Trouble jetting my Polini 177

[KTy]

Thank you Lucifer

I probably know why I had a mechanical defect... I had an air leak because of the rubber manifold, I couldn't find it and because of that I seized 3 times :haeh: Then you also have to know that the cylinder was overbored in its last size... Heat, mechanical stress and thin skirt should explain the broke :wasntme:

As for my experimentations, I put the 130 main and at the same time I put an AV264. It was too rich from 1/3 to 3/4 of throttle.

Then I put back my X2 needle clip to the top position, it was much better, but still "4T-ing" from 1/3 to 1/2 of the throttle.

So, I put back the CF262 (=AV262 (?!)), I put the needle clip to the 2nd position from top, and I will tell you tomorrow !

What I am affraid of is that the Leo pipe delivers a "weak" signal at low RPM, so I adjusted the jetting to have a smooth city-ride (low and lower-mid-RPM), but because of that, I may run too lean at "upper-mid-RPM" without knowing it... What do you think ?

I am still running 17-18° of timing advance.

Actually, I don't want to gain revs, I want torque ! Not that easy with the Leo pipe, but that's probably one of the few that can be mounted on an 8" scooter without touching (driving solo).

Is there any tweak that one can do to this pipe in order to gain torque and loose some power at high-rpm ??

[KTy]

So, with 130, X2, CF262, needle clip 2nd position from top and 55 idle jet, it is almost perfect, it is "4T-ing" only at a very narrow RPM range, something aorund 1/3 of throttle. But before it's ok, and after it is also ok... It is just anoying while city-driving at low-rpm. I know this would disapear if I put the needle clip on the top position...

Should I play with another needle size ? or with a different round-slide cutaway (40) ?

How to make sure I am not running too lean in the upper-mid-rpm ? (paranoid !!)

Does reading an EGT sensor at all RPM would help a lot ??

Bearbeitet 28. September 2006 von KTy

[Lucifer]

at wich position is your air/mixture screw?

Maybe there's a chance to lean your low-speed jet, often a 50 or 52 will do perfect, and take the AV264 again, or elevate the needle one more step, i guess you schould try these jettings too! Even if the don't work fine, you get essential information....

But, again, no one can adjust your carb from far away... ;)

To check lean mixture at mid range, pull the choke (flat out at constant speed) and, on the other hand, close the sprit-supply for a short while (the sprit level lowers drasticlly in the float bowl and leans the mixture quickly),..., it's just the same as with the SI-carb...

I don't beleive in EGTs, it's just a nice parameter on a motortestcenter at exact conditions! Keep in mind, you never know, at which kind of EGT-reading your piston will size! Even if you have sized sometimes at a special driving-condition, you won't have any knowledge on all the other conditions....;)

[KTy]

Yesterday, I adjusted the *mixture* screw, it is about 1 turn. Now it is fine, it is "4T-ing" only from time to time in very specific load and throttle condition. Because I don't have reed-valve and because I think the Leo pipe is not a very homogenous exhaust, I will keep this setup as a "working one".

I will try what you said: AV264 + 50 idle jet + playing with the needle clip.

And Btw, I have the feeling that the clutch is slipping at high-rpm under maximum acceleration... (new standard PX125 clutch)... :wasntme:

[ric_two]

Yesterday, I adjusted the *mixture* screw, it is about 1 turn. Now it is fine, it is "4T-ing" only from time to time in very specific load and throttle condition. Because I don't have reed-valve and because I think the Leo pipe is not a very homogenous exhaust, I will keep this setup as a "working one".

I will try what you said: AV264 + 50 idle jet + playing with the needle clip.

And Btw, I have the feeling that the clutch is slipping at high-rpm under maximum acceleration... (new standard PX125 clutch)... :wasntme:

...then you have to change the clutch springs :wasntme: simply get DR or malossi ones......

[Lucifer]

Fix your clutch before you will get into real trouble..., the 125er won't work, it's far too weak!

I would change for a Cosa with PX200 primary transmission - it's perfect for the usual 177er - probably with stronger springs.

When you are 1 turn out with the 55 idlejet, a 52 should work well, a 50 together wih a higher needle position maybe too.

Try the choke-test etc. before you change jetting,....

The aim is to get as much information on the behaviour of your kit, under different conditions. The more careful you do these tests and write down your findings, the more reliable your engine will be afterwards.

[ric_two]

Fix your clutch before you will get into real trouble..., the 125er won't work, it's far too weak!

I would change for a Cosa with PX200 primary transmission - it's perfect for the usual 177er - probably with stronger springs.

When you are 1 turn out with the 55 idlejet, a 52 should work well, a 50 together wih a higher needle position maybe too.

Try the choke-test etc. before you change jetting,....

The aim is to get as much information on the behaviour of your kit, under different conditions. The more careful you do these tests and write down your findings, the more reliable your engine will be afterwards.

sorry, i think that kty's 177er wasn't built for high rpm's? I use nearly the same setup, with an original 125er T.S. Clutch plus DR springs and it works fine enough for an slightly modified Polini......

[KTy]

The safe way would be to change the clutch, it is true :D

Back on the "method",

Lucifer wrote

To check lean mixture at mid range, pull the choke (flat out at constant speed) and, on the other hand, close the sprit-supply for a short while (the sprit level lowers drasticlly in the float bowl and leans the mixture quickly),..., it's just the same as with the SI-carb...

So, what is the bottom line of this technik ? What should be expected ? If the engine behave "better" it means that I was running too rich, rigth ?

[Brosi]

So, what is the bottom line of this technik ? What should be expected ? If the engine behave "better" it means that I was running too rich, rigth ?

The other way round. The choke does enrich the mixture. So if it runs better you were running to lean...

[Lucifer]

the small-block Clutch isn't able to transfer the power for long, a tuned Polini will send t the rearwheel....

Usually the basket brakes after a short while..

And: especially fpr "low-rpm" tunings the 200er primary is perfekt! Too high reving engines often get problems in 4th gear...

Jetting: both methods are fairly "rough", of course! As you pull the choke the mixture enriches drastically (lesser with big carbs), depending on the revs and slide-position at this certain trial-point! If the engine splutters emediately, your settings may be ok! If the bike gains speed, your (far) too lean at this point! Even if nothing happens, you are too lean!

Check from the opposite side: leaning out the mixture makes the engine sound very "light" together with a markable loss in power - but be careful! If nothing happens or you gain speed, your setting is probably too rich at this point!

My advice would be to do these tests on a slighly rising and straight road away from traffic.

Another test is to make accelerartions out of sertain speeds, in different gears,...

Perfect jetting makes your motor picking up very quickly, always responding, andalso coming down quickly (but not abrupt) to idlespeed, when the slide is closed! Does it take longer, or does not come down to idle revs - especially whem the engine is hot - your primary setting is too weak! Some spluttering at low speed ist normal for any tuned bike, especially when cold. If a (quickly) heated up engine splutters anywhere, it's too rich. Nevertheless I personally prefer a slightly rich idle, due to often very low temperatures, precipitous and steep hills,...

[KTy]

I tried the choke test at mid-rpm and instantly the engine "splutter".

Two more hints:

* I ran in the highway for a short time, the engine spluttered just before reaching maximum RPM. This is caused by the 130 mainjet, but I may keep it for safety...

* While accelerating (throttle between 70% and 100%), if I go back to 30% of throttle while the engine is in its upper-mid-rpm range :grins:, then the engine splutter again. This time I think it is because of both my idle jet and my main jet being too big.

[KTy]

Ok... I was rigth to be a little paranoid...

I was still driving with the following setup on a PHBH28, main 130, needle X2, needle clip 2nd from top, atomiser CF262 (=AV262 ? See here), idle 55 and 40 cutaway. Adjusted Polini 177, 18° timing and Leovince exhaust. A little rich at low speed, seems okay at full throttle, hard to tell in between.

I also mounted a KOSO II rev-counter that is also a nice temperature gauge.

I went on a highway (limited to 90km/h) for the first time since I finished my running in. I was gently following cars, the throttle opened between 50% and 70%, keeping an eye on the temperature. After 30s on the highway at constant speed, I knew something was wrong because the temperature was increasing dramatically. I kept driving for 1 or 2 more minutes, temperature raised up to ~130°C, I even had the feeling that I was hearing some knocking... I was psychologically resigned to seize .... And I almost did !! The engine died, I manage to engage the clutch immediately, I waited about 10s freewheeling, then I re-engaged the clutch, the engine started and I parked. When I started the engine, the gauge was reporting 145°C, I cooled down the engine with some fast ON-OFF throttling, down to ~90°C.

Just a note about the temperature reading: I almost sure it is at least 20°C *below* the real cylinder head temperature, it is because of the sensor I am using. I have another temperature sensor, a thermocouple one this time, I will try to measure with it later.

So, I get back home with no problem; indeed I could keep the engine below ~100°C with either 0-30% throttle and 70-100% throttle driving.

Then I changed the atomiser for an AV264 and I put the needle clip on the 3rd position from top... Impossible to drive, 4Ting all the time, except at 70% of throttle :)

So I put back the needle clip to the 2nd position from top, and I am driving with that since then.

What I can say is that the engine is smooth in acceleration, but it usually rattles at "constant speed" between 30% and 60% of throttle. I went again on the high-way in the same environmental conditions , and followed cars at 90km/h like the other day, throttle opened between 50% and 70%. This time I was 4Ting a little bit from time to time, but the temperature was kept down around ~80-90°C.

So here is my question: How is that normal that switching from a CF262 to AV264 atomiser makes me change from "engine ready to seize running at mid-rpm" to "engine almost constantly 4T at mid-rpm" ... ??? Please, explain to me !!

Newt move is to lower the idle jet to 52 and/or to find another needle more appropriate !

Thank you for your help

[KTy]

hum...kay

I have put the needle clip at the top, engine is still 4Ting around 25-30% of throttle, that's annoying.

I will have to see if it's too lean at mid-RPM ...

Knowing that with CF262, X2 needle and needle clip 2nd from top it was perfect except too lean between 30% to 70%, what can I change ? Smaller (30 ?) throttle Cuttaway ? A magical needle ?

[KTy]