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Post by 926am on Jun 13, 2020 10:50:49 GMT -5
Hello, I’m getting popping/backfiring/lose of power when I back-off wide-open-throttle. I have a rock crawler cam, which I’ve read could be off even when installed correctly. Can the timing be checked w/a timing gun? I’d hate to try the ‘reinstall a tooth off’ method til it works.
What’s strange is that this problem occurs when hot. Its fine when warm/cold. And wot is mostly good. Could this indicate a fuel mix problem? (Jets, vac leak, etc) I’ve went up & down in main jet size but the nature of the problem remains exactly same. (#145 main/ 40 idle)
I know its hard (Impossible!)to diagnose over the net, but I’m just looking for suggestions. It has a 32mm carb, k&n air filter, & stainless exhaust.(stock cdi) Plug reading looks textbook (medium-dark gray) Gasoline is fresh, gas filter is new.
Could a petcock be restricting fuel flow? Wouldn’t that happen at wot also? Can this be checked?
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Post by chewbaca on Jun 13, 2020 14:46:50 GMT -5
sounds like a possible vacuum leak and a probable exhaust leak
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Post by 926am on Jun 13, 2020 15:03:54 GMT -5
Yeah I was thinking that too.
Places to check: air filter, intake manifold, exhaust manifold. Am I missing any?
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Post by chewbaca on Jun 13, 2020 15:11:46 GMT -5
take the exhaust pipe off and look for black outside the seal and then just replace the gasket with a new one then replace all the vacuum line with new better quality stuff. both are super cheap to do and the stock vacuum line is very poor quality.
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Post by 926am on Jun 14, 2020 10:54:17 GMT -5
Ok, I replaced intake gasket & tightened carb clamp. Slip-on muffler seemed a little loose so I used a pipe expander to tighten it up. Tightened up exhaust manifold bolts. I took for a test ride but no change. Checked valve adjust-good. (Adjusted between loud chatter and rpm drop)
While I wait for a new exhaust gasket, could this problem be ignition? Could a faulty coil perform well when warm/cold but fail near wot?
(I start driving the bike after I hear the choke come off, rpms & power are always smooth right up to wot & as I roll off. After 10 min at high speeds (50-60mph) is when prob starts. Always when I roll off from wot.)
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Post by chewbaca on Jun 14, 2020 21:50:01 GMT -5
do you drop all the way down or just let of a little?
the idle circuit is extra rich to help keep the cylinder cool at idle, but at higher rpm it can pump a overly rich mix
into a hot exhaust system and the extra fuel will pop if it doesn't cool before it hits the O2
so a leak or a shorty without a cat or even a wrap can all do that
the feeling of power loss can be attributed to the engine breaking that happens automatically. It's different than what someone used to a motorcycle with gears and a clutch would feel
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Post by 926am on Jun 15, 2020 10:46:55 GMT -5
Its only when i back off a little. As I drop to mid-throttle (or less) power is smooth.
I know these motors can be sensitive especially when there are mods.
Its just so strange that its good when cold but not when hot.
I have a new exhaust gasket on order, but I was looking for other possibilities.
You think I should try to lean out the idle circuit?
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Post by chewbaca on Jun 16, 2020 9:14:18 GMT -5
no you kinda need the idle a little rich so your motor stays cool at idle. there isn't really enough rpm to cool it well with the fan and when you are not moving the block gets no cooling at all. it would be worth doing if you had an oil cooler though
you can get something like what you are describing with a partial intake blockage
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Post by 926am on Jun 16, 2020 13:04:48 GMT -5
Or could it be a blown head gasket? No visible leakage for oil or coolant. Perhaps I should retorque the head...
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Post by chewbaca on Jun 16, 2020 20:51:56 GMT -5
well if you want to check the head for leaks it's best to just get a new gasket and crack it open. A leak will cut a channel in the soft metal and you must remove the channel or the leak will come back quickly and worse even with a new gasket. You can do it yourself buy honing the damaged surface with 600 grit wet-dry sand paper and WD40 on a flat piece of glass.
coffee table stereo cabinet doors mirrors all work well as long a you can't see ripples in them
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Post by dollartwentyfive on Jun 18, 2020 9:10:18 GMT -5
Hello, I’m getting popping/backfiring/lose of power when I back-off wide-open-throttle. I have a rock crawler cam, which I’ve read could be off even when installed correctly. Can the timing be checked w/a timing gun? I’d hate to try the ‘reinstall a tooth off’ method til it works. What’s strange is that this problem occurs when hot. Its fine when warm/cold. And wot is mostly good. Could this indicate a fuel mix problem? (Jets, vac leak, etc) I’ve went up & down in main jet size but the nature of the problem remains exactly same. (#145 main/ 40 idle) I know its hard (Impossible!)to diagnose over the net, but I’m just looking for suggestions. It has a 32mm carb, k&n air filter, & stainless exhaust.(stock cdi) Plug reading looks textbook (medium-dark gray) Gasoline is fresh, gas filter is new. Could a petcock be restricting fuel flow? Wouldn’t that happen at wot also? Can this be checked? this is a carburetor problem. air bypass valve to be exact. the hose has come loose, has rotted, or the diaphragm has rotted. i'll have to take a look at mine to give specifics.
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Post by dollartwentyfive on Jun 18, 2020 9:24:42 GMT -5
ok, like i said, it's the air bypassvalve, and it is operated by manifold vacuum.
i've eliminated the vacuum operated gas valve, replacing it with a manual shutoff.
my manifold vacuum connects directly to the air bypass valve and nothing else.
there are 2 ports on the valve. one on top that points backward, this connects to the manifold
the other one points to the left and connects to a port on the left side of the carb.
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Post by 926am on Jun 18, 2020 18:50:25 GMT -5
I have an aftermarket carb, so I don’t think I have a bypass valve. My intake manifold vacuum fitting is blocked off (rubber cap.) I wrote that the problem only occurs when warm & wot, but I think high rpms/speed is more accurate. When I give it full throttle from a stand still it seems pretty smooth. Only when doing 45-55 mph do I encounter the problem.
Its been a challenging problem. First I thought it was bad gas (there was rust in tank) so I cleaned it out & put in a tank liner. Fuel filter was still catching particles after, so I drained & cleaned out the lines/carb cleaning. Then, the muffler was getting loose so I fixed that. Checked cyl head bolts & one seemed less tight than others.
Currently: waiting on exhaust manifold gasket, and head gasket. Frustrating!
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Post by dollartwentyfive on Jun 18, 2020 20:05:59 GMT -5
I have an aftermarket carb, so I don’t think I have a bypass valve. that's what air bypass valves are for, to prevent backfires on deceleration. i believe you are throwing a lot of unneeded repairs at this problem.
another thing you should be aware of with the cfmoto 244. the "choke" is run off the alternater. if you have purchased a 12v model of this choke, it won't last long. i've burned out 3 of them before i discovered this. i found a workaround but it wasn't easy to fabricate. the problem is you simply can't remove it or unplug it, you have to disable it in the "off" position. if your ride doesn't perform well, then this can be your problem. but the backfires are caused by the missing air bypass valve. i've put over 10,000 miles on my 244 so i know my way around them.
good luck.
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Post by 926am on Jun 19, 2020 6:22:27 GMT -5
Yes, I feel I am throwing a lot of repairs at this issue too! But thankfully its not my main bike so I can take some time w/it.
Does the air bypass valve have another name? I googled it for my cvk carb but couldn’t find anything in the diagrams, and everything is connected properly.
The choke seems to be working perfectly. Its a genuine Honda unit & the system is 12volt. It pulls off after about 3-5 min.
Getting back to the timing, its an after-market cam (endigo rock crawler) & I’ve read that these could be off by a couple teeth & the motor will start and run fine, except for higher rpms. I have a timing light gun, can this be checked?
Thanks for any insights.
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