Carb tuning question

[SilveradoSS]

Hi, all. Got a question for the forum experts. I have one of the Baja PX250 cruiser style motorcycles and I'm having trouble tuning the carb. I just bought a new carb and set the needle clip to the next to last notch from the bottom. The bike runs well in the upper rpm's, however at cruising speed, the engine feels like it is surging and when I roll on the throttle at cruising speed, it feels like it is flooding out before the engine picks up. Then it accelerates normally.

Where am I going wrong? I've adjusted the idle screw, actually until its probably too far out, with little to no effect on the idle speed. The idle speed actually goes up as the screw is closed which is weird. I can completely close off the idle mixture screw and the bike keeps on running. I had this same problem with the original carb too. Do I have a fuel delivery problem?

[makenzie71]

put the clip on the top notch

[SilveradoSS]

Thanks for the reply makenzie71. I'll give it a try and get back to you.

[SilveradoSS]

put the clip on the top notch

Alright, I put the clip all the way to the top notch and now the engine breaks up at anything more than 1/8 to 1/4 throttle. I tried to operate the choke while riding, but problem just got worse. Also, while I was removing and reinstalling the carb for the 1,000,000th time (ha!), the stud stripped out that holds the carb to the manifold. So I'll have to buy another manifold before I can continue. The stripped bolt might be related to the poor running due to an air leak but the carb is double o-ringed, so I'm inclined to think that the problem will persist even after the manifold is replaced. Any other suggestions?

[Weldangrind]

A vacuum leak usually presents itself when you rev the engine; upon releasing the throttle, the engine does not immediately return to idle, but rather takes a few seconds.

Try the clip in the middle notch and see what happens. If you can increase rpm by closing the air / fuel screw completely, then I'd say that your pilot jet is too big, but that's not a big deal if it idles properly.

[SilveradoSS]

Weldangrind, this thing is driving me crazy! I bought it for $1200 and after all of the parts that I've replaced and the damn thing still won't run properly. About ready to shove it off a cliff. I just ordered the manifold and will wait until I get that replaced before I continue. Please keep the info coming. I'm still making note of what I can do when the part gets here.

By the way, how much air should be coming from the crankcase hose? I've got a pretty good amount of air coming from the hose on mine. My luck, the engine is bad and I'm chasing a ghost issue.

[makenzie71]

I hate trying to help people with carburetor woes over the internet...it can be such a hit or miss type thing. My rule of thumb has always been that if you don't know what's wrong with the carb, change "something". Anything. If it makes it worse, go the other way. If it makes it better, keep going.

So put the clip at the extreme opposite :)

You should get a pretty good bit from the crank case breather. The breather is releasing all the pressure you get when the piston goes back down. Imagine the force the engine is producing when it fires....it's a lot of the same going the other way.

[SilveradoSS]

The breather is releasing all the pressure you get when the piston goes back down.

Makes sense. I was worried I had a broken ring or something.

Anybody know how to check the valve settings on a parallel twin type engine. That is something that I haven't checked yet.

[makenzie71]

http://faq.ninja250.org/wiki/How_do_I_adjust_the_valves%3F

[SilveradoSS]

http://faq.ninja250.org/wiki/How_do_I_adjust_the_valves%3F

Did a search after posting and I see there are several how to's for this adjustment under Honda Rebel valve adjustment when googled. Thanks.

[makenzie71]

Rebel is about the same. I just like the Kawasaki site. The screw tappets pretty easy across the board. That's one of the biggest reasons I went with a pre-Katana 750 motor for my GS750.

[Weldangrind]

Weldangrind, this thing is driving me crazy! I bought it for $1200 and after all of the parts that I've replaced and the damn thing still won't run properly. About ready to shove it off a cliff. I just ordered the manifold and will wait until I get that replaced before I continue. Please keep the info coming. I'm still making note of what I can do when the part gets here.

By the way, how much air should be coming from the crankcase hose? I've got a pretty good amount of air coming from the hose on mine. My luck, the engine is bad and I'm chasing a ghost issue.

We'll get it figured out. Once your new parts arrive, we'll have an easier time troubleshooting. I'm guessing that jet size is an issue.

[SilveradoSS]

We'll get it figured out. Once your new parts arrive, we'll have an easier time troubleshooting. I'm guessing that jet size is an issue.

That just seems strange that the stock jetting would be so far off. I've noticed some fuel puddling (not really puddling, more like a little wet fuel) in the runners to the cylinder when taking the carb off. Could I have a float problem? What are the odds of both carbs having the same float problem? How does one go about adjusting the float?

[SilveradoSS]

Now that I think about it, the fuel in the runners is probably due to the enrichment circuit on the carb. There is a external diaphram with a lever that pumps fuel into the throat of the carb when the throttle is opened from the closed postion. Probably pumps fuel in while I'm disconnecting the throttle cables.

[SilveradoSS]

I finally got my intake manifold in for my bike. I replaced the bad one with the new one and I think I figured out what my problem is. After putting on the new one, I began squirting carb cleaner around on intake parts and found the engine idle dipped and choked out when I sprayed the cleaner around the intake base where it mounts to the engine. I'm gonna get some sheet gasket and some form-a-gasket and see if I can finally get this thing running correctly. I'll let you know what happens. Thanks to those who have helped me so far.

[SilveradoSS]

Well, I think I have it ironed out. I bought some o-rings from the local parts store and replaced the o-rings at the intake to head mounting points. The old ones were leaking air into the cylinder and leaning out the carb. After placing the needle clip to the next to lowest setting, I finally have adjustment with the mixture screw and the choke is now working properly. Bike seems to be running well now. :D

[Weldangrind]

Glad to hear you got it figured out. Happy trails!

[SilveradoSS]

Thanks to all for the help!