Triple Webers on 1977 280Z

[mfairfax]

I just purchased a 1977 280Z as a project for my son and I.  We are new to the Z car world.  The car runs pretty well considering it has been sitting for a few years and is drivable after getting a new set of tires.  The car is stock with the exception of triple webers and some modification to the vacuum advance that I don't understand.  We are in the process of putting together the priority list for this project which will probably take a few years.   But, in the meantime I would like to make the car a bit more drivable. 

 

The immediate performance problem is that the engine "bogs" down when accelerating in 1st and second gear.  The car doesn't stall out completely but seems to be starving for fuel.  To compensate, you have to start out with at high rpms.  The power loss is dangerous when pulling into traffic and especially dangerous for my son who is just learning how to drive a manual (so no, he is not driving the car alone or on a daily basis right now).  Once you get the RPMs up, the car runs great.  The car idles fine also.  I know there are probably a 1000 things that could be contributing to this problem but I thought is would be worth a shot to get some initial feedback from those with some experience.  My gut says that whatever was done to the distributor to modify or shut off the vacuum advance is the issue. 

 

Thanks in advance for your input!

[siteunseen]

Is there a vacuum hose hooked up to the distributor?

 

I'd think the Webers need some attention, there's a lot to getting them run right.  That's why I have a set in a box under my bed.

 

Here's something I've read that was very informative in my opinion, http://www.classiczcars.com/topic/35221-tripple-weber-jet-sizes-and-adjustment/

post #4 is where the info starts

Edited August 24, 2015 by siteunseen

[Patcon]

I agree with Siteunseen. It is probably the jetting or tuning in the Webers, not the vacuum advance. If I was in your place I would get a good complete set of SU's from Z therapy. They will be easier to keep tuned and are very simple to work on. Triples can be very challenging to get right. 

[Zed Head]

.  My gut says that whatever was done to the distributor to modify or shut off the vacuum advance is the issue. 

 

Thanks in advance for your input!

Many carb people don't run vacuum advance.  It goes away when you hit the throttle anyway.  Even the early 280Z's (75-77, I think, definitely not 78) with EFI don't have vacuum advance until they're in top gear.  There's a switch and solenoid that lock it out.  Actually that might be the part you don't understand, you might have the top gear switch.  Vacuum advance adds a little pep at part throttle, and some fuel efficiency but doesn't do much when the throttle is opened at low RPM.

 

Have you measured initial timing?  Confirmed that centrifugal advance works?  Adjusted the valves?  Every little bit helps, in addition to carb tuning.

[rossiz]

while the triples are cool and many enjoy a little bit of added top-end performance, i can attest to the simplicity and ease of use that a nice set of su's provides. i rebuilt a set myself, but mostly because i wanted to get to know the carbs - there's not a whole lot to be saved vs. getting a set from zspecialties if you count your time at all. if your triple setup is in decent shape, you should be able to sell them for enough to offset the cost of the su's considerably. and fear not, your son will have plenty of fun w/the su's - they are not a big downgrade. lots of folks race these carbs happily. 

 

once they're bolted on and the float levels set (the hardest part) you'll be surprised how simple and effective they are.

[240260280z]

To set up your webers there are a few important things to do:

 

0. Make sure all 3 carbs are the same type (model and s/n are on the top cover).

1. Make sure the linkage is sync'd between all carbs and there is no slop. the 6 throttle valves all have to open and close together

2. Make sure there are no air leaks into the intake manifold

3. Make sure the carbs have the same internal components (fuel jets, emulsion tubes, air correctors, chokes, etc).

4. Make sure the fuel level in all 3 carbs is the same and ~ 29mm down from the top of the carb body (bottom of cover gasket)

5. Read all you can about webers in the archives on this site.

 

Please have a look at the carb jets, chokes, etc and report back to this thread then we can walk you through tuning.

 

Find a friend with a wideband O2 sensor that you can tune with.

Buy and STE Synchronometer.

Edited August 25, 2015 by Blue