• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

Need some weber DCOE guidance

spock345 said:
I was able to scrounge up some 130 mains, 180 air correctors, 32mm chokes and a range of idle jets. Currently I have 50F9, 55F9, 55F8, and 60F8 idle jets.

So far it idles fine but I noticed something odd, it runs about 15-20 degrees cooler than with the SUs at idle. Any reason why this would be?
Click to expand...
Could be idling quite rich. Do you have a wideband?
 
Isn't the idle mixture pretty much not based on the idle jets, only on the idle adjusters?

Idle jets are misnamed on DCOE's I think. They're midrange.

Throttle closed almost all the way - pulls through the idle circuit, as metered by the adjuster screws, technically supplied by the idle jets.
Mid range- pulls through the progression holes via vacuum generated by the partly closed throttle valve, fed by the idle jets.
As the throttle opens more, they fade out and the mains kick in via vacuum generated in the venturi and fed by the main jets.
 
I had a wideband on mine when initially setting up. Lol, they do lots of funny things. Rich spikes over bumps. Richer turning hard right, leaner turning hard left (might be due to the way they're tilted when installed on a Volvo).
 
spock345 said:
I was able to scrounge up some 130 mains, 180 air correctors, 32mm chokes and a range of idle jets. Currently I have 50F9, 55F9, 55F8, and 60F8 idle jets.

So far it idles fine but I noticed something odd, it runs about 15-20 degrees cooler than with the SUs at idle. Any reason why this would be?
Click to expand...
Assuming the ignition timing hasn't changed, a richer fuel mix will often run cooler than a lean mix. I think the idle jets you have listed are all going to be on the rich side for what this engine needs - I'd start with the 55F8 (leanest), but I think it's still going to be on the rich side. For street use, I haven't found a use for 60 idles other than 2.5/2.6 liter strokers. I'm also not the smartest DCOE person out there, so take this with a grain of salt.

For comparison - we're using 55f8 on a local engine - B20+.060," 10:1, custom made tuned header, 293 degree cam, 2.5" ID exhaust and 45s with 36mm chokes. This engine should need more fuel than the one you're working with. Yours will run and drive with the 55f8 but don't be surprised if it's on the rich side - that's better than running lean, and it's probably ok while you sort out the rest of the jetting. I think you'll want to make further adjustments to the idle circuit before long.

Once you get it sorted to the point that it's drivable in regular traffic, I think you'll really like the DCOEs.

Cam
Portland
 
Well, I tried with some 50F9 jets I had lying around but could not get it to idle right, then I noticed the cold start device on the front carb leaking. So that would cause issues.
 
Are they closing all the way? Those cold start devices are basically really simple idle circuits that are tuned really rich.
 
The DCOE choke mechanism can be damaged by a backfire through the intake such that it will leak whether open or closed. Seems unlikely on relatively new carbs, so maybe it's easily corrected. Hopefully.

Once damaged and unable to seal, vacuum in the intake pulls fuel past the cold start bits. You might be able to get the engine to rev ok, and you might be able to get it to idle ok, but it'll go full rich at steady throttle cruise.

Cam
Portland
 
volvorelix said:
The DCOE choke mechanism can be damaged by a backfire through the intake such that it will leak whether open or closed. Seems unlikely on relatively new carbs, so maybe it's easily corrected. Hopefully.

Once damaged and unable to seal, vacuum in the intake pulls fuel past the cold start bits. You might be able to get the engine to rev ok, and you might be able to get it to idle ok, but it'll go full rich at steady throttle cruise.

Cam
Portland
Click to expand...
Any way to repair it after a back fire? I assume there is a rubber seal somewhere in there.
 
Lots of these engines suffer lots of lean pops through the intake, so it's not one of those 'if this ever happens, that will always follow' things. Could be that there's something preventing the valve(s) from closing fully (spring retainer popped out, spring broken, crud holding it open); or the machined surface that provides the seal might not be machined quite right. It's not a rubber seal that's compromised - it's a machined brass/aluminum interface.

Given that the engine they were on before was relatively tame and the jetting that these carbs came with AND that it would only run with the choke active, it seems likely that the carbs have had more, and possibly more significant, pops through the intake than they ought.

Have a look here, and you'll see what's involved in 'fully disabling' the cold start provision. You might be able to staunch the bleeding with a good cleaning, or stronger springs over the plungers, or spacers or some other thing. I've seen some weird approaches to this (grub screws in the exit, which is in the throat just downstream of the throttle plate - kept fuel out of the stream but didn't prevent leaks to the outside world), solder blobs plugging the supply holes in the bottom of the bowls, stuff like that. I'd see if I couldn't get it corrected without modification first.

Oops: the link: https://www.carbparts.eu/books/cold_start_elimination_kit.pdf

You'll get there. Might go crazy along the way, but that's part of the fun.

Cam
Portland
 
volvorelix said:
Lots of these engines suffer lots of lean pops through the intake, so it's not one of those 'if this ever happens, that will always follow' things. Could be that there's something preventing the valve(s) from closing fully (spring retainer popped out, spring broken, crud holding it open); or the machined surface that provides the seal might not be machined quite right. It's not a rubber seal that's compromised - it's a machined brass/aluminum interface.

Given that the engine they were on before was relatively tame and the jetting that these carbs came with AND that it would only run with the choke active, it seems likely that the carbs have had more, and possibly more significant, pops through the intake than they ought.

Have a look here, and you'll see what's involved in 'fully disabling' the cold start provision. You might be able to staunch the bleeding with a good cleaning, or stronger springs over the plungers, or spacers or some other thing. I've seen some weird approaches to this (grub screws in the exit, which is in the throat just downstream of the throttle plate - kept fuel out of the stream but didn't prevent leaks to the outside world), solder blobs plugging the supply holes in the bottom of the bowls, stuff like that. I'd see if I couldn't get it corrected without modification first.

Oops: the link: https://www.carbparts.eu/books/cold_start_elimination_kit.pdf

You'll get there. Might go crazy along the way, but that's part of the fun.

Cam
Portland
Click to expand...
Well, I'll take it apart and report back. Hopefully it is just a gasket or something.
 
volvorelix said:
Hopefully. There aren't any gaskets nor seals in there, but maybe it's an easy fix.

Cam
Portland
Click to expand...
Well, I think I found the issue. It was leaking from the screen at the bottom of the outer cover of the cold start device down. Not sure where to go from there. The screws holding the little cover for the accelerator pump/throttle shaft connection were also very loose.
 
The screen on the outside cover of the cold start device is nothing more than a port for air intake filtration when the cold start valves are open. I would suspect that the pistons behind the cover are jammed open or not fully seating. I fought this issue initially on my DCOEs when I first had them due to poor machining tolerances so when there was a backfire through the intake they would jam open as the return springs were not strong enough to recover and reseat them. I ended up eliminating them all together as I live in a very mild year round climate. I used the method by which you basically are locking the pistons in place. There is a danger in this method though that I've been warned about... if you have a substantially harsh intake backfire you can end up tweaking the the throttle plates ever so slightly as the choke mechanism is also the built safety valve for intake backfires, so keep this in mind. A better method might be to just use a much heavier spring to keep them in place if not needed for functionality.
 
When I got my 40's the cold start gizmos were really, really stuck in place. I managed to free one of them up, but broke the other after lots of soaking and patience. But replacement parts were easy and (relatively) cheap, so it wasn't a problem.
 
There are also versions of the DCOE that don't have the cold start devices at all. That was the type we used on the AH Sprite race car. We ended up going back to SU carbs because the Weber didn't like all the vibration. We had to safety wire the jet cover and I forget what else.
 
Even with anti vibration mounts I've lost venturi grub screws, float bowl cover screws, and jet cover screws. If you don't safety wire everything you have to constantly check for missing hardware. These engines produce some seriously vibrations and harmonics, especially older worn out ones that have lost any resemblance of balance over the years. I've had valve covers rattle loose as well as other items bolted to the engine.
 
You must log in or register to reply here.
Back
Top