Author Topic: Weber carb set-up (Read 151884 times)

Tintop · « **Reply #425 on:** December 22, 2013, 06:34:57 PM »

You won't be going from 40mm (1 9/16) down, your actual size will be determined by the chokes you use. 1 3/16 is just over 30mm, and you likely be using 30 or 32 chokes so there is actually little or no difference. The key will be in port matching the manifold at both ends. Check back in this thread for photos of the RC manifold, it appears to offer the best transition, and uses the stock boots. If I remember correctly scotty is running 30 chokes with an 836.

BPellerine · « **Reply #426 on:** December 22, 2013, 06:53:41 PM »

check with 754 for dimensions he uses webers and is a machinist as well.your carbs are 28s?I have 38s and they are the smallest that I know of.bill sorry I just noticed they were 40s

754 · « **Reply #427 on:** December 22, 2013, 06:57:14 PM »

I have been talking to him, he means 28mm venturis. Anyone got a clear pic of an MPD. Splayed manifold to show Slick?

scottly · « **Reply #428 on:** December 22, 2013, 07:41:21 PM »

Reply # 24 on the first page of this thread shows my MPD manifold. The carb side is 40mm ID to match the Weber bore, and the ID tapers down to the same ID as the spigots, like a velocity stack.

slikwilli420 · « **Reply #429 on:** December 22, 2013, 08:18:57 PM »

The carbs are labeled 40DCOE28 on the name plate and after looking them over they have 32mm venturis.

Tintop · « **Reply #430 on:** December 23, 2013, 05:16:50 AM »

Just a red X(s) scottly, no pics on pg 1, post 24.

scottly · « **Reply #431 on:** December 23, 2013, 08:28:48 PM »

The pics still work for me, Brian?
Willi, the suffix of 28 refers to an OEM setup. Mine are DCOE2, which were used on Alfa Romeros. I'm not at home now, so I don't have my reference book at hand.

Tintop · « **Reply #432 on:** December 24, 2013, 06:26:01 AM »

The 40DCOE28 according to my listings was original equipment on the Alfa 1300 GT Junior (1290cc), and used 28 stock chokes. 40DCOE2's were used on the Lotus 7 (1500 xflow), Abarth 1000, and Alfa 1600 Giulia & 1300 Sprint Veloce. Interestingly the 40DCOE2 was also the aftermaket carb for the Cortina 1500, Datsun 610, bunch of Toyotas, Opel Kadet, & Triumph TR6 & GT6.

Checked pg 1 again scottly, still just seeing a red 'X'. If I click on the 1st X I can get that to open, but not the rest.

BPellerine · « **Reply #433 on:** December 24, 2013, 09:27:07 AM »

post worked for me as well .bill

Tintop · « **Reply #434 on:** December 24, 2013, 11:10:25 AM »

I can get them to open if I click on the link & then 'open', weird.

slikwilli420 · « **Reply #435 on:** January 15, 2014, 03:51:28 PM »

So I'm getting ready to set up my webers and wanted to get an idea of baseline jetting. Scottly posted some jetting info back around post #110 but I'm not sure if it's for a stock 750. The bike will be stock for now until I get my either 836 or 915 motor built. Any jetting info would be a big help.

Tintop · « **Reply #436 on:** January 15, 2014, 07:10:10 PM »

scottly's jetting was for an 836, but the idle, emulsion tube, and accel part should be a good starting point. Mains maybe a bit on the rich side though for a stock motor.

scottly · « **Reply #437 on:** January 15, 2014, 07:49:38 PM »

Quote from: slikwilli420 on January 15, 2014, 03:51:28 PM

So I'm getting ready to set up my webers and wanted to get an idea of baseline jetting. Scottly posted some jetting info back around post #110 but I'm not sure if it's for a stock 750. The bike will be stock for now until I get my either 836 or 915 motor built. Any jetting info would be a big help.

My jetting is on post #5; the jetting on post #110 is from Marko Johno.
Trust me, 125 mains and 45 idles will get you up and running, whether 736 or 836, as long as the accel system doesn't drown the motor.

slikwilli420 · « **Reply #438 on:** January 16, 2014, 12:42:52 PM »

Should I adjust the accelerator pump and return jets considering my stock motor? I know there are a million factors at play here, but being in the ballpark and then getting an idea of a jet size or two up or down on key pieces will give me a good range of tunability. Is there any jetting information out there for how the kits came from RC Engineering?

BPellerine · « **Reply #439 on:** January 16, 2014, 06:21:01 PM »

there is a post on this thread some where with the rc info I think near the start I wiuld not play with the pumps until you get it started .I run webers on a stock engine but they are 38dcoes.if you set your idle even a little to high for intial start be ready to lower it quick!I set mine up as per the book I have and it fired up at 3000 rpm!were your carbs ever on a bike if so try them as is .mine were supposedly off a 750 so I cleaned and checked everything and put them on they work fine but I may go up from the 115 main I am running.I had never had webers before these so if I made them run anyone can!hahabill

Tintop · « **Reply #440 on:** January 16, 2014, 07:38:31 PM »

Do you have a Weber manual?? If not P/U the Haynes off Ebay. Not the best, but it will give you the basic baseline setup to get it started. Can you post a photo of your carbs? There are different versions, and they setup slightly differently, ask me how I know.

Make sure your ignition is timed (use a light) as it's very easy to mistake ignition issues for a carb problem. Most important thing is to get the idle setup, and the carbs balanced. Everything else works off of that. As Bill mentioned if they came off a bike they're already likely in the ball park.

A caution if/when you remove/replace the accel jet. There is a small alloy washer that must be replaced on the jet. If it's not they can/will leak raw fuel into the intake, and wash down the cylinder. Get some spares, they're cheap.

slikwilli420 · « **Reply #441 on:** January 17, 2014, 12:24:50 PM »

These are 40DCOE28 so I think they are from an Alfa Romeo and these specific carbs have 3 progression holes. The manual I have is the "How to build and power tune Weber DCOE carbs" and the tuning manual by Passini that combines his parts 1 and 2. Based on the engine these were sized for, it seems like I will be able to go to 30mm chokes (32mm in there now). I will have to look at the rest of the parts and post the sizes.

I am having a manifold made up (RC type design) so can I add small 5mm ports to each for a mercury vacuum balancer that I used on the stock carbs or should I use the type that you hold over the venturi? If I can add those and then just keep them plugged with brass screws like stock carbs that might be nice.

As for the linkage, I am using the Pierce dual universal linkage kit. I will either have the linkage pull off the right side of each carb or if I can get it to work, I will have them both in the middle to hide them, using my pull cable to actuate then have an external return spring to assist in closing.

My ignition is a Dyna S that I will check again when its time to start up again. I did fry my old "S" a couple years ago so I hope I dont have the issue again or Im going to a Pamco.

Tintop · « **Reply #442 on:** January 17, 2014, 02:43:14 PM »

Sounds like you have the manual side covered, that Passini book is great. I think scottly runs 30 chokes, those seem to be about right for the SOHC. Pierce are my go to for parts, and if you call them with an issue, they can be very helpful.

I use the Syncometer from Pierce, but the mercury type works well. Word of caution - make sure the tubes are closed off (pinched) when you first start it, and until it's warmed up and idling. If the rpm's jump up at the start the high vaccum can suck the mercury into the engine.

754 · « **Reply #443 on:** January 27, 2014, 03:12:27 PM »

Here is some measurements. For willi

Looks like the center studs are 2.062 and 3.25 apart. An 1/8 drillbit WONT go between the carbs. Looks like 73mm centres on the middle ports.
Anyone that knows how easy it is to pull the jets, please chime in.

Tintop · « **Reply #444 on:** January 27, 2014, 03:55:00 PM »

The idles, mains (with emulsion tube & air corrector), and the accel bleed are all accessible by removing the the top cover. The float is attached to the top cover as well. Accel jets are under the large brass screw at the junction of the 'T' (1st photo). You can get the everything you need to from the top, without having the remove the carbs, or disturbe the linkage / cables.

754 · « **Reply #445 on:** January 27, 2014, 04:06:27 PM »

I know all that, just in some locations the stock frame gets in the way..

Tintop · « **Reply #446 on:** January 27, 2014, 05:10:25 PM »

Then your choices are to create a special tool(s), remove the carbs, or modify the frame where it interferes.

BPellerine · « **Reply #447 on:** January 27, 2014, 05:47:14 PM »

just looking at your setup Frank it looks like your carbs are at least 1/2 ins closer than mine as my linkage is centre pull and take up some room so that would give you the 1/2 ins that I need to clear the frame to pull the emuls tubes and mains the idles clear ok.can not pull the top cover without removing carbs in any configuration unless maybe a chopper.pumps clear ok too.hope this helps.bill

slikwilli420 · « **Reply #448 on:** January 27, 2014, 06:01:19 PM »

Based on how close cylinder 2-3 are on the RC version, I have decided to have two different manifolds made. One will have a 95mm center to center distance between the center spigots, and the RC replica will be about 76mm. That will give me just enough room to cap off the ends of the throttle shafts after they have been cut down. I will have both on hand to help decide which to use and then how to do the linkage which will be a single pull from the center. I chose the universal linkage kit from Pierce.

Frank, what is the actual distance center to center between spigots 2 and 3?

Tintop · « **Reply #449 on:** January 27, 2014, 06:01:54 PM »

Different manifold was the last option I forgot to add.

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Author Topic: Weber carb set-up (Read 151884 times)