MBK head temps

So, I finished my AV10 build a couple weeks ago, and just last week got and installed the Trail Tech Vapor setup. From what I read, here and in the manual, I set up the temp sensor and reset the computer so it would recognize it. I didn't see anything about having to calibrate it, though, so I'm unsure....

Anyhow, I'm getting what seem to be insanely high temps on extended rides. If I'm putting around my neighborhood at 35-40mph, it'll hover around 385-390. However, if I hit a steep hill or open it up for a full speed run (I'm hitting 54mph right now) the temps will steadily climb to max out around 460.

Which seems way too high.

I haven't had any seizures, soft or hard. When I come to a stop, or even just slow down, after riding at that temp, the sensor indicates the temp slowly lowering again. The engine sounds happy too, for what that's worth. It idles perfectly and starts up with 3' of pushing. I have no air leaks.

Here's my setup, for reference:

AV10 stock cases

Malossi 2-petal reeds

19mm doppler intake

19mm phbg (92 main, 50 idle, 60 starter, 50 slide, needle 2nd notch from top)

Malossi E12 air filter

doppler 50cc cylinder

malossi high comp head

doppler exhaust pipe

dopppler er3 clutchless variator

doppler er2 clutched drive pulley

Treats mbk cdi le partie, timed at 1.5mm btdc

Should I drop to 1.2 or 1.3mm btdc to try and put more heat in the pipe? Thoughts?

Re: MBK head temps

Andy Pabstalaniec /

retard timing as much as possible until you start to lose performance I suppose. Oil mixture can also affect temp, you could try running a richer mix.

Re: MBK head temps

i like waffles /

id try 1.2/3mm of timing see what happens anyway. i think hot moby temps are the dark secret locked in the basement. Ive given up on caring and messing about at this point, i just run castor oil at 32:1 and let shit happen, if yer at like 460 i prolly would not continue blasting though, until it cools off. i hit 480 one night when i could not see my temp display and musta had a intake leak, and shes all good.

Re: MBK head temps

NEMA Victor (3 Knees Down) /

Ah the good heat from a semi-race setup... yea, 380 is where you'll end up being at after a good tune.

Right now, your main is a bit low, start at 100. Retard timing to 1mm and work from there. I wouldn't go past 1.3mm btdc. You'll always want the most heat to the pipe. Oh and some people run less than 1mm from what I hear. If you are pretentious, check for proper squish.

Other than that, I've never gotten my polini 50 w below 400 during a ride. WOT it will hit 420 F after 5 mins or so. Pure race setup at that point since I don't need to be WOT all of the time on the track. Even the liquid cooled bikes run hot and start to boil if ANYTHING is out of tune.

Also, if you are running saber, don't go less than 80:1. Synthetics in general will mess up your break in if you put way too much since you'll gum up and cause more heat than lube. (edited)

Re: MBK head temps

^When I first started it up I was running a 98 main, but it was way too rich. Here in MN we've been in the mid-high 90's for a couple weeks. It 4-strokes with a 94 in it, so the main seems to be ok. I'll try mixing a little wetter in for the next tank, and if that doesn't do much I'll adjust the timing to 1.1 or so.

Also, I'm running a b8hs plug. I understand that the lower the number the 'hotter' the plug, but I dont really understand what that means in regards to performance and tuning. Anyone have a simple explanation?

That being said, do you think the high temps are holding performance back? Or would the cause of the high temps be the cause of not-as-great performance? I gotta say, I'm really happy with 54, but I know Christophe at Tomahawk gets his (almost exactly the same) setups to 60+.

Re: MBK head temps

i like waffles /

id try reducing timing, it doesnt take that long to try it out, and you would probably see a marked decrease, every motor/setup seems to be finicky in its own little way. mine actually didnt decrease much, but everyone is different.

plug temp has to do with the ability of the plug to self clean, too cold of a plug and it will foul, to hot of a plug and you will be dealing with detonation or pre ignition. so if your current plug looks good on a plug chop, you could switch to a hotter plug and it will be a lighter color. 8 is pretty cold, you can try a 7 if you like. higher compression and higher revs usually require a colder plug.

heres a fancy chart about plug tempeture

also read this, pretty informative.


High temps will always rob performance, my kit accelerates much better from when i first start it to about 300something. its what makes watercooled engines vastly superior to air cooled, you can get real aggressive with the timing and keep the engine in a prime range. (edited)

Re: MBK head temps

Retard the timing until there is no change in performance, getting the heat to the pipe will make the pipe work harder and stuff the combustion chamber earlier.

Gap the plug tighter for high revs like 0.38mm (.015 inch) and maybe try a Champion L78C which has a slightly longer reach then the NGK plug so the kernel will be lit up more central to the combustion chamber.

Run it on bean oil if she is still heating up, worth the extra $ in protection.

Re: MBK head temps

NEMA Victor (3 Knees Down) /

The temps may be holding performance back, but also, may be the peak of your performance. This is what tuning and porting is for. You didn't mention if you at least case matched...

Adjusting the timing is not an option, it is necessary. To be even more accurate, use a degree wheel and learn some theory.

Christophe does more than just put parts together and tuning. There is a lot of port work and preparation to get EVERYTHING tight.

Re: MBK head temps

Ok, I'll definitely be changing my timing. Kim has my 19mm puller right now, so it'll have to wait a few days. I did mix a wetter batch of oil (I usually run 50:1, and mixed this one at 40:1) and that helped out. I rode to work this morning, and I went from 460-470 yesterday to maxing out at 430 today. I know it's still way too hot but a 30* drop just from the oil is good.

Oh, and I did case match when I built the engine. I also polished the exhaust port and smoothed out the 3rd port for the reeds (there was some really rough casting).

Re: MBK head temps

is the head you're using the one with or without decomp? maybe try lowering your compression.

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