+3mm bore with tall cams & 13:1 comp

Anyone running a setup like this on their YZ450F:

+3mm

13:1 compression

taller (more lift) cams

???

I just got mine (YFZ450 - quad) back together and I can't kick start it. It will pull/push start just fine, but I just can't get it spinning fast enough (by kicking) to have it catch.

Bear in mind that my quad is not the typical YFZ quad. I converted to kickstart-only last August and have done everything I could to make it as close to the YZ450F as possible with the exception of lights (dune riding at night). Dry, it's damn close to 300lbs and runs methanol with a touch of nitro too.

Is there a trick to kicking the higher pressure machines???? Anyone with experince in starting a similary large/built 4-stroke????

its the alcohol thats making it hard to start.i dont think you will be able to kick it fast enough to start.

It's not the meth, cause I've tried it both ways - gas and meth. Pull and push starts fine either fuel. Just can't kick/spin it fast enough by foot.

I was hoping that someone had done a similar thing (regardless of fuel) to their bike. Probably not many though.

Thanks anyhow.

i havent done that exact unit,but have built many big high comp kick start motors.never been a issue with a manual compression release.

my kickstart drz is +4.5mm,13.5 to 1 comp,hotcams,no auto decomp.no problem with the manual decomp to get it over top dead center.

my buddy has a 13.5 to 1 444cc yz426 and its the same deal.starts right up.

once its running does it run correctly?ruling out any mechanical issues.tight valves (have you personally checked)?cam timing?same deal,checked your self? jetting close?aftermarket carb with no choke?

Yeah... valves are in spec, cams are right, etc. I just can't kick that pig fast enough to turn it over. Damn push down the driveway will get me going. The problem though, is that you can't push start anyting in the sand!!!

I've kicked it (seriously) at least a couple of hundred times and only once was it close. I just dropped some serious coin for the porting, cams and springs and now have a machine I can't start.

I did not do the head work. Mickey Dunlap did and sent it back assembled. I don't know if he used a spring-in-spring setup or not. The stock setup is not like that. Do I need stiffer springs with the porting and cams? Could I just re-install stock cams and springs? I know I'd be loosing the performance gains, but if I can't start it, there's not performance at all.

:thumbsup:

if anything the cams help the situation since they bleed off the cylinder pressure at low rpm.

removing them will make it harder to kick over.does it have auto decomp?manual?none?

Just an idea but have you tried putting the e-start back on it? (or did it ever have an e-start?)

It had an e-start but he took it off. I would add the 5lb e-start back to it and lose 5lbs to make up for it. Hell, you probably already lost 5lbs trying to kickstart that beast so much :thumbsup:

Does that carb have a HOT START on it? (i should know, but dont care about 4wheelers).

If so, they will get stock open. YOu will be able to bumpstart the motor, but not kick start it unless hot.

Remove the plunger which you will probably find stuck in the carb. Clean it, grease it and put it back in.

It had an e-start but he took it off. I would add the 5lb e-start back to it and lose 5lbs to make up for it. Hell, you probably already lost 5lbs trying to kickstart that beast so much :thumbsup:

There's no going back to electric start!!!

There's no going back to electric start!!!

Mechanical or ego based decision?

There's no going back to electric start!!!

Mechanical or ego based decision?

Honestly? Both. There's no reason to need an electric starter... I kick my bike, I kick my quad, plus I've removed and tossed/given away much of the electrical components.

Right on! Hey, does the YFZ450 have the same senser that YZFs do that weaken the spark when in neutral? You probably have already covered this, just a thought.....

i use to build a lot of alchol machines like 350 xs with 15-1 compresion i used motoplat ignitions when they were avaiable , we also used wd 40 and squirted it in the carb to start them it ignited much easyer than the alcohol.you should also look @ a vortex ignition with the curve programed for alcohol and a good start up curve . Ron

I put the stock ex cam in last night in the cam mod postion and it fired via kicking. It takes several/many, but at least it fired and responded to the throttle.

I need to get it to idle now. The sound of the drag pipe had my wife (who was working in the yard) giving me some nasty looks so I wrung the throttle a few times and shut her (the engine) down.

Was tickled pink to be finally able to start it though. I'm going to an area tomorrow that I can run/tune it on pavement (cleaner environment than in the dirt) w/o the sound pissing folks off.

What kind of drag pipe did you go with? Also, I was looking at some 450's at the dealer today and couldn't figure out how you got the kickstart to work without contacting the rear fender? Howd you do it?

What kind of drag pipe did you go with?

A homemade jobby via Autozone: $5.84 :thumbsup:

Also, I was looking at some 450's at the dealer today and couldn't figure out how you got the kickstart to work without contacting the rear fender? Howd you do it?

If you you look behind the right rear fender of a stock one closely, you'll see a curved line molded in the plastic. That's specifically there to accomodate the kicker arm. All you need to do is cut along it and you're there. You need to relocate the rear brake fluid resi, that's easily done.

I'll be honest... I didn't that know I could "stoop so low" as to buy and ride a quad, but this thing, with it's mods (tons) is a riot in the sand and fast. I've done everything possible to make it like the dirt bike other than (3) things:

Lights

(1) extra front tire

(1) extra rear tire

In it's new configuration (which I have not yet dial in) I expect to be nearing 60hp and 60mph up our sand hill. I still prefer the MX track and my CRF, but for running the sand hill, this is a hot machine.

Here's a pic from last week:

f8998a7d.jpg

Look close and you can see the pipe.

Obviously I don't roll it around w/ the paddles and the plastics are off cause I'm still working on it. I'll post another pic like next week when she's all back together.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now