Triple side draft tech question

[Busta Nut]

Sorry if this may seem like a stupid question but I have very little experience with carbs and knew even less when I bought all this shit a decade ago. I bought two 40mm DCOEs for my 510 project. Found a 240z at an irresistible price and bought that. 510 project got put on the back burner so I thought I would be a good idea to put them on my Z. Bought another and slapped them on my Z. Never ran great but good enough to drive. Recently started driving again and thought I'd check things out. Turns out the number on the carbs don't match(big surprise there,huh). 2 for a 510, 1 for a Z. Is there some kind of kit to make them all the same so I can tune the Z properly??

[Stupid_fast]

Other people here know a lot more about these carbs, but for starters ..

Are the carbs the same size? I think you can change the choke size? Are they the same size? If its just the jet sizes that are different that's easy, 10 minute fix.

There are lots of things that would need to be known ... if the carbs are all DCOE 40's they can be tuned the same. Do you have a carb synchronizer?

[Busta Nut]

I have a synchronizer and thy are all 40s. I can take some pix when I get home late tonight.

[Busta Nut]

So here are a couple pix. All three are 40DCOE 151

The two for the 510 read 033 01

The one I bought later for the Z reads 277 06

Both appear to be identical from the exterior

510

240z

I've had a Carter fuel pump on there with a crap gauge that didn't read accurately since I bought them.

I was told that the Carter pumps fuel at about 5-6 psi. Which is too high for the carbs, so a Holley pressure regulator and gauge was recommended to me and I never installed them until last night.

That's when I noticed that the carbs were different and it ran worse than ever. Fuel pressure was a perfect 4psi. I'm gonna get to work early tomorrow and open up my carbs to see what's up internally. Are the ports in the carbs the same? Is all I need to do is change a couple internals?

[hang_510]

i've read that when using unmatched carbs (a random pair) that tuning can be a problem.

your 3rd may not match the other 2 and be causing issues trying to tune it.

 

 

with the fuel pump that close... i run my pressure just under 3.5, it ran poorly with the pressure higher.

[Busta Nut]

i've read that when using unmatched carbs (a random pair) that tuning can be a problem.

your 3rd may not match the other 2 and be causing issues trying to tune it.

 

 

with the fuel pump that close... i run my pressure just under 3.5, it ran poorly with the pressure higher.

 

I know for a fact that the carbs not matching is causing an issue. I'm wondering if I CAN make them all match by changing some internals or is the the porting inside the carb different?

[Stupid_fast]

I know for a fact that the carbs not matching is causing an issue. I'm wondering if I CAN make them all match by changing some internals or is the the porting inside the carb different?

 

check the jets on all 3... see if there are any that are different.

[Busta Nut]

Never even took these little tops off before.

Found my first problem

510 carbs

240z carb

Still need to find out if a conversion is possible or are the carb just too different?

[Busta Nut]

Just an update. Viking Auto Parts in Novato, CA had a ton of knowledge on weber carbs of all kinds. Brian over there really knows his shit. It's mostly VW parts but they are a Weber dealer. Apparently my bodies are all the same. Internals can be changed to match. Time to rip down some carbs!

[Stupid_fast]

Just an update. Viking Auto Parts in Novato, CA had a ton of knowledge on weber carbs of all kinds. Brian over there really knows his shit. It's mostly VW parts but they are a Weber dealer. Apparently my bodies are all the same. Internals can be changed to match. Time to rip down some carbs!

 

Yeah, that's what I was trying to explain. . Those parts are the jets, little tuning parts that are set differently per car model.. all those jets and little tuning parts you can buy in all different sizes, so you should be able to match all three carbs. Go with the stock Z settings and tune it from there, should run nice.

 

 

Good luck

[Busta Nut]

Got somewhere tonight. I think I got all the numbers I need. Carb teardown was pretty simple. Found a schematic online of a 40 DCOE here:

http://www.webcon.co.uk/weber/40dcoe.htm

Took the horns off first to access the auxiliary venturi. There is a set screw with a lock nut on the side of the carb. With it removed, the venturi slides out.

Choke tube is right behind it held in by the air bleed screw.

Then unscrewed the top of the carb and removed it. Careful not to tear the gasket. Floats come up with the top.

Needle valve is held in by the floats. Slide the pin out to remove floats. Needle and seat can be removed with a 10mm wrench.

Next, I pulled the main jet off the bottom of the emulsion tube and separated the tube holder from the tube exposing the air corrector jet.

The tube on the Z carb was pretty tight and I couldn't separate it by hand so after removing the main jet, I threaded it back in the carb by only a few threads. Used a punch through the tube holder and VERY gently tapped it free.

Down in the center of the carb is the pump spill/pump exhaust.

Off to the right of the carb is the pump jet. Watch for the small washer.

Random Pix

[Stupid_fast]

Very cool.

[Busta Nut]

Very cool.

 

 

Thanx! Love getting my hands all up in her!! Got some prices today. Can't get the parts till next week. Aaaaah!

 

 

[Busta Nut]

Quick Update. Viking auto in Novato is helpful but slow to get back to me. Got impatient and remembered Pierce Manifolds in Gilroy,CA. That's who I originally got the carbs from. They have everything in stock. Perfect! Going down there next week anyways.

Here's are the numbers I had to record. If I'm missing something. Please let me know. My only experience is what you see here and word of mouth. Any feedback is appreciated!!

Part 510 240z

Choke/Venturi 32 30

Aux Venturi 45 45

Main Jet 135 115

Emultion Tube F15 F11

Air Corrector Jet 170 200

Idle Jet 55F2 45F9

Pump Jet 40 40

Pump Spill/Exhaust 55 55

Needle Valve 175 175

[EricJB]

Make the Z carb match the 510 carbs

 

32 chokes

 

170 air corrections

 

135 mains

 

 

55 idles (might be a bit big)

 

 

I've never run f15 emulsions, f11's many times. Run which ever you have the most of. The hole pattern in them determines what rpm the main circuit comes on. They can be pricey, Good luck.

[Busta Nut]

Make the Z carb match the 510 carbs

 

32 chokes

 

170 air corrections

 

135 mains

 

 

55 idles (might be a bit big)

 

 

I've never run f15 emulsions, f11's many times. Run which ever you have the most of. The hole pattern in them determines what rpm the main circuit comes on. They can be pricey, Good luck.

 

Parts aren't too bad. Chokes and venturi are the highest at around $20ea. Everything else is under $10. Is there something that explains what the numbers mean? I understand the jets and chokes. Pretty obvious, bigger number bigger hole. Not too sure of the Air Correectors and emulsion tubes. You mentioned the emulsions determine what rpm the main circuit kicks in. I have two F15 and one F11 but I have no idea what it's gonna do with one or the other. What RPM did yours kick in at? And if you think the 55 idles are too big, could I just use the 45? I don't have any internal mods to the engine either. Don't know what kind of factor that plays in?

 

 

 

[Busta Nut]

Man! When does a new page start??

[EricJB]

The #'s on the idle, air correction and mains are the size in millimeters. A 135 main is 1.35. An 055 idle is .55. Most of my tuning experience has been with IDF and IDA downdrafts. We used to swap the f11 emulsion tube for f7's to make the main circuit come in earlier. I dont know if the f15's are higher or lower. Somewhere in the weber tuning manuals there is a chart that shows the range for them.

 

The fuel comes up through the main jet, while air comes down through the air correction jet. They emulcify (mix together) in the emulsion tube and are drawn in through the auxillary venturi. The hole pattern in the emulsion tube determines when that happens.

The reason I said the .055 idles might be a bit big is, most of the time 045 to 050 is plenty big in everything i've seen from 40mm to 44mm carbs. Also, I would run 3psi fuel pressure. I run the same Holley regulator on a pair of DCOE's, on a LZ23. It runs 050 idle jets as well.

 

The engine runs on the idle jets ,between idle and main circuits. if they are too small, it will sputter (nose over) and spit. If they are too big, it will chug. It really doesn't matter at an idle, since the air/fuel screws limit the fuel flow.

 

Let us know when your ready to sync them.

[Busta Nut]

The #'s on the idle, air correction and mains are the size in millimeters. A 135 main is 1.35. An 055 idle is .55. Most of my tuning experience has been with IDF and IDA downdrafts. We used to swap the f11 emulsion tube for f7's to make the main circuit come in earlier. I dont know if the f15's are higher or lower. Somewhere in the weber tuning manuals there is a chart that shows the range for them.

 

The fuel comes up through the main jet, while air comes down through the air correction jet. They emulcify (mix together) in the emulsion tube and are drawn in through the auxillary venturi. The hole pattern in the emulsion tube determines when that happens.

The reason I said the .055 idles might be a bit big is, most of the time 045 to 050 is plenty big in everything i've seen from 40mm to 44mm carbs. Also, I would run 3psi fuel pressure. I run the same Holley regulator on a pair of DCOE's, on a LZ23. It runs 050 idle jets as well.

 

The engine runs on the idle jets ,between idle and main circuits. if they are too small, it will sputter (nose over) and spit. If they are too big, it will chug. It really doesn't matter at an idle, since the air/fuel screws limit the fuel flow.

 

Let us know when your ready to sync them.

 

This is great info! Thanx! Is there a tuning guide online or on this site somewhere? I assume if you get a bigger main that you'd need a bigger air corrector, but that's not the case in these carbs. This is what I was thinking of doing. I have NO idea what this would do. Just a guess.

 

Chokes 32

 

Mains 135

 

Airs 170

 

Idles 45

 

Emulsions F11

[skyblue]

Man! When does a new page start??

 

i think it's every 20 posts

[Busta Nut]

So. I put my parts in today and I think I got it tuned pretty close. The only thing is I'm getting very intermittent backfire from the intake on very slight throttle, and constant backfire from the exhaust on decel and very slight throttle. Slight throttle like when I'm trying to cruz on a level or light downgrade. Anyone?

 

 

 

Pics to come.

[Busta Nut]

Went down to Gilroy to visit Pierce Manifolds.

 

 

Bag O' Parts. Even my girl couldn't keep her hands off'em.

 

After talkin' to the guys down there, this is what I ended up with:

 

choke 30

 

Mains 135

 

Airs 170

 

E-tubes F11

 

and the bag read 50 for the idles but I ended up with 55s. Installed all the parts.

 

 

 

As I was putting the chokes in I noticed this

 

 

They sure don't make things like they used to. I wanted to smooth things out but I figured I'd see how thing feel first.

Got it running and took back to the shop.

First thing I needed to do is be able to access my fuel pressure reg. better.

 

Some spacers and different bolts were needed.

 

....aaand here it is now.

 

 

After looking around I set the fuel pressure at 2.5psi and popped all the linkages off and started tuning

 

 

 

These were the sites most helpful to me for the tuning process. I've seen a couple posted on here before. Some not.

 

 

http://www.racetep.com/webjettune.html

 

http://www.redlineweber.com/html/Tech/idf.htm

 

http://www.redlineweber.com/html/Tech/dcoe_adjustment_layout_typical_i.htm

 

http://www.piercemanifolds.com/

 

The guys over at Pierce are real helpful. They explained a lot. Might give'em a call if I can't figure this backfire issue out.

[Busta Nut]

First thing I noticed was the smooth acceleration from a stop. It used to sputter quite a bit before it would switch to the main circuit and then it ran like a bat out of hell. Second thing I noticed is when I got on the main drive. Put my foot to the floor and not as much power as I had when it was mix/matched. I'm guessing that's the chokes. Should've listened to EricJB. Then, before today, if you tried to cruz it would backfire through the intake on a few cylinders. Only if I tried to cruz though, ran great otherwise, but idle was a mess (high at times, low other times). Now the transitions are smooth and it's drivable at cruz. A lot of backfiring from the exhaust on decel and light throttle. Sounds like a popcorn machine. I've read that it's caused by too rich a mixture or my timing is off. I thought I read the timing at 15 degrees. Gonna go back and and recheck the valve clearance and timing next.

[Busta Nut]

OK. I guess my question was too stupid for a response. This is what I ended up doing. Started from the beginning.

 

Readjusted valves. .008 intake, .010 exhaust cold engine. Three were a little tight. Rechecked the timing, 14 degrees at idle, goes to 37 when reved. Good advance.

Disconnected all the linkage, backed all the stops out. Turned them back in 1/4 turn from initial contact

 

 

Spun in all the mixture screws then backed them out 1.5 turns

 

 

All air bleeds closed and nuts locked

 

 

Started the engine and warmed it up. Ran like shit. Fuel pressure @ 2.25 psi. Matched all the carbs to the lowest one using syncrometer

 

 

This is where I was an idiot and someone should have brought this to my attention. There is a smog machine at my disposal where I work. Doh! Much better than doing it by ear. Initial readings when it warmed up.

...pretty bad but expected.

 

Started to turn the mixture screw 1/4 turn (in or out) till the readings got better. As I adjusted each one, the readings started to come down.

 

The best it's ever ran!

 

Hooked all the linkage back up and went for the best test drive this car has ever had. NO hesitation on accel, NO backfires from intake or exhaust, Super smooth transitions through the circuits. I LOVE IT!!!!