Pete S

I would try a new spark plug, they can break down under compression plus it is a cheap, quick and simple check.

The timing can be out. Either an internal fault in the coil or the flywheel has become misaligned on the crankshaft. Less likely and more difficult to check.

I use Skybound Aviation, I believe you carb is a Walbro WB37, they supply repair kits. Best to get a dealer to rebuild the carb if you are not familiar with the procedure.

Is the spark plug wet after your start attempts?  ie. is fuel getting past the carb, if not the carb would be a good place to start looking.

It sounds as if the carburettor throttle butterfly is too far open. The idle adjustment screw sets the position of the buttrerfly when the hand thottle is released hence the idle rpm, adjustment anti clockwise reduces the rpm at idle.  Of course the issue could be something else; is something stopping the butterfly closing onto the idle adjustment screw?  Less likely, check for an air leak between the carburettor and engine, a lean mixture can cause increased rpm although I would expect the engine to be difficult to start.  As the problem appeared following the pull start replacement, a check of anything that may have been disturbed during that would be a good place to start.

GPS height is generally considered not accurate enough for aviation. The following is a quote from Garmin:

GPS heights are based on an ellipsoid (a mathematical representation of the earth's shape), while USGS map elevations are based on a vertical datum tied to the geoid (or what is commonly called mean sea level). Basically, these are two different systems, although they have a relationship that has been modeled.

The main source of error has to do with the arrangement of the satellite configurations during fixed determinations. The earth blocks out satellites needed to get a good quality vertical measurement. Once the vertical datum is taken into account, the accuracy permitted by geometry considerations remains less than that of horizontal positions. It is not uncommon for satellite heights to be off from map elevations by +/- 400 ft. Use these values with caution when navigating.

Addition of a third jet to a pulse pump carburettor to enable mixture correction at high rpm.       https://www.kartwiki.com/index.php/Ibea

I suspect that the cold temperature is keeping the head cooler than normal hence the oily deposits on the bottom of the plug.  You mentioned that you had replaced the head, what was the reason?  If the engine is starting easily and accelerating to full power without hesitating when warmed up, the low jet is almost certainly set correctly, and as you say the high jet is fixed so carb would seem to be ok. With a few exceptions fuel/carb problems (filter dirty, diaphrams worn out, primer valves failing) usually cause a weak mixture which can cause engine damage. A rich mixture won't damage the engine but can cause issues over time (carbon build-up fouling the plug and excessive deposits on the piston and head). 

It will be interesting to see if changing the oil reduces the oily deposits, after cleaning or replacing the plug.

As an aside, to get the most accurate plug colour indication the engine should be at normal running temperature, run at full power for a minute or two and killed from full power.

Going on the colour of the plug electode, the mixture is spot on. You do seem to have a small build up of carbon around the bottom of the plug, what oil are you using?

I am not familiar with this set up so wondering, does the central part with the 4 holes unscrew from inside the small gear? If so the pipe wrench solution won't work.

MathewClay, check your pm.

Just to expand what Mark said, the 2.42 is the ratio between the diameter of the large pulley to the diameter of the small pulley so it does not have units.  It means that the engine will rotate 2.42 times to get the prop to rotate once, hence reduction.

I think that as posted 130 is the prop diameter but pign is the pinion size (diameter of the small pulley). I found this link which may help you, or someone else here to nail down exactly what you need.

https://www.southwestairsports.com/ppgtechinfo/simonini/simonini_mini2_plus/service_manuals/MINI2PLUSENGLISH.pdf

Extract:

REDUCTION RATIO AVAIABLE

1:226 Crown gear 129 mm / Pinion 57mm

1:230 Crown gear 129 mm / Pinion 56 mm

1:234 Crown gear 129 mm / Pinion 55 mm

1:242 Crown gear 129 mm / Pinion 53 mm

1:3 Crown gear 138 mm / Pinion 44 mm

From the information it looks like the reduction is 1:234.

Always ready to be corrected of course.

My Atom 80 is well past 11 hours and has no sign of similar discolouring.  Could that part of the exhaust been exposed to intense UV light (e.g. welding)?  I notice that the orange nut/bolt marker above the silencer in the top picture has also changed colour.

Not the same part of the frame/harness but illustrates the principle.

It is normal for the chrome plating on exhausts to develop colouring, with heating, over time. Colours range from orange/bronze to blue.

Thanks, I will order some to play around with.

5 hours ago, richjones said:

I’ve just bought some netting from an online supplier called hucks nets.  I bought pidgeon net and it cost me about a tenner for plenty to replace my netting twice. It’s identical to the original netting. 
It took a couple of hours to figure how and to fit it and done. 
I haven’t fitted the boas or the sewn fabric hem at the ends of the net. Just ties in some dyneema cord and looped Ito we the puns. Works a treat just not quite as pretty. But then it wasn’t pretty held together with red string and cable ties  

Brilliant, that is really worth knowing. Could you post the part number for the netting, there are several pigeon nets listed on the Hucks site. 

 I know you will call me a pedantic old git but, how do you keep the pop from spilling at 0G?

I agree with the two previous posters, the problem lies with the inlet needle and its seat. I think you have wear such that the needle seats and seals at times but does not at other times. I would replace them and retest.

This may help.

CAA Quarter Mil Chart Legend.pdf

I am not sure if the advice has changed but the Vittorazi Manual on the Parajet website has the oil/fuel ratios below.

This is not an uncommon problem with relays (and switches) where no arc suppression has been added to the circuits.  A good fix would be to add a suppression and cure the problem rather that continually replacing the relay. The circuitry is is pretty simple and is explained in the link here. https://www.nutsvolts.com/questions-and-answers/relay-contact-life

Hope this helps.

That joke is wearing thin

On 05/02/2020 at 13:49, toploader said:

Taking my tank in to show them at parajet tomorrow to see what they think. Its quite interesting that the tygon pipe  is known to be the right stuff for the job but i actually wonder. My old pipe out of my tank has gone really hard and brittle and the new stuff is going really soft straight away.

Any update on your problem and/or answers from Parajet?

I thought this was a pretty good deal and delivery was fast:

https://www.amazon.co.uk/gp/product/B00I5WHZA8/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1