Weber Triples finally installed and running...sort of...help?

[Konish]

Fellas,

Finally got these DCOE 40s cleaned, mounted on the manifold and installed. Initial tuning was...interesting and I'm still a *long* way away from perfection, but I think I need to clear up a few things before I go chasing after ghosts.

 

The car starts, runs and responds to throttle instantly, the car revs FAST (much, much faster than the SUs) but:

 

1. The car idles like a dang tractor. I knew it would be rougher than the SUs and according to the synchrometer they are pretty well balanced (could be better), but it's about as rough as a car missing on a cylinder.

 

2. If I blip the throttle to 3000 rpm or so and I abruptly close out the throttle, the revs drop really low and the car about dies until it catches it's breath again...once it does the idles rises and stabilizes.

 

3. Fuel starvation...I think. My guess is that problem 2 as well as some other issues are a direct result of fuel starvation. The other thing that makes me suspicious is that car pings pretty badly with anything above really small throttle openings. If I crack it and open it gradually, I can generally stop it from pinging, but as soon as I get more aggressive it starts the ping. Also after running a while for tuning purposes, the idle starts to hunt (+/- 100 rpm) and for some reason if I drive the car in a tight turn, it'll die (my guess is fuel sloshing to one side of the bowl). Starting requires one throttle pump and it fires right up and it idles fine.

 

4. Unless I use a pretty stout helper spring, the butterflies will not close all the way if the car is running. Without the spring, small, gentle throttle inputs makes the throttle hang and the car revs much higher unless I manually pull up the linkage arm. When the car is off, they close tight from any position. Vacuum keeping them open that last small bit? The helper spring makes this a non-issue but I didn't want to put a band-aid on a bigger issues although I have seen plenty of Triple set-ups that have them

 

I'm running a stock mechanical with a Holley pressure reg. with a gauge which I don't trust, but the pressure is below 3 psi and no amount of adjustment makes a difference. My setup is:

Mains 130

Emms F-11

A/C 170

Drains 40

Pumps 45

Idles 55F11

Starters 100F5

Chokes 30 (for my type of driving I was thinking about going to 28s if it'll help the dipping idle issue)

Needle valves 175

 

I'm using the stock metal lines from the tank that exit on the right front frame rail, but have removed the stock metal feeds for the old SUs (lines mounted to the head). Right now, I have a line going from the output side of the pump into the reg, then to the carb closest to the cockpit. The last carb has a "T" fitting with a fuel line back to the stock metal return line.

 

I'm guessing that I'm going to end up needing to install an electric fuel pump. Even with all this, the car feels much more responsive and eager to rev over the stock SUs that were on the car and I'm pretty happy they are at least running and drivable. Any suggestions for a fuel pump, mounting location and wiring strategy?

 

Oh, and pics to follow...

 

R/

Dustin

Edited February 25, 2010 by Konish

[Dtsnlvrs]

Tell me a little bit more about your motor (cam, size, head work etc), your trans, and you diff ratio...also tire size. Get rid of the mechanical pump and get a Facet pump....you want around 30gph at 3psi unregulated, use the factory fuel rail, it has an orifice on the return side that will provide the right pressure if you use the facet pump in the link. What ignition are you using? etc...I can probably get you close via the forum, but I would suggest you buy "How to Build & Power Tune Weber & Dellorto DCOE & DHLA Carburettors (Speedpro) (Paperback)"to really get them setup right. I would think with the pinging, you have too much advance and or have a really lean idle curcuit. Oh and you will need to use a helper spring...even in factory applications they had external return springs.

[Tony D]

Sounds like you have float height or fuel delivery problems from the right turn stalling and the pinging issue. As well as possible vaccum leaks---check all that first. Those 30mm chokes are for down low driving, that puts the mains on line much earlier than power sized chokes would, pinging without knowing what region is a guess, see comments below about recurving the distributor. Your mains are one size smaller than what I used on 45's to make 280+ HP, so they are likely well in hand for total fueling...if your float bowl is maintaining the right fuel level. The stock mechanical pump should be more than enough for that setup. If you have problems with the throttles returning to match the idle stop screw, it's not vacuum doing it, did you check synch barrel-to-barrel on each carb to check for a bent throttle shaft? They should be open about 0.003-0.005" (use a tapered feeler gauge when you have them off) for initial setup, this works well for setting the linkages to the right length, and then you can move the idle speed screws to appropriate idle speed. They will NOT be 100% closed, if they are, you will not idle at all, and will run the 'chop throttle stall' almost like you describe. YOU DON'T STATE WHAT CAR YOU HAVE, but if it's not a 240Z, and you have the BIG return line like on a 260Z, without a restrictor jet in the return line you will likely dump FAR too much fuel down the return and the carbs will suck down the pump supply too quickly. Put something like a 0.050 or 0.065" jet in the return line and see what your fuel pressure at the carbs does under load using a 't' and a pressure gauge taped to the windshield. Free Revving will tell you little to nothing.

 

Universally, I've traced new conversion with 'rough idle' to low idle speed, up your idle speed to at least 850 or 900.

If you are using a lightened flywheel it will react differently than a standard flywheel.

 

Without a dashpot to hold the carbs off idle, you simply go rich (no air compared to the fuel now suspended in the runners) and the speed drops. The idle speed raised from stock to slightly below 1000 will make this less of a concern. You didn't say it 'died' just that it dipped and then rose back up---indicative to me that your idle speed is not high enough.

 

With a cam, an idle speed of 1100 or even higher may be dictated. It's not uncommon for large cams with no vacuum to have to idle as high as 1700 rpms to keep the engine smooth enough that it won't die. The same car, with the same cam, but with EFI on 45mm ITB's would amazingly idle as low as 450rpms---so low you could swear you could count the pulses coming out the open headers!

 

I don't think anything is wrong other than your idle speed is set to low. It's a common mistake. Even on hot SU's this is recommended. RPM's make vacuum through a carb (as will ignition advance, which should be recurved for use with Triples---I run 15 initial with no vacuum advance on most triple setups I do), and that keeps them functioning.

 

On the vacuum note, if your valves are not adjusted before you synched...tsk tsk tsk! Back to square one, adjust those valves and recheck synch, THEN set the idle speed and idle ignition timing.

 

Good Luck!

Edited February 26, 2010 by Tony D

[Dtsnlvrs]

Well said Tony...I was limited in time to respond, and wanted to gather more info from him.

[Konish]

From the PO who built the engine:

L28 Block, non-turbo (280/280ZX 1976-1983) N42 block

1mm oversized piston, flat top

Head: 260 E88, with stock nissan B cam

HKS 2mm head gasket

1989-1983 280zx 'magnetic' distributor

He also said he shaved the head to bump up the compression 1.5 from stock but I'll have to confirm with him next week.

 

Sounds like you have float height or fuel delivery problems from the right turn stalling and the pinging issue. As well as possible vaccum leaks---check all that first. Those 30mm chokes are for down low driving, that puts the mains on line much earlier than power sized chokes would, pinging without knowing what region is a guess, see comments below about recurving the distributor. Your mains are one size smaller than what I used on 45's to make 280+ HP, so they are likely well in hand for total fueling...if your float bowl is maintaining the right fuel level. The stock mechanical pump should be more than enough for that setup. If you have problems with the throttles returning to match the idle stop screw, it's not vacuum doing it, did you check synch barrel-to-barrel on each carb to check for a bent throttle shaft? They should be open about 0.003-0.005" (use a tapered feeler gauge when you have them off) for initial setup, this works well for setting the linkages to the right length, and then you can move the idle speed screws to appropriate idle speed. They will NOT be 100% closed, if they are, you will not idle at all, and will run the 'chop throttle stall' almost like you describe.

 

Floats were checked and set (actually 2 were on the money and one was only slightly off). I figured the fuel was sloshing to one side of the bowl.

 

Pinging occurs through the entire rev range at anything approaching 1/2 throttle...anything less and I can accelerate without it happening.

 

The throttle stops on the carbs are all a little different (some of the bends on the levers are a little wonky and from carb to carb they are not totally symmetrical) so I set the throttle stop screw until I *just* saw movement of the butterfly and butterflylever through the rear-most (closest to head) progression port. I should've been more clear, I never had them set so they were completely closed (off the stop) but anything more than just perceptible movement in setting the stop screw made the engine race.

 

What I can't figure out from having already removed these once is that when the car is off or I have the carb in my hand, the butterflies close to the stop screw with no hesitation and are very positive and smooth in operation. Under idle, they can "hang" unless I use the helper spring or pull them up by hand...as soon as I turn the car off, they close. It took me a while checking the throttle linkage, removing the carbs and some head-scratching before I realized this.

 

From memory barrel to barrel synch is very close if not dead nuts.

 

YOU DON'T STATE WHAT CAR YOU HAVE, but if it's not a 240Z, and you have the BIG return line like on a 260Z, without a restrictor jet in the return line you will likely dump FAR too much fuel down the return and the carbs will suck down the pump supply too quickly. Put something like a 0.050 or 0.065" jet in the return line and see what your fuel pressure at the carbs does under load using a 't' and a pressure gauge taped to the windshield. Free Revving will tell you little to nothing.

 

I have a 240z (1971) but I removed the stock fuel lines mounted on the head and went with 1/4" line from feed and return...which as you surmised may be one of the reasons why it appears that my carbs are starving. I did some research and it seemed like a lot of folks were bypassing the metal lines along the head due to vapor lock issues. With this info, I'm going back to the fuel rail and see if the carbs act less lean.

 

Universally, I've traced new conversion with 'rough idle' to low idle speed, up your idle speed to at least 850 or 900.

If you are using a lightened flywheel it will react differently than a standard flywheel.

 

Without a dashpot to hold the carbs off idle, you simply go rich (no air compared to the fuel now suspended in the runners) and the speed drops. The idle speed raised from stock to slightly below 1000 will make this less of a concern. You didn't say it 'died' just that it dipped and then rose back up---indicative to me that your idle speed is not high enough.

 

With a cam, an idle speed of 1100 or even higher may be dictated. It's not uncommon for large cams with no vacuum to have to idle as high as 1700 rpms to keep the engine smooth enough that it won't die. The same car, with the same cam, but with EFI on 45mm ITB's would amazingly idle as low as 450rpms---so low you could swear you could count the pulses coming out the open headers!

 

I don't think anything is wrong other than your idle speed is set to low. It's a common mistake. Even on hot SU's this is recommended. RPM's make vacuum through a carb (as will ignition advance, which should be recurved for use with Triples---I run 15 initial with no vacuum advance on most triple setups I do), and that keeps them functioning.

 

On the vacuum note, if your valves are not adjusted before you synched...tsk tsk tsk! Back to square one, adjust those valves and recheck synch, THEN set the idle speed and idle ignition timing.

 

Good Luck!

 

My vacuum advance has been disabled and I've been running 35 total advance and like 15ish (from memory a month or so ago) static. I was thinking the same thing at work today about the idle speed dropping off and raised my idle speed to 1000ish rpm and things are *much* better. Guilty as charged...I did not set my valves as I simply needed it back on the road (daily driver) and working outside in the dark after work sucks. My plan involved re-doing everything after my valve adjustment...which seems counter-productive but circumstances dictated otherwise.

 

I really, really appreciate the input. It actually confirms a lot I was theorizing about today at work and it's nice to see that I was at least in the ball-park of what I thought was happening.

 

More to follow

[Dtsnlvrs]

Well, start by dialing that timing back a bit...just from my rough calculations...you have a comp ratio over 9.25:1. Set it for about 30-32 ALL IN by 3000. Get it warm, and set the valve lash...then go back to tuning...I would reccomend you buy a good weber tuning book...the Speedpro series is one "How to Build & Power Tune Weber & Dellorto DCOE & DHLA Carburettors"

 

As far as the carbs closing, you have to run an external return spring...there is no other way around it....Consider it a requirement....both by the DOT, and the SCCA. EVERY application I have seen for DCOE style carbs, both Factory OEM and Aftermarket, used some sort of return spring on the throttle linkage or the shaft.

 

Also, look into changing out the Idle jets to a 50f9...you will have to try out a few different jets...nut the f11 series idles have far too much emulsification for our cars...other than that...your jetting looks ok for starters. Where are you located, and are you getting oxygenated fuels...that can make a HUGE difference in jetting

Edited February 26, 2010 by Dtsnlvrs

[GOTHALOSISM]

^^^ listen to the Sarge he knows these carbs better than any one else I know. He helped me out immensly when I was running dual SU's. He tuned mine to almost full potential in under 10 mins.

 

 

Also TonyD is to be revered and coveted on here as well.

[Konish]

Update:

 

Tony:

The stock fuel rail went back on. I did look over the rail pretty closely and you nailed it, the return fuel rail had a *very* small orifice silver soldered to the end...I'm talking a push-pin diameter. Ran the fuel lines just like the SUs had been plumbed and man the car was running better than ever. Also, I got back all the adjustment in my FPR and turned to just under 4 psi. Best part is that no more stalling when turning and the idle has smoothed out a bit more (even more than just turning up the idle).

 

Russell:

I backed off the timing a bit and in the middle of monsoon winds and bit of rain out in front of my house I had to do it by ear...needs more but I lost quite a bit of the ping. Still though, wide open into the upper half of the rpm range still pings. Without help or a timing light I just had to guess...yes it's ghetto but the weather was getting nasty.

 

I figured the spring was a requirement as pretty much every setup I've seen had them. I was just wondering if I was ultimately covering up a symptom of a bigger problem. I buy fuel on base here in Japan and I doubt it's oxygenated.

 

I still need to do all this correctly by buying the tuning book, adjusting the valves and timing, new plugs, wires, cap and rotor. Synch the carbs and readjust the idle mix screws. I'm also thinking about getting a Innovate LM-2. I've been wanting one for a while and I figure now is as good a time as any as I have a feeling I'll be spending time on tuning and would rather not throw money at a bunch of jets without at least knowing which direction I need to go. I still get a bit of an idle hunt, but it may be due to my marginal ignition components.

 

I'm pretty happy going from some old, nasty Webers, to clean (relatively) mounted Webers that I've never had any experience with to a finally running car. Truth be told I thought I was just going to throw in the towel and get some ZTherapy carbs...glad I stuck it out thus far.

 

More to follow...

 

R/

Dustin

Edited February 27, 2010 by Konish

[Dtsnlvrs]

YES, get a wideband...that will give you an idea of where to go jet wise when you get it on a dyno....what is the octane rating of the fuel you get on base? Look to building a collection of jets...I would recommend original weber peices not the asian knock-offs...I buy mine from a guy in Italy on ebay ALFA1750'S CARBURETORS PARTS STORE.

[Daeron]

YES, get a wideband...that will give you an idea of where to go jet wise when you get it on a dyno....what is the octane rating of the fuel you get on base? Look to building a collection of jets...I would recommend original weber peices not the asian knock-offs...I buy mine from a guy in Italy on ebay ALFA1750'S CARBURETORS PARTS STORE.

YOU CAN NOT have "too many jets!!!"!!!!!

 

!!!!

 

 

You can spend hours, and hours, and hours tweaking your jet combination trackside, or at a dyno, and you could start out thinking you've got every jet for a Weber ever made.. but trust me, After a few hours you will discover one that you need!!!!

[Konish]

Edited February 28, 2010 by Konish

[Dtsnlvrs]

Awesome job, now get that thing on a dyno and really dial it in