The 50cc bike thread - help needed

I have two 50cc bikes, a Honda CRF-50 and a Yamaha TTR-50E.

One would think these would be simple to keep running... I was having issues with the TTR-50 racing at idle. So I tore the carb down, gave it couple good ultrasonic baths, shot all the various ports with carb cleaner, replaced the idle/pilot jet, replaced all the gaskets, replaced the air filter, and put it all back together. It is still getting too much gas. When I try to start it, I can smell it even with no choke on. I pulled the plug and it was wet. I dried it and put it back in. I turned the fuel screw all the way in (this is the screw used to set the idle). The bike started and I turned the fuel screw back out 1-1/4 turns. The engine is still going way faster than idle and backing the screw completely out of the carb does not slow things down at all. I am pretty sure the throttle is totally closed and the slide bottomed out. All the jets are stock.

Any ideas?

check your float level and or make sure its not hanging and flooding , are has a hole in it that stops from working correctly

Aaron

I am having a heck of a time finding any info about how to set up a stock carb for this bike. It is a Mikuni VM11. I can't even find info for it on the Mikuni website I have the service manual for the bike and even it doesn't say anything about the air and fuel screw settings. I've searched at PlanetMinis.com and that seems to be full of folks that mostly hot rod the 50's, so all the discussion there is about after market carb settings.

Right now, I can get it to idle at a reasonable rpm. If I give it any gas, it bogs and tries to die. On my KTM, this usually indicates a clogged idle/pilot jet. However, the jet in this bike is brand new. I did not want to mess with trying to get the old one clean as I have never had much luck with that on my KTM. If I can get the bike to make the leap to higher rpms, it will rev fine. If I let off the throttle, it takes about 15-20 seconds for the engine to fall back to idle speed.

When I pulled the carb apart, the choke piece was stuck in the carb body. I got it out and cleaned it and the place where it slides into the body. It felt like it was able to move freely without any binding or sticking when I put it back together. But now I am wondering if it might be staying stuck open? However, when I move the choke lever at the steering stem, it does affect the running of the engine, which I would not expect unless the piece were moving.

I will check the float level. I'll likely also just replace the spark plug, just because.

Hanging idle usually means intake leak. Are you sure you don't have an air leak between the carb and the cylinder?

WoodButcher said:

Hanging idle usually means intake leak. Are you sure you don't have an air leak between the carb and the cylinder?

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Well, I cleaned the mating surfaces and added new gaskets because the old ones were squished flat. Then I torqued the studs holding the carb to the cylinder intake. I also made sure the boot from the air box is on properly. So I don't think this is the issue, but at this point I am willing to double check. I will probably tear it down again tonight.

On most carbs, the pin that holds the float in place is easily removed. On this carb, I could not get it out, so I can't get in there to check the float needle. I even tried tapping it out but I did not want to wail on it and risk breaking something. I am wondering if the mating surface might be gunked up a bit, allowing gas to bypass the needle more than it should. I plan to check the float level as well.

On my daughter's DR200, there was an o-ring around the float seat that failed. I don't remember seeing on in her xr70 carb though. Those small ones might not be that complex.

My son has a 50cc honda. His solution to fixing carb issues he couldn't resolve with cleaning etc. was to purchase an aftermarket carb. fixed it. Good luck wiwth repair!

wanabeguru said:

My son has a 50cc honda. His solution to fixing carb issues he couldn't resolve with cleaning etc. was to purchase an aftermarket carb. fixed it. Good luck wiwth repair!

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I don't want to dump a bunch of money into these bikes. When I go to sell them, I'll be lucky if I can get $800 for them. So a few hundred bucks for a new carb is a big hit. The bike ran perfect previously, so the carb should work now assuming I can get it cleaned and properly adjusted.

My son's CRF50F was fiddly with the carb. Ran good once warmed up but seemed to take forever. I'm glad he finally moved to the CRF70F. I haven't touched the carb on that one and that thing purrs like a kitten from the get go. Probably credit to Poser since he did most of the maintenance on it before I bought it. I'd like to see him chime in here.

I think I may have the TTR 50 running right now. I pulled the carb again and removed the float needle. The float level was still set perfect. I could see no evidence of wear on the needle tip (which is rubber). I went ahead and gave the carb another good dosing with the carb cleaner spray just for good measure. I reassembled it and fired it up. It starts pretty easy.

Once running, I had to fiddle with the throttle stop screw (raises and lowers the slide tube/needle) and the air srcew (which feeds air into the pilot circuit). At first, it would settle into a decent idle. If I tried to give it gas to quickly, it would bog and die if I did not let off the throttle quickly. I could roll on the throttle very slowly though and get it up into the higher rpms. However, it would then slowly return to idle when I let off the throttle. I would slow the idle with the throttle stop screw, then bring it back up a little at a time with the air screw. Each time I came out on the throttle screw a little (lowering the slide) I would go in on the air screw a little. Each time I did this the bog off idle got better and it returned to idle from high rpms quicker. When I finally got it to the point where it was not stumbling off idle, I think I was 2-1/4 turns out on the throttle screw and maybe 1-1/4 to 1-1/2 on the air screw.

Oil change and new chain/sprockets are next for this one. Then it is time for the rebuild of the CRF 50 carb. It didn't have the starting/idling problems of the TTR50, so I am hoping it is less of a hassle.

Tourmeister said:

Well, I cleaned the mating surfaces and added new gaskets because the old ones were squished flat. Then I torqued the studs holding the carb to the cylinder intake. I also made sure the boot from the air box is on properly. So I don't think this is the issue, but at this point I am willing to double check. I will probably tear it down again tonight.

On most carbs, the pin that holds the float in place is easily removed. On this carb, I could not get it out, so I can't get in there to check the float needle. I even tried tapping it out but I did not want to wail on it and risk breaking something. I am wondering if the mating surface might be gunked up a bit, allowing gas to bypass the needle more than it should. I plan to check the float level as well.

Click to expand...

If you're still having problems with the float pin, what i do is hold the pin over a very small quarter inch socket and tap it out with a small punch .The chance of breaking off a tab are much less. those pins have a splined side and usually only come out one way. Hope that helps.

So the TTR-50 is done. It runs pretty good once warmed.

The CRF-50 is done. It was MUCH less hassle. It runs great. I had to replace the right fork internals. These forks have no oil at all, just a spring and some grease on the sliders. The previous one was bent a few years ago when a cousin ran into a trailer when we were at a big family gathering. I did not realize it was bent until last week when I removed the plastic shrouds that cover the lower fork. That fix was VERY easy and the new bits were only about $70 for the whole thing preassembled.

The CRF-110 started right up and runs great. I won't even be messing with it.

The XR80R got a carb rebuild. I've not started it since, but I rode it before the rebuild to heat the engine for an oil change and it was not running real great. I stopped when the chain came off the rear sprocket!! I knew it was loose, but I did not realize it was THAT loose! No damage and I just pushed it back to the garage.

I have new sprockets and chains coming for all four of the bikes (ordered before the incident with the XR80R happened). They all got new air filters and oil changes as well. I did overfill the two small bikes a little, so I need to find a large syringe and some tubing to suck some back out Tires and brakes all look good. So I should be all done by next weekend hopefully.

I have been putting the bikes up on a table in the garage to make them easier to work on. That's fine for the smaller bikes that I can lift up onto the table. Having them high is nice. It makes me REALLY want to get a decent lift table for working on my KTM and GS!

CRF-50


Ultrasonic bath


TTR-50


The XR80R on the work table, the CRF-110 in the foreground


Almost ready for action, waiting on new chains/prockets


My KTM whispers to me while I work on the other bikes...


Soldered brass float from XR80R getting a cleaning


And my GS just because I finally got around to washing it

I got the KTM 530 EXC out for some much needed riding last Friday (for me and the bike). First I hit some trails in the Sam Houston NF with Rsquared and his brother in law. I am STILL sore from that Afterward, I hit some back roads in search of BBQ for lunch. Found that in Iola and then raced the nasty weather home.





The KTM is running good, but now the battery appears to be toast I had to kick start it all day. Also, the clutch may be on its last legs, so I went ahead and ordered a replacement kit for it when I ordered the battery.

The two 50's are done. They got new sprockets and chains installed last week. I went to do the chain and sprocket on the XR80R today and noticed that the tires are starting to crack Also, when I removed the left crank case cover to access the front sprocket, the paper gasket shredded. On top of that, once I got it removed, I noticed that the crank case is chipped slightly around the outside face of the gear shift shaft seal I am thinking that happened when the chain popped off a few weeks back when I was zipping around the yard to make sure the bike was running fine and to warm it up for an oil change. I am NOT going to replace the case because of this. The chips are small and don't appear to extend behind the seal I am going to ride it and hope that it holds and is not a problem. I might attempt a JB weld repair if I really feel motivated. A new case is about $230 for that one part, but then I'd have to totally tear down the engine and no doubt that would involve other seals, parts, etc,... I don't want to dump that kind of money into this bike if I can avoid it.

That silver spot just above the shift lever is where it is chipped.


New tires, tubes, rim strips, and case cover gasket are on the way. It seems that no matter how hard I try to get all this stuff done early before our trip, things keep getting pushed closer and closer to departure time. I hate having tons of stuff still left to do right before a trip! I still need to get everything in the trailer to make sure how it all needs to go in and I don't want to be doing that the day before we want to leave If I can get these tires mounted and the new chain installed on this bike, I will hopefully be good to go as far as the bikes are concerned. Although, I still have to swap the battery and install the new clutch plates for the 530 EXC... I am told that is easy...

Oh... and the rear shock on the 530 is leaking

I know how you feel with bikes to keep running. When the kids are small it is like maintaining a fleet. Colton is old enough now he does most of his own maintenance with a little guidance from me. I am looking forward to him being able to do his own tire changes.

The smiles and memories will be worth it.