gx 340 carb on predator?

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yerf_dogger

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can you use a gx 390 carb on a predator 212cc?

I am confused... I see on nr racing they offer that carb as a performance carb with other mods.

will it work as a simple bolt on?
 
Doc Sprocket

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It can work if your engine has been highly modified to the point that it requires a much greater fuel/air volume than stock. Putting a larger carb on a stock or near-stock engine can actually worsten performance.
 
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rmm727

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Its not a bolt on. You would need an intake and figure out throttle linkage. The butterfly turns the opposite direction. Otherwise, I agree with the above post.
 
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yerf_dogger

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currently have isky cam, 1.3 rockers, lifters, chrome push rods, flywheel, billet rod, robertsons header, intake, 26lb springs and re jetted my carb, walboro fuel pump, AR3910X plug, lapped valves advanced timing, smaller head gasket, gx 140 E-tube.

I was looking at a mikuni carb but found a gx 390 carb on ebay for 25 bucks.

my buddy is gonna port and polish my head once it comes in. (gx 160)

It runs crappy at idle and boggs down at WOT.

thinks its getting too much air to fuel... but my spark plug looks fine so I have just had it parked for the past few weeks.

any advice would be helpful. My son is pretty bummed that we built the motor and now it runs like crap!
 
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Honestly, if you're putting that much (and more) into your engine, you should revisit the Mikuni. They are much more tuneable than the 390 carb, and will result in better throttle response throughout.
 
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yerf_dogger

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rmm727 said:
figure out throttle linkage. The butterfly turns the opposite direction. post.
Click to expand...

that would be much better considering the throttle on this engine is backwards in my opinion.

I had to custom make my linkage out of a heavy gauge wire. Took me hours to finally get it all dialed in:thumbsup:
 
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Sinbad001

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Typically you only need a bigger carb when you make the engine bigger. ie: big bore kit. You can build the hell out of an engine and put a carb on that is to big and it will run like crap. Also, the more you build an engine for power, the smaller its operating range becomes. That is why a dragster engine only runs at top rpms and will run like crap if you were to try and run it on the street at verying rpms. It is easy to over build an engine, especially when messing with cams, and end up with something that doesn't run good.
 
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yerf_dogger

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Sinbad001 said:
Typically you only need a bigger carb when you make the engine bigger. ie: big bore kit. You can build the hell out of an engine and put a carb on that is to big and it will run like crap. Also, the more you build an engine for power, the smaller its operating range becomes. That is why a dragster engine only runs at top rpms and will run like crap if you were to try and run it on the street at verying rpms. It is easy to over build an engine, especially when messing with cams, and end up with something that doesn't run good.
Click to expand...


Im not sure I agree with everything you said. These engines are designed to run 3600rpm constantly.

By building the engine you wont limit its range you increase its range. You just have to find the proper air to fuel ratio across the entire power band.

Of course you will have more torque at lower rpms but youre still gonna be making power at 6500 rpms as well.

Without any modding the engine is only safe to maybe 5000 rpms. If you want a broader range of power you add different cams, and such.

If you were going to narrow your power band why would anyone do any modding to a stock engine?

:popcorn:
 
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You're both right, and you're both wrong. What you're missing is-

It depends on what you are building the engine for! You can-

-Build a high-rev screamer that will have a limited and high powerband that will likely idle like crap.

-Build a low-end torque-monster that will burn tires coming off the line and out of the corners, but fall flat on it's face at top end.

-Or, an engine can be built that will NOT have the grunt of the torque-monster or the top end of the screamer, but will perform much better than a stocker and have a good, balanced powerband.

The lesson: There's more than one way to modify an engine.
 
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yerf_dogger

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well personally I dont care to take this kart over 40 mph or even 35 for that matter.


they just cant handle the abuse.

what I do want is torque and a few more revs.

this is why i have it geared the way I do.

I ended up getting carried away with this one, but got a good deal on many parts so figured why not???

flywheel and rod were only 100 bucks for both.

then when i ordered the cam I had to put springs and new rockers. figured for 30 bucks more I mght as well add a few extra parts.

now I just need to get it tuned right and it will be more than enough kart for a ten year old to grow into and learn a few lessons.

:kewlsmiley:
 
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Sinbad001

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A cam can't make great power at low rpm's and high rpm's or else there would not be cam choices. You have to choose where in the rpm range you want to make power and then choose the appropriate cam. The stock cam is the one that covers the most range but is not great at all ranges. Look at an off road 4x4. It has a cam that makes torque and power at low rpm. A dragster has a cam that makes power at high rpm. One cam can't do both. It is the same with kart engines. They already come with a cam that makes its besy torque and hp at low rpm's. Virtually all after market cams available are for raceing and are meant to make power at higher rpm. The low rpm power is sacrificed. One cam can't do both.
 
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zbuck

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:wai: By the description. That is for a 50cc engine, Which I assume would be to small for your 212. But heck anything possible, its your choice.
 
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