocket, guide bottoms, adjuster?

What did compression check yield?

Edited May 25, 2018 by Vertigo

[Attala]

I have copied your response and are in the process of sending to my mechanic.

[Vertigo]

When the chain gets worn, it will often knick the case on the left side under the sidecover, below the timing chain front lower guide.
If you see any scrapes there-or a broken aluminum case edge, pretty good bet you found problem.

One that has a stretched chain/worn chain glides/malfunctioning adjuster will often run, but have a strange "slapping" sound, particularly at lower revs (where you can actually hear it above the normal engine sound). It will often be very pronounced while fast-cranking (boosting) or with spark plug out, and sounds like a sliding/slapping, not really a knock as such. That's the chain brushing against the case as it spins.

I have removed plugs, and completely backed out the valve adjustments, for diagnosis. It relieves the cam from spring pressure, allows starter to spin faster, which accentuates the "slapping chain"  noise scraping on the case, as compared to normal cranking with valves adjusted to spec/spark plug in.

Hope that helps

[Vertigo]

Too late to edit addition-its very possible to run w jump time-although will affect power/compression. If it the goes a second tooth, well, not likely to run. If chain is worn/loose/adjuster ineffective or guides worn, can often also see sign of chain rubbing on lower/front part of head, near cam sprocket, can see by removing cam cover on L side.
Jumped timing will often cause an engine to "start hard", meaning it turns over less vigorously, may "seem" like a low battery or weak starter. Often the timing jumps on start up-as the starter directly turns the crank, the cam begins turning a second later-and if loose, jumps, causing late timing. lower compression. Timing also more likely to  jump if shifting under full power at high revs.

One other note-a loose chain can have the effect of making high rev operation feel more powerful, due to the dynamic effects of retarding cam events. This comes at the expense of low rpm operation, which affects idle quality as well as off-idle torque. Engine may "hesitate".
An oil pump (or clogged filter) contributes to valve train wear-and worn cam bearings can exacerbate loose/worn chain, as can too much head milling for compression, or running without cylinder  base gasket. With used equipment no one knows what was done previously.