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anybody ever tried this?

Started by Gil Gallad, November 04, 2019, 02:57:46 PM

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Striker1423

Snow machine is like the culturally proper term. But Michiganders call them sleds, sleighs, and snowmobiles. If you say snow machine here you sound snobby lol.

Gil Gallad

problems, problems  :bang: ok, this is what i've got: home made reed cage [pictured elsewhere] with rd350 lc reeds in it, cheapo ones, but hey ho. i got the engine running using these reeds, so i decided to change the petals for 0.5mm thick carbon fibre petals. my problem is, now the engine won't even fire, as though no fuel is getting through. anybody with more experience of reeds [which is probably half the known world] think these petals are too thick? should i try 0.4mm or even 0.3mm? basically i'm at a loss with this one  ;D
cheers, gil.

Striker1423

Quote from: Gil Gallad on August 16, 2020, 04:57:01 PM
problems, problems  :bang: ok, this is what i've got: home made reed cage [pictured elsewhere] with rd350 lc reeds in it, cheapo ones, but hey ho. i got the engine running using these reeds, so i decided to change the petals for 0.5mm thick carbon fibre petals. my problem is, now the engine won't even fire, as though no fuel is getting through. anybody with more experience of reeds [which is probably half the known world] think these petals are too thick? should i try 0.4mm or even 0.3mm? basically i'm at a loss with this one  ;D
cheers, gil.

Mmm. Insufficient vacuum could be a culprit, but that negative pressure has to translate somewhere.. so a reed not opening could be an issue. However, I would think you have an issue of a reed not sealing. No seal means no pressure building in the lower end to send fuel where it needs to be.

Gil Gallad

hi mate, thanks for the reply. when i fitted the petals it was a bright, sunny day [rarity in england, i know] and i held the reed cages up to the sunlight, checking for any gaps. there definitely weren't any. lack of vacuum is a thought though. newly rebuilt crank - new seals etc. rebored barrels and new piston kits, so should have decent vacuum. perhaps a t250/gt250 hybrid engine just isn't supposed to have reeds fitted? the thing is though, with the cheap chinese petals in it ran fine, but they were thinner  ;D
cheers, gil.

sav0r

I don't know, Gil. It seems like you suspect the reeds, so why not change back to the first set? It should be a pretty quick and easy test to perform.

Otherwise, make sure you are getting air, fuel, and spark.
www.chrislivengood.net - for my projects and musings.

Jspooner

Quote from: sav0r on August 17, 2020, 09:44:19 AM
I don't know, Gil. It seems like you suspect the reeds, so why not change back to the first set? It should be a pretty quick and easy test to perform.

Otherwise, make sure you are getting air, fuel, and spark.

^^^^^^^this^^^^^^
"Just quit brain fucking it and get it done"

Gil Gallad

i did exactly that and got an even stranger phenomenon  :umm: can't remember if i've posted this before, but until i've built the headers for this engine i've just been using a pair of standard gt250 exhausts. so, i rebuilt the reeds, carbs on etc, and left the exhausts off. she went first kick and revved real nice - albeit a bit loud. i fitted the exhausts and kicked and kicked - nothing, wouldn't even pop. thinking i might have fouled the plugs i swapped them for a new pair. kicked and kicked - even less, no pop, no bang, no nothing. so i took the exhausts off again. kicked her over and she went first kick. i know the exhausts are clear, so i can't blame them. so the question is wtf do i blame?  ;D
cheers, gil.
p.s. thanks for the suggestions, btw.

quocle603

Gil is killing it!

Love the boost bottle you made! Measurements of the cooper pipes you used?



Do not underestimate the power of a two-stroke.

1975 Yamaha RD350 (modified), 1973 Yamaha RD350 (stock), 1971 Suzuki T500, 1981 Yamaha XS650 HS2, 1982 Honda MB5, 1980 Puch Maxi, 1979 Puch Magnum, 1993 Tomos Bullet, 2003 Malaguti Firefox F15 LC

teazer

Quote from: Gil Gallad on August 18, 2020, 06:40:07 AM
i did exactly that and got an even stranger phenomenon  :umm: can't remember if i've posted this before, but until i've built the headers for this engine i've just been using a pair of standard gt250 exhausts. so, i rebuilt the reeds, carbs on etc, and left the exhausts off. she went first kick and revved real nice - albeit a bit loud. i fitted the exhausts and kicked and kicked - nothing, wouldn't even pop. thinking i might have fouled the plugs i swapped them for a new pair. kicked and kicked - even less, no pop, no bang, no nothing. so i took the exhausts off again. kicked her over and she went first kick. i know the exhausts are clear, so i can't blame them. so the question is wtf do i blame?  ;D
cheers, gil.
p.s. thanks for the suggestions, btw.

A couple of thoughts.  Carbon fiber reeds are much stiffer than fiberglass and are great for high RPM motors, but are harder to crack open. I forget what reed boxes you are using but a large intake volume will make it harder to start too.

With the pipes, that's interesting and may be a function of back pressure.  There's not much useful information on the pressure in an exhaust - outside of pressure wave effects, but all exhausts run with an average pressure.  Small stingers increase that pressure slightly and stock exhausts tend to be higher because of the sound dampening measures inside.

I'd speculate that the combination of high (relatively) exhaust pressure plus stiff reeds are working to keep the reeds basically shut.  Try removing teh baffle tubes and see how that works and try softer reeds until you get some decent chanbers that send a nice negative pressure wave back to drop cylinder and crankcase pressure sufficiently.


Gil Gallad

thanks for the advice teazer, much appreciated. looks like i'd better get the headers made up pretty damned quick, then i might get somewhere  :haw:
quocle, i don't know if this boost bottle works properly yet, only running the engine will prove one way or the other, but dimensions of copper pipe are: the top bit is 28mm pipe x 180mm long with 2 blanking caps on it. the legs are 15mm pipe x 45mm. plus i hope you're good at soldering  ;D
cheers, gil.

Gil Gallad

all in all and from what i've read and researched, the figures i could do with as a base setting are standard ramair gt250 inlet, transfer and exhaust durations in degrees. then the same for the x7, which was virtually the same engine but had reed valves fitted. or even throw in a set of figures for the rg250, in essence  again the same engine, but water cooled. all similar engines, but with a vast difference in power, and none of them used pistons with windows in them. i'm either looking in the wrong place or these figures don't exist, because i'm buggered if i can find them  ;D
cheers, gil.
p.s. sorry i don't know the designation of the x7250 or the rg250 over the pond  :umm:

teazer

Neither was available in the US.  Perhaps Canadians got them but I doubt it.

IIRC, RG250 had piston port intakes but supplemented by a small crankcase reed.  They were not the same as say and RD250/350 design.  In some ways they were ahead of the curve with crankcase reeds.  Fortunately it was easy to open up RG250 reed passages and that really seemed to improve them. 

I don't remember the port layout but they had boost ports IIRC.  TR500 Mk111 was also piston ported with cast in boost ports.  Very interesting design  as I recall.

Our RG250 was way faster than our stock(ish) RD400 but that may have been more to do with infinitely better handling and brakes.


Gil Gallad

having a lot of problems with this sob. i rebuilt it back to how i had it originally. ignition timing stayed the same, and the only thing i changed was the pilot jets, as i didn't think it was getting enough fuel at start up. now the only things it does are kick back and afterfire. there's fuel getting through, there's good sparks [using b6es while it's on the bench. i've tried it with b8es plugs and it's just the same. kickback and/or afterfire. any suggestions? i'd be most grateful  ;D
cheers, gil.
p.s. pilot jets went up from #25 to #30

teazer

kicking back is usually a sign of too much advance or really lean mixture, but usually advance. 

Try checking it with a degree wheel and spark plug tester or plug wire 10mm from the motor and see if it's firing when you think it should be.

Did you go back to the softer/thinner reed petals or is this with the same carbon fiber reeds?

quocle603

I had the same issue with my RD when I kicked it over and it was too advanced.
Do not underestimate the power of a two-stroke.

1975 Yamaha RD350 (modified), 1973 Yamaha RD350 (stock), 1971 Suzuki T500, 1981 Yamaha XS650 HS2, 1982 Honda MB5, 1980 Puch Maxi, 1979 Puch Magnum, 1993 Tomos Bullet, 2003 Malaguti Firefox F15 LC