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Hi all. I have been having a few issues with false air and I’m quickly running out of ideas. I’m hoping someone here has had similar issues and might help with alternate solutions. Firstly a bit of background:My set up was
Dell’orto 13/13 (66 polini jet as spark very black with 68)
Gianelli fire exhaust
Polini speed engine
Polini 43mm racing 12 pin
Mazzuchelli 12 pin
Malossi filterAll parts were brand new and assembled with correct procedure.
I ran this block for between 150-300Km before a seizure and im sure it will have had the same issues. I feel it ran too hot because of the leaks however cannot prove this now.
This was the outcome:
Covered by my thumb the piston pin hole has ripped in to port. The shrapnel in the top I cant grip enough with pliers to pull out! Its pretty deep though. The head is ruined.
The cylinder wall shattered, piston wall torn and ripped out the clip and everything went all over- not good!!
Thankfully the carters are okay and crank cleaned up with lots of compressed air and cleaning. I’m also a bit of a hoarder so I have a few spare blocks and one was prepared to a 43mm DR Evo 12 pin.
The new set up, don’t 3Km total:
Tuned piaggio carters (intake filed maybe too much but it runs and pulls well)
Original crank 12 pin
DR Evo 12 pin
Same 13/13 dellorto 66 jet
Same gianelli fire
Same malossi filterWith this I wanted to run it for longer as I have been building my lady a bravo and want to enjoy lots of rides without 2 new cylinders every 150KM ish …
I’ve been trying to eliminate all leaks before I run it fully. Not had full throttle yet.
The first thing I did was use an old 700c 18mm bicycle inner tube chopped in half with the valve kept. I jubilee clipped this over the outlet and the intake nice and tight then pumped up with the tire valve to 6-7 PSI with lots of soapy water. Block seems to have no leaks at all so I went on to the deo test.
I got the block back in and have tried so much to get the intake sealed.
I used a new plastic for the inlet.
I’ve tried using loctite SI 9550 copper silicon gasket under the inlet plastic, and also on the outside before attaching the carb and even at the outlet.It looked like the float bowl on the deo test so I changed it over to an older float bowl. Used a very thin bead of the copper gasket on the outerside of the seal on the float bowl and still had the same issue.
Everything is always nice and tight! Exhaust is sealed good!
I’ve tried a different 12/12 with the same issue
I took this seal out of a ciao mix carb and tried with that both with and without fresh copper silicone gasket:
STILL the same issue!
The deo test for sure looks like my carb. I can spray all day long at the top end without any changes.
All gasket paste was given 24 hours cure time. I know its not best to use near fuel but I drained and cleaned the carb / intake / plastic beforehand and just wanted to rule out the problem.
Deo test:
https://youtu.be/zGip49CH258I concentrated round the carb because it’s where I think the leak is but I can do a more indepth one on other areas if you like.
I’ve also been told small leaks like this are common and don’t need fixing and that 400km from a block is normal. I just can’t accept this if its not running full throttle the whole time. What do you think?
I have a new ciao headed 46mm polini on the way for the speed engine. I got a CP evo block for the bravo with a 46mm polini and bravo head that I really don’t want to damage.
Any help appreciated.
Wow this is really odd. It looks indeed like the plastic thing around the inlet itself. I would recommend using that without the black rubber gasket.
Can you say anything about your inlet? When you put the carb on, is it tight? Or a bit loose.
If i read correctly, you’ve tried 2 carbs? Is it possible to test another new one? And not Spaco (imitation brand)
46 Pinasco, Malossi RV, Schijfrem, Fox Vario
Gele RacefrikandelThe airfilter is very nearby, so it will always suchs gas inside from the deo.
Also through the choke slide opening.The gas/oil mixture must be at least 1:40 with this kind of revs.
Is the spark plug not to cold?
I think you need ngk 7 or 8.Tuning the main jet: put in bigger jets until it sounds like a fourstroke, and then go one step back.
Maybe the dammage is because of the faillure of a wrong piston circlip.
Thats what I think.
And to lean with the mainjet.Did you drive it very carefully while you run in the engine?
No high revs for longer than e few seconds.
Not downhil with the gas closed.(never do that with a two stroker)Gr. Wim.
Een oude brommer is alleen leuk als sleutelen uw hobby is.Make sure you never, use these clips again. They are most likely the cause of your seizure:
It is best to buy these:
I push them in by hand to prevent them from bending.Also make sure, your piston pin is the correct length. If it is too long, the springs will not fall into their groove.
Okay I will never again use those clips!
Run in I do 4 heat cycle and full cool downs 5-10 mins run time each
Warm up then a 10 min very gentle ride with only 25% throttle. No holding throttle in any long spot just nice slow acceleration and deceleration. Full cool down. (the new block just finished this before the leak checks start)
4-5 short trips (10 mins )trying to stay under 50% max throttle varying speed often smoothly. Full cool down.
Warm up and ride 15mins varying speed up to near full throttle. Cool down.
Warm up and run the bike from 1/2 to full throttle smoothly for 15-20 mins
Thats pretty much my break in. Usually takes a day or 2. Then I ride it like I stole it… 2-stroke after all! Maybe not the best idea…
Luckily its pretty flat where I live and I can avoid all up/down hill during break-in
I’ll take the rubber gasket & carb off again and get a photo of the inlet. It looks okay but not 100% perfect and smooth like the speed engine’s, but I’ve seen worse… the carb fits on nice and snugly.
I’ll also do another deo test trying to cover off the air filter side with some plastic (not covering the filter it’s self)
I never throttle close down hill. Even while idling when stopped I blip the accelerator often for the lube. Right now it runs around 45:1 during break in then usually 50:1.
I’ll mix up some 40:1 and replace the fuel, at least for break-in. It’s all about prolonging that engine life!
I had an NGK 7 with the 68 jet in the SE and downed to NGK 6 with the 66 jet. I can try the 7 again, then the 8 I have in the Evo engine. I’ll be back from work late ish this evening but will update photos tomorrow in the morning.
Thanks gentlemen
Before true carb and spark tweaking, I feel like I should sort the air leak as best I can. 10/6 the new cylinder arrives and as soon as the new polini gasket set arrives I’ll throw the speed engine back in. I have homemade gaskets I cut to size but the paper quality maybe inferior to polini. We will see how impatient I get!
I want to know if I get the same issues with the SC too because it was never checked for leaks with the carb and outlet attached. Only before installing the engine.
Like semmad said:
Tuning the main jet: put in bigger jets until it sounds like a fourstroke, and then go one step back.this is to me the biggest factor in preventing seizure’s.
Even if you have false air leaks this will still give you a proper driving bike.
Only thing is that you cant properly adjust the idle, it will always idle high (because of the extra air)Dont mind the colouration of the spark plug too much. It gives you a fair reading if you ride full throttle for 5 km’s, than full stop, shutdown and remove the plug. If you go 5km full throttle but than have to go back through the city to your house(stopping and accelarating) the readout isn;t trustworthy anymore.
Also a home made seal is good enough if made from gasketpaper.
Sometimes even better than a brand name because you can create more “flesh” around the edgesGood luck!
and mix quality oil!
I think the oil is good. Pretty sure its Castrol T2 high performance racing oil. Maybe I switch to the “scooter” version. I like silkolene Pro 2 too but my local shops don’t stock it :(. I don’t like Amazon, cheap but greedy fuckers.
This morning I’ve increased the spark to a hotter one. New BH7 now and swapped the jet for a 72. I will leave this for the break-in but until I can go full throttle it doesn’t matter too much.
The DR has the correct clips in thankfully. I don’t know what kit the clips that destroyed the cylinder came in, but it wasn’t the polini for sure… I should have used what they sent!
I was going to remove the centre stand today and put a side stand on so I can fit a better exhaust but my ciao is a 1976 SC has a straight bolt through the stand. Not a hollow bolt with the clips on the end.
I got a new centre stand delivered years ago but can’t find the clips for the outside!! Measured 13mm and I’ll try to order just them. I think I remember trying to install it and the bolt was too thick for the holes in my frame. I just finished painting and didnt want to drill…That didn’t last long. I had to grind away a tiny bit to get the 100mm disks at the rear to spin freely without scraping the frame…
Forced to stick with the gianelli fire for now. I think I hate everything about it.
My last purchase was a left curl proma cannon I cant wait to try! Need to get the stand gone! Also got a couple other nice exhausts I cant use because of this…
https://www.jmpbonderdelen.nl/vespa-ciao-si/framedelen/diverse-framedelen.html
Gr. Wim.
Een oude brommer is alleen leuk als sleutelen uw hobby is.
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