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Post by benhonda on Feb 1, 2019 18:03:38 GMT -5
I was given a '89 yamaha jog 50cc 2 stroke. I have replaced the stock fuel pump and carb Bike starts right up, idles good, can rev up while on the kick stand if you blip the throttle but if you hold it wide open it will bog down after a couple seconds.
If you give it full throttle from a stand still it will start to take off then bog out a second later. If you give it 1/3 to almost 1/2 throttle it runs down the road good, even manages 25-28 mph But you can't go past full throttle
Also, it can only run as mentioned with the air pilot screw fully screwed in. backing it out 1-2 turns causes the idle speed to drop and if you try to rev it up it bogs out at even lower throttle inputs.
I have already tried adjusting the main needle in the slide up and down. It didn't make much difference.
I checked for a leak in the carb boot (sprayed with starter fluid while running) and it checked out as good.
Being that it is a new carb I can't imagine what to check next. I'm guessing that it is not getting enough fuel but I have no idea why.
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Post by tsimi on Feb 1, 2019 18:39:28 GMT -5
Is the scooter stock 50cc or does it have any engine modifications?
What are your jet sizes? Pilot jet and main jet numbers?
From what you describe it, it seems to be starving of fuel. Not getting enough. The airscrew is a good indicator.
All the way in means you are cutting off the air and therefore it drives better. If you unscrew the airscrew it starts to get worse, meaning more air goes in and the air/fuel ratio gets worse.
Is the main jet maybe glogged?
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Post by ryan_ott on Feb 1, 2019 19:02:00 GMT -5
Are you using OEM air box and filter?
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Post by benhonda on Feb 1, 2019 19:34:39 GMT -5
Are you using OEM air box and filter? I did try putting on the OEM air box, it was only a tiny bit better.
I will pull the bowl off and look at the main jet tomorrow.
The other thing I should have mentioned is that when I first put the new carb on a few days ago, gas was pouring out of it. The original fuel pump's diaphragm had worn out so fuel was going down the vacuum line and into the carb.
When I got a new petcock/pump today the bike was spitting fuel/oil out the carb a fair bit, even at idle. It has gone away some now, but I am wondering if when I first put the carb on fuel went into the engine while the piston was down causing few/oil to go into the muffler and if maybe it is clogged. I would think a partial clog could effect the bike at higher throttle while letting it run fine at idle and lower throttle input. Not sure how to best try and clean it out though. Will check the main jet first but since it is a new carb is "should" be fine.
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Post by Happypancake! on Feb 1, 2019 20:30:41 GMT -5
Did you check for an air leak?
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Post by benhonda on Feb 1, 2019 20:38:01 GMT -5
Did you check for an air leak? i checked at the carb boot, sprayed it with starting fluid while the bike was running. I figured that was the most likelypart to be cracked/letting in air |
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Post by benji on Feb 1, 2019 20:56:21 GMT -5
Sounds like your carb may not be filling up with fuel or your carb is clogged. Pull it off and clean out the bowl, and make a note of what the jets are. Then compare em to your old carb. And always use the airbox, don't remove it. The airbox is not the problem, the carb more than likely is.
Also, what fuel pump? Do you mean petcock? If so, its vacuum operated. If you didn't run the vacuum line to right spot, exactly what your describing can happen.
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Post by benhonda on Feb 1, 2019 22:27:35 GMT -5
Sounds like your carb may not be filling up with fuel or your carb is clogged. Pull it off and clean out the bowl, and make a note of what the jets are. Then compare em to your old carb. And always use the airbox, don't remove it. The airbox is not the problem, the carb more than likely is. Also, what fuel pump? Do you mean petcock? If so, its vacuum operated. If you didn't run the vacuum line to right spot, exactly what your describing can happen. ok, so I only started working on scooters/mopeds less than a year ago...have I been calling these vacuum actuated valve things fuel pumps when they are actually just a fuel shutoff that opens via the vacuum of the engines?
pic one is what was on the tank originally. I thought it was a vacuum actuated fuel pump. I couldn't find one to buy, so I got a fuel shutoff valve petcock as seen in pic 2. Then I ran (what i thought was a vacuum pump) what is seen in pic 3. Is the part in pic 3 not even needed on this bike? I am used to seeing these "pumps" on 50-150cc 4 stroke scooters, even ones that have fuel shutoff valves. So I thought they were a pump.
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Post by ryan_ott on Feb 1, 2019 23:48:43 GMT -5
If the fuel tank is above the carb no fuel pump is needed, just a petcock either manual or vacuum is needed to stop fuel flow when the engine isn’t running. You can remove the 3rd pictured part it’s the same as the other 2 just a different style.
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Post by 190mech on Feb 2, 2019 2:42:54 GMT -5
Kinda think it needs a total carb cleaning,ALL passages flushed with Gumout,including the pilot,needle jet,& main too,stock airbox installed,then see what happens...
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Post by geoffh on Feb 2, 2019 9:27:53 GMT -5
Do all of the above,but pay attention to the air box mine leaked and was much better when sealed with duct tape You may have a restrictor in the inlet which will need removing. Geoff   |
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Post by benji on Feb 2, 2019 9:43:29 GMT -5
[/div]
[/quote] use #1, that is the correct one. It is a vacuum-actuated petcock, not a pump. #2 is an on/off/reserve switch, and I've had some leakage with those. Also, since there is no vacuum attachment on #2, I'm assuming you have an unplugged vacuum line. Bingo. There is your problem. I think. |
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Post by benhonda on Feb 2, 2019 13:14:05 GMT -5
If the fuel tank is above the carb no fuel pump is needed, just a petcock either manual or vacuum is needed to stop fuel flow when the engine isn’t running. You can remove the 3rd pictured part it’s the same as the other 2 just a different style. If that is the case I will just leave it as-is. The manual petcock is hard to reach and it would be easier to just leave it on and let part #3 do it's job.
Going to pull the carb off shortly and check the main jet + compare it to the jet in the original carb.
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jer
Scoot Member
Posts: 81
Location: Wyoming-Silicon-Genessee Valleys
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Post by jer on Feb 2, 2019 16:56:27 GMT -5
But you can't go past full throttle
Don't feel bad, my man, I doubt anyone here can easily achieve that lofty goal 
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Post by benhonda on Feb 2, 2019 19:25:04 GMT -5
so I pulled the carb off. No obstruction on the main jet. Compared it to the main jet in the old carb, there was no number on the new jet but the old one looked just a tiny bit bigger...so I put it in and then set the needle at the highest point. All to no avail, no difference. I looked on youtube and saw a guy who had the same bike and a cone filter but he had to wrap most of it with tape so it wouldn't get as much air. So I double checked the stock airbox that I had been using...no filter! So there was no real restriction from it. So I put on a cone filter and wrapped it half way with tape. This helped but not fully. I ended up wrapping it just over 3/4 of the way around and BAM, bike runs great now! So if the stock airbox had been complete/filter then the bike would have been running the other day. I have had other scooters and mopeds that I put cone filters on and it may have required small adjustments to the carb. But this bike is far more sensitive to air intake restriction. It still doesn't have a working front brake, but everything else is working on it. Got it up to 38mph with a slight downhill grade. Not bad considering I weigh 260 and the bike is almost as old as I am.  |
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