Cylinder head mods

[Copo427ss]

Just a quick update, I drilled my jet out some more, disconnected the rev limiter and added a uni dual stage foam filter to the end of the carb. The cart is fast be still running way to lean. Gonna have to drill a few more sizes at work tomorrow. I can't remember what the stock size for the jet was in thousandths. But I had previously drilled it out to a .036", and today drilled it to .039". And after some good runs down my property the plug is still white. This thing is thirsty now. Throttle response is pretty good and getting better with richening it up.

[Copo427ss]

So I have played with the jetting some more. I drilled the jet out to a .041", installed a dual stage uni filter to the end of the carb and eliminated the rev limiter, and the exhaust is modified. This motor cranks now. Has good throttle response, climbs steep grades with ease and will easily spin the tires climbing. I really wish there were performance cams available. That's what this engine really needs. Right now the cart pulls hard enough that you can feel it seat of pants.

[rude dude]

If you take the engine down again I would love to see some pics of the head porting, this is the first post I have seen on head porting. In the Harley bike world it is all about port shape now, velocities, runners etc, old school was bigger is better

[Copo427ss]

Originally Posted by rude dude

If you take the engine down again I would love to see some pics of the head porting, this is the first post I have seen on head porting. In the Harley bike world it is all about port shape now, velocities, runners etc, old school was bigger is better

I took pics of before, during and after. It really blew my mind when I saw the ports on these heads. I mean for an engine that's not seeing anywhere near 5000rpm stock. They have huge ports. The runner is so smooth you'd swear it was polished. Then the bowl is just drilled down past the runner. Anything you do to make the intake port not so cavernous is an improvement. I don't know how to post pics from my iPhone. Maybe I'll try my laptop tomorrow. I wish my boss didn't sell the flow bench. It would have been great to see the before and after. I can tell you what I did was a huge improvement. I had the exhaust modified, both clutches with power kits and a kn filter in it. Once I did the head shaving and head port I had to jet up. Then I jetted up more after putting the uni filter on the end of the carb. I don't know what it's putting out for hp now but I can tell you I'm pretty **** impressed with the results. The engine sounds so much smoother and throatier. I would say it would make a difference just changing the ports on a stock engine. But it really starts pulling around 3000 so the rev limiter must go. Even honda is going more for port velocity on there dirtbikes now. If you did I side to side comparison to 3 years of heads each year had a better velocity port design.

[Copo427ss]

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[Copo427ss]

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[Copo427ss]

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[Copo427ss]

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[Copo427ss]

Sorry for multiple posts but can't get it to attach all the photos to one post

[Copo427ss]

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