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Discussion Starter #1
So I’ve had my KQ-300 for about 3 months now and I love it. The bike has plenty of power for my needs but I keep reading about various performance mods that have been available over the years?

I’m just curious to know what all mods were/are available? From my research there are,
1. Big bore kits
2. Slip on mufflers, (Cobra Exhaust?)

What else is there or has there been for these sleepy little engine? Any cams available from other engines with similar top ends?

Also, is there any benefit to changing the jetting on a factory bike?

My KQ has the idle screw set to 2-5/8 turns out from lightly seated as the book indicates and it is a little rich at idle, it will start no choke every time if I crack the throttle open, and that’s hot or cold. For those who tune these Mikunis does turning the screw in lean or enrich the mixture?

Thanks!
 

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These bikes really don't respond to mods very well in the horsepower gain department. Big bore kits are probably the easiest way to gain power but with many headaches with re-jetting and overheating problems. The amount of power gains for the cost involved will have to be in the mix in your decision . In my opinion and 2 cents.....I would leave well enough alone....but that's just me.

As far as re-jeting ....I tried to go up 1 size on the main jet ( 117.5 to 120 ) and it did not like it at all....went back to stock.
 

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I installed a Kimpex muffler when my stock one rotted out and it responded it it nicely. It may just be the lack of the old plugged up spark arrestor... but a noticeable smoothness down low and more punch on the top end.

I also run a lightly oiled UNI filter and I went 1 notch up on the carb needle. Other than that, I would just buy a bigger machine if you want bigger performance.
 

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Discussion Starter #4
Both of those posts are great insight, as I indicated the bike is more than adequate power wise for my needs. I have other machines that satisfy my need for power. Just curious more than anything else.

Funny you mention the factory spark arrestor, my service manual mentions removing the plug and cleaning the carbon out of the muffler on a regular interval! From the looks of it, my plug has never been out and I don’t think it’s a wise idea to try to extract it now!

To my knowledge Kimpex is the only current manufacturer of aftermarket exhausts for these bikes?
 

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All I've found specifically for the kingquad 300 and quadrunner 250 are...
big bore kits
performance camshafts and chains
And high flow filters
Might be more performance parts out there but i haven't found them.

Im running K&N air and oil filters. My stock filter was garbage when i bought the quad. When i do my timing chain I'm thinking about trying a camshaft from hotcams.

I've decided not to go to far out of my way trying to build power. Just upgrading when things need fixed or replaced.

From what I've read the problem with big bore kits overheating is caused by going lean. If you don't rejet the carburetor and tune it correctly it will be lean and overheat.
 

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Muffler and filters are good ideas from my experience. Don't start changing a bunch of stuff if you are happy with what you have, just enjoy it. Your bigger units can do heavier applications. I have a 300 kq as well and it does all I need to do. Always remember that "Wants" and "Needs" are 2 entirely different things. Enjoy!
 

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Removing the plug to get to the spark arrestor if it looks or hasn’t been removed is probably not a wise idea. The plugs tend to rust in place and usually cause more damage trying to remove them then anything.


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Removing the plug to get to the spark arrestor if it looks or hasn’t been removed is probably not a wise idea. The plugs tend to rust in place and usually cause more damage trying to remove them then anything.
Agree! You may end up twisting out the whole bung if it's rusted too thin. Plus, the "drain" on the back of the muffler really doesn't affect the actual spark arrestor in the muffler tip.
 

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Discussion Starter #9
I pretty much new all that had been said already but sometimes it helps to hear it from someone else! My 99’ KQ300 runs great and makes 180PSI cold on my compression tester. I’d love to have a little more punch but I already have my reservations about tearing down a perfectly good engine in hopes of trying to make it into something that it isn’t and never will be.
 

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I look at it this way. The KQ isn’t a speed demon, it’s more a torque monster with all the gear options available, low/super low range. A lot of people say this thing would pull a house. And your better served leaving it the way it is and it’ll serve you well.


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I’m really glad I found this forum. I’ve been reading a lot. Lots of good info here.

My 98 is smoking pretty bad. I’ll borrow a compression tester from my neighbor next week but I’m pretty sold on a top end rebuild using weisco a piston most likely +.5mm, probably regrind the valve seats and possibly new valves depending on the condition. I’m considering shaving a little off the head, maybe .030” to increase the compression a little bit. I don’t want to get too crazy with it.

I’m a big guy 6’6” and 270lbs so a little extra power wouldn’t hurt especially when I have my 10 year old or a deer on the back of it. I would love the big bore kit but I’m skeptical of its longevity and overheating issues. I’ve read that cams are available but I haven’t been able to find them anywhere.


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I look at it this way. The KQ isn’t a speed demon, it’s more a torque monster with all the gear options available, low/super low range. A lot of people say this thing would pull a house. And your better served leaving it the way it is and it’ll serve you well.


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i couldnt say it better myself. i moded the heck out out of my old 300 but 1 thing i left alone was the engine. that little 300 was a hard worker with tons of gear selections, there was no need to push more power out of it. besides, if you start to push too much power you may find yourself replacing those u-joints and/or half shafts more often than you like.
 

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If your looking for a performance camshaft try hotcams. Last time i checked they still made a camshaft for the KQ300.

They also listed several other engines with compatible cams.
 
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