How do you tune The engine during race day if the weather gets colder or hotter?

Not very much unless there is a huge change but generally richen the hsn a fraction if it gets hotter and lean it if it gets colder.However in 20 years racing I don't think I've ever had the conditions change so drastically in one day that I've had to really retune..Methanol burning engines do like cool early mornings with plenty of humidity though so a day that begins cool and damp then dries out and gets very hot in the afternoon might certainly mean running a tad richer later in the day.

edit..reverse that..teach me to type while stoned...richen for cold/damp weather and lean for hot dry...sorry

Not trying to be funny Giz, but I always believed that to be the other way around.
On a cold day the air is denser, so you get more air (O2) in the cylinder per stroke, requiring more fuel (a richer mixture) to run normally with better power output. Conversly on a hot dry day the air is generally less dense, so you get less air (O2) in the cylinder per stroke requiring less fuel (leaner mixture) and not quite as much power output ?

If I start racing in the early morning on a cold autumn day, I generally end up leaning a tad between the heats and the finals as the air temperature heats up quite noticibly during the day.

Same principal as drag racing, where they are down on power in the heat, or at high altitudes, but can end up taking power out of the engines or tweaking the clutch packs as the cooler evening air comes on for the finals to stop lighting the tyres up of the line because of the extra power the engines make in the cooler conditions.

The other posts probably have you covered. I printed out the chart from this web page http://www.rchobbies.org/cars_eng-tuning.htm and put it in my wallet as a sanity check. Was in there for a couple years never used it. Every time I went for it at the track along came a person better at tuning than me and would get me straight. Not entirely sure it's accurate, certainly looks valid to me.

Nice article. Very informative and a good reference guide.

An idle coming in high then settles low , is a rich LSN masking a high idle gap.

If it goes up and then down on a regular basis during still idle " Without revving it " then its an air leak.

Loosen the pinch bolt on the carb , push it in REAL hard and tighten it while pushing it in.

Also check the head bolts ..

This is not particular to a brand of engine , this is a common thing that either tuning or maintenance can fix.

Adding a head shim can help idle yes. But check for air leaks first. then try re visiting the LSN tune VS Idle gap relationship.


Hope this helps

Cheers MM

bubbles in the line?

Fuel tank lid O Ring worn, fuel tank lid spring weak, crack in tank, crack in internal fuel tank pick up stem, pin hole in fuel line from tank to motor.

Take your tank out. Empty it completely of fuel. Seal the outlet nipple with some fuel line. Submerge the tank in a sink of water and blow into the inlet line. If you got bubbles anywhere, there is your problem. If not, flush the tank out with a bit of fuel and refit it, then change all your fuel hoses with some new stuff.

Also check the fuel inlet banjo on the motor (HSN assembly) is nipped up tight. These seal on alloy washers not rubber ones, so this assembly can vibrate loose on ocassions.

+1
don't forget to check your fuel filter seal as well

This may seem to be a very basic question, and forgive me if I am being a dumb arse.
Let me first say I am as sick as a dog today so head is not working too well.
I just finished rebuilding my buggy from ground up and was also going to change the rod and bearing in my MG66 while it was out of the buggy.Well I took the back cover off, removed the cooling head and button also removed flywheel assy, but for the life of me could not see how to get the piston/rod or crank out.
So how is it done?
I also tried to remove carby (is that done by removing allen head bolt and pulling up?) but it would not budge.
In the end I have reassembled and refitted to buggy, motor will be out again on Sunday so I can do the rod and bearing then.

YOU WILL NEED TO REMOVE THE SLEEVE FIRST ..oops caps lock..oh well...anyway remove the sleeve and then there will be enough movement in the piston to pull the rod off the crank pin backwards (make sure the crank is as far forward as it will go) removing the sleeve will be easy peasy or a complete bastard..You can slip a cable tie into the sleeve and out the exhaust port then turn the crank and the sleeve will pop up with the piston (easier if you leave the flywheel on till the rod/piston is removed) if it cuts the cable tie instead you might need to gently tap the bottom of the sleeve from the rear cover side with a WOODEN dowel..be careful its easy to mark and damage the sleeve.The play in the new type rods in the MG66 is pretty much nil so I've found them to be a really tight fit to remove and worse to refit a new one ..just be patient and don't force or hit it.I also rub a TINY amount of a special copper/aluminium paste I have for ultra high temp stuff like exhaust fittings around the sleeve when my engines are new and my sleeves always come out easy.

Oh and grizz1 yes I think I got it the wrong way round..was pretty stoned writing that the other night..and now I'm confused and not sure either way.

Yeah, you got it upside down bro Check out that article mikenix linked up. It explains it all really well.
Off to the track to mop up two days of non stop rain so we can hopefully race tomorrow.

yeh I was wasted...oh well..hasn't rained a drop here in 7 weeks now....everything is a dustbowl and my sheep got little or no grass....

Just received my 7 port yesterday, broke it in on my RC8 truggy.
Its got a insane amount of top end BUT my low end seems to be bogging or something.

Example :
Its got great punch off the line. But lets say when I come wide open throttle down the back straight, hit the first turn at medium speed and try to get back on the throttle again it does no respond, I have to give it a hand full of throttle to get it moving again.

I am guessing the clutch is engaging too early and bogging it down?

any ideas?

sounds like it may be running a little lean on bottom. richen it about an hour and go from there.