Malossi 172 top end

Anything related to Vespas... ask tech questions, post helpful info, or just read and learn.
Dek
registered user
Posts: 9
Joined: Tue Mar 24, 2020 11:51 am
Main scooter: Vespa T5 classic
Contact:

Sun Oct 18, 2020 1:08 pm

I run the following T5 malossi 172 with a si 26/26g carburettor, 125 main, bgm big box, 21 tooth clutch and kytronic ignition smart booster set at 24 btdc on curve 1.
It accelerates in 1st 2nd and 3rd very well but when changed into 4th doesn't make much difference in speed 60 mph on GPS flat out.
So I suppose my question is that the expected top end speed for that setup, I thought it would be more.
Also pulls up hills very well.
Cheers

Dek
registered user
Posts: 9
Joined: Tue Mar 24, 2020 11:51 am
Main scooter: Vespa T5 classic
Contact:

Sun Oct 18, 2020 1:45 pm

Oh, also has a pinasco race crankshaft

paul d
registered user
Posts: 303
Joined: Thu Jun 30, 2011 10:00 am
Main scooter: T5 172 Tv 240
Location: Galway Ireland
Contact:

Mon Oct 19, 2020 12:50 am

It should be quicker. I've a feeling the bgm big box might not rev enough but has boosted your low down torque. If the scooter is reving out the same in 4th as in 3rd then the exhaust might be the problem. I think it'll pull a 22 tooth clutch with that set up which would give an extra 5% ish top speed. A sito plus exhaust would allow it to rev higher with the 21 tooth which would give more top speed too. Maybe the first experiment I'd do is to remove the kytronic and set the timing to 15 or 16 degrees. In my very many miles of 172 experience, the kytronic isn't needed on a standard 172 set up like yours.

Dek
registered user
Posts: 9
Joined: Tue Mar 24, 2020 11:51 am
Main scooter: Vespa T5 classic
Contact:

Mon Oct 19, 2020 9:58 am

Thanks for the reply, I was wondering about the kytonic iI, will give it a try. Thanks

Andy Beard
registered user
Posts: 16
Joined: Wed Oct 07, 2020 4:45 pm
Main scooter: Vespa P-range
Location: Sheffield, Yorkshire
Contact:

Sat Oct 24, 2020 1:43 pm

Hello Dek, are you getting anywhere with your engine mate? Running a similar’ish setup as yourself, BGM 177 + Pinasco 57mm crank + Pinasco Si 26/26 vrx + SIP Road XL + Kytronik 24btdc curve 1 + Pinasco lightened flywheel + 23/65 gearing. All matched & inlet timing optimised.

Pulls great low down, uphills & into headwinds with no problems, only given it a very brief WOT thrash for 1/4mile of dual carriageway (67mph gps) but CHT skyrocketed & I bottled it!

My issue is the Si 26/26, it’s been a PITA to dial in, only started to get anywhere by switching the air corrector from 160 to a 140 to enrich the idle circuit, the main jet is at 135 a plug chop shows lean but a bigger main jet starts to show signs of bogging, keeps CHT down but loses rpm’s & power!

Tried loads of Kytronik curves & can get way more power & smoothness at low rpm’s but not as successful at higher rpm’s, it’s possible the cylinder might want raising to increase rpm’s but this could lose some torque (my 16 stones needs some)!

Thought the SIP Road 2 was strangling it, swapped to an XL but only helped a little (500rpm max) I keep coming back to the carb mate & gather many think them impossible to dial in, which I’m inclined to agree with!

Plan is to go with an Si 24/24 & keep the auto lube, hopefully get it dialled in & compare the results but I’m expecting to have to move up to a ‘proper’ carb or lower my expectations!

Keep the Faith Dek!

paul d
registered user
Posts: 303
Joined: Thu Jun 30, 2011 10:00 am
Main scooter: T5 172 Tv 240
Location: Galway Ireland
Contact:

Sun Oct 25, 2020 12:35 am

Hi Andy. I'm not familiar with the BGM cylinder kit but if it needs a 135 main jet to run right, it's in a higher state of tune than a malossi 172. My 172 is on a standard T5 carb and with a scorpion exhaust it runs perfect with a 125 main. I think a 125 main jet is on the limit as regards flow from the standard fuel tap. If I was you the first thing I'd do is buy a fast flow tap.

Andy Beard
registered user
Posts: 16
Joined: Wed Oct 07, 2020 4:45 pm
Main scooter: Vespa P-range
Location: Sheffield, Yorkshire
Contact:

Mon Oct 26, 2020 8:03 pm

Hello Paul, 1st thing I did was fit the SIP mk2 fast flow tap mate, no problems with fuel starvation issues, the Si 26 is just a plain t@#t to dial in, never had any trouble with an Si 24 + drilled filter & passageways though!

With the Si 26 + Venturi the recommendation is to up jet by 10 points, that’s got me to a 135 & the plug chop’s indicating lean, if memory serves, a 140mj is about the limit for an Si carb!

Logic & intuition is telling me to go to a well set up Si 24 with drilled filter & to stop dicking about, ‘kin noise of the induction is getting on my tits anyway!

Cheers, Andy.

Post Reply Previous topicNext topic
  • Information
  • Who is online

    Users browsing this forum: No registered users and 2 guests

cron