Bike only runs when gassed or on choke

[gary200211]

Hey guys. You all were so helpful last time I had an issue, so I'm back for more!

I first noticed a few weeks ago a slight bog during the idle. I'd be around 1300 rpm, and it would randomly drop to like 1000-1100 for a second, then go back up. My first instinct was maybe a spark plug issue. I kind of just let this go since everything seemed to be working fine.

Lately I've been doing a lot of highway driving. Not too far, 20 miles a day maybe. Yesterday everything started fine, then after my highway ride I went to start my bike again and it started up but was really sputtering. It eventually died on me. I struggled really hard trying to get it back up and running, and it finally started up on choke. second I flipped the choke over, it instantly died. (this is fully warmed up btw) after practically killing my battery and a few loud pops (sounded like a gun shot) I got it back up and running. If i ever let off the gas it would die. I made it home, when under gas it ran fine. Doing 75 on freeway np.

Today I started working on my bike. I removed the carbs, cleaned everything up really good, and reinstalled. same exact problem. I could get it running full choke but it would immediately die after 3 seconds when taken off. It even completely died at full choke at one point.

I changed the spark plugs, because I thought maybe they were bad. They were. They were pretty black. I fired my bike back up, and it ran again! was idling excellent off choke and everything. I revved the engine a couple times, it sounded great. After it fired up I had it running a good 20 minutes making adjustments after it was warm as needed. I thought everything was ok.

hour later I warmed my bike back up and went for a ride (freeway again) second i turned off on the off ramp and pulled in clutch to come to a stop, the engine completely died, instantly. I had to restart on full choke. This time, my choke wasn't getting up to the normal 3kish rpm, it was barely sitting at 1500 on full choke. I ended up making it home again having to keep the throttle open at all times even at a stop. Second i pulled up into my drive way, it instantly died when i let off the gas.

I thought i fixed my problem and now i'm back to square one!

Note: my mixture screws are currently about 3 turns out. I started with the 2 1/2 and this seemed about right. Air filters all fine, its getting gas, etc.

Sorry for the essay. Just wanted to clarify everything that's going on.

[Jet⚡Black]

Hey Gary,
Have you done, any modifications? Such as new jets, pods etc?

Were your fouled plugs black and sooty or black and oily?

When was the last time the valves were adjusted?

Your bike is running rich; a few things can cause that, from simple intake leaks all the way to tight intake valves.

Answering the above will help me/others narrow down the problem, so you're not doing 5 things you don't need to do.

[gary200211]

Hey jet,

Nope, never made any modifications.

The plugs were a bit wet. looked slightly oily.

This particular bike sat in a buddies garage for 6 years without running. When I got it from him we cleaned it all up and I've put maybe 4-5k miles on it. Never adjusted any valves, and not sure how to even begin to attempt that.

I thought maybe I was running pretty rich too. When I pulled my carbs off yesterday and checked my mixture screws, they were over 5 turns out. I quickly changed that as of yesterday. about 3 turns out now. I'm pretty bad at adjusting it.

[eaglerider]

Adjust the valves..99.9% sure that will "cure" your problem.

[Jet⚡Black]

5 turns does sound a bit much, compared to where you were first at...
I'm feeling a bit lazy today, so I am just going to cut and paste a tutorial that's close enough to my own procedure anyways.


1) Warm up the engine to full operating temp.

2) Turn up your idle a few hundred RPM using the throttle stop screw (basically you want a fast idle). This will make it easier to hear small changes in RPM. Watch for overheating--pointing a big shop fan at your engine will help it from getting too hot during the fast idling. The whole procedure shouldn't take too long though.

Each time you change the screw setting 1/4 or 1/2 turn or so, wait about 5 seconds to let the idle speed normalize. It usually take the carb and engine a moment to react to the change.

3) Turn the fuel screw IN until the idle starts to drop and miss. The engine should die if you bottom out the screw. Your pilot jet is too big if it doesn't die when the screw is bottomed out--it should die before it gets that far in.

4) Then begin turning the fuel screw OUT. The idle should peak and become smooth. Keep going and look for the idle to begin to drop/miss again.

5) The goal is to find the setting that provides the highest and smoothest idle. If it's unclear exactly were that point is then set to the midpoint between step #3 and step #4. For example, if the idle starts to drop at 1 turn out and starts to drop at 2 1/2 turns out then 1 3/4 of a turn out should be the correct setting.

If the peak/smoothest RPM is reached somewhere between 1-3 turns then your pilot jet is correct (the 1-3 turns applies to most carb types). If you end up less than 1 turn out then your pilot jet is too big and you need a smaller one. If you end up more than three turns out or the fuel screw seems to make little difference as you continue turning it out than you need to go up (bigger) on your pilot jet.

To re-emphisize: If the idle never drops when you're turning the fuel screw in, you need a smaller pilot jet. If the idle never drops when you're turning the fuel screw out, you need a bigger pilot jet.

Typical fuel screw settings are in the 1 1/2 to 2 1/2 range.

6) Once you've got the fuel screw set, re-adjust your throttle stop screw (idle screw) to an appropriate idle speed.

And that's it! Your pilot circuit is now VERY close to ideal. From here you can experiment with how small adjustments affect low-end (i.e. small throttle openings) response and make adjustments for weather. The hardest part is usually gaining access to the screw while the engine is running. Also, you may really have to listen carefully to detect the rpm changes in the idle. 100 or 200 rpm differences can be tough to detect when the change happens over several seconds.

And lastely, a little bit about the difference between fuel screws and air screws:

Two stoke carbs normally have air screws and four stroke carbs normally have fuel screws. You can tell if a carb has an air screw or a fuel screw by it's location on the carb. An air screw will be on the intake side of the carb while a fuel screw will be on the engine side of the carb.

They sort of work opposite one another. An air screw adjusts how much air is being delivered thru the pilot circuit: in is rich (less air) and out is lean (more air). A fuel screw adjust how much fuel (or air/fuel mixture) is being delivered from the pilot circuit. In is lean (less fuel) and out is rich (more fuel).

But aside from setting those lil buggers correctly; I and I know Eagle both strongly suggest adjusting the valves. The bit of oil on the plug is an indication that they need some adjustment, the valve's aren't opening enough, to get full combustion and a proper operating temperature; to burn off the oil to make it that nice brownish tan color we are looking for.

[gary200211]

Yeah I've been running 5 turns out for a couple months now. In fact my last post was related towards that, I was unable to get my idle to drop after giving it throttle. Turning the mixture screws out more solved that.

Does it matter if the bike is on full choke or not when adjusting the mixture screws? I can't run it without it. Also, should I do this before or after I adjust my valves? and is there some kind of guide or tutorial, preferably with pics on valve adjustment.

Thanks a lot guys this gives me something to do this labor day weekend!

[Blaine]

Sept 2, 2012 15:39:58 GMT -6 gary200211 said:

Yeah I've been running 5 turns out for a couple months now. In fact my last post was related towards that, I was unable to get my idle to drop after giving it throttle. Turning the mixture screws out more solved that.

Does it matter if the bike is on full choke or not when adjusting the mixture screws? I can't run it without it. Also, should I do this before or after I adjust my valves? and is there some kind of guide or tutorial, preferably with pics on valve adjustment.

Thanks a lot guys this gives me something to do this labor day weekend!

When adjusting th choke needs to be fully open with the engine warm. I would start with a valve adjustment.

[gary200211]

Hmm an update: I was just out there messing with things, and I noticed on the right carburetor, the mixture valve. there was a vacuum on it. I noticed it because I put my screw in to adjust it, and before even turning anything. my idle went up. I was like what the? I held my finger over, and sure enough its pulling air through there. My idle went up, and it even ran off choke for the first time (engine is cold too). After turning off the engine even a tiny bit of white smoke started coming through.

What the heck?

Edit: lol.. how embarrassing. I pulled off the carburetor and sure enough sitting there underneath was the mixture needle. I guess it somehow fell out while i was on the freeway driving yesterday. I'm not sure what caused that to pop out. but its back in. will let you guys know how things go.

Who've thought.

[Jet⚡Black]

There's supposed to be a tension spring to keep it from backing out...
The order into the hole goes: O-ring then washer then spring then jet.

I still think you really need to do a valve adjustment, but it is really important that jet business sorted too. I suggest doing the valves first; so you're not tempted to just ride it ignoring the valves, if you get the jets squared away first.

The valves on this bike tighten over time. Which means they can and will stretch, if that happens you're going to have a broken valve slamming around in the head...if it snaps at 5k rpm, that broken valve will slam around in the cylinder 5000 times per minute not including the bouncing...it's not a pretty sight.

If it sounds intimidating read the many threads here on it; post before you start, and I or someone else will be happy to walk you through it, if your questions don't get answered from searching. Make sure to change the days in a search to something like 700 default I think is like 7 days, which most times brings nothing relevant back.

The worst part is dismantling everything to get to the valves, the actual adjusting is a breeze. In the words of Rob Schneider in his last 5 appearances in a movie..."You caaan do eet!"

[gary200211]

Yeah I guess at some point someone lost the springs. it's in neither side. I've never actually pulled that particular jet all the way out to check. stupid me.

Thanks again Jetblack I'm definitely going to look into this valve adjustment thing. I wasn't searching deep enough into the history to that's why nothing was coming up, good call.

Thanks all

[eaglerider]

One of the big reasons I advise to read, read...get a manual and read it to learn about your bike. If you have no idea what to look for, you have no idea what might be missing. Nothing bad ment by what I said above...but educating yourselve(s), even just a little before trying to fix something, will prevent lots of mistakes, and get your bike up and going faster, so u can enjoy the ride.

[gary200211]

Oh I completely agree. I'm all for doing it yourself and learning. That's why I'm here =) Google is my best friend. I'm 100% self educated and continue to learn more and more each day, especially browsing these forums. I haven't been able to get my hands on a manual yet, though I do have an online version of a haynes manual that's been a bit help.

Last thing I expected though was the darn screw falling out. Didn't realize there was a spring that was supposed to be in there missing

I still plan on checking these valves here in the near future. still reading up on it some more. doesn't seem too bad.

and again, as always, i really appreciate your guys words of wisdom. thanks

[wanchesenative]

Don't be scared of the Valve Adjustment. I was where you are now and intensely dreaded it. I am not by any means a mechanic, but I can "turn a wrench." The ONLY complicated thing about it was taking EVERYTHING OFF in order to make room to get to it. Look through the posts here and get 'er done. It makes a HUGE difference in how she runs.