1959 GS150 Oil to Fuel Mix
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Enthusiast
GS150, LI200, TX200, PX125, T5200, SX200, PX125 CUTDOWN
Joined: 31 Jul 2019
Posts: 54
Location: South West England
Wed Aug 14, 2019 2:06 am quote
all,

I got a shitty looking plug and last 1/4 throttle seems to be bogging out . i was told to use a 4% oil fuel mix on this puppy....compression seems ok, no problems in starting or idling, just bogs a tad at 3/4 throttle and up with a small loss of power/acceleration, i upped the main jet and it made it worse. I've only ever done 2% mix on my p series vespas. so 4% seems odd to me.

If i drop to 3% and give it a blat to check plug, will i do any damage do you reckon?

ta!

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Member
P Series / Li / LML / Motobi
Joined: 24 Jun 2019
Posts: 33
Location: 3rd Rock From the Sun
Wed Aug 14, 2019 3:17 am quote
I'm prepared to be shot down on this....

Modern Oils do not need to be mixed in that high a ratio. if you are using a good quality fully synthetic oil in your premix then i would stick with the 2%

4% was meant for the days when premix oil was pretty much the same as you stuck in your gearbox
Banned
2:6
Joined: 11 Jan 2007
Posts: 7422
Location: San Francisco
Wed Aug 14, 2019 5:41 am quote
owners manual says 6% for the GS150

On my 160 (5%) as well as my MotoBi (5%) I run them at 4%

Not all oils will mix at 4%, with some of them collecting at the bottom of the tank and clogging the fuel lines.

oils designed to be used with oil injection (motul 710) will mix at 4%. I've also had good luck with Motul 800 road race, it's designed to run at 3% so the bump to 4% is not too bad.

Motul 800 off road will not work. it's designed to run at 1.5-2% and takes 30 min or more to fully mix into the fuel.

YMMV
Enthusiast
GS150, LI200, TX200, PX125, T5200, SX200, PX125 CUTDOWN
Joined: 31 Jul 2019
Posts: 54
Location: South West England
Wed Aug 14, 2019 9:24 am quote
Will give it a go . What could possibly go wrong ! This is scootering lol ...
Veni, Vidi, Posti
74 50s x2 78 P200 84 Cosa 58 AllState 68 Sprint 80 50special + projects
Joined: 22 Nov 2010
Posts: 6996
Location: seattle/athens
Wed Aug 14, 2019 4:41 pm quote
Gravelrash2004 wrote:
I'm prepared to be shot down on this....

Modern Oils do not need to be mixed in that high a ratio. if you are using a good quality fully synthetic oil in your premix then i would stick with the 2%

4% was meant for the days when premix oil was pretty much the same as you stuck in your gearbox
But the demarcation line for Vespas is whether it's the older piston ported or newer rotary valve induction system. 2% for rotary and 4-5% for piston ported, whatever the manual says. So no 2% in this model please, dunno about 3%.

Are you watching your temperature, got a gauge? Again, dunno if that would save your ass if you go too low.
Hooked
Honda elite
Joined: 19 Jun 2007
Posts: 499
Location: California
Wed Aug 14, 2019 5:53 pm quote
Is there any validity to the small end bushing as a bearing on the connecting rod in the GS 150 requiring the higher oil %? If the bushing has been upgraded to a needle bearing could oil percentage be reduced?
Hooked
1955 Allstate 1958 lambretta 1965 Allstate 1968 sprint
Joined: 20 Jul 2017
Posts: 347
Location: Central california
Wed Aug 14, 2019 6:32 pm quote
Oil mix
Iggyday: you ask that question to 10 scooterests and you will come up with a different answer every time. I believe in what gravelrash says. The new synthetic oils are heads and tails better than what was produced back in the day. Knowone can argue that point, but everyone has their own take on it. I have modified jet skis, scooters, and have always used 2%. Never had an issue. Know with that being said, I have crossed into the dark side. I have a 58 series 1 lambretta. Just had a brand new Mugello 200cc engine built. 4% is what is used in a lambretta.
So at the end of the day, it is your decision. By the way I use Motul 710. Seems to work well. In the Lambretta I use RedLine two stroke racing oil which was recommended by the scooter shop that built the engine. Scott
Banned
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Joined: 11 Jan 2007
Posts: 7422
Location: San Francisco
Wed Aug 14, 2019 9:28 pm quote
more data points:

on my S2 TV175 I've run it on 2% for years with no issues.
Hooked
1955 Allstate 1958 lambretta 1965 Allstate 1968 sprint
Joined: 20 Jul 2017
Posts: 347
Location: Central california
Thu Aug 15, 2019 11:45 am quote
Oil mix
Oops: thatís good to know. Most Lambretta people that I have spoken with seem to use 3-4%. You can tell most of the time because they do smoke a bit more. Are participating in the rally this weekend in SF?
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