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WOT engine bogs and dies 125 2 stroke

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2007 Suzuki RM 125 

High RPM the motor just cuts out totally and bogs to a stall. When I try to start the motor again it’s very hard to start. Now that’s it’s happened to me so many times I just reach down (motor always looks way hotter than normal when this happens) and turn the fuel lever off and pop the fuel line off between the tank and in-line filter (so dirt doesn’t get past the filter into the carb) and kick the bike over a few times and when it starts again I put the line back on and fuel lever to on. Since I haven’t figured it out yet I just completely try to avoid high revving the bike or wide open throttle (and that sucks because it’s a 125) On long straights or hills, or exiting corners, seems to be when this happens the most (and on jump faces) I’ve all stock jets and carburetor settings (since this has been happening I replaced the #370 main, with the #400 but I suspect the float height is also set too high, or worse worrying that the powerjet is getting stuck open. But I’ve also talked to other people at the track who have the same issue on a 2014+ KX85 which doesn’t have a powerjet as far as I’m aware, and having the same issues, so I don’t know if it’s the float height again or too lean a main jet... there’s also bikes that sound very lean on the main but are hammering all the jumps and not having problems with the motor bogging completely, really hoping someone is familiar with this issue and can help shed some light on the problem! Thank you for your time!

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9 minutes ago, Borthwick203 said:

2007 Suzuki RM 125 

High RPM the motor just cuts out totally and bogs to a stall. When I try to start the motor again it’s very hard to start. Now that’s it’s happened to me so many times I just reach down (motor always looks way hotter than normal when this happens) and turn the fuel lever off and pop the fuel line off between the tank and in-line filter (so dirt doesn’t get past the filter into the carb) and kick the bike over a few times and when it starts again I put the line back on and fuel lever to on. Since I haven’t figured it out yet I just completely try to avoid high revving the bike or wide open throttle (and that sucks because it’s a 125) On long straights or hills, or exiting corners, seems to be when this happens the most (and on jump faces) I’ve all stock jets and carburetor settings (since this has been happening I replaced the #370 main, with the #400 but I suspect the float height is also set too high, or worse worrying that the powerjet is getting stuck open. But I’ve also talked to other people at the track who have the same issue on a 2014+ KX85 which doesn’t have a powerjet as far as I’m aware, and having the same issues, so I don’t know if it’s the float height again or too lean a main jet... there’s also bikes that sound very lean on the main but are hammering all the jumps and not having problems with the motor bogging completely, really hoping someone is familiar with this issue and can help shed some light on the problem! Thank you for your time!

Had an 05 CR 125 with the same issue. The problem was too lean on the main jet. Does yours stumble before it dies or does it just reach a certain point and bog out. Is there lots of spooge and smoke? Also check your needle clip position.

With my CR it turned out that the powervalve Linkage was also busted and it was stuck closed. So check That your engine is mechanically sound as well

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First thought is lean= partially clogged jet, power valve all gunked up causing poor high rpm issues due to being stuck, might be a good idea to clean out your carb and jets to see if that helps... Most issues are carb related with my limited experience, i had to remove the jug on my cr80 once or twice a year to clean up the powervalve and check rings. (Im a clean freak when it comes to my 32/1 mix old 2 smoker)

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in this video it happens, and yes like will05w says there is sort of a stumble right before the worst of the bog so there is almost a warning sign of it

powerwashed the bike, pulled the carb, cleaned, adjusted float height, got everything really really clean, assembled, and then pulled the carb again to adjust the float height again and cleaned some more

everything is really clean, the float height was too high before and was always spilling thru the overflow, now the bike can be tilted over without overflowing so might need a little more adjustment because i think fuel should spill out when tilted over at 22.5• angle ... 

i can only think now that it is truly the main jet that’s too lean and causing the problem, but will go thru everything to be sure, looking at ordering a #440 and #470 main (up from #370 stock) (needle clip in middle position) and manual says 30:1 but with the main jet being so lean i’ve mixed 28:1, 26:1, 24:1, 20:1 now just to make it more rideable 

 

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I would not recommend going morefuel/oil mixture the manufacturer recommends as that causes problems itself, most 2 strokes  do better in the higher rpms with less oil in the mix, when i tode my cr80 i did 32/1 for trail riding, and 40/1 when blasting around the track(built motor with non stock internals) this was what i did to get my little bugger to rev to 14,000 rpm or so, might recommend goong with some amsoil dominator oil or even castor oil and going 32/1 on the mix with fresh mix and see if that helps

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On 6/27/2020 at 2:21 PM, DanDeVries said:

Have you looked at the spark plug what color is it?

half is a nice mocha and other is a bit darker but not black/oily, and there is some carbon build up, the gap was out of spec also over 30 and we brought it back within spec i think 26, is it normal for the plug color to be split half/half like that?

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Fixing the float height cured a similar problem for me. Honestly, it sounds like you are still struggling to get yours set correctly. Anything disrupting uninterrupted fuel flow is suspect. A friend struggled with this for most of a year, and discovered a previous owner installed the wrong petcock which had a higher pickup point for reserve. If your bike has a reserve setting, try running it on that setting. Then check your petcock internal screen, and your needle/seat assembly. As previously mentioned, if it ran well before, jetting shouldn’t be the issue. However, I once had a small piece of debris temporarily partially block my main jet. Have you looked through it for a perfect clean circle with backlighting? The carb should overflow fuel when you tilt the bike on it’s side. 

Edited by motrock93b
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7 hours ago, Borthwick203 said:

half is a nice mocha and other is a bit darker but not black/oily, and there is some carbon build up, the gap was out of spec also over 30 and we brought it back within spec i think 26, is it normal for the plug color to be split half/half like that?

I would put a new plug in and see what it looks like after a ride I would also go back to the jetting that was working before the problem started 

 

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i have the float height adjusted now so it will overflow when tilted over but not when stood upright and the fuel flow seems good, definitely better flow with a lot of fuel in the tank, and a new sparkplug from the oem parts fiche, and have another larger main jet on the way, and after draining the fuel and disassembling the petcock found out the filter was very dirty and the inner seal for the on/off was damaged by ethanol, i would go back to the stock original jetting but i can’t imagine the motor running mechanically sound for very long as the main jet was really just way too lean, and to imagine the previous owner recommended 36:1 in north carolina i’m really confused, because here in massachusetts 30:1 (stock, by the book) was just way too lean, the first time i rode the bike was after i got home and it’s always been like this, i think maybe the reefs are boyosen and it has a fmf sst/powercore2 , i’ve tried both either AV100LL 20:1 or 24:1 premix ratio, i think i’m getting closer and the motor isn’t bogging/turning off like it was before, just really surprised me to change so many sizes on the main jet and not have more of an effect, i guess that’s a very slight adjustment when only changing one size, i think the needle will be adjusted a little bit next i’m going for a lean and clean bottom for technical riding then more fuel in the mid and up to help smooth out the power

Edited by Borthwick203

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Posted (edited)

I know this is hard to digest, but 30:1 fuel mix will cause your bike to run leaner than 32:1.

Look at it this way: the more oil in your premix the less fuel that is available to burn. It then requires more air to burn efficiently.  Dont go below 32:1 on your mixture, you would probably benefit to a 36:1 or so the way it sounds.

Edited by Trevor Spires

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30:1 32:1 36:1 will make it run no different at all 

Even 50:1 probably would not make a difference

It does sound lean on main jet 

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9 hours ago, Trevor Spires said:

"It then requires more air to burn efficiently."

You got that part backwards. 

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Sounds very lean on the main to me also. Also sounded like a 65 in 2nd gear pinned without mercy. You sure its a 125, those chinese are iffy.

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