# Why Would a Carb Surge and Then not Surge and then Surge Again?



## orangputeh (Nov 24, 2016)

Had a problem that I have never run across before.

Had a HS828 that would not start. Good spark. Cleaned this carb out in May and found some rust at bottom of bowl so took off carb and cleaned it.

First time using it since May and it started and ran until we shut off engine and it would not restart. So cleaned it out again and it started right up. It runs ran at full throttle and idled down fine. Ran it for about 15 minutes and went from full throttle back to idle and it RAN FINE.

Here's the problem. Restarted it and it starts easily. Runs fine at full throttle but surges at idle. Sometimes it surges or hunts and sometimes It doesn't. I have never had a carb do this where sometimes it idle fine and sometimes it goes back to hunting.

Of course I suspected the idle circuit. Took out the pilot jet and cleaned it. sprayed carb spray into the hole but could not see if spray was coming out of the tiny holes near inside the carb. I suspect my problem may lay here.

It runs fine at full throttle. starts right up. sometimes it idles fine and sometimes it hunts. Could it be something else? I'm thinking maybe changing the gasket and the front plate next. maybe I have a leak in those areas. 

I have worked on at least 100 carbs in the last couple years and have never seen this problem before.

Stumped.


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## RedOctobyr (Mar 2, 2014)

As was mentioned in another thread that I saw today, the governor might play a part. When I see an engine surging, I figure it's running lean. But in playing with the governor on my Tecumseh, I found that if I installed a linkage into a different hole in the arm, for instance, I could produce surging, with a carb that's running totally fine. 

Are the governor parts are free, and moving easily? You could try a bit of oil on the pivots, if something seemed a bit sticky. 

Does adding partial choke help smooth it out? That might at least help simulate opening up a restriction in the carb.


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## tdipaul (Jul 11, 2015)

.
fuel quality?

drain all the fuel into a clear bottle and see what settles to the bottom!



.


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## JLawrence08648 (Jan 15, 2017)

Water in the gas? This will cause your symptoms. Water will sink to the bottom of the carb, and will sink to the bottom of a clear soda bottle. It's always a process of elimination, eliminate this.


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## JayzAuto1 (Jul 25, 2016)

I'm gonna agree with R/O & TDI.... When I get a stumper like that, I start with the basics from the beginning. 

1: Drain/Flush fuel supply. I also have a separate fuel tank, with a line on it, as an aux fuel supply. (Just to be clear, it's 
mounted to the work bench, with a long hose that I can just slip on the carb for quick testing. I use a Tecumseh Tank)
2: Check and adjust governor settings.
3: If it's still acting up, add choke when the problem is present. If it clears up, then you've nailed a fuel problem definitively.

Since your Honda exclusive, it should be evident within a few minutes. 
And I'm sure you have a spare Honda fuel tank (or ANY fuel tank, as long as it's known good/clean), to also use an an auxiliary fuel supply source. 

No sense chasing a fuel issue unless you KNOW it's a fuel issue......ie. valve adjustment, sticky rings,

let us know what you find,

GLuck, Jay


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## JayzAuto1 (Jul 25, 2016)

Forgot to add, once or twice, I've found a damaged/swollen rubber disc in the fuel shut-off valve on a Honda. Can't remember the exact circumstances, maybe hard/no-start?? Maybe high idle fuel starve?? IDK.... but it kicked me around enough to make sure I don't forget it's there......

GLuck, J


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## tadawson (Jan 3, 2018)

Had that happen on a mower. Finally ended up replacing the pilot jet outright, since apparently years of fuel had affected the plastic and it shrunk and went lean. New pilot jet (same part no) and 5+ years of no issues, and no other changes.


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## orangputeh (Nov 24, 2016)

tadawson said:


> Had that happen on a mower. Finally ended up replacing the pilot jet outright, since apparently years of fuel had affected the plastic and it shrunk and went lean. New pilot jet (same part no) and 5+ years of no issues, and no other changes.


from these posts I was thinking maybe water so am gonna drain all gas.

and drill out pilot jet .

if that don't work the owner has okayed a new OEM Honda carb install.


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## tadawson (Jan 3, 2018)

Pilot jet replacement is easy . . . I tried to drill mine, but the plastic got furry and that didn't work out, and I didn't just keep going bigger . . . probably could have, but didn't feel the desire since the part was over the counter and done . . .


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## JLawrence08648 (Jan 15, 2017)

A few days ago I was finishing a customer's snowblower, Tecumseh, that I had cleaned the carb in my ultrasonic cleaner, removed the Welch plug, used a welder's tip cleaner, non adjustable carb, it was surging but it would run smooth for seconds, then surge, then run smooth, repeating. I drained the gas from the carb and the tank in to a clear 2l soda bottle. The gas came out cloudy then settled leaving water in the bottom. I am very careful of my gas container, emptying it completely before filling, even draining the remainder in to a soda bottle to check for water. Before I work on any piece of equipment, I always drain the gas checking for color, clarity, and water. After refilling the snowblower from a second gas container that I first filled a 2l soda bottle to check for water, there was none, the snowblower ran perfect, no surging. It was the gas. Where did the water come from? I don't have a garage or shed so all my equipment is tarped, and tarps after awhile leak. But then how did that much water get into the gas tank through the little vent hole?


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## gregg (Nov 23, 2012)

Condensation from temperature fluctuations.


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## paulm12 (May 22, 2015)

gregg said:


> Condensation from temperature fluctuations.


Yes, condensation in both the OPE tank and your portable gas can. Lately I have been paying alot of attention to the gas can that others use to refill their equipment. Even when they fill with fresh gas, I have found quite a bit of water, and also some dirt particles inside. I always refill their equipment from my tank, and I fully clean my cans every year or 2. I have even taken the gas can from my neighbors, emptied it out, rinsed and cleaned it, and given it back. Some are filthy inside, just from normal use over time. 
.


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## orangputeh (Nov 24, 2016)

update 1/25/19

changed gas . no change

found out this is an aftermarket japanese carb. I couldn't find any numbers on it to see if it's for a gx240 . i changed out the pilot jet and it is running much better . however it still needs some choke for it to run well. this is a NEW carburetor. 

maybe the main jet is the wrong size for this gx240? or should I drill out the pilot jet a little? it's very clean.

another tidbit. when I go from full throttle to idle it backfires sharply once . if i gradually go from fast to idle it does not backfire.


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## tadawson (Jan 3, 2018)

Not sure what they get for the pilot jets where you are, but there are multiple sizes if drilling it doesn't work.

Not sure what to say on the backfire, other than that also confirms that you are running lean.

Did you put in the same pilot jet, or look up the one flr the gx240 specifically? If you have other Honda engines with different/larger pilot jets you can borrow, you might consider testing first . . .


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## vinnycom (Nov 6, 2017)

orangputeh said:


> update 1/25/19
> 
> changed gas . no change
> 
> ...


its running lean. why? in general - dirty carb or mixture screws need adjustment or jet too small or too much air(vacuum leak)


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## Lottstodo (Feb 16, 2018)

Maybe check valves adjustments,


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## orangputeh (Nov 24, 2016)

vinnycom said:


> its running lean. why? in general - dirty carb or mixture screws need adjustment or jet too small or too much air(vacuum leak)


pilot jet or main jet too small?


i forgot to check the carb gasket. when the owner put the new carb on I wonder if he put a new gasket.

i turned in the mixture screw all the way in and turned out 2.5 turns. will check the shop manual on that.


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## DriverRider (Nov 20, 2016)

Lottstodo said:


> Maybe check valves adjustments,


+1
On an older engine that runs funky always check clearances and guide wear.:wink2:


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## RedOctobyr (Mar 2, 2014)

I'd check for air leaks around the carb, before digging into valves. You could just spray some carb cleaner around the carb/engine gasket, while running, as an easy test. If the engine sound changes, you have an air leak.


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## JLawrence08648 (Jan 15, 2017)

2 1/2 turns? Little too much I think?

Can you get an adjustable jet for that carb? I think you can off eBay from one person.

The backfire is normal, you have gasoline in the combustion chamber which becomes excess when you lower the idle to fast.

Is it getting sufficient fuel through the fuel line?

Do you have a mini fuel pump? That may be failing?


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## orangputeh (Nov 24, 2016)

RedOctobyr said:


> I'd check for air leaks around the carb, before digging into valves. You could just spray some carb cleaner around the carb/engine gasket, while running, as an easy test. If the engine sound changes, you have an air leak.


kicking myself

basic and i should have already done this. thanks.

this was basically it. I sprayed some carb cleaner and it evened out . so took carb off . cleaned up everything and put it back together. I did put another pilot jet in and turned in the air mixture screw out 2 turns instead of 2.5 turns re. the shop manual.

running pretty ggod now.

should have run that carb spray test first. it had a leak on the inside part of gasket. new gasket but for some reason was not making a good seal.


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## orangputeh (Nov 24, 2016)

tadawson said:


> Not sure what they get for the pilot jets where you are, but there are multiple sizes if drilling it doesn't work.
> 
> Not sure what to say on the backfire, other than that also confirms that you are running lean.
> 
> Did you put in the same pilot jet, or look up the one flr the gx240 specifically? If you have other Honda engines with different/larger pilot jets you can borrow, you might consider testing first . . .


i replaced the pilot jet from a known good running 828. it runs a lot better but still need some choke.


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## RedOctobyr (Mar 2, 2014)

JLawrence08648 said:


> 2 1/2 turns? Little too much I think?
> 
> Can you get an adjustable jet for that carb? I think you can off eBay from one person.


I'm confused. If it has a mixture screw that can be backed out, isn't that already an adjustable jet?


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## JLawrence08648 (Jan 15, 2017)

RedOctobyr said:


> I'm confused. If it has a mixture screw that can be backed out, isn't that already an adjustable jet?


I was thinking it was an adjustable mixture screw on the side, low, and the main jet on the bottom was fixed. From the Honda lawnmowers I've worked on, Hondas don't have an adjustable main jet.


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## Giggleherz (Jan 26, 2019)

(Took out the pilot jet and cleaned it. sprayed carb spray into the hole but could not see if spray was coming out of the tiny holes near inside the carb. I suspect my problem may lay here.)

I had a bad surge problem with my Tecumseh 11 HP snow blower. I thought I had over revved the engine when it was new and somehow damaged it. I was watching a yutube video from (DonnyBOY) mechanic, he said take the pilot jet and break off a wire from a wire brush and run the wire through the jets orifices. 
I was thrilled it worked perfectly, it only took a few minutes and I think the orfice was dirty from the factory because I used new gas and a new can.
I lisitened to that thing surge for six years and after that fix it runs like a kitten. I always keep the tank full and it has always started on the first pull. The blower is almost twenty years old and not one problem other then the jet.


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