GX200 clone doesn't want to rev

Thelegg

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Hi, so basically I need some advice on what to do with my go kart engine.

It's a GX200 clone which ran fine In stock form with a 12 tooth centrifugal clutch and 66 tooth axle sprocket. I was mainly using the kart in a field so fitted bigger tyres (went from 11" diameter to 13")
Also at this time I fitted a cone air filter, a straight through exhaust, heavier valve springs, removed the governor completely and re-jetted the stock carb.

First time driving the kart it was very clear that the clutch was struggling to turn the bigger tyres so I installed a torque converter. Now when driving the kart it accelerates lovely on the flat but struggles a little uphill and over bumps and once it gets upto speed it just feels somewhat slow like it could rev higher/go faster but something is limiting it.

I've tried adjusting the main jet but have concluded it's spot on as any bigger or smaller causes it to run much worse so do I have a gearing issue here or have I reached the limit of the clone carb so should be thinking about fitting a mikuni carb ?

Cheers all
Any advice appreciated

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Brianator

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What kind of TC, 30 series (with backplate)? What's the tooth count on the TC sprocket? Roughly how much does the kart weigh with you on it? The driven pulley is adjustable, set it to the next hole that adds tension to that wound spring to keep it in "low gear" longer, it's also better for climbing hills.
 

JTSpeedDemon

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A 12/66 with 13" rears? That's my exact setup! Is the new TC also a 12T sprocket?
Another thing to consider, a little less likely, is that heavier valve springs do allow you to rev higher, but they rob engine power in the process, since the engine has to push stiffer springs. What weight are the new springs?
 

BigWes

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also is your linkage to your carb working good? have someone push your pedal with it not running and make sure you are getting full wide open throttle. Look and make sure your throttle is going fully open. Also it's completely possible that your gaskets may have gotten crossed up if you took the carb off the engine to rejett the carb. If not then look more into your T/C setup.

I prefer a T/C but I am by no means a guru on setting up the springs and stuff. I can align anything...mainly because I have tools to do it. I didn't used to so don't think I'm bragging because before I did I will say where there's a will there's a way...anyhow

Your clone carb should pull your setup just fine. I feel something else is amiss.

Keep looking and don't get discouraged or give up or spend a wad of money you don't need to either.

But if you just want the Mikuni...then by all means get a Mikuni...I have one on a recent upgrade and I am still undecided about it. I will say this...it has made in Japan stamped on the side of it...not the other place.
 

Thelegg

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The TC is a Chinese version of a 30 series, I don't think it has different holes for the spring but guess I could drill some any pics of where these other holes are located ?
The sprocket on the TC is a 12 tooth

Valve springs are 26lb

I cleaned the carb when I tried different jets the other day and double checked that the gaskets where correctly fitted, throttle linkage all free and opens the carb to full throttle with no issues. I don't really want to fit a mikuni if it won't solve my problems lol thanks for all your responses

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---------- Post added at 03:00 AM ---------- Previous post was at 02:16 AM ----------

Oh and I weigh about 12 stone but the kart will still feel like it has more to give when jacked up off the floor with no one on it so don't think it's my fat arse holding it back 😂

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Brianator

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So you're about 160lbs, how much does the kart weigh (approximately)? It could be the driven clutch going into overdrive too soon, it's fairly common with a gear ratio that's not ideal for the weight it's trying to push, you're at 5.5:1 right now which may not be horrible with your tire size as long as the kart isn't really heavy...

Post some pics of your kart and the setup please, it may help. If you have a GoPro or something similar try setting it up to film what the TC is doing, that could spot something going on.
 

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JTSpeedDemon

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No wonder! 26lb valve springs is nuts! That's for heavily built racing engines! At most you should have 18 lb springs! Sounds like it's time for you to either downgrade your springs or build the engine to suit.
 

Thelegg

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Thanks for the quick responses, I've looked closer at a spare torque converter (same as what's fitted to the kart) and I think it has adjustment holes :) I've also attached a pic of the kart, I have no idea what it weighs but I can lift it up onto axle stands. Think I'll order some lighter poundage valve springs, odd tho as I bought the cone filter, jets and springs as a package so would've thought the company would of researched if they were to heavy :(


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JTSpeedDemon

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Where'd you buy said package from? Whoever put it together doesn't know what they're talking about. Even 18lb valve springs is dangerous without billet aluminum components.
 

Thelegg

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It was www.prokartengineparts.com upon checking back on the site there actually 22lb springs. Do you think I should buy 18lb springs or chuck the stock ones back in as I'm still running the original cast flywheel.

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JTSpeedDemon

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Hmm, never seen that site before, but they actually look pretty legit. At any rate, it's not a good idea to have heavy springs without billet components. I recommend throwing the stock springs back in. You'd be surprised how fast 5200 RPM feels
 

Brianator

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Those are indeed the adjustment holes for the driven, choose the one that adds spring tension.

Your kart wouldn't weigh much so that shouldn't be a factor.

I agree with JT, toss the stock springs back in, make sure they're properly adjusted and you'll probably have a different animal on your hands!
 

bob58o

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If it won't rev out when jacked up off the ground, I wouldn't imagine that gearing is the issue. Probably not the TC either. To be sure, take the belt off while jacked up and test.

Considering your recent modifications... I'd be looking at carb / throttle cable / valve issues. And yes 26lb springs are too much for an engine with stock internals. 26lb springs might flatten the lobes on a stock cam and could possibly fudge up the stamped rockers on a gx200 clone.

Edit. I see they are 22lb springs. 22lb springs aren't unheard of with a stock engine, but your cam will probably run out of breath before you rev high enough to need them. Stock springs should get you to ~65km per hour. I'd try the stock springs, if for no other reason but to try to isolate plausible issues.
 

Thelegg

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I've got a week off work so I'll swap the springs over one day and report back with my findings :)

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BigWes

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Stock springs. That kart doesn't look overly big or heavy. Try those stock springs and see what it does.
 

Thelegg

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Hi all. so stock valve springs and changed the tension of the TC spring and WOW doesn't it ever fly haha I did try to get a video but I couldn't actually hold my phone and drive due to new found speed 😂 thank you all so much I'll try and get some videos recorded when my nephew's come up and have a go :)

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Thelegg

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Hey, when I was finding my stock valve springs to re-fit I found a flywheel advance key (8° advance) I was just wondering if they provide any gains or do they just move the power band ?

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bob58o

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I’d try advancing the timing and see how it does. Figure you got the TC helping on the bottom end where gear reduction can be as much as 14.7 :1. The advanced timing might help on the big end when the gear reduction is only 4.95 :1.

I’m not sure 8 degrees will be right with a stock cam, but it’ll be fun to test. Timing will probably have to be tuned to your particular set up. Gear ratio, tire size,, TC adjustments may all play a role as to the rpm where you want to make power.
 
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