Rough idle on a rebuilt GTS 250
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Member
Vespa GTS250ie
Joined: 07 Jan 2020
Posts: 13
Location: Columbus, Ohio
Sat Apr 04, 2020 4:38 pm quote
I rebuilt 2008 GTS 250ie engine over the winter. Scooter (29,000 miles) was run with no oil by the previous owner.

I bought the scooter and replaced the crankshaft, piston, rings, oil pump following a ScooterWest video. Engine runs strong, starts OK. BUT I continually have to goose the throttle when stopped to keep it from stalling. It seems to idle when I hold the throttle, but when I let go it dies. I am currently running injector cleaner with the gas and it is running better but no improvement to the idle.

Any ideas?

Here is what I've done to date.
* Tightened all ECU hose clamps to stop air leakd
* Applied a thin layer of silicon between the intake manifold and block to stop any air leaks
* Made sure injector hose firmly attached
* Replaced battery
* Made sure spark plug wire on tight

I look forward to your ideas.
Thanks
Mac[/list]
Moderaptor
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
Joined: 26 Aug 2007
Posts: 38724
Location: Pleasant Hill, CA
Sat Apr 04, 2020 4:46 pm quote
Ensure the idle bypass passage is clean:

https://cheekythoma3.wixsite.com/itsme/idle
Member
Vespa GTS250ie
Joined: 07 Jan 2020
Posts: 13
Location: Columbus, Ohio
Sat Apr 04, 2020 5:19 pm quote
Good info. I will clean the bypass and the ECU. It couldn't be any worse that replacing the crankshaft.

Mac
Member
Vespa GTS250ie
Joined: 07 Jan 2020
Posts: 13
Location: Columbus, Ohio
Thu Apr 09, 2020 8:02 am quote
Tried several times to clean bypass channel without removing the ECU. Motor generally runs better but does ot solve the problem of the engine ding at idle. So off with the ECU for a good cleaning.
Addicted
GTS 300ie Touring
Joined: 03 Jun 2018
Posts: 550
Location: Limassol, Cyprus
Thu Apr 09, 2020 11:45 pm quote
.....Just a thought, you said that you made sure the spark plug wire was on tight, but you did not mention that you'd replaced the spark plug. I presume on an engine rebuild you would have put in a new spark plug in?
Hooked
GTS 250 a.b.s.
Joined: 11 Apr 2013
Posts: 468
Location: Noord Brabant, Netherlands
Fri Apr 10, 2020 1:24 am quote
My 2006 gts 250 sometimes stalls as well on idle.
After the last (and first dealer) service they told me it has something to do with a little bit of play in the throttle body.
With that the ecu cannot set it to a correct opening on idle, it's a few degrees off sometimes.
Hence the staling.
My GTS has 32.000 km on the clock now.
Member
Vespa GTS250ie
Joined: 07 Jan 2020
Posts: 13
Location: Columbus, Ohio
Fri Apr 10, 2020 4:30 am quote
Touring300 wrote:
.....Just a thought, you said that you made sure the spark plug wire was on tight, but you did not mention that you'd replaced the spark plug. I presume on an engine rebuild you would have put in a new spark plug in?
I did replace the spark plug early on. Good catch. I appreciate any other ideas.
Member
Vespa GTS250ie
Joined: 07 Jan 2020
Posts: 13
Location: Columbus, Ohio
Fri Apr 10, 2020 4:39 am quote
UPDATE - I am thinking that since I rebuilt the engine, all the factory setting are meaningless. So why not turn the idle screw to fit the new engine settings? I've been told that this works from someone that has done it.

Also, if the throttle cables stretch, do I adjust them at the throttle body. Since there are two of them , how do I tighten them to remove slack which would also effect idle speed?

I appreciate the collective knowledge. In this COVID lock down there is plenty of time to think about such things.
Moderaptor
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
Joined: 26 Aug 2007
Posts: 38724
Location: Pleasant Hill, CA
Fri Apr 10, 2020 8:25 am quote
macswinford wrote:
UPDATE - I am thinking that since I rebuilt the engine, all the factory setting are meaningless. So why not turn the idle screw to fit the new engine settings? I've been told that this works from someone that has done it.

Also, if the throttle cables stretch, do I adjust them at the throttle body. Since there are two of them , how do I tighten them to remove slack which would also effect idle speed?

I appreciate the collective knowledge. In this COVID lock down there is plenty of time to think about such things.
You may have rebuilt the engine - you did not dismantle and 'rebuild' the mechanical bits of the ECU in the throttle body.

Do not touch the idle screw ever, or reset the TPS unless you actually replace the throttle body.
Member
Vespa GTS250ie
Joined: 07 Jan 2020
Posts: 13
Location: Columbus, Ohio
Fri Apr 10, 2020 9:46 am quote
Thanks Jimc for your advice. I have read similar warnings to never adjust that screw in the Haynes manual.
Moderaptor
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
Joined: 26 Aug 2007
Posts: 38724
Location: Pleasant Hill, CA
Fri Apr 10, 2020 6:11 pm quote
macswinford wrote:
Thanks Jimc for your advice. I have read similar warnings to never adjust that screw in the Haynes manual.
Not just there - reiterated in the link I gave above. Please follow it.
Member
Vespa GTS250ie
Joined: 07 Jan 2020
Posts: 13
Location: Columbus, Ohio
Sat Apr 18, 2020 4:33 pm quote
UPDATE: I removed and cleaned the ECU. It was not too dirty, but it was much cleaner when I was finished. All was reassembled but the same problem of the engine dying on Idle still happening.

So I think its time to let a Vespa dealer check it with a diagnostic tool. I wish I knew someone local that had the proprietary diagnostic tool.

Could the fuel injector be causing this problem? Can it be cleaned?

Mac
Molto Verboso
2006 LX150 (carbed) | 2007 GT200
Joined: 29 Jun 2016
Posts: 1011
Location: Toronto
Sat Apr 18, 2020 5:08 pm quote
Do you know if the bike maintenance intervals were kept up? (Maybe not if it was run with no oil.) Maybe it's something like valve clearances out of spec?

I must admit I am confused by your mention of ECU cleaning and tightening of hose clamps for air leaks. I don't have a GTS myself, but isn't the ECU a computer box? What hoses connect to it? Are you cleaning the electrical connections?
Member
Vespa GTS250ie
Joined: 07 Jan 2020
Posts: 13
Location: Columbus, Ohio
Sat Apr 18, 2020 5:40 pm quote
As I rebuilt the engine, I noticed this bike had a hard life. Maintenance was minimal and every screw and bolt was a battle with rust and corrosion.

I have previous experience adjusting valves on my Honda and I was real careful to do it correctly on the Vespa. I feel confident that the valves are set where they should be. The engine was out of the bike when I adjusted the valves so was easy to access everything.

I suspect a bad ECU. But i want to know for sure before replacing the part. Thus, I need access to the Vespa diagnostic tool.

Thanks
Moderaptor
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
Joined: 26 Aug 2007
Posts: 38724
Location: Pleasant Hill, CA
Sun Apr 19, 2020 7:56 am quote
berto wrote:
Do you know if the bike maintenance intervals were kept up? (Maybe not if it was run with no oil.) Maybe it's something like valve clearances out of spec?

I must admit I am confused by your mention of ECU cleaning and tightening of hose clamps for air leaks. I don't have a GTS myself, but isn't the ECU a computer box? What hoses connect to it? Are you cleaning the electrical connections?
The ECU is integral to the throttle body on a GTS.
Molto Verboso
2006 LX150 (carbed) | 2007 GT200
Joined: 29 Jun 2016
Posts: 1011
Location: Toronto
Sun Apr 19, 2020 8:52 am quote
jimc wrote:
berto wrote:
Do you know if the bike maintenance intervals were kept up? (Maybe not if it was run with no oil.) Maybe it's something like valve clearances out of spec?

I must admit I am confused by your mention of ECU cleaning and tightening of hose clamps for air leaks. I don't have a GTS myself, but isn't the ECU a computer box? What hoses connect to it? Are you cleaning the electrical connections?
The ECU is integral to the throttle body on a GTS.
Ah, I follow now. Thanks, jimc!
Member
Vespa GTS250ie
Joined: 07 Jan 2020
Posts: 13
Location: Columbus, Ohio
Fri May 01, 2020 6:07 pm quote
I discovered a hole in the intake hose where a hose to a carbon canister fit intoo a brass fitting. The Brass fitting had actually broken off leaving a sizable hole. This caused the mixture to be lean and the engine died.

I found a sheet metal screw just the right size and screwed it in. It blocked off the air and my rebuilt GTS absolutely Purrs now. I posted my 15 week project rebuild on Instagram @ Macswinford if anyone cares to look. It took way too long and I'm over budget,,,,imagine that.

Thanks for your help. These forums are what is great about the Internet: International shared knowledge.

IMG_2432.jpg
Hole in intake where a brass fitting once came out to attach to a hose leading to a charcoal canister which did not exist on this bike.

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