Motobecane av10 ripper heating up

Jonathan Feldman /

I've been battling this for awhile and I'm ready to hear what all y'all think of my issue.

Essentially, my bike heats up slowly ( but surely) to 400 degrees on straight aways. Doesn't need to be WOT / full variation. Itll heat up doin like 40 at part throttle as well. With this being said, it does not run STUPID HOT. I've had bikes that have run HOT AS FUCK and this doesn't fall in that category. It cools off pretty well sitting at idle, temps drop pretty consistently.

The set up: av10 / Doppler 50 cylinder / Doppler head ( squish ~1.2mm ) / some rando carbon reeds / gianelli black gun pipe / 19 oko / le Partie cdi ( 1mm timing) / er3 clutchless / Doppler clutch pulley.

I don't think it's a lean issue for a couple reasons but I could be wrong. I've had this set up mounted on two different av10 bottom ends and both did the exact same thing. None ran cooler than the other. Also I'm jetted about as rich I can right now. Take off is four strokey as fuck till the pipe starts to hit. Even with clutch pulley. It's given that with a multi circuit carb you should be able to perfectly tune it all the way through the throttle range but... with how peaky the Doppler 50 / black gun is, it feels kinda hard. I'm not sure how to jet it to rev clean off the pipe while not going lean on the pipe. Also, I've ran a 19 phbg / 21 phbg as well. Same exact shit. Also, I've sprayed the bitch down with carb cleaner.. didn't really come up with shit.

Thanks for reading that, only a bit more I promise.

I have a couple hypotheses on my issue but I'm not sure how wingnutty each one is.

1. Black gun is just too peaky for daily riding. I've heard this from a couple people and while I don't fully understand how the different cone sizes / header lengths etc would affect temps but I'm willing to consider it. I've had Doppler pipes on Peugeots and definitely have noticed a less peaky / more broad powerband. Additionally those bikes didn't have this issue.. but they were Peugeot so it's kind of hard to compare.

2. Clutch pulley ( this one would make the least sense ) but all I can think of is that it's forcing the engine to rev high even at mid range throttle / low speeds. And it's just forcing it to heat up.

3. Inadequate cooling head ( probably makes the most sense ). This has been a battle for French bikes as long as time has existed and it's worth keeping in mind. Many people who have literally my exact set up claim low ass temps but it's just so hard for me to believe. When I put a derbi head on my peugeot, it was a fuckin game changer. Dropped 40 degrees easy. I can rip that bike all day with no issues. God I wish I could say that about the Moby.

The only readily available head that I can think of that has significantly more surface area is the polini head. Admittedly it has a dome / squishband that's a total bag of ass but regardless it is one honkin thicc ass head. I know it's 70cc but I'd still consider giving it a go with a lot of dremel work to the combustion chamber etc.

The bidalot head looks absolutely beautiful in everyway but god damnit I dunno how to find one. I guess I could buy the mvt kit and steal the head off but woof that sounds expensive just for a head.

last fuckin thing, I know a lot of people just go " whatever rip it, shit just runs hot. " but I still ain't accepting it. I honestly think it's possible to build a everyday ripper av10 Moby. Yay. Dreams.

Alright that's all I got, hit me with y'all ideas / thoughts / feedback as a whole. Thanks. XOXO, Jon(edited)

IMG_20181212_161806_446.jpg

Re: Motobecane av10 ripper heating up

I don’t have any advice or comment other than to tell you I love this bike and it looks p good, and I don’t usually like the frenchy bikes much.

I hope you figure it out but WHATEVER BB ITS A FASS MOPAD IT RUN HOT ITS Kewl JUS RIP IT

Re: Motobecane av10 ripper heating up

What's the compression? Frenchies do run hot, would be nice to have a liquid cooled head that fits on Moby/Peugeot.

Re: Motobecane av10 ripper heating up

400 degrees is it all that hot but it sounds like your idle circuit jet needs to be leaner 42 - 45 so you can run your needle a little bit richer.

You should be running a w 7 or w 5 needle.

Is your timing at 1.2 mm or 1 m m.

You need to get your squash down to at least a .9 mm preferably .75 mm.

And hopefully you're running a 7 or 8 on the spark plug keep it cool.

But with wide open blasting you should be hitting 400 + no problem should be plenty safe up to about 430f all day on a Moby.

Re: Motobecane av10 ripper heating up

^^^ crazy wayne over here. nobody says "squash" instead of "squish" except for his crazy fucking ass

Re: Motobecane av10 ripper heating up

I think Sean is on the right track. Leaning out your idle mixture should help eliminate the low throttle rich condition and give you a little head room to add some fuel up top.

That said, my setup is almost identical (slightly different carb and reeds) and that fucker just runs hot as hell. Mine isn't running particularly well at the moment (I'm redoing a bunch of stuff and it's all torn apart), but it got up to around 400°F pretty reliably during races. As long as it didn't go much higher than that, it would rip along happily at 13000RPM all day long. As long as you're below 430° or so, you'll probably be fine in the short term (although I imagine it will accelerate cylinder wear pretty prodigiously).

Another Frenchy-specific issue you might be experiencing is float bowl foaming; the engine isn't really attached to anything, so it tends to vibrate around like a dog shitting a peach pit. Particularly if you have a big long donky-dick intake, the vibration at certain RPMs can be enough to whip the fuel in your float bowl into a froth. As you can imagine, having a bunch of bubbles in your float bowl causes weird transient lean spikes that are pretty much impossible to tune for. The vibration on my bike was so bad it actually broke the casting on my old VM18 carb, and I'm having a ton of difficulty dialing in my OKO because of it. That could be contributing to a lean condition at certain RPMs.

The carb angle change as the engine variates could also be an issue, but that usually causes a rich condition at high RPM, not a lean one. If your carb is spigot mount, you could try cocking it a little bit and seeing if it makes a difference.

If you're concerned about it, watercooling the head is pretty common on Frenchies. Do some searching in the forums; there are a few guides floating around on sealing the waterjacket to allow you to use a watercooled head on an air cooled cylinder. I know of at least one guy who uses a thermosyphon setup (no water pump) on a race bike with no issues, so I imagine it should work just fine on a street bike. I'm reasonably sure Doppler makes (or at least made) a watercooled cylinder with more or less identical geometry to the air cooled version, so you should be able to install that head without messing with the squish too much.

Also, rad bike. I dig it.

Re: Motobecane av10 ripper heating up

first of all, a high performance french build that runs over 400 but under 450 is like the ne plus ultra magic unicorn awesome jamz. heat is power and i'm a firm believer that you want to get that sucker as hot as you possibly can without seizing it. 450 is flirting with disaster but if it stops there you are perfecto. I think the magic number on these is like 430 for steady state blasting but it will climb if you load it.

its all in the head on these bikes, not even so much the mass/finnage but in the chamber. pretty much every aftermarket frenchie chamber is setup stupid IMO. too divergent with too much surface area. you need to cut that back to like 40-45% which amounts to like a 4-5 mm wide band around the outside. then you gotta get down like 6 or 7 percent divergent which means a parabolic cut, and nuzzle that piston right up to it for 1mm or less at the edge.

still, i don't think you're going to get much better when you're on the potato. I'd just maybe pull the head back off (eh, moby, that sucks) or maybe use a cheap borescope- been meaning to get one of those cell phone jobbies that cost like 20 bucks... and see if you're getting a clean wash pattern on the piston or excessive carbon/burnt oil.

if youre not seizing and your not burning a bunch of carbon on the piston (which will eventually seize) i'd say you're good to go. learn to stop worrying and love the bomb.

Re: Motobecane av10 ripper heating up

Get someone make you a WC head. Best thing ever.

Run high timing, high comp, no prob

Re: Motobecane av10 ripper heating up

^I think someone just volunteered

Re: Motobecane av10 ripper heating up

Cristian Luna /

Ugh this makes me want to get my 40t back on the road

« Go to Topic — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account