Help with carb/jet/tuning on 18hp Duromax 440cc(stage 1)

miniblazinbmx

miniblazinbmx

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New motor, new build, 18hp Duromax 440cc
stainless header
stage 1 air filter pod
stock governor
stock EPA carb (non-adjustable)

choke on-starts/idles and puffs a little black smoke at times..
half choke-runs better/idles better, revs out but backfires..
choke off-idles, and sputters and dies with any throttle..

idle screw doesn't seem to change much. no vacuum leaks..
Is it running rich? and if so how is possible to run richer after adding better air/exhaust? Would it not be the other way around i.e. running lean??

going deeper, Ive got a 42 and 43 main jet here and my stock is considerably larger, maybe closer to a 45 or 46 but it isn't labeled. the e-tube is massive, I've not gotten the pilot screw out to check yet..

Ive got a vegas carts 24mm bored here that needs jetting, and also with closed off adjusting screws.

and Ive got a 34mm slide carb that wont work with the stock governor(probably a stage 2-3 upgrade part).

So, I need to know some ideas where to start as far as jetting and making adjustments, even if it means I have to buy a $20 ebay adjustable carb, or modfiy this vegas one to start. (The company that makes that carb is actually ARC racing just fyi).

The kart runs but having a carb that isn't adjustable while making upgrades is maddening.. I appreciate any and all reasonable advice and suggestions.
 
madprofessor

madprofessor

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Not sure what you mean by "fouled plugs", but the sooty part and black smoke part make sense when running rich. A plug will get jet black all over with soot, but only the kind of soot that wipes off with a single swipe of a dry rag. The black smoke was a soot wannabe, but it fell out of the exhaust before it could stick.
Not betting the farm on it, but I'd bet the next planted row of skunky kush that you're doing some putt-putting around with that thing instead of flooring it most of the time. How about that plug, is it the "upgraded" E-whatever plug with a cross cut into the end of it, or a standard plug with an electrode that's OEM to that engine? My performance guy says always run stock plugs if you're going to be doing any putt-putting around, and change it out for a racing plug only when you're at the track. Otherwise your plug can foul out in just minutes.
And that king of fouling usually means hard chunks of carbon trying to bridge the spark gap, and draining off the coil power to ground, followed shortly by getting all oily.
 
miniblazinbmx

miniblazinbmx

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madprofessor said:
Not sure what you mean by "fouled plugs", but the sooty part and black smoke part make sense when running rich. A plug will get jet black all over with soot, but only the kind of soot that wipes off with a single swipe of a dry rag. The black smoke was a soot wannabe, but it fell out of the exhaust before it could stick.
Not betting the farm on it, but I'd bet the next planted row of skunky kush that you're doing some putt-putting around with that thing instead of flooring it most of the time. How about that plug, is it the "upgraded" E-whatever plug with a cross cut into the end of it, or a standard plug with an electrode that's OEM to that engine? My performance guy says always run stock plugs if you're going to be doing any putt-putting around, and change it out for a racing plug only when you're at the track. Otherwise your plug can foul out in just minutes.
And that king of fouling usually means hard chunks of carbon trying to bridge the spark gap, and draining off the coil power to ground, followed shortly by getting all oily.
Click to expand...
The "fouling" Im speaking of is in fact more like a smoky soot that wipes off rather easily. I can hit it with a wire brush and clean it up.. but it does the same thing to the exhuast.

I tried the Vegas Carts 24mm stock bored today and played with jets, I couldn't even keep it running.
Put the stock back on because at least with that one it will idle.

Back to square one..

Could someone please explain how and why its seemingly running rich instead of lean with added airflow? I thought these motors came running lean.. not rich.. what am I missing?

The plug is stock, which I have no idea what that means for this. Someone suggested a hotter plug.. but I still tend to lean on a jetting issue and I too figured too much fuel.. is it possible the pilot is too large and main too small? or vice versa? Everything is stock minus the air filter and exhaust.

I have symptoms of both it running lean and rich at the same time.
 
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madprofessor

madprofessor

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Apparently there's no knowing what the OEM jet was when that engine was brand new, regardless of what was in it when you got it, without a jet sizing device. Pretend you don't know and just stick different jets in it for comparison, apples to apples. If it has a .042 in it now, try a .038 and a .046 or similar, everything else staying completely unchanged, see what it does.
About the extra airflow/running rich mystery.................The motor inhales fuel based on drawing a vacuum on the carb jet. The motor has a set amount of cylinder space to pull a vacuum on when the piston travels from top to bottom on the intake stroke, creating that vacuum. The airflow resistance of an undersized intake increases the vacuum the piston's able to create, and that vacuum lessens with a greater airflow. Hence a greater airflow reduces the amount of vacuum being drawn on the carb jet, reducing the amount of fuel being sucked through it. In theory then, a given amount of fuel sucked in with a stock jet would actually decrease with the decrease in vacuum of a greater airflow, requiring a slight carb jet size increase just to get the same amount of fuel as before.
If the theory confuses you, don't feel alone, it confuses me too. Now get this part..............Too much air and not enough fuel is not only running too lean, it's also a crappy mix for combustion, as is running too rich. You can get incomplete combustion either way, resulting in a sooty residue with maybe some black smoke too. So.................remember that part about trying various jets?..................
 
miniblazinbmx

miniblazinbmx

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Quick update for the weekend.. I plan to drop more detailed info later on this motor.

I've drilled up a total of about 6 sizes today from whatever stock would have been, and it is just now starting to yawn and wake up a bit.
I was able to get some solid test runs in without it bogging to stalling out finally. My main jet was considerably smaller than the e tube inlet and now it is about the same. It still chokes a little under hard throttle, and I'm currently fighting with a driven pulley issue, but tuning wise it seemed to be much happier today after some increasing jumps in the main jet size. I know there are others looking for this same answer and so far g a making progress.. I plan to do a bit more dialing in of the jets this week and will report back with what I end up with so hopefully it can help some others dealing with the same problems.

my plug looks much better.. and the engine cold starts with half choke instead of full now..

stock jet is fine for a generator motor idling at 3600.. but to give it any amount of waking up it def needs a bigger jet. Its like they run so lean its barely enough to keep them running at all.

Also there isn't enough road here in my neighborhood to see what this thing will do.. it pulls pretty damn hard
 
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