My thoughts on chinadoll break-in procedure.

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Davezilla

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Mar 15, 2014
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The idle with the longer dogleg intakes could be a result of the fuel in the blowback staying in the manifold so its idling way rich and wont idle any lower without killing the engine... of course if you have an idle mixture circuit and adjuster on your carb the engines tend to like a little more fuel at idle in order to idle nice and smooth, but that's what works on a 4 stroke or a 2 stroke with a reed valve where there's no blowback to deal with. On the shorty intakes the blowback just sends that fuel out the carb intake so it may go a bit richer at idle but not as rich as if most if not all the fuel in the blowback can linger in a long intake instead of most of it blowing out the carb.
 

mapbike

Well-Known Member
Mar 14, 2010
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The idle with the longer dogleg intakes could be a result of the fuel in the blowback staying in the manifold so its idling way rich and wont idle any lower without killing the engine... of course if you have an idle mixture circuit and adjuster on your carb the engines tend to like a little more fuel at idle in order to idle nice and smooth, but that's what works on a 4 stroke or a 2 stroke with a reed valve where there's no blowback to deal with. On the shorty intakes the blowback just sends that fuel out the carb intake so it may go a bit richer at idle but not as rich as if most if not all the fuel in the blowback can linger in a long intake instead of most of it blowing out the carb.
Yes and the initial fuel air mix has to travel farther and cant be effected more by that blowback as there is more chance for the two to crash together in route at low rpms.
 

bluegoatwoods

Active Member
Jul 29, 2012
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Interesting thread, Maniac. Thanks.

I can't claim that I really understood it all that well. I have the 'basic' understanding that the carb takes air and mixes it with fuel that has been aerosol-ized. (If that's the right word) But the dynamics of the flow through the intake is all new to me.

But that doesn't mean that I can't learn it. I guess it's about time to put the 'search' function to use. And I'll also have to revisit that thread and see if I can't get a better picture in my mind as to just how that apparatus of cannonball's is constructed.
 

GoreWound

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Dec 1, 2014
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my exhaust is off right now, and I am just about at the end of my break in period (I am sure I could just fill it up with a lighter oil mix than ~20/1 but I just want to finish off my Gerry-can first) so i can take some pictures just for a comparison.

like I said I'm roughly at 20/1 but I'm not using any fancy brand of oil, mine came from the gas station.

I haven't been riding her hard but I've not been babying it either.
85% of the break in has been done with a stock carburetor, the rest with an SHA clone.

so we are looking at a fairly heavy oil/gas mix and a very heavy gas/air mix.
i'll be back with pictures in a moment.

edit: here's a picture, my ipod died after taking it so i guess if i should take more I gotta wait.
 

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Eric2.0

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Sep 22, 2010
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So many different ideas on break-in. I even heard you use normal two stroke oil at first, because Synthetic is so slippery that it won't let the rings break in well. Then switch to synthetic.

Oyy vey.
 

Davezilla

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Mar 15, 2014
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So many different ideas on break-in. I even heard you use normal two stroke oil at first, because Synthetic is so slippery that it won't let the rings break in well. Then switch to synthetic.

Oyy vey.
it's ideal to use regular dino oil at first but not totally mandatory... the problem with most synthetics is that they are too slick and may not let the rings fully seat, I'm pretty sure this myth has been busted by now but on the other hand, it'll definitely break in better on dino or a special break in oil that some companies make for 2 smokers.
I like to run dino oil for the first tank then switch to the intended mixture for the rest of the life of the engines. Seating the rings is done by placing a heavy load on them by making lots of cylinder pressure... that means LOTS of full throttle acelerations then slow back down and do it again. Staying at any speed won't push out the rings as hard as a full throttle burst as cylinder pressure will always be highest under load at full throttle.

The most important thing to remember about breaking in an engine is to not let it overheat, and a fresh engine can overheat rather quickly since there's a lot of extra friction on the rings and cylinder wall so the easiest way to avoid overheating is to keep your trips short, no more than 10 minutes for the first run, then go up to 15 minutes for the next several runs. It's best to let the engine cool all the way down between runs also since running it for 15 minutes, then giving it a 10 minute break won't let the engine cool very much, then on the next 15 minute run it'll be at or above operating temp by the time it has run for around 5 minutes. These engines cool down pretty fast and 30 minutes is enough time to let one cool, it also helps to place a fan blowing at the engine but not totally necessary as using a fan to cool it down may bring the time from 30 minutes down to 25 etc...

Once you've got about 5 or 6 15 minute runs in it's safe to bring the run times up to 30 minutes or more if you wish, by this time the rings are still far from seated but you should notice the engine loosening up a little. By the time you're done with the first tank of fuel you can run it as long as you wish but keep an eye on the temperature. I use an infrared "point and shoot" thermometer to watch mine by parking the bike and taking a quick reading. These can safely run at temps as high as 360F but some people like to keep them under 300F. at somewhere around 400F is where damage starts to happen like scuffing the inner cylinder walls or even seizing a piston.
Part of the overheat prevention is done for you at the factory because they set up these carbs really rich and this helps keep things nice and cool, a Fred head or a Puch head, or any large billet or cast head will also keep the temps in check really well. Mine stayed at around 320F during break in with a Fred head installed. There are a few billet heads that won't help the cooling that much like the ashtray head, the RSE head, and I've seen another smallish square shaped billet head with really thick fins that wouldn't be able to keep a fresh engine cool enough for a long run on a fresh engine. The stock heads are the worst hands down for keeping things cool so keep trips short as I mentioned earlier if breaking one in with a stock head... Also, this is NOT the time to tune the carb if you got a stock or one of the small billet heads... let it break in first then you can lean it out afterwards, these heads will get up to 360+ rather quickly as it is.

It's ok to swap carbs on a fresh engine too, just set it up a few jet sizes richer.

The whole break in procedure is really doing only 2 things... loading up the engine to seat the rings, and keeping the trips short to prevent overheating... Just about everyone's procedure covers these 2 parts in their procedure and the rest of the break in can be done however you choose, the main idea is to not let it get too hot in this time because of the extra friction until the rings match up to the cylinder better and better.
 

bluegoatwoods

Active Member
Jul 29, 2012
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Central Illinois
A little update on my progress. I'm breaking in a brand new engine right now. Mostly because of this thread, I decided to break it in using my normal running mix. This is a 40:1 mix using 2 stroke oil bought at an auto parts store. I'm sure it's petroleum oil. But I don't know anything else about it. It doesn't appear to be anything special.

Results seem good at the (nearly) 2 gallon mark. Engine is smooth. 4-stroking does not occur when the engine is warmed up unless the choke is closed. It has good power at low revs.

There is a hill on my commute that is steep and long enough that very few people will pedal all the way up. I do. And my kids have done so. But whenever I see another bicyclist on that hill, they're walking the bike. I've been climbing this hill at, I estimate, 15 mph on only partial throttle. Less than half.

The engine seems to be a little more cold-blooded than previous happy times I've had. It seems to want a bit more choke. But I've been riding in fairly cold temps. We'll see what happens when it gets a bit warmer.

I went through my first gallon or so using an NGK spark plug that I'd used in a previous engine. Back then, it had a nice color to it. After running a bit in this engine I took a look at it and it seemed a bit white-ish. So I pulled out my carb needle in order to make the mix a bit more rich. I found that I was on notch 4 of 5 toward the rich end. Toward the end of the needle. That seemed strange. I went ahead and put it on the lowest notch, figuring that going rich was preferrable to going lean. For the time being, anyway.

I also put in the fresh spark plug that came with the engine. I suppose I've run it about 70 miles on this plug. I plan to do some mods on the bike tomorrow. I'll have a look at at that new spark plug as well.

So I've got a couple of small indications that I might be running leaner than I'd like. I'll try to verify that and correct it, if necessary.

But all-in-all, breaking it in at 40:1 seems to have worked well enough. Engine seems to be running good.
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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Here's another example of one of my break-in's
This motor is on my Occ jackshaft chopper and has about three tanks through it so far...pulled it today to repair a stripped exhaust stud.
This is the view in the exhaust port.
Notice the nice even ring face and very little blow-by evidence?
It has good ring seal and compression and was broken in on 40:1 right from the start like this thread describes.



Looks good to go for several thousand happy trouble free miles....