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Old 05-15-2019, 12:41 PM
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Default Predator 420 fouling spark plugs

Ok guys, I recently put a 420 in the go kart. I haven't even driven the thing yet other than just a trip up and down the road to test gearing and such. When I pulled the plug yesterday I noticed the plug was completely black, carbon black. I cleaned it with my rag and put it back in but want to know if I should worry about it or not.

The engine has the governor removed but I have yet to run it beyond 4,000 RPM. There is a custom exhaust and custom air intake from GPS.com. I have not modified the carb jet, although the air intake I purchased from GPS.com did come with a new jet.

Will installing the jet resolve the carbon issue I'm seeing on the spark-plug?
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Old 05-15-2019, 01:21 PM
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fouling spark plug could be oil from worn rings / blowby.

.039-.041" jet should be right where you want it. Call them up and ask what size they drill the jets to.

IIRC you can get a set of micro drill bits for cheap on amazon or ebay, but i forget where the cutoff point is in size before you have to buy another larger set.
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Old 05-15-2019, 04:10 PM
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fouling spark plug could be oil from worn rings / blowby.

.039-.041" jet should be right where you want it. Call them up and ask what size they drill the jets to.

IIRC you can get a set of micro drill bits for cheap on amazon or ebay, but i forget where the cutoff point is in size before you have to buy another larger set.
It's 100% not worn rings. The engine hasn't got 1 hr on it. Is it running to lean? To rich?
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Old 05-15-2019, 04:18 PM
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What about break in?
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Old 05-15-2019, 04:20 PM
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What about break in?
I don't follow what you mean. Are you suggesting that because the engine hasn't been broken in yet, the plugs could be becoming black?
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Old 05-15-2019, 04:22 PM
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I don't follow what you mean. Are you suggesting that because the engine hasn't been broken in yet, the plugs could be becoming black?
You said that it's got less than an hour on it. I believe that there's a break in process.
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Old 05-15-2019, 05:16 PM
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To break an engine in, take it out on a parking lot or similar take it around a couple times, varying the rpm.
Do that for maybe 15 minutes?(ish), then I think you let the engine cool down, then you do it again, again varying the rpms, but on average higher. Then keep increasing average rpm with a few more break in sessions.
I think that's basically what I read in a racing kart handbook.
But IDK, I didn't memorize the break in process.
And that scientific of a process might be angled towards racing engines.
IDK.
Also, was the spark plug dry black or wet black?
Dry black would be carbon, indicating a lean mixture(which would make sense since you've increased airflow, but the jet is still stock), and wet would mean either oil in the combustion chamber, or it's getting flooded with gas.
That's my 2c, don't hate if I'm partially or completely wrong.
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Old 05-15-2019, 05:19 PM
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That’s what I did for my engine, soon we will know if it’s wrong. I sure hope it is okay like that, mine is a 208cc Briggs btw
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Old 05-15-2019, 05:22 PM
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If that is what the handbook said(it sounds like it would work), I can't see why it wouldn't work.
P.S - I noticed you changed your username!
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Old 05-15-2019, 05:30 PM
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There is a break-in process in the owners manual.

https://www.google.com/url?sa=t&sour...tTBxOHRv4g8AFK


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Old 05-15-2019, 05:32 PM
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Well then, I guess that process mostly applies to racing engines. *shrug*
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Old 05-15-2019, 08:21 PM
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I very seriously doubt that the break-in is something to worry about right now.

Quote:
Originally Posted by 67StingrayJ View Post
I haven't even driven the thing yet other than just a trip up and down the road to test gearing and such. When I pulled the plug yesterday I noticed the plug was completely black, carbon black.
There is nowhere near enough run time on it to tell anything. It hasn't been run under the right conditions to do ap lug reading either.

Did you run it with the choke at all?
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Old 05-15-2019, 09:25 PM
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Originally Posted by 65ShelbyClone View Post
I very seriously doubt that the break-in is something to worry about right now.







There is nowhere near enough run time on it to tell anything. It hasn't been run under the right conditions to do ap lug reading either.



Did you run it with the choke at all?
That's my guess too, choke may have still been on albeit maybe not much, but enough to foul it out.
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Old 05-15-2019, 10:12 PM
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Thanks for getting this topic back on track. I don't know how the heck it went into how to break in an engine, my gosh.

The choke is only on for a little bit, till the engine gets warm. Definitely not any longer than a min or so. Like I said, the engine is brand new and I'm sure the choke is working properly. Meaning when it's off it off all the way.

I almost wonder if it's running too rich. The exhaust I have on it is very low resistance, and so is the air intake. Also, when I give it gas (throttle) it almost dies at first. I have to be really careful how I press the gas.

Thoughts?
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Old 05-16-2019, 01:10 AM
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Normally a fouled plug is an indication of running rich. You would maybe have to look at your jet. You have changed a few other things on the engine that might require a different jet. Change the jet out and test. There is no harm in trying, and you aren't going to break anything
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Old 05-16-2019, 07:29 AM
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Well usually a 212 break in process is let it run for 3 hours without appling heavy throttle i let mine sit for a hour let it cool and repeat.
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Old 05-16-2019, 09:59 AM
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Quote:
Originally Posted by 67StingrayJ View Post
The choke is only on for a little bit, till the engine gets warm. Definitely not any longer than a min or so. Like I said, the engine is brand new and I'm sure the choke is working properly. Meaning when it's off it off all the way.

I almost wonder if it's running too rich. The exhaust I have on it is very low resistance, and so is the air intake. Also, when I give it gas (throttle) it almost dies at first. I have to be really careful how I press the gas.

Thoughts?
That's why it doesn't make sense that the plug is sooty. You've done mods that should make it run leaner and it's still on the stock jets, so it should be running lean. If it was rich to begin with, it ought be running better now. It could be that the idle is rich, making the plug black, and the main is lean, causing stumble on transition. It could also be that you haven't run it at high load long enough to burn the soot off.

The significant tip-stumble you describe makes me think it is in fact lean. I'd put the bigger main jet in anyway and see how it responds.
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Old 05-16-2019, 12:36 PM
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Quote:
Originally Posted by 65ShelbyClone View Post
That's why it doesn't make sense that the plug is sooty. You've done mods that should make it run leaner and it's still on the stock jets, so it should be running lean. If it was rich to begin with, it ought be running better now. It could be that the idle is rich, making the plug black, and the main is lean, causing stumble on transition. It could also be that you haven't run it at high load long enough to burn the soot off.

The significant tip-stumble you describe makes me think it is in fact lean. I'd put the bigger main jet in anyway and see how it responds.
Thanks Shelby. If the idle was to lean, would there be anything one could do to bring it more in line with where it should be?

Should the new Jet be larger hole, or smaller hole?

I'll put in the new Jet I have and report back. I'm still working out gearing on another thread but once I have that worked out I'll get the kart into action for sure.
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Old 05-17-2019, 12:30 AM
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Quote:
Originally Posted by 67StingrayJ View Post
Thanks Shelby. If the idle was to lean, would there be anything one could do to bring it more in line with where it should be?

Should the new Jet be larger hole, or smaller hole?
If the idle is lean, you can increase the idle jet size. Drill the jet to a bigger hole. This might allow you to stomp on the gas without it dying.

Before doing that, you can test the mixture. Run with a lil bit of choke or try to restrict the air filter a bit. Put a sock or tape or something around the air filter to restrict it a bit. Does it get better or worse. If it gets better with the choke or an air restriction, you know you are lean and need a larger jet.

Not to cross-thread (pun intended), but how did the gearing work out during the test run?
How was the acceleration? How was the speed?
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