|
|
Post by 90GTVert on Jun 14, 2024 8:31:50 GMT -5
Yap crazy but I still think there's more than one problem For example you just mentioned the idle whants to hang usually that's a sign of being lean (pilot jet) Know this problem that small debris you still have some knocking. The PWK may just be different than all of the Dellorto carbs that I almost exclusively used on everything. With a Dell, if I can get a good idle mixture adjustment without the screw way in or out, then the pilot is usually good to go. With this, I've made sure the mix screw is in an acceptable range of turns out when it idles well, and it still hangs. If I richen up the idle mixture more than it likes, it may hang less but then it wants to flood if it idles and has to clear out. I really don't understand why everyone loves these PWKs so much... but it is showing potential to go quicker. If there were a 32-34mm VHST I think I'd try it. I do think it's possible that it's a little too aggressive with the timing on the MHR-ish curve... even though I modified it for a little less advance between the flat section and peak and everyone else gets away with it just fine without that. I am getting curious about the stinger size now. Someone on YouTube mentioned that maybe it's a little small with the extra mixture moving now with the bigger carb. I discounted the idea since it's literally the exhaust designed for this setup and what most people use, even with big carbs... but then most people don't need a 220 main jet only to still see basically 1300F EGT by 70MPH or less. I have the S6 exhaust. It's slower with that, but if the stinger is larger I may wind up trying it. That's supposed to be for their R/T 100cc, which they want you to use a 34mm carb with and makes more power, so if it gets just as hot with that then I think I could almost rule out stinger size. I do have the knock sensor and pigtail now, but the Lithuanian seller of the gauge was not in a hurry and just shipped it. |
|
|
|
Post by Lucass2T on Jun 14, 2024 15:17:18 GMT -5
|
|
|
|
Post by aeroxbud on Jun 14, 2024 15:57:22 GMT -5
It looks like they use the VHSH 30 CS on Lambretta and Vespa scooters too. So no reason it wouldn't work on a Malossi RC-one. Provided there is room.
|
|
|
|
Post by Lucass2T on Jun 14, 2024 16:57:28 GMT -5
|
|
sinfull
Scoot Enthusiast
Posts: 413
|
Post by sinfull on Jun 14, 2024 17:47:11 GMT -5
Agreed, time to go back to the tried and trusted VHST
|
|
|
|
Post by 90GTVert on Jun 15, 2024 6:11:27 GMT -5
It's funny how it seems like everyone likes a PWK. So many are used on both 2Ts and 4Ts... but then the VHST was said to be one of the most popular carbs for tuners and racers in Europe and the VHSH is popular in racing karts and Vespas. Agreed, time to go back to the tried and trusted VHST It's junk now. Ruined with corrosion. Depending how it goes, if I try something else, it would be after I figure out what's happening here. At some point I'll wave the white flag and surrender, but at this point I'm genuinely curious about what's happening. There are enough PWKs in the world that they can't all be junk or I'd think we'd hear more horror stories. I did get the engine apart the other day. Looks like the locator pin is still in there, but the tabs or whatever you call them on the ends of the ring are gone. The one on the left is an old ring, and how this used to look.  I assume it's got something to do with sanding the ring land. Maybe from sanding around the locator or maybe because it's practically impossible to sand the top of the ring land without sanding other parts. Maybe I made the depth greater and the ring tried to push in more against the pin and snapped those off? It didn't damage around the ring land as is common if the ends butted up. There's some new scuffing on the exhaust side of the piston and more evidence of detonation on the edges of the crown. It may be wise for me to either use the flat 16* curve or make a less aggressive curve. I could use more than 16* so it isn't breaking up and fouling out of the powerband. Maybe make it flat 16* all around the powerband instead of declining advance there. I don't think that's the issue, because there's not enough temperature difference in 16* flat and the MHR-ish curve that it solved the problem. Might just mitigate risk a bit for now. Thinking about the lean hang going back to idle and potential pilot/needle issues, I don't think that's the cure, at least not totally, because I'm still WOT and it's getting hotter and hotter. If it's basically 1300F by or before 70 and climbing, there's no way I could run it WOT to go too much faster without it failing. From the new scuffing, I was probably on the edge of that already. I'm throwing fuel at it, still 25-45 jet numbers above what appears to be typical and there's a lot of fuel above the main jet. It's showing up on the plug now, even to the extent that they look way rich and the 220 that still runs well looks to me like it's washing a bit. If the carb is putting fuel in there and it's not cooling, then why would another carb that flows a similar amount solve it? I guess velocity and mixture quality could come into play, but that gets complicated. For now, I'm going back to the idea that it could be exhaust related. I know my luck. Like when I had my turbo Mustang and I blew head gaskets repeatedly before eventually figuring out that one intake runner of a commonly used top brand unported intake flowed significantly different than all of the others. If there's some stupid error in 1 of a million parts, I'm just the guy to wind up with it. I don't think it's the issue, but it would take me 5 minutes to run a bore scope down the stinger and make sure I'm not the lucky millionth customer that got a big blob of weld blocking part of the stinger entry or something. I do have 2 AA pistons on the way. I searched and Malossi Store said low availability and coming from Luxembourg. I've never ordered there before and most non-English language European companies will not reply from past experience. I asked if the pistons were in stock anyway and they got back to me quickly. They said if it lets you put it in the shopping cart, then they have it. I asked Thursday night and they said they would process it by Monday and ship Wednesday so I ordered Friday morning. 2 pistons qualified for free shipping, so it was $207 total. 1 piston would have been about $150 due to international shipping cost so it made sense to get a spare. If it doesn't eat one, then hopefully I'll get to wear one out with mileage someday. |
|
tysta
Scoot Member
Posts: 79
|
Post by tysta on Jun 16, 2024 0:58:05 GMT -5
I don't think it's the exhaust I would not touch it!
Why people love pwk simple it's just one of the best carbs in the world and very easy to work with.
I keep telling you it's ignition related. I seen this problem sereval times during my 27 years as professional,
For some reason ( keep in mind iam not seeing the engine)
Your configuration is not working with that timing you should retard the ignition a decent amount and confirm readings once they 100% correct readings then tune the carb only after that you can start advancing the ignition.
Why I say that let's exclude you might have odd problem on your engine/carb
That ignition comes from Europe in Europe we have 95 98 and 100 oc fuel with very little content of ethanol
Also the octane are measured ( Ron + Mon / 2)
Our fuels in most countries in Europe will put any us fuel in a corner.
When I came to us I had to build my engines at work differently from what I used to!
So you could even just try your older ignition just 2 or 3 degrees retarded just to see your engine running.
Also confirm those coolant Temps if possible check in and out Temps just to ensure proper cylinder dilatation.
|
|
|
|
Post by 90GTVert on Jun 16, 2024 5:48:18 GMT -5
I don't think it's the exhaust I would not touch it! Why people love pwk simple it's just one of the best carbs in the world and very easy to work with. I keep telling you it's ignition related. I seen this problem sereval times during my 27 years as professional, For some reason ( keep in mind iam not seeing the engine) Your configuration is not working with that timing you should retard the ignition a decent amount and confirm readings once they 100% correct readings then tune the carb only after that you can start advancing the ignition. Why I say that let's exclude you might have odd problem on your engine/carb That ignition comes from Europe in Europe we have 95 98 and 100 oc fuel with very little content of ethanol Also the octane are measured ( Ron + Mon / 2) Our fuels in most countries in Europe will put any us fuel in a corner. When I came to us I had to build my engines at work differently from what I used to! So you could even just try your older ignition just 2 or 3 degrees retarded just to see your engine running. Also confirm those coolant Temps if possible check in and out Temps just to ensure proper cylinder dilatation. With the MVT that was on it, I had to advance it so I wasn't seeing 1300-1400 degree EGT. Current S6 ignition ran slightly cooler with 16 degree flat timing (about 20 degrees cooler EGT) than the MHR-ish curve. The MHR-ish curve that has advance at lower RPM should be 17* at 13,000RPM and falls to about 14* by 14,000, with 15.5* at 13,500 (roughly peak power). That happens to be the same range of timing that the MVT had when I saw EGT drop by advancing it, but the MVT had 45 degrees of advance out of the powerband... which seemed like a bad idea and is pretty much why I swapped since you can't change that much with any of the MVT curves (even if I had the EPROM). I don't want to argue with someone that has been there and tuned in Europe first hand, especially as a pro, but European octane ratings are typically RON vs our Anti-Knock Index (R+M)/2 so generally RON of 95-98 is said to be similar to our 91-93. I can get 94, which is basically equivalent to 100 RON rating, but I'd have to drive a good bit for 1 octane and overpay to boot. I can get ethanol free, but again overpaying and most sell it midgrade instead of premium locally for some reason and I don't really see the major benefit aside from when the scooter sits. I use 93 E10, pumped into a 5 gallon jug... usually 3-5 gallons at a time... so there's less contamination of lower octane since most pumps are single hose for 3 grades and many discussions have been had about how much fuel you get is actually whatever was previously selected vs what you choose. Plus, the two people that I've rode with using the MVT and MHR ignitions, both curves I've used now, are using premium pump gas (91-93 AKI) with the same engine and had no significant trouble dialing in their 34mm PWKs with smaller, more common, jetting. The one thing that does bug me is that I expect EGT to change with timing anyway, because you're moving more or less of the combustion heat into the pipe depending on advance. CHT really doesn't seem to reflect changes there much with the LC setup, especially the more effective ones (modular heads). I got wider, more useful, swings with AC engines monitoring CHT. Fancy stuff that you're more likely to see in a research lab would tell a more detailed story, but I don't think I'll be getting a research grant anytime soon. I have a wideband, but I can see the thick smoke rings and the bowl not running low, so I'd rather not put a bung in the exhaust and foul out my sensor. As far as the actual cylinder cooling, I can pull in from a ride and put my hand on the outer head or cylinder so it's definitely not way hot. Coolant temp reading (from the outer head) shows 120-140F mostly right now. Might start rising a little with it now getting into real summer heat, but not a lot. |
|
|
|
Post by 190mech on Jun 16, 2024 6:48:54 GMT -5
I think Wobbly has mentioned that EGT drops during detonation (too bad KiwiBiker search is inop). Ring ends can break due to being gapped too close or the ring getting super hot causing it to expand more. EGT readings (as well as CHT) are not instant so they should be read with caution..
|
|
|
|
Post by 90GTVert on Jun 16, 2024 14:30:28 GMT -5
I think Wobbly has mentioned that EGT drops during detonation (too bad KiwiBiker search is inop). Detonation or pre-ignition should cause more of the heat to happen earlier, so less heat should transfer to the EGT sensor in the pipe and more will transfer to the head. EGT is supposed to lower and CHT raise. Ring ends can break due to being gapped too close or the ring getting super hot causing it to expand more. Spec is 0.006". An 0.007" feeler fit when checked on assembly with the new ring, so that's as far as my checks went, but it exceeded spec anyway. |
|
|
|
Post by 190mech on Jun 16, 2024 18:53:04 GMT -5
Sounds like you have those bases covered..Another thought is the head to piston squish angle, if the head angle is less than the piston then there will be a greater space at the bore edge causing issues..Frits Overmars says the squish should be 1 percent of the stroke (on a quality build) and the combustion chamber determines the compression ratio.Just grasping at the weeds before we go over the waterfall here!!
|
|
|
|
Post by 90GTVert on Jun 16, 2024 19:06:51 GMT -5
I did try to look at the stinger with the bore scope. It’s too long to get more angles and too close to be in focus. Only thing I see is a little booger where the stinger is meeting the convergent cone.   It’s not ideal. Doesn’t seem huge. With me welding, I could pretty well guarantee if I cut it apart, ground it, then welded it back… I’d make it worse. |
|
tysta
Scoot Member
Posts: 79
|
Post by tysta on Jun 17, 2024 1:13:20 GMT -5
I don't think it's the exhaust I would not touch it! Why people love pwk simple it's just one of the best carbs in the world and very easy to work with. I keep telling you it's ignition related. I seen this problem sereval times during my 27 years as professional, For some reason ( keep in mind iam not seeing the engine) Your configuration is not working with that timing you should retard the ignition a decent amount and confirm readings once they 100% correct readings then tune the carb only after that you can start advancing the ignition. Why I say that let's exclude you might have odd problem on your engine/carb That ignition comes from Europe in Europe we have 95 98 and 100 oc fuel with very little content of ethanol Also the octane are measured ( Ron + Mon / 2) Our fuels in most countries in Europe will put any us fuel in a corner. When I came to us I had to build my engines at work differently from what I used to! So you could even just try your older ignition just 2 or 3 degrees retarded just to see your engine running. Also confirm those coolant Temps if possible check in and out Temps just to ensure proper cylinder dilatation. With the MVT that was on it, I had to advance it so I wasn't seeing 1300-1400 degree EGT. Current S6 ignition ran slightly cooler with 16 degree flat timing (about 20 degrees cooler EGT) than the MHR-ish curve. The MHR-ish curve that has advance at lower RPM should be 17* at 13,000RPM and falls to about 14* by 14,000, with 15.5* at 13,500 (roughly peak power). That happens to be the same range of timing that the MVT had when I saw EGT drop by advancing it, but the MVT had 45 degrees of advance out of the powerband... which seemed like a bad idea and is pretty much why I swapped since you can't change that much with any of the MVT curves (even if I had the EPROM). I don't want to argue with someone that has been there and tuned in Europe first hand, especially as a pro, but European octane ratings are typically RON vs our Anti-Knock Index (R+M)/2 so generally RON of 95-98 is said to be similar to our 91-93. I can get 94, which is basically equivalent to 100 RON rating, but I'd have to drive a good bit for 1 octane and overpay to boot. I can get ethanol free, but again overpaying and most sell it midgrade instead of premium locally for some reason and I don't really see the major benefit aside from when the scooter sits. I use 93 E10, pumped into a 5 gallon jug... usually 3-5 gallons at a time... so there's less contamination of lower octane since most pumps are single hose for 3 grades and many discussions have been had about how much fuel you get is actually whatever was previously selected vs what you choose. Plus, the two people that I've rode with using the MVT and MHR ignitions, both curves I've used now, are using premium pump gas (91-93 AKI) with the same engine and had no significant trouble dialing in their 34mm PWKs with smaller, more common, jetting. The one thing that does bug me is that I expect EGT to change with timing anyway, because you're moving more or less of the combustion heat into the pipe depending on advance. CHT really doesn't seem to reflect changes there much with the LC setup, especially the more effective ones (modular heads). I got wider, more useful, swings with AC engines monitoring CHT. Fancy stuff that you're more likely to see in a research lab would tell a more detailed story, but I don't think I'll be getting a research grant anytime soon. I have a wideband, but I can see the thick smoke rings and the bowl not running low, so I'd rather not put a bung in the exhaust and foul out my sensor. As far as the actual cylinder cooling, I can pull in from a ride and put my hand on the outer head or cylinder so it's definitely not way hot. Coolant temp reading (from the outer head) shows 120-140F mostly right now. Might start rising a little with it now getting into real summer heat, but not a lot. Well you shouldn't be able to hold you cylinder after riding your scoot since the coolant alone should be at least 50°c As far gasoline you can even use 81 if you like to just need to adjust compression ratio and squish. Again I don't know how you have your engine setup but for example you can have too much compression and the squish can be too low that will cause problems like the one you have right now. As I seen on those cases the intake it's awfully wrong with a stupid inclin foward leaving the carb way of. I would suggest to create a spacer to tilt the carb more Retad the ignition more and start tuning from there. If you can't make the spacer let me know I can help with that since I have a milling machine. |
|
|
|
Post by 90GTVert on Jun 17, 2024 5:57:11 GMT -5
Well you shouldn't be able to hold you cylinder after riding your scoot since the coolant alone should be at least 50°c As far gasoline you can even use 81 if you like to just need to adjust compression ratio and squish. Again I don't know how you have your engine setup but for example you can have too much compression and the squish can be too low that will cause problems like the one you have right now. As I seen on those cases the intake it's awfully wrong with a stupid inclin foward leaving the carb way of. I would suggest to create a spacer to tilt the carb more Retad the ignition more and start tuning from there. If you can't make the spacer let me know I can help with that since I have a milling machine. I don't know that I can always hold the cylinder, but I can touch it and it's not burning me. Maybe not the smartest to go grabbing stuff, but real world I think a lot of us have touched enough coolant hose, heads, etc... to have some idea if it's way off. From what attention I do pay to CHT, it doesn't look way off either. The abnormal heat appears to be in the exhaust. The head is not modified from original. Squish is essentially to spec. Was 0.54mm last time with 0.55-0.6 as Malossi's spec, but with the gaskets 0.54 was the best I could do. It was either that or go more above 0.6 (forget the exact other option now), but I'd rather be 0.01 tighter. 0.54 is 1.23%, 0.55 would be 1.25% and I'd have to go to 0.44 to be at 1%. 0.01 should be insignificant and I've used 0.55 and larger with the same results on past assemblies. I'm curious what the advantage is of a carb sitting upright if the fuel level is known to work. John has suggested putting another pipe in the intake to level the carb, but I thought it was to be sure fuel supply was correct. I guess the difference in gravity could have some effect on how fuel is drawn up, but if anything wouldn't the angle actually make it easier for fuel to get up into the intake path vs having to go straight up? No one should manufacturer tilted bowl carbs if the tilted carb throws everything off. Thanks. I've said it before I think, but for anyone offering ideas or suggestions please don't take my comments as arguing. I'm thinking along and hoping that maybe for all of the expense and effort I will learn along the way. I'd rather question anyone than follow blindly with no understanding of why it's supposed to work. As happy as I'd be if this thing stopped trying to eat pistons, I'd be a bit sad if it quit and I didn't have a good idea of why. I have another person with an interesting theory about flow that makes sense, but they are PM-ing me so I want to make sure it's OK if I quote them here before I post their thoughts. |
|
|
|
Post by Lucass2T on Jun 17, 2024 7:12:43 GMT -5
I'm curious what the advantage is of a carb sitting upright if the fuel level is known to work. John has suggested putting another pipe in the intake to level the carb, but I thought it was to be sure fuel supply was correct. The general consesus is to have an as short and straight as possible intake tract. Having the carb sitting fully upright (like with the all dirtbikes running PWK's as OEM) with a slightly longer intake as a compromise might be worth trying. Have you investegated how Malossi/Polini cup racing scooters are setup intake wise?   I remembered a video from not too long ago about rear placed turbo's the assumed lag because of long charge tubes. From the video lag looks negligible. Not sure to what extent this is also applicable in non boosted applications, but it might be interesting to take into consideration regardless. |
|
