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L20b no power under load help


MapleNuts

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I have a 75 610 wagon i just rebuilt the carb on.


When the car is in park it idles a little rough at normal rpm, so i have it idle at little higher rpm and it seems to run smoother.


But when i put it into gear it suffers a lot, and It nearly stalls out when set at normal rpms when put into gear.


Could this be due to vacuum issues/leaks. I haven't checked the pressure off a vacuum line yet.


I have new park plugs in, cleaned the rotor and cap, and the points seem to be making decent spark so dont think it is electrical.


Anything helps, just want to see this baby on the road again! Thanks!


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Having rebuilt the carb likely something is out of whack.

 

Listen near the back of the carb and have someone turn the ignition on off on off (not start) You should hear a clicking sound from the idle cut solenoid. Without this, there will be no fuel getting to the idle circuit.

 

Check the bolts holding the cab on, are they tight? Did you use a new gasket on this?

 

Look for vacuum leaks.... cracks in the large hose from the intake to the brake booster. The fitting on the intake for this also has a smaller hose to a metal line down to the automatic transmission... is this on and secure? There is a vacuum line to the air filter underside. Is it in place and secure??? There is a vacuum line to the AB valve behind the carb. Is it on?

 

Find the EGR valve, remove it and wire brush the exhaust deposits from it. If dirty the valve won't close properly and leak vacuum at idle.

 

 

Before adjusting the mixture on the carb be sure that the valve lash is correct and the ignition timing set properly. This is important and if not set you will have to reset the idle mixture over again when you do... so do it first.

 

Now...

Set the idle so it will at least run. Turn the idle mixture screw in or out to find the smoothest fast idle. There will be about one full turn where it runs well and drops off on either side. Set roughly in the middle of this. Turn the idle speed screw back down. Turn the idle mixture screw in or out looking for the smoothest fast idle, set about in the middle of this range and turn the idle speed down. Repeat this until you cannot improve the idle quality and the idle is about 750-850. If it takes 7 tries then that's what it takes. 

 

If timing was properly set and the valves adjusted the idle should be nice and strong now.

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Having rebuilt the carb likely something is out of whack.

 

Listen near the back of the carb and have someone turn the ignition on off on off (not start) You should hear a clicking sound from the idle cut solenoid. Without this, there will be no fuel getting to the idle circuit.

 

Check the bolts holding the cab on, are they tight? Did you use a new gasket on this?

 

Look for vacuum leaks.... cracks in the large hose from the intake to the brake booster. The fitting on the intake for this also has a smaller hose to a metal line down to the automatic transmission... is this on and secure? There is a vacuum line to the air filter underside. Is it in place and secure??? There is a vacuum line to the AB valve behind the carb. Is it on?

 

Find the EGR valve, remove it and wire brush the exhaust deposits from it. If dirty the valve won't close properly and leak vacuum at idle.

 

 

Before adjusting the mixture on the carb be sure that the valve lash is correct and the ignition timing set properly. This is important and if not set you will have to reset the idle mixture over again when you do... so do it first.

 

Now...

Set the idle so it will at least run. Turn the idle mixture screw in or out to find the smoothest fast idle. There will be about one full turn where it runs well and drops off on either side. Set roughly in the middle of this. Turn the idle speed screw back down. Turn the idle mixture screw in or out looking for the smoothest fast idle, set about in the middle of this range and turn the idle speed down. Repeat this until you cannot improve the idle quality and the idle is about 750-850. If it takes 7 tries then that's what it takes. 

 

If timing was properly set and the valves adjusted the idle should be nice and strong now.

Thanks for the help! turns out there was a vacuum line on the manifold hiding from me under the carb. couldn't find any loose lines it might have been connected to so i plugged it up and now its running just fine! 

 

You seem like you know a decent amount, so if i could pick your brain for one last thing that would be great!

couldn't find a clear answer on this so do you know if the 280zx front suspension+brakes will work on my car (75 610 wagon).

Thanks again

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Micromachinery can confirm this but, yes, I believe it will, just like the zx struts will fit almost all Datsun cars. You will have to remove the zx lower spring perch, spring and top hat as these are too wide to fit the 610 strut tower. In their place you 610 parts will fit instead. At this time you have the option to cut the spring to increase the spring rate or replace with boughten stiffer springs. The lower 610 spring perch can be clamped in place with split collars ($30 or less) or you can get adjustable coli over sleeves for a lot more that go about the same thing. These collars will still need clamping or welding in place.

 

 

Some things t think about before you jump on this popular strut swap....

 

The zx struts will likely upset your camber towards the positive or the top of the tire leaning outward from the vehicle. Camber plates can remove some or all of this.

 

The zx strut will also lower the ride height and you may even add to this. Either way this will upset the steering geometry in two ways. It will right away show a toe out, that will need adjusting in, to a straight ahead position. The side to side steering center line will be lower (because the body that holds the steering components is now lower) than the connection to the struts at the knuckle arm.  Now when traveling over a rolling road the tie rods will tend to pull the rears of the front tires inwards causing a brief toe out which affects the handling caller bump steering. This can be eliminated by adding 'bump steer' spacers on the bottom of the strut where the knuckle bolt on bringing the steering components back to their horizontal position again. 

 

One last thing is the brakes. The larger front calipers will need more fluid to work them. Your 610's 3/4" master will have to move farther to provide it. This extra travel will make it seem mushy. No worries, it will still work but just be a little soft. What you can do, is replace it with a larger diameter like a 13/16, 7/8 or even the 15/16 like the on on the zx you got the struts from.  I have Maxima struts and brakes and they also used the 15/16" master and this is what I did.

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That's merely some of the things that you should research yourself before doing this so there are no surprises. The zx strut swap is probably one of the most documented strut swaps there is and extremely popular. The brakes are nothing short of superb, specially with today's rims and grippier tires. Lowering the ride height also lowers the vehicle center of gravity making it much more stable in turns and lessening weight transfer to the front when braking. 

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