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Old 03-21-2012, 07:02 PM
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Default Completely new to karts - Honda GX160

I'm in an automotive class and as a fun side project we were able to get some go kart kits for us to build with a couple Honda GX160's (not clones).

It's been a few years since I took a class with small engines, but I still remember all of the basics. We have a budget allotted for us to get some performance upgrades and at the end of this, we'll be racing karts against each other to see who did the best with what they could, but this is where I need some help.

To start, I don't think the kit we got includes a clutch or torque converter. Second, we have around $300 (or more, if it's really worth it) for upgrades to our karts.

I've already looked up some basic kits and information for improvements. Some kits I found are:

Affordablegokarts.com "Best Bang for the Buck" Kit

Gokartsusa.com "Stage 1 Kit"

Nr-racing.com "Stage 3 Hop Up Kit"

Does anyone have any information as to which of these would be recommended, or what exactly I should be getting to maximize performance?

The track type would be a small, cement/concrete track. The karts we ordered look exactly like this one, though with a different engine:


Thanks in advance for the help, sorry for the long post!
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Old 03-21-2012, 07:47 PM
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Well if you don't have a clutch, you definitely need that. Also, are you planning on removing the governor? Because this will drastically improve performance. You must know the risks though. Here is possible list to get your power/speed up.

Remove Governor-$0
Straight Header-$37 (less if you get one used or fabricate your own)
High Flow air filter-$29 (w/ adaptor)
#90 main jet-$6
Emulsion Tube-$15 (helps low end)
New cam-$50-150 (depends on choice)
Billet Flywheel-$105
Billet Connecting rod-$60

That would be $302. You would need a clutch also which would be about $30.
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Old 03-21-2012, 08:15 PM
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Thanks for the help!

I will absolutely be removing the governor. I found a pretty detailed guide on how to remove it for this engine.

Do you have any suggestions for where to buy these parts or if there are any bundles that would include all of this and drive the price down?

I noticed some of the things you listed - like the Billet flywheel - seem extremely cheap compared to what I've seen around. Flywheels that I've been seeing (ARC ones) have been highly recommended, but at around $200. Is there any special way to come across these prices?

By the way, love the Carl Sagan quote. He was a great man.
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Old 03-21-2012, 08:17 PM
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Find out what your competition is doing for gear ratio and add 5 teeth or so. That is with the same driver weights between you. If its not a permanent thing i wouldn't bother with the rod or flywheel. Just yank the governor and get some racing 10.8 springs. If you had the money i would do the rod and reuse your flattop piston. But the $100 flywheel isn't a performance upgrade its just for safety. And the Honda wheels are good to 6000+ anyway.

Delete governor, header, intake, bored carb from NR racing or Dover, torque heavy cam, 18lb springs if you get the billet rod, port the head mildly. One size thinner head gasket, 6deg advance flywheel key.
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Old 03-21-2012, 08:29 PM
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My competition will most likely be simply ordering a kit with all required parts, most notably this AGK kit.

For a cam, would something like this cam from NR work well?


Also looking at a 22mm Mikuni carb with a K&N air filter due to some recommendations.

Thanks again!
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Old 03-22-2012, 11:39 AM
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Not sure how much skill and tuning ability you would have so the Mikuni is less reliable than a bored stock carb that has already been jetted correctly and uses the existing throttle setup.

It doesn't matter what engine kit they competition is getting, you need to find out the gear ratio/tire size and be able to beat it. Not in top speed but in torque around a small track.
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Old 03-22-2012, 01:09 PM
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What sort of top speed are you looking at? Also are you sure that those carts will be stable at high speed?
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Old 03-22-2012, 04:10 PM
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Quote:
Originally Posted by slideways View Post
Not sure how much skill and tuning ability you would have so the Mikuni is less reliable than a bored stock carb that has already been jetted correctly and uses the existing throttle setup.

It doesn't matter what engine kit they competition is getting, you need to find out the gear ratio/tire size and be able to beat it. Not in top speed but in torque around a small track.
Right now, we both have the same tire size, drive gear, and are looking at the same clutches, which would be a Max-Torque clutch for about $50. 12" diameter tires, 5:1 gear ratio (72:12), with engines that would run around 5200 RPM with the governor removed. According to the calculator, that'd be a theoretical 31 MPH top speed.

It's not really the top speed I'm worried about right now, though; being that we're going to do this in a small area (still don't even have a track made!), I doubt we'd ever reach top speed, so torque and handling is going to win the race. I've tried opting for all of the high-torque options, from the cam to the clutch.

No-go for the Mikuni carb then, eh? I guess I assumed it'd be better than a bored OEM option, but I guess not!

Luckily I know a guy that can do milling for me as he has his own professional shop. We'll be able to do the porting, as well.

Thanks again for all of the help!
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Old 03-22-2012, 04:48 PM
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A word of advice-if you remove the governor and put in heavier valve springs, you must get an upgraded rod and flywheel. This is because valve float is one of the last defenses against possible rod and/or flywheel failure. With heavier valve springs, if you over rev it without upgrades, someone could get hurt. Also here is a link to the flywheel I saw http://www.affordablegokarts.com/mm5...egory_Code=CF1 all the products I listed can be found on AGK.
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Old 03-22-2012, 05:05 PM
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Hey again,

I was just looking through AGK's site for a while, composing a list before you posted. Managed to get down to this:

$ 37 Header:
http://www.affordablegokarts.com/mm5...ory_Code=GGPP5

$ 29 Air Filter:
http://www.affordablegokarts.com/mm5...ory_Code=GGPP5

$ 6 Main Jet #90:
http://www.affordablegokarts.com/mm5...gory_Code=AFC1

$15 Emulsion Tube:
http://www.affordablegokarts.com/mm5...gory_Code=AFC1

$ 59 Cam:
nr-racing.com/raceparts.htm
Camshaft, 230 - Torquer
SPECIAL HIGH TORQUE GRIND FOR SMALL TRACKS, 5500 rpm, 18 lb Springs Required, 9.5 to 1 Compression or lower

$105 Billet Flywheel:
http://www.affordablegokarts.com/mm5...egory_Code=CF1

$ 59 Billet Rod:
http://www.affordablegokarts.com/mm5...gory_Code=CRP1

$ 8 Valve Springs x2:
http://www.affordablegokarts.com/mm5...ory_Code=CHVT1

$ 15 Head Gasket:
http://www.affordablegokarts.com/mm5...tegory_Code=PG

Total cost:
$333 + Shipping & Handling +/- school discount
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Old 03-22-2012, 07:39 PM
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That definitely looks good. You may also want to remove the low oil sensor to prevent engine shutdown mid-race (that would suck).
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Old 03-22-2012, 08:27 PM
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Lose the flywheel and spend the money on a bored and blueprinted carb from Dover Power or NR Racing.

You should have the slightly smaller 18cc head on the 160 so that will promote torque. Get a thinner head gasket and do a mild porting job on the head (search on 4cycle.com)


How much heavier is your driver than the other team?
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Old 03-22-2012, 08:33 PM
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Quote:
Originally Posted by Jcotz View Post
That definitely looks good. You may also want to remove the low oil sensor to prevent engine shutdown mid-race (that would suck).
Thanks, I'll definitely try it. I saw that mentioned in the governor removal guide I was looking at earlier and it looked like a pretty straight-forward job.

Quote:
Originally Posted by slideways View Post
Lose the flywheel and spend the money on a bored and blueprinted carb from Dover Power or NR Racing.

You should have the slightly smaller 18cc head on the 160 so that will promote torque. Get a thinner head gasket and do a mild porting job on the head (search on 4cycle.com)


How much heavier is your driver than the other team?
Thanks for the advice.

There is probably a 20lb difference between the other driver and I, with the other driver being the heavier one. ~140lbs vs. ~160lbs.

The OEM flywheel is sufficient for unrestricted RPM's, though? Seems like everyone has been saying how dangerous it is, even if it's genuine Honda, and how easily the non-Billet/aluminum flywheels can break.

Side-note: Is it possible to remove the limitation the governor places on the motor without actually cutting the gear out from within the crankcase, but performing all of the other steps?
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Old 03-22-2012, 10:02 PM
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If you were racing this constantly every week or whatever at a sustained rpm over 6000 i would definitely go with the billet flywheel. But for one race or a day of races in a parking lot it wont hurt to just take care of your stock one (dont hit it with a hammer) and save the money for more horsepower mods.

Good to hear you have the weight advantage. With the same motor and drive setup you will have a pretty close race even with more mods to your engine. Each thing only adds up to a little bit and a better driver or handling kart will make the difference.

Try to find a higher stall speed clutch spring for whatever clutch you choose.
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Old 03-23-2012, 01:01 AM
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Look for a gxv160 mower with a 'tin top'
They have cast aluminium flywheels which are far better than the gx cast iron ones.

Also, I would get a flat top piston and a .010 gx200 head gasket. This should increase compression a fair deal.
Edit: newer gx160's already have a flat top and a larger cylinder head area. If you have an older one a flat top would be good.
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Old 03-23-2012, 05:57 AM
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Quote:
Originally Posted by slideways View Post
If you were racing this constantly every week or whatever at a sustained rpm over 6000 i would definitely go with the billet flywheel. But for one race or a day of races in a parking lot it wont hurt to just take care of your stock one (dont hit it with a hammer) and save the money for more horsepower mods.

Good to hear you have the weight advantage. With the same motor and drive setup you will have a pretty close race even with more mods to your engine. Each thing only adds up to a little bit and a better driver or handling kart will make the difference.

Try to find a higher stall speed clutch spring for whatever clutch you choose.
Thanks for the help again!

I think I'll be ditching the new flywheel then in favor of a new carb. Any good recommendations?

I see a few options for the GX160, but could you tell me the differences between the options? E.g. blueprinted vs. non-blueprinted, Honda OEM vs. Mikuni, Japan vs. Thai. Looks like blueprinted in superior to non, but if you're racing in a league (which we're not), you can't use it. Mikuni has a higher cost, but hasn't been recommended much. NR says Japan is higher quality, but does it justify being almost two times as expensive?

Sorry for all of the questions - I'm trying to absorb as much information as possible so I'm not clueless when it comes time to actually install everything. I really appreciate all of the help!
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Old 03-23-2012, 09:36 AM
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If you can afford it you want a "bored Honda carb". This will be a Keihin which is the better carb. The clone motors use a copy of this but it doesn't flow quite as well. You can run any carb you want. Blueprinted is a good thing. It just means a builder has gone through and tricked the flow and jet sizing of every part they can. Like i said. NR RACING is a very good place. Email Russ and tell him your plans, he will have all your other parts too.

Dover Power is another very good place that many racers use. Jerry builds a carb called the "holy moses" but i'm sure he builds a bored version too for someone with no rules like you.
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Old 03-23-2012, 10:46 AM
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Bored Honda GX200 carb over a Mikuni, then? With the hop-up kit 3 from NR-Racing, a 22mm Mikuni would be $30 more than a bored GX200 carb.

Thanks for the clarification on the meaning of blueprinted. Couldn't for the life of me figure out what they were talking about and I couldn't find much info on my own.

Coincidentally, NR-Racing is located very close to my school, so I may see them in-person and talk, though I just talked with someone from NR over the phone. I told him basically what I was trying to do and he advised me to check out the hop-up kits again because it would have everything I needed.

With the Hop-Up Kit 3, is there anything I'd be missing?
http://nr-racing.com/hopupkits.htm#STAGE_3_KIT
Selecting the GX160, bored GX200 carb (gas), 230U 0207 camshaft, kart header, and no flywheel.

Thanks again!
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Old 03-23-2012, 11:25 AM
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Looks good to me. If you get to meet with them i'd just describe your situation. Ask him which cam is best and go from there.

The Mikuni slide carb will outperform a butterfly style carb. BUT since you are in a school with limited tools and time to tune and try the thing you are going to be better off using a stock type carb. The throttle hookup on the Mikuni is completely different, you would need a few different jets to make the thing even run right and its just going to be a bigger pain in the end. The key is going to be having something reliable that doesn't stumble on takeoff or hardly run because the parts don't all work together. Keep it as close to stock as you can for reliablility.


Don't forget the mild port job on the head, ask him about how to do that too. Just smooth the port slightly and take down some of the short side radius. Don't go hog wild or you will lose power.
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Old 03-23-2012, 02:09 PM
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Wow, thanks for the warning! I saw some pictures of a Mikuni carb and thought it was odd that there was a series of tubes coming off of it, but didn't think much of it. Being that time is a huge factor in this project, there's no chance we'd be able to fine-tune a carb like that within our time restraints.

Our teacher has his own porting kit and has experience porting all of the small B&S engines in the lower-level autos classes, but I'll make sure I touch base with Russell on how to do it correctly.

Thank you again so much for all of your help. This could not have been done without it! Hopefully I'll be ordering the parts at the start of the next week and we'll be well on our way to a successful project.
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