“Kop Kart”(police kart)-18Hp Yerf Dog Resurrection; Father/Son summer build

miniblazinbmx

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Hey everyone been a few weeks or so since Ive been on here, I'll get some pics up very soon.

I need some help from you carb gurus right now.. as I cannot seem to find an easy way to tune this thing to stay running..

Before I go further let me be humble and admit I'm not very good when it comes to these small engine carbs. My patience and experience are very limited when it comes to tuning.

Ive got the DuroMax 18hp 440cc in, stage 1 air filter, adapter, and a stainless header. Its the stock carb and the adjustment screws are capped or plugged, I tried removing them but had no luck. All I have is a plastic idle adjustment screw which seems to pretty much be set and regulated by the governor anyway.

The kart will only stay running anywhere near half decent in half choke.
With the choke off, trying to revv it, it stalls and dies.
once it warms up or you give it enough throttle to get into the powerband it tries to rev out finally. however its tossing blue flames 6", which is pretty rad.. but I dont think its supposed to do that. Its also fouling the plug.

Parts sites offer jets for this GX390 clone, so I got a 41 and 42 jet from OMB.
When I pulled the stock jet it appears to be quite bigger than the "upgrade" versions.
I tried the 42 and it poured gas out of the bowl in into the intake. it was definitely smaller than the stock......

In my mind Im assuming more unrestricted air flow means its now starving for fuel, however its also fouling my plug and sooting the inside of my beautiful stainless exhaust header.

Ive searched and not found much info on these motors yet, especially upgrades. Ive seen the RBG videos on YT and watched a hundred carb tuning videos.
My carb isnt adjustable and I cant tell whats actually happening here..
an aftermarket wont work with the stock governor(not ready for stage 2 yet)
and I have no idea how or where to start with this but Ive been chasing my tail for weeks over this. II can get main jets in every size but I dont know about the pilot.

Our aftermarket CVT driver is also sticking and not disengaging the belt when releasing throttle. I may have to open it up and modify, but for now the main issue is getting it to run with the choke off.

I also looked at the vegas carts 24mm stock bored, but if you get that they dont come with jets so Id still be at square one here. Other sites such as ARC that sell the same carb want your internal specs.. which I also dont have info on with this engine.

..Out of time and patience.. any help is appreciated.
 

madprofessor

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No carb expert myself, but there's certain basics that I've learned regardless.................
For one thing, black soot on a plug is usually indicative of running rich. It shows up the most after running low to medium rpm's, not too sooty at high rpm's, but you had to run low to medium to get there.
Another thing is that any flames at all from an exhaust is burning fuel, and unless you have an afterburner injecting fuel into a hot exhaust, it's a product of incomplete combustion in the engine. Again, running rich. Really rich.
One more thing, no jet can force fuel to pour out of a carb bowl. It's the suction of the intake stroke that draws the fuel from the bowl. Even a fuel pump won't do it, the carb float closes off the incoming fuel when the bowl level rises by plugging the needle valve into the seat.
So.................no idea beyond a stuck open needle valve how fuel can pour out of a bowl into an engine................... Running rich means too much fuel, not enough air, or both at the same time.................. Idle screws only raise/lower idle rpm's, your governor doesn't affect idle rpm in any way, it only forces the throttle back from exceeding governor's rated rpm's.................... If you change a stock main jet size to larger/smaller, you need to change the low jet size accordingly. Ex.: My 212's main/low sizes were .029/.016 stock sizes, then got hotrodded up to .036/.022 sizes....................About that choke, what's a choke? Just an air valve (butterfly or other) that strangles off the air supply to the carb inlet. Since that seems to be the opposite of you apparently running rich, I'll wild guess the anomaly of that where it only runs on partial choke as being the fault of the mismatched low jet.
Almost forgot................Every book in the Bible comes before you get to Armageddon.
 

miniblazinbmx

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No carb expert myself, but there's certain basics that I've learned regardless.................
For one thing, black soot on a plug is usually indicative of running rich. It shows up the most after running low to medium rpm's, not too sooty at high rpm's, but you had to run low to medium to get there.
Another thing is that any flames at all from an exhaust is burning fuel, and unless you have an afterburner injecting fuel into a hot exhaust, it's a product of incomplete combustion in the engine. Again, running rich. Really rich.
One more thing, no jet can force fuel to pour out of a carb bowl. It's the suction of the intake stroke that draws the fuel from the bowl. Even a fuel pump won't do it, the carb float closes off the incoming fuel when the bowl level rises by plugging the needle valve into the seat.
So.................no idea beyond a stuck open needle valve how fuel can pour out of a bowl into an engine................... Running rich means too much fuel, not enough air, or both at the same time.................. Idle screws only raise/lower idle rpm's, your governor doesn't affect idle rpm in any way, it only forces the throttle back from exceeding governor's rated rpm's.................... If you change a stock main jet size to larger/smaller, you need to change the low jet size accordingly. Ex.: My 212's main/low sizes were .029/.016 stock sizes, then got hotrodded up to .036/.022 sizes....................About that choke, what's a choke? Just an air valve (butterfly or other) that strangles off the air supply to the carb inlet. Since that seems to be the opposite of you apparently running rich, I'll wild guess the anomaly of that where it only runs on partial choke as being the fault of the mismatched low jet.
Almost forgot................Every book in the Bible comes before you get to Armageddon.
All valid points and I agree.. not sure where the excess fuel came from honestly.. this kart has been doing weird **** every time I run it and drive it.

I would guess running rich too based on some symptoms, however it does appear to be starving when running I cant post videos here for some reason or i would show it.

how would aftermarket air and exhaust affect a stock carb, and are they set to run rich or lean or ideal from factory before they seal up screw holes like morons?

Oddly enough I do have reason to believe my stock jet had worked loose causing a baseline miscalculation in my efforts to tune.

flames, soot, and fouling all point to rich mix to me. but hoe does that make sense with more air flow? would it not lean out with unrestricted air??
when idling I can switch the choke off but as soon as I give it gas it falls on its face.

Anyone had any luck removing the caps from the screws? the are countersunk and also sealed good with red loctite. IF I remember thats a minimum of 500 degrees to bust it loose if you even can access it.

Lastly, is there anywhere to buy pilot jets for these? I dont mind trying to open them up myself but I dont know what im up against here as far as rich or lean.. and what jet is doing what at the moment.
 

madprofessor

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I don't have any experience with the Duromax engines, only know the universal standard stuff.
There's more than 1 rating of "red" Loctite threadlocker, you need to go by the number. I use red #271 Loctite for permanent locking.
 

miniblazinbmx

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Well, last few weeks have been fun..

It's been a battle with a sticking and low engaging clutch, a bent driven pulley causing some jerking and bad starts, stalling, running lean or too rich in the carb, our belt was a bit too short.. our brake band gave out and got replaced with a manual disc setup for now. I had to rebuild the tensioner setup again.. our light bar quit working before we even got it wired up.. small victories and defeats as always but making our way along..
 

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miniblazinbmx

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And more..
 

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Bansil

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Miniblazinbmx. :cry:....

Sorry to inform you...that....that...ugh.....it's time to turbo LS swap, with a transaxle.....you got to make the leap.....I'm sorry brother 😞☹️😢

Lol 😆

Definitely not dirty, oily and greasy.....I...ugh...is it an Operator issues :unsure:


:p I kidd, I kidd.....

Friendly PM bump....;)
 

Functional Artist

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Some times ya gotta pretend your a US Marine
...adapt
...overcome
...&/or figure it the :censored: out

Stick with it, your makin' great progress (way more than the set backs) :cheers2:
...& havin fun
...& figurin'
...& havin more fun (didn't I already say that?) :unsure: I'll check :thumbsup:(nope, I said more fun, that's different) ;)
 

miniblazinbmx

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So after disassembling the driver again, I decided to install half the upgrade kit(red springs only) to see if it helped our creeping issue. Surprisingly it did both, and helped a lot with the jerky starts from a standstill or in hard acceleration. We are still fighting with a bent driven pulley but the new one showed up today, so fingers crossed all the driveline issues are handled after this weekend.
Our kart was engaging at low rpms and idling a bit high until we messed with jetting and spring tension on the governor lever. It is running better each time we take it out. Still have a few Allen screws backing out even with blue loctite so may try a dab of red and see if it helps.
These springs helped a lot and I think maybe the weights too might have been too much for ours, but definitely doesn’t creep or take off when starting anymore so thankful for that.
 

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miniblazinbmx

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I’ve also added a tow hook recently off an old Nissan or Honda trunk floor..

And decided to go ahead and tackle the rear removable engine cage I had been daydreaming about. There is no real purpose to it aside from aesthetics and something to mount our plate onto.. but i designed it to come off easily and I can still access the drivetrain without taking it off to make quick adjustments. Added some stainless hardware, an 80grit polish, and some matte clear to finish it off more like a raw metal rather than painting to match. The other sections were welded into the chassis so those got painted. This one didn’t. I’m kinda digging it.. 😎
 

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miniblazinbmx

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Now back onto playing with electrical and finish designing and mount some fake taillights(real lights, but only running lights). Although I’m on the fence about using a black rubber seal
Or a chrome bezel to match the other hardware.. thoughts?
 

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miniblazinbmx

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Um...that's not one of the available choices :huh:
...black or chrome?
It's gonna end up in the black.

I found some thick 1" tubing I want to fab up some rat rod inspired tube style mounts, and probably weld those directly to frame. I have a diff style LED in blue that actually press fits into the tube perfectly, so i got some red ones coming this week and excited to try the new light setup. Pics soon..

New driven pulley tonight and test runs..
 

miniblazinbmx

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It costs me a couple of hours this evening but I managed to rip apart half my kart as needed, thanks to the overengineered labyrinth of self-fabricated parts, but I got everything on and adjusted with minor setbacks and headaches. After some measuring before the install I did actually confirm my other pulley was out of round and causing issues too. With the clutch gone through and upgraded last week and a smooth rolling driven pulley this week, taking off is ALMOST a dream. We have.. what I can only imagine is chain backlash under some hard throttles.. so this week ill hook up the gopro and rip it on the block some more and try to see the playback footage for what's actually happening. All in all it drives and handles very well for a kids yard cart with a demon in a cage strapped to it.. things are progressively getting better, and as expected its constant G forces! I am working on some more electrical mapping and taillight pod fabrication currently..but kids school stuff tomorrow, and this weekend I'll let him install roll cage padding:thumbsup:
 

miniblazinbmx

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This is pretty much what I had in mind for a electrical mounting plate idea. Simple and clean. Easily tucked halfway underneath the seat but also with fuses and battery easily accessible. Nothing a Hobart 140, a few minutes after dinner, and some machine screws couldn’t handle.

In fabrication I know you’re supposed to remove the zinc or iridite coating. But this is go karts and apparently we make it up as we go so..

turn the heat up a little and let her rip.
Add a little extra unwanted heat for the custom oil can effect. 😂

it’s getting padding between the frame and plate to help absorb shock on semi-sensitive circuits. And of course everything is waterproof.
 

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miniblazinbmx

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But red, instead of blue..


and here’a a couple sneak peeks of this ****show I’ve been obsessed with for the past few months.
We’re redoing the front suspension this fall and still need to attach lights, wiring, and padding. It also needs some upholstery work on the seat but.. it’s a project..
 

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