OP
@swmldr_bill avatar
UTC

Hooked
GTS250, Rally 200, 125 t.s.
Joined: UTC
Posts: 180
Location: Olde Canberry
 
Hooked
@swmldr_bill avatar
GTS250, Rally 200, 125 t.s.
Joined: UTC
Posts: 180
Location: Olde Canberry
UTC quote
I'm running a 1972 Rally 200 with Pinasco kit, long stroke crank and Spaco 26mm carb.

I'd been having trouble setting a good idle speed. Yesterday I noticed that sitting on the bike caused the revs to rise, and when I got off it the revs decreased to a normal idle. This was fairly annoying, as every time I stopped at a red light I had to stand up straddling the scoot to keep the revs from going high.

Anyhoo, I rode it to my local dealer/service point, and the guys there immediately suggested that the movement of the motor relative to the frame was causing the throttle cable to be somehow pulled or moved. We took off the top of the carb box and had a look - the throttle cable didn't seem to be pulling on the slide actuator, but I disconnected it just to be sure. Got on bike: revs rose. Got off: revs dropped.

Later I replaced the section of the carb from the banjo to the float with that from another carb (genuine Dell'Orto this time) - still no change.

I'm baffled. Any ideas?
@eldorado avatar
UTC

Hooked
1980 Vespa P200E, 1981 Serveta Jet 200, 1982 BMW R100, 2003 BMW F650GS
Joined: UTC
Posts: 153
Location: Chicago
 
Hooked
@eldorado avatar
1980 Vespa P200E, 1981 Serveta Jet 200, 1982 BMW R100, 2003 BMW F650GS
Joined: UTC
Posts: 153
Location: Chicago
UTC quote
Check every outer cable and tube that goes from your frame to the carb box. Choke cable could be too tight and when you sit on the bike, the engine is pushed closer to the frame, slack in choke cable closes choke all the way, revs high (this assumes you tuned it with the choke cable too tight and slightly activated). Happened to me the first time I replaced the choke cable - the outer didn't have enough slack between the frame and carb box, would come a little loose and then bind in a tighter position. Hard to explain. But every time I got of the bike it would stall out within seconds as the choke became slightly activated. The fix was just to pull a bit more outer out of the frame.

Open your carb box, look inside while you or a friend puts weight on the seat. See if anything moves inside the carb box when you do that. You know it's not the throttle cable at least. My guess is not the choke, maybe fuel line, though that would be weird. Maybe it's kinked against something when you're sitting then opens up when you stand?
OP
@swmldr_bill avatar
UTC

Hooked
GTS250, Rally 200, 125 t.s.
Joined: UTC
Posts: 180
Location: Olde Canberry
 
Hooked
@swmldr_bill avatar
GTS250, Rally 200, 125 t.s.
Joined: UTC
Posts: 180
Location: Olde Canberry
UTC quote
Thanks Eldorado, sounds plausible. Strange thing is - just went for a ride today, and the problem seems to have gone... fingers crossed it'll stay that way.
UTC

Member
74 smallframe 90
Joined: UTC
Posts: 19
Location: boston
 
Member
74 smallframe 90
Joined: UTC
Posts: 19
Location: boston
UTC quote
my smallie would die every time i sat on it, turns out sitting on it was pinching some electricals, maybe check the wiring?
@nigelthefish avatar
UTC

Ossessionato
ET2, PX150
Joined: UTC
Posts: 3410
Location: Denver CO
 
Ossessionato
@nigelthefish avatar
ET2, PX150
Joined: UTC
Posts: 3410
Location: Denver CO
UTC quote
Fuel line slightly crimped when you're not on it and uncrimps when you compress the suspension by sitting on it?
@eldorado avatar
UTC

Hooked
1980 Vespa P200E, 1981 Serveta Jet 200, 1982 BMW R100, 2003 BMW F650GS
Joined: UTC
Posts: 153
Location: Chicago
 
Hooked
@eldorado avatar
1980 Vespa P200E, 1981 Serveta Jet 200, 1982 BMW R100, 2003 BMW F650GS
Joined: UTC
Posts: 153
Location: Chicago
UTC quote
Glad it seems to be running well. I would still take a minute and make sure every cable/tube running from the frame had a little extra slack outside the frame so it won't get stretched when you get off the bike.
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