Why am I not revving out higher? Puch e50

Why am I not revving out higher? Shooting for 13k+ rpm and looking for ideas.

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Right now I'm hitting 11k, maybe 11.5 based off of gearing calculator. Setup is Athena ajh copy with split exhaust port ported wide, decked 3mm and with correct piston to correct squish and keep the ring out of the exhaust at BDC. Boyesen dual stage reeds and 24mm oko carb. The spark plug threads shot out of the airsal head pictured, right now I'm running a 70 low comp head with single base gasket. HPI mini rotor, initially set to 1.8mm btdc but I've played around with the stator a bunch and not sure what it currently sits at, launches well and stays cool tho. Kamikaze pipe. 18x56 gearing.

I know my port timings are fairly aggressive. To port map, I set the piston to bdc and taped in some graph paper, crayola crayons are terrible for this lol. Probably not super precise but a good idea of what it's at. Port durations are 196 exhaust, 132 transfers for a blowdown of 32. So the ports are definitely in the pretty aggressive range, enough according to some sources that my low end would suffer. It launches pretty hard tho, but that's mostly due to clutch I bet, not sure what rpm I'm engaging at but it's up there.

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Pipe hits pretty hard but I'm hitting the rev wall, and I feel like there should be more. Pretty sure gearing isn't holding me back. Retarding timing didn't result in any more rpms, just made launch shittier. Pipe *should* wind out pretty far based on what I've read about it, but I have a simonini I might try. Can lowering compression result in increased rpms? I have a head gasket and a few different thickness base spacers to play with. Any other thoughts?

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Piston clears all the ports it's supposed to at bdc. It's actually an Athena small reed piston, modified with gas ports, oiler holes for exhaust bridge and intake skirt cut for 360 intake timing. I tried using the Teflon reed kit piston from treats but the ring pin was too close to the ports, between the exhaust and main transfer. The ring pin on this piston rides between the intake booster port and the secondary transfers. (edited)

Why am I not revving out higher? Puch e50

I had the cylinder decked 3mm to correct the height issue this cylinder comes with. I'm using a 70cc low comp head, piston clears and goes up far enough in the cylinder where it's supposed to. Given the port timings should have me revving out, I'm betting adding in a head gasket might help.

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If I retard the ignition more than where it is, it becomes a dog getting out of the hole and the clutch to engage. But I could try raising the engagement of the clutch in combination with retarding, it's lightened enough where Im not super far in on the screws for the kickstart springs and I could engage a fair amount higher if needed. It still has a bushing clutch bell, if anyone has a source on reverse cut or kickstart bells so I can get a needle bearing pressed in that would be rad. also have a simonini pipe to try, though I expect that to perform similar to the kamikaze, if a bit milder perhaps. Probs gonna try head gasket, then simonini, then raising clutch engagement combined with spark retard.

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Forgive me if I repeated myself, I copied the majority of this from a post somewhere else. Thanks!

Any other ideas to try?

Re: Why am I not revving out higher? Puch e50

Probably Fred /

Two stage reeds can be limiting you, I'm surprised they haven't broken yet actually

Re: Why am I not revving out higher? Puch e50

Hmm that's a good thought. This looks a lot like the reed block I have, rubber lined where the reeds sit.

https://www.treatland.tv/honda-MB5-carbon-reed-block-p/mb5-reed-block-carbon-reed.htm

I don't have the carbon ones it came with tho so I can't try those. But I do think I have some 0.4mm carbon fiber polini reed paper somewhere, I could cut some up...

Re: Why am I not revving out higher? Puch e50

I think you need might need to cut the header and/or drop gearing a bit if you want that real high shit. 13k is up there, how long is the pipe?

Re: Why am I not revving out higher? Puch e50

Matt Mahloch -- MBM Customs /

I have a couple thoughts on this

- are you sure your intake, transfers and reed block are big enough/matched to flow what the 24mm carb can? I think the reeds pretty much just stay open at that high of rpm so not sure the material/stage would effect anything so long as they open enough.

- it's been my experience with high blowdown that a pipe like the bk100 revs higher than a Simonini style that I feel is better with less blow down. Might try a pipe like that if you can get your hands on one.

- I don't think lowering compression will help rev.

- I'd also try adding timing since that HPI pulls so much out of it.

^thats by no means religion but stuff I'd do if it was my own bike.

Re: Why am I not revving out higher? Puch e50

simo def rips harder with less blowdown. i was hitting over 13k on a mildly ported metra kit. 13x42 gearing clocked at 52 with a radar gun down the straight at the grange. too bad the rest of that bike was a pile of shit.

Re: Why am I not revving out higher? Puch e50

"HPI mini rotor, initially set to 1.8mm btdc but I've played around with the stator a bunch and not sure what it currently sits at, launches well and stays cool tho."

"- I'd also try adding timing since that HPI pulls so much out of it."

this is what i was thinking. 1.8 could be pulling you back to like 13, 14 degrees at high rpm.

also i have no idea what 196 exhaust timing is like, that is just off the charts high. I've never ported anything past 185, even then i find going past 180 to be extremely tempermental to tune. You're barely trapping anything at that point, you would have to have your pipe design super dead on.

Re: Why am I not revving out higher? Puch e50

that blowdown is 24% which is pretty fucking ridiculous. I would raise transfers a little- you want to be closer to 18-20% for that exhaust duration. (edited)

Re: Why am I not revving out higher? Puch e50

Blew up a clutch & bell, this one might be on hold for a little bit til I can source some of the euro cut bells. I wanna send them off to get lightened with needle bearing too. Might save up and try an HK, or mill down the face of a KTM clutch so I can keep my kickstart pawl.

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Definitely gonna take this time and do some more research on exhaust design, and figure out what would work better for a pipe.

I'd need to get a 90* attachment or flexshaft for the Dremel to raise those transfers without spacing the whole thing up, which is something I've been wanting to get anyway...

Quick n dirty pipe measurement puts me at roughly 24" from center line of header to beginning of stinger, 31" with stinger included. Header is ~30mm and starts to taper out pretty much immediately after the curve. Belly is a bit under 4" at fattest point. I'm not gonna hack this pipe up, I'll tryn find something less exotic for that.

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I'm pretty sure I'm a fair bit more advanced than 1.8mm, I was flirting with 380 at full blast uphill. For the exhaust and blowdown numbers as high as they are, it was still a rocket off the line, though I bet that was mostly due to clutch and gearing.

Re: Why am I not revving out higher? Puch e50

what are you trying to do?

why 18x56?

you are fucked with that type of blowdown. go tomar of have a bad time unless you weigh like 110lbs.

i've touched 12k with a homoet 6p awhile ago pretty easily with extremely similar timing. no real power under 9k and a hard time getting from 0-40 when you are trying to make 55mph out of 12k. save this project for a pistonport derbi with a start 5 rear clutch.

Re: Why am I not revving out higher? Puch e50

Cool clutch fail, looks like the bent post scored the bell before it gave up. Else why should the bell bust, right?

Also a little confused on that gearing, what's the point of going big to big?

My first thought was pipe. Second is timing. Also compression doesn't help rpm but I don't think that's your limit.

Try stuff and test! Adjust and test! Timing and reeds and jets are all easy to compare same day same runs, one change at a time. Try the pipe too and check how it does with same set of timing options etc

Re: Why am I not revving out higher? Puch e50

timothy rendall /

are those honda wheels you're using ?

Re: Why am I not revving out higher? Puch e50

The 18x56 sprockets put me at a similar ratio to 15x45, but it gives me the option of going down to a way shorter ratio without having to switch the rear. Also I think the giant rear sprocket looks sickkk.

I'm betting the pipe might be the factor holding me back, I wanna try something with a little more header. I needa do more research on pipes, I just assumed a high revving pipe would pair well with high port timings but there's something more to be revealed there.

The wheels are from a Peugeot 103.

Re: Why am I not revving out higher? Puch e50

What the actual fuck is with the Glamour Shots photos in this thread? It's like lens flare from a 70's porno in here...

Off hand 196 degree exhaust port timing seems a bit out of range. Doesn't that put the power band at about 10-12K???

Re: Why am I not revving out higher? Puch e50

Matt Mahloch -- MBM Customs /

That port timing is fine. That's close to what I run on my 77mph Puch Gila. I've ran as high as 212* on my 67mph Puch Metra 65, it would turn 14,100.

From one of the 2 stroke books intake should be 10-15% larger than carb and be 35% of bore. I'd make sure you're pulling in enough air.

What angle are your transfers pointing? They should progress from flat with the piston, so 12* ish to around 45* on that top shooter. That top transfer is so wide I might divide it into 3rds or arch a shape in it so not all the flow is at 45*. This might be getting picky but will ultimately lead to moving more air.

I might even throw a circuit pipe on there if you have one. It's not all about that blowdown number but look at how much area you have open on the exhaust all the way to where the port closes. You'll have to have a pipe that hits super hard to cram that charge back in there.

Not sure what others run for temps on that kit but 380* is pretty cool for trying to make big power/high rpm. That makes me think more timing is needed or less fuel. Show a picture of a cut spark plug if you have one.

Re: Why am I not revving out higher? Puch e50

What is your gearing ratio!? It looks ridiculous for a high rpm set up

Re: Why am I not revving out higher? Puch e50

Matt, I really appreciate your input as someone who has experience pulling this kind of stuff.

The intake manifold is same as Athena ajh, pretty big where intake mates with cylinder.

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I opened up the intake and added a mild top transfer, I got this idea from looking at my polini. I didn't run it before doing this to compare tho :/

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So I'm pretty sure my intake area is enough to flow a 24mm.

I don't know forsure what my transfer roof angles are, but from looking at them it seemed like the mains were fairly flat, while there was a fairly steep angle on the top side booster port. From what I remember it was kinda hard to see into the secondary transfers to see what that angle looked like. I haven't modified those tho, so it should be same as stock ajh.

My ring gap rides between the booster and secondaries so like what do you mean when you say divide it into thirds? Just changing the angle inside the booster that already exists and making it ramp between different angles inside? or carving some new ones next to that main booster with a flatter angle.

I donated my trash proma to a raffle bike :/ but bk100s on the list to get after I get a new bell and clutch figured out.

I never did like the procedural plug chop with the fresh plug, kill it at top rpm thing. Besides I was using the choke to kill it. But the plugs would come out looking pretty good, like coffee with some cream lol.

Rocco, gearing is 18*56, equivalent to between 14*45 and 15*45. So not ridiculous insane, but forsure to get the revs up hopefully.

Re: Why am I not revving out higher? Puch e50

just posting to tell you I love the korado seat

Re: Why am I not revving out higher? Puch e50

> jordan * Wrote:

> -------------------------------------------------------

> Matt, I really appreciate your input as someone who has experience

> pulling this kind of stuff.

>

> The intake manifold is same as Athena ajh, pretty big where intake mates

> with cylinder.

>

>

> I opened up the intake and added a mild top transfer, I got this idea

> from looking at my polini. I didn't run it before doing this to compare

> tho :/

>

> So I'm pretty sure my intake area is enough to flow a 24mm.

>

> I don't know forsure what my transfer roof angles are, but from looking

> at them it seemed like the mains were fairly flat, while there was a

> fairly steep angle on the top side booster port. From what I remember it

> was kinda hard to see into the secondary transfers to see what that

> angle looked like. I haven't modified those tho, so it should be same as

> stock ajh.

> My ring gap rides between the booster and secondaries so like what do

> you mean when you say divide it into thirds? Just changing the angle

> inside the booster that already exists and making it ramp between

> different angles inside? or carving some new ones next to that main

> booster with a flatter angle.

>

> I donated my trash proma to a raffle bike :/ but bk100s on the list to

> get after I get a new bell and clutch figured out.

>

> I never did like the procedural plug chop with the fresh plug, kill it

> at top rpm thing. Besides I was using the choke to kill it. But the

> plugs would come out looking pretty good, like coffee with some cream

> lol.

>

> Rocco, gearing is 18*56, equivalent to between 14*45 and 15*45. So not

> ridiculous insane, but forsure to get the revs up hopefully.

I'm really confused, this bike is going to be pulling ridiculous gearing (48mph @ 13,000 Rpms) why? When you could be hitting high 50s and pulling weight out of your rotational mass.

Re: Why am I not revving out higher? Puch e50

Matt Mahloch -- MBM Customs /

For the top most auxiliary transfer that already exsists I was thinking if the roof angle is 12* or whatever you could then blend from the edges to the center increasing the angle but then I’m thinking that might make for some weird flow pattern, probably better to stick with one angle the more I think about it. Maybe 30* and aim the top side transfers at the intake and set at a 45*. If you put the cylinder in the sink and run water through the transfers you can see how they’ll flow pretty good. That’s my flow bench. The intake does look big enough but the reeds seem small. It having them in front of me I do t know. But you could do the math easy enough.

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