Jetting Help - T5 172

Hi SIP Board peeps.

Can any of you experienced T5 tuners out there help a newly kitted scooterist?

My setup is this:
T5 Malossi 172, Taffspeed pattern cyl head profile, Malossi read valve (case inlet mildly tuned - not as far as the Malossi kit leaflet spec), Delorto PHBH30mm (running with no air filter - until I get my order from SIP). Jetting Main: 135 (took it down from 140 today), Idle 55, Air corrector 70, Needle X3 (2nd clip position from top) airscrew 2 turns out, Sip Performance pipe. , Cosa 21T clutch. Spark Plug: Bosch W2CCand W3CC (approx NGK B9 & B8-all in a 1969 GT frame.

The engine was fully re-built when the kit was added (inc new crank). Now any of uz with even without a pocket calculator handy will work out that to be a whopping investment - one that I don’t want to b*** up.

The kit is just finnishing running in (done 400 mls) and I am starting to open her uop a bit. The way she is performing has me ‚bricking it‘ that I am gonna seize/trash the engine coz it aint set up right.

To get me on the right path, can anyone (a few of the SIP team are running this set-up right?) give me a ballpark jetting for this set-up?

A sthe engine has ‚bedded in‘ and loosened up, the bottom end has improved a bit - not bad at all I have to say approx equal to the standard T5. Where the standard left-off I now get ‚waaaaaaaaaaarp‘ in 1st & 2nd and sometimes in 3rd - the take off is really amazing! (picture scooterist only attached to the scoot by the handlebars). I have not run her at full throttle for more that a 2 mins - not dared to: The engine feels rough after hard acceleration and will not pull 4th well. Today I was experiencing power fade in 3rd at full throttle (acceleration then deceleration) and still no performance (powerband) in 4th - I suspect overheating as after hard acceleration in 2 gears the ‚powerfade‘ occur - my clutch hand now ackhes from hovering over the clutch leaver incase she starts to seize.

So as mentioned can anyone please advise ballpark jetting I can get this right & rule it out of the problem?

NB Since I adjusted to run leaner (see above) the powerfade/roughness (overheating?) has become worse (but the bottom end crisper). She is not ‚4stroking‘ as I would recognise it (I have experienced this on an overjetted roraty valve) but overrichness may be disguised by the read valve (this is my 1st).
Plug reading: Hard to tell I am running Full Synth and have not been confident enough to run to a propper ‚plug-chop‘. From the plug colour that I can see it’s milk chocolate brown, milk chocolate (think cadburys milk tray - not milkybar kid) base was with slight oil deposit before down jetting today, after today’s ride there was a small light deposit on 1/4 section of the insulator.

Well I should perhaps try a tank of cheap & cheerful mineral oil to get a better reading - but under the circumstances would you? Any advice is more than welcome - I think I should re-visit the jetting - anyone else running this set-up or have better advice?

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With regards to the head, if it has had 1mm skimmed off it use the gasket, if you have just had the combution chamber enlarged and no skimming dont use the gasket.

With the question of not pulling 4th, try going back to the original gearing until you get it running right, then up the gearing again. I have also heard a lot of people complaing about not being able to pull 4th and it slowing down so they are having to thrash it in 3rd to maintain speed. The only thing I can think of is that its not set up right or the powerband is high and not being reached in 4th. If the later is the case, the down gearing will cure the problem.

The only sort of weird sound I have had from the crank area was when I used a cheap (non original rubber instead of metal) oil seal on the clutch side, they have a habit of working themselves loose and rubbing on the crank. In extreme cases spin around with the crank. One solution I have found for this problem is to use a genuine seal and put locktite around the edge when assembling it. The noise I had was also accompanied by rough running especially when cold and loss of gear oil. The loss of oil was not dramatic but it was needing a top up every week. My seal had not actually come out all the way but had moved enough to wear approx. 1mm groove in the crank. If you are not experiencing all the symptoms I have described and have used an original seal dont bother taking it apart as its quite a lot of work getting to it.

You will generally get pinking at sustained high speeds. You will start to hear a rattle, its like something metalic rattling in the cylinder, its gets worse if you dont drop the revs. It is caused by the fuel being ignited by heat alone, so any sign of pinking means you are overheating. If you are using a W2CC it most definatly will not be the plug causing it. 4-stroking is different to pinking, my idea of 4-stroking is that it is like forgetting to put the choke in, i.e. the engine bogs down. Pinking is very apparent and you cant mistake it, sounds like a bearing is about to go.

My advice is to get the main jet sorted first and then move on to other areas.

The symptoms you are describing sound like your main jet is too large, it will seem rough when high in the rev range and when you have between half to full throttle.

Try coming down one size at a time.

I think a 135 main jet may be a bit rich, try a 130 if u dare. On these engines you should get pinking when it starts to overheat, sounds like something rattling in the cylinder, if you do slow down or it will sieze. Do not use low quality oil, you will in time get a build up on the plug so just be patient. Other people I know with a similar setup to you are using a 125/128 main jet, depending on the exhaust. My guess is 128 with the Taffy, but go to 130 to be safe especially as you have no filter at the moment. If the machine is smooth at high revs just leave it alone for now until you get more miles on the clock. I am also using fully sythetic oil and it is pretty impossible to get a good reading without at least 1000 miles on the plug, even then there is not that much build up.
Another thing to watch for when using the reed valve is to watch for air leaks, check everything just to be safe.

With an unbalanced crank you get a lot of vibration through the floorboards, I should know as I cut mine myself and it is most definatly not balanced, still runs ok.

MMmmmm… well - can’t offer any advice yet mtl - still need some more for myself!

I got my new jets & other stuff before the weekend - 1st tried a 130 main with New atomiser AV264 & New Needle X7 (leaner alround - was previously 135, AS266, X2) - disasterous (no seisure though) . Pretty rough pulling through 1/2 to full throttle in 1 st & second … then in 3rd. acceleration followed by deceleration and cutting out - yes engine dying completely and re-starting after closing throttle or changing up (but no actual seizure) this sounds like almost seizing though?. Well I decided to rebuild the reed block (fiddly B****tard with the engine in frame arn’t they?) replaced the rubber carb mount with a metal one, added the air filter hose (like standard one) pulled the head to check for any teltale signs replaced head but without the gasket, went back up to a 138 main.

Now more the questions: 1) Should I run with or without the Malossi head gasket (head is re profiled) 2) as I took the Malossi carb rubber off I now put that plastic ‚restrictor‘ in the reed mouth - kind of oval inlet hole and two lips that direct the mix onto the petals - should this be in there does it help or restrict flow? 3) W

Well the performance is starting to get there 1 st second & 3rd less responsive than before slower acceleration but pull into the powerband and accelerate to a healthyly high rpm. 4th however is complete pants - slower that 3rd and does not reach power revs and actually slows down at full throttle. (Still not actually 4 stroking though) - but performance is worse than original 125/SI24 setup on a leo pipe! There was an earlier thread with someone who suffered this I’ll go look that up after posting this - Could it be the up-gear effect of the 21 tooth clutch and the peaky nature of the kit/pipe combo? still should pull 4th though shouldn’t it?

Other ramblings:
Anyone know the difference between the ‚long‘ AS series needles and the ‚short‘ AV series - they have equivelant numbers - but how do they compare?
Well my plan is now to work back down in main jet size - leaving the rest of the set-up the same and see if I can get some better relationship to performance - shit this set up is supposed to be good for at least 75-80mph. By the way the crank area is really rattly with the occasional sort of ‚zing‘ sound at tickover been like that since kit and new crank was added - it does not feel any play at the fly wheel though and no movement there when pulling the clutch - not very normal should I be concerned or do others sound like that?
Ta again for any advice on any of this.

Tks again mtl

Will the orig 20 tooth clutch drive gear geat fit the cosa clutch then? I really like the new Cosa over the old clutch but cannot remember how different (if any) the drive gear was…

I’m gonna try your suggestion and perfect the jetting from there. I really do not want to go back in the cases again yet as I am not getting the traditional air leak symptoms (bad ide/ refusal to start, running on or racing revs)

I used an original metal seal - will drain gear oil to check for petrol though as a precaution, check out the flyside seal while I am at it. Not sure on the head skimming - the guy that did it for me used a Taffy head as the pattern. Any idea what the squish clearance should be ( approx 1mm measured with a piece of soldersound right?) or if the Taffy head comes skimmed or not.

Anyone know if the AS and AV series atomisers for the PHBH carb are interchangable or not? I’m going by the MB Developments carb tuning guid that lists AS (what the carb came equipped with) as a ‚long‘ type and AV as ‚short type‘ anyone know if theyare interchangable or if they belong with different shapes of float bowl or whatever?

Guess I can ask Taff & MB on these points - I’ll let you know what they say.

Re the noise from the crank - could I have a dodgy crank? - it is new - anyone know if they tested/balanced by Piaggio before sale or sold ‚as is‘ ?

I’ve got some pics of the inlet and read block I would like to show/discuss - can U post pix on this board? How?

Ta for advice (interchangeable drive gear)

the only advice i can offer here is
at least stick to semi synthetic oil while running in,actually i find running in on semi is better than on synthetic oil because it dosn’t lube as well as synthetic it causes a bit more friction between the barrel and piston,thus bedding the two better.disagree all you like,but it’s just wot i’ve found over the years!!!

Is it sorted out now, if so post you setup here to help others.

The taffy head should be skimmed already. Sorry I have no idea if the 20 tooth fits on a cosa clutch.

You can post your pics at

just make an account and u r in business.

Cheers for the advice mtldirect.
So I deffo could drop the main jet then - I’ll give it a try. I’ll have to wait for my parts order though (taking ages this time).

please advise re ‚pinking‘ vs ‚4 stroking‘ what it sounds/feels like?. I dunno if I explained the symptoms too well in my 1st post - maybe I put too much info in there. The problems (roughness and powerfade) got worse as I downjetted and leaned the needle a notch.
It’s like this: good power and acceleration when I hit the powerband in 1st & 2nd only - if I hold her open in 2nd - starts to get rough, if I go on and ‚give it some‘ in 3rd I get some acceleration followed by deceleration with throttle still wide open. The hotter the cylinder is (ie after hard 1st & 2nd) the worse it is in 3rd etc and I cannot hold her open in any gear for long without severe ‚roughness‘ - so high rev running is far from good (possibly verging on disasterous). Bloody crap I know - but I cannot tell the difference between too much and not enough fuel mix!
I checked the reed block for tightness yesterday, but will pull it and put it back together to make sure of no air leaks. Anywayy leaning the clip further/adding more air with the air-screw will tell me if downjetting is the way to go?
Any advice on airfilters? I’m waiting for a Malossi rubber ‚carb to frame‘ thing - no filter in it though - what else fits (without hitting the frame)?