Messed up new honda engine? Why?

Shadow_storm56

Member

Equipment
Lawn mower
Oct 22, 2020
167
15
18
Canada
So we put a brand new honda engine on our strawberry weeder and for some reason it's all outta wack. Blows black smoke, no power, back fires... the only thing I did was loosen the fuel bowl enough to drain the fuel and tighten it back. The gas went rotten in the time it was sitting in our shop. Acts like it has diesel in it but I put gas in it myself, I think it's gx390. Help plz
 

Matt Ellerbee

Well-known member

Equipment
MX6000
Jun 27, 2019
426
258
63
Canton, Georgia
How long has it set before this problem started? You said the gas was rotten in it. Did you pull carb and clean? Could have a tiny speck of something in the jets. But maybe not, as black smoke is unburnt fuel.
 

Shadow_storm56

Member

Equipment
Lawn mower
Oct 22, 2020
167
15
18
Canada
How long has it set before this problem started? You said the gas was rotten in it. Did you pull carb and clean? Could have a tiny speck of something in the jets. But maybe not, as black smoke is unburnt fuel.
Maybe 2 months, I didn't clean the carb though... very strange
 

NCL4701

Well-known member

Equipment
L4701, WC68 chipper, grapple, BB1572 box scrape, Howes 500, 16kW IMD gen
Apr 27, 2020
474
347
63
Central Piedmont, NC
For a little gas engine such as a Honda GX390 or anything similar, it needs 4 things to run: spark, fuel, air, compression.

It is sort of running so compression is all but eliminated.

Spark: if it’s running fine cold and messing up when it’s hot I’d revisit the electronic ignition module but that’s not what you describe.

Air: I’d take the air cleaner off while the engine is somewhere where the air isn’t incredibly dusty. Start the engine. Watch the choke plate (not the control knob or whatever controls it, the actual plate in the carb throat). If the choke is operating normally and the problem persists it’s in the fuel side of the carb.

If the air and spark are eliminated that leaves fuel. Not much that will cause excessive fuel: choke not releasing (eliminated above); jets misadjusted (makes no sense unless someone messed with it since it last ran right); stuck float (quite possible); generally gummed up carb (not highly likely but possible).

I suggest take off the air cleaner, run it without it long enough for choke to come off to check choke operation and eliminate the air filter, air box, and anything else air related. If no change in symptoms with air cleaner assy removed and choke operating normally sounds like a carb cleaning and inspection of float is in order.
 

Chanceywd

New member

Equipment
Kubota L2501
Mar 26, 2021
14
4
3
central ny
So we put a brand new honda engine on our strawberry weeder and for some reason it's all outta wack. Blows black smoke, no power, back fires... the only thing I did was loosen the fuel bowl enough to drain the fuel and tighten it back. The gas went rotten in the time it was sitting in our shop. Acts like it has diesel in it but I put gas in it myself, I think it's gx390. Help plz
Is it possibly oil from the engine being tipped the wrong way during handling or installation? I did that recently changing a push mower engine and the oil from the crankcase got into the crankcase breather tube making quite a problem getting it to run until it cleaned out.
 
  • Like
Reactions: 1 user

Tughill Tom

Active member

Equipment
B3200
Dec 23, 2013
393
55
28
Turin, NY
You'll need to clean the Carb and fuel system, find non-ethanol gas and high octane and run it like you stole it.
 
  • Like
Reactions: 1 user

Jim L.

Member
Jun 18, 2014
697
23
18
Texas
X3 on ethanol gas being the problem. Carb needs taking off, apart, and good cleaning.

Non-ethanol gas if you can find it. Otherwise put fuel stabilizer in to prevent clogging.
 

JWool

Member

Equipment
B2650HSDC FEL & Front Snow Blower, ZT-Z421, GL11000 Generator
Dec 29, 2013
78
5
8
Northern MI
Agree with get some non ethanal gas, around here its called REC Fuel at the stations that have it.
or some VP 4 stroke or similar from like tractor supply.
VP 4 Stroke Gas.jpg

Small engines are horrible with the ethanal gas the Alcohol seperates and swells rubbers seals.
Once I started using rec gas or VP in all my small engines they start right up after sitting and run great.
 
Last edited:

Matt Ellerbee

Well-known member

Equipment
MX6000
Jun 27, 2019
426
258
63
Canton, Georgia
I run all of my OPE on non ethanol. Mower, weed eater and chainsaws. They start every time. Everyone should. Price is a bit higher, but in small use stuff it’s much cheaper than rebuilds.
 

GreensvilleJay

Well-known member

Equipment
BX23-S
Apr 2, 2019
2,347
451
83
Greensville,Ontario,Canada
You need to clean ENTIRE gas system, tank, new lines, carb,etc. Expect to waste 3-4 hours of your life getting rid of the mess ethanol has made. 'gas' with any ethanol in it has less BTU(hp) for the ounce, absorbs water out of the air and will attackthe fuel system components. 'silly' things like the water it acquires, sinks to the bottom of the tank, so it's FIRST into the carb, and if bad enough engine won't run. You call it quits for the day...next time, it won't even start.....carb gets bunged up due to corrosion.... yeah water reacts to the brass,tin, steel,aluminum in the carb,causing even more grief. Luckily the Chinese carbs are only $20.....
Cure, once totally cleaned out... use NON Ethonal HItest with fuel stabilizer AND when done, shut off tank, run carb 'dry'.
 
  • Like
Reactions: 1 user