420 Duromax No Start Woes

MondaySux

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Hear me out... Duromax 420cc Stage 1 Gov Delete.

Just got finished pulling out the original piston. The reason is that the engine just does not turn on. It is still new, maybe 2 hours on it, but it sat for about a year. Turned it on a few times within the year now, no start...

Did all this (not in this order): I have spark and all. Cleaned flywheel, new ingition coil, adjusted valve lash. It was just about perfect, though. Repositioned air gap on coil to .30. Already had a racing spark plug. Compression test. No leaks. Valves are PERFECT, rods are PERFECT, cam lobes PERFECT!! Failed to start w/ starter fluid and no carb. Redid wiring. Gave up on stock carb. Got it a brand new REAL Mikuni 38mm round slide for it to get rid of that old janky pos stock carb. All that.

I tried everything you can think of. When I took the head off, the cylinder walls looked and felt very bad!! Maybe from water even though it was covered. Engine was seized but I unseized it with pb blaster/mystery oil and thought maybe I ruined the piston rings except that it held compression like a champ, even the intake sucks in so much air it would suck you in like a typhoon.

Anyways I removed the piston (it's just about as great condition as new and rings too. I cleaned the whole thing) and got a new flathead 90mm piston. I honed the cylinder walls with a huge 4-inch hone but only did a comfortable amount of honing to clean out the walls. Now they are smooth but still stained.

The new piston goes in, gapped the rings, and it is so dang hard to turn! I can't turn it without it being a workout, and it makes scraping sounds. I use driver pulley form torque converter and it sounds horrible. Removed piston, all good with no scoring and still all lubed up and no damage to new piston and rings.

I ditched the new piston and used the original. All good. I though "ehh" on higher conpression.

I'm almost getting ready to get rid of this engine and scrap it for a new one though. Cant believe it's brand new and doesn't start. Although the parts I got for it can be used for another engine. I'm getting tired of it. It ran great woth a Stage 1. That's all it ever ran actually? How or why would it all of a sudden be a timing will beat me? Thanks in advanced guys.
 

MondaySux

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Everything is back together with original piston. All torque specced, valve lash set, assembly lube and new oil. Everthing checked.

Had only tried to start on the floor a few times with no carb. No Start. Not even little explosions here or there.

You can hear how well it holds compression from the sound as well.

Will try again tomorrow.
 

Denny

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Too much air is worse than not enough. Put a carb on it and use the choke along with the starting fluid. Also get rid of the overpriced junk racing plug you don’t need and put a stock plug back in it. Just because it says racing on it don’t make it better. Just more expensive and sometimes worse!
 

MondaySux

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I do have 2 brand new stock plugs and never tried those. I'll check the gaps on them to make sure they're in spec. When I say it has a lot of intake air I mean normal and works as it should and is not leaking elsewhere. I have a gopowersports sock over the filter and you can see it pull air when cranking like it always did.

Thanks for the tip. Come to think of it, the autlite racing plugs cant even be gapped to begin with.
 

dana

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If you have spark and the timing is right it should fire with starting fluid and no carb.
 

MondaySux

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If you have spark and the timing is right it should fire with starting fluid and no carb.

I have spark and timing should be correct.

I got rid of the autolite racing plug and used copper plug as suggested. With the carb and starter fluid I attempted to turn on once and it jumped around all crazy and fired up for a second. I think it will work.

Ever since then I have not attempted to fire it up again as I had many other projects
 

MondaySux

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I will report back soon. I need to get a frame for this thing to get everything going!



Only thing I did is change plugs
 
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