440cc duromax won’t start

[Rat]

Exactly! A lot of the time though a sheared key leads to kickback or what at first glance would seem like a failing compression release

The kickback depends on how far the flywheel decided to drift.

The shaft does turn when I try to start it.

Ill pull fly wheel tomorrow and check. How would I fix the timing after that?

IF it turns out to be a sheared key, fixing it is going to depend on the level of damage done to the keyway of the crank and/or flywheel if any.

Typically you can just knock down any ridge along the shaft keyway edge with a file, stick a new key in it and reassemble as you would after any other flywheel removal.

 

[Rat]

I don’t know if it has compression. I have a compression kit some where can’t find it. Going to store Friday for one.

no pop at all. that’s why I thought it wasn’t getting spark.

It’s getting fuel and air

Old school comp test: pull the sparky, put your thumb over the hole, pull the cord.

If you can seal it enough to feel it suck your thumb as the piston drops, and can't hold the air pressure in as the piston comes back up... you have plenty enough compression to start and run.

 

[ReSydro]

When I started it a month ago it stayed on for 5 min shut of and when I went to start it back up it backfired and shut off and here we are now.

 

[ReSydro]

I’ll check all this tomorrow asap. As long as I can find the problem I can fix it with a little knowledge. I’ll try the thumb compression in the morning

 

[Rat]

When I started it a month ago it stayed on for 5 min shut of and when I went to start it back up it backfired and shut off and here we are now.

That sounds almost like it flooded.

Something else that might be worth a look at is the in tank filter, and some have a small screen in the petcock bowl on the carb.

This is one of those things that has got to be so simple and stupid to be so easily overlooked.

Try starting it with the killswitch unplugged, they can occasionally screw up too

 

[Thepartsguy]

When I started it a month ago it stayed on for 5 min shut of and when I went to start it back up it backfired and shut off and here we are now.

Backfire might be the tell! I didn’t lap the 8hp flywheel when I swapped it It ran less then a minute backfired and shut off.

I tried to restart it and it and about broke my hand. Sounds like rat is probably right on the money with the sheared key.

 

[ReSydro]

Ok I actually checked compression it’s at 25 psi.

 

[ReSydro]

What would be the best after market carb for the Duromax 440cc?

 

[ReSydro]

Didn’t have time to pull fly wheel yet. Will for sure tomorrow

 

[Whitetrashrocker]

How did you check compression? 25 seems awful low.

 

[ReSydro]

Compression tester. What should it be at?

 

[Rat]

Ok I actually checked compression it’s at 25 psi.

Um Yikes! Anything under 90psi is bad.

problem being you that can't get it spinning fast enough pulling the cord to get the compression relief on the cam to get away from the exhaust lifter.

Iirc the optimum for freshly seated new rings is in the range of 150psi

 

[Rat]

The irony in this is I am currently in possession of a kart with the same exact issue trying to figure it out. It has a 301 Hemi Predator on it which only starts with ether, and only runs (like trash) with 1/4 choke, but no ability to idle.

Lash is good
Plug seems good
Airgap needed reset, 0.30
Charging coils needed removed, their unused output wires were rubbing the flywheel.

Obviously this is lean behavior, but the plug and exhaust is pitch black with soot which indicates the opposite and this is also a new issue which is why it's in my garage

 

[Thepartsguy]

The irony in this is I am currently in possession of a kart with the same exact issue trying to figure it out. It has a 301 Hemi Predator on it which only starts with ether, and only runs (like trash) with 1/4 choke, but no ability to idle.

Lash is good
Plug seems good
Airgap needed reset, 0.30
Charging coils needed removed, their unused output wires were rubbing the flywheel.

Obviously this is lean behavior, but the plug and exhaust is pitch black with soot which indicates the opposite and this is also a new issue which is why it's in my garage

Just serviced a fourwheeler doing the same thing today. Start it on ether and turn the choke mostly on. Then it would lurch and jump forward then shut off.

It took 10 minutes of BS’ing with him and I got the carb off. A bunch of junk in the passage between the needle and seat and fuel inlet.

Some compressed air another 10 minutes to re-assemble.. Easy $50

The lung test with no needle in the seat it was like they didn’t drill the seat big enough.. only a very small amount of air going through the seat. (Until) the dirt blew out and i could blow air through it enough to KNOW fuel would flow through fine.

 

[ReSydro]

S

Um Yikes! Anything under 90psi is bad.

problem being you that can't get it spinning fast enough pulling the cord to get the compression relief on the cam to get away from the exhaust lifter.

Iirc the optimum for freshly seated new rings is in the range of 150psi

so it is a compression issue???

 

[Rat]

so it is a compression issue???

not necessarily, you just need a way to spin the engine fast enough to know for sure the compression relief is out of the way and not distorting the results

 

[Rat]

Just serviced a fourwheeler doing the same thing today. Start it on ether and turn the choke mostly on. Then it would lurch and jump forward then shut off.

It took 10 minutes of BS’ing with him and I got the carb off. A bunch of junk in the passage between the needle and seat and fuel inlet.

Some compressed air another 10 minutes to re-assemble.. Easy $50

The lung test with no needle in the seat it was like they didn’t drill the seat big enough.. only a very small amount of air going through the seat. (Until) the dirt blew out and i could blow air through it enough to KNOW fuel would flow through fine.

Yeah after I posted I pulled the bowl plug with the fuel off to empty it, and cut the fuel back on, flow is fine there too.
I'm suspecting a situation the pilot is a bit small but the Main is too big... which shouldn't be a major issue because it was running great before it decided it was done.

It was passed to me to look at because it did this before and was fine again after a week sitting, but it was noted it had significantly less power.

I do know there's A key issue on the axle, drive gear is 90° off key, which is easily the power loss but the not running bit can't be related.

I've ruled out all major mechanical so the only thing to do is poke at the carb more, and maybe tell dude to replace it... has a mixture circuit that can't be adjusted anyway

 

[ReSydro]

Might as well buy a new engine. 500cc Duromax. I don’t think I can adjust my mixture on the carb either. Goin to put all new gaskets tomorrow and a maikuni carb. If nothin happens. It’s trash.

 

[ReSydro]

Thanks for all the help guys. I appreciate it. Be safe

 

[Rat]

Might as well buy a new engine. 500cc Duromax. I don’t think I can adjust my mixture on the carb either.

theres a notch in the carb collar against the isolation plate that will have a brass screw... if it's "tamper proofed" then it's been set in there and intentionally made to shear off and you'll just see a brass nub instead of a screw head.

Goin to put all new gaskets tomorrow and a maikuni carb. If nothin happens. It’s trash.

99.9 % of the time when it's a carb related issue in a carb with a fixed mixture adjustment, it's best replaced with an aftermarket OE style replacement that has full adjustability... or any better carb that you can tune properly is good too.
The only "extra" carbs I have laying around will bee too big (Genuine Keihin PWK-36) or too small (PZ19) and even if the PWK was a good size there diagnostic time and labor, the carb cost, more time and labor to tune it and dial it in to the engine and the sets of jets to do so... dude would be into it for more than the engine is worth new and I don’t charge as much as I could or probably should.

The oversight issue with the tamper proofing mixture screws is that you can't adequately clean that circuit... so then once it's partially plugged you end up with an issue that cannot be fixed.