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Post by frost1003 on Oct 4, 2020 0:37:54 GMT -5
I've got a 50cc scooter that was running good. It's developed an issue where it will crank up and run just fine cold.
After I drive about 2 miles and the entire engine is warmed up, it basically dies. It will crank up and idle just fine once the engine is warmed up; but once I give it just the slightest throttle, it dies. It acts the carburetor bowl runs out of gas and dies. This seems unlikely because it runs fine while it's cold. I'm wondering if there may be a crack in the metal somewhere that gets larger when it's hot, and sucks in air and runs too lean. I've looked around the intake area, and sprayed starter fluid around the carb and intake area while it idles and couldn't detect any revs in rps. Any suggestions why it idles fine while it's hot, but dies immediately with throttle?
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Post by GrumpyUnk on Oct 4, 2020 9:03:52 GMT -5
It likely falls on its face because the mixture is too lean. Air will get moving faster than liquid fuel. The fuel 'acceleration' inside the carb takes time, airflow into the intake gets going NOW. Accelerator pump on these carbs, if you have one, is by a lever on the linkage side that is moved when you open the throttle.
If yours is newer, it may have an internal accelerator pump which I have not take apart yet to figure out.
With the older system you should see a bit of fuel get squirted from the tube at the front of the air inlet coming from about 4:00 o'clock. Open the throttle and it should squirt. Otherwise it might stumble and die.
Also, if the fuel mix is on the lean side at idle, it will be more likely to stall/stumble. If you have not adjusted the mix, or your mixture screw is still behind a brass(?) cover, it may be the idle port has gotten some schmoo inside, and is not flowing well, perhaps not enough for the transition. Last thing would be the pilot jet getting plugged or partially such. It flows fuel from idle up to partial speed, transitioning from idle to full boat. If obstructed, medium flows could be lean, leading to stumble or hesitation, etc.
so... acceleration pump or equivalanet can cause stumble/stall on opening the throttle. or the 'transition' circuits of the pilot jet.
tom
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Post by 2stroked on Oct 6, 2020 9:02:10 GMT -5
I've got a 50cc scooter that was running good. It's developed an issue where it will crank up and run just fine cold. After I drive about 2 miles and the entire engine is warmed up, it basically dies. It will crank up and idle just fine once the engine is warmed up; but once I give it just the slightest throttle, it dies. It acts the carburetor bowl runs out of gas and dies. This seems unlikely because it runs fine while it's cold. I'm wondering if there may be a crack in the metal somewhere that gets larger when it's hot, and sucks in air and runs too lean. I've looked around the intake area, and sprayed starter fluid around the carb and intake area while it idles and couldn't detect any revs in rps. Any suggestions why it idles fine while it's hot, but dies immediately with throttle? When did the valves get adjusted last? |
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Post by frost1003 on Oct 6, 2020 20:21:28 GMT -5
I'm not sure if the valves have ever been adjusted? I bought it used and it's just recently developed the issue.
I've seen how to adjust it. I need to buy some gauges but I've adjusted valves before on other scooters. I wouldn't have thought of that in this case. But it would be worth checking. Thanks.
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Post by GrumpyUnk on Oct 7, 2020 9:31:39 GMT -5
Most times, if the valves are too tight, it will be harder to start after it has warmed up. The higher temp will tend to close the clearance even more, so valves that are too tight will not seat well when up to running temp, and will have enough leakage to cause low compression. Low compression will make it harder to re-start when hot. If yours fires right up when hot, but you cannot open the throttle without a stall, you likely don't have valve problems, but more likely have carburetion or fuel supply/float bowl fuel level problems.
In addition to the fuel, the stuff mentioned in the other post still applies. Your idle system provides tightly controlled fuel flow with very small aounts of fuel. The adjusting device is a tapered needle, set at the factory, and hard to access as sold by some. If too lean, it will not provide fuel to run the engine past slow idle rpm. The accelerator pump helps transition from idle to pilot. Pilot provides 'middle' speed, between idle and high speed systems. If the pilot is plugged, it may not start(it also feeds the idle), and may not run well as yours is doing now.
tom
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Post by frost1003 on Oct 14, 2020 20:56:07 GMT -5
So after adjusting the valves it seemed to make a big difference it the engine performance in starting when its cold.
It started right up and idled perfectly after adjusting the valves.
The engine still bogged down and cut out when given throttle while the engine is cold.
I'm pretty sure now that it's a clogged main jet in the carb. I'm gonna take it apart and clean the pin holes with a paper clip and spray it down with carb cleaner. Hopefully, that'll fix it. I'll report back.
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Post by GrumpyUnk on Oct 15, 2020 8:25:52 GMT -5
Most engines will 'bog down and cut out' when you give them a lot of throttle when cold. If it does that with minimal throttle, that is not quite normal. If you open the throttle gradually, the rpms should increase until you start to move, at which time you should be able to open the throttle even more.
The engine will likely be a bit 'stumbly' for about 2-3 minutes after starting. When I start a cold engine, I tend to sit for a minute to let it warm up, not quite as long as the byvalve will take to turn off, but for a good 30 seconds, I won't do anything at all to the throttle. After it has run for 30, I start to give some throttle. When working, I can gingerly open the throttle and ride off without stumble or hesitation.
Make sure your accelerator pump is working as it can cause stumble if not.
tom
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Post by frost1003 on Oct 16, 2020 23:17:57 GMT -5
Well, I've taken the carb apart and cleaned it well. The jets are clear.
I put it back together and it's still starting just fine while cold, idles and runs fine while it's cold.
Once it's warmed up it cuts out. I can start it while it's hot and it idles fine. When I give it the slightest throttle, it dies completely.
I'm thinking it might be a choke problem? I'm on my 3rd electric choke that I've swapped out. I am wondering if it's causing some issue once it's warmed up?
I adjusted the air screw and ended up where I started with it. It idles best where it's at. It's a brand new carb.
I also adjusted the valves. I'm a little puzzled over how it's acting.
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Post by GrumpyUnk on Oct 17, 2020 8:45:32 GMT -5
Repeating:
"Make sure your accelerator pump is working as it can cause stumble if not.
tom"
The accelerator pump is on the back side of the carb, mounted low. It has a vertical shaft that is poked by the throttle linkage when the throttle is opened. A thin lever moves and pushes on the shaft, causing a bit of fuel to squirt into the carb. That squirt is supposed to prevent the engine stalling when the throttle is opened.
Remove the air cleaner tube from the inlet side of the carb. Observe the inlet, looking at the tube that sticks up from about the 4:00 o'clock position while you/someone operates the throttle. You can do the same by moving the linkage manually. While moving you should see a squirt of fuel come from that tube. If you don't, check the flat lever on the linkage to see that it moves the shaft on the pump. If it is, and you no have squirt, the pump could have damaged check valves or diaphragm.
tom
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Post by mikehailwood on Oct 17, 2020 12:07:59 GMT -5
To add to tom's comments regarding the accelerator pump....I realize that you've cleaned the carb numerous times. It might be informative to follow the path fuel takes on its' way to the accelerator pump and from the pump to the carb throat. Once this is understood, you'll know just where to thoroughly clean those passages for the pump to get the maximum fuel through them.
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Post by tortoise2 on Oct 17, 2020 13:20:24 GMT -5
Ignition elements are also considered wear items . . and GY6 parts are soooo cheap! |
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Post by frost1003 on Oct 23, 2020 7:18:26 GMT -5
Ignition elements are also considered wear items . . and GY6 parts are soooo cheap! Thats also true. I ended up putting the original carb back on and changing several rubber vacuum lines. That seemed to do it. It runs and idles now. Thanks for all the feedback! |
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Post by FrankenMech on Oct 23, 2020 12:47:50 GMT -5
Using a replacement carb would have been important information to include in your first post...
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Post by mikehailwood on Oct 23, 2020 12:53:58 GMT -5
"Using a replacement carb would have been important information to include in your first post..." And....we'll never know what the problem was with that carburetor. |
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Post by FrankenMech on Oct 23, 2020 22:19:38 GMT -5
The replacement carb probably wasn't jetted correctly for his application.
Who knows what other changes there were that were not disclosed  |
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