accelerating from 20mph to 45mph

[jmoak80]

Hi all,
I have searched this forum a bit and i haven't really found anything about my issue. I'm a newbie and i love this forum, ya'll are great help. Thanks in advance

I have a GV 250 that i recently cleaned the carb on (old gas). I saw the video posted sometime ago by another user and it was great info. When i got it back together it started and revved and runs fine however it is slow getting up from 20 to 45 mph. it has good acceleration to 20 mph and sometimes i can feel it kick me up to 50+mph no problem but most of the time it takes 15 seconds or so to get to 45 then it really wants to go 60+mph.

I was thinking a couple of things. Maybe i got carb cleaner in the diaphragm intake, this causing the carb diaphragm to slow and/or act erratically. Maybe the accelerator pump is clogged (i confirmed it was unclogged when i put back in, but you never know) maybe the drive belt is worn or slipping?

Has anyone ever had a problem like this?
any help would be greatly appreciated. thanks you

[mrbios]

That was probably my carb videos if so glad they helped.  To test the diaphragm review the video - basically when you put your finger inside the carb on the air filter side and push the slide up it should not just fall down and you should feel resistance and hear a sucking noise just like in the video.  If you have even a small leak it will fall up and down with almost no resistance. 

I'm not sure how much difference3 the accelerator pump makes and I don't think it is the cause of your problem. Is the idle steady or erratic? I would verify that all the hoses are on and you don't have a vacuum leak.  You could try spraying water with a spray bottle while the scoot is idling with the seat off to test for leaks. 

It sounds like a fuel delivery problem or a vacuum leak - you could remove and inspect your spark plug for signs of a lean burn (white or very light plug color). 

I doubt the belt is slipping but it is possible if a previous owner (po) didn't operate it correctly and used the engine to hold the scooter in place at lights instead of the brake.  That gets the clutch and belt really hot.

Report back.  The GV is a good machine once it is properly tuned. 

[jmoak80]

Thank you for the response. I will perform the tests as described. I will keep you posted i promise. Thank you again.

[jmoak80]

I checked the entire vacuum tube system with water, i'm not seeing any leaks anywhere. The spark plug looked fine. The scooter isn't giving me much power anymore at higher speeds. it used to sort of take off sporadically between 20 and 45mph. now it gradually gets up to 50-55 (takes like 30ish seconds ) and doesn't really want to break that speed. The vacuum chamber falls rapidly when you push up but does make a faint slurping sound. So i guess i'm going to find the rebuild kit and tackle that next. I have the repair manual, for whats it is worth. do you think this is the proper plan of attack? Any help would be greatly appreciated.

[mrbios]

... The vacuum chamber falls rapidly when you push up but does make a faint slurping sound. So i guess i'm going to find the rebuild kit and tackle that next. I have the repair manual, for whats it is worth. do you think this is the proper plan of attack? Any help would be greatly appreciated.

Yes, good work so far and thanks for the update.  In my case the carb clogging hesitation issues was a marathon not a sprint ... however, I learned a ton and as I made those videos you have lots of photos and general knowledge at your disposal that I did not so the chance of success is even greater. 

Unfortunately, there is no "rebuild kit" for the OEM kymco carb.  Yes, there are "kits" for "GY6" scooters but the parts will not fit.  I do have an OEM carb that Jay (a guy on this forum) was nice enough to give me for parts - it has a good diagram and other useful parts but the carb has an issue that could not be addressed even with multiple cleanings so it is parts only. 

In your case you  need to order the diaphragm costs $30 (I think).   I am concerned with ordering Kymco parts since I don't have a local dealer and my last order from Chaparral has not arrived and I ordered almost 3 weeks ago.

Anyways, if you pushed the diaphragm and did not encounter a lot of resistance and slow downward movement then you have a vacuum leak and that will kill your highspeed power 50mph+  Have you inspected it for damage - crack, pin hole etc?

Report progress as we look forward to you getting this thing working properly.  I just applied dielectric grease to my switches today and I'm at 19,400 miles.

[jmoak80]

I still haven't figured out what the throttle hesitation issue is. I pulled the carburetor out again and throughly cleaned the main and secondary jets. I also tested the diaphragm by attaching a vacuum to the outlet of the carb. With the carburetor out i turned the vac on and actuated the throttle body, sure enough the gate lifted proportionally to the amount of throttle i gave it. I know this test might not be entirely accurate because the amount of vacuum might have been too much giving me the impression that the diaphragm is 100% operational  and not leaking but it did offer some piece of mind. I ordered a new diaphragm anyways and i will install when received. My next line of attack might be the fuel pump, it could be slow. I know in the manual it specifies an certain amount of fuel (maybe 14cc in ten sec). It could be a faulty fuel pump or an undersized fuel filter (that test should confirm). i will keep everyone posted.

[mrbios]

....impression that the diaphragm is 100% operational  and not leaking but it did offer some piece of mind. I ordered a new diaphragm anyways and i will install when received.

My next line of attack might be the fuel pump, it could be slow. I know in the manual it specifies an certain amount of fuel (maybe 14cc in ten sec). It could be a faulty fuel pump or an undersized fuel filter (that test should confirm). i will keep everyone posted.

1.  how much of a hesitation are we talking about? 

2. Has there been any noticeable improvement?

3. How is the idle?  Stable, unstable?  Requires twisting the throttle just to keep the motor running?

It is always hard to read about a persistent problem but you are learning and making progress.  Anytime something is tested, cleaned, replaced - you can rule it out and move on.  Something has been accomplished even if the problem still remains. 

Good work testing the diaphragm with the vacuum  pump.  Basically, it is a leak test more pass / fail than a specific rate or inches of mercury etc.  Be careful with the old and new diaphragm as it is easily damaged and requires care at all times.  A tiny bit of grease around the edge where the groves makes the seal helps it to go in to place as the top is tightened down. 

I don't recommend replacing the fuel pump... yet because if the carb bowl is full of gas it should take off with no hesitation until the bowl is empty or runs low then it is up to the pump to refill it.  A weak pump usually shows up at high rpm / full throttle for extended amounts of time like on the highway - a weak pump that can't keep up with the max demand for gas will give the sensation of running out of gas.  You could disconnect the line going to the carb and squirt gas in to a clean container to observe flow (then pour it back into the tank). 

No need to keep cleaning the jets - esp the main jet as it is basically just a hole and a very short run.

Next test:
1. Take the pilot screw aka idle screw (not pilot jet) and turn it clockwise and count and record the number or turns.  Turn it all the way in and start the scooter.  does it run differently?  If not then the pilot jet passage is clogged.

2. Next turn it counterclockwise 3 tuns (the max) any improvement?

TIP: Each time you drain the bowl before working on the carb tighten the screw right away to avoid loosing it.

If all other issues are ruled out then a friend on this forum has a source that can get a genuine replacement carb for around $235 brand new.  Hopefully it won't come to that and the risk is that there is another problem so the carb issue must be ruled out.

[jmoak80]

I would say that the bike does very well getting to 35 mph. the power tops out at 45-50 mph running flat ground at about 5-6k rpm. it doesn't act like it is out of gas rather the power just tops out, like i need more throttle or something.

There is no noticeable improvement what-so-ever.

It idles great. nothing uneven. it does for time-to-time load up and stall from idle when i get on it but that is very rare.

I never took the pilot screw out and cleaned after the bike had been sitting with bad gas. I will fiddle with it sometimes this week. keeping my fingers crossed..

- If this doesn't work i would definitely love to purchase an oem carb, especially since it is not on my dime. I can be the hero for money. yay!

thanks again for your tips, they are greatly appreciated.

[mrbios]

Good info. I would not describe your problem as a "hesitation".  What you posted indicates that the pilot jet / idle mixture is fine and there is nothing wrong.  Your problem is the delivery of fuel at high speed which is mainly driven by the main jet.  The is very little to clean when it comes to the main jet so I would have to suspect the diaphragm or slide is not lifting all the way?  This is a high speed fuel delivery problem.

[jmoak80]

Indeed, high speed fuel delivery was the issue. I got a new diaphragm with the air slide attached and installed. It worked. Thanks for the tip about the grease, it made the diaphragm stick perfectly into the grove, and installing the spring and brass cap was very simple.

When i carefully took the cap off of the carb i noticed that the old diaphragm was slightly out of alignment and kinda stiff, that put a smile on my face. What is odd is that high speed fuel delivery wasn't a problem before the carb got gummed up. maybe me cleaning it all out and messing with it caused it to get noticeably erratic and bad, then subsequent cleanings caused it to fail outright-- just  a thought.

Once i installed the new part i noticed that the slide had much more resistance when i pushed it up and let it go, that too put a smile on my face.

[mrbios]

Indeed, high speed fuel delivery was the issue. I got a new diaphragm with the air slide attached and installed. It worked....

What is odd is that high speed fuel delivery wasn't a problem before the carb got gummed up. maybe me cleaning it all out and messing with it caused it to get noticeably erratic and bad, then subsequent cleanings caused it to fail outright-- just  a thought.

Once i installed the new part i noticed that the slide had much more resistance when i pushed it up and let it go, that too put a smile on my face.

Fantastic news - thanks for taking the time to update with valuable info about the fix and hope to others with the same issue.

100% agree with your thinking.  Just as I mention in my video the diaphragm should not be removed as there is nothing to clean in there and the risk of damage and introducing a new problem is high. "In order to save the village we had to destroy it."

Glad you used the grease - it works like magic.  In my leaning curve I first used hi-tack which is like shellac and that was a terrible choice as it streaked into the carb!  Grease is the way!!!

I feel your excitement.  Don't forget - I introduced a tiny leak in my diaphragm and experienced the same issue and called my local dealer which should have been able to tell me the exact cause but didn't.  Greatest feeling to feel the power is back!  Good work persevering through the problem!