Cylinder head temperatures

[tig5]

Hey guys, any of you running a cylinder head temperature gauge? I became a fan of them after running a Vespa through Death Valley in a sand storm. Managed to prevent a blowup by dropping down a gear and increasing the oil flow rate. Mate wasn't so lucky.

I've recently put one of the Trailtech Gauges on my Postie running a Zongshen 140cc engine. The probe for the gauge is a ring that replaces the washer on the spark plug.

I've only just bought the engine and carb and have got the carb tuned to where it seems to be running well. Haven't done a plug chop yet because I don't want to hold a new engine at full throttle. I live in Darwin where it is hot, 35c (95f) each day and humid.

I'm a bit worried because on a 15 minute ride without thrashing it I managed to get a head temp of 200c (400f). Doesn't that seem way too high? Oil cooler is fitted, bike is finally running well but could be a bit lean. Any thoughts on what type of temps you'd like to be seeing? Don't have the jetting specs with me but from memory it is a 92.5 main and a 17.5 pilot, Fakuni carb. Outside foam on the air filter has been removed.

Cheers

 

[my67xr]

Are you running an oil cooler with the 140 ?
If not i hope you have a joiner hose on the oil port's down on the bottom end, from the case to the clutch cover
If there isn't a cooler or bypass hose fitted then the top end can run hot and dry from a lack of oil
Some ebay seller's mention the cooler is optional to run it or not,
but forget to mention it can't be run with the supplied plug's unless the clutch cover is modified by drilling a hole between the oil gallery's inside the cover, or fitting a bypass/joiner pipe on the port's outside of the clutch cover to the port on the case so it can pump oil up to the top end
This only affect's a few engine's but can be a costly repair if you need to source a new head and have someone fit it etc

It'll also pay to check the valve/rocker clearance's if you haven't already done it

pic borrowed from the net

If you have fitted an oil cooler with the engine then i don't think there is too much to worry about considering you are taking the temp from one of the hottest part's of the engine
The self cleaning temp of a spark plug is somewhere between 450° C and 800° C depending on how rich or lean it's running

Is it a 22/25mm carby or a 28/30mm carby ?
Either way i would think at least the main jet was too small @ 92.5, I usually run a #20 pilot jet on those Mikuni's too.
Guess the high temperature weather up there would be making it a bit richer too

The stock jetting on a 22/26 is #15 pilot and a #95 main
Stock jetting on the 28/30 is #20 pilot and #100 main

What air filter are you running, and is it oiled ?
How does your bike start and idle ?
Do you need choke to start it?
Can you start the bike and ride away or does it need a bit of a warm up ?

Are you able to get an Ohm's reading from you temp sender unit, does the sender units' wires plug into the head unit ?
You might be able to match up a threaded temp sender and drill and tap your sump plug and connect up the new sender there and see what temp's the oil is getting to in the bottom end of the engine.

 

[tig5]

Hey mate, thanks for all that.

I do have the stock oil cooler installed. I didn't realize that the oil needed to pass through those banjo points to ensure proper lubrication - that is definitely good to know.

This is the carb I'm using: Mikuni High Performance VM22 PZ26 26mm Carburetor Carb For Motorcycle Dirt Pit Bike ATV QUAD 110cc 125cc140cc Motocross-in Carburetor from Automobiles & Motorcycles on Aliexpress.com | Alibaba Group

22/26 I'm presuming? I initially tried jetting the bike with a junky cone shaped pod filter that had a rain cover installed (handy for the postie) and encountered a lot of flat spots, especially above half throttle. I then replaced the pod with a uni filter and removed the removable outer foam layer, just to reduce the profile of the filter and stop it hitting my leg. The 92.5 main was aready in there at the time and the bike went like a rocket so I left it in. I ended up richening the needle to the bottom clip as a safety precaution as I was mostly riding around half throttle due to break in period and figured, all things considered, it could be running a bit lean. Didn't notice any performance improvement or decline after doing this.

I will admit I haven't oiled the filter yet. The uni will need a home made rain guard as well. I'm thinking these 2 additions will help to richen the mix a bit and I think I'll also try the 95 main again.

Bike starts easily, idles great, don't need choke to start it (ambient airtemp is usually 30C in Darwin) Tried riding the bike with choke on, developed a few hesitations but rode ok, choke on didn't drop temp much.
Bike doesn't need any warming up. Overall I love the way it rides. I have a 17T on the front and the postie really hauls. It was just the temps had me freaking out a bit. Half the internet thinks sustained temps over 350F will kill an engine, some claim clone kart engines run best above 400F, then 4t watercooled is a whole other story. Haven't found anything definitive. This postie will be doing some long stretches with a decent load in hot climate so I'd like to avoid doing anything dumb to ruin its chances!

Thanks again for the input.