Can it be a Seize?

[Granty]

Running in a stage 4 200 lump with a 30mm delly, open mouth & clubman. 400 miles in & now at 1/2 throttle working up 3/4 throttle, plug chops all show dry, brown plug . Set up is
Stage 4 200cc
42mm Clubman
30mm dellorto
50 pilot jet
70 choke jet,
Av 264 atomiser
X7 needle 2nd notch from top
40 slide
125 main, run open mouthed

Got 20 odd mile in today, just over 1/2 throttle and started to lose power, clutch in, conked out. Checked the plug and it's a perfect brown choccy colour. Going to check timing and pressure test early next week but the question is can this be a seize if the plug is a good colour, the scooter restarted and i drove it home slowly no problem.

Keen to hear thoughts - thanks G.

[missing lynx]

Could be. I had an Indian gp with a brand new stage 4 200 engine that just kept sezing while I tried to run it in when I checked the bore tolerance it was far to tight so got rid of it to a friend they got it honed out and after that it was fine

[Warkton Tornado No.1]

Your starting point would be knowing the brand of piston & bore clearance. Do you know that? Ball park is 0.0035” but that would apply to a preferred, cast piston.

The jetting information looks about right.

Many people have a misconception of what ‘running in’ entails for a fan cooled @ engine speed Lambretta. Personally, I don’t apply rules of engine speed & will happily drop down the gears to give an engine the cooling air it needs, along with a variation in the load.

[Adam_Winstone]

I've always found the AV264 too weak when I've used it on 200+ with X7. I have found it to be ideal for smallblock up to 175cc with X13, typically 28 PHBH.

I've happily run AV266 with X7 on 200 and 225 with 30mm but they're always rich with a 40 slide, and the 45 slide doesn't clear up a bit through 1/3 to 1/2. However, you may have seen me mentioning the AV265 which Dellorto no longer list (used to) and which Readspeed put into production a few years back. These have been fitted to a number of my bikes and mate's that have been dynoed.

As others have said, running in a tight bore could easily seize because of more miles and clearance being needed, regardless of jetting. However, if you're running a weak setup, which IMO yours is (try the AV265), then a tight bore will quickly nip!

I should know, I recently nipped a fresh bore Rapido; resolved by fitting a richer atomiser, doing Stax and back without issue.

Good luck getting it sorted.

PS - You may find the AV266, or even richer, especially if you are using an advance/retard ignition.

[Granty]

I'm double checking timing and then a leak down test tomorrow, I've got an AV266 that I'll put in it if the 1st couple of tests go well. I have the same set up in another bike and it runs superbly, but this one is different altogether ... i also mis-counted my running in miles at actually just over 400, i thought i was on 500+, maybe still in the foothills but will defo richen this one up a bit for sure. Thanks for the responses all - G

I've always found the AV264 too weak when I've used it on 200+ with X7. I have found it to be ideal for smallblock up to 175cc with X13, typically 28 PHBH.

I've happily run AV266 with X7 on 200 and 225 with 30mm but they're always rich with a 40 slide, and the 45 slide doesn't clear up a bit through 1/3 to 1/2. However, you may have seen me mentioning the AV265 which Dellorto no longer list (used to) and which Readspeed put into production a few years back. These have been fitted to a number of my bikes and mate's that have been dynoed.

As others have said, running in a tight bore could easily seize because of more miles and clearance being needed, regardless of jetting. However, if you're running a weak setup, which IMO yours is (try the AV265), then a tight bore will quickly nip!

I should know, I recently nipped a fresh bore Rapido; resolved by fitting a richer atomiser, doing Stax and back without issue.

Good luck getting it sorted.

PS - You may find the AV266, or even richer, especially if you are using an advance/retard ignition.

[Warkton Tornado No.1]

I’m not wishing to contradict anybody concerning the atomiser size, but often remind fellow users of the simple test of whether an adequate size has been selected. Simply remove the main jet & start the bike on the stand.

In this instance I would bet that the set-up will be found to be rich - as it should be with a 264.

To back up that simple test, there is the science:

https://www.airheads.org/wp-content/upl ... Manual.pdf

wherein you will see in the first paragraph of section 3.2.1 Dell’orto’s own recommendation.

Do the maths & you will assure yourself that if there is any problem within your current carburation, it certainly isn’t the atomiser/needle jet…….

However, I missed the fact that you have a 40 slide & I would say to borrow - to try - a 45 & your’s can easily be converted. You can even ‘try’ a 42.5 by converting your’s. It’s the kind of thing Terry Frankland was doing decades ago

[Granty]

Nice, simple test that, what am i listening for, looking for?
I'll check timing properly tomorrow, on a quick look tonight with the gun the timing looks well into the 19-21* territory, I'll bring that back to 17*, I've noticed the seal between the downpipe and box not airtight either. One thing at a time as they say -- G

I’m not wishing to contradict anybody concerning the atomiser size, but often remind fellow users of the simple test of whether an adequate size has been selected. Simply remove the main jet & start the bike on the stand.

In this instance I would bet that the set-up will be found to be rich - as it should be with a 264.

To back up that simple test, there is the science:

https://www.airheads.org/wp-content/upl ... Manual.pdf

wherein you will see in the first paragraph of section 3.2.1 Dell’orto’s own recommendation.

Do the maths & you will assure yourself that if there is any problem within your current carburation, it certainly isn’t the atomiser/needle jet…….

However, I missed the fact that you have a 40 slide & I would say to borrow - to try - a 45 & your’s can easily be converted. You can even ‘try’ a 42.5 by converting your’s. It’s the kind of thing Terry Frankland was doing decades ago

[Fast n Furious]

It does sound like you might have semi-seized it. Best to confirm if this has happened or not first before messing with anything else.
These little cheap endoscope cameras that plug into your phone at one end and down the spark plug hole at the other, can be a quick way to check for for scoring and rubbing spots.
Now't beats a strip down check of course, but they can prove to be a useful indicator.
As a rule, on a rebuilt motor, I record the kickstart compression pressure. I can then use this as a marker if I have to check it again later on for whatever reason. Again, another good indicator telling me if that engine needs a stripdown.

[Warkton Tornado No.1]

Nice, simple test that, what am i listening for, looking for?

With the main jet removed, the atomiser/needle jet will be the restriction & should provide a massively rich mix, that is, too much fuel to air ratio. The 264 should be massively rich & then some.

F n F is quite correct with further good advice.

However, if it were me I’d really want to know the piston to bore clearance, compression ratio & squish. You might well be daunted by the prospect of a top end strip down, but you could well be chasing your tail trying to find the cause of a problem if you avoid doing so. Conversely, you might well be able to find that bit more power & reliability, especially in the instance of safely being able to eliminate a head gasket…..

[Adam_Winstone]

Lots of ways to skin a cat, and I don't disagree with what has been said, however, I test all of my setups stage by stage and regularly demonstrate to others that you can ride a bike around with no main jet fitted, until you approach 3/4 throttle when the motor drowns/bogs dramatically. It's an interesting lesson in carb stage progression.

Also, do note that you can end up with strange needle and atomiser combinations if the needle comes onto the taper early enough, allowing a reduction in atomiser size, and providing that all other factors allow. My example of this in action was riding back from Euro Lambretta Germany (sometime around 2000) with Darren from Maidenhead,. His Suzuki 225 converted iron barrel was a dream to ride with; great on small roads but equally happy to be held at speed on the motorway, easily sticking with my Taff tuned TS1 225. Indeed, I was so impressed by the performance and reliability that I stripped his 28mm PHBH when we got home... and I was shocked by what I found!!!! He was running an AV260, X2 needle and 108 main jet, which seemed ridiculously weak!!! I then spoke with the Taff brothers about this and they said that those settings were not unusual for tuned Vespa settings, although not typically Lambretta. If anyone would have told me these setting I'd have walked away! Turns out that by getting onto the taper earlier, all was well.

However, when running an X7 needle the AV264 often runs lean and the AV266 often runs rich (both supported by dyno results... not my say so (yes, influenced by adjacent progression step components), which is why the AV265 has been put back into production for one of the UKs most respected tuners and dyno operators. NB: Not me introducing my opinion, just relaying the data.

Please note that I am not challenging anyone, you can argue with the dyno data all you like, but I don't want others to immediately discount my previous comment, which IMO is still totally valid.

I wish you well in resolving this issue and hope that you can stop your motor from seizing.

Adam

[Granty]

Wee update -- timing checked and reset to 17* TDC. Leak test done tonight and there's a leak somewhere, soapied the main area and found a leak at the exhaust gasket, will take the head cowling off, clean up, new gasket and test again .. this could be it hopefully - G

I'm double checking timing and then a leak down test tomorrow, I've got an AV266 that I'll put in it if the 1st couple of tests go well. I have the same set up in another bike and it runs superbly, but this one is different altogether ... i also mis-counted my running in miles at actually just over 400, i thought i was on 500+, maybe still in the foothills but will defo richen this one up a bit for sure. Thanks for the responses all - G

I've always found the AV264 too weak when I've used it on 200+ with X7. I have found it to be ideal for smallblock up to 175cc with X13, typically 28 PHBH.

I've happily run AV266 with X7 on 200 and 225 with 30mm but they're always rich with a 40 slide, and the 45 slide doesn't clear up a bit through 1/3 to 1/2. However, you may have seen me mentioning the AV265 which Dellorto no longer list (used to) and which Readspeed put into production a few years back. These have been fitted to a number of my bikes and mate's that have been dynoed.

As others have said, running in a tight bore could easily seize because of more miles and clearance being needed, regardless of jetting. However, if you're running a weak setup, which IMO yours is (try the AV265), then a tight bore will quickly nip!

I should know, I recently nipped a fresh bore Rapido; resolved by fitting a richer atomiser, doing Stax and back without issue.

Good luck getting it sorted.

PS - You may find the AV266, or even richer, especially if you are using an advance/retard ignition.

[Granty]

Well -- there's the answer, leak down test shown air leak at exhaust gasket, whipped the pipe off to have a look and see slight marking on the piston ... top end coming off shortly ... struggling to get a pic uploaded.

[Warkton Tornado No.1]

It’s pleasing to know that the very likely cause of any issues has been found & that you have posted that.

Air leak tests are so easy & necessary. My own ‘kit’ is simply a cut up scrapped MTB inner tube that fits most - these days(!) - exhaust round stubs & the inlet stub. No gauge as you soon realise if there is air loss as the tube section deflates.

As for jetting of Dell’Orto carburettors, there is the theory & then again the experience of users.

The PH range has a huge loyalty amongst Lambretta modifiers, yet compared to the rest of the product range, my opinion is that I fail to understand why. The PH range superseded the VHB’s & in so doing went to a round slide & eliminated the VHB’s built in overflow feature! However what the PH does have going for it is the two stroke atomiser orifice & the choice of solid or rubber mounted options.

The overflow feature - or lack of it - is the fundamental cause of any hot restart issues.

Then there are what I would politely call ‘idiosyncrasies’ as in, yes, we can look toward the theory of adequate float bowl needle valves & a 200 ‘ought’ to be safe. It’s not, so perhaps that indicates as to why so many utilise oversize atomisers…..

My experience with Dell’Orto’s is predominantly with VHB, VHSB & VHBC’s. Even with the 39 mm bore VHBC’s set up for racing engines, there has never been any need to oversize the atomiser as an additional ‘safety measure’

Anyway, I’m sure that any right minded member of the LCGB tries to contribute any help they can & I’m pleased to hear that the OP’er seems to on the way to success. Often the thought process with any problems takes us on a bit of a journey, don’t you think

[Adam_Winstone]

That said, a slight leak on the exhaust gasket face is likely to have only a minor influence on the motor running hot as the whole idea of an exhaust port is to release spent gasses to the outside air. Yes, it can still have influence but I very much doubt that was the issue.

I look forward to seeing what the cause actually was.

Yep, all positive help from contributors that are trying to help.

Adam

[Warkton Tornado No.1]

Would you believe it, but via a Mychron 4, there was indicated a massive spike in temperature. Ironically, the cause was the EGT probe coming just a tiny bit loose. The actual device installed to protect the engine - by telling the rider of an extreme in temperature - was the cause of such an extreme.

The probe was M5 threaded into a bush welded in place in the exhaust header. So, in my experience, just the space between the threads was sufficient for the engine to run weak.