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Author Topic: GX340  (Read 1877 times)
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Zippy 13N
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« on: August 22, 2013, 09:38:59 PM »

Ok I cant find much about the 340 so ill ask!  I have not messed with many Hondas and never a single cylinder Honda.  I have a 340 now that is in GREAT condition!  My question is, what is different about the 340 and the 390 other than 50cc's.  (ex. Is the 340 the same bore with a different stroke or is it a different bore and stroke?)  The reason I ask is because the 340 I have, has a tapered PTO and I am going to change the crank (if I can find one) to a straight shaft to use for racing.  I know I know people want to go bigger CC most of the time BUT this is going on a starter ride.  Its for a girl that has no experience so the size is not an issue I just want to know what parts I can get/use that will work for this motor.  When she gets experience I will add more power but power isn't the issue at this point.  Thanks guys!
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Derrick Nichols
Zippy 13N
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« Reply #1 on: August 22, 2013, 10:56:31 PM »

I tried some different searches and found some useful info.  From what I am gathering the 340/390 are the same stroke different bore. Right?  If so I can find a crank out of either that has a straight PTO and in the future I can bore it to a 390+. 
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Derrick Nichols
catfishdan
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« Reply #2 on: August 22, 2013, 11:02:06 PM »

yes the 390 crank will work.. the 340-390 are what is considered honda big blocks by the karting world.
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Dan

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« Reply #2 on: August 22, 2013, 11:02:06 PM »

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Zippy 13N
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« Reply #3 on: August 22, 2013, 11:09:36 PM »

Thanks catfish!  I'm going to try and find another crank these motors have a nice head design and are built durable so I think it will be good from a starter all the way to a full blown racer
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Derrick Nichols
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« Reply #4 on: August 22, 2013, 11:24:50 PM »

could make a good engine but it is only 20.6ci so would depend what class you are building for
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Dan

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Darkviper
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« Reply #5 on: August 23, 2013, 12:12:21 AM »

We have guy that runs GX340 in fxs it runs really great if built right. It anit huge difference in sizes of bore the 390 is 23ci and 420 is i think 25. That is plently of power if you using it for fxs or even fx once built. You can punch it out if you wanted to and i think the heads are the same.
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Jonathon Kaup
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Zippy 13N
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« Reply #6 on: August 23, 2013, 05:27:23 PM »

Hit the jack pot today guys. Still gonna hang on to the 340 but a local business owned by a good friend gave me a 390 for FREE!!  Thanks for the help!
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Derrick Nichols
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« Reply #7 on: September 06, 2013, 03:07:02 PM »

I am getting ready to have my son tear down a 340 and rebuild it for his small engines class.  We were thinking of boring out.  How big can we go, 390, 420, 440?  Does anyone know if the 340 bore is nickel treated or is it a cast iron sleeve?  Can I just bore out my 340 and put in the new pistion?  I'm wanting to keep it pretty much stock, maybe just some porting since it is coming apart.
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Dan Borba
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