32mm Polini PWK Carburetor experiment

  • Just bit the bullet and ordered a Polini 32mm reworked PWK Carburetor, comes standard with a 122 main and a 42 pilot, also ordered some Polini Jets sizes 42-52 pilot and 140-158 main, I'm unsure on needle sizes and types as I've never really messed with this before so haven't ordered any of them.
    Am I best to throw the biggest main and pilot jet in and see how it runs then plug chop from there? I've ordered 5 BR8ES plugs to mess with as well.
    Hopefully gonna keep the standard airbox and completely cut the lid out.

  • No, start with the air screw, pilot jet and work your way up.

    You can actually remove the main jet whilst you're dialing in your jetting. Since main jet only operates at 3/4 or WOT.

    I posted a guide on here about jetting.

  • @Calum cool I'll check out the post, just mainly wondering if it's safe to start out on the standard settings or jump onto the highest ones I have, will be getting the jetting about right on current engine before rebuilding with new piston etc, so not too worried about seizing but don't wanna damage the bottom end if poss.

  • @Glynn123 Detonation is an engine killer and occurs under load. It won't be a problem whilst you're just getting it setup. I.E. ticking over on the drive won't cause a problem. It'll obviously won't run right.

    Fueling becomes a problem as heat is increased. Heat increases under load. That's where pre-ignition will occur.

  • @Calum ah right so it's safe to plug chop under little loads for example small stretches of road once engines up to temperature, aslong as the baseline for the pilot jet is found from an idle plug chop. Another little thing, will the oil pump still be safe to use or should I turn it up/premix? Would prefer to keep it honestly.

  • @Glynn123 Plug chop is different.

    When jetting the carburetor, the plug chop is used as an indicator of how the main jet, and/or power jet, is operating.

    This is the last thing you will need to jet since alterations to other components may affect the main jet. So the first thing you want to do is get all the other pieces of the puzzle working nicely. Then before applying load to the engine you will need to make sure the engine doesn't break up or bog. Once you're happy it's running right up to 3/4 throttle and small instances of full throttle don't cause any problems, then worry about the plug chop.

  • Got the carburetor on nicely yesterday, with heat the airbox went on well, cheers Calum!
    Cutout the lid of my airbox completely and fitted a new air filter, it was butchered anyways.
    Upon first start the caburetor was obviously way lean, would only run on choke and it sounded crackely, so swiftly shut it off and fitted one of the mid range pilots I had and removed the main jet, as to your guide Calum.
    Bike ran nice, could adjust the pilot circuit nice and it seemed to have a sweet spot with the screw fairly far out. Bike would splutter badly when going full throttle, obviously due to the main jet being removed, but up to 3/4 seemed to rev nice so didn't touch the needle yet. Fitted the 142 main jet out of my kit, which was alot bigger than standard, think the second size up from my kit, bike ran nicely up to temperature on the spot, revved fairly clean but has a bog when pulling throttle wide open from idle, I know this is likely the main jet being lean but I didn't want to change it until I have the needle and pilot correct.
    Went for a 5 mile run into town for some petrol, bike splutters and ran crackely up to about quarter throttle when riding the bike at a constant rpm, seemed to smooth out past that, so I'm guessing pilot is still lean?
    However it also had similar symptoms while accelerating until higher rpms, once onto the main and the ypvs opened the bike went awesome, bags of power and sounded very crisp, however i didn't ring it out too much. Temperatures are staying good while riding.
    I'm thinking tomorrow I will raise the needle a notch and swap out to the next size up pilot jet and try another test ride, I've got the next couple days off work to play about with this, and this carb is brilliant to work on.

  • @Glynn123 Post a pic of her fitted dude. 😉

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    Apologies for the state of the bike, I've not had the best of conditions or time the past few days I've been off work for testing.
    I raised the needle one notch this morning, which seemed to help a lot with the throttle response, no bog when going from idle to wot
    I also tried a step leaner pilot and main jet, upon riding around my drive it seemed to of made no difference to the spluttering issue I was having, so I then went up two sizes of pilot jet to see if it prefered the richer pilot, after about 50m up the road I went back home and swiftly removed it, spluttering worse than ever and barely wanting to run anything less than high rpms with wot
    I then fitted the standard size pilot the bike came with, which is the smallest pilot jet I have and went for a ride. The bikes going allot better and seems fairly happy through most of the rpm, top end seems great and it's idling/cold starting nice. However I still have the spluttering issue under load, I've narrowed it down to roughly 1/8th throttle to about half throttle bad splutter, I'm guessing this is the crossover from the pilot to the needle jet? I'm unsure where to go from here, should I try lean off the needle again now I have a smaller pilot than before? The bike is practically unrideable through town behind cars doing 20-30mph, have to keep whipping the clutch in as it's spluttering so bad.

  • @Glynn123 She looks cool, defo no leaks anywhere like a nicked pipe for example???

  • @NINJA not as far as I'm aware, no power jet on this carb and no leaks from any breathers, float height is good, both brass nossles either side of slide are breathers as far as I'm aware? I've just got the pipes open

  • @Glynn123 More tuning required then, is the PV opening correctly, as that may be a hindrance and what's that big silver round thing on the right???

  • @NINJA pv is on the same settings it used to run on, cleaned and setup it all about a 1000 miles ago roughly so shouldn't be that.
    Silver things a plug for the emmisions bottle that usually goes in the airbox

  • @Glynn123 Would putting the bottle back on not be worth a shot? As that may be affecting the mixture ratio, I know my bike ran better with the bottle on rather than with it removed. 😉

  • Looks like your missing a bolt from the crank cases near inlet though.

  • @NINJA possible but I don't see a blanked out airbox causing issues, just a smooth run through a new filter.

    Yeah that top bolt is missing, its been like that since the previous owner rebuilt it, I've got a bolt kit on order which hasn't arrived yet but I'm certain it doesn't leak, tried spraying isopropyl on it while revving etc in past

  • @Glynn123 OK as you've increased the airflow with the larger carb, then I would look at the other 2 elements aka fuel and spark. If there is sufficient fuel reaching the carb & barrel with no blockages, then perhaps a different plug may help? What's your current plug like and have you performed a plug chop since you installed the carb? Maybe doing that will give you some clues in which direction you need to go???

  • @NINJA I'll try a different plug and maybe go for a regular 15 minute run with varied rpm tomorrow to get a baseline, hadn't tried a new plug yet but bought a set of four BR8ES to play around with, I'm thinking of dropping the needle again to test but its a ballache with the split cables etc haha

  • @Glynn123 I'd look at your plug first before changing any of the jets etc. As the colour of your plug will indicate which direction you need to go in. Maybe even try a colder grade plug or an Iridium one and see what occurs with those???

  • @NINJA been running it on an iridium for a while now, bought the standards just for plug chopping