Tuning twin 45DCOE's ?
Discussion
Hi Nev,
If you've got the figures for setting them cold do that - it's what I used to do because it seemed less hassle than messing round with a hot engine. No burnt fingers!
Definitely best getting carbs set up on rolling road if you can to make sure jetting is right. You can always do some intial setting up using the old trick with a length of small hose, sticking one end in your ear and the other in each carb inlet in turn and then adjusting them so they all sound the same.
Haynes used to do a manual on tuning Webers which might be useful if you can still get it.
If you've got the figures for setting them cold do that - it's what I used to do because it seemed less hassle than messing round with a hot engine. No burnt fingers!
Definitely best getting carbs set up on rolling road if you can to make sure jetting is right. You can always do some intial setting up using the old trick with a length of small hose, sticking one end in your ear and the other in each carb inlet in turn and then adjusting them so they all sound the same.
Haynes used to do a manual on tuning Webers which might be useful if you can still get it.
Yeah, I want to get it rolling roaded, but (like many things) it's time and money.
As a temporary measure I just wanted to set the air flow up properly, as I notice it's out .... I've got a proper synchometer and that shows values varying between 3 and 5.5 (whatever it measures in .... cfm ?)
I've figured out how I can change the balance between the two carbs, but anywone know how I can change the balance between the two chokes on the SAME carb ? (45DCOE)
Cheers !
As a temporary measure I just wanted to set the air flow up properly, as I notice it's out .... I've got a proper synchometer and that shows values varying between 3 and 5.5 (whatever it measures in .... cfm ?)
I've figured out how I can change the balance between the two carbs, but anywone know how I can change the balance between the two chokes on the SAME carb ? (45DCOE)
Cheers !
Hi Nev,
There shouldn't be any great difference between the two chokes on the same carb - well not unless you have a twisted throttle spindle (Leadfoot strikes again!). The only seperate adjustment you can make betwen the two chokes is with the idle mixture screws near the mounting flanges which do allow for some fine tuning between the two chokes.
If you do have a big difference between them, suggest taking carb off and checking that both butterflies close together. If not, you have a twisted spindle.
Actually, with a Seven type car you might manage to check with the carb in situ by taking out the auxiliary and main venturis and shining a small torch down the chokes.
Another possiblity for rough running could be a blockage somewhere in the carb or a leak between the carb and manifold - the latter of which could make a chuffing sound and could also account for a difference in measured flow at the inlet. You could try running some thick oil (gearbox etc) between carb and manifold and seeing if that makes a difference. If there is a small leak the oil will temporarily seal it.
There shouldn't be any great difference between the two chokes on the same carb - well not unless you have a twisted throttle spindle (Leadfoot strikes again!). The only seperate adjustment you can make betwen the two chokes is with the idle mixture screws near the mounting flanges which do allow for some fine tuning between the two chokes.
If you do have a big difference between them, suggest taking carb off and checking that both butterflies close together. If not, you have a twisted spindle.
Actually, with a Seven type car you might manage to check with the carb in situ by taking out the auxiliary and main venturis and shining a small torch down the chokes.
Another possiblity for rough running could be a blockage somewhere in the carb or a leak between the carb and manifold - the latter of which could make a chuffing sound and could also account for a difference in measured flow at the inlet. You could try running some thick oil (gearbox etc) between carb and manifold and seeing if that makes a difference. If there is a small leak the oil will temporarily seal it.
Managed to find some info about DCOEs on the web, including :
www.cruzers.com/~twakeman/TR/WeberDCOEinfo.htm
Apparently later DCOEs can be altered for flow between individual chokes (a couple of screws on each carb, under a small white cap).
So last night I spent 20 minutes playing with my syncrometer and a screwdriver, and I managed to get the four chokes from 3.0 / 3.0 / 4.0 / 5.5 to a nice steady 4.0 / 4.0 / 4.0 / 4.0 and I had to alter the idle mixture on one choke slightly.
Idling is better, with less "pure body rock" and the number one choke now doesn't spit back occasionally at idle
This will do now, until I can afford a proper rolling road session.
Thanks for all the feedback everyone
www.cruzers.com/~twakeman/TR/WeberDCOEinfo.htm
Apparently later DCOEs can be altered for flow between individual chokes (a couple of screws on each carb, under a small white cap).
So last night I spent 20 minutes playing with my syncrometer and a screwdriver, and I managed to get the four chokes from 3.0 / 3.0 / 4.0 / 5.5 to a nice steady 4.0 / 4.0 / 4.0 / 4.0 and I had to alter the idle mixture on one choke slightly.
Idling is better, with less "pure body rock" and the number one choke now doesn't spit back occasionally at idle
This will do now, until I can afford a proper rolling road session. Thanks for all the feedback everyone
Really ? I've got the original spec sheet / build sheet from Connaught, and that says to set both exhaust and inlet gaps to 0.014" hot.
Mind you, I've got to figure how to get the alloy rocker cover off, dunno what size allen bolt are on, but they dont appear to be either metric OR imperial ?!? (5mm is nearest, but that's slightly too large)
Mind you, I've got to figure how to get the alloy rocker cover off, dunno what size allen bolt are on, but they dont appear to be either metric OR imperial ?!? (5mm is nearest, but that's slightly too large)
Where are you? we have a rolling road in Berkshire www.rollingroadtune.co.uk we would be pleased to help you.
john
john
Hi Nev,
The Haynes manual is called "Weber Carburettors" ISBN number 1 85010 061 6 - excellent diagrams and pictures.
Also if you're into Crossflows then
"Rebuilding and Tuning Ford's Crossflow Engine" by Peter and Valerie Wallage is worth having ISBN 1-85010-938-9 £14.99 when I bought it.
Have Fun
The Haynes manual is called "Weber Carburettors" ISBN number 1 85010 061 6 - excellent diagrams and pictures.
Also if you're into Crossflows then
"Rebuilding and Tuning Ford's Crossflow Engine" by Peter and Valerie Wallage is worth having ISBN 1-85010-938-9 £14.99 when I bought it.
Have Fun
quote:
Really ? I've got the original spec sheet / build sheet from Connaught, and that says to set both exhaust and inlet gaps to 0.014" hot.
Mind you, I've got to figure how to get the alloy rocker cover off, dunno what size allen bolt are on, but they dont appear to be either metric OR imperial ?!? (5mm is nearest, but that's slightly too large)
FWIW, Ratrace always set mine hot.
The rocker cover allens are bloody infuriating. In the end, I've used a screw driver that just fits in the diameter of the hexagon!!!
quote:
Rocker cover bolts? From memory they're 1/4" UNC but it's been some time since I ran a X-Flow so might be wrong. Certainly not metric unless somebody's been messing around a lot.
Took mine off yesterday, couldn't find an allen key the right size untill I found my american set and the 1/4" one fitted, thanks I never knew what they were called, UNC, I'll remember that! They arent metric for certain, and i'm not sure if there is an imperial equivalent!
Apparently yes, American inches are suppossedly longer - though that could just be typical Yank bragging.
The 1/4 inch actually refers to the diameter of the thread, with UNC standing for Unified Coarse as opposed to UNF which stands for Unified Fine. Both very standard in pre-metric days so it shouldn't be a problem finding allen key to fit.
Having said that, seem to remember getting some fasteners which had non-standard head sizes so maybe you've got similar problem.
The 1/4 inch actually refers to the diameter of the thread, with UNC standing for Unified Coarse as opposed to UNF which stands for Unified Fine. Both very standard in pre-metric days so it shouldn't be a problem finding allen key to fit.
Having said that, seem to remember getting some fasteners which had non-standard head sizes so maybe you've got similar problem.
If you are suffering poor running and suffering problems balancing the carbs, it would be would worth checking the Thackeray washers between the carbs and the mounting studs which are often overlooked. The carbs are designed to allow slight movement on these washers, on occassions a rubber washer at probably twice the cost does the trick, normally available from most specialist suppliers. Try Southern Carbs, I think they are still in the Wimbledon area SW19
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