cr125 weird idle drops down when forks are compressed ?

tomtruxell
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tomtruxell
07 cr 125, it idles good and sounds and runs good, but I noticed when idling good if I compress the forks, or push the bike back and forth, the idle drops down to the point where it almost stalls sometimes. Idle does not fall down if I just compress the rear suspension. Seems weird right? Please let me know if this is an issue that can be fixed?

I did not notice a problem while riding the bike. It has a stock mikuni carb, 45 pilot, runs good, 144 big bore kit, new vforce3 reeds, carb boot clamps are tight. I just recently bought the bike and put it all together after cleaning everything good too. Last night I checked the float height, not with the proper float height gauge but it looked to be around 8.5-9mm, service manual says 7.5mm so I adjusted it and got it looking close to 7.5. Before I did that I noticed the bike had to be pretty much laying on the ground to get any gas to come out the overflow. After adjusting float height the gas will come out when the bike is at about a 45 degree angle leaned over, is that about right?

Thanks!
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Paw Paw 271
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Paw Paw 271 1/20/2017 7:26am
1/20/2017 7:26am
With out knowing all the previous history of the bike I would suggest looking at these things.
1. Float height may be a bit high.
2. The throttle cable routing may be causing a binding and changing the idle.

See if your idle speed changes when you just turn the handle bars from left to right and back. If so, then you have found the issue.

Paw Paw
seth505
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seth505 1/20/2017 7:41am
1/20/2017 7:41am
That is really weird. Also, perhaps check the ignition connections. Just like the throttle cable can bind/be pulled, maybe something weird is going on with the electrical connections under the tank? Good luck

Like mentioned above, it can easily be messed up when turning the bars depending on how the cable is routed and the CDI on the Honda is pretty big behind the # plate there.
tomtruxell
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tomtruxell 1/20/2017 9:49am
1/20/2017 9:49am
Thank you for the replies and suggestions. I will have to check everything tonight after work. I don't really think it's a throttle cable issue I could hear the slide bottoming out when I let go of the throttle and the throttle feels nice. When I got the bike the TPS was unplugged and taped up, I noticed the TPS mechanism on top of the carb slide was sticky and slow to return, and I imagine that's why it was unplugged so I left it unplugged. I've read people say it runs fine with it unplugged. I don't see how that could be causing the weird idle drop issue. Maybe there's an issue with the needle clip and stuff because I did change the needle clip position I'll have to check all that again
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RyanLester761 1/20/2017 10:27am
1/20/2017 10:27am
I was thinking the throttle cable too- or throttle housing. I can picture you pulling the front brake when compressing the forks, and at the same time, rolling the throttle forward. You mentioned the slide is snapping closed, so it doesn't seem likely. You have play in the throttle yes?

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tomtruxell
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tomtruxell 1/20/2017 11:31am
1/20/2017 11:31am
After work I'll do some more testing to figure out exactly how or when the throttle idle drops down. Yes play in the throttle. The first time I noticed this issue was when I was pushing my bike into my basement with it running and at first I thought wow that temperature change really affects the jetting haha and then realized it was from pushing it forward and hitting a small step, or compressing the forks with the front brake on.
tomtruxell
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tomtruxell 1/20/2017 4:07pm
1/20/2017 4:07pm Edited Date/Time 1/20/2017 4:07pm
It seems like its a fuel sloshing/carb issue. When I turn the bars the idle doesn't really change, the cable still has slack. The more aggressively I shake the bike up and down, or the more the fuel sloshes around, the more it will drop the idle very low or stall out. If I lean the bike over about 20 degrees the idle holds very nicely, if I lean it more towards 45 degrees the idle drops low, this could be normal? I was trying to turn up the idle with idle screw but had to go out with the gf..
My buddy has the same bike with a keihin carb I'll ask him to see if his acts the same way.
Thanks
bronwynrayne
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bronwynrayne 1/20/2017 8:49pm
1/20/2017 8:49pm
A very easy thing you could try is a carb rebuild kit, then making sure that your float height is adjusted properly.
Do you have a full tank of gas in it?
tomtruxell
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tomtruxell 1/20/2017 9:22pm
1/20/2017 9:22pm
Ya I just don't see anything wrong with anything though, it doesn't leak gas, everything including the gas shut off valve piece in the carb looks in nice shape, and it wasn't dirty at all. It doesn't seem to make a difference how much gas is in the tank, I've tested it with a smaller amount of gas in it, and more than half full. Nothing changed with the idle when I adjusted the float height from approximately 8.5 mm down to about 7mm, just eyeballing though with a 8mm allen key. The carb is in the correct position in the boots, level. It says TMX05a on the right side of the carb.

Maybe it's just normal I don't know, it didn't seem to be a problem when I was riding it, I've only had one woods ride on the bike though. I just wonder if the gas sloshes around in the bowl, when I bounce the front end up and down, if that just causes more fuel to get sucked up through the pilot circuit or up out of the carb somehow and floods it out, which then I should try a lower fuel lever in the bowl/more float height when adjusting. Thanks.

bronwynrayne
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bronwynrayne 1/21/2017 11:28am
1/21/2017 11:28am
tomtruxell wrote:
Ya I just don't see anything wrong with anything though, it doesn't leak gas, everything including the gas shut off valve piece in the carb looks...
Ya I just don't see anything wrong with anything though, it doesn't leak gas, everything including the gas shut off valve piece in the carb looks in nice shape, and it wasn't dirty at all. It doesn't seem to make a difference how much gas is in the tank, I've tested it with a smaller amount of gas in it, and more than half full. Nothing changed with the idle when I adjusted the float height from approximately 8.5 mm down to about 7mm, just eyeballing though with a 8mm allen key. The carb is in the correct position in the boots, level. It says TMX05a on the right side of the carb.

Maybe it's just normal I don't know, it didn't seem to be a problem when I was riding it, I've only had one woods ride on the bike though. I just wonder if the gas sloshes around in the bowl, when I bounce the front end up and down, if that just causes more fuel to get sucked up through the pilot circuit or up out of the carb somehow and floods it out, which then I should try a lower fuel lever in the bowl/more float height when adjusting. Thanks.

I had an idle issue on my yz and I rebuilt the carb. Everything looked great inside, but it did fix the issue. Not the issue you have persay, but it is a very cheap thing to try. There is obviously something wrong with it, regardless of how it looks to you... if you take your floats out and shake them, they shouldn't make any noise, did you check that aswell?
bronwynrayne
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bronwynrayne 1/21/2017 11:33am
1/21/2017 11:33am
Another thing you can try that I see a lot of people do is to swap out that mikuni for a keihin. The Air Stryker is apparently a common swap. If you continue to have issues with it, that would be worth checking out.

http://motocrosshideout.com/2013/02/21/cr250cr125-pwk-air-striker-conve…

Here is the site I found that info on, it's very comprehensive.
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wsc96 1/21/2017 12:35pm
1/21/2017 12:35pm
The PWK swap worked well on my 250. Haven't done it yet on my 125. Would be interesting to find out what's causing your issue though given it seems uncommon without any other symptoms. Good luck and keep us posted.
seth505
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seth505 1/21/2017 12:41pm
1/21/2017 12:41pm
bronwynrayne wrote:
Another thing you can try that I see a lot of people do is to swap out that mikuni for a keihin. The Air Stryker is...
Another thing you can try that I see a lot of people do is to swap out that mikuni for a keihin. The Air Stryker is apparently a common swap. If you continue to have issues with it, that would be worth checking out.

http://motocrosshideout.com/2013/02/21/cr250cr125-pwk-air-striker-conve…

Here is the site I found that info on, it's very comprehensive.
The bike will rip with the Mikuni on there as long as it's in good working order, mine does.
bronwynrayne
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bronwynrayne 1/21/2017 12:45pm
1/21/2017 12:45pm
bronwynrayne wrote:
Another thing you can try that I see a lot of people do is to swap out that mikuni for a keihin. The Air Stryker is...
Another thing you can try that I see a lot of people do is to swap out that mikuni for a keihin. The Air Stryker is apparently a common swap. If you continue to have issues with it, that would be worth checking out.

http://motocrosshideout.com/2013/02/21/cr250cr125-pwk-air-striker-conve…

Here is the site I found that info on, it's very comprehensive.
seth505 wrote:
The bike will rip with the Mikuni on there as long as it's in good working order, mine does.
Husband's 04 250 ran well with it too, till some unfixable part broke inside of the carb, and stopped working... now we're back with the mikuni but it's doing ok now. Just a little touchy.

Might be worth the cash to pick one up OP!
tomtruxell
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tomtruxell 1/21/2017 4:39pm
1/21/2017 4:39pm
I did not shake the float I guess I should take it back apart and check that. I haven't had a two-stroke in years but this bike seems to run pretty good I don't really have any complaints with the carb besides for this, I do ride friends 2 strokes often enough. I had a 02 cr 250 years ago, I don't remember having any complaints. I have read about the keihin but don't want to spend the money unless I have to. Thank you and I will keep you posted
tomtruxell
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tomtruxell 1/22/2017 12:09pm
1/22/2017 12:09pm
I still have to take apart the carb and inspect everything but this morning I noticed the idle really only drops down when you compress the front end it does not drop down when I shake the bike left and right or if I just compress the rear shock. And the faster I compress the front the more the idle drops down. Also I adjusted more slack into the cable and that did not help and I was pushing down on the handlebar clamps not on the grips this time, no difference. So I wonder what this does to the fuel level in the bowl to cause the engine idle to change. I tested my buddies 02 crf 450 his idle doesn't change haha.
tomtruxell
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tomtruxell 2/6/2017 10:34am
2/6/2017 10:34am
I just took the floats off and shook them and they aren't making any noise or rattling or anything bad. Everything seems perfect. With the bike running I turned off the gas and even when the idle starts surging from running out of gas the idle will still drop down alot when I push the front end down and up. So maybe it's not a float or carb issue, I don't know. The bike runs good, rode it yesterday for a couple hours, but it does have an inconsistent idle when stopping due to this issue, like if I stop on a hill and have to turn around, but it doesn't seem to be an issue while riding since obviously it's not idling while riding.
xnationalwrench 2/6/2017 1:54pm
2/6/2017 1:54pm
Check the left hand crank seal for any lwaking and then spray around the intake manifold and see if you hear/see any difference.
tomtruxell
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tomtruxell 2/6/2017 2:05pm
2/6/2017 2:05pm
Thanks for the suggestions. I sprayed brake cleaner all around the intake manifold between engine and carb and no change in idle. Took off the left side stator cover and it's all dry and clean back in there. This sure is strange.

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tomtruxell
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tomtruxell 2/6/2017 2:15pm
2/6/2017 2:15pm
here's a video. I'm only pushing the front end down with 1 hand. The idle drops down even further and almost stalls or can stall if I push down harder with both arms repeatedly.
xnationalwrench 2/7/2017 7:29am
2/7/2017 7:29am
Have you checked the choke circuit? And while its not the problem your idle seems high, you might set your air mixture screw just to make sure that is off the list. Do you have a shop manual? you might double check the low speed jet and the float level, and then the spark plug cap.
tomtruxell
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tomtruxell 2/7/2017 7:42am
2/7/2017 7:42am
Yeah I the choke circuit looked good and clean, I was spraying brake cleaner through it, and the choke works good like normal. The float was good, I adjusted it a couple times to see if it would make a difference and it didn't, and when the gas is off and the bike is running out of gas the idle will still drop when I push the front end down. Nothing happens when I push the rear of the bike down. I'm thinking it has to be something electrical, which is weird. I've had the idle lower and played with the idle alot and the air screw it didn't help or fix the issue. I have a manual I found online. the spark plug cap seems to snap on normal, what should I check for with that? my buddy has the same bike maybe I can try swapping some parts. thanks
tomtruxell
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tomtruxell 2/7/2017 9:38am
2/7/2017 9:38am
The only other problem is my gas cap doesn't seal good, it leaks a little when I'm riding or have the bike layed over with lots of gas in the tank, gas comes out under the gas cap. Could that be the problem? Some kind of pressure changes in the tank when the gas sloshes around somehow effecting the carb and how much fuel the engine is able to suck in out of the carb? Cause the gas sure does slosh around inside the tank when shaking the front end up and down. But the idle doesn't change when I push the back of the seat down aggressively and only the rear suspension moves.
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mattyhamz2 2/7/2017 10:33am
2/7/2017 10:33am
Have you checked you cables? Sounds like you could have a problem with the throttle cable being routed wrong and when you compress the forks it is taking the tension off of the cable, which allows the idle to drop down.
tomtruxell
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tomtruxell 2/7/2017 10:38am
2/7/2017 10:38am Edited Date/Time 2/7/2017 10:42am
Yes, that's not the problem. The throttle closes all the way, clearly heard and visible, and enough slack in the cable, and idle doesn't change when turning the bars. All the obvious things have been checked. The fuel shut off plunger looks like new and everything works right it seems. The needle is tight, doesn't move independently.
tomtruxell
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tomtruxell 2/7/2017 2:02pm
2/7/2017 2:02pm
Here's the latest observations, if I just roll the bike backwards real quick I can make it stall that's how much the idle drops, and it drops more pulling the bike backwards than pushing it forward. And no it has nothing to do with pulling on the throttle. If I push down on the seat idle does not change. If I lean the bike all the way over to the left side the idle doesn't change!, and gas leaks out the overflow. It's so crazy weird. I'm gonna take it over my buddies and hopefully swap carbs, he has a keihin on his same bike. I also did some tests with the gas cap loose and tight and that didn't make a difference.
xnationalwrench 2/7/2017 2:22pm
2/7/2017 2:22pm
tomtruxell wrote:
Yeah I the choke circuit looked good and clean, I was spraying brake cleaner through it, and the choke works good like normal. The float was...
Yeah I the choke circuit looked good and clean, I was spraying brake cleaner through it, and the choke works good like normal. The float was good, I adjusted it a couple times to see if it would make a difference and it didn't, and when the gas is off and the bike is running out of gas the idle will still drop when I push the front end down. Nothing happens when I push the rear of the bike down. I'm thinking it has to be something electrical, which is weird. I've had the idle lower and played with the idle alot and the air screw it didn't help or fix the issue. I have a manual I found online. the spark plug cap seems to snap on normal, what should I check for with that? my buddy has the same bike maybe I can try swapping some parts. thanks
Check the plug wire (without the cap on) with a meter then check with the cap on. If the fuel cap blocked remove the cap with a small amount of gas in the tank and start it up to see if that cures the problem.
tomtruxell
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tomtruxell 2/7/2017 7:07pm
2/7/2017 7:07pm
We put my buddies keihin carb off his 07 cr 125 on my bike and it pretty much fixed the problem, although not 100% but it was pretty good and my idle would only barely noticeably drop a tiny bit when I did all the things that would make my idle drop a huge amount or stall with the mikuni carb on my bike. We put the mikuni back on and it still almost stalls or will still when I pull the bike backwards real quick. But on his bike with his keihin carb his idle just not change whatsoever when I do the tests. we did not try my mikuni carb on his bike, didn't think of it till now haha.

So I think I'm just gonna get a keihin carb for my bike, I can't figure out anything wrong with the mikuni carb. his keihin has no tps and I think it's a longer carb cause the air boot and subframe doesn't fit as easily. His bike has boyesen reed cage and mine has vforce3 and mine has 144 big bore.
mattyhamz2
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mattyhamz2 2/8/2017 7:22am
2/8/2017 7:22am
I know you said it wasn't the cable, but is there any play in the throttle with your carb on the bike?
tomtruxell
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tomtruxell 2/14/2017 9:28am
2/14/2017 9:28am
I think I figured out the problem! The carb vent hoses were probably not routed correctly. When I bought the bike the carb was in a box, clean with brand new vent hoses. I bet they were routed wrong, because I put on a keihin carb from a 2000 cr 250 and I transferred the hoses over to the keihin carb, because the keihin hoses looked very bad, and I got confused and I'm now sure I didn't route the hoses correctly and the bike stalls when I pull it backwards or compress the forks quickly. After work I'll fix it up and update.

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