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Old 12-14-2011, 05:06 PM
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Hello everyone. This is my first post so sorry if may i appear a little naive i am fairly new to working on gokarts. However, i am not new to working on engines because I race motorcycles and am also an aviation mechanic so rest assured any information given will definitely be used to it's full potential! and will be much appreciated<3

I recently purchased a new duramax 7hp engine

http://www.maxtool.com/us/products/XP7HP.asp

and I'm looking to gain some more power. Now i have read Oscaryu1's very well written "lil 5hp guide" and am now wondering how much of that would be acceptable to try on my new duramax engine?

Another big question i have is should i break the engine in before i modify anything?

Lastly i also kind of just want to know in general.. What would you guys do in my position? lol i know this may seem like a silly question but Im serious. I'm not really SET on anything right now. I'm just looking to have some fun and get my hands dirty doing it. So right now i have a 50lbs offroad kart with a new 7hp engine and am basically looking for the best route to take as far as modifications go.

Any information or ideas you can give of any kind will be of help and again greatly appreciated even if it doesn't answer a question i asked(ie how reliable duramax is, if 7hp is a sufficient enough power source to supply to my kart, resources for more gokart parts or discussions, etc...) Thank you so much in advance! I love you guys
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Old 12-14-2011, 05:27 PM
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Step One: Figure out what it is you're after. Speed? Jumps? A stump-puller that'll climb a wall?

Why don't you post up a couple of pics, and tell us what you'd like to get out of it.

And- welcome to the forum!
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Old 12-14-2011, 11:48 PM
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I'm probably not going to be jumping it and as far as speed i'm shooting for 30mph but no more than 45mph. I dont need to neccessarily climb walls but I will be taking this camping and there are a good amount of hills where i usually go and i would like be able to drive up them with out any issues. if i could drive 35 and have enough torque to handle a couple of hills I would be MORE than happy. With proper gearing how possible do you think this would be with MY stock engine and MY kart?

if this is attainable without modding the engine then I'll probably keep it stock. I have a hunch I'll need more power though and will have to do the modifications lol

if i gear my stock engine to go 30 how much torque will it still have left?(7hp engine, 40lbs engine, 50 lbs kart, 180lbs dude) will my 7hp duramax even be able to push 270 lbs 30mph??? sorry for all the questions lol and thanks for welcoming me!

[IMG]H:\DCIM\100_PANA\P1000220.JPG[/IMG]
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Old 12-15-2011, 07:04 AM
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According to the specs listed, this engine has the same bore and stroke as the 196cc clones that are commonly seen that go kart racers use and what Harbor Freight use to sell (Greyhounds)

You can buy cams, header pipes, springs, k&n style air filters, etc with these engines... Depending on what you want to do you could spend anywhere from 75 dollars to 300 bucks... or more...
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Old 12-15-2011, 05:50 PM
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Your speed expectations seem fairly reasonable. For actual calculations, I need your rear tire overall diameter in inches.
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Old 12-15-2011, 08:23 PM
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id go for a comet torque converter instead of a normal go kart centrifugal clutch. more money but its worth it. this gives you somewhat of a "transmission" instead of being stuck in first gear.

if you still want more, the next thing id do is upgrade the exhaust and intake. this isnt very expensive but you will probably have to rejet the carburetor. (jet kits are sold) #90 is used most often with these mods.

after that it gets into the big stuff. and one leads after another. no governor, flat top piston, mill head, billet rod, upgraded valve train, performance cam, then you can even get a stroker rod and crank, billet flywheel, pretty much every part can be upgraded.

these engines are designed for things like tillers and snowblowers so they wont push like a race car, stock...
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Old 12-16-2011, 09:24 AM
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Quote:
Originally Posted by Justin9 View Post
According to the specs listed, this engine has the same bore and stroke as the 196cc clones that are commonly seen that go kart racers use and what Harbor Freight use to sell (Greyhounds)

You can buy cams, header pipes, springs, k&n style air filters, etc with these engines... Depending on what you want to do you could spend anywhere from 75 dollars to 300 bucks... or more...

thats intriguing i can't wait to put it in my kart. I was thinking about spending another $75 on it or so for the engine alone. What would you recommend i get if I'm only willing to spend $75?
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Old 12-16-2011, 09:48 AM
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Quote:
Originally Posted by toystory_4wd View Post
Your speed expectations seem fairly reasonable. For actual calculations, I need your rear tire overall diameter in inches.
i have a 25'' circumference but the tires are worn and i plan on getting new ones so the specs might end up changing a little
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Old 12-16-2011, 09:56 AM
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For $75 i would get an upgraded exhaust and air filter (with billet adapter), flat top piston, and a bsp-1 cam (exactly what I am doing ) don't forget to remove the governor. You will then have to plug chop to find the best jet, probably around #90 like blue suggested. This will get you around 9hp and around 5500rpm, and cost around $75
If you wanted to spend a little more you could get a mod 2 cam, 18lb valve springs and a billet rod. This would cost another $80-100
You can spend up to a grand on these motors but it is hardly worth it unless you are in a clone racing class.

Some links to check out:
Affordablegokarts.com
Nrracing.com
Arcracing.com
Dynocamsclonestore.com
Karting.4cycle.com
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Old 12-16-2011, 04:27 PM
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Quote:
Originally Posted by 5h4de5_O-O View Post
i have a 25'' circumference but the tires are worn and i plan on getting new ones so the specs might end up changing a little
25" circumference, or 25" diameter? Big difference. I need diameter for calcs. Best to actually measure it as published specs are often out a few percent.
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Old 12-16-2011, 08:03 PM
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my apologies i thought the circumference would have been of more help to you. However, i did measure the diameter and it came out to 7.96''. i just purchased some tires with a 12'' diameter though to replace my old worn out ones. Thank you for the helpp too! i very much appreciate it:]
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Old 12-16-2011, 08:16 PM
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I'm a little concerned about the weight combined with the hills. Here's what I have so far:

12T clutch
66T Axle
Final drive ratio= 5.5:1
Governor maxed to (projected approximate max) 4200RPM
Projected max top speed 27.26MPH

I "theoretically" maxed out the governor to try to regain some top end. I don't think performance will be satisfactory with a final drive of 5:1. At 5.5:1, some top end is lost but can be regained by playing with the governor. Further engine mods could allow lower gearing with a higher top speed. A CVT is well worth considering, too.
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Old 12-17-2011, 11:31 AM
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would you recommend i just remove the governor? how dangerous is this?
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Old 12-17-2011, 12:41 PM
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It's not "dangerous" if done right. By that, I mean selecting an appropriate gear ratio so the engine is not underworked, and you operate it accordingly. This means not free-revving the engine, or allowing it to overrev unnecessarily.

I always suggest folks leave the stock valvesprings in when removing the governor and retaining other stock internals. When the revs get a little high, valve flutter tends to limit things before components start failing.
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Old 12-17-2011, 02:41 PM
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okay so after doing a little poking around and using the information you guys have given me (which helped alot, thank you) this is what im thinking about doing:

Removing governor
upgrading intake
upgrading exhaust
rejetting carburetor
removing head gasket and lapping the head and block
aluminum flywheel
Sand and polish exhaust and intake ports


and those CVT's look pretty cool but i might hold off on that until i get a little more familiar with everything. So what do you guys think about this list?

am i missing anything obvious???

is there anything i am getting/doing unnecessarily?
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Old 12-17-2011, 02:49 PM
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I highly recommend doing one mod at a time.
If everything is done at once and engine does not run properly, a lot of unnecessary backtracking will have to be done.
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Old 12-17-2011, 04:21 PM
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Quote:
Originally Posted by Russ2251 View Post
I highly recommend doing one mod at a time.
If everything is done at once and engine does not run properly, a lot of unnecessary backtracking will have to be done.
Words to live by.
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Old 12-17-2011, 05:23 PM
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alright i'll make sure to do them one at a time. should i break the engine in first before i do any of these mods?? it's straight from the factory
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Old 12-17-2011, 05:32 PM
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I have seen where break in is recommended, however, I have seen generators with this identical engine. A generator never runs below 3600 rpm for its entire life. It cannot be run at half speed.
How is this engine broken in?
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Old 12-17-2011, 05:36 PM
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i imagine the best way to break it in would be to use it in the way in which you intend to use it for the rest of its life
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