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.