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2013 420FPA won't rev

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Buddy brought me his kids 420FPA. Won't rev up.  Starts and idles fine.  If you feather the throttle sometimes it will rev, but usually backfires and dies afterwards.

 

I pulled the fuel pump, and put the new style filter on it.  The old one was full of junk and I thought surely that would be the problem, but after I got it back together not change.

 

Guessing the fuel pump would be the next logical step?   Want to make sure there's not some kind of other issue that would cause the problem.

 

A shot of starter fluid will allow it to briefly rev up before it does, so that kinda tells me it's a fuel supply issue.

 

Anyone have any other possibilities before I order a new fuel pump?  @melatv @toodeep @retro

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Only thing I can think of is a crack on intake sucking in air when u rev it?? Is that possible anywhere?

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Possible. 

 

I replaced the spark plug to eliminate that.

 

Did the jumper to coil red from battery + to make sure it wasn’t one of the 2005 sensors on these 420’s.  No change.

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Hi: Somethings to check

Fuel injector

Air Filter

Ign. timing

Breather cap

Muffler

Compression

 

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Haven't messed with it yet.  Got swamped at work this week so hopefully will look at it this weekend.

 

I'm guessing to check the injector I need to pull it off and see if it's spraying?

 

Does the same thing with the air filter off, but it does need a new one.  It's not dirty, but the foam is coming apart at the seam.

 

Breather cap.....?  Fuel tank vent in the cap?

 

I do need to check the exhaust.  Didn't think about that one.

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even with an exhaust issue ... i would think it would try and rev some... fuel issue would be my thinking (from the description) the backfiring ...  has me thinking. but it just happens when you feather the throttle ? 

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Found a new OEM fuel pump on ebay for a decent price.  Ordered it.  If it works, great.  If it doesn't, I'll take it back off and put it on the shelf for the wife's 420.  Not like new OEM parts are getting any cheaper.

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New fuel pump on. No change.

 

Cloudy, cold, and a 30mph wind blowing so it will have to wait for a nicer day,

 

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Just for kicks, try swapping the regulator. I haven't had any issues with the 420 and regulator issues but you never know. I had a few in the past that was hard starting, wouldn't rev up and those was just bad fuel. Everything about the gas said it was good (smell, no ethanol, gave a poof when lit) but it wasn't good enough to give the explosion needed in the chamber. The older 420 is nice because you can just swap the fuel in the sub fuel tank (pump) to test it.

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Hmmm, maybe I ought to try new fuel first.  It smells right, looks right, but that would be something simple to eliminate before i go down too many other rabbit holes.

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OK, messed with this thing again yesterday.  Hopefully with new info yall can give some guidance on this EFI devil.

 

Drained tank, put in fresh gas.  No change. 

 

Cranked it up, and while spraying starter fluid in spurts into the intake, it would run and rev fine, which tells me it's not a spark/ignition problem.  Has to be fuel delivery, right?

 

Pulled of IACV, and it spins easily and freely when I cycle key on and off. 

 

Pulled off injector.  With injector off of the fuel line, when I cycle the key on gas GUSHES out of the fuel line.  If I put the injector on the line, I get several "squirts" but they don't seem to be very substantial, but then again, this thing shouldn't use THAT much gas, right?. 

 

I'm leaning towards a clogged/ faulty injector, but I don't know how much gas should be shooting out of that thing.  What say ye?

 

 

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now you've checked and it has a good spark, and revs when you give it some starting fluid,  plus you have a supply of gas from the line, I'm thinking (yes like you) the injector. partially plugged. 

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Well I ordered an injector from PSN.  I hate throwing parts at stuff, but at least it was a cheap part ($12 shipped).

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Injector seems to have fixed it.  The one PSN sent was missing the little plastic nipple that holds the electrical plug in place, so they're sending me a replacement, but I installed the one they sent and held the plug in place and the machine now starts and revs like it should, so looks like the injector was clogged and not allowing fuel through.

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