First time firing up the engine, problem! :(

L

lolitsdaelan

New Member
So after much blood sweat and tears, I finally got the bike finished and on the road. I drop the clutch in as I'm pedaling, bike turn over just fine. I then pull the clutch in again, and the bike begins to rev as hard as it can (terrifying). I also noticed that before pulling the clutch in a second time, my throttle didn't function at all. I've looked into the carb and can see that the little lever thing pulls up as I engage the throttle (which i think is good). Anyone know what the white lever on the carb does? I haven't touched it and its not mentioned in the manual. Also, my throttle broke when I was installing it (go china!), a small plastic piece fell out. But like I said, I've been able to verify that the throttle does in fact engage the carb.

Any ideas??
 
the plastic piece on the carb body is a secondary petcock. the fuel is turned on when it's turned up or down, and it's off when it's sideways.

your throttle cable is probably too tight or it's binding, that's why it's revving up.

check for binds or kinks, first. the throttle should turn smooth and free, without any "catching" or roughness.

since you know it's starting, check the little spring-loaded screw on the side of the carb. that's your "idle screw." turning it in increases idle (makes it rev higher,) out decreases it.

it should be set 3.5 to 4 full turns out. to check this, with the engine off, screw it all the way in till it stops. don't force it in, just till you can feel it stop. then back it out 3.5 full turns.

now, with your air filter box off, look into the carb at the slide. that's the little grey cylinder that's at the end of the throttle cable inside the carb. that moves up and down when you twist the throttle, opening to let more gas in.

it should be all the way down, covering the opening of the carb. if there's a gap, your cable is too tight.

there's a "barrel adjuster" on the cap that screws into the top of the carb that holds the throttle cable housing, with a knurled, round nut on it. loosen the nut and screw the adjuster and watch the slide, screwing it in till the slide stops moving down. now, twist your throttle slowly, and adjust the cable up or down a bit till it feels right. you should have a tiny bit of play before the cable pulls the slide up. just a tiny bit, any more and it'll be sloppy and you won't get full throttle. too tight, and it revs up like crazy at idle. then screw the little finger nut down against the base to lock the adjuster in place.


when that's all set, look back into the carb's throat and watch the slide as you screw in the idle screw slowly. it should move up slightly. if it does, unscrew slowly so it slides down, and unscrew till it stops sliding down. then screw back in slowly till it just barely moves up.

next step, looking at the slide again, twist your throttle slowly and watch to see if the slide moves up until you can't see it anymore. this is WOT, or Wide Open Throttle.

once you've got all this done, start 'er up. if everything else is right, it should be pretty close to perfect. you'll probably have to turn the idle screw slightly in or out to find the best idle.
now put the air filter box back on and ride it.

also, there's a choke lever on the front of the carb. down is off, up is on. that's for cold starts. you want it on, or half on when you first start it cold, then turn it off (down) after a minute when it warms up. after awhile, you'll figure out the best starting method for your bike.

if this seems over-simplified, sorry. just trying to make it as easy as i can...
 
Dude bairdco That explanation has got to be made into a sticky!!! It couldn't be explained better with a video.

lolitsdaelan another thing you want to look for is if the slide is sticking at any point in the throat of the carb. If it is you need to loosen the clamp that holds the carb. on the intake, just a little or the carb. will fall off. I also have learned the slide will stick sometimes cause the engines cold. If it does that just use the choke to keep the idle low until the engine gets warmed up.

At any rate, Glad to hear you got it running. You'll be riding soon. Welcome to the addiction, Enjoy the ride.

Bairdco Kudos Bro.
 
Well this has proven to be a real pain in the ass, this thing better be awesome once it's done!! =P

So I made the adjustments needed, and as I dropped the clutch in, chain falls off. As I look closer into it, the back wheel is now bent :(

So after the holiday I'll have to run out and buy a new back wheel, project is on hold until then =\
 
You should learn to true your own wheel sometime,cause bicycle wheels get bent or warp often, engine or no engine. Unless you plan on buying wheels everyfew months.
 
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Well I bought the bike used from a guy, and not knowing anything about bikes really, it never occurred to me to check for some sort of bend or imperfection. I doubt that the few times I tried to start it caused solely caused it to bend, if so, then damn those engine put some torque out!
 
bairdco said:
...now, with your air filter box off, look into the carb at the slide. that's the little grey cylinder that's at the end of the throttle cable inside the carb. that moves up and down when you twist the throttle, opening to let more gas in.

it should be all the way down, covering the opening of the carb. if there's a gap, your cable is too tight.

there's a "barrel adjuster" on the cap that screws into the top of the carb that holds the throttle cable housing, with a knurled, round nut on it. loosen the nut and screw the adjuster and watch the slide, screwing it in till the slide stops moving down. now, twist your throttle slowly, and adjust the cable up or down a bit till it feels right. you should have a tiny bit of play before the cable pulls the slide up. just a tiny bit, any more and it'll be sloppy and you won't get full throttle. too tight, and it revs up like crazy at idle. then screw the little finger nut down against the base to lock the adjuster in place.


when that's all set, look back into the carb's throat and watch the slide as you screw in the idle screw slowly. it should move up slightly. if it does, unscrew slowly so it slides down, and unscrew till it stops sliding down. then screw back in slowly till it just barely moves up.

next step, looking at the slide again, twist your throttle slowly and watch to see if the slide moves up until you can't see it anymore. this is WOT, or Wide Open Throttle.

...
Click to expand...

When I turn my throttle handle, it lifts the cable housing up out of the cap. I'll check it in daylight, but the black cable housing and it's metal termination lift right up out of the carb cap. Should I duct tape it in place so it will force the cable and (I guess) barrel where it needs to go ... or ... is it more likely that there is something gummed up in there holding the my throttle wide open position? Thanks. wee.
 
TravelingBikeBuilder,
That is caused by a very loose adjusted throttle cable. That would happen when you release the throttle hand grip and/ or twist the hand grip forward with said loose cable.
Follow bairdco's instructions carefully, especially on how to adjust the cable using the ""barrel adjuster" on the cap that screws into the top of the carb that holds the throttle cable housing".
Do not take shortcuts.
bairdco has done an awesome job describing the how to's and why's of cable adjustment and idle speed adjustment. They are, in a way, related to each other. If you cannot get the cable to adjust correctly, we will help you work it out.
 
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Hi bairdco!

Your post was extremely helpful for me.

I've already got 270 miles on my first build (66 HT / NT carb). But still dealing with a little 4 stroking in the mid-range and some loss of power WOT. So been doing a lot of reading here.

I had been using the cable adjustments at the throttle and the carburetor cap to set the idle. I didn't understand why the idle set screw did nothing.

I followed your simple instructions of how to adjust the cable and saw the light! I spent ten minutes on it:

1. First removed the air filter housing.
2. Loosened the idle screw almost all the way out.
2. Then loosened the lock-nut on the cable adjuster on the top of the carburetor cap and the lock-nut on the throttle end of the cable.
3. Then observed the barrel as I twisted the adjuster nuts at both ends so that the barrel was all the way down. I started with twisting the adjuster on the carburetor cap so it was all the in and then finished using the adjuster on at the other end.
4. Then tightened the lock-nuts both ends.
5. Then observed the barrel as I adjusted the idle screw to see that there a slight gap at the bottom.

I then pedaled, popped the clutch...and nice! It was running and idling sweet. And giving it the gun (twisting the throttle) is smooth and returns back on release easily.

I knew I was adjusting the throttle cable wrong but I didn't know the right way. Now I do thanks to you. =)

Russ
 
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Stumbled across this post and I am new to all of this and I’d just like to say this is an extremely useful post! Great and simple information...thank you!
 
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