Have you Decked the cylinder

Its the stock oem cam.

Port work was mostly exhaust port match up to gasket ID, de-burr casting marks and polish. intake de-burr and polish mostly.

Low compression will hurt low-end power more than top-end. Occasionally, you'll see guys lower the CR for full-race car motors to slightly improve the top-end, at the expense of low-end.

Matt this seems to make the most sense.

I am going to theorise that the low comp combined with the porting is most likely the scenario.



And now a point that I had failed to remember for the previous post.

It seems to be running a little lean as there is a more than occasional popping with deceleration. I am understanding that there is a 168 or 170 main jet in the carb now. I had also believed that 170 was the largest I had heard of for this carb is this true????

[MIKE400EX]

Lean pop when "off the gas" usually is caused by an exhaust leak near the head or the idle mixture (screw or pilot /slow jet) is too lean. You'll need a #42 pilot jet in there for the 440. Try first just opening the idle mixture screw up 1/2 turn at a time to cure the lean pop. 170 is by far not the largest jet made for the stock carb. If you took out the cam, double check that it's timed correctly and not off a tooth. I wouldn't think it's a compression problem due to stack-up or piston choice, it's still got to be higher than stock. I'm sure you posted somewhere, but what piston and head gasket are you using?

[Matt Fisher]

Light cleanup work won't do jack to change the powerband. It may add a smidge on the top-end, but won't move the effective power up or down any significant amount.

I'd say that the low compression combined with the lean jetting is killing your bottom end. Er, your bikes bottom end.

I believe the same jets used in an FCR will work in the stock carb, and I'm positive that you can go at least to a 185. I've seen over 200's used in FCR's, so there's plenty of room to go.

The stock cam will offer the most bottom end. The 479 should offer more torque than the 450/451, but not like the stocker. The more mild the cam, the more bottom-end.

It's also possible that the cam's slightly retarded now due to the decking and thinner gaskets, but by only a degree or so. This would move the powerband up slightly, but only slightly.

Lean pop when "off the gas" usually is caused by an exhaust leak near the head or the idle mixture (screw or pilot /slow jet) is too lean. You'll need a #42 pilot jet in there for the 440.

Mike that is what I was told is in there and never took the time to check if its a 42 or not. I will be checking the head pipe where it attaches to the head first.

Try first just opening the idle mixture screw up 1/2 turn at a time to cure the lean pop. 170 is by far not the largest jet made for the stock carb.

I was thinking of the idle mix tonight but left it alone as I was too busy, and would the bigger jets be avail from the normal sources say like K&N???

I'm sure you posted somewhere, but what piston and head gasket are you using?

J&E 11:1 piston w/ cometic .025 gasket also .012 base gasket and decked .012

And I am certain the cam is in the same as when disassembled.

Light cleanup work won't do jack to change the powerband. It may add a smidge on the top-end, but won't move the effective power up or down any significant amount.

Maybe the exhaust was slightly more than light but the intake was very minimal.

[QUOTE] I'd say that the low compression combined with the lean jetting is killing your bottom end. Er, your bikes bottom end. [QUOTE]

OK matt first I hope your winking at my four wheeled friend

Second this does make sense

I believe the same jets used in an FCR will work in the stock carb, and I'm positive that you can go at least to a 185. I've seen over 200's used in FCR's, so there's plenty of room to go.

OK I still need some help with where to find the jets.

The stock cam will offer the most bottom end. The 479 should offer more torque than the 450/451, but not like the stocker. The more mild the cam, the more bottom-end.

Ok this is where I need to give some attention. I do like the boost to the mid and top as it gives the bike a good feel in these rpm ranges. It was way to bottom heavy before .

I am thinking to try the stock cam with a valve job first before doing any cam work to see if it works out better for my type of riding. (I am getting into some hare scrambles in the so I still want to keep the bottom end)

The change in the mid and top did feel like they would help out in the woods. I am hoping if I get the CR problem under controll it will boost the bottom enough to make me happy and let me move on to getting confused with suspension upgrades.

[MIKE400EX]

I wouldn't switch cams any more than necessary to be on the safe side with the rockers. Every time you switch cams, and keep the same set of rockers, the rockers (and cam) have to wear in a little. The more times this happens the more chance you have of wearing through the thin chrome plating on the rockers. Definetly do a valve job though, if there is any question. When I took mine apart, after very minimal hours and no hard racing, the valves did need to be ground - probably needed it from day 1. Seats were OK, but I did them anyway. Don't forget to put some new valve seals in there. I think that your gage reading should be somewhere in the 130-150 PSI range with that piston/deck combo. Most any street bike shop has K&N jets, there's got to be a place local to you.

[Matt Fisher]

Originally posted by 440EX4me
Ok this is where I need to give some attention. I do like the boost to the mid and top as it gives the bike a good feel in these rpm ranges. It was way to bottom heavy before .

Get the bike running properly first, then worry about more mods.

After looking at my cam and the way the 400Ex oils the cam, I'd strongly suggest FST's oil cooler, or your own version of it. I'm using a stacked design (like the stocker) with about 2x the stockers capacity. I do need to weld a bracket to the frame for mine, though. Between both coolers, I will feel much more confident about pushing it harder on hot days, and will also have reduced the chance for detonation.

Thanks again for the input.

I think for now I am going to get the valves fixed up and see where we are then. I figure no sense (like Mike said) messing with a new cam now. I will wait till after I get it to make some comp before going any further with the engine.

Its gonna kill me to remove the head again and put the oem cam back but it just seems to make sense.

I am looking into the FST oil cooler after I finish this post. It seems like a very good "insurance policy".

And Matt I know what you mean by getting it running right first, but this suspension is seriously kicking my butt So i guess i think about it too much.

I will post the results after the valve work is done. This may take a little since I do not have a shop local that I have the confidence in and will need to find one.

[Matt Fisher]

No reason to wait on the motor to do suspension work, they certainly aren't related. I meant don't bother with the cam until it's running properly. So we're all saying the same thing.

I would spend a few more hours on it, maybe the rings just need to seat better? Go back and double check the valve clearance. Is it possible you re-installed the rings incorrectly? If you have a burnt valve, it will often totally kill compression, not just lower it.

You should be able to get the cam in there by just pulling off the cam cover, not the whole head. It (the cover) has to came off to put the oil cooler on anyway.

Matt Fisher No reason to wait on the motor to do suspension work, they certainly aren't related. I meant don't bother with the cam until it's running properly. So we're all saying the same thing.

I agree but I still do not need anything extra to be thinking about till this is done

I am hoping to have some time thur night to re set the valve lash so we will see what happens there.

You should be able to get the cam in there by just pulling off the cam cover, not the whole head. It (the cover) has to came off to put the oil cooler on anyway.

But I will need to pull the head if there is valve trouble to contend with. I do believe this is the problem but who knows for sure.

How does the FSt oil cooler plumb into the system???