Carb ice? Not!

ravenous · May 4, 2014

Heres a few pics of my cooling/heating system for my KX500.
The carb heater could be sized for any carb including a
smarty.This one adds about 3/4" to carb length.I could reduce
this to 5/8" or so.Diameter could be shrunk a bit,too. I plumbed
this in parallel with my thermo bob bypass hose.It helps to put
it in the bypass circuit because when the stat closes it forces
coolant thru the heater. Im sure it would work fine without a
stat too, I just never tried. With this setup I never have to
worry about over/underheating or carb ice.One shut off valve
on either side of the heater lets you adjust flow or remove your
carb without losing all your coolant.
OK. Thats it for me,Im dirt biking for the next 6 months!

summitboy · May 4, 2014

Its too bad Thermobob doesn't make a true 130F stat for our 2 stroke bikes. I know he was gonna make the 160F stats but im thinking he decided against it since i have never heard back from him. Having said that i don't believe a guy may not even need stats at this point. I believe the ice is the true issue and not engine temps and carb heater setups like this are a great answer. Too bad there isn't a 80-100watt KTM style heater as an option as well.

Ravenous do you have any data on temps before you did the Thermobob and then the single rad with the tunnel cooler ? Just wondering what you saw before and after ?

After a season of biking i'm starting to think the stock rads are a little useless and a tunnel cooler setup may be more efficient at least on the trail. In the deep it may be to much without a goo tstat though. Ideas ? Thoughts ?

ravenous · May 5, 2014

My temps were out of control before this setup. In deep powder at slow speeds I would overheat.I saw as high as 250 deg! Riding fast on a real cold day I could not warm up. As low as 80 deg.So I needed some temperature
control. I know some guys are getting away without it,but I can't see
how? The fast warm up you get with a stat is great too.
But like some of you have said 180 deg is kinda warm for a 2 stroke.
So if thermobob wont make a cooler one,I think I will,if possible.
The machine work for the housing would be simple.But maybe low
temp stats are not that common? Does anyone know where to find
one,maybe 130-160 deg?
Or maybe it doesnt matter that much.The old KX is still making great
power at 180 deg.
I did try the tunnel cooler with no stat and it never warmed up.

o2bncamo · May 5, 2014

All Yamaha 4-stroke snowmobile thermostats are 150 deg. They are cheap and easy to find.

summitboy · May 5, 2014

The KTM stats are 55C Thats what we need for the 2 strokes if a stat is needed. The trick with it though is u need a true block off of the stat with the bypass. All these stats have the weeping holes. The KTM has one in the edge as well as in the plunger. They let too much coolant by when closed hence why the Bob works so well. Its really the secret. But he doesnt make a 55C or 75C (130 or 165F) stat as of yet. We don't want a 165F stat on these 500's

With my setup i do see temps rise going up the trail to the 200F mark. But as soon as im in the powder they drop to the 90-130F range depending on the outside temp. The bike runs fine at the lower temps unless i have some ice at which time i lose my idle. Just recently i had a trip where the bike stayed in the 130F range and no icing conditions and the bike idled all day and it ran flawless ! It was a *** kicker for sure. So thats the trick, no ice !

dhdey · May 5, 2014

i just put a skidoo heat exchanger on the back of my cr500. it worked amazing but developed a crack on the first ride. what is that exchanger from?

dhdey · May 5, 2014

summitboy said:
Its too bad Thermobob doesn't make a true 130F stat for our 2 stroke bikes. I know he was gonna make the 160F stats but im thinking he decided against it since i have never heard back from him. Having said that i don't believe a guy may not even need stats at this point. I believe the ice is the true issue and not engine temps and carb heater setups like this are a great answer. Too bad there isn't a 80-100watt KTM style heater as an option as well.

Ravenous do you have any data on temps before you did the Thermobob and then the single rad with the tunnel cooler ? Just wondering what you saw before and after ?

After a season of biking i'm starting to think the stock rads are a little useless and a tunnel cooler setup may be more efficient at least on the trail. In the deep it may be to much without a goo tstat though. Ideas ? Thoughts ?

you need a stat for sure, i tried my setup without one at first on a warm day last week. the engine went down to 60* as soon as i hit snow.

i put in the 55C* ktm stat and it worked perfect, the other outlet from the head just went around my copper carb heater and back to the engine. it would climb to 150* max then instantly drop to 130* when the stat opened

summitboy · May 5, 2014

I tried dual KTM 55C stats. They didnt do anything. Bike would still drop to 90-110 in deep snow. They just let to much coolant through closed. I really dont think u need stats to be honest. I know a few guys running none and the bikes run fine with heat in the carb. Ive been running no stats for a while and i see between 90-130 in deep snow.

Up the trail 180-190ish. Down the trail 160ish. I noticed when it warmed up outside 130-140 in the deep and no ice bike ran, idled, pulled like freight train. With the Smarty at 1/4 to WOT it always always run great even with a little ice. I just lose my idle in that right condition. I also notice it takes a little to get heat back in the pipe when it runs in the colder weather.

I also believe anything over 120F u are losing some power. If a guy could run a true 120-130F constant all day it would be pretty good. The only way to do that on my setup is to maybe run a snow cooler and a real closed stat with a bypass. Im gonna wait and test a coolant heated Smarty first. Then decide if more temp is truely required.

The other thing that changes in these motors is engine work. I have some fairly
specialized porting from Millar Racing that may have some effect on this. Adams motor pulls hard ! I found most of the 4 strokes i have tried feel somewhat flat and lack that big 500 power hit. Just my 2 cents !

dhdey · May 6, 2014

once i sheilded the engine, i had no problem keeping the temps at 120-130. but had problems keeping the bike cool on hard pack/climbing. tunnel cooler is for sure the answer but a thermostat is a must. my bike ran like crap at 60F. i think alot of people blame the small amount that gets past the thermostat for engine running cold in pow. but i think its just the snow hitting the case and cyc dropping the temps.

summitboy · May 7, 2014

If you look at Ravenous setup I don't see any shielding and he runs a snow cooler and one rad. That should be even more cooling than my setup. If you sift through some of Thermobobs data (also talk to Bill) and graphs you can see why his setup works better than a stock ktm/Kawi stat. No coolant movement only through the bypass. That's the reason he gets super consistent temps. It's just too bad he doesn't have a 135F setup.

Ravenous has consistency in his system but I don't like the temps he sees for my personal setup. 185F is too much for a 2 stroke. It's power loss. Ice racers swear by stats in the 500s but I believe that is a different ball of wax. Very little load on the motor and fast speeds in somewhat colder weather. Like I said earlier 100F with proper carb heat (no ice) runs fine in a few setups I've seen.

It's too bad Bob won't make the 130F Bob setup. That would be the ticket with extra cooling for the trail and a good coolant heat setup IMO.

summitboy · May 7, 2014

Just some info for the stat guys. Thermobob will offer a 150/160 Thermobob kit for us starting August. They are smaller housings and Ts. He also said he can offer 130 or 140 if there was a demand for it. I highly suggest if you want the cooler stats for your 500s and 300s and 250s to send Thermobob a email expressing interest. It wont happen unless we get a call for them.

ravenous · May 7, 2014

Good to know about thermobobs new low temp stats. I will try
one for sure.
BTW I do run shielding on my bike.
You couldnt have seen the plumbing details with it in
place.So I left it off!

portgrinder · May 8, 2014

nice setup. thats cleaner than mine for sure.

If the stat guy was going to make custom ones, i would get it at 90F

mtn-doo · May 8, 2014

Yes, that would be the ticket for sure. The low temp Thermo-Bob with the recirc line feeding the carb. Integrating the two systems together makes sense and compliment each. That is ideal.

"EVERYONE" send "Bob" an email campaigning for a low temp setup. I emailed him this morning. Here is his address, watt-man@cox.net

That Stat system coupled with a water heat system for carb ice is the goal this summer. We are all working together to get it done.

mtn-doo · May 8, 2014

ravenous said:
My temps were out of control before this setup. In deep powder at slow speeds I would overheat.I saw as high as 250 deg! Riding fast on a real cold day I could not warm up. As low as 80 deg.So I needed some temperature
control. I know some guys are getting away without it,but I can't see
how? The fast warm up you get with a stat is great too.
But like some of you have said 180 deg is kinda warm for a 2 stroke.
So if thermobob wont make a cooler one,I think I will,if possible.
The machine work for the housing would be simple.But maybe low
temp stats are not that common? Does anyone know where to find
one,maybe 130-160 deg?
Or maybe it doesnt matter that much.The old KX is still making great
power at 180 deg.
I did try the tunnel cooler with no stat and it never warmed up.

Yes Rob, There is a 55C stat available. I feel the perfect 2-stroke temp. I have a couple in my shop. They are also a smaller diameter which will be nice in the finished housing. It is the 2002 KTM 200 EXC Stat. Part #54635017000

dhdey · May 8, 2014

ravenous said:
Good to know about thermobobs new low temp stats. I will try
one for sure.
BTW I do run shielding on my bike.
You couldnt have seen the plumbing details with it in
place.So I left it off!

still curious what that exchanger is from?. the skidoo one i have is too big and i think what you have is perfect

and are you gonna make those rings for around the carb intake?, i would be interested in buying one

portgrinder · May 9, 2014

a little off topic here but if you look around you can find little coolers and rads.

theres a real nice small rad that most turbo yama guys take off their machine. its maybe 5in x 5 in. most aftermarket sled shops have tons of them.

if i needed more cooling, ide get one of those and hang it somewhere around the tubing on the front of the tunnel so it would get lots of snow thrown at it. would work good. probably cool twice as good as a sled style cooler

ravenous · Jan 5, 2015

So I have about 30hrs on this setup with thermobobs new 70deg C stat.
It works perfectly. The motor stays in the 150 to 158deg range under all conditions and carb icing is ancient history.I really dont see much benefit to
running cooler than this, but other stats are available now if you think its important to run colder.

summitboy · Jan 5, 2015

Nice job Ravenous. Your setup must be the most stable i have seen yet on the 2 stroke front. Excellent

M5- · Jan 8, 2015

ravenous said:
So I have about 30hrs on this setup with thermobobs new 70deg C stat.
It works perfectly. The motor stays in the 150 to 158deg range under all conditions and carb icing is ancient history.I really dont see much benefit to
running cooler than this, but other stats are available now if you think its important to run colder.

Ravenous. With your current cooler and stat setup are you still running the shielding. I'd like a little more consistency in my setup, temps are still all over the place, too hot on the trail and sometimes too low in the deep but 75% of the they are good.

M5

Carb ice? Not!

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