Modern Vespa

Hi all
So merrily on way to work on 2005 GT200 when under load (uphill or on motorway nearing full throttle) when it starts to "hold back" or "bog down" albeit briefly then fine again then repeated this intermittently.

So various things tried over the course of the last week

Carb off and clean (quick visual check and a blow out with air)
Inlet manifold ok
Pipe put back on underneath of carb that had come loose
Fixed little plunger type jet (one that is actuated by a lever attached to main throttle on rear)
Coil new
Plug new
Ht lead new
Air filter cleaned

More responsive and generally better but problem is still persisting
(Under load i.e. uphill or full throttle on motorway scoot is "bogging down" intermittently?
Any help appreciated

Check the vacuum lines, fuel lines and fuel pump.

How's the belt? When was it last changed, and how many miles on it?

I've ordered a fuel pump yesterday as it does feel like fuel starvation?

Last year around July and done about 7000 miles!

Have you disconnected the evap system yet?

Mine all showed those signs, and more, after years of riding.

They all ran much better after bypassing the canister.

Bill

^^^ This. Listen to this guy, he has put more miles on his GT200s than anyone on this forum.

A few years back I helped another MV member with a very similar problem on his GT200. Turned out to be a tear in the diaphragm of the fuel tap. It's easy to check. Pull the vacuum line off the fuel tap (the line on the bottom) and see if fuel runs out. If it does, replace the fuel tap.

-Craig

Here is the old thread with some discussion about the symptoms. See if these still sound like your issue: UPDATE!!!! Arizona mechanic help needed.

-Craig

On a UK scoot?

Certainly not on a UK GT200!

Thanks I'll look at thet when I get home!

Yes mate a U.K. scoot

No evap, then as per JimC.

My money would be on a tear in diaphragm (I had this once on a car carb).
You said you'd cleaned the carb- did you do the jets too?

Good luck!

I replied from my phone, that doesn't show the location of posters.
Should I have seen that it was a UK scooter, I wouldn't have offered my advice.
Bill

[quote="WLeuthold"]Have you disconnected the evap system yet?

Mine all showed those signs, and more, after years of riding.

They all ran much better after bypassing the canister.

I would if I knew what that was pal!!! Pray, tell me more?

[quote="WLeuthold"] I replied from my phone, that doesn't show the location of posters.
Should I have seen that it was a UK scooter, I wouldn't have offered my advice.


How so?

Ok guys I'm a bit lost, I'm assuming That a U.K. scoot doesn't have a evap system or is it you don't want to offer advice to a Brit?

EVAP systems are North America only.

Ah I see, thanks for that. I thought I was being lambasted!

Yep

[quote="Brettyboo"]

Checked this, but just wondered, does engine need to be running or not for his check?

You don't want the engine running.
Just pull the bottom hose on the fuel tap and see if gas drips out.

-Craig

Ok, I tried that and no gas dripping out, hopefully fuel pump will sort the issue!!!

Went back and looked at the thread where you helped the guy out with similar problems on his scoot, made me think about how unimportant some of my problems are..............

I know that the evap canister is unique to US scooters.

I like many of you Brits.

Bill

Lol, ok buddy 😁

Hopefully replacing the fuel pump sorts it for you. I also saw a good suggestion that you check/replace your fuel/vacuum lines. If those are the culprit, replacing the fuel pump won't do you any good.

If it's not fuel delivery, it could be transmission-related. Depending on what belt you put in there, 7,000 miles may be pushing it. Since you're at the replacement interval, I'd suggest putting a new OEM belt in. Best case scenario it fixes your problem, worst case scenario it's insurance against a belt breakage that can be quite a mess to clean up (don't ask me how I know.. ) While you do the belt, check your rollers for wear/flat spots. That can also cause issues with the transmission's operation.

Also, we're still pissed about 1812.

Hi, the belt was oem and I put Dr pulley rollers in at the same time, just out of interest how could the belt make it "hold back/splutter" intermittently?

The fuel pump didn't sort it so I've ordered a fuel tap (for the sake of $15 it's worth a try)!
I'm at the end of my rope with it, as it's fine one day then no good the next?!?

Still? 🙄

If the belt is worn it becomes prone to slippage, especially under high load. The hesitation you are describing could possibly be your belt slipping. At 7,000 miles it's time to change out the belt anyway, so even if it's not the problem it's something that should be done soon regardless.

Oh ok, makes sense! I will do that ASAP then!

Have you replaced the fuel and vacuum lines? These have completely outlived their useful life if they are original. The lines will crap out before the fuel pump or petcock.

I haven't even thought about changing them!

Another job on the list!