420cc Valve Lash w/ Arc billet flywheel


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Hey guys I’m new to building engines…please go lightly lol

I’ve read through many forums so far about this issue and I can’t find the answer, so I called Arc directly and asked what may be the issue.

I added 50lb valve springs and their billet flywheel. Stage 1 performance package through go power sports. Governor delete and low oil sensor delete.

Before I add my Twister crank and billet rod I wanted to put the engine together and see how it ran. Well, sure and behold. Doesn’t run well lol

I set valve lash after exhaust bump at TDC at .004 on both. Then .004 exhaust and .005 intake. Then I even traded .0015 and .003 but it doesn’t matter what I set at because the kickback is horrible every so often and the pull start is a little more tough to pull. When I called Arc they told me to bring exhaust lash to 0 and intake at .003 to reduce kickback? Does this sound right? Has anyone tried that? Feel like there’s a lot of compression when I tried to pull start the engine. I seated the flywheel nicely with valve grinding compound and am using a stock half moon key parallel to crank like you should?

I also should mention that the engine will turn over on choke like it has to, but to keep it running I need to half choke it with the idle screw turned up. When I take off half choke it stalls out. There is a 118 upgraded jet in the carb. The carb has been completely cleaned. Good ethanol free gas and use a fuel filter as well.

What the hell is going on!? Lol


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"Loose Cannon Creations"
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Jacksonville, Florida
Firstly, ARC was just telling you an alternative to norms you could try. Most folks believe in a valve lash of .003" on both valves.
Secondly, not confident your "exhaust bump" (compression release) got the job done, confuses lots of people. Here's a couple of videos done by pros I trust as opposed to kids in their mom's basements who have good intentions but the wrong skills...................
How to Install 18lb Valve Springs & Adjust Valves GX200 / Predator 212 Hemi & Non Hemi Go Kart - YouTube
Predator 212 Hemi Valve Adjustment How-To - YouTube
Thirdly, here's a thread I did way back that's helped some people with the dreaded and painful "kickback" issue....................
(10) How much pullrope are you using????? | DIY Go Karts
Fourthly, your half-moon (woodruff key) stock timing key matched with the larger jet could be giving you run troubles. I'd definitely advise a timing advance key to get all that fuel burnt. Here's a video that explains it real simply.....................
Flywheel Removal and Advanced Timing Key Install on a Predator 212cc - YouTube


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What you call the exhaust bump is a compression release designed to help prevent kickback. It is built into the camshaft. By setting the exhaust valve lash at .000 clearance you will get the most benefit from the compression release .
Once you get your engine running correctly don't rev it too high with the stock connecting rod. It is probably the weakest part of the stock predator engine.
If you already have the ARC rod I would put it in now. All your other go fast parts might get you into trouble.


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Engine experts telling you to set for 0 lash? Well that's different.
The whole point of setting lash is to adjust for the gap being reduced as the parts heat up.
Engine designers/engineers figure this out and spec the gap to reduce to 0 when warmed up, not when cold.
0 lash would cause the valve to be held open after warmup.

You don't normally compensate for high compression issues or heavy valve springs by keeping valves open on warm, running engines.

Changing ignition timing plays a roll as well.