LCGB Forums

Seems a common problem with piston ported top ends.
I've a breeth sweet that on 2 different p.p engines bogs/ floods when starting from hot.
My mate has Very similar set up and no issues.
I've run no filter for years and and no increased wear issues and only want a filter to prevent the spit back from making everything under the panels filthy.
I 've tried down jetting the pilot but being rich low down suits my riding style ie some where safe to go to if temps rise.
Any one had any success with drainage mods I was thinking of constructing some sort of flap a fair to open to aid hot starting.
Modern 2 stroke enduro bikes have hot start levers that lean off to get round this issue.
Thoughts please.

Is this you Avanti Derek? I put a reed valve on mine and it's transformed

Not looking to transform anything.
Love the engine and power delivery to bits.
It's also an issue with my rt190 or ist 195 the MB one..
I think I'm trying to releave a symptom rather than fix the issue.
Going to spend a day dialing in the pilot which is over rich to compensate for a lean spot when running on the shaft of the needle.

Scooterlam wrote:Seems a common problem with piston ported top ends.
I've a breeth sweet that on 2 different p.p engines bogs/ floods when starting from hot.
My mate has Very similar set up and no issues.
I've run no filter for years and and no increased wear issues and only want a filter to prevent the spit back from making everything under the panels filthy.
I 've tried down jetting the pilot but being rich low down suits my riding style ie some where safe to go to if temps rise.
Any one had any success with drainage mods I was thinking of constructing some sort of flap a fair to open to aid hot starting.
Modern 2 stroke enduro bikes have hot start levers that lean off to get round this issue.
Thoughts please.

Have you tried the Breathe Sweet elbow without any filter on it?

The reason I ask is, like you, I got sick of the constant mess from my piston ported Rapido (Ø71 x 61) so that set me out on a bit of a mission to initially just find an adequate sized elbow that didn't 'choke' the Ø30 mm carburettor & my cynicism that standard bellows for the SH22 are anything like adequate. Even a Ø40 mm GF elbow caused problems & my experience led me to fit a spigot ring & increasingly larger elbows until there was no restriction to performance. All fitting under a side panel but the manifold is as shortened as a downdraft (CDC) type can be.

The 'icing on the cake' was the fact that I managed to prove (to myself!) that it was possible to obtain sufficient flow with a homemade elbow & filter that meant the engine is really responsive, clean & will probably last a tad longer as the result.

Thanks for the reply,

Can I take from your reply that you were unable to jet the flooding out or were you happy with the delivery it gave you?

What makes me think mine is fundamentally just a jetting issue is my friends, oh so similar set up is fine with a filter but 2 of mine aren't.

as a side issue each time I strip and change rings the barrel, piston and rings go to Ron and are measured to build his knowledge base of how the kit is doing in a real world test. I believe he does this with other kits he services and my non filter wear is no greater than filtered ones.
also why don't scooterists oil their filters ( I follow the heard and don't oil on scooters but do on my enduro)

Scooterlam wrote:Thanks for the reply,

Can I take from your reply that you were unable to jet the flooding out or were you happy with the delivery it gave you?

What makes me think mine is fundamentally just a jetting issue is my friends, oh so similar set up is fine with a filter but 2 of mine aren't.

as a side issue each time I strip and change rings the barrel, piston and rings go to Ron and are measured to build his knowledge base of how the kit is doing in a real world test. I believe he does this with other kits he services and my non filter wear is no greater than filtered ones.
also why don't scooterists oil their filters ( I follow the heard and don't oil on scooters but do on my enduro)

I seem to take a different approach to others but it works for me.

For a start, I'm wary of having tailpipes that are restrictive. Small pipes, on the capacity we are relating to, might encourage torque, but also tend toward heat build-up & lack of over-rev IMO.

Carburation wise, I go for the smallest practicable atomiser that will cope with the largest main jet likely to be utilised. There is a common tendency to fit over-large atomisers in my view. It's not difficult to establish which atomiser is adequate simply by running with no main jet for that purpose. You only have to look @ carburettor set-ups on Forums to see the wildly varied choices of atomisers (amongst other carburettor factors) for similar states of tune!

As I wanted to re-direct the spray from the inlet roughly vertical, that put me on the path to looking @ the means of doing that with an elbow. I would have loved it if a standard, cut back bellows had worked for me as I must have loads I'm never likely to use, but that experiment failed.

Once I'd established to myself that any elbow acts as a plenum & volume is key, not how smooth it is inside or how nice the curves are, I then stuck a filter on to the cut-back air-cooled VW inlet pipe just to see if the carburation was affected & was greatly surprised that it wasn't.

So, figuring that filtered air has got to be better than not, I concocted the current arrangement which is non-oiled (@ least initially, though two stroke spit back is bound to have seen to that by now!)

With all due respect to Ron or anybody that considers wear similar for filtered or not, my money would be in favour of running a filter. Any proper test/comparison has to be done on an almost clinical basis, running two identical machines in terms of carburation, exhaust, fuel/oil, ignition as well as payload/journeys to be taken seriously.

I never thought the day would come where I'd prefer a filter on a tuned Lambretta, but it has, purely as the knock-on effect of wanting to get rid of the mess created with an open carb.

What I would say, though, is that size does matter!