05' PX 150 - Jetting a New 24/24
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Enthusiast
05' PX150
Joined: 13 Mar 2019
Posts: 55
Location: Bellingham, WA
Sun Jul 07, 2019 8:41 am quote
Greetings.

The threads in the idle air mixture screw hole in my original 20/20 got messed up so I went ahead and replaced the carb with a 24/24. I had previously replaced the exhaust with a SIP Road and replaced the jets in the 20/20 with the recommended BE3, 102, 160 and 55/160 to accommodate that exhaust. The scooter ran very well at that time.

When I ordered the new 24/24 the supplier told me it would probably come with "whatever jets were laying around" when they put the carb together and to use the jets previously mentioned that I had in the 20/20 which I did.

Now that I have it all together and on the road I'm finding that I have to adjust the idle air mixture screw quite a bit more than 1.5 turns out which is fine I guess. But the scooter doesn't seem as responsive as it was. I'm not sure it "bogs" on acceleration but it does seem to hesitate just a slight bit even at high speeds in the higher gears.

My question is might I try playing around with different jets and if so what is recommended? FYI the new 24/24 came with a 150, BE4 which I haven't tried using.
Ossessionato
05 Stella, '62 VBB, 76 Sprint V, 63 GL
Joined: 16 Jun 2011
Posts: 2079
Location: Chicago. Well, Evanston, but that's almost Chicago
Sun Jul 07, 2019 8:53 am quote
Unfortunately, if you're running stock other than the SIP Road, it's probably never going to run well with a 24/24. The motor simply doesn't need that much airflow.

Enthusiast
05' PX150
Joined: 13 Mar 2019
Posts: 55
Location: Bellingham, WA
Sun Jul 07, 2019 9:14 am quote
Huh, I'm not entirely surprised by that response.

Should I have just replaced the 20/20 with a new 20/20? Maybe I should consider upgrading the motor to match the carb - this wouldn't be the first time I approached a problem bass ackwards.

Is running it the way it is - a stock motor with the 24/24 - going to do any damage?
Ossessionato
05 Stella, '62 VBB, 76 Sprint V, 63 GL
Joined: 16 Jun 2011
Posts: 2079
Location: Chicago. Well, Evanston, but that's almost Chicago
Sun Jul 07, 2019 9:48 am quote
No damage, but you'll always struggle with it, especially at quarter- to half-throttle, which is where you probably do the bulk of your riding.

If you want do anything but get used to disappointment, I'd say go back to a 20/20.

If you want to drive forward, realize that there's a LOT of knowledge (and tools) you'll need to accumulate before you do anything but turn expensive parts into expensive junk.

You can definitely start working on a plan, but start by searching on here for, if nothing else, the correct set of basic design goals you'll need to establish before you can begin to design anything.
Enthusiast
05' PX150
Joined: 13 Mar 2019
Posts: 55
Location: Bellingham, WA
Sun Jul 07, 2019 10:33 am quote
Understood. I'll likely go back to the 20/20 in time.

Thanks chandlerman.
Lurker
Joined: 04 Jul 2019
Posts: 1

Sun Jul 07, 2019 8:06 pm quote
chandlerman wrote:
If you want to drive forward, realize that there's a LOT of knowledge (and tools) you'll need to accumulate before you do anything but turn expensive parts into expensive junk.

This is the best response I have seen posted to anyone here on any topic in my 3 years of lurking.
Hooked
lml 2t Vespa lx50 2t
Joined: 21 Jan 2018
Posts: 102
Location: wales
Mon Jul 08, 2019 1:02 am quote
After mucking about with mine and riding hand on clutch waiting for it to soft seize I put mine back to standard with the emissions stuff as well...almost. 😊 Here in U.K. we have 125cc, so I left the 150cc and jetted it as per the manual which now gives me the power of a 125cc de restricted.
Plus I found every engine is different with jetting and most advice re jets is a good starting point but what works for one engine may not for yours.
I now ride it hard and don't get any seizures or need to keep my hand hovering over the clutch lever.
Hooked
PX 150
Joined: 06 Aug 2007
Posts: 282
Location: Dublin, Ohio
Mon Jul 08, 2019 2:38 am quote
If you switch to a carb with a larger bore, you will sacrifice speed that the air passes through the carb and you can sacrifice mid range torque because of that. Years ago I was trying to decide between a 42 and a 44 mm Mikuni carb on my big bore Harley Road King and a good friend of mine who owns a company that specializes in head work advised me to go with the 42, unless I cared only about max hp on the top end. It was great advice. With my Harley and its big bore pistons and head work, I could have used the 44 and had a bit more at high rpms because the motor could support the flow. With our stock PX150s, they probably don't flow enough to support the 24/24 even at high rpms; hence, your loss of performance. It seems conventional wisdom around here is to go to a 24/24 if a 177 kit is installed, but if a simple kit like a DR177 is bolted on with no additional port work and the stock crank, I would certainly ask people here with actual experience before switching to the 24/24. On that question I am clueless.
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