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Hi to everybody here, from the bottom of Australia. I am new to this forum caper so please bare with me.

Bought a used Toro 16-38XL Wheel Horse ( 71226 - 210001267 ) a while back, it has a B&S 28Q777 0690-E1 010815ZD on it.

It ran ok for first 12mths, not at full throttle though, kept coughing/backfireing, but 3/4 was enough to get the grass down. Anyway it decided to get worse after sitting outside for 6 mths so i pulled the carb ( a walbro 63 ) to strip & rekit it. Being the heavy handed sod that i am i managed to strip the threads in the post trying to get the emulsion tube out.
So that ruled out the kit & a new carb came into play. Well needless to say at $350 for a walbro copy or $150 for a nikki from B&S then e-bay was calling out to me. Looked around for B&S units from the states but the freight from there is nothing short of extortion, which only left China, joy - oh - joy. Bought a supposed 698620/799727 nikki copy and hoped for the best.
Well that wasnt going to happen was it!! Put it on & it ran like a cow, 3/4 choke needed & hunting something kronik. Sucking air me thinks, so one thing leads to another to the point where the top of engine is virtually rebuilt.
All new gaskets & o-rings, new magneto, 2 new flywheel keys ( that was a pain ), heads been pulled and valves reseated & sealed, all new filters etc etc.
Cant see any sign of cracks in head or manifold, mounts both seem flat, no oil leekage when running, compression about 80lbs, leak down shows no leakage on gauge but can hear slow air into crankcase via pushrod tunnel, getting past rings me thinks which would be normal? No fumes via dipstick after running and the cylinder wall looks new, no scores or marks.
By all acconts the original walbro carb (63) on it is off a 28cid L head engine, it ran with a white filter for pump feed, but the mower is grav feed so have fitted a red filter, and mower has 2 gal. tank above carb. I bought another China carb supposedly for a 33cid but it looks identical except for mixing tube sitting higher in venturi & it runs the same way - full throttle perfect on 3/4 choke but black smoke if slightly more & surging if slightly less.
Have tried drilling jet on first china copy from orig. 1mm out to 1.4mm, but no go, runs without choke but backfires & plays up. Being a chokeamatic cant set the choke manually & not sure if it good to run the engine on high choke long term.
Have just bit the bullet & bought a Briggs 799727 grav carb which i should get in a week or so, but i have little faith that that will be any different, they more than likely come from same factory, unless the copies are the reject units from said factory.

Any thoughts you guys have will be much appreciated. If nothing else i am getting a crash course in small engine mechanics & i think i've d'loaded enough parts lists & info etc to go into the parts business myself lol.

Firstly ordering parts from China off the web through ebay.
When you do a search, open the part you are looking at in a new tab ( ctl+click ) then do the same with the words "other items"
If the only thing that comes up is mower / Atv/ small engine/ mini bike parts & similar then you have found a supplier that should be selling quality after market parts.
If OTOH they have 6,000 items listed from women's undies through to heavy construction stuff then they are general merchants and to be avoided.
Parts makers in China work on paper thin margins, so there is no such thing as scrap.
Thus the parts that Briggs / Nikki / Kohler reject as being substandard, get on sold to some one else and eventually end up usually on the site of a Hong Kong general merchant.

Now for your engine.
As it was bought with the wrong carb on it good chance there were other sins.
Side valve carbs are generally jetted slightly richer than OHV carbs but as both were for a 28 cubic inch engine they should have run.

Start the engine and hold the throttle fully open at the carb, thus defeating the governor.
Tell us what happens, and how it happens.

Check the valve timing.
To me it sounds like he has the cam fitted one tooth advanced.
Watch the rockers.
as the piston approaches TDC both valves should be closed then just before TDC the exhaust ( I think ) should open just a touch then close almost right on TDC.
If it is a later model it will be the inlet.
Because of this auto low speed decompression, compression readings are fairly well meaningless which is why you do leak down tests.
If decompression happens near 1/2 way up the cam is out of time.

These OHV engines leak between the push rod tube & cylinder and usually require both the head & block to be very lightly skimmed when gaskets are replaced.
Sounds like yours is doing the same.

Hello there Bert, thanks for the response.

Some extra info on what ive done to it;

All the fuel lines are new, tank has been flushed & cleaned, inline tap works fine. Petrol flows freely through carb with solenoid removed.
With or without air filter or box makes no difference to engine behavior.
Gov has had static adjustment & 2 new springs fitted. Dont have tacho yet so cant do a dynamic. But seems close to final setup, by ear anyway.
Valves are 4 thou on inlet & 6 thou exhaust. Have tried opening them out to full spec but no difference.

First the guy i bought this off is a back yard mechanic who aquires trades-ins etc & rejigs to sell, so who would know what the engine is...or was, may have just swapped the shrouds lol.
Yes take ur point about China & ebay. Got caught with the 1st coil replacement, it turned up with plug lead 4" long but needed to be 9". He swore black & blue it was the right part even after comparison photos - so buyer beware. Looking at Chinese carb maker sites, a lot do appear to be small govt enterprises, less than 50 employees working in a ' back bedroom' , no offence meant to our near neighbour lol. Still even so i wouldnt have thought a carburetor is something anybody could knock up on a lazy sunday afternoon lol.
Anyway getting back to my engine, i had noticed the small extra lift on the inlet valve which i assumed was the decompression briggs use, it occurs nearly at the top of the stroke so i assume that rules out a cam issue, and i note that they seem to be prone to gasket & head failures along push rod tunnel, logical as there is little metal or torqueing there. Later heads to mine seem to have lots of bracing in that area. I have my doubts if the engine has ever been apart, both the head & rocker gaskets where far better quality than the new briggs gaskets ive used, rocker seems to be moulded rubber ? & head is a lot thicker.
When i did the leak down there didnt appear to be leakage within the tunnel, i could just hear slow air in crankcase through holes at bottom of tunnel. Could not feel air at any of the external mounts which led me to think it was just going by the rings as the engine was cold at time. Did spray some CRC into cylinder but didnt seem to make any difference.
Cant start the engine at the minute to try throttle, but last time i did, it will run fine at full throttle with about 3/4 + choke, best it has, since ive had it anyway. A wisker more & it starts blowing black smoke (too rich) a wisker less & gov starts hunting wildly (too lean) ?
Having to hold choke closed a bit fiddly so cant get idle right, but adjusting screw seems to make little or no difference - been from fully in to way out - no joy.
Something i find odd is that even though appears to be lean the plug is black & wet, maybe from intermittent richness while fiddljng with choke.

Heres a question out of left field. If a carb is over jetted or if the venturi is creating too much vacumn is it possible to pull too much fuel for the amount of air going by the choke plate, hence too rich, & thus closing the plate down will bring the ratio back to normal. Fairly odd but just a thought.

The better head gasket is an aftermarket item.
I fit either Rotary or Stens both are thicker.
Rotary is black & Stens is silver.
THe rocker cove gaskets I am currently using come from China and are neoprene cork.
Blue Hylomar on the rocker cover & axel grease on the head means it will always strip clean provided I don't do it up too tight.

The set up seems a bit strange.
Just to be sure, the throttle butterfly is the one nearest the engine and has no spring on it. The choke is the one nearest the air filter and has a fairly strong spring on it holding it fully open
I have seen more than one fitted backwards and some hooked up backwards.
Some of the tops of the throttles have multiple holes so they can either be pushed or pulled and again I have come across the odd one with the rod in the wrong hole so the governor opened up the throttle rather than closing it down
Going from too lean to too rich like that is quite weird.

What would be really handy is some good clear and sharp photos showing the carb & governor from the top & sides in the choked position, full throttle & slow idle.
And tomorrow ( if you can ) go out & start the engine.
with one hand, hold the choke fully off and with the other hand open the throttle lever on the carb slowly.
As you do this you should feel the governor working against you trying to close the throttle .
Let us know exactly what the engine did & when it did it

And for what it is worth, you have a 2001 mower and a 2001 engine which is correct for your machine.
The model numbers vary from the USA to Aust, but this is your mower https://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/toro/riding-products/71242-16-38hxle-lawn-tractor-2001-sn-210000001-210999999/engine-briggs-stratton-model-28q777-0690-e1-4
If you go to the TORO USA site ( not the Australian one ) and go to the support section - manuals and type in the USA model number ( 71242 ) you will be able to download the owners , service, & parts manual for your mower.
The files all have numbers and the service manual with the number 492-4763 can be ignored it is the "quality of cut " book and 492-91?? is the electrical manual cutely called the Demystification Guide.
Most parts suppliers will have your mower listed as a "Wheeled Horse" a brand that Toro bought out in the 80's

Not to sure how to add photos, hopefully its worked.

Some snaps of the spare carb i got...its identical to the first one. Throttle at idle has gov toward front of engine, increasing throttle pushes gov to the rear. Full throttle has gov hard against its stop. Choke rod is in outside hole on opp side to mixture screw.

Thanks Bert, have managed to find stacks of literature on both the mower & engine. One thing i find frustrating is the seemingly infinite no of carburetors or at least part numbers that briggs uses, yet they give no info on the specifics ( jet sizes etc) of them. Trade secrets obviously.

Jet sizes are not all that important on a governed engine.
On some of the older SV engines the fractional Hp increases were nothing more than a bigger jet and in some cases a different governor spring.
On a lot of the newer engines they just fit a restrictor plate between the carb & the manifold.
The plastic manifolds are easily distorted if you do the nuts up too tight.
The images look about correct to me.
I gather you can get the choke to engage when you open the throttle lever all the way to the top.
Double check that carb solenoid and the wiring to it.
With the plastic manifold the carb is not grounded very well as the only full metal path is through the governor shaft & throttle lever.
So if the ground wire on the solenoid is not good the solenoid will not trip , you should be able to both hear it turn on & off with the ignition & feel it.
On some carbs the idle circuit draws fuel off separate from the main jet so they will briefly start with the solenoid closed as it only blocks off the main jet.

Once you have established that the solenoid is functioning properly try removing the ground wire from the coil.
If the engine runs properly then you have a problem with the wiring and will need to study the Demystification Guide.

And because the coil uses a Hall effect trigger it is direction sensetative and should be marked, up, to engine, flywheel side or something similar.

Yeah throttle lever extends past WOT till it engages the choke rod which then closes the choke, so to start when cold its full throttle full choke. The solenoid in photos is actually the one off the orig. walbro carb, the first china copy carb's solenoid was faulty & kept shorting back through the long govenor spring on the rod & eventually melted it. I measured continuity from the pins to the outer case of it, so it was junk. Seems that spring is the only return path back to engine. Would that be an issue.
The coil is mounted right way round but will double check tomoz when i crank it over.

Yes that will create a problem.
Put simply it was the wrong solenoid.
Some ground through the carb some ground via the plug.
The graound on the plug usually goes to a tiny 1/8" bolt that holds the lower shroud on which is very often loose or missing so you get a bad ground.
The single wire type is for carbs that bolt directly to the engine or use a metal manifold.
And yes the two types do regularly get mixed up.
You can toss it all together, they are not an EPA requirement down here but do make a good back up should the ground wire to the coil fall off, you have a secondary stopping mechanism other than running around the front and zapping yourself trying to remove the spark plug.

So for the purpose of diagnosing, you can replace it with a standard UNC bolt with an O ring under it, thus eliminating one potential source of problems.

And on that topic, it looks like the replacement was a Nikki type, with the white plastic jet holder between the float body & carb body.
If so the main jet just sits in the bottom of the tube , held in by the O ring.
Very easy to knock it out if you are not watching what you are doing, particularly if you start tossing compressed air around.