OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Honda Engines Honda GXV160 giving slight dark smoke puff when revving?

Hi All,

Question pertains to a Honda GXV160 thats on a Honda HUT216 utility mower. Hasn't seena lot of work and well serviced by myself. I've noticed a tendency for it to give a small puff of dark smoke when increasing the throttle speed rapidly or if you hit a patch of particularly thick grass etc.

I'm wondering if this is a sign of potential issues or perhaps relatively benign?

I'll just give a lil info:
- oil was recently changed, it's a bit of a combo blend of a number of 4 stroke oils I had consolidated into 'one' larger container (has some 5W-30, 5W-40, SAE30, 15W-40 in it - all were top quality oils) - changed every 6-12mths, last done a month ago.

- air filter is immaculate, has a snorkel kit on it - just have the single large airfilter on the mower, have some flyscreen/mesh at the snorkel end to remove larger particles

- no smoke when running and no oil consumption issues

- haven't adjusted the carb since I've had it - other than cleaning it each season.

- fuel is always good, always place a stabiliser in when I buy 10L or so of it.

Much thanks in advance for your assistance.

Hi N1KK0,

Dark black smoke is over fueling , if the flyscreen/mesh in the snorkel end is a non factory fitted item you may
have restricted air flow giving the mower a richer mixture.

Run the mower until hot then adjust the fuel mixture , first remove the mesh if it's not standard.

Cheers
Max.

Hi Max,

Much thanks for the reply - that does make sense.

Curious thing is though I've run the air filters as is for 5yrs or so without this occurring. This all seemed to start at the last oil change - which again is an odd thing as I've been using this 4-stroke oil combo blend for several years without issue.

The ONLY thing that was different at the last change was I added some Liqui Moly Ceramic engine oil additive when I did the change.

Just mowed another section now and is giving dark smoke more noticeable than ever - will do your carb adjust - if that does not amend I might dump half the current oil in the mower and top up with fresh. It's possible I added a tiny bit too much of the additive when I did the change, so perhaps it's a tad thin now with it's addition.

FWIW the Honda recommended oil for the engine is 10W-30 - so the combo oil should not be far off that.

Hi N1KK0
Remove the filters and see if it still smokes, don't mow without them inplace just to see if helps

@NormK,

Will do - it puts out noticeable smoke puffs when you throttle up, so start up, if you slow the engine and then get back to cutting revs, hit a thick patch of grass etc. But there seems to be a slight amount of smoke even when in normal usage But I will check and report back.

As luck would have it the handebars broke at the point where they're screwed on, so as to be able to fold down for transportation - has broken there before and I'd added an extra steel backing plate and welded - but will have to weld again.

So will likely not be able to test until this weekend but much thanks for the replies.

Sometimes you have to check things like is the spark plug breaking down under load or a restricted exhaust system.


Cheers
Max.

@maxwestern,

Much thanks - good suggestions, will check those too on the weekend (have house guests the next few days).

I'm not sure if it's a terrible way to do it but I clean the sparkplugs every few months by removing them and hitting the electrode end with a butane gas torch for a few seconds. This seems to carbonise the impurities etc and makes them very easy to remove with a light rub with a wire brush.

Is this going to damage the spark plugs or is there a better way to clean them in between changes?

I removed the exhaust muffler/baffle box a few months ago and that seemed fine - no issues with it.

Hi N1KKO
If a Honda is running right you should not need to clean the spark plug

Sorry I just managed to get around to being in a position to TRY and find this issue. First had house guests, then needed to repair where the handlebars had broken at that point just where they screw onto the bottom section - I might again be in the running for the ugliest weld competition!

So I started by removing ~half the oil and replacing it with fresh stuff - I figured this would negate the additive's addition being an issue

Next step was as per NormK's suggestion removing both airfilters (and I will note that the snorkel is a stock Honda snorkel, I have the OEM style air filter with it's foam prefilter on and the top section (which generally was made to have a Victa style filter in it, only has a cylinder of domestic fly screen in it - the though being just to remove the biggest crap but as the carb was NOT tuned for two filters I didn't want to affect this much - the fly screen would have no impact on airflow).

So ran with both filters off - and any smoke was very negligible - was the middle of the day so harder to see but this definitely assisted.

So then as per maxwestern's suggestion I tried the fuel mix adjustment - I have a cheap hours meter/tachometer but found that following this process from the diagram was hard to get achieved correctly.

Allowed engine to warm, then screwed the screw completely in - which even with the throttle set to idle gives a very high RPM (I was getting 3300-3400rpm) - you then screw it out and the RPM decreases, but the instructions say to set it to the point where at idle throttle the RPM are highest? And this was when it was screwed nearly completely in - but at this level it was maxing the engine out and throttle changes did nothing, other than when I moved to the off position.

So something seems awry here - I had to remove the throttle cable for the handlebar repair but am pretty sure it's spring loaded section up the top was replaced correctly so I don't think it's the throttle giving the issues as when I check it down on the governor section this all appears to be pulling back the correct amount.

So not sure how to follow this diagram when it gives a massively odd result - the previous setting of this fuel mix screw seems to have been very different as I had to screw it in a LONG way.

So this seems to have made more of a mess. :-/

Ok is the governor adjusted correctly, this is the only reason it would rev high, it should come back to the idle adjuster screw as soon as the motor fires up

Hi N1KK0 and Norm,

On some engines I've adjusted the mixture screw in the same position as this Honda and it doesn't seem to make much difference to the RPM,
the manual just says to fully seat the screw in then turn the screw out to 2 and an 1/8 of a turn , then if it needs a slight adjustment from that
position you can turn the screw a little more or less.

I've never had the motor over rev from this screw adjustment so sounds like a governor problem or (linkage / spring problem etc )


Cheers
Max.

Hi Max,
I don't often see a problem with the spring/linkages on the Hondas but the Chondas are a real dogs breakfast and some do take a bit of butchery to get them to work. On some of the Aldi type really cheap stuff I don't bother too much with because the set up is rubbish. If I can get the plate with the governor springs all set up from a Sanli or similar setup I put that on the Aldi type and I can then get them running fine and have the throttle control

In theory, if the idle side was set extremely rich, the idle stop screw (plastic head) would be screwed in a fair way to compensate for the idle mixture wanting to stall the engine. I would lightly seat and unscrew 2 & 1/8 turns (as max has posted), then undo the plastic idle stop screw until you get around 2000rpm and only then have a decent play with the mixture screw

One thing I do recall is when honda fitted their snorkels, they recommended changing the main jet in some instances. Similarly, when victa did their snorkel kit for the gcv, they managed it by changing the size of a nozzle stuck in the motor end of the snorkel. Most used black nozzle, some used another colour.

As Norm said, if it was running right, you should be able to go years between cleaning plugs. If it was carboning up, maybe your muffler is also now full of carbon. I have faced this issue with my big bob as the previous owner ran it with a clogged filter (gxv120). Once I sorted out the mixtures and filter, the first hard run saw me nearly light up 100sqm of dry grass by the amount of black and red hot carbon mixture shooting out the muffler

Firstly, to Maxwestern, Tyler and NormK - much thanks as always for your replies and assistance - I'm unsure how many folks who ask for assistance truly thank you but in my years as a member you gys (and others) have never ceased to give good, well thought out and thoroughly explained advice - much thanks for this - really makes a big difference for folks trying to maintain their own gear as labour costs make it very hard to take to shops for repairs etc.

I will have a play with the carb adjustments on this mower (Honda HUT216) and see if I can get it back to being relatively happy. I've had the mower for several years, was near new when i bought it 2nd hand from a chap in WeeWaa, who'd due to the drought there covered his entire yard in a thick layer of hard wood chips - which was a new one for me to see but go figure. But the mower was near new.

Removed the air filter and can confirm that the linkages and springs etc are all operating correctly and in place - no damage to any of these so am pretty sure this is all fine (as mentioned I've never adjusted these at all).

It's never had it's governor or carb adjusted by myself nor the previous owner. I've always turned the fuel off and allowed mower to stop due to running out and used stabliser and carb cleaner additives in the fuel. This smoking - which isn't major but annoying only came to be after I used this oil additive (Liqui Moly Cera Tec, which I think I accidently used above it's 6% recommendation) - so I suspect thats the main issue.

The snorkel on it came from off a Masport 800AL 21" mower - that I bought with issues on it's SP - and has proven to be a bridge too far in my repair skills (I might have to post another thread about what the experts feel are the best things to do with it!) - it came with a Honda GXV160 engine fitted. The engine is nearly new and had a snorkel fitted to it - so as this mower was 'out of action' and the HUT216 used all the time, I mowed the snorkel section only over to the HUT216.

This was done several years ago and never had an issue with it - as folks know the snorkels work very well, it's very rare to get crap/dust in the main filter section when I clean'check it. My understanding on Masport's original idea with this snorkel was that 2 airfilters were run - the standard oval pleated GXV160 filter with a foam prefilter in the lower part of the unit - with a Victa style cylinder pleated filter in the top of the snorkel. This seemed excessive to me - and as the carb on the HUT216 was not set for 2 filters, I've always just used the single lower filter and some flay screen mesh on the top snorkel inlet to remove larger dist/grass. Seems to work well as bottom filter is always very clean.

I also made the bottom airfilter compartment as 'air tight' as possible - by siliconing up it's inlet holes, also added some electrical tape to form a better seal/gasket when the top of the filter was placed on and screwed down. This all seemed logical witht he snorkel fitted as no point drawing in 'clean air' from high if dirty air easily entered down low.

I've never done any valve adjustment to the engine either - it might be due some time - have previously done on my GCV160 engine and wasn't as hard as I'd feared. Being I've used it for around 5yrs - and the manual says this should be done annually is this somthing I should make time to do? Or is it largely unneeded and best avoided unless issue suspected? I ask as I know from doing on the GCV160 you need to make a new silicone gasket for the valve cover and so is a bit of a PITA in that regard.

The engine oil used in the 4 stroke mowers is a blend of a number of left overs from our car (changed from petrol to diesel when we moved rural so it's all top end stuff 5W-30 to 15W-40 and also some SAE30 given by a friend) - which knowing what went in would have to be not far off the Honda recommended 10W-30.

I add this last info just as background - as I don't think any of it is a factor in the slight smoking (which might have been overstated by me as I'd not even worried about it until my wife mentioned but I had noticed it more after this).

I have a few days until i can mow again - due to wet weather so as per Tylers tip I might try and get the muffler off and ensure that carbon hasn't blocked it up badly too - good idea.

Will report back on progress - much thanks.

PS. The shop manual for the GXV160 tells me that at idle I should be chasing a 1700rpm and 3200rpm at full throttle.

PPS. Seems we might have been having some confusion (am sure it was on my end) about which screw to be turning - as there are two in that general area. The one I've been only adjusting is what the shop manual refers to as the 'Throttle Stop Screw'(TSS) which it states is only for setting the idle speed to 1700rpm - this is the largish plastic screw.

The 'Pilot Screw', which is smaller and metal - I've not touched - but seems the advice was given about THIS screw - oddly the manual states that this is ALSO used to specify the idle speed?

Given the Pilot screw has not been adjusted - should I only adjust the TSS so that idle is at 1700rpm? And should I leave the pilot screw alone completely?

Thank you in advance. Happy to throw pictures up if it's felt the will assist.

Hi N1KKO
Some of the more modern hondas have a little nub on the pilot metal screw which prevents more than 1/4 turn either way.

If the screw is free to turn fully, I would screw it in (counting how many turns from original position), then 2 1/8 out as a starting point.

If you screwed the plastic throttle stop screw in completely, it would (as you found) idle around 3300 rpm. Just back this out to 2000rpm, have a slight play with the idle mixture pilot screw, then set it back to 1750rpm.

Regarding the masport 800sp, please do post another thread. They are a good mower with a multispeed drive system. The transmission is made by general transmissions and has a variator pulley not multiple gears, commonly wanting to slip from speed 8 to speed 1 on its own (which is a crawl) is the main thing i have found with them.

Hi Tyler,

Thank you for your reply - excellent as always!

Yes, I only noticed the pilot metal screw yesterday when as per Max, Norm & your terrific advice I was looking over the linkages etc - it had a tad of gunk on it so wasn't evident at first but upon lookin at the shop manual today I realised this was also a carb adjustment screw - silly me as always.

I will follow your advice - raining a tad here here at present but written down and will venture down to the shed to do.

I will do on that Masport mower as well - I won't 'cross post' but I picked it up a few years ago, the current owner had the drive belt go on it and couldn't be bothered repairing - so sold off cheap - but I've never been able to get it running properly. The SP belt tension system was just a nightmare as it was in a mess when I got it. But I will post up as currently wondering if it's possible to repair. :-) Much thanks again.

Hi N1KK0,
Just so you understand this screwing the large plastic screw clockwise is opening the butterfly/governor lever which is why the revs are high, back it right out and see where the revs sit

Conveniently I happen to have a photo of a working 800 sp belt guide pattern on my phone somewhere, when you post up your one I will try to dig it up

Apologies for resurrecting this thread - the HUT216 had been away for the very dry winter & early Spring - but back out and in active use now.

Cut a long story short - it still isn't running quite right when it gets duress on it when cutting - so to me the areas that might need adjustment are either the governor or the carb.

I've got the carb set at factory levels, I'm meticulous about draining fuel from it and using stabliser etc - so I doubt it's the issue.

I tried to adjust the governor previously (before storage) and it wasn't as easy as on the GCV160 that I also have. Would the governor seem to be the likely 'lowest hanging branch' to start with?

Only other things to note are I've never adjusted/checked the valve clearances on it - by the log book it'd be due, I've done before on a GCV160 - was pretty easy - but unsure if this might be factor.

The oil in it is a combo of SAE30, diesel 5W-30 and 15W-40 - so I don't think viscosity should be an issue as Honda recommends 10W-30 in it.

Thank you in advance.

Governor should have no affect - provided it isn't surging or rev spiking I would negate it.

I still reckon its running rich.

My diagnostic process would be:

What spark plug is in it? bp5es or 6es? If 6es, swap to the hotter 5es for cleaner burn

Confirm with a honda dealer (with the model number) if a snorkel requires a smaller main jet to be fitted (I believe it technically should)

Inspect bore/head with an endoscope and confirm carbonisation levels.

In any case, the first thing I would do is start running it on 98ron with a Polyether Amine based injector cleaner. This ingredient will help most with decarbing. Most cleaners don't have it, Caltex techron, stp complete fuel system cleaner (silver bottle) or rislone High-Performance Injector Cleaner all have it. As does Yamaha ring free (go to a boat dealer).

PEA is the best decarb fluid around

Hi Tyler,

Much thanks in advance for the reply & assistance - its very much appreciated. :-)

Yes isn't doing this, so thank you for eliminating.

The current plug was an NGK BPR6ES. I've cleaned it regularly but upon removal it had far more carbon on it than I've previously seen. SO a tad unusual.

In trying to adjust the carb last season, it's possible I got it well off where it should be - as mentioned I was using a cheapish RPM monitor and couldn't really find improvements from changing. So unsure if my attempt to get back to 'default' levels have been less than ideal.

I will try and grab a few of the NGK BPR5ES as you have recommended - thank you.

I will see how I go - the airfilter-snorkel assembly is a factory one that i removed from a GXV160 engined Masport that I had (subsequently sold off). I only run the large bottom single airfilter in it rather than the two that one can do. I use it purely to ensure that the air intake is higher up and well away from the dust zone. The top snorkel intake only has a layer of flyscreen inside it - so offers very little to no resistance to the airflow at all.

So valid point - but if I'm only running the single airfilter, even with the snorkel I can't imagine this would really make it much harder for the engine to draw the air in vs just the single bottom filter. I'll note that I've run it like this for 5yrs or so - and not had this problem occuring previously, which makes me think that it's unrelated to the snorkel with single filter. But is a good catch by you.

Ok will do - I just happen to have a cheap and cheerful endoscope so I will see what I can ascertain but I suspect judging by the sparkplug that it's going to be grubbier than I'd have hoped.


Point taken - just curious and I know this is a point of contention for many - but why the 98RON recommendation? I always use 91RON on anything that specifies it and ensure that fuel stabiliser is added to the storage container as soon as I get it home. Fuel stored in a flammables cupboard thats in a cool area.

I've used injector cleaner in it very regularly BUT I suspect it might have been rubbish - which I kind of knew being that it was a Valvoline product.
I will keep a look out for some of those ones you advised. Much thanks for that.

Just trying to find one of the P.E.A containing fuel injector additives - but obviously value depends on how much of the good stuff they put in the additive - as many seem to have only a tiny amount:

Caltex Techron Concentrate contains 15-20% Polyether amine
Rislone Hy-per only as 0.1-1%! Seems very dodgy as they openly state that it contains P.E.A but has very little of it!
A well regarded US one Regane Gumout has 10-30%
The STP one is very confusing, seems to have a bunch of stuff but no pure PEA but some similar ones.
If you can find it Red Line® SI-1 Complete Fuel System Cleaner has apparently the highest at 28-34%.

Annoying that a lot of ones seem to either have a very small amount - which would have likely no benefit or seem to use very tricky names which make it unclear if they have it at all.

Amazing when you look at the SDS that so many of them are very questionable in benefit i.e all kerosene or napha etc. All the Australian brands were really shitty when you looked into them - Penrite, Nulon etc very low levels of PEA.

PS. FWIW the best value by far was the Redline SI-1, contains 28-34% PEA - so you could use much less of it for same effect. This was the cheapest i found for a single bottle: https://www.ebay.com.au/itm/186140803269

@Tyler,

Just curious - you've recommended the BPR5ES rather than the BPR6ES I have been using - I know this is the next 'hottest' compatible plug on NGK's scale - would you feel if going to a 'hotter' plug will assist, is moving a single increment likely to be discernable as opposed to going with the BPR4ES etc?

I wouldnt go to a 4es but a lot of gxv160s take a 5es. Who knows if it makes a difference but it stands to reason any hotter plug will help reduce deposits and give cleaner burn

Tyler,

Cheers for clarifying - used one of my rare trips into town to pick a BPR5ES up, will toss in and when it dries up a tad here (as our Eastern seaboard drought was broken over the last few days) will report back thoughts.

Ok - as recommended by Tyler, I got out the very cheap and nasty endoscope I have - inserted it into the mower this morning but alas I really could not discern much at all - it's just such a cheap one that the focal length seems to struggle with showing much.

What I can safely say though, just from eyeballing it through the hole myself using a torch, is that there's a significant amount of carbon in the cylinder - certainly more than I've seen previously.

Due to the recent break of the dry spell here - I'm going to have to mow today - I'll pop the BPR5ES plug in and see if that assists - the PEA injector cleaner is onroute - but I don't know if I'd be recommended using something more robust to remove some of that built up carbon in a separate process?

I'm still unsure if I should adjust the carb screws to make it a tad less rich or if this oil 'blend' I put together from left over odds and ends, has somehow played a part in this.

Hmmmm ok just did 45mins or so chipping away at the 3500m2 of surging Kikuyu....alas the BPR5ES doesn't seem to have changed much, still getting puffs of black smoke when I hit a thicker patch of grass. I'll yank the plug when I go back out but I suspect it'll already have a good deal of carbon on it.

I'm suspecting it's either the carb settings or perhaps something odd has happened with the oil blend and its caused problems - when everything I mixed did have a working/hot weight of 30 or above - but it seemed surprisingly thin when I took checked the level before starting. Alas due to my diligent mixing I have around 6L of it.

I might buy a litre of bog standard 10W-30 and see if that still has the issues - if nothing else I'll eliminate it as the problem.

Any other ideas welcomed - dunno if I should try and adjust the carb now or if moving too many variables at once just confuses isolating the problem?

Just finished the front 'yard' 90mins straight mowing - the pleasures of living on acreage thats not able to be done by rideon. Checked the plug before starting and sure enough it was filthy, really no difference at all from the BPR6ES in terms of the amount of carbon on it.

I removed the thin foam prefilter on the airfilter to provide a tad moree airflow - as I'm just trying the 'easy' stuff first -. ANyway the amount of smoke is just as bad as ever - might even be a tad worse to be honest - if I have the engine at idle RPM and then accelerate with no cutting load at all there's quite a big shot of black smoke that shoots out - very pronounced.

SO I think I can eliminate the plug (though I think the hotter plug is a good idea anyway), I think the airflow to the carb isn't the issue, so eliminate that too.

That leaves the carb settings, oil and perhaps anything else as the things to try and alter/adjust?

Any ideas welcomed. :-)

PS. I likely need to find the cause of the smoke first - but if there's a best way to reduce/remove the carbon thats built up in the cylinder head etc - please feel free to let me know - prefer something non-mechanical (i.e not have to open cylinder head completely) but dunno if I can remove the exhaust outlet and flush/soak with carb cleaner etc? Again I won't do until I've reduced the smoke as otherwise kinda pointless.

As already mentioned black smoke means a rich mixture, too much fuel or not enough air, nothing to do with the sump oil (unless you have tipped the motor the wrong way and blocked up the air filter with oil).

Is the choke opening completely when off?

Someone may have used some wire to clean out the main jet, or the two holes in the bolt which holds the float bowl onto the carb, and enlarged the bores. The fuel inlet needle attached to the float might not be seating properly.

Just some thoughts, I have found those motors tend to be not too fussy with the fine details.

Hi MowingManiac, thanks for your reply.

Defintely didn't tip the wrong way - learnt that many years back the hard way. Airfilter checked this morning - no issues with it at all.

I'm unsure of this offhand - no issues starting it first pull as has always been the case. I could check but I assume this'd need the carb removed from the plastic body - which is a bit of a PITA, seems all the rods etc are moving properly, carb is a tad grubby on the outside but as I'm very careful to always use stabilised fuel, shitty carb cleaner in the fuel (better stuff onroute thanks to Tyler's tip) and turn off fuel tap prior to turning engine off - I'd think it should be pretty spotless inside.

As I've had it nearly from new and certainly never done this I'd think it can be ruled out - but if you feel the carb needs to be pulled apart and checked let me know. Sounds like I'd only have to remove the fuel bowl to do this?

Thats been my experience as well - it'd worked very well for years and then this just started occurring. Part of my reason for thinking it might be the oil blend was that was one of the only variables that changed around the time it started occurring - but again the oils put in were all good quality and essentially when totalled about the weight Honda states 10W-30.

Is a puzzler.

I have had issues with some of these Hondas for some reason with the choke not coming off and I have had to put a small spring on them to ensure the choke fully opens. And then with these vise versa, you have to ensure the choke fully closes or they will not start. Sometimes they can be a fine balancing act to get right

Yeah no choke issues for this one super easy to start right from the first day I had it.

Unsure what the next thing to try is? Smoke has definitely gotten worse from when first noted on here.

I have it running 'better' now.....Red Line SI-1 fuel cleaner (recommended by Tyler) arrived. I will start using.

Wondering if it's worth trying to remove some of the carbon build up that seems to be in the cylinder & piston head? A mechanical disassembly would seem a tad much - but I've read spraying carb cleaner down sparkplug hole, allowing to soak can loosen and assist removing it.

Any thoughts on if it's worth removing the carbon & if so how to do welcomed. :-)