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dapper
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Mon Nov 22, 2021 11:40 pm

Well, I did a search on posting images and without trawling through everything, there was the infamous lengthy BLOA saga, so I'm not quite sure what you are referring to . I have not posted any images whatsoever. I simply posted links to YT videos which I thought may be helpful to other scooterists in making small easily carried tools to rallies home or abroad which could be manufactured in one's shed from cheap scrap materials, so that comment was it bit leftfield, but hey, whatever. Just to clarify, I had no intention to "just drilling two holes either side of the conrod's active area" which is why I was researching the experience and expertise of fellow scooterists who had experience of carrying similar work on their own engines, hence my referral to port timings and the importance of accurate measurements, rather that what you elude to. I am a time served engineer with some 50 years experience with working accurately to exacting fine tolerances, so set my standards very high. Anyone who rebuilds an engine on a 60 year old shopping trolley and blats down a motorway at 70+mph should know exactly what they are doing as they're taking their life in their hands.
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dapper
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Mon Nov 22, 2021 11:50 pm

dapper wrote:
Mon Nov 22, 2021 11:40 pm
Well, I did a search on posting images and without trawling through everything, there was the infamous lengthy BLOA saga, so I'm not quite sure what you are referring to . I have not posted any images whatsoever. I simply posted links to YT videos which I thought may be helpful to other scooterists in making small easily carried tools to rallies home or abroad which could be manufactured in one's shed from cheap scrap materials, so that comment was it bit leftfield, but hey, whatever. Just to clarify, I had no intention to "just drilling two holes either side of the conrod's active area" which is why I was researching the experience and expertise of fellow scooterists who had experience of carrying similar work on their own engines, hence my referral to port timings and the importance of accurate measurements, rather that what you elude to. I am a time served engineer with some 50 years experience with working accurately to exacting fine tolerances, so set my standards very high. Anyone who rebuilds an engine on a 60 year old shopping trolley and blats down a motorway at 70+mph should know exactly what they are doing as they're taking their life in their hands.
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dapper
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Tue Nov 23, 2021 12:01 am

dapper wrote:
Mon Nov 22, 2021 11:40 pm
Well, I did a search on posting images and without trawling through everything, there was the infamous lengthy BLOA saga, so I'm not quite sure what you are referring to . I have not posted any images whatsoever. I simply posted links to YT videos which I thought may be helpful to other scooterists in making small, easily carried tools to rallies home or abroad which could be manufactured in one's shed from cheap scrap materials, so that comment was it bit leftfield, but hey, whatever. Just to clarify, I had no intention to "just drilling two holes either side of the conrod's active area" which is why I was researching the experience and expertise of fellow scooterists who have had experience of carrying out similar work on their own engines, hence my referral to port timings and the importance of accurate measurements, rather than what you elude to. I am a time served engineer with some 50 years experience with working accurately to exacting fine tolerances, so set my standards very high. Anyone who rebuilds an engine on a 60 year old shopping trolley and blats down a motorway at 70+mph should know exactly what they are doing as they're taking their life in their hands.
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dapper
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Tue Nov 23, 2021 1:25 am

So sorry for the repetition, but didn't realise its had gone onto a second page. Not deliberate and trying to keep all things amicable between all parties.
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Warkton Tornado No.1
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Tue Nov 23, 2021 12:58 pm

dapper wrote:
Mon Nov 22, 2021 11:40 pm
Well, I did a search on posting images and without trawling through everything, there was the infamous lengthy BLOA saga, so I'm not quite sure what you are referring to . I have not posted any images whatsoever. I simply posted links to YT videos which I thought may be helpful to other scooterists in making small easily carried tools to rallies home or abroad which could be manufactured in one's shed from cheap scrap materials, so that comment was it bit leftfield, but hey, whatever. Just to clarify, I had no intention to "just drilling two holes either side of the conrod's active area" which is why I was researching the experience and expertise of fellow scooterists who had experience of carrying similar work on their own engines, hence my referral to port timings and the importance of accurate measurements, rather that what you elude to. I am a time served engineer with some 50 years experience with working accurately to exacting fine tolerances, so set my standards very high. Anyone who rebuilds an engine on a 60 year old shopping trolley and blats down a motorway at 70+mph should know exactly what they are doing as they're taking their life in their hands.


I'm somewhat confused now.

I was merely trying to make an image visible to you via adding an email address to the 'share' function on the Dropbox link that I posted within this conversation.

My reference to the history of posting images was just to indicate that other users appear to have had issues with the same facility. It was only a comment that i am also having problems in sharing an image that may be useful, not any opinion concerning anything that you have added by means of links to videos. Nor was it any comment upon your competence.

Perhaps I am overly concerned that anything that is written here is visible to all Forum users & consequently 'they' may be interested enough to read any exchange without feeling the need to get any further involved.

For the record, pistons used in modified Lambretta engines may come from a number of sources. My preference, other than avoiding unnecessary expense, tends toward the intrinsically stronger pistons used within motorcycles, snowmobiles etc. I have used either cast or forged pistons & each have their particular advantages.

As far as adding ports to the inlet side of a piston which has none, nor any form of internal shape or thickening to the moulded form (cast or forged) then IMO there may as well be one large window. An example of the type of piston that would be modified in that manner is the Suzuki TS 250.

When it comes to pistons that are for reed valve engines, my preference is for windows, rather than the cut-out variety, if there is a choice. Such pistons tend to have been formed with internal mouldings obviously with the addition of ports in mind, @ the time of manufacture. However, that is not always the case. Sometimes, dependent upon when the piston design was conceived, there may be only two round holes. An example of the type of piston that would be like that may be an early Yamaha DT 250. Despite what other's may advocate, inevitably my choice would be to modify those two round holes to two windows that I think more conducive to the characteristics of the engine. That is precisely what I did with a TS 70 mm cylinder that I built*

I hope the above clarifies & helps somebody.....

* I am aware that the TS cylinder should ideally have appropriate graded pistons, but the engine had thrown a rod, consequently having a perfect bore with additional slots in the inlet & exhaust skirts. i decided to utilise those new 'features' for transfer, obviously on the inlet side, with the bottom end communicating directly with the enlarged boost port. i repegged the piston. The owner of that engine & I are extremely pleased with the results, though there is more to come.

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dapper
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Wed Nov 24, 2021 1:05 am

Ahh, so you're referring to the old issue with Flickr and Photobucket which some users of this forum experienced. Now I understand. Not obvious from your post. I understand your concern for the structural integrity of the piston and its integral strength in regard to modifications to to its skirt walls without supporting reinforcement with the weakening effect of drilling windows for the reed valve. However, what I'm trying to overcome is the spit back issue and associated excessive fuel consumption. I installed the Avanti kit strictly in accordance with Ron's instructions ( who've I've met up with on a few occasions as he's based not far away from me) and spent a good few hours working with and discussing a friends engine casing which was suffering issues which turned out to be a porous casing which was the initial cause of the problem. He's a great guy and is happy to pass on his knowledge and advice to all scooterists. I haven't been in touch for a while as he's a busy man and has enough on his plate and isn't getting any younger like all of us. Not sure if you've found enough time yet to view the YT links I posted but thought they'd be useful to everyone out there. I've made the rear hub holding tool which is the easiest and works very well. I've photocopied the base of the gear selector and am working on making my own first prototype of the layshaft holding tool and have friends who run a factory close by who have a mega CNC machine who could knock out loads at very reasonable costs. ATB
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Warkton Tornado No.1
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Wed Nov 24, 2021 3:09 pm

IMO there are methods by which spit back may be controlled.

The fundamental issue remains with piston ported engines the amount of inlet duration which can be improved by decreasing it by altering the piston length &/or the stroke &/or the conrod. They are not always practicable solutions, but given a blank canvas....

The choice of carburettor is often overlooked. Whilst Dell'Orto manufacture some excellent products, I do not think the round slide PH range is one of them in a two stroke application. In fact, respected two stroke tuning manuals will refer to the superiority of the guillotine type slide that was pioneered with the USA Magnum products, but most people will be aware of the Lectron carburettor that nudged the likes of Keihin & Mikuni into following suit. The reason that the Dell'Orto VHSB/C is predominant in karting with Rotax engines is due to the rules of racing, but, that said, they are very good products.

For the reasons just stated, along with the fact that there is no float bowl overflow/anti hot flood measures with the PH range means that I find the loyalty of Lambretta owners to the product rather baffling. Even the old VHB carburettor had a bowl to which an overflow could be added & when converted to a two stroke carburettor with the shrouding in the venturi, it is - IMHO - a far better product.

That said, the loyalty of many will remain with the PH range, despite the extortionate costs of components, say, compared to the outright cost of a PWK made under license by the likes of Koso, OKO, Stage6 etc.

The next means of making spit back more tolerable is to add an extension upstream of the carburettor. With a Lambretta that has the carburettor on the LH side, this can usually be done & with adequate size can incorporate filtration.

Now we get to adding a reed valve to a piston ported engine. Theoretically, besides allowing for 360° inlet duration, reeds should reduce spit back. However, the effectiveness of the reeds is dependent upon their proximity to the piston. That can be borne out if a reed valve cylinder is viewed as it can be appreciated how the designer has endeavoured to meet that criteria. Even with a reed cylinder of such preferable geometry, improvements can be made & are measurable, such is the nature of fluid dynamics.

However, all of the above said does not mean a reed valve manifold added to a piston ported cylinder is a bad thing. Just don't expect the same benefits as a well designed reed valve cylinder can provide.

So, in conclusion, I think the best way of tolerating that last annoying bit of spit back is to add an extension, preferably filtered.

"Out of sight, out of mind"

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dapper
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Thu Nov 25, 2021 12:28 am

I concur with your views on the Dellorto carbs and the adherence of some Lambretta owners to a "known" brand and do indeed know several who swear by them and have derogatory comments for any other make of carb. I do actually run an OKO PWK carb on both of my scoots having carried out all the pre-requisite checks on float height, passageways, etc. so I am happy that I've covered all possible issues. I agree with you that they are much easier to tune as they have fewer components. There seemed to be a lot of scare stories about float bowl capacity and other issues which were easily resolved. I know of a reputable dyno tester who made similar derogatory comments about them, but wasn't aware of the mods/checks required prior to install. I appreciate your time in replying but would add that I've tried a Breathe Sweet filter on the inlet bellows, but have re-starting issues once running due to the build up of spit back in the bottom of the bellows, which once removed, resolves the issue. I have a drain fitted into the bottom of the bellows but this doesn't seem to solve the issue. Once filter-less the engine runs fine.
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Warkton Tornado No.1
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Thu Nov 25, 2021 10:05 am

dapper wrote:
Thu Nov 25, 2021 12:28 am
I've tried a Breathe Sweet filter on the inlet bellows, but have re-starting issues once running due to the build up of spit back in the bottom of the bellows, which once removed, resolves the issue. I have a drain fitted into the bottom of the bellows but this doesn't seem to solve the issue. Once filter-less the engine runs fine.
Thank you for your full response :D

Before suggesting that inlet duration may be excessive, may I ask what size pilot jet you run? PWK's of 34 then a 30 were run on a Stage 4ish 200 & it ran faultlessly with both. I mention that only as I thought the 34 would have been overegging it, but it was excellent across the range. Keihin designed a great product there but strangely, their own 39 mm that I have does not allow for atomiser/needle jet change, unlike the smaller sizes made under license.

Subsequently the radically ported TS 70 x 60 was ran with the 34 & I was frankly amazed that it started after the full rebuild with a half-hearted kick 'just to get the juices flowing'. That had guestimate jetting, but most notably a bigger pilot, as you would expect.

The 200 - having space beneath panel - incorporated as big a DIY elbow as could be fitted whilst the TS had a sock. Both filters were DIY utilising filter foam & a hot glue gun. Neither had hot start issues as I know only too well plague the lesser Dell'Ortos. Even the VHB I mentioned suffered, which is why I know that there is the facility to add a bowl overflow. How crazy that the later PH's deleted that opportunity.....

Another of my firmly held beliefs :roll: is that any elbow needs to be as large as possible, acting as a plenum. In my experimentation over some years, I have fitted just elbows with no filtration to reach this conclusion, as they alone can cause engine bog-down.

I have no experience of the Breathe Sweet but from my observations of any images, the elbows that I have concocted from tapered silicone radiator elbows appear to be much larger in size & bend radii.

Are you aware that Harry of Pro Porting now supplies an elbow?

Yet another of my firmly held beliefs :roll: :lol: is that the best fuel is Super unleaded & that the ignition should not be too retarded. The 200 was set by the owner @ 21° BTDC & there was no good reason to change it. The TS was set by me @ 19° BTDC & it fookin' well flies. Prior to rebuild, it was 66 x 60 & reputedly pushed over 30 BHP on the dyno. The owner (who still hasn't paid me - Ha!) says his/my new engine probably produces an extra five. Not bad for an old git like me using a sub £100 blown up eBay cylinder following my own instincts, one of which is to increase crankcase volume, starting with using good OEM type crankshaft webs, not the full circle HPC variety. It may go against what some respectable tuners may advocate currently, but bottom end transfer porting is worth doing IMO as an aid to lowering primary compression.

Warkton Tornado No.1
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Thu Nov 25, 2021 8:37 pm


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