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Adam_Winstone wrote:Hmmmm, interesting...?
Well, my road tests have suggested that the progression becomes too rich too soon as I work up the progression stages / throttle positions. Tickover and takeoff can be set fairly easily with the pilot slide, slide and initial relationship of needle shaft diameter and fixed needle jet, however, I then find that it gets too rich too soon unless I start to restrict it by fitting a restrictive main jet (not a good idea!). Yes, i can delay this richness by dropping the needle (raising clip), however, it is coming onto the taper too quickly.
OK, I can increase the L1 distance so that it doesn't come onto the taper so quickly, however, this then puts me outside the range of needles that I commonly see others quoting. Also, I could reduce the taper angle (first identifying letter of the Polini/PWK/Keihin needles) but this too takes me away from the range of needles that others are quoting. Considering that the commonly quoted JJH, JJK, JJL needles all have the same 3 degree taper, which appears steep when compared to the Dellorto and Amal needles that I am accustomed to... and had me thinking...
Taking the Amal MKII carb first, as it is the simplest and has just one common 2-stroke needle (2D1), the needle shaft diameter / taper length / tip diameter gives a taper angle of 1.9 degrees. Considering that Amal used to pride themselves on the simplicity and ease of setup of this one needle design, you would think that the 1.9 degree angle should probably be a pretty good starting point for any 2-stroke carb that relies on needle + atomiser function. OK a big difference from the 3 degree JJK that is currently working best on my Polini / Keihin carb.
So, let's then look at the common X7, X13 and X2 needles. These work out as X7 = 2.0 degrees, X13 = 1.8 degrees and X2 = 1.7 degrees. Now for anyone who will have played with this range of needles, you'll know that this is not necessarily so much about the taper as it is about how long the taper is; how quickly it starts to richen up. All have the same 2.5mm shaft, the same 1.8mm tip but vary on the taper length 20, 22 and 24mm respectively.
So, where does this leave me? The too much too soon suggests that I should be looking at needles that do not come onto the taper so quickly (longer L1 - middle letter) and possibly a shallower taper (first letter - angle of taper). The shallower taper would be much more in keeping with the taper and progression speed of all of the other needle /carbs above.
Hmmmmmm, food for thought!
Adam
PS - I'll eventually get this dynoed, if I don't blow it up first (LOL).
Adam_Winstone wrote:coaster wrote:Its a long time since I played with PWK's but Im sure I usually had a problem with a boggy spot somewhere in the mid throttle range and was advised to try a JJQ which did make a huge difference. I could be wrong but I THINK I remeber it only differing from the JJH in the taper length. All my info is up in Norfolk and Im locked down in London so cant check for you Im afraid
... I'm not going anywhere in a hurry, thanks.
coaster wrote:I have a fairly extensive collection of needles and jets which I;d be happy to loan you if that might help, just post back when you are done. I might have another go with my pwk's at some stage but probably not this year
Pm me your address if you want then
Colin
Warkton Tornado No.1 wrote:I've just checked three atomisers that I have to hand. They all have just eight holes! You have a four stroke atomiser, I reckon. I would imagine the 18 holer is too
That'll be your problem. I don't have the information with me, but two stroke & four stroke atomisers vary, as do the float weights.
There was an on-line pdf of Dell'orto's tuning manual. The information contained will still be relevant
Adam_Winstone wrote:Warkton Tornado No.1 wrote:I've just checked three atomisers that I have to hand. They all have just eight holes! You have a four stroke atomiser, I reckon. I would imagine the 18 holer is too
That'll be your problem. I don't have the information with me, but two stroke & four stroke atomisers vary, as do the float weights.
There was an on-line pdf of Dell'orto's tuning manual. The information contained will still be relevant
Bugger, I just lost my long response... fat fingers and small phone!
Basically, from info I can find, all can be applied to 2-stroke use, with them being fitted as standard to their respective size carbs; the Polini site states 8-hole standard fitment for 24-30mm and 30-hole for 32 and 34mm bodies.
I'll be interested to try the 8-hole in my 34mm with the more commonly quoted needle range.
Cheers
Adam
Warkton Tornado No.1 wrote:Adam_Winstone wrote:Warkton Tornado No.1 wrote:I've just checked three atomisers that I have to hand. They all have just eight holes! You have a four stroke atomiser, I reckon. I would imagine the 18 holer is too
That'll be your problem. I don't have the information with me, but two stroke & four stroke atomisers vary, as do the float weights.
There was an on-line pdf of Dell'orto's tuning manual. The information contained will still be relevant
Bugger, I just lost my long response... fat fingers and small phone!
Basically, from info I can find, all can be applied to 2-stroke use, with them being fitted as standard to their respective size carbs; the Polini site states 8-hole standard fitment for 24-30mm and 30-hole for 32 and 34mm bodies.
I'll be interested to try the 8-hole in my 34mm with the more commonly quoted needle range.
Cheers
Adam
I've found the Dell'Orto comprehensive instructions that relate to all carburettor's, & like Polini, they say that an atomiser intended for four stroke can be made to function on a two stroke.
That's fine & dandy, but there is a distinction between the two types, so I can't imagine why anybody would like to try, apart from trying to prove something
I'm happy to lend you one of my atomisers (or needles etc) but I reckon you'll need to get one anyway
ULC Soulagent wrote:Very interesting topic going on here, I purchased two delly vhst 28 when I worked in the scooter trade( bought for peanuts) and even though they were apparently designed for the 4-stroke engine but using some of the phbl d- range needle set. I set about converting it over fully, Blue printed it and along with adding 2-stroke atomiser bush and all the internals of the phbl card range bar the floats which was two single self floating units.I initially got good results from the acceleration side and top end part sussed but when it came too cruising on the mid section setup,The carb had me baffled and after destroying my 4 top ends, 3 imola’s and a Ts1 I gave up and went back to a phbl with no issues since. I’m keen on these pwk & Oko copies from China and obviously they need work too make them right but I’m reluctant too get bit on the arse twice
Sorry if I’ve taken it off topic.
Regards
Shane
ULC Soulagent wrote:Very interesting topic going on here, I purchased two delly vhst 28 when I worked in the scooter trade( bought for peanuts) and even though they were apparently designed for the 4-stroke engine but using some of the phbl d- range needle set. I set about converting it over fully, Blue printed it and along with adding 2-stroke atomiser bush and all the internals of the phbl card range bar the floats which was two single self floating units.I initially got good results from the acceleration side and top end part sussed but when it came too cruising on the mid section setup,The carb had me baffled and after destroying my 4 top ends, 3 imola’s and a Ts1 I gave up and went back to a phbl with no issues since. I’m keen on these pwk & Oko copies from China and obviously they need work too make them right but I’m reluctant too get bit on the arse twice
Sorry if I’ve taken it off topic.
Regards
Shane
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