I just bought a 2004 kfx700. It is clean as hell and it came with a title.The guy I bought it from said it had a knok in the engine but I can not hear it. It starts up the first time you hit the start button, but smokes a little. I started to ride it and I could tell it dose not have the power it should have and it gets worse the more you ride it. I have not checked the timing yet but I will tomorrow.

I did try to do a compression test but I can not find any two people that agree on how to do it. The test came out 30 psi on the front side and 60 psi on the backside. I hit the start but one time to get this result but if I keep hitting the start button the psi gose to 40psi on front and 60 psi on rear. The spart plug on the front was pretty black and the one on the rear was black but not bad. I guess the more I rode the atv I did start to hear something but it ws not a knok or a ping not sure how to tell you what it sounded like but it did die on me and the oil light came on. After the atv died it started wright back up with no lights on but it did not want to move very well.

Where do I start guys, please help me.

 

compression test- simply screw or hold the compression gage in the spark plug hole while cranking it over. Make sure your plug leads are no where near your gage, hand or open plug hole- as you could get shocked or start a fire when raw fuel spits out the plug hole and ignites on the open plug lead

both those readings seem real low to me-

try squirting a tablespoon of 2 stroke oil in each cylinder and see if that raises the compression ratio- The oil will temporarily seal up any minor deviation in the cylinder which will raise the compression ratio- if it does, I'd suspect worn rings or minor scuffs on the cylinder wall- if it doesn't raise the ratio- might be a burnt, cracked or chipped valve, piston a or a larger score in the cylinder wall.

There are many other issues to cause loss of power- but this is a good starting step to find out the mechanical condition of your cylinders...

 

Sorry to say but it's time to split the case find out.
Worn out piston/cylinder and/or rod bearing is shot, most likley due to dirt ingestion.

 

I don't know if splitting the case is called for just yet- even though the previous owner said it had a knock- the op said he didn't hear anything. So far- all the symptoms he mentions point to a tired top end.

 

OP says ALL symtoms of typical rod bearing failure that I hear from my customers and this is what I usually find when I split the case. Let's hope it is something else on this guy...

 

oh my god, what did I get into. I will try the 2 strock oil fist than check timing. I just bought the book on this atv but I half to wait till it gets here befor checking the timing. I do have a Prairi 650 book, I wonder if it would help me with the timing. Some one told me that it could have jumped timing and it would make it run this way. They also told me that the white smoke is coolant leaking into the pistion.

Is the stock bore 82 mm on this atv? I know I will half to take the top end off to see how the jugs look but how big should I go on the bore? I what a good trail bike and I what to drag race so what should I do? I just hope the heads are in good shape.

 

I did what you told me too I put a tablespoon or more of 2 stroke oil in each cylinder I got 90 psi on the front pistion and 90 to 120 on back. On the back pistion the bike started up so the reading got higher but I turn the atv off as fast as I could. I think the reading was 90 or so before the atv started. So where do you think I should go from here?

 

well- I'd do a leak down test next- but you brobably don't have the equipment for that-

If your compression shot up to 90-120 from 30 with oil in the cylinder- I'd suspect maybe piston rings, head gasket and a fresh cylinder hone depending on how it looks.

since you'd have to pull the top end off anyway if you were to split the case- I'd just start with removing the top end and see what kind of condition it's in. If it looks bad (rings, cylinder & head gasket) that could cause the low power, pinging & smoke...check your coolant also for contamination- people always confuse a ping, a knock or a rap- totally different diags. Parts are fairly cheap and it's not too hard with the aid of a manual and basic hand tools.

 

Thanks for all your help. You dont know how much I have leared from you. Just so I clear on what you think I should do. I plan on rebuilding the top end, after I get the top end off, is there anything I should be looking for like on the rod, side to side play etc.

 

you'll have to reference the manual for bearing / bushing tolerances & torque specs- there will be lots of charts in the manual. I would think either way, whether you end up splitting the case or not- it's going to need a top end- (piston, rings, gasket set...) there's really no way to visually determine if the piston & cylinder is within spec without a set of calipers & a bore dial indicator- which you'll need to have done at a shop (any machine shop)
If you buy a new piston kit- all you'll need to do is have the jug (cylinder) honed out if the gouges aren't too deep. You can do it yourself with a honing kit- not expensive, but you'll need the proper tools to spec it out.

this is where Northern Tool, Harbor Freight at Wholesale Tool comes in handy- I rebuilt my first engine (motorcycle) when I was 14- it was a great experience- and there was no internet to get quick instant answers. There's a lot of guys on here like Hayashi that can help you out if you get stuck.