9 replies to this topic

[bakker110]

I'm trying to work out which jets I need to put in my weber 40 dcoe.
I have no idea where to start and I'm not sure what is already in it.
All I know is that it isn't running right and I've narrowed it down to this as the carb came off a different car.
Hopefully someone will have an idea which ones I need.

It is on a 1293 engine for a start.
If you need to know any more about the engine spec please ask, as I am unaware of how much information you will need to make a guess.

I can take the carb apart and take the jets out if someone will be able to identify the jets already in it, should they have a marking etc or if they are obvious via the picture.

Hope you can help.

Thanks

[mini7boy]

Weber components all have their sizes marked upon them. These markings can be quite small and hard to read, so I use a small
loupe(one-eyed magnifying glass used by jewelers). They are available cheap at most camera shops. Make sure you have good lighting
when you try to read them. Reading glasses may help if you use them.

Once you have read the sizes, post here the sizes of: chokes, auxiliary venturies, main jets, air corrector jets, idle jets, accel. pump jets, exhaust bleed(#43 in diagram).
You also need to make sure that the float level is adjusted correctly and that the fuel pressure(regulated) is between roughly 2-3 psi.

If you are not sure of the name for some of the parts, either a good book or a website from a Weber retailer will identify them.
This page will identify most of the parts. http://www.pierceman...1_cal_parts.htm
The auxiliary venturi is the big part that has a little "bridge" that spans across on top of the choke. It is #17 on this exploded diagram
http://www.pierceman...40_DCOE_151.pdf

Here's a handy form to fill in. http://www.pierceman...com/jetting.pdf
Disregard the references to primary/secondary. DCOEs have only primaries, but they are not called by that name. Just use the primary slots on the form.

You also need to post here the specs of your engine: head ported or not, cam, compression ratio, ignition info,exhaust.

There are several good books available that cover Weber DCOE style carbs. You have a DCOEon your engine.

The book I like best is: http://www.amazon.co...o...6051&sr=1-2

This book is also available on Ebay. Just search on: Hammill Weber and you'll find lots of entries.

The nice thing about this book is that it really goes out of its way to provide very specific recommendations for A-series engines. He mentions the A-series specs for each Weber component
and in the back of the book has a section on the A-series where he lists the specs similar to those typically used in Mini Miglia.

It's a really excellent book and well worth the investment if you don't have much or any help from someone who really knows how to setup Webers on A-series engines.

The book by David Vizard, http://www.amazon.co...i...6320&sr=1-1

Also available on Ebay from many sources.

It has some pretty good information on Weber setup and it also has very detailed information on all other engine subjects. He has several tables listing Weber specs for various states of engine tune for both the 40 and 45 Weber DCOEs. These are a bit dated, however.

A really excellent source for Weber bits is: http://stores.shop.e...c0Q2em14?_pgn=1
His prices are better than most and he operates in a very professional manner.
I live in California and buy parts from him due to his price/service levels.

He has his own non-Ebay website which sometimes has prices slightly cheaper than on Ebay. http://www.fastroadc.../shop/index.php

Edited by mini7boy, 06 June 2009 - 11:29 AM.

[bakker110]

Thanks very much for the advice. I have stripped it down this morning and this is what I've come back with.

Pump jets - 45
Pump exhaust - 60
Mains - 145
Air Correctors - 175
Float Level - 12mm
Emulsion tubes - F16
Idle Jets - 50F2


Engine spec is:
1293
Piper HR255 cam (calver spec)
Electronic Ignition
10.5:1 CR
MG spec Head w/ light work
Maniflow 1.75 exhaust with reverse cone megaphone
Maniflow stage 2 LCB

Also on the carb is short trumpets and a swan neck manifold, and I have pipercross socks on it too.

The outline of the problem is:
slightly lumpy idle (possibly cam)
cuts out when pedal is fully depressed
needs easing up the rev range to get over backfiring flat spot
backfiring from idle to quarter throttle - running weak?

I didn't take the chokes out but there are no problems on tickover.

[mini7boy]

at a very simple level, the pump exhaust should be zero instead of 60.

this could easily explain your "cuts out when pedal is fully depressed" problem.

on a more subtle level, it's not a requirement, but most people use the F2 emulsion tubes and 50F9 idle jets. A 50F2 is leaner than a 50F9 and may also contribute to your cutting out problem.

You don't mention which chokes and auxiliary venturi sizes you use. Those would be helpful.

The 12mm float level is correct if you have the plastic floats.

It's important to try to only change one thing at a time so that its effects can be more easily determined.

I would try the zero pump exhaust first and see if it fixes the "cuts out" problem you report.

I wouldn't change anything else until trying the zero pump exhaust.

If this fixes your cutting out problem, you could leave it in and then test a 50F9 idle jet.

If you lumpy idle isn't due to the cam, I would try the 50F9 idle jets. These are a little richer than your 50F2s. Maybe you can borrow some for a test.

If you own or could borrow a pair of the F2 emulsion tubes, that might be worth an experiment, but only after you have tried these other things I recommend.
If your car runs well on the F16s, the money required for the F2 emulsion tubes probably isn't justified just to try them out. Better to borrow some if you don't have them.

Please report back any test results you achieve. Good luck !

[HARBER07]

Can i just ask a quick question - where is the pump exhaust (jet?) and how can i change it? I have the same cutting out problem but this is the first ive heard of a pump exhaust. Its not the bit at the bottom of the float chamber is it?

[WiredbyWilson]

The only jets I have ever had changed on my weber were the mains and the tubes - it is very difficult to get them running without putting them on an RR.

I have a 1330 running a Morpsedd PH3 cam and think I now have 145 mains, F2 tubes and but I "think" your air corrector may be wrong....

Will have a look at mine later if i can - but I can't see the pump jets being the problem, as I have always used the original ones in my carb.

Wilson

Weber exploded diagram - useful!!

Edited by Wilson1330, 07 June 2009 - 03:17 PM.

[bakker110]

Thanks for that.

I will try some of those options.

When I put the carb back on the car this afternoon it ran much sweeter than it had been doing. I think it may have something to do with the fact I haven't run the car on the road since I put the socks on it, but it may be something else.
Like I said I will try some other jets maybe next week to see if it runs a bit better.

Cheers

[bakker110]

Can i just ask a quick question - where is the pump exhaust (jet?) and how can i change it? I have the same cutting out problem but this is the first ive heard of a pump exhaust. Its not the bit at the bottom of the float chamber is it?

Yeah I think it is. Thats the one I took the marking off earlier.

[HARBER07]

Cheers for that - i blanked it off though as an experiment and it was a pig to drive.

[mini7boy]

the pump exhaust is in fact at the bottom of the fuel well. It is screwed into the bottom.

It is only one player in accelerator pump performance. Obviously the pump jet and exhaust play roles, but the pump stroke is also adjustable.

The entire accelerator circuit needs to be coordinated with the idle and main circuits.

You can't simply change one circuit without considering the others. They all work together.

Everything that I have heard/read from the experts says that A-series like a blank/zero pump exhaust.

The symptom reported "cuts out when pedal is fully depressed" sounds like an accelerator problem.

The 45 pump sounds reasonable, so a zero exhaust is worth trying.

I have only been responding to bakker110's postings.

I agree that a rolling road is the right way to get a Weber sorted, but given his strong bad symptom, I was just recommending a "try it and see" approach.

With Webers, there is not just one combination of parts that is the right one. There are different combinations of parts which will work.