Kymco 150 bogging down

[Sweetlou]

Trying to figure out why my kymco 150 is bogging down. When cold the bike idles fine but any throttle input will stall motor.

Once warm eventually it will take throttle and respond. When fully warm it's almost fine but I still get a distinct off idle bog. Video attached.

So far I tested the auto choke and it functions, tested polarity of auto choke (it was backwards), and drilled out the air/fuel screw and tried adjusting it. It does not respond to adjustment which I thought is odd.

http://s3.photobucket.com/user/onlyelement14/media/E7837EC1-3A76-4491-B3E7-E7ADB96BCF49.mp4.html

Any insight?

Lou

[245luigi]

Props for posting a video!!

Did you check for any air leaks??

[mrbios]

Trying to figure out why my kymco 150 is bogging down...
Any insight?
Lou

I heard the miss of the motor when you blipped the throttle.  Most likely the pilot jet circuit is clogged.  Clearly you have a condition of lean misfire or skipping.  This happens when you open the throttle off idle and there is not enough fuel supplied by the pilot jet or "slow jet" and so the motor is getting more air but only the same amount of gas suppled at idle.  Once you pass 1/4" of twist (excluding the removal of the initial cable slack in the throttle which does not count) then you get into the larger "main jet" which does not clog as often simple because it is a much larger "pipe" and the main jet has a main jet needle that regulates gas flow but also serves to poke a hole in the jet if it gets clogged.

Why not a vacuum leak?  You could have a vacuum leak but it would effect the idle (irregular) and the entire range of throttle - although a small vacuum leak would be more noticeable at low speeds, rpms etc.  Also, vacuum leaks are fairly rare - most scooters here are less than 10 years old, rubber has not had time to crack, miles ridden are very low - less than 10K and modern motors make extensive use of electronic sensors which vastly reduces the number of vacuum hoses and thus the potential for vacuum leaks.  Old motorcycles I worked on from the 80's with an inline 4 cylinder had quite a few vacuum hose, same with cars - like spaghetti.  The Grandvista and other similar models use a throttle position sensor no vacuum to advance the timing (spark advance). 

Use seafoam or a related carb or fuel injection cleaner at a higher concentration level.  If that fails do a visual inspection by accessing the the area around the carb to look for possible vacuum leaks.    If that fails, it is time to remove the carb and clean it on the bench.  If you do the last item take lots of digital pics at every step and DO NOT REMOVE THE TWO SCREWS ON THE TOP OF THE CARB (the "hat" where the diaphragm is - the diaphragm is easily damaged and costs about $35 to replace!!) and there is NO reason to open that area as there is nothing to clean. 

If the carb is clogged how did this happen?  Scooter sits for a year or much more with old un-stabilized gas like my 2005 Kymco GV250.  After a year or two it was parked at 1600 miles and sat for around 5 years.  It was purchased and take to the dealer.  They did a so so job of cleaning and said if that is not good enough replace the carb $350 for a new oem carb (aftermarket carbs can be used ~$50 but an adapter must be made for the electronic TPS to attach to the carb). 

Short story long... I'm in the exact same boat as you.  I cleaned my carb twice, accidentally took of the part I said not to and my scoot would not go over 45 mph!  Took it apart and got it right and make things much better but I still have the hesitation the same as you have.  Bought and after market carb from the same mfg Keihin CVK but aftermarket car makers sell carbs that assume your motor uses a vacuum hose for spark advance rather then the electronic TPS that Kymco uses - and virtually all modern cars starting in the late 1980's.  I saw a post online where a guy did a DIY adpter on his aftermarket carb to fit the TPS and I'm considering doing the same when I have time.

Before doing this the last part to check / clean is the idle mixture screw which affects 0 to 1/4 inch of twist of throttle.  I will remove the screw (counting the turns) shoot carb cleaner and stick a bristle from a wire brush in there then compress air and reassemble and test.

Final Chapter:
Any condition that results in lean burn (too little gas) regardless of the reason - clogged jets, vacuum leak or gasp both problems... cause the engine to run too hot and slowly burns it up.  So the little issue of a sitting vehicle where the owner lets it sit and does not add a $5 can of fuel stablizer or drain the fuel before storing it results in annoying and expensive performance issues later on and potentially a lean burn that harms the motor.

[Stig / Major Tom]

Any condition that results in lean burn (too little gas) regardless of the reason - clogged jets, vacuum leak or gasp both problems... cause the engine to run too hot and slowly burns it up.  So the little issue of a sitting vehicle where the owner lets it sit and does not add a $5 can of fuel stablizer or drain the fuel before storing it results in annoying and expensive performance issues later on and potentially a lean burn that harms the motor.

Reading your tech posts is like going to school. I hated school - but you're making me reconsider!
Thanks for taking time to give us your input.
It is so refreshing to hear a guy say "don't do this, I did and it screwed things up!" I think we all learn more from a remark like that than most other instructions!
Ride safe - we need guys like you!
Stig

[mrbios]

Reading your tech posts is like going to school. I hated school - but you're making me reconsider!
Thanks for taking time to give us your input.
It is so refreshing to hear a guy say "don't do this, I did and it screwed things up!" I think we all learn more from a remark like that than most other instructions!
Ride safe - we need guys like you!
Stig

Thanks Stig.  Mistakes happen and anyone that thinks they can undertake repairs without errors is kidding themselves.  Errors can be reduced by watching a youtube video - with all my tools and knowledge I usually do it because I want to be as prepared as I can be and minimize problems. 

I learn by doing (+ reading / videos) ... when you learn by doing you're doing real learning.  Most of what is taught in a formal setting like school does little to prepare the student for the real thing. 

That said it is important to school oneself in getting to the root cause of the problem and understanding basic dynamics.  I don't believe in just changing spark plugs and wires for no reason.  Get the the root and fix the problem.  Then if you still want to change wires, plugs, air filter, brand of gas or whatever feel free to do so.

[Sweetlou]

Ok, so I checked auto enricher, it works when hooked up to 12v

I pulled carb and cleaned jets. Pilot jet was a little clogged I think. Main jet was spotless but I cleaned anyway. Reinstalled.

What is my baseline for the fuel screw? I've been reading the net but it seems every model is different. I got her running good when hot but I am way out, like 4 turns or something crazy. Any advice? I read somewhere as you screw out, the idle should rise and then eventually fall again. Mine never falls!

[mrbios]

What is my baseline for the fuel screw?

The baseline is best established in two ways:
1. Before making an adjustment - turn in until the screw lightly seats and count the number of turns and record that on paper. 
Or else...
2. Start with the standard which is 1-3/4  to 2 turns.  The max is generally 3 turns as more will not deliver more fuel and the screw could get loose.

Regarding the Idle falling.  The scooter must be fully warmed up so the electric choke aka enricher circuit is off (if not in will interfere with the proper adjustment as it adds extra fuel while the motor is warming up). 

In your case go with 3 turns.  However, the root cause of your problem is probably not the screw but a clogged passage way resulting from old gas. 

Old gas clogs she smallest passages first and works its way to clogging the small holes in the pilot (slow) jet and largest passages like the main jet.  The smallest passage and most difficult to clean is the idle mixture screw passage.  You need to remove that screw very very carefully and empty the contents into a plastic bag.  Typically it will be the screw needle, spring, washer and a tiny o-ring.  Next, you need to shoot carb cleaner in there and compressed air (wear safety glasses!!).  I am experiencing the same basic issue you are with my Grandvista 250.  The original owner let it sit for years. 

If you can't clean those passages the carb has to be replaced.
 

[tanuki]

My new to me, 2004 Grand Vista seems to have fuel starvation/delivery problems.
Warm up from a cold start is fine so the enricher seems work but when I open the throttle it wont rev past 4-5 thou before bogging and sometimes dying.
I replaced the factory fuel filter days after I bought it. The new filter is a clear type so you can see fuel moving through it.
There are numerous vacuum hoses running around that engine bay, where can I find a "map" of those hoses?
There is a hose, a very short one, coming off the top left of the carb that when pinched closed seems to allow the carb to work better and the engine revs all the way up.
Should this hose be connected to something? It has been cut off at an angle very deliberately so I don't think its damaged.
Thanks

[mrbios]

My new to me, 2004 Grand Vista...
There are numerous vacuum hoses running around that engine bay, where can I find a "map" of those hoses?

Should this hose be connected to something? It has been cut off at an angle very deliberately so I don't think its damaged.
Thanks

question #1
When I get a chance, I will upload high resolution pictures to my 2005 GV 250 and that will show you exactly where the hoses should run.

question #2
The short hose is not supposed to connect to anything.  It allows fuel to escape if the carb bowl overfills with gas because the float valve fails to close all the way.

Watch the video links I posted.  4 videos that are less than 20 min long.  They will show you exactly how to remove and reinstall your carb and trouble shoot the lean issues you are experiencing. 

A typical story unfolds as follows:
1. scoot sits and the smallest passages clog with old gas - the pilot jet circuit.
2. someone goes in to clean the carb and opens the little hatch under the seat and pulls the top of the carb and does not correctly reinstall it and / or disturbs vacuum hoses which introduce vacuum leaks.

Restricted passages = lean (too little fuel), vacuum leaks (more air, same amount of fuel = lean.  Lean results in loss of power, smooth running, top end, off idle hesitation and scooter runs better when warming up because choke is on - choke = rich helps to counter the lean condition.

If you watch and follow my simple videos it will show you exactly how to get your scooter running perfect, no gimmicks and it will stay that way.

WARNING: the carb costs around $275 new and there is NO aftermarket carb that will work without physical modifications to the intake boots, etc, so be very careful when you work on it.  Take your time.

Carburetor Cleaning & Theory three part series:

Carburetor Cleaning Part I   
Carburetor Cleaning Part II   
Carburetor Cleaning Part III   

Kymco Carburetor Remove & Reinstall 

[tanuki]

Just wondering if anyone has replaced the fuel filter on their GV250.
If so, which filter did you use?
The factory filter doesn't look like anything special but if there is Id like to know.
Thanks

[mrbios]

Just wondering if anyone has replaced the fuel filter on their GV250.
If so, which filter did you use?
The factory filter doesn't look like anything special but if there is Id like to know.
Thanks

I replaced the fuel filter with a new OEM unit at 8 years / 10,700 miles.  No difference in performance, just a part of doing all the maintenance and establishing a new baseline where I have a record of what was done and when.  It was really brown looking.  The price is high but you don't need to do it very often - every 10K+ miles / 8 years should be fine.  You could easily substitute a car filter but why not just the right part.

1 x   Grandvista 250 2008 - STRAINER ASSY FUEL - 1691A-KEC2-E00   $16.68

I also replaced the original air filter at the same time.  No difference in performance. 

1 x   Grandvista 250 2008 - ELEMENT ASSY AIR/C - 1721A-KKC3-900   $19.80