Bike Doesn't Run - Tried Nearly Everything - Starts But Dies

[theflash1327]

Hello again,
Second build and twice as many problems as the first..
I bought a used engine from a guy i was buying a bike from. I have no clue what the displacement is. It is a flat head 2-stroke. I will post pics soon.
Anyway, I installed it and it kinda started, and I finally messed around with it enough to get it running. It ran and started easily, but got a top speed of only about 15mph. I started messing with it and one day when i went to start it up it didn't work. I could get it started by pedaling very hard, but it would just die out.
Right now i can get it started if i put it at 3/4 choke, and it will run at a low speed and then die. Any other choke won't work for starting or running. I realized the throttle didn't go all the way down in the slide. I fixed that. But still no success. It gets fuel flow to the fuel line but the line is a little lose on it fitting. But it still doesn't seem to leak. I just checked for an air leak with WD40 but there didn't seem to be a problem. I think it is still an air problem. (Too much air?) I haven't opened the carb completely cause i don't even know what to look for if I do.
Any help would be awesome. I want to get it running this weekend if at all possible.

Edit: Also forgot to add that I checked for spark and it was not strong so I just replaced the plug and wire. Better spark now. And the clutch seems to be working fine. I am running a 24:1 mix. And the guy who sold me the engine said he had taken it out only a few blocks. It seemed to have been sitting in his garage for quite a while.

I also thought it may have been flooded so I got it running for about 30 seconds with the fuel valve off to see if it would use up any excess gas. I tried messing with the c-clip a few times but it hasn't seemed to work. However, i haven't moved it since I put a new gasket on the carb which also seemed to do nothing, but i don't know if i should try the c-clip again?

 

[DuctTapedGoat]

Does your carb have a red cover and a choke lever on the handlebars? If so, it's a CNSv2, and that's the common issue with them.

I'd suggest to replace with an NT carb.

 

[theflash1327]

No, it is an NT carb..but the cover over the filter broke anyway. i attached it but is it possible that this is letting in too much air somehow? Should i try just replacing the carb altogether?

 

[DuctTapedGoat]

Where's it broken, that's gotta be your problem. Don't replace the carb - get a new filter cover first. Well, first seal that filter up as best as you can and try that to ensure that it's your problem, then if you get a new cover, it's for aesthetics.

 

[theflash1327]

it's broken on the side where the screw goes in to hold it on. that tab snapped off with a bit more. i put a bracket on to attach it again, but there is still an opening and you can see part of the filter sponge.

 

[theflash1327]

But wouldn't it still run even if the whole filter was off?

 

[DuctTapedGoat]

What's your definition of "run"?

By my definition, your bike "runs", just not well.

You can "run" it with the filter off - just not well.

 

[theflash1327]

Ok, haha. That makes sense. Also I found another thread i must have missed before with a similar problem: http://motorbicycling.com/f4/bike-wont-run-unless-choke-8984.html

Could it maybe be the jet needs to be drilled bigger? Or maybe there is just something wrong with the jet? I will try to seal up the filter cover tomorrow and get back to you. Thanks for all your help!

 

[DuctTapedGoat]

One thing at a time though now, lets see how well it runs after you get that filter cover sealed up first.

 

[onanysunday]

This may or may not be your problem but I once had that same issue. My bike would start on choke and then die out right away when choke was off. The problem was a lack of fuel flow (from the stock petcock) as well as a clogged jet. I fixed this with a combination of ordering a new fuel valve from sickbike parts (to increase fuel flow) and cleaning my main jet - the opening is only the size of a pinhole and it is easily clogged with a bit of sediment which prevented gas from feeding the engine.

Have you checked your fuel valve to make sure it also isn't clogged? Take your fuel line off your carb and turn the gas on. Does any gas dribble out? Do you have a fuel filter? If not, definitely buy an in-line filter and install it somewhere in the fuel line. When I took my old petcock off it was completely clogged.

Have you checked your jet to make sure it isn't clogged? Remove your float bowl on your carb and unscrew the jet to check if the tiny hole is free from sediment. Try this and let me know if it works.

 

[theflash1327]

Wow! I got it! I taped the carb cover and that helped. I also decided to check the head bolts and they were pretty loose. This helped too. But that was just something I did separately. In the end it was the jet. It wasn't clogged but when I took the bowl off the carb the jet came out too. Haha. It wasn't screwed in all the way. I put it in all the way and the throttle slid better and of course that is why there was too much air. Now it works great! Thank you for your help! I'm glad to know people will always help here!