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Potentially basic carburetor question

gixxerjeff

gixxerjeff

Optimistic Underdog
Joined
Nov 17, 2008
Location
Santa Rosa
Moto(s)
Some fast ones and some dirty ones.
Name
Derp
My trusty DR125 sat unused for a little too long. The ethanol gremlins left their telltale white death throughout the carburetor. I've been here before, too many times. I cleaned every orifice and replaced both jets, just like always. It started immediately, again...like always. But then it suddenly sneezed and died.
Aware of the strong smell of fuel I restarted it to find a massive amount of fuel being pumped in to the airbox while it runs.
I was surprised to see how much fuel was pouring it's way against air going the other way. Did I fuck my float up when I was in there? Unlikely but possible. Wrong jet perhaps? The carb is obviously coming back off. I'm just wondering what I should be looking for.
 
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Overflowing float bowl should just drain out the bowl vent,/overflow..... external to the carb an airbox.

Unless the vent was routed into the airbox....??
 
augustiron said:
Overflowing float bowl should just drain out the bowl vent,/overflow..... external to the carb an airbox.

Unless the vent was routed into the airbox....??
Click to expand...

Nope, it's spitting back through the airhorn, bigly.
I just now pulled the carb back off and dropped the bowl again. All looks happy in there. There are only 2 lines coming off the petcock. One is fuel feed, the other goes across the top of the carb to what I suppose is a bowl vent. I buttoned everything up and it fired up immediately. It soon sneezed and died again and now won't restart which is okay...I don't want to run it for too long. Now I'm worried about filling the crankcase with fuel.
 
gixxerjeff said:
Nope, it's spitting back through the airhorn, bigly.
I just now pulled the carb back off and dropped the bowl again. All looks happy in there. There are only 2 lines coming off the petcock. One is fuel feed, the other goes across the top of the carb to what I suppose is a bowl vent. I buttoned everything up and it fired up immediately. It soon sneezed and died again and now won't restart which is okay...I don't want to run it for too long. Now I'm worried about filling the crankcase with fuel.
Click to expand...

I think that second line is supposed to be connected to vacuum to actuate the petcock... not a bowl vent.
 
Sounds like vacuum is pulling way too much gas up past the needle jet. There really isn't another way for that much gas to get into the throat of the carburetor
 
Look at a carb fiche for that bike and make sure the jet needle, needle jet and emulsion tube are all in properly.
Also eyeball the replacement main jet as some cheapos are a crapshoot on correct sizing.
 
And per Chris, check proper hose routing against the fiche also
 
augustiron said:
Also eyeball the replacement main jet as some cheapos are a crapshoot on correct sizing.
Click to expand...

Everything looks good and right. This thing is too fuggin simple to stump me like this. (hangs head in shame).
I'm done with it for today. Tomorrow I may rip it back out and spin the original main jet back in.
I agree though, it seems like misrouted vacuum. It's the only thing I can think of that would pull that much fuel backwards.
 
I have bench checked floats by pulling the float bowl off, hooking up a slave tank and working the float with my finger. It can be a little messy, but will let you know if the float is working. Another possibility is if there is an o ring beneath the float valve where it goes into the carb body. I'm sure you havent hooked up the vent line to the fuel line? Hope this is some help.
 
I'd be going back and rechecking the carb, especially float and over the flow tube venting. If the overflow is blocked and the float isn't working, there isn't anywhere for fuel to go BUT up and out the carb into the engine AND airbox.

If you aren't set up to bench test, either pull the airbox so you can see into the carb to determine what's happening or try pulling the carb, then reattaching fuel line from the tank with the carb next to the engine. You should be able to determine if the float and overflow is working or not with either of these two methods.

I'd be flabbergasted if the little 125 had a vacuum line activated petcock, or that it has anything to do with the petcock.

Unlikely, but I have seen it happen on few thumpers where the float was stuck open and the petcock left on.... its floods the engine and crankcase with fuel as it seeps past the rings. The excess gas/oil volume is then pushed out the crankcase breather, which is usually routed to the either the airbox or the rubber boot attaching it to the carb. To check, temporarily disconnect the crankcase breather hose terminus from the air box or boot (if that's were it goes.)

My money is on faulty float and overflow vent if you aren't seeing fuel anywhere else.
 
Thanks CJ.
You got me thinking about that overflow tube. I don't think I blew it out or ran a wire through it. :rolleyes
But even if it was plugged that would mean I had something else going on with the float. Unlikely but always possible.
Surprisingly, it is indeed a vacuum operated petcock. (reserve, prime, run).
My gut says this is a vacuum routing issue. There's just too much fuel being pulled back into the airbox.
 
Check the vacuum diaphragm in the petcock. Pull vacuum line off of the petcock, and check for gas in the line. You can suck gently on the line into the petcock, and you should not get any gas in the vacuum line. It should let gas into the carb line when vacuum in applied, but no gas should be in the vacuum line itself. I there is, the diaphragm in the petcock is torn.
 
^^^^
Will do. I had to go onto work today. Hopefully I can spend some more time with it tomorrow.:thumbup
 
Wow… never would have guessed the petcock on that bike would be vacuum. Usually only see that on street bikes or steel fuel tank dual sports. Bobl is spot on about checking it’s function.

I had a new to me XR650L years ago that was having fueling issues and after a couple of evenings of chasing my tail, I looked at the hose routing diagram in the service manual and realized the previous owner had misrouted a carb vacuum line when they desmogged it. Definitely a :facepalm moment and a few wasted hours.

Good luck!
 
OaklandF4i said:
Wow… never would have guessed the petcock on that bike would be vacuum. Usually only see that on street bikes or steel fuel tank dual sports.
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Well, you're actually pretty damn accurate there. It's a DR125S (for street) It came with lights and mirrors and a license plate. It also has a steel fuel tank.
It's a 1994. It was a little ahead of it's time in terms of the ADV trend that we're seeing now. :laughing
 
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gixxerjeff said:
Well, you're actually pretty damn accurate there. It's a DR125S (for street) It came with lights and mirrors and a license plate. It also has a steel fuel tank.
It's a 1994. It was a little ahead of it's time in terms of the ADV trend that we're seeing now.
Click to expand...

:thumbup I was envisioning a DR(Z)125 play bike. Looking back to your post, you actually did write DR125. My forum reading comprehension is weak in this thread evidently. :laughing

After googling it, looks like a really cool little bike! Albeit one that isn't running properly. Not many sources for that excess fuel being introduced, confident you will find it. Now I'm curious and feel invested... :teeth
 
OaklandF4i said:
After googling it, looks like a really cool little bike! Albeit one that isn't running properly. Not many sources for that excess fuel being introduced, confident you will find it. Now I'm curious and feel invested... :teeth
Click to expand...

I'll keep you in the loop, I promise.
It is indeed a very cool little bike. I bought it for my 31 y/o son when he was 13. When he moved on to bigger bikes my daughter learned to ride on it and ripped it all over Carnegie until I picked her up a TTR225. That's why it started to sit. Knowing I had the lights and mirrors in my toolbox it dawned on me that I have a 5 mile commute on rural wine country roads. Allow me to introduce you to my new 90mpg commuter! "It's alot more fun riding a slow motorcycle fast than a fast motorcycle slow!" I spooned a set of DOT Bridgestone Battlax's on it and knocked the cobwebs off the registration. As soon as the fueling issue is sorted it's going to be perfect for what I have in mind.
 
I just remembered another way to determine if the petcock is leaking fuel into the vacuum line. Pinch the vacuum line closed, and run the bike on prime. That will take the diaphragm out of the equasion.
 
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