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Engine dies trying to throttle back up

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by Kevin
(Rhode Island)

I have a DeWalt compressor I got for free, needed a new carb, governor adjustment and regulator.

It fires right up now, as long as the unloader valve is open, or disengaged so that it can start at idle. I let it warm up for a bit then slowly increase the throttle manually, then engage the unloaded valve. Then it runs fine and builds pressure.

DeWalt 5.5 HP with Honda engine
DeWalt 5.5 HP with Honda engine Photo: aircompressorsdirect.com

It gets to 120psi and then kicks down to an idle. If I use enough air it attempts to throttle up but just dies. It seems like its not getting enough fuel, but its a new, although cheap aftermarket carb. And these carbs don’t appear to have much in the way of adjustment. Only fresh gas.

It won’t restart under load, I have to disengage the unloader valve, start it at idle with choke, and then slowly throttle it up again. Its a Honda GX160, 5hp I believe.

Pretty much the most common engine Honda makes.


No start/restart
by: Doug in s.d.ca.

Kevin –

Is there a part/model number on the thing?

Is the throttle control a mechanical thing from the unloader or an air cylinder? (Or?)

When you get it to pump fiddling with the carb, *once it gets to pumping*, does it keep on without your help, and then go idle at cut-out?


by: Kevin

The compressor is a D55270.

The throttle is controlled by an air cylinder plumbed into the unloaded valve. Its either on or off, idle or full throttle, and it switches quickly, nothing gradual about it.

Yes, once its running and building pressure it runs great, builds to 120psi quickly then to idle. As soon as I use enough air for the unloaded to kick in, it goes wide open throttle and dies.

I talked to a small engine guy, he’s 90% sure it has to do with the cheap ($10) aftermarket carb I bought. I have a $75 genuine OEM Honda carb on the way, hoping that does the trick.


Dies at load time
by: Doug in s.d.ca.

Yeah, sounds like the carb alright, and you could probably mess with it and get to work, but let’s see what the new carb does, since you’ve already ordered it.

Please keep us posted.


I fixed the same problem – engine dies on throttle up
by: Jay

My compressor starts (No air, pilot valve open, in start position) builds air on its own (up to 140psi, claims 135psi max?) If I release the air out of the tank slowly, it revs up and rebuilds. If I drain air quickly it goes to rev up and shuts down. Carb is clean (did not check fuel line) any other tips? 212CC predator (harbor freight)

Fixed.. My issue was the spark plug. installed new and it cranked, idled, revved back up when psi got low… at least 3 times I tested it


by: Kevin

Great news that you got yours fixed!

I have the new genuine Honda carb, but haven’t had a chance to install it. I did troubleshoot with another carb off another Honda.

Will update when I find out more.


Another update
by: Kevin

Put new carb on, new spark plug, changed out low and nasty compressor oil and refilled with DeWalt Synthetic oil. Still running the same. Checked valves for adjustment, they were fine. Gonna do a compression check today.

Maybe something to do with the governor? gx160 engine that was having trouble staying running, this was on a wood stacker conveyor. The borrowed carb didn’t change how my compressor ran, so now I thinking it might be something else. Def will try a new spark plug. And have new compressor oil so I will drain and refill that.


Air cylinder on D55270
by: Doug in s.d.ca.

Kevin – is that air cylinder single or double acting? If single, is the spring working?

I’m also wondering if there’s a valve in the line(s) – maybe a restrictor to slow the cylinder down?


It’s fixed!
by: Kevin

Doug, not sure about the cylinder, but good news, its fixed!

Between the new carb, compressor oil, spark plug, swapping in a different coil and a slight idle adjustment, its running just about 100% now. As long as I let it warm up for a couple minutes, it will cycle from full throttle to idle and back again without issue 95% of the time, every once in a while it stumbles kicking up to full throttle, but I can live with that. I mostly use this for filling tires and an air nozzle for cleaning off car parts.

Haven’t tried it with a good impact gun yet, but I think it’ll be up for the task. Because I got it for free, and only invested about $200 into it, it’s a great stop gap till I can save up for my full electric shop compressor. Thinking about getting a Quincy.


by: Doug in s.d.ca.


So the last thing was a different spark coil?

So there’s no free lunch, but for 200 you got a good lunch…

Thanks for keeping us posted.


by: Kevin

Yah, the new used coil, bumping the isle up and just making sure it’s warmed up. I’m sure it Helps that lately it’s been closer to 40 degrees here than 20.

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