Ok, my 50 has been running like crap recently and has been unreliabe. I have been cleaning the carb a lot, but it still doesnt like to idle and it bogs in low rpms. It is a stock motor with a cdi, fmf pipe, uni filter, and head breather. The adjustments dont seem to do anything either. Also, my friend has a stocker like mine, and the motor pulls quite a bit harder than mine, and the clutch grabs quicker/solid-er than mine. So where should i start? Im thinking new o-rings, jets, and clutch springs.
Xr 50 Motor Issues
XR 50
1 - 11 of 11 Posts
Joined
·
221 Posts
Ok, my 50 has been running like crap recently and has been unreliabe. I have been cleaning the carb a lot, but it still doesnt like to idle and it bogs in low rpms. It is a stock motor with a cdi, fmf pipe, uni filter, and head breather. The adjustments dont seem to do anything either. Also, my friend has a stocker like mine, and the motor pulls quite a bit harder than mine, and the clutch grabs quicker/solid-er than mine. So where should i start? Im thinking new o-rings, jets, and clutch springs.
Joined
·
666 Posts
x2 for checking the idle jet circuit and using a carb cleaner - especially if air screw (Centre screw) & idle fuel adjustment (Front screw) don't clearly altering the RPM and stability during idle as you are suggesting.
You may also check a couple of other areas if the bike was sitting for a while and still can't get any joy:
- change the gas just in case, and run a solvent additive like acetone through the first tank of new premium gas - gas can gum things up after sitting for a while.
- check gas flow from the main tank - should be a reasonable flow.
- Start with the front fuel screw being 1.5 - 2 turns out - too much bogs it down when first cranked as rich mixture takes time to clear, too little fuel makes it hard to start and inconsistent idle even if hot and is a symptom of a clogged idle circuit.
- Change the spark plug to new - theres nothing worse than trying to diagnose a carb issue to find that a plug is simply breaking down.
- finally check you have inserted the slide and needle assembly all back in the correct seqence - that is needle into slide up to the clip, followed by circular drainpipe retaining clip, followed by spring and above spring the washer that sits in the carb screw cap. Put back wrong and the needle will float about giving you grief. Then make sure cap is screwed back on firmly.
- If std pipe pull the spark aresstor out and thoroughly clean it - if you have been running rich for a few previous sessions these are notorious for carbon buildup.
You may also check a couple of other areas if the bike was sitting for a while and still can't get any joy:
- change the gas just in case, and run a solvent additive like acetone through the first tank of new premium gas - gas can gum things up after sitting for a while.
- check gas flow from the main tank - should be a reasonable flow.
- Start with the front fuel screw being 1.5 - 2 turns out - too much bogs it down when first cranked as rich mixture takes time to clear, too little fuel makes it hard to start and inconsistent idle even if hot and is a symptom of a clogged idle circuit.
- Change the spark plug to new - theres nothing worse than trying to diagnose a carb issue to find that a plug is simply breaking down.
- finally check you have inserted the slide and needle assembly all back in the correct seqence - that is needle into slide up to the clip, followed by circular drainpipe retaining clip, followed by spring and above spring the washer that sits in the carb screw cap. Put back wrong and the needle will float about giving you grief. Then make sure cap is screwed back on firmly.
- If std pipe pull the spark aresstor out and thoroughly clean it - if you have been running rich for a few previous sessions these are notorious for carbon buildup.
Joined
·
221 Posts
It has new plug, fresh 91 gas, and the needle is good, but ill check the other possible causes too. Also, it seems to run a little better when its hot, which i guess is normal. Also, when i cleaned the carb, carb cleaner would spray through both jets and the fuel inlet thing fine, but ill double check it.
The other possible cause is that the motor probably has quite a bit of hours oon it, i may do a top end rebuild soon with a tb88 kit+carb
Joined
·
666 Posts
Out of gear is the motor running crisp from idle to full throttle ? If he's a good friend swap in his carb for a quick diagnosis if it doesn't seem to be revving cleanly.
Have a look at the plug colour after a session - if its not brown then some carb tweaks needed. It will be hard to diagnose semi auto clutch issue if the power is down, but lockup should be instant with no sign of slippage if you try holding the bike back in first gear with your feet.
Hows the resistance on the kickstarter compared to your friends bike ? Might also be needing valve adjustment if never done. Compression down gives sluggish performance all over, but if the rings are past their life expect some smoke out the exhaust and oil usage - any indication of oil blowby in the FMF pipe ?.
TB88 is a wake up call to these motors and a great option if you are stripping to replace rings.
Have a look at the plug colour after a session - if its not brown then some carb tweaks needed. It will be hard to diagnose semi auto clutch issue if the power is down, but lockup should be instant with no sign of slippage if you try holding the bike back in first gear with your feet.
Hows the resistance on the kickstarter compared to your friends bike ? Might also be needing valve adjustment if never done. Compression down gives sluggish performance all over, but if the rings are past their life expect some smoke out the exhaust and oil usage - any indication of oil blowby in the FMF pipe ?.
TB88 is a wake up call to these motors and a great option if you are stripping to replace rings.
Joined
·
1,324 Posts
Might be the CDI crapping out, 'eh? Try a buddies stock CDI man, I tried an aftermarket one once and I had ZERO spark, so maybe yours is getting weak spark running shitty. Something to ponder.
Joined
·
221 Posts
That would suck, mine is a takegawa :/
Joined
·
472 Posts
You could check the timing for errors, remove the stator side cover and the cam sprocket cover and check for the two alignment notches to match. Also make sure all of your wiring harness is completely sound, nothing disconnected/frayed/burnt. Your FMF pipe could have also messed with the tuning of the bike, if the plug is burnt its too rich (black), if the plug is chalky (white) its too lean. Try that, and then come back with a result.
Joined
·
221 Posts
I started the 50 today first kick, and it idled, which was weird. The plug was black and a little bit carbon-y, but where the spark gaps, it was white/light tan. It still has the bog on the low end, but runs ok higher up in the range. Im going to go up on the main jet, what size would be good?
And unrelated, where do stock 50 frames usually bend?
And unrelated, where do stock 50 frames usually bend?
Joined
·
472 Posts
At the neck I would suspect. Thats what happens on almost all of the Chinese bikes I have seen.
Joined
·
1,552 Posts
Did you rejet for your pipe? (if you needed to)
Did it always run like this?
Airfilter is clean?
Magneto is clean?
And when you clean the carb, be sure you remove every jet and clean it. Be sure float hight is set correctly. Be sure ALL the tiny ports inside the Venturi (where the air flows through) are CLEAN on both the airfilter side and the head side of the engine. Sometimes these jets are removable too - remove them and clean if possible.
The best way to clean a carb is with carb cleaner followed by air (be careful. High pressure on the jets, but less pressure on the actual carburetor, any seals are delicate especially in any sort of diaphragm style carburetor (not common on a 50, but common enough to mention)
Changing your main jet will not help your idle issue/low end bog issue. The main has most of its effect on 1/2 to full throttle. Your pilot circuit is your problem.
Start with setting your air screw (or fuel screw on some carburetors)
To better understand how to properly jet your engine read this. Its the most informative article on jetting I have read to date. Carb Tuning 101- Spankys Jetting Guide
Did it always run like this?
Airfilter is clean?
Magneto is clean?
And when you clean the carb, be sure you remove every jet and clean it. Be sure float hight is set correctly. Be sure ALL the tiny ports inside the Venturi (where the air flows through) are CLEAN on both the airfilter side and the head side of the engine. Sometimes these jets are removable too - remove them and clean if possible.
The best way to clean a carb is with carb cleaner followed by air (be careful. High pressure on the jets, but less pressure on the actual carburetor, any seals are delicate especially in any sort of diaphragm style carburetor (not common on a 50, but common enough to mention)
Changing your main jet will not help your idle issue/low end bog issue. The main has most of its effect on 1/2 to full throttle. Your pilot circuit is your problem.
Start with setting your air screw (or fuel screw on some carburetors)
To better understand how to properly jet your engine read this. Its the most informative article on jetting I have read to date. Carb Tuning 101- Spankys Jetting Guide
1 - 11 of 11 Posts
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
