Atomiser/ Needle

Anything related to Lambrettas... ask tech questions, post helpful info, or just read and learn.
YAMLAM
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Mon Aug 05, 2019 9:44 am

had a slight heat seize coming back from a rally at the week end ,had been going about 10/12 miles at around 50/55 , going up a second hill nearly at the top bike started to struggle then and loose power, just as it went to nip i whipped in the clutch and coasted to a stop in a layby,
scoot smelt really hot , plug colour looked spot on with a tiny spec or too of ali on the electrode.
Its a Rapido 225 with LTH reed block ,BGM V3 clubman,PHBL 25mm ,
Pilot 51, AQ266,D26 needle 2nd clip ,51 Pilot ,125 main 350 pump jet.
18Deg.btdc
i dropped the clip one to richen up a bit but it doesnt pull cleanly, and i need to drop down to 3rd on any slight hill.
ive been riding on this set up for over a year,with no problems , so am wondering if i should go AQ268 and different needle ,or is the heat issue down to timing or ,as Harry Barlow, who done the reed conversion suggest that the Clubman tail pipe is too small and holds too much heat in .
win or lose have a booze

Warkton Tornado No.1
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Main scooter: Lambretta SX200
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Mon Aug 05, 2019 1:14 pm

"ask Harry Barlow mate, he did the work."

Oh! You already have! :D

Jesting aside, IMHO, an exhaust bleed needs to be an inch bore minimum on a 200. The fact that Lambrettas are fan cooled also indicates that going up a hill two up in fourth is doing the engine no favours.

The only advantages that small tailpipes give is low down grunt, but it is a massive trade off. Better to have a large tailpipe that stops heat build up & also allows over-rev without incurring damage. Group Four racers run no fans but do have the advantage of AvGas. It is the exhaust bleed of @ least an inch, 1-1/8" in some cases, that allows them to shed the heat & allow for over rev, like, say @ Cadwell Park.

I know that some traders claim almost to have invented the wheel & consequently their products are trusted (by the time any glitches have been sorted out by the buying public & Version XYZ is available....) but a kitted engine tuned by the likes of HB is likely to be a good 'un & is going to shift some air that will just back up & cause a lot of heat.

YAMLAM
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Tue Aug 06, 2019 11:40 am

Stripped carb last night , pump jet is a 200, not 350, thats still sat in my PHBH30 ! could it be a lack of fuel or fuel/ tail pipe dia ?
win or lose have a booze

Warkton Tornado No.1
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Main scooter: Lambretta SX200
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Wed Aug 07, 2019 12:45 am

YAMLAM wrote:
Tue Aug 06, 2019 11:40 am
Stripped carb last night , pump jet is a 200, not 350, thats still sat in my PHBH30 ! could it be a lack of fuel or fuel/ tail pipe dia ?
Tail pipe diameter as already suggested.

As for the float valve, if you look @ what the numbers mean, 200 should be more than adequate, but I know a lot of you PH range users get nervous about that. I think your engine is breathing alright, but not exhausting well enough.

YAMLAM
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Wed Aug 07, 2019 11:17 am

i recon your spot on , wasnt going fast enough to cause a fuel issue,
win or lose have a booze

Warkton Tornado No.1
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Wed Aug 07, 2019 1:38 pm

YAMLAM wrote:
Wed Aug 07, 2019 11:17 am
i recon your spot on , wasnt going fast enough to cause a fuel issue,
From first owning Lambrettas, inevitably tinkering with them, we would always make our own 'Clubmans' by adding a big, long cone @ the front, gutting them & slicing an inch out of the side for ground clearance. The tailpipe would be fashioned from large steel tube using a pipe bender.

I run exactly the same on a long stroke Rapido/TS250 engine that pulls TV200 top equivalent. However, nowadays, I dare not use it without a muffler. No heat build up though, & it will over-rev if need be. That is always a sign that the exhaust is not restrictive.....

As far as I am aware, apart from my own ( :oops: ) the only genuine 'old school' Clubmans that are 'available' are Ralph's (Saxelby) & Ron Moss's, but the Gori does get good feedback. In the 70's there were a few 50 mm diameter 'U' pipe Ancilottis, & I still have mine in the garage rafters. No idea how good today's copies are, though.

I have fettled other owner's scoots that were big capacity & kitted & had precisely the same exhaust as you. I'd guesstimate I could get a very civilised mid 20's BHP from them through optimisation, but they would hit a brick wall @ their top end so I would not countenance their use for WOT runs or plodding uphill two-up in top gear.

Adam_Winstone
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Wed Aug 07, 2019 5:52 pm

Anyone had a look inside AF's large tailpipe bigbore exhaust?

The Scootering clubman feature showed these to have very good low-mid torque and peak BHP at low RPM, which might be 'just what the doctor ordered' on a low revving big cc motor but the low RPM ceiling does make me a little nervous about the internal design being perhaps too restrictive (?). I'm currently considering my options for a very long stroke motor that I'm hoping to keep the revs down on, so this may be ideal... but I need to ensure that it doesn't achieve these figures by being so restrictive internally that I'm going to run into 'gassing up'.

Hmmmm?

Adam

Warkton Tornado No.1
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Wed Aug 07, 2019 10:23 pm

Hey Adam.

With any exhaust, a priority is to ensure that heat does not build up, as you know. If a tailpipe, bleed, whatever you want to call it, turns out to be too large, then it is easy to introduce a restrictive sleeve within. It does not need to go the whole length

Before racing got the way it is currently, I experimented with tailpipes going down as small as about 20 mm on a Group Four, which was good for torque & short, twisty circuits, but SO restrictive on anything longer than Twisted Sister type tracks &, of course, the power would tail off dramatically as the heat built up during the event.

Whilst I'm on my soapbox, I can't get my head around a sprung 'U' pipe connection with the rest rigidly mounted! How hard is it to build in discrete AV mounts that will help the function & help stop the thing dropping to bits? :roll:

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