Datsun 260z low power issues

[Jaimebeflexin11]

Hello my name is Jaime and I just got a 74’ 260z that I’ve been working on. The car is for the most part stock except for the exhaust and carbs (dual Weber’s 32/36). I’ve had the same issue with the car since I bought it and don’t really know where to look anymore. The car does not seem to have any power when trying to accelerate rapidly and sounds like it’s bogging going up hill or when the engine has any load. The car also has a slight hesitation on takeoff. The car idles well and can get up in rpms when in neutral but on the road in gear is a different story especial in fourth gear. I’ve rebuilt the carbs, replace both fuel pumps, cleaned the gas filters, installed a fuel regulator to get the fuel pressure I needed and still the car doesn’t have the power it should. The engines compression has been checked and is good, spark plugs have been changed, timing has been adjusted. I rebuilt the carbs myself and am maybe leaning towards the carbs being the issue or could this be a fuel delivery issue? 
 

I would really appreciate any help. This is my first project car and I feel like I have used up all the knowledge I have. 

[Mark Maras]

The fact that it revs fine with no load but has reduced power when under a load indicates a lean condition. Confirm fuel delivery with a pressure and volume test. Check all fuel filters and after that start on the carbs.

[heyitsrama]

I usually see people on this site using SU or have EFI setups, maybe someone who runs a 32/36 can offer some advise...... in the mean time i found https://www.racetep.com/manufacturer/carbs-and-injection/weber/weber-carb-tuning-and-technical-info/jetting-and-tuning-downdraft-and-sidedraft-weber-carbs.html

Edited April 25, 2020 by heyitsrama

[Zed Head]

Since the car is new to you and might have had many previous owners I would give everything a thorough look to define what exactly you have and how it is set up.  Might not even be an L26, it could be an L24.  Check the stamping and castings on the block and head.  Might have the wrong heads on it, we've seen people create low compression engines by using the wrong heads just to get an engine running so they could sell the car.  Could be that the cam timing is off, that would have a big effect.  Clogged exhaust, smashed exhaust pipes, who knows.

Plus, you said you measured "compression" and checked timing, but did not give nay numbers.  The numbers are important.  Also, "timing' is usually just the initial timing.  But does the advance mechanism work?  You might be running 7 degrees advance at 4000 RPM.  You can check that with a timing light.  And you didn't mention checking or adjusting valve lash.  That is the very first item in the Tuneup chapter.  Very important.

Just some thoughts.  Make a list and start filling it up with numbers and observations, and post them here.  No offense, but you really have not done a lot, there's a bunch more that will help.  That's good news, there's hope.  Plus it's fun.

[Jaimebeflexin11]

Thank for the tips. I will try to write some results down. It’s the original L26. The exhaust has been swapped out. I swapped out the exhaust because the one it came with was pieced together. The compression was 165 +/-2 on all. The advance works. The time was set to 8 degrees. I’ll be checking the valve lash since I have not done that. Checked for vacuum leaks on the carbs and didn’t find any. 

[YZFMax]

I also have a 260z with the dual weber setup.  I took the car out for a spin for the first time this season, and my sentiments were exactly the same.  Found the car to be underpowered and slow in accelerating.

When I spoke to the local Datsun performance shop, he referred to the 260z motor as boat anchor.  He basically said that it won't be easy getting power out of these motors, and not worth the effort to even try.  

 

[Zed Head]

On 4/25/2020 at 7:44 AM, Mark Maras said:

The fact that it revs fine with no load but has reduced power when under a load indicates a lean condition. Confirm fuel delivery with a pressure and volume test. Check all fuel filters and after that start on the carbs.

If these were mine and I knew how to make a Weber run richer I'd just go straight to that.  Most carbs you'd just raise the main jet needle and it would get richer everywhere.  

Do that and if it gets more power you'll have a clue.  It will probably stink like gas at cruise but you'll know how to solve the problem.

There is a bunch of Weber stuff out there - https://www.racetep.com/manufacturer/carbs-and-injection/weber/weber-carb-tuning-and-technical-info/jetting-and-tuning-downdraft-and-sidedraft-weber-carbs.html

p.s. pretty sure that the L26 engine has at least as much power as the L24.  That was the whole point of increasing the displacement.  I would avoid mechanics who make blanket statements like that guy above did.  They usually don't know what they're talking about.  And, you might have been just talking to some kid at the parts counter.  Who knows.

Edit 2 - and they, the 240Z and 260Z, had the same 0-60 times, 8.0 seconds.  Since they didn't come with Webers it might just be that a PO's efforts to make more power had the opposite effect.  Not uncommon.

Edited April 26, 2020 by Zed Head

[siteunseen]

I agree with Zed Head. That mechanic don't know or confused what he's heard which is the 260 carbs are boat anchors. The short block and head are good to go.

Find another Z specific shop or a good VW mechanic, they ran those carbs too.

[7tooZ]

My 71 came with Weber’s when I bought it. It always smelled bad and loaded up all the time. The intake manifolds were part of the problem letting fuel build up in the manifold. I finally bought a set of ZTherapy SUs and have never regretted it. 
I remember hearing that the Weber’s were put on by shops to solve the tuning problem. Band aid solution. 

[Jaimebeflexin11]

Yeah I’m not great at tuning the carbs. I’m newer to working on cars so I’m not sure if maybe the carbs are not running effectively. I don’t really like taking the car in to the shop unless I can’t figure something out. It hardly backfires and starts up and idles around 700rpms. It just doesn’t have any power once I hit fourth gear or when going up hills. I’ll try to run it rich and see if that gives me anymore power. Maybe I’m running it to lean. 

[Zed Head]

Check the simple things like making sure the throttle blades open all the way.  You never know.