| T O P I C R E V I E W |
| janmarine3 |
Posted - 18 Jul 2010 : 10:21:03
Hi guys, I have fitted twin webers to my Rapier's 1725cc engine .It is basically stock engine with 4 into 1 exhaust.I Need help tuning pse - can anybody give me all the specs for the jets and general setup to start with. At the moment it is spluttering and backfiring thru the carbs , and only revs above 2500 when the chokes are both open. I will clean them properly first but i have no idea what the specs should be.The carbs & manifold come off a Holbay engine.
Thanks beforehand guys.
Jannie |
| 10 L A T E S T R E P L I E S (Newest First) |
| djnippa |
Posted - 28 Aug 2014 : 18:10:06
Does anyone have a spare or know where I can get a set of Extended Auxilliary Venturi's for a Weber Carburettor 40 DCOE 90/91 or 34/35's
I've asked all the Weber guys and they have nothing.
One of my filters lids fell off, and I've lost one of the venturi's.
So I actually only need one.
They are the 104 mm aluminium tube that sticks out beyond the carb horn.
thanks
UPDATE
Even though they were expensive, I managed to find 5. So I now have an extra set of 4 for sale. If you need them please contact me. |
| janmarine3 |
Posted - 07 Aug 2010 : 06:28:43
Thank you . I have saved the info and will use it asap.
|
| 1922 |
Posted - 21 Jul 2010 : 19:26:42
Years ago I bought a set of K&N filters from Holbay. I think they came with new main jets and air jets but no emulsion tube. So you might be better off with the standard emulsion tube.
Heres a picture of the bit of the workshop manual that lists the standard settings - just in case it's any help.
Good luck with the tinkering |
| janmarine3 |
Posted - 20 Jul 2010 : 19:53:01
I will look up the book on the net - thanks.
I took the car for a spin again and it is still very rough, at idle around 1000 RPM, similar to a faulty plug or plugwire, and a stutter at low revs, and missing in the exhaust.The engine revs freely and quickly in the high ranges.It is actually an amazing fun vehicle for it's age.I have the 1725cc engine in and matching synchro box .I have not seen any Holbays in South Africa at all.
My friend's stock of jets is depleted and we could not tinker further, will do it soon though. |
| 1922 |
Posted - 20 Jul 2010 : 18:35:10
Excellent news. You might be able to increase the accelerator pump stroke to help with acceleration (or the jet, I forget which applies to a DCOE).
Try to get your hands on a copy of that book by John Passini - I think I found someone selling it on amazon. |
| janmarine3 |
Posted - 20 Jul 2010 : 10:48:31
Hi again.
I made use of the info you gave me , managed to scrounge some jets from a friend and changed the air jets to 200, main jets to 150 , also changed the emulsion tubes from F14 to F41, and 4 smaller air jets under the covers, not sure what they are called.
Plenty power and sexy noise, small stutter at lower revs - especially when accelerating, ( possibly because the aux venturis are not in )and stil a slight stutter when pulling the carbs open suddenly, but overall I am happy so far, will tinker some more and get it spot on.Thanks again. |
| janmarine3 |
Posted - 19 Jul 2010 : 06:31:04
I still have all the original extended venturis & much other stuff , 36DCD weber & manifold, twin Zeniths & manifold etc.
I will ask a friend who races a mini with sidies and will ask for help there too. Thanks for all the sensible info and advice so far, will let you know what transpires. At this stage I want to keep the cam standard, bucks are low.Just done the engine over too.Will look for the book you mentioned too. |
| 1922 |
Posted - 18 Jul 2010 : 20:23:26
If you are cutting bits off the wing I guess you must have a series car.
I have an excellent book 'Weber carburettors 2. Tuning & Maintenance' by John Passini.
I quote 'For the 40DCOE there are extended auxiliary venturis now available, the only engine fitting them as standard is the Sunbeam Rapier H120... anyone who at some time thought that chopping them short would be an advantage, had to buy new ones again.'
They are there to prevent low speed gasp by reducing the pulsing at low speed. I think you are going to have this trouble unless you replace them (hopefully you pulled them out and didn't cut them).
Definately too much air, the standard jets are for the carbs sucking through the factory air filter. You are going to need to increase the main jet size (probably several sizes) and maybe reduce the air jet size. I can't help you with the settings unfortunately as I have not tried it. You need a rolling road and a weber specialist - or a lucky guess. If it helps any, I think the same carbs were used on the early '70s 1750 Alfa Romeo.
Also if you are thinking of putting in a high lift cam maybe you should do this before you get the carbs rejetted - it might make a difference to the settings you need.
When properly set the DCOEs are great carbs, on a long cruise I got better fuel economy than on the twin Stromberg CDS. |
| janmarine3 |
Posted - 18 Jul 2010 : 18:33:42
Hi 1922 . I got the carbs with the aux extended venturis, ( no space & I had to cut out the left wing ) without air filters or airbox, but took them out & fitted those flat stainless screen filters over the four horns. Maybe that is the problem , too much air ? The carbs are also still at an angle to the inlet manifold, but some say it should still work like that. Carbs were leaking a bit and I adjusted the floats , ok now ?
|
| 1922 |
Posted - 18 Jul 2010 : 14:35:19
They are 3 different setups of emulsion tube, air jet and main jet listed. They all work.
The highlights are:
Main jet = 115, Air jet = 200.
Main jet = 100, Air jet = 140.
Float height 7.5mm. All have 30mm chokes. I've got all the other settings if you need them. The correct carbs have the small extended auxilliary venturi sticking out the main chokes.
I've heard it said that they don't work well with a standard cam but I can't remember if I ever tried.
They will splutter and spit back a lot if you try to run without an air filter - it really upsets the mixture. Did you get the air filter with the carbs? |
