sam1904

Good question. Let me Google “what and where are my aux venturis’, go look and get back to you tomorrow!

Hi all,

I have a mostly stock 76’ motor (Tii Dist, unknown cam) which I installed 40 DCOE’s on around Xmas and they have put a smile on my face every drive. At a recent check valves and timing were good.

My current jetting is shown below and the car runs really well….mostly. I also have an A/F meter in the car which has been a huge help and provides the A/F ratios below.

The car starts and idles well at around 13:1 and with any meaningful throttle gets slightly richer through a WOT reading of around 12.5 – 13:1 (I was originally running closer to stochiometric but found enriching slightly made a great difference.)

The only issue is that at tip in / transition from a trailing or idle throttle the car leans out to 15-18:1 ish for a brief moment, hiccups and then as throttle travel increases transitions quickly and moves to the high 12’s. If I balance the throttle in that position I can hold it in the 15-16:1 range.

Reading the books I am thinking that as my idle A/F ratio and WOT ratio seems good, and it is just the transition where I have an issue (E.g. low RPM Main jet zone) I need to decrease the size of the air correction jets a little (from 200 to 175?) and if that then makes me too rich at higher RPM's I would then decrease main jet size a little (I still have the 120’s that came from IE) (See what I did there, I preempted the “buy the book” comments ?)

For the Weber gurus amongst you how does my logic sound?

Many thanks as always!

Sam

Cut one turn off front and rear (Ireland stage 1 springs, 2 dot pads at rear)

Drives really nicely. Minor rub with driver  footwell that was solved with science (f=ma ☺️)

5 hours ago, Hans said:

I assume the "weld" in jbweld means you'll never get that sucker out if needed?

I thought you said it was just #4 running lean.

Did you sort out the thread size issue?

I'd want to be sure that was my problem. I still think the carb to manifold looks odd. I'm pretty sure my gaskets are thinner.

 I'd do the propane test around each of  those likely leak areas.

Thanks, Some thoughts.

I did find an interference (with help!) where the cold start casting was hitting the manifold and this was preventing the rear carb seating fully on the gaskets, and especially #4. After removing the interference the flow rates through 3 and 4 came up but 4 is still around 10-15% lower.

I have sprayed starter fluid at any possible leak sources and there is a (minor) change in tone, with that said all of those leak sources are also within 12” of the open stacks so the effect could just be the starter fluid getting sucked in that way…

I am still concerned about the threaded connection from the ¼ pipe nipple into the rear of the manifold. It is absolutely a ¼” Pipe thread. The issue is that as with every tapered pipe thread, especially those where the female thread is a softer material (Aluminum vs. brass in this case) there is the opportunity to ‘stretch the thread’ through either repeated installations or in my case over tightening. In this case when first installed the nipple would seat with 1-2 wraps of Teflon with 2-3 threads still proud of the casting. At this point the same nipple (and another the same) will thread fully (e.g. 3-4 threads deeper) into the female thread even with far more Teflon tape. As such the average OD of the female taper is now larger allowing the tapered male thread to install more deeply. It also feels far looser and has more “angular” play during installation…

You are correct that JB-Weld would be a permanent installation. However at this point it is a little bit of a moot point. If there is thread damage (which there is – even if not leaking) the manifold is at a point where if this fitting comes out again something different is going to have to be done… JB Weld would be the last option I feel…

Before I go any further I have a 4 channel manometer arriving this week and am going to take a more detailed look at vacuum over each butterfly as my 40DCOE151 DOES have vacuum take offs… (Carbtune Pro Xmas present from my in laws! – always marry the daughter of a mechanic ? )

Will report back!

Sam

Great posts, thank you. Which Wurth product do you use?

On 1/2/2021 at 4:35 AM, NickVyse said:

Fit it permanently with some liquid metal, job done

Out of curiosity by liquid metal do you mean JB Weld?

Thanks?

Sam

No they do not, when I removed the coldstart castings there was deep interference on number 4 very mild interference on number 3 and none on 1 or 2. I will be starting the car again in the next day or so but looking at the images it does look like this is the reason why the gasket on number four was not being fully compressed and it does sites there could have been a gap. 

4 hours ago, Hans said:

What about the gaskets?

Is that your manifold in the picture? Did you have trouble getting fitting seated? In #4?

I used paper gaskets between all surfaces and believe any slight gap that was caused by the casting issue noted above has now been corrected.
 

That fitting shown is a pipe thread and hence does not fully seat, I did actually have issues in that I removed it and re-installed too many times and potentially stretched the thread slightly but believe I have overcome that with liquid PTFE.

 Thanks

 Sam

Quick update. 
Checked the shaft and it appears straight with no issues.
I did however file off the edges of the coldstart housing and it seems to have closed up a gap between the carb and number four runner on the manifold. Will start up tomorrow but appears to be the culprit!

4 hours ago, Son of Marty said:

Thanks for adding that I can't seem to be able to figure out how to add arrows and highlights on this computer because I'm the dummy all the books were written for ? 

4 hours ago, halboyles said:

This is a common problem with the one piece manifolds.  The cold start mechanism (AKA "choke") hits the manifold before completely seating.  By grinding off some of the base of the cold start mechanism, you'll eliminate the problem.

Son of Marty - hopefully I see you at the Vintage because I owe you a beer. Looks to have closed up a gap, will start it up tomorrow (daughters sleeping) and update but the interference was almost all on the #4 side so it makes sense. 

Halboyles - you can tag along also, I already owe you one for the linkage help

?

Thanks! Was about to post this..

1 hour ago, Stevenc22 said:

151's don't have a vacuum take off. You can remove the choke housing with the carb in place and seal it off with come block off plates.

Thanks for the reply

So out of curiosity what are the screws with the ?? in my photo below?

It is a plain tapped hole with a 1mm 'orofice' or hole in the bottom and a threaded plug.

Thanks all. Next steps

1. Have pinched off the booster and that appears good.
2. On a separate post it was suggested that my choke body may be hitting the manifold and creating a gap
3. I am going to check for a twisted shaft and report back (these are new but I did move the arm from one side to the other..)

Thanks all, such a great resource

Sam

OK...second thoughts...bad idea...I will pull it off!

Absolutely great eye - thank you!
 

I really don’t want to have to pull everything off so I may see if I can get in there with a tapered grinder on my Dremel and clearance it in situ......

I may look to dampen everything down or even hold a Dyson with the other hand to catch any debris.

4 minutes ago, Son of Marty said:

Sam looking at your older posts it looks like the choke on the rear carb around your #4 is hitting the manifold and may be the cause of your air leak.

Thanks for taking the time to have a look! I am not quite sure what you are referring to as I do not have a choke hooked up on this set up. May have just been a trick of the camera angle?

All, before I push ‘buy’ on a 4 channel manometer I wanted to verify there is indeed a vacuum takeoff on my 40’s. I have read that the Spanish vs. the Italian do have them but after scouring every single parts diagram I can find in my Weber book and on line the port below is not identified on any I can find.

By a process of evaluation – A,) because I don't know what else it could be and B,)  be because it appears to be a port with a stepped bore (around a 5mm thread and then a 1mm orifice at the bottom) right over the throttle shaft I am fairly certain that the port indicated below is the vacuum take off but just wanted to double check?

Many thanks,

Sam

All, I have a situation around cylinder flow / air bleed screws that I cannot visualize after reviewing all my books / posts on this site etc. I set up my twin 40’s and they are running well. A quick summary is below for background from another post:

I have a stock (and old) motor and until recently thought a stock cam. I just noticed that it has a yellow and red paint stripe / ring on it so it now appears it is at least a regrind but I have no idea what! I have the IE mechanical Dist, step header and stainless exhaust. I gave IE my set up and then to start just bolted on the carbs as supplied. The markings made by IE on the box state:

• Main: 120

• Idle: 50F9

• Air: No change

There were also 115 Mains and 45 F9( (Idle jet / bleed?) in a baggie that I assume were what the carb came with to IE. As of now I do not know the rest of the set up and wish I had pulled everything out and made notes before installing! I am also not sure if IE verified float levels prior to shipping and as such will need to check this.

The good news is it starts well and runs well. No stumbles and seems to stay in the high 13:1, low 14:1 range throughout the range only leaning out slightly further at high RPM's (high 14's). As it is  fun car and not daily driver I am going to go a little richer on the mains to try and get in to the 12:5:1 range and am thinking 125 or 130? (likely 130)

My question here is around a flow imbalance and the need to make a large adjustment to the air bypass screw that I encountered in initial set up:

After initially balancing the carbs between #2 and #3 I then compared flow from #1 to #2 and #3 to #4. With the latter #4 was flowing less (20% ish) than #3. I was (just) able to level them out by opening the air bleed screw on #4 to bring that flow up (measured with squirrel cage) but the screw is 2 ½ turns out (essentially all the way) which just doesn’t feel right.

My questions are what would cause a flow difference between two cylinders on the same carb, I just can’t visualize the ‘flow bypass’?

• Valves? (Set 500 miles ago but will re-do)
• Could a vacuum leak on #3 or #4 reduce the relative flow on #4? (I cant find one but am always wary of the brake booster take off)?
• Something else?

Many thanks

Sam

5 hours ago, man_mark_7 said:

Very nice! Are there any other mods to the motor? Where did you end up for jetting? I recently installed DCOE 40s on my otherwise stock (except for IE header and stainless exhaust) '73. I have been going back and forth between 50f8 and 55f8 idle jets. Here's where I am now. I still run richer than I'd like throughout the RPM range though. 

 

I have a stock (and old) motor and until recently thought a stock cam. I just noticed that it has a yellow and red paint stripe / ring on it so it now appears it is at least a regrind but I have no idea what! I have the IE mechanical Dist, step header and stainless exhaust.

I gave IE my set up and then to start just bolted on the carbs as supplied. The markings made by IE on the box state:

• Main: 120
• Idle: 50F9
• Air: No change

There were also 115 Mains and 45 F9( (Idle jet / bleed?) in a baggie that I assume were what the carb came with to IE. As of now I do not know the rest of the set up and wish I had pulled everything out and made notes before installing! I am also not sure if IE verified float levels prior to shipping and as such will need to check this.

The good news is it starts well and runs well. No stumbles and seems to stay in the high 13:1, low 14:1 range throughout the range only leaning out slightly further at high RPM's (high 14's)

As it is  fun car and not daily driver I am going to go a little richer on the mains to try and get in to the 12:5:1 range and am thinking 125 or 130? (likely 130)

Finished installing the 40’s and first shake down drive. Was a little concerned I would not feel a huge benefit as I had my synch-linked 32/36 running so well. After the first drive all fears gone - just do it, awesome! I actually don’t know if it is much (or any...) faster right now but at the very least it is the same and with 40’s under the hood and THAT noise. So, so glad I did it!
Also with Ireland’s recommended and supplied jetting staying right in the 12-13.5:1 range throughout!

Even though it is a new one-way valve I also need to check that again as I struggle as to if a minor leak around the thread could cause such a significant misfire and as such wonder if it is not sucking a lot of sir through the one-way valve?

Thanks. This is actually a Korman manifold and I am pretty sure I have the right thread as it engages well. Unfortunately the more I messed with it and reinstalled it the deeper it went which is why I think I may have exerted too much force and the taper has essentially stretched the aluminum thread. I am assuming this is the case and not the fact that the male threads have become diminished?

I also had the issue of meeting making the turn to the booster so I assembled a plastic elbow, I wonder if this is potentially not another vacuum leak sauce and I may see if I can source of brass variant. 
 

I do like your idea of just assembling a T and will try tomorrow, hopefully I also find something that has a slightly larger male taper and as such also helps solve the problem!

5 hours ago, visionaut said:

 

Well I have DCOE 40 Typo 151 Spanish Webers - and they take the slot-in trumpets. And the Aux venturis rattle without the centering sleeves.  And you really want the Aux venturi centered within the bore, not pressed against one side. So it's all odd.

 

... these posts also made me remember I have a set of cast aluminum BMW Autosport 90-deg DCOE 40 carb adapters/filters stashed away somewhere that I should dig out and put up for sale that I ran when I first had my dual 40s...

 

Tom

Let me know what you have!

Thanks

Sam