Shaking, back and forth motion at 1st and 2nd gear

[jalexquijano]

Okay! Suppose it is a vacuum leak! Besides of the brake booster braided hose and check valve, which other braided hoses (vacuum related) will need to be replaced? I even read in one fórum that it could be the brake booster leaking inside!!!!

Edited June 1, 2015 by jalexquijano

[Stanley]

So you checked the plugs and they're all still clean?

 

I suggest putting in a new PCV valve if you haven't done that already. It's about $3 I think. You can easily test it without any tools but I forget the details. It's in the FSM I think. Check PCV hose, Brake booster hose, and all other hoses and connections attached to the balance tube. PCV hoses go bad from the heat of the exhaust manifold; if it looks crappy suggest ordering a new one if it's leaking or not. But I think you'd easily hear whooshing when it's idling from any vacuum leak big enough to cause the problem. Sometimes you need to wiggle a hose to hear it whooshing.

 

When my brake booster got a leak I needed to step real hard on the brake to stop the car, and there was a whooshing sound when applying the brakes.

 

The big metal tube on the front of the block, that the PCV hose connects to, has a connection for another little rubber tube that goes to  the flow guide valve. If that system (except it's hose to the air cleaner which doesn't matter) isn't connected, might be a vacuum leak. See FSM for details and testing procedure. Possibly a gunked-up flow guide valve could stick open (mine was stuck closed until I cleaned it) and cause a vacuum leak, not sure about that though. You could put a rubber cap on that connection temporarily, to rule that out. 

[jalexquijano]

So you checked the plugs and they're all still clean?

 

I suggest putting in a new PCV valve if you haven't done that already. It's about $3 I think. You can easily test it without any tools but I forget the details. It's in the FSM I think. Check PCV hose, Brake booster hose, and all other hoses and connections attached to the balance tube. PCV hoses go bad from the heat of the exhaust manifold; if it looks crappy suggest ordering a new one if it's leaking or not. But I think you'd easily hear whooshing when it's idling from any vacuum leak big enough to cause the problem. Sometimes you need to wiggle a hose to hear it whooshing.

 

When my brake booster got a leak I needed to step real hard on the brake to stop the car, and there was a whooshing sound when applying the brakes.

 

The big metal tube on the front of the block, that the PCV hose connects to, has a connection for another little rubber tube that goes to  the flow guide valve. If that system (except it's hose to the air cleaner which doesn't matter) isn't connected, might be a vacuum leak. See FSM for details and testing procedure. Possibly a gunked-up flow guide valve could stick open (mine was stuck closed until I cleaned it) and cause a vacuum leak, not sure about that though. You could put a rubber cap on that connection temporarily, to rule that out. 

 

Ok Stanley,

 

Can you point out in the following picture where should i check? I have a Brand new pcv valve in my storage room. However, i think that my mechanic has already removed all the emmission crap from the balance tube. This is a picture of what i have on my engine. By the way, I have a Vacuum Test gauge, where do i plug it in to test any leaks. Please point out that also.

 

I really appreciate all your help to troubleshoot this back and forth issue.

[Patcon]

A video of what its doing might help the communication too.

[Stanley]

Wish my carbs and linkage were that shiny. The hoses look OK, you might check the PCV hose at that sharp bend. It's hard to tell with the braid cover on it.

 

To the left of the front carb, you see two hoses, the one from the vent of the float bowl lid, and the vacuum hose from the carb to the distributor. Between those two you can see a metal line with a hose attached to it. That metal line comes from the evaporation tank above the right rear wheel, and the rubber hose goes to the F.G.V. (flow guide valve) which is attached to the fender near the coil. There's also a hose from the air cleaner to the F.G.V. Air can flow from the air cleaner to the evap. tank if there's any vacuum. Gas fumes can flow from the evap tank to the F.G.V. and from there to the crankcase. But air can't go from the crankcase to the F.G.V. and out either of the other two hoses. If it does, the valve is shot and there's a vacuum leak.

 

I don't know how to use a vacuum gauge to find a leak, but it's handy to have, especially with SU carbs. I hooked mine to that  middle hole on top of the balance tube. Maybe I can find the photo.

[oranngetang]

A video of what its doing might help the communication too.

As would answering if you checked the plugs or not.

[jalexquijano]

I had an extra PCV valve! just replaced it yesterday! I will try the car today to see if the former pcv valve was shut!

[jalexquijano]

Sounds like a big vacuum leak or a fouled plug. If there was a vac leak big enough to cause that, you would be able to hear it by listening to the engine while the car is idling, unless it's a bad or clogged PCV valve.  Maybe you checked that already.

 

Cars don't lug (run under load in at too low rpm) very well with a fouled plug. If you slow down for a bump without downshifting the rpm drops, and if you have a fouled plug it would shake. When you bring the revs up it runs better. This happened to me recently. I cleaned the plugs (and leaned the rear carb) and that fixed it instantly. Plugs can foul fast, in a day or two.

 

Fortunately we have old cars so it's very easy to check and clean the plugs, unlike some new cars that require a wheel to be removed. I use a small wire brush, I get them in packs of three at O'Reilly for a couple dollars. Also some carb cleaner, good rubber gloves with big cuffs, safety glasses, and a disposable P-95 mask. I have a small ratcheting torque wrench set for spark plug torque per FSM, with a socket and extender. I pull one plug at a time, blast it with carb cleaner, give the tip and electrode a good brushing, blast it again, wipe the threads, and reinstall. Takes about 10 to 15 minutes to clean all the plugs if you're not in a hurry.

 

If it's not vacuum leak or fouled plug, or misplaced plug wires, that's good information, then you can rule that out and check other things.

Stanley,

 

Thanks for your valuable opinion, I already swaped the PCV valve and will change all the NGK BP6ES Spark plugs before testing the car again. My mechanic thinks he should look at the clutch to see if this could be the problem. I do not think so, as the car has no problems when shifting. Anyhow i decided to purchase the following braided hoses and parts from JDM to get them replaced:

 

http://jdm-car-parts.com/collections/hoses-pipes-valves-nissan-datsun-fairlady-240z-260z-280z-280zx/products/brake-master-vacuum-braided-hose-for-datsun-240z-260z-and-280z

 

http://jdm-car-parts.com/collections/datsun-240z-260z-280z-280zx-nissan-fairlady-z/products/brake-booster-check-valve-datsun-240z-260z-280z

 

http://jdm-car-parts.com/collections/datsun-240z-260z-280z-280zx-nissan-fairlady-z/products/brake-master-vacuum-braided-hose-intake-side-240z-71-73

 

http://jdm-car-parts.com/collections/datsun-240z-260z-280z-280zx-nissan-fairlady-z/products/pcv-braided-hose-for-datsun-240z

 

Please confirm which other vacuum hose or parts will i need to replace to narrow down any vacuum leak posibility.

 

Jorge

Edited June 3, 2015 by jalexquijano

[jalexquijano]

Just took my mechanic home to test the car and he had the following observations:

 

1. The glass fuel filter does not remain fully filled when turning the engine off. He recommends getting rid of the following electronic fuel pump which is installed in the rear axle:

 

http://www.summitracing.com/int/parts/crt-p60504/overview/

 

2. Once installing the former one which picture i have attached to and still Works, which i believe is an AIRTEX E8012S model. Tune up the carburetors again and this should solved the back and forth low rpm shaking.

 

Do you concur?

Edited June 3, 2015 by jalexquijano

[Zed Head]

Just took my mechanic home to test the car and he had the following observations:

 

1. The glass fuel filter does not remain fully filled when turning the engine off. He recommends getting rid of the following electronic fuel pump which is installed in the rear axle:

 

 

Do you concur?

This is not a sign of a bad pump. 

[Patcon]

I agree some air in the filter is not a s sign of a bad pump.

[jalexquijano]

This is the Actual fuel pump my car has installed near the gas tank, a Carter P60504. It used to measure 3 psi! I dont know it it is still reaching the same measurement.