gp150 engine

[alcoholic maniacs sc]

just removed the clubman exhaust ( casa Anncilotti) and fitted a deadstock standard pipe to my 1970 Gp150 and its made no difference at all to top speed. Gone back to 118 main jet in 22 dellorto- does about 52/53 on flat with GPS .digital speedo . feels like better torque from low revs with standard exhaust, when driving through traffic, two up, it pulls smoothly in 4th from low rev when pottering and before with the big bore it needed more revving at low speeds in 4th, i think the back pressure of the factory spec pipe suits the 150 better than a big bore.
cant say if it accelerates slower as the difference isn't noticeable.
nobody seems to fit standard exhausts anymore but most of the epic long distance rides of the 60's were using a factory exhaust. i am a little worried about heat build up in the iron barrel on A roads at constant high throttle though, not used a standard pipe since the early 90's.

[scooterslag]

just removed the clubman exhaust ( casa Anncilotti) and fitted a deadstock standard pipe to my 1970 Gp150 and its made no difference at all to top speed. Gone back to 118 main jet in 22 dellorto- does about 52/53 on flat with GPS .digital speedo . feels like better torque from low revs with standard exhaust, when driving through traffic, two up, it pulls smoothly in 4th from low rev when pottering and before with the big bore it needed more revving at low speeds in 4th, i think the back pressure of the factory spec pipe suits the 150 better than a big bore.
cant say if it accelerates slower as the difference isn't noticeable.
nobody seems to fit standard exhausts anymore but most of the epic long distance rides of the 60's were using a factory exhaust. i am a little worried about heat build up in the iron barrel on A roads at constant high throttle though, not used a standard pipe since the early 90's.

Had a clubman on my stock SX150 for a while and when it fell apart I refitted the standard plumbing as I needed to keep the bike on the road . The clubby was a bit quicker through the gears and would rev out but other than that- I find the standard pipe a gem, it makes power from nothing at all, gives great torque and hill climbing ability and makes it easy to ride. Innocenti sure knew what they were doing.

[ktmh5]

A GP150 will do 60/65 as standard, wont it?

I had one that Simon Farrell built when I was 17 that went that sort of speed. I don't think he'd tuned it.

In your dreams!

[nsaints]

A few years back folk were justifying kits and performance exhausts to keep up with modern traffic speeds..

Friday just gone I was travelling along a busy A road for a dyno, scoot maxing out at 50/55 due to over rich
Artic lorries up my arse and being overtaken, blown all over the road
The return journey at 60/65 felt safer as I wasn’t being hassled by lorries and frustrated drivers

I agree standard exhausts are and sound great. Doing no more than 55 on a standard machine isn’t great when you’re putting yourself in danger on busy roads

[scooterslag]

A few years back folk were justifying kits and performance exhausts to keep up with modern traffic speeds..

Friday just gone I was travelling along a busy A road for a dyno, scoot maxing out at 50/55 due to over rich
Artic lorries up my arse and being overtaken, blown all over the road
The return journey at 60/65 felt safer as I wasn’t being hassled by lorries and frustrated drivers

I agree standard exhausts are and sound great. Doing no more than 55 on a standard machine isn’t great when you’re putting yourself in danger on busy roads

I guess its all down to what you want/need from your scooter. Mine is mostly used for trips to work, local ride outs and running errands etc so my stock SX does just fine. Sure on duel carriageways and open road it does struggle but I don't venture far on it. If I still did the rallies then a upgrade would be on the cards

[dragoonpvw]

I have a p standard 63 li150, stock exhaust and carb. Bgm ignition and a standard oversize piston for its rebore and have had 60 out of it GPS both ways on a stretch of road. I can always get 58 and cruises easy at 52 all day. Just have to put it together clean and do a real break in. Half the guys who cant believe it also dont believe in a break in so I wonder if there is a correlation.

[Stoink]

Marktheskin,
Points ignition or electronic? If its electronic, a lightened flywheel gives a surprising improvement with very little changes if any to carburation. Not the mid weight, the light one. If you have points ignition, I'd steer clear of an expansion till you upgrade to electronic. If you upgrade to electronic then the question becomes do you upgrade your crank to the thicker gp style crank (a good base for further upgrades) or stick with the li taper. It adds up quick...
an indian 175 conversion cylinder, head and piston can be picked up pretty cheap. Cheaper than a good quality expansion chamber. Make sure you do not get a kit made for a tv175. It will not work with a standard stroke/rod 58mm crank. Depending on what you already have (elec. ign. ?) The light flywheel and a 175 topend is a pretty inexpensive bang for your buck formula. If you have to get the ignition, get that first. Build on that.

[Warkton Tornado No.1]

Marktheskin,
Points ignition or electronic? If its electronic, a lightened flywheel gives a surprising improvement with very little changes if any to carburation. Not the mid weight, the light one. If you have points ignition, I'd steer clear of an expansion till you upgrade to electronic. If you upgrade to electronic then the question becomes do you upgrade your crank to the thicker gp style crank (a good base for further upgrades) or stick with the li taper. It adds up quick...
an indian 175 conversion cylinder, head and piston can be picked up pretty cheap. Cheaper than a good quality expansion chamber. Make sure you do not get a kit made for a tv175. It will not work with a standard stroke/rod 58mm crank. Depending on what you already have (elec. ign. ?) The light flywheel and a 175 topend is a pretty inexpensive bang for your buck formula. If you have to get the ignition, get that first. Build on that.

The GP 150 should already have the larger taper crankshaft.

Reducing flywheel weight is good for the engine in terms of loads & less inertia makes for snappier acceleration. However, is an electronic an "upgrade?" A correctly set OEM points ignition (preferably converted to 12 v) with a 'J' flywheel is likely to be far more reliable if this & other Forums are anything to go by

An Indian 175 conversion kit to suit a non 175 engine can be made to work well, but factor in many hours fettling. Dog rough, but if porting tools are available & a methodical approach adopted, then they can be made to go extremely well.......@ least with an expansion chamber that allows for over-rev. I'm not saying a 'Clubman' exhaust won't work, but choice is imperative. Even an optimised 175 can gas up with the majority. That's why supplementary silencers are required on the larger (safer) tailpipes.

[Stoink]

"A correctly set OEM points ignition (preferably converted to 12 v) with a 'J' flywheel is likely to be far more reliable"
More expensive and more work than just purchasing a lightened flywheel. Plus points not advisable if your run an expansion chamber. Higher reving, faster points wear.
"An Indian 175 conversion kit to suit a non 175 engine can be made to work well, but factor in many hours fettling. Dog rough, but if porting tools are available & a methodical"
Well I guess the the 175 kits sold by vendors such as a.f. rayspeed don't measure up to your standards? Weather they are 150's bored to 175 with a piston to suit a 58mm stroke, I dont know, but they run fine when bolted on and carburation adjusted properly. Im not suggesting the trash kits off ebay. Since he has the 150 already , he just needs a rebore and piston. Again, cheap, and faster than his current 150. An easy enough job he can do the teardown and assembly of while learning his bike. And yes, electronic is definitely an upgrade

[Warkton Tornado No.1]

"A correctly set OEM points ignition (preferably converted to 12 v) with a 'J' flywheel is likely to be far more reliable"
More expensive and more work than just purchasing a lightened flywheel. Plus points not advisable if your run an expansion chamber. Higher reving, faster points wear.
"An Indian 175 conversion kit to suit a non 175 engine can be made to work well, but factor in many hours fettling. Dog rough, but if porting tools are available & a methodical"
Well I guess the the 175 kits sold by vendors such as a.f. rayspeed don't measure up to your standards? Weather they are 150's bored to 175 with a piston to suit a 58mm stroke, I dont know, but they run fine when bolted on and carburation adjusted properly. Im not suggesting the trash kits off ebay. Since he has the 150 already , he just needs a rebore and piston. Again, cheap, and faster than his current 150. An easy enough job he can do the teardown and assembly of while learning his bike. And yes, electronic is definitely an upgrade

A correctly set OEM points ignition (preferably converted to 12 v) with a 'J' flywheel is likely to be far more reliable"

More expensive and more work than just purchasing a lightened flywheel. Plus points not advisable if your run an expansion chamber. Higher reving, faster points wear.

FYI the first generation of AF electronic flywheels were based upon the 'J' range flywheels. Brand new, they can still be bought considerably cheaper than the current AF electronic flywheels, let alone good used ones, considerably cheaper. I have fitted/utilised first generation AF flywheels/stators on road & race bikes & they are fairly bullet proof. In fact, just such an item replaced points on a race (Group Four) Lambretta but not for any reason other than wanting to eliminate the need for a battery. Points systems were all we had when racing in the 70's here in the UK, but they were relatively trouble free & coped with the revs.

"An Indian 175 conversion kit to suit a non 175 engine can be made to work well, but factor in many hours fettling. Dog rough, but if porting tools are available & a methodical"

Well I guess the the 175 kits sold by vendors such as a.f. rayspeed don't measure up to your standards? Weather they are 150's bored to 175 with a piston to suit a 58mm stroke, I dont know, but they run fine when bolted on and carburation adjusted properly. Im not suggesting the trash kits off ebay. Since he has the 150 already , he just needs a rebore and piston. Again, cheap, and faster than his current 150. An easy enough job he can do the teardown and assembly of while learning his bike.

You guess right. Sorry to say that even AF 175 kits are rough. However, the reason they do not "measure up to my standards" is because they tend to be rock hard (chilled) iron bore & undersize. That may not bother you, but it concerns me. Honing an additional thou out of a tight bore is a skilled, laborious task that takes hours whilst achieving cylindricity. Perhaps I'm missing a trick here & you have a way of eliminating the process......

More likely though you were were attempting "Top Dealer Trumps" in which case I'll show my card:

Rolon chain.

To some of us, that equates to the most dire quality chain money can buy. Yet, no prizes for guessing who sells it.


And yes, electronic is definitely an upgrade

You should equate what that statement means. I can for my part. I fitted a current generation AF lightweight electronic ignition to a major rebuild. Purely by chance, I slung on an old, ex race Piaggio CDI & it fired up with only half a half-hearted kick. Would it work with the CDI supplied, or any of the other 'Ducati' CDI's I had? Would it f*ck!

So, for my opinion on good electronics. OEM Vespa. Original AF lightweight. Motoplat including OEM Serveta. PVL. Selettra/Malossi.

That's an opinion based upon actually using all of the systems mentioned along with others that are commonly available.

I must confess, that is 'all' that qualifies my opinion. Oh! Almost forgot! I also have five GP's (two in Group Four state), one SX200, one TV200 & a Honda NC30 in my garage.

I wonder what your opinion is based upon......