More GT200 carb problems
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Member
2006 GT200
Joined: 18 Jul 2020
Posts: 25
Location: Chandler, AZ
Wed Jul 22, 2020 7:24 am quote
I just got through cleaning the carburetor on my '06 GT200, got everything back together, and can't get it to run right. Here's the most noticeable issue. It runs best when the pilot screw is all the way closed. From Robot's videos, it is supposed to be at around 2 1/4-2 1/2 turns out. But that causes it to misfire badly, and the exhaust smells really rich. The further in I turn it, the better it runs. Almost normal with it turned all the way in. I don't understand how it can run at all with the screw turned all the way in. I have worked on a lot of carburetors, and never seen this happen before. The spring, metal washer, and O ring are in place on the screw. I rode it about 10 miles, and it runs ok. But that is not supposed to be happening. Any suggestions would be appreciated.
Molto Verboso
2006 LX150 (carbed) | 2007 GT200
Joined: 29 Jun 2016
Posts: 1014
Location: Toronto
Sat Jul 25, 2020 3:07 am quote
Is the autochoke working properly? Maybe it's not closing, and resulting in the bike running really rich?
Member
2006 GT200
Joined: 18 Jul 2020
Posts: 25
Location: Chandler, AZ
Sat Jul 25, 2020 7:08 am quote
That is a possibility, but I'm not sure how to check it. It was running fine, but I left ethanol gas in it for too long and it plugged up the carburetor. I removed and cleaned the carburetor, and put everything back exactly the way it was, including the pilot screw (the screw with the D shaped head) When I started it, I noticed it was running really rich at idle and misfiring. I turned that screw in a little, and it got better. I kept turning it in till it seated, and it smoothed out and started sounding almost normal. But I know that screw is supposed to be out 2 1/4 to 2 1/2 turns.
Molto Verboso
2006 LX150 (carbed) | 2007 GT200
Joined: 29 Jun 2016
Posts: 1014
Location: Toronto
Sat Jul 25, 2020 8:19 am quote
VintageScooterDude wrote:
That is a possibility, but I'm not sure how to check it.
You connect it to 12V and confirm the plunger extends - should come out a little more than 5mm as I recall. (The wiki pages here have a link to shop manual with full details.)
Member
2006 GT200
Joined: 18 Jul 2020
Posts: 25
Location: Chandler, AZ
Sat Jul 25, 2020 5:03 pm quote
Thanks, I'll try that.


Ok, when I connect 12V to the choke unit it moves out just a hair over 3mm, and that is after leaving voltage connected for 10 minutes. It feels very warm, almost hot. It takes several minutes for it to retract.

Since applying voltage to it makes it extend, I'm assuming extending is what enrichens the mixture. So I taped off where the auto choke unit goes and started the engine without it. Still too rich, and still runs with the pilot screw turned all the way in.

Before removing the unit, I started the engine (completely cold) and kept my finger on the unit for several minutes. It never got warm. With the unit unplugged I checked for voltage where it connects to and got nothing. None of the fuses are blown.

Does the autochoke unit operate the same every time you start the engine, even if it is already warmed up, or is there a temperature sensor that controls it. When I removed the carb, which requires disconnecting the small coolant hoses, I disconnected what I believe is a coolant temperature sensor wire, as it was in the way. I figured that this controlled the temp gauge and fan. If so does it also control the autochoke unit?

Before removing the carburetor to clean it, the engine started and ran fine. I have owned this scooter for over 5 years and 12K miles and the only issues I had were a vacuum petcock failure and a water pump leak, both repaired.

I'm going to pull the carburetor and check everything very carefully and put it back. If it still doesn't run right I will probably just replace the entire carburetor and choke unit with a new one. I have worked on a LOT of motorcycle carburetors, and never saw one where the engine would run with the pilot screw turned all they way in. The engine would always die if you turned it in too far. The screw itself looked fine, and the spring, metal washer and O ring are in place.
Moderaptor
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
Joined: 26 Aug 2007
Posts: 38731
Location: Pleasant Hill, CA
Sun Jul 26, 2020 4:44 pm quote
If you look at the circuit diagram:
https://manuals.wotmeworry.org.uk/Vespa/GT125%20GT200%20Euro2/
you'll see the choke has 12V applied to it all the time the ignition is on, but it is grounded by the CDI/ECU only when the engine is running.

It enriches by default, so if there's no voltage applied to it it'll stay fully rich, and the engine will run very badly when it's warmed up.

It switches off the enrichment by extending - this should happen quite rapidly.
Member
2006 GT200
Joined: 18 Jul 2020
Posts: 25
Location: Chandler, AZ
Mon Jul 27, 2020 12:39 am quote
Ok, I guess I had it backwards then. Remove the voltage, and it stays full rich? That means it stays hot all the time while the engine is warmed up? So when the plunger is extended it is in the "off" position?
Member
2003 GT200L - 2011 GTS 300
Joined: 15 Sep 2019
Posts: 15
Location: England
Mon Jul 27, 2020 12:59 am quote
I had endless carb trouble after my GT200 had been sat for a few months. I did an electrical test on the auto choke and it moved out a few mm and got warm so for weeks I never suspected the choke and replaced all the other usual suspects. Then just by chance I got a brand new choke from somebody on ebay who had bought the wrong one but it was right for me. It instantly solved all my problems and I wish I'd done that first!!
Moderaptor
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
Joined: 26 Aug 2007
Posts: 38731
Location: Pleasant Hill, CA
Mon Jul 27, 2020 7:13 am quote
VintageScooterDude wrote:
Ok, I guess I had it backwards then. Remove the voltage, and it stays full rich? That means it stays hot all the time while the engine is warmed up? So when the plunger is extended it is in the "off" position?
Correct.
Member
2006 GT200
Joined: 18 Jul 2020
Posts: 25
Location: Chandler, AZ
Fri Jul 31, 2020 1:35 am quote
Ok, after taking the carburetor apart and finding nothing wrong, I finally gave up and just installed a new carburetor complete with a new electric enrichener and a new air filter. It is running fine now.
Ossessionato
2014 Commuter BV350(44,000)/2015 Scoot Life BV350(10,000)/2010 El Diablito SH150i(30,000)
Joined: 27 Dec 2013
Posts: 2447
Location: Orange Park Florida
Fri Jul 31, 2020 2:33 am quote
VintageScooterDude wrote:
Ok, after taking the carburetor apart and finding nothing wrong, I finally gave up and just installed a new carburetor complete with a new electric enrichener and a new air filter. It is running fine now.

This was what I was thinking when I first read this thread. I didn't post it because I didn't know your financial situation.
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Granturismo 218
Joined: 04 Feb 2013
Posts: 6208
Location: NWAOK
Fri Jul 31, 2020 8:21 am quote
VintageScooterDude wrote:
Ok, after taking the carburetor apart and finding nothing wrong, I finally gave up and just installed a new carburetor complete with a new electric enrichener and a new air filter. It is running fine now.
I know you tend to favor carburetors over fuel injection and other "new" technology. But you should remember the stacks of used carburetors you would see in about any shop you walked into in the 70s and even later. And this was when mechanics really understood carburetors, and knew how to clean and adjust them. Because they had to. A lot. There are a lot more fuel injected Vespa models in the US, and I don't think there have been a lot of people who suddenly had to change the throttle body. It goes back to the 1968 VW Bug being a lot easier to work on than a 2020 Honda Civic discussion. Yes, it is easier to work on, and the odds are significantly higher that you will work on it.
Member
2006 GT200
Joined: 18 Jul 2020
Posts: 25
Location: Chandler, AZ
Sat Aug 01, 2020 12:09 pm quote
I prefer things I can work on. I also prefer simplicity. I don't know what happened here (yet) but I have worked on hundreds, possibly thousands of carburetors over the past several decades, mostly either because someone left fuel in them too long and it gummed everything up, or because of other changes made to the engine, the carburetor needed to be retuned. Out of all the carburetors I have worked on, only a very few caused problems like this one did. Most of the time things went perfectly. I'm sure I could have found and fixed the problem. Chances are the original carburetor is fine, and the problem was in the electrical enrichener. But I wanted to get the scooter running as soon as possible, so I decided to just replace everything for now. I just finished rebuilding and retuning a Harley Sportster carb, and it worked beautifully. Again I appreciate all the help.
Moderaptor
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
Joined: 26 Aug 2007
Posts: 38731
Location: Pleasant Hill, CA
Sat Aug 01, 2020 4:31 pm quote
One possible thing has occurred to me - as it used to happen on the X9 125 carbs. The butterfly spindle's holes either side would become slightly oval (it didn't take much) and it became pretty impossible to get a usable idle mixture and even fast running was erratic. The solution was to epoxy the holes shut and re-drill.
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