Carb. problems....still

I've been posting for a couple of weeks on the QT50 I'm working on, so some of ya'll know the deal, not going to drag all the boring details in again. Tried pretty much all the suggestions from before and got some results. It cranks on the first try, idles smooth as silk and runs OK. Same problem, won't go past 20, starts bogging down. Was wondering though, and I need some input, I did swap carbs. out. I have a 1980 QT50 that I've been using for parts, that carb. was in pretty damn good shape. Somehow oil got in it when it sat for all those years and preserved pretty much everything. The 1983 QT50 that I'm rebuilding, its' carb. was totally trashed. All the gas inside it varnished, well, you get the picture. I pretty much put the 80 carb on the 83 one I'm rebuilding. Question: could that be my problem, wrong carb. set up? All pieces, I mean ALL, fit and interchange. In fact, I did use a part or two off of the 83 carb and put it on the 80 carb. From what I've researched, these two engines should be exact. Both are 49cc, both used Mikuni carbs, all threads, needles, bowls, etc. etc. are exact. Was wondering maybe, for EPA reasons, Yamaha made a suttle change in their design from 80 to 83? Did a plug chop, has a brand new plug, and it's dark. Too rich. Maybe I should put the 1983 main jet on with the 1980 carb? They are both identical. This 83 I'm working on has only 200 original miles, can't believe it would be something mechanical. I blew out the intake pipe with carb cleaner, no avail. One thing I did notice, when on the stand, breather off, wide open throttle, small amounts of gas droplets will come out of the air intake. Got a feeling the master is too big, just hard to believe because this is the original factory set up.

Anyway, thanks in advance for any input.

Re: Carb. problems....still

Can you adjust the needle in the carb. Set it lower in the jet. That will lean it up a bit. Also, make sure your carb isn't choked somehow. Check your choke lever to make sure it's all of the way open. I say that because that happened to me once. I was using the choke to start it, and when I would give it throttle, the choke lever wasn't comming all of the way up. It was bogging my top end. Just some ideas.

Needle adjustment.....

Thanks.... so good info. The needle sits literally on top of the bowl. When the bowl lifts up, as in full of fuel, then the needle cuts the flow off. This choke set up is kind of different. When disengaged, it has no effect on the throttle or its' linkage, I think. Maybe I'd better take a closer look at that.....

thanks for the input.

Re: Needle adjustment.....

Ron Brown /

Scott,

The needle Chris is refering to, is a long, tapered needle, extending from the bottom center of the slide, if you have one.

Have you tried testing with the air box/filter removed?

The fuel droplets at the intake could be an indication that the float level is too higH, this would make it run rich.

Ron

Re: Needle adjustment.....

Bada Bing, Bada Bang..... Learn something everyday. Yes, it does have the long tapered needle going down the slide. And, since at work and thinking, it does have a cable adjustment to the whole thing on the throttle cable. OK, starting to make sense now. Maybe I need to pull off the original slide and tapered needle and put it on the original jet...................... and probably do the same to the choke slide. Think that might help???? One question though, the float is hinged on the carb and the fuel needle, like in the first post reply, is laying on top of that bowl float. How do I adjust that?

Re: Needle adjustment.....

Ron Brown /

Scott,

First off, I hope I am not offending you by replying to this post. : ) Seee the "Hey Wuss" thread.

The tapered needle is usually adjustable. If you remove the cable from the slide assembly, then you should be able to lift the needle from the slide. It is usually held in place by the slide spring. There should be grooves, usually 5, at the top of the needle. If you put the clip in the top groove, the needle will be lowered and you will get the leanest possible adjustment. Keep in mind that this is a mid-range adjustment and may not help your full throttle problem.

As for the float, there should be a small tab near the float hinge that presses on the float needle. You can adjust the float height by bending this tab. If you do not have specs for this, most floats are adjusted correctly when the float is parallel to the carb gasket face. Having the correct specs is best.

Ron

Re: Needle adjustment.....

Ron Brown /

Scott,

I forgot to mention the cable. If you have a little free play at the throttle cable when the throttle is closed, about 1/16" of cable play, and the throttle slide opens all the way when the throttle is opened, then your cable is ok.

Ron

Appreciate the good info....

Will try these out when I get to the house. Appreciate all inputs. Since nobody mentioned that I could have wrong carbs in it, I will assume I don't and it also seems like it doesn't matter anyway. Something in the carb is not working correctly, got to fix it.

thanks.

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