Avid Carb Heater Install - CR500

jethro450 · Nov 17, 2015

I realize some things seem elementary and therefore no one posts anything about it, but sometimes guys just wanna see pics or video. So here ya go. Avid Carb Heater Install.

I have the Avid carb heater for the stock CR500 carb. Just attempting to fit the two pieces together showed huge differences in size. The carb seemed too big by a ways for fitment.

The carb has a lip on the intake clamp area that was 0.040" or almost 1 mm bigger in diameter than the fitment side of the avid heater. Anyone else have that much of a difference?

Skeptical I could get that much shrinkage and expansion from the two pieces, I tried the "freeze the carb" and "heat the heater" method. I heated the heater to 500 degrees F in the oven for 30 minutes! Froze the carb over night in ice. No go. Not even close. I tried 3 times. Rubber mallet and all.

So I gave up on that and got my dremel out and carefully ground down that lip all the way around, not completely off, keeping it as uniform and even as possible. I didn't re-measure but I bet the difference now was about half what it was before. Now, when both carb and heater were at room temp, I could at least get the heater barely started onto the carb.

Important side note: You have to have that lip. Or at least I did. The flat area behind the lip (where your airboot clamp goes) was actually smaller by 5 thousandths than the carb heater. Meaning the carb heater would just fall off! So I couldn't grind that lip gone because it was/is the part that'll secure the heater on.

At this point a light bulb went on in my brain as I peered :face-icon-small-sho over into the corner of my garage and saw a tool my wife said I would never use and was a waste of money. My press! (To her credit this was the 2nd time I've used it... ever)

So I put wood on both sides and carefully pressed that baby together. It's on pretty darn tight. It might be on for life. But it worked.

I should also mention that I made sure the rotation of the heater was such that hoses would miss the choke lever and clear the top of the carb. I placed a mark on the carb and heater before pressing them together to make sure my rotation was accurate before assembly. See pics.

Clearance to stock shock spring is a few mm (so TSS, being smaller in diameter should be no problem). Clearance to frame is 3/8" or so.

I should mention that this is a 07 CRF450 frame. CR500 motor. But the point of this thread was to just let you know how I got the dang carb heater on. :face-icon-small-hap

Robbie · Nov 18, 2015

Sorry for your problems. I have 5 different carb heater styles. All of them have a different inside diameter. They should be about .005" undersized. There is no way you will be able to expand the heater unit 1/32nd of an inch. I recommend that if you have a problem like this call Avid 1 406 862 6296. You are lucky that you didn't damage your carb.

TheHilltophood · Nov 18, 2015

I also had a problem fitting my carb heater on (Avid carb heater, stock KTM 300 carb)...

I tried the heat and freeze method, didn't work for me either.

I ended up using a flat file, and hand filed the lip of my carb enough so I could slide the heater on by hand. I then removed the carb, wrapped teflon tape on the carb intake for a better seal, then twisted the heater back on. Fits nice and snug.

needpowder · Nov 18, 2015

I had to sand my carb a bit to get it started too.

Hawkster · Nov 18, 2015

There appears to be different opinions here .

Who is throwing whom under the bus here ?

Was the order incorrect ?

It really sucks when you purchase a product and you have to go threw extreme circumstances to make it work if this is the case . It is also sacrilege when one purchases a product as an upgrade and it ends up costing downed ride time .

SEOINAGE · Nov 18, 2015

I knew this thing required sanding of the lip, but it further makes me less interested. I think I'm going to run some hoses around my carb. Just need to find the right kind, and right size valves. Going to route it around carb then right back inline on it's way to radiator, should work if I can find a 5/8" or 15mm valve to stop the direct route to rad.

jethro450 · Nov 18, 2015

I called Avid. And to his defense, I didn't get the carb heater from him, it was given to me. He said the only blue one's he's ever made were for different carbs. So that's why I had to sand/grind it down. No big deal. It's on. I'm happy. If it won't come off, I'll just buy another carb for summer running. :face-icon-small-hap

TheHilltophood · Nov 18, 2015

jethro450 said:
I called Avid. And to his defense, I didn't get the carb heater from him, it was given to me. He said the only blue one's he's ever made were for different carbs. So that's why I had to sand/grind it down. No big deal. It's on. I'm happy. If it won't come off, I'll just buy another carb for summer running. :face-icon-small-hap

Why not just remove the hoses and make/buy some "plugs" for the carb heater inlet & outlet, and just leave the carb heater on in the summer?

wwillf01 · Nov 18, 2015

TheHilltophood said:
Why not just remove the hoses and make/buy some "plugs" for the carb heater inlet & outlet, and just leave the carb heater on in the summer?

Or just put on a shut off valve?

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Answ3r · Nov 19, 2015

I wonder if you could machine a CNC float bowl with heater passage on, so that would require no grinding of the lip and no modification of the carb itself.

That would be sweet.

Sky12 · Feb 16, 2016

avid heater questions

Did you just get the intake heater or did you get the thermostat also? How is everyone dealing with the two outlets out of the head for those using the avid thermostat? Clearence issues with the new tss system?

wwillf01 · Feb 17, 2016

Sky12 said:
Did you just get the intake heater or did you get the thermostat also? How is everyone dealing with the two outlets out of the head for those using the avid thermostat? Clearence issues with the new tss system?

I have a steel frame.. And have both.. The collar fits but has to be retained to run the coolant lines in a different configuration. I went tunnel cooler which gave me more room... Before that it was very tight...

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needpowder · Feb 17, 2016

It fits fine with tss. You do have to **** it sideways a tad to make it clear the frame. I also went tunnel cooler and deleted the left rad so i had plenty of room for the t-stat where the left rad used to be. I think you will still have room though if you plan to run your rads.

Sky12 · Feb 17, 2016

Thanks alot. The guy I talked to at avid said the only tricky part was the cr running two 15mm outlets instead of one 19mm. He seemed to think that in cold Temps the thermostat would never get hot enough to open running both outlets (only one with thermostat). On the contrary if I plug an outlet the single 15mm will choke the cooling system and not allow the coolant to circulate properly to cool the bike. I don't think I would have room to run two separate thermostats and am not sure that would be the answer anyways.

SEOINAGE · Feb 17, 2016

Can I just be the one to say a carb heater isn't needed? I've ran in deep CO powder all season with a cr500.
I'll outline my issues I have had and what I did to fix them.
Hoses would get plugged up and would have to dig the snow out or it ran rich. Put a T in hoses and ran the additional route behind radiator.
Carb slide froze once while I had the gas off and took it apart to jet, soon as fuel got back in it stopped being frozen.
Throttle cable broke open up by bars and snow got in the cable, started sticking. Replaced cable with an oem cable.
Prefilter gets covered in too much powder and runs poorly, wipe it down periodically.
Prefilter broke apart at seam, sucking in snow, big pile behind carb, couldn't keep temps up, ran rich. Slide never stuck even with snow in it, and it was cold. In fact the snow had oil in it from blow back from reeds closing. Duct taped prefilter, cleaned snow out, and temps back up to 120.
Decided to replace prefilter with a larger one that won't need to be wiped off as often, and I get more air flow now.
No thermostat, just my two rads, only overheating issues were on a trail this weekend, with a tail wind that matched my speed or was faster. Got no cooling, stuffed snow behind rads worked for a few miles, then just rode close behind someone and kept temps nice and low.

I know it is just one person, but I have yet to see a need. I have even taken my intake off after a day where the outside of carb was completely iced over, and there was nothing sticking on the inside that could cause performance issues, well no sign of ice at all.

wwillf01 · Feb 17, 2016

SEOINAGE said:
Can I just be the one to say a carb heater isn't needed? I've ran in deep CO powder all season with a cr500.
I'll outline my issues I have had and what I did to fix them.
Hoses would get plugged up and would have to dig the snow out or it ran rich. Put a T in hoses and ran the additional route behind radiator.
Carb slide froze once while I had the gas off and took it apart to jet, soon as fuel got back in it stopped being frozen.
Throttle cable broke open up by bars and snow got in the cable, started sticking. Replaced cable with an oem cable.
Prefilter gets covered in too much powder and runs poorly, wipe it down periodically.
Prefilter broke apart at seam, sucking in snow, big pile behind carb, couldn't keep temps up, ran rich. Slide never stuck even with snow in it, and it was cold. In fact the snow had oil in it from blow back from reeds closing. Duct taped prefilter, cleaned snow out, and temps back up to 120.
Decided to replace prefilter with a larger one that won't need to be wiped off as often, and I get more air flow now.
No thermostat, just my two rads, only overheating issues were on a trail this weekend, with a tail wind that matched my speed or was faster. Got no cooling, stuffed snow behind rads worked for a few miles, then just rode close behind someone and kept temps nice and low.

I know it is just one person, but I have yet to see a need. I have even taken my intake off after a day where the outside of carb was completely iced over, and there was nothing sticking on the inside that could cause performance issues, well no sign of ice at all.

In utah I have seen 4 and 2 strokes freeze... Now letting it idle does free it up in some cases.. Or you can enclose the carb so it catches engine heat... 90 percent of the time not an issue but for the other 10 percent it sucked...

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needpowder · Feb 17, 2016

Sky12 said:
Thanks alot. The guy I talked to at avid said the only tricky part was the cr running two 15mm outlets instead of one 19mm. He seemed to think that in cold Temps the thermostat would never get hot enough to open running both outlets (only one with thermostat). On the contrary if I plug an outlet the single 15mm will choke the cooling system and not allow the coolant to circulate properly to cool the bike. I don't think I would have room to run two separate thermostats and am not sure that would be the answer anyways.

You might be able to fit a thermobob on the right hand side. I think it's a little smaller than the avid. Im thinking up high near the opening in the shroud. Then run your carb heater off the avid t-stat on the other side.

summitboy · Feb 17, 2016

Its too bad that heater is a square block for fitting. Kinda lame how you have to clock it. Its a cost thing. The other issue with it is it only runs coolant down 3 sides not all the way around the venturi.

As far as stats go this is what i can tell you. Its really not needed. Port grinder years ago told us all that lol. The carb heat is much more important than a higher temp engine. I know i know you need temp to keep ice free. Well not really.

What i found with a single outlet TB3 with 1 rad on a CR was it bypassed too much and the temp never really increased in the deep snow. On the trail the tunnel cooler does help but it is also condition dependent. On a cok hard trail even scratchers will only take so much temp off. In the deep snow you get lots of cooling and if you run the carb heat say off the bypass it just is too cold. If you plug the bypass and allow just the tstat to block flow you end up with other issues such as higher cyl temps and increased chances of boil over. I also found the TB3 housing gets so cold that the carb heat line wasn't hot enough.

The best way to run a carb heat line is off the back of the cylinder on the 89-2001 cyl. There is a flat plate that used to have a fitting on the earlier 500's. Drill and tap it and it keeps your line super short to your heat flange. Even if the engine gets to 80F the venturi has been free of ice.

Now i found so far the cooler hasn't been worth the effort for the reduction in temps i see say as compared to a stock type setup. It really is only worth having for up the trail temps imo. Having all the extra hosing etc adds to the reliability of the setup etc.

I've heard guys having stable temps within 5C of stat temp but have never seen this on a CR500 More so it seems like the the KX motor. Now every bike is going to be different because this is very condition dependant. Also my cooler is fairly small but it does work.

wwillf01 · Feb 17, 2016

Sky12 said:
Thanks alot. The guy I talked to at avid said the only tricky part was the cr running two 15mm outlets instead of one 19mm. He seemed to think that in cold Temps the thermostat would never get hot enough to open running both outlets (only one with thermostat). On the contrary if I plug an outlet the single 15mm will choke the cooling system and not allow the coolant to circulate properly to cool the bike. I don't think I would have room to run two separate thermostats and am not sure that would be the answer anyways.

I will post a pic of mine tomorrow for you.

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portgrinder · Feb 17, 2016

I had mine wrapped with clear hose and i think it provided more heat than the Avid setup. I've had my throttle stick due to ice with the avid. i use a valve and turn the flow on/off to the heater as needed. If left on all the time, the slide wont stick.

Mating a machined piece to a cast piece never designed for it is always going to have some issues. i had to grind a few spots to make mine fit. not really a big deal, but it was kindof sold as an easy fitup.

Avid does make quality stuff, and the price was right. I've used them lots in the past. dont really blame them at all. i could have made one better but it would have been likely 4x the price to get machined locally

If anyone wants to wrap with hose, i put pics on here somewhere maybe 3 years ago. it worked slick.

The valve you want is the one used on the XP's carb heater. pretty easy to find.

Avid Carb Heater Install - CR500

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