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2004 rm125 bogging problem

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Hi there. Need some advice with my 2004 rm125

I’m not very good at explaining these things but Ill try and be as in depth as I can

Bike

2004 RM125. Vhm cylinder head (with a stock insert) Fmf sst pipe and shorty silencer. Boyesen carbon reeds.

Fault

I have a ‘bogging’ problem. This started at Wilden Lane just over a month ago. It would bog down as if I was in too high a gear. I fitted a new plug and the problem had gone. At the next round a couple of weeks later it did it again, and changing the plug didn’t help. I found my vhm cylinder head had split and was leaking coolant. Also when I taken the head off the inner o ring had split and let some coolant into the cylinder. Also, some of you may remember my post a few weeks back, the insert on the head had several nasty looking dents in, as if the previous owner had got some debris in there, or lost a circlip or something?

Repair

I found a new vhm head at a discount price so I got that. I purchased a wiseco piston, fitted a new small end, gaskets, the new head, had the cylinder honed, checked and cleaned the carb and reeds, fitted a new air filter (normal after a ride) changed the gearbox oil, new spark plug. I also fitted an hour meter and an alloy throttle tube.

Since the above

I did 3 heat cycles, about 10 mins each. Then yesterday I did an enduro with WOR. Thought it might be a good way to run it completely in, and I’ve done one before and enjoyed it. The bike was fine really. Thought it felt more powerful than before which is standard I suppose with a new top end. On this enduro there was a few really fast roads (think they call them fire traps between the trees) I’m new to mx in general so I’ve never got to the higher speeds or gears anyway, but yesterday on these fast roads I managed to ride faster than I ever have. Must have been pushing 50mph on one of the roads. As I've ridden 2 stroke road bikes I was aware of the need to clutch in at the end of these straights and blip the throttle a few times.

Present Fault/s

Four different things happened on these fast roads. Either it was fine, or it cut out as soon as I rolled off the throttle, or as I was reaching the higher rpm it bogged right down or sometimes as I applied throttle it died altogether.

It’s worth noting that the conditions yesterday were horrendous. It was at the top of a mountain in a forest near Bala North Wales. I haven’t seen rain in this country like that in years. It was constant, none stop driving rain, sometimes sleet. The wind was bad too, and it felt like it was -10. There were also lots of deep long puddles, some of which I hit at speed.

I checked and changed the spark plug. The old one was quite wet. There was oil visible on it. However I ridden slowly from the track back to the van. I have always had a bid of spooge run down from my pipe on the swing arm/calliper/inside of number plate. So I thought maybe it’s too rich rather than to lean. I would have taken the bowl off the carb there but it was just too wet and my bike was caked. I hoped the new plug would cure it as it did at wilden a while back. I also turned the air screw to 2 turns out. I changed my air filter too for a fresh clean and oiled one. Also the bike had fresh fuel and the right mix of oil.

After all this the bike was just the same! It was still ride able, just annoying. I found myself just not going quite so quick on the straights. Or I did and it was ok. Very inconsistent. I convinced myself it was the jetting, but couldn’t work out why the jetting would be out as its been fine all year (ridden every weekend almost since July)

Today at Apex

Today I went to apex to ride with a good friend of mine. I fitted another fresh air filter too. Bike did exactly the same! As soon as I got on a straight, it just bogged slowly and died as if it ran out of fuel. Before the bogs’ the bike sounds and feels crisp. It’s like there is no fuel. It always kicks back up after a couple of kicks and is fine again till the next straight.

After the above happened today at apex, I went back in after one lap, to try and get to the bottom of it. My mate let me put the bike in the back of his truck to work on in the dry. I did the following things….

Drained the fuel out and filled with fresh fuel

Cleaned the fuel tap

Checked and cleaned my jets and bowl

Checked the plug (little bit wet again)

Checked the position of the stator

Checked the coolant level, and made sure it wasn’t bubbling when running

Checked and cleaned the reeds

I found the float bowl to have a bit of water in, also some dirt. This is why I drained the tank and cleaned everything out.

I tried it again, and it’s still the same! Bogging quite badly. So I pulled in again.

I purchased the bike with the pipe already fitted, so I always trusted the jetting. Today I noticed the main jet is a 460, when stock is 360. Quite a difference.

After the above, I removed the pipe to check the piston out. There is now just over 3 hours on the bike. The piston looks good, still has the large ‘W’ on the side that wiseco put on. There is no blow by, from what I can see of the cylinder it’s still nice and cross hatched. I did notice on the piston there were some very light, vertical scratches. I couldn’t feel this with my fingers. Strange thing is the old piston had the same scratches, only there were lots more of them. I put a post on here with a picture of the piston and someone said they couldn’t believe it was only 17 odd hours old (I since worked it out to be just over 20) This is why I got an hour meter now so I can keep track of my hours instead of forgetting and trying to work out where I had ridden and how long for with pen and paper!

One more, worrying thing to add. When washing it, I started it up as normal. As it was idling I could hear a very faint rattle which I think was coming from the clutch. I’m sure I’ve never heard this rattle before. Obviously Ill have a look in there when I next work on the bike, weather this is related to the bogging problem or not I’m not sure.

I haven’t touched the bike yet, other than washing it. It’s all put away and locked up now until at least Tuesday. So if someone was going to ask have I tried this/that or the other then no, not yet. I only got back from apex a couple of hours ago.

Sorry this post is so long, just wanted to explain everything as best as I could

Thanks for reading, looking forward to the replies!

All the best, Andy

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If your that rich on the main, then what is your pilot jet? With the SST pipe, I would think about a 350 to 355 would be about right on the main. Also did you ever check to see what groove the slide needle c-clip is in? I would think it should be in the 2nd or 3rd groove. As you already know that 460 main is way to big for the bike. Pick a mix 28:1 or 32:1 and get your jetting lined out before any other mods are done.

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How did it run in July? If it ran good then, the jetting would be off now with colder weather. As Padgett said adjust the jetting. The sticky at the top of the forum can help a lot.

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Thanks guys and I hear u about the jetting. Although this needs fine tuning I don't think this is my problem as I said I've used the bike for months without this issue. I really want to get to the bottom of this

Also, what year did Suzuki go to a powerjet carb? Was it 05?

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Thanks guys and I hear u about the jetting. Although this needs fine tuning I don't think this is my problem as I said I've used the bike for months without this issue. I really want to get to the bottom of this

Also, what year did Suzuki go to a powerjet carb? Was it 05?

Yes: 2005 Mikuni TMX38SS W/ power jet & throttle position sensor

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If it happened out of the blue I would investigate electrical. Do you know anyone with a donor bike you can try the stator, CDI, coil from? One part at a time obviously.

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I don't know anyone with the same bike no. Wierd thing is how well the bike runs from bottom to mid, it roars. And top is good initially but then it bogs.

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The one time we had a bog issue with one of my sons 125s it was on high speed jumps.I was changing jets,needles trying what you would think would be the problem.In my case, new set of reeds solved it.

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What's done that after only 3 hrs :smirk: wisecos expensive here too. £90 which is about $200??

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