Rayp

Certainly good valve sealing and adjustment is the basis of a sweet running engine. Don't just do the exhaust, I've found that the thirty degree inlet vales on 5hp BS engines seem to suffer a bit and benefit as much from a re- seat  as much as the supposedly harder worked exhaust.
Quite often poor starting on 21s and Ospreys was down to nothing more technical than throttle cable adjustment not applying the choke  fully. Back in the day it did seem that the standard fit throttle control only had just enough throw to give both full choke and stop. Couple that with a bit of wear and slop in the pivot of the lever on the carburettor throttle plate and it was a choice of one ore the other but not both. We would often set them up for a reliable full choke and fit a handle bar mounted kill switch to look after stopping.

Hello Ray, Just to say that I fully agree with the advice offered re Valves etc, as I'm an advocate of pulling the head off of any engine I get irrespective of condition and give the Top End a good going over.  The result is very few issues with starting and running.
Only other thing to mention is that the 'Sooty' appearance of the Exhaust emission is usually caused by Over Rich Fuel settings, it will also retard your chances of an easier start.
The 'Book' says the INITIAL Needle Valve setting on a 5hp Pulsa Jet/Vacu Jet Carb is 1 1/2 turns from a gently closed position. It is further adjusted (finely) to obtain the best running setting.  This is assuming the Needle Valve Tapered end is not damaged or worn.  Check your Plug gap is 0.030".
Lastly, even if your Carb setting is correct, if  your Air Filter is tatty and clogged up, then your fuel mixture becomes Rich. Always worth replacing it and servicing it regularly. Let us know how you get on. 
Regards.

Probably one of the truest statements that I've ever read. Years ago I gained a bit of a reputation locally as a Gx Honda guru, ( before all the Chinese stuff got about)people used to ask me what my secret was in sorting out so many problem engines and I said there was none, simply pop the head off,de coke, grind the valves in, new plug and air filter plus fresh fuel and then 99% of them would be sorted. It was rare that I had to delve deeper,usually took less than two hours from start to finish.

First thing to do get rid of any oil muck grease with stiff brush or scraper  lash on  plenty paraffin  also protect your coils from getting damp when cleaning.
Also let the paraffin soak into the muck grease for about twenty minutes. I sat my engine in deep roasting tin to clean parts 
Don't buy Nitro mors does not work buy a  good quality paint stripper then lash it on with paint brush wait till paint blister  then a sharp scraper
keep lashing on the paint stripper keep scrapping till  its clean like  the photo of gear box.
Then wash down with paraffin then clean down with petrol, because the paraffin leaves traces of oil
Then let the petrol dry of outside.  I used 1/2" paint brush with long bristle to get undercoat between the fins on the cylinder head.
Photo of engine  1st  under coat. after cleaning.
Hope that helps you
 
 

Does this help?
 
 

If one of the bushes you require is #28 in Mark's diagram above, I may be able to help. If I remember rightly, that Bronze Bushing is 1/2" bore x 9/16" x 3/4" flange (part nbr 6229).
I need to make one myself .
If you need others like PTO Lever Rod bushes or the Fender Seat pivot bushes on the earlier models (different sizes and part nbrs), I also have made these for my Tractors.
I'll have to check my stock of Gunmetal Bronze, but sure I have enough to make a few more.
Send me a PM of you need any more help.  

Meadowfield is the boy to help you with that or look on our sister site red square and look in the manuals section 
 

Thankyou Richard and Meadowfield - another hurdle overcome!

As Richard says, they are far from precision!
I would just give them a good clean and pack them with grease. We've had a lot more hours than I imagined from ours after cleaning...
Even now they are a little rough, but functional!

Hello Ray, The standard bearings for the front wheels have only one Shield on the outside/Flanged side, so that the inside is greased via the nipple (Zerk).
Replacement bearings can have double shields, but do not require greasing via the nipple for their life.
 
You can carefully remove and dispose of the Inner Shield of the 'Double Shielded' bearings and clean out, re pack with grease if you wish. You can then grease later via the Nipple (Zerk).
 
The bearings themselves are not best quality (i.e. precision ground) and are light/medium duty pressed/folded metal type.  
I purchased mine from the U.S. some time ago at a reasonable price.
If you need to buy replacements/spares, have a good look around Auction Sites and Google search for best price/quality. 
The good ones for example are made by Heim in U.S., but I couldn't find them at the time.
Part numbers are Toro 110513 or 251210. 3/4" bore x 1.3/8" flanged single outer (or double) Shield.
I have a couple of (tired) used ones if you get real desperate.   

Hello Ray, I can't remember what Model you may have?. Does it have Bolt/Washer (pre 76ish) or 'C' Clip (post 76) Retainers for the wheels?.
I may have enough shims to sort your dilemma. Good to see your trying to set them up correctly

I have a handle of the type your looking for located never Glastonbury Somerset

I've finally made up my mind and bought an Abac 3HP (photo attached). 
The suspicions of one member were confirmed when I read on the internet that 80% of non-industrial compressors are made by one factory in China and merely painted and badged as required.
I spoke to one 'well-known' company asking them about what I had read and they said that there was a load of nonsense on the internet and that I shouldn't believe it.  I did not tell them that I had read this on their Company Website!!! 
P.S. I've now got to work out what filters/connections and airlines I need.