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 1 
 on: Today at 04:53:02 PM 
Started by mtiberio - Last post by fordboy628
Good info thanks, just sharing what heard. Les and I have been friends since 1975 and his engines are legendary,  but longevity is not one of his strong points. I enjoyed this weekend and it would have be the right one to be running.

It would be very interesting to know what the customer's stated requirements in this instance were.  And how the engine builder planned to address those requirements.


I'm certain you gents know this, but it doesn't hurt to repeat it.    Very high specific outputs usually preclude "longevity", depending on what is meant by that ambiguous term.    Racing sanctioning bodies are now mandating longer "service intervals" for engines that compete in their series.

What happens from a practical standpoint is this:

A/   For professional, cost is no object racing, (you decide which series those might be, but F1 for certain), well, cost is no object, SO, unobtanium and tohellwithcostium get utilized.
      The expense rivals the total GNP of small third world nations . . . . . . .

2/   For professional racing where cost IS a consideration, compromises are made between cost and longevity/output.
      Serious engineers and "bean-counters" might negotiate with officials of sanctioning bodies about what sort of performance is desired Vs longevity.

d/   In amatuer sports, ie, where the competitor writes the checks, the size of the competitor's wallet determines what the level of performance achieved might be.
      This is, of course, the widest range of performance variation, based on the wide range of competitor's ability to "pay the freight".

I have been doing this for almost 50 years now, and I'm thankfully at the end of my run, soon to be "fly-fishing centric".   BUT, my memory remains sharp and focused, and I do not remember a time when competitive racing endeavors were cheap.   Competitiveness has ALWAYS been expensive, both in cost and longevity.

JMHO and 2˘,

 cheers
Fordboy

 2 
 on: Today at 03:00:19 PM 
Started by JimL - Last post by JimL
Thanks for the thoughts, fellows.  This little 250cc engine only uses about a 1" carb bore.  These are an undersquare engine with more stroke than bore.  They aren't built to rev much, but are pleasant to cruise around the back roads.

It is running very well, now, with about 7" of intake manifold length.  Now all I have to do is figure out why the turn signal circuit keeps flaming out....Chinese wire harnesses are pretty poor.  I have always said, if China were to send their Navy to attack the U.S., we will need a much larger Coast Guard to rescue the poor fellows when their ships all break down on the way over!

 3 
 on: Today at 02:58:04 PM 
Started by JimL - Last post by kiwi belly tank
Only 150 & 175 CD's, no 2 inch model. Early CD's adjust the needle from the bottom, later CD-2's adjust through the damper tube in the piston & require a special tool.
  Sid.

 4 
 on: Today at 01:32:04 PM 
Started by mtiberio - Last post by jimmy six
Good info thanks, just sharing what heard. Les and I have been friends since 1975 and his engines are legendary,  but longevity is not one of his strong points. I enjoyed this weekend and it would have be the right one to be running.

 5 
 on: Today at 12:04:50 PM 
Started by JimL - Last post by fordboy628
I think you'll find it's a pulse wave problem where the lead cylinder is killing the pulse to the trailing cylinder so there is no correct jetting using one carb with a mechanical jet control (cable slide). Give them a carb each or you might want to try an SU carb, they don't have a mechanical control on the jet & will respond to pulse fluctuations. Harley's respond well to a single SU for the same reason & they are a variable cfm carb so you really can't over carb them into a flat spot condition. CD Stromberg's work the same but nobody seems to use them.
  Sid.

Stromberg CDSE's can be found very cheap and they are easily and cheaply converted into std variable venturi carbs such as SU's.    175 CDSE's have a 1.75" throttle plate and are plentiful.    Not certain if there are 200CDSE's   (maybe Jag V12 ? ? ?)  but 2" SU's are out there on ebay and the like.

I've seen lots of older Harleys using single SU's.    Seems to work well.

 cheers
F/b

 6 
 on: Today at 11:54:30 AM 
Started by JimL - Last post by fordboy628
Nothing to do with LSR anymore, but some interesting stuff I just ran into.  I built a "pattern" copy of a 1938 Triumph Speedtwin, using a Chinese V-twin that came by way of a good friend.  I needed to move the carb from a "vertical downdraft" position between the cylinders, to a side mount position.  While trying to get an interesting look, I made up a manifold that tucked in tight and kept the carb out of my right knee.  There should be a pic attached of the bike.

Trying to get it jetted correctly turned into a nightmare.  After days of struggle, I reworked the manifold to accept an old Honda SL350K1 carb (very simple round slide, that always ran well).  It was giving me similar problems to the trouble with the flat slide Mikuni I started with.

To shorten the story...here is what I finally realized.  There were only two RPM ranges (above idle) where the engine would seem to run cleanly.  No matter which carb I tried, or what I did with the jetting, those narrow RPM ranges did not change.

Today I cut the manifold as short as possible and the bike runs well.  The key lesson here is the fixed RPM points that were useable, when everything else was ugly.  I hope this might help someone, someday.

JimL

P.S.  I built this (in this style and size) because I came across a 1938 Triump Speedtwin gas tank, and the 1935 BSA M2 forks.  It is kind of like building a car around that cool gas cap you find at the garage sale!

Jim,

Just to make sure I am getting this right, you made a forward facing inlet manifold "extension" to move the carb away from the "troublesome right knee location" that is standard on carbed V-twins?

Without some dimensions to confirm, it appears that you might have doubled the intake length, AND, added a 90 degree turn into the mix as well?


My own experience with projects that "extended" inlet manifold length is some what mixed.    I would distill it and comment that in situations of normally aspirated carb installations, the throttle response was very poor until high enough rpm was achieved to promote "reasonably high" gas flow speeds.   Often, these experiments proved "difficult" to drive, because of the throttle response issue.

On the other hand, supercharged applications fared better, but mostly they were full race, wide open throttle situations where low speed driveability was ignored.    For a street driven "pleasure vehicle" however, low speed throttle response can only be ignored at the displeasure of the end user . . . . . . .

Older, and presumably wiser, I now spend a bunch of time with simulation programs such as PipeMax (tm) and others before cutting parts.

JMHO & 2˘, hope you and others find some value in it.

 cheers
Mathhelpsalotboy

 7 
 on: Today at 10:55:43 AM 
Started by RichFox - Last post by RichFox
Gary Williams was a very large part of my early LSR endeavors. At the time we were in the SDRC And later ran a V8 Monza in Production and Gas coupe classes. Set the D/Pro record at El Mirage at one time. Passed away May 26 in Vermont. I have no other information.

 8 
 on: Today at 10:26:05 AM 
Started by JimL - Last post by kiwi belly tank
I think you'll find it's a pulse wave problem where the lead cylinder is killing the pulse to the trailing cylinder so there is no correct jetting using one carb with a mechanical jet control (cable slide). Give them a carb each or you might want to try an SU carb, they don't have a mechanical control on the jet & will respond to pulse fluctuations. Harley's respond well to a single SU for the same reason & they are a variable cfm carb so you really can't over carb them into a flat spot condition. CD Stromberg's work the same but nobody seems to use them.
  Sid.

 9 
 on: Today at 12:21:58 AM 
Started by JimL - Last post by JimL
Thanks Pete.  Regarding the new carb fit....No, but it is very close.  I have a different carb ordered that might fit a little tighter.  Truth is, with the hardtail rear and the friction damped girders in front, this thing is not comfortable to ride for very long.  I just built it to see what it would be like and for some hobby time in the shop.  It has moveable pegs/pedals and drop bars to set up as a vintage style café racer....now that it runs good I will switch it over to see how it feels.

You can build fun cheap stuff when you have a Chinese bike serial number, license plate, and title.  I recently bought a 2007 non-running Chinese scooter that will become a pattern copy of a three-wheel 1949 Mustang Delivercycle (flathead with a separate trans driving an Amazon sourced Peerless chain-driven rear diff).

My pattern copy of the 1915 Smith Motorwheel (on an Electra 7-speed Cruiser bicycle) is still what I ride the most.  It is easy, quiet, and pleasant in the neighborhood cruising at about 8-10 mph.  I may build a pattern copy of the 1910 Wall AutoWheel to see what it was like.  Oregon is very easy about these type bikes with no registration or insurance required (35cc or smaller and 15 mph max speed).

All those years building stuff for Bonneville leaves you with lots of tools, a good JD-squared tube bender, and enough experience to finish things.  Not a bad deal at my age.

 10 
 on: Today at 12:21:06 AM 
Started by JimL - Last post by Peter Jack
Jim, you definitely got the look right!  cheers cheers cheers

Pete

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