Vacuum leak gremlin wreaking havoc ; (

[Angela]

Ok, so I thought I'd be starting the summer months enjoying the car show circuit....maybe even being brave enough to drive my 'Goon to the Eagle Rock show now that the freshened L16/closed chamber A87 peanut head & new 5 speed was installed but it appears I have a vacuum leak & my poor wagon is essentially parked

[datzenmike]

The studs and nuts for the adapter between the carb and the intake are known to come loose and the gasket then leaks. Over tightening can also crack the adapter. Use a thread sealer to prevent the bolts coming loose.

 

You don't have a header on her do you?  Only stock intake and exhaust?

[Doctor510]

Mike posted while I was posting, sneaky dude.

 

A hidden vacuum leak on a 510, well, let me think.  Disconnect the vacuum line from the distributor advance canister and plug it, the line not the canister), see if that helps.  What carb are you running?  If stock one, the vacuum secondary diaphragm may be leaking.  If Weber , be sure that you are not leaking around the adapter plate, check with carb cleaner while idling.  Be sure the PCV valve is tight.  Good luck.

[Angela]

The studs and nuts for the adapter between the carb and the intake are known to come loose and the gasket then leaks. Over tightening can also crack the adapter. Use a thread sealer to prevent the bolts coming loose.

 

You don't have a header on her do you?  Only stock intake and exhaust? ]Mike posted while I was posting, sneaky dude.

 

A hidden vacuum leak on a 510, well, let me think.  Disconnect the vacuum line from the distributor advance canister and plug it, the line not the canister), see if that helps.  What carb are you running?  If stock one, the vacuum secondary diaphragm may be leaking.  If Weber , be sure that you are not leaking around the adapter plate, check with carb cleaner while idling.  Be sure the PCV valve is tight.  Good luck.

 

Thanks Mike & Dr. 510!

 

I'll check those studs & the adapter. I'm running a Weber DGV 32/36 with a cannon intake manifold & stock everything else...even air cleaner (using an adapter). I believe we did check the PCV valve, used plumber's tape on it & tightened it back down. I was beginning to worry I was looking at having stuff machined or finding some sort of gushy gasket to help even out the mated surfaces. Feels like I'm chasing gremlins.

[Stoffregen Motorsports]

It's not likely in your case since you said it ran fine and then it didn't, but it may be worth a shot to check the gasket surface on both the head and the intake manifold. For some reason, in the past decade or so it has become industry standard to clean off old gasket material and RTV with a Scotch-Brite Roloc disc on a air grinder. The results of this method often leaves surfaces wavy enough to surf on. If you have done this to your intake or head it is a possibility that the gasket has lost it's seal and is leaking.

 

Depending on how bad the surface are, you can clean them up with a block of alunimum wrapped in 220 grit emery paper (or wet sandpaper). Lubricate the cutting with WD40. It may take a few minutes on each surface, but it can be restored.

 

Also, most people don't but I actually torque the bolts and studs that hold the intake and carb on. I have seen a lot of them over-torqued and warped or cracked as a result.

 

Have you tried pulling the PCV hose off and plugging the valve with your finger while it's idling? If it gets better, this may be your problem. Another source of vacuum leaks that often gets overlooked is the vacuum advance unit inside the distributor. They do go bad over time.

[datzenmike]

Vacuum advance shouldn't affect it. It's a port just above the throttle plate, so little to no vacuum sensed at idle. As the throttle opens the plate rises up to and above the port sending vacuum to the distributor. This is so that there is no advance at idle and effectively you are running on your static 12 degrees advance set with a gun.

 

Totally an emissions thing imposed on all cars from the late '60s. Before this distributors ran manifold vacuum, about 18 in hg. (at idle) and why it was always stated to disconnect the hose and plug it when timing these engines. Engines like lots of advance at low throttle opening and idle even more so. Next time you are timing your distributor set to 12 degrees and note the idle. Now advance the distributor and notice the idle jumps up and runs smoother and faster than at 12. Having no vacuum advance at idle is effectively running the engine retarded. It is no good for idle quality but it does reduce emissions dramatically..

[Stoffregen Motorsports]

You're right.

[datzenmike]

But not as good as a broken clock. It's right twice a day.

[Angela]

The studs and nuts for the adapter between the carb and the intake are known to come loose and the gasket then leaks. Over tightening can also crack the adapter. Use a thread sealer to prevent the bolts coming loose.

 

You don't have a header on her do you?  Only stock intake and exhaust?

 

Mike posted while I was posting, sneaky dude.

 

A hidden vacuum leak on a 510, well, let me think.  Disconnect the vacuum line from the distributor advance canister and plug it, the line not the canister), see if that helps.  What carb are you running?  If stock one, the vacuum secondary diaphragm may be leaking.  If Weber , be sure that you are not leaking around the adapter plate, check with carb cleaner while idling.  Be sure the PCV valve is tight.  Good luck.

 

 

The studs and nuts for the adapter between the carb and the intake are known to come loose and the gasket then leaks. Over tightening can also crack the adapter. Use a thread sealer to prevent the bolts coming loose.
 
You don't have a header on her do you?  Only stock intake and exhaust? ]Mike posted while I was posting, sneaky dude.
 
A hidden vacuum leak on a 510, well, let me think.  Disconnect the vacuum line from the distributor advance canister and plug it, the line not the canister), see if that helps.  What carb are you running?  If stock one, the vacuum secondary diaphragm may be leaking.  If Weber , be sure that you are not leaking around the adapter plate, check with carb cleaner while idling.  Be sure the PCV valve is tight.  Good luck.

Thanks Mike & Dr. 510!

I'll check those studs & the adapter. I'm running a Weber DGV 32/36 with a cannon intake manifold & stock everything else...even air cleaner (using an adapter). I believe we did check the PCV valve, used plumber's tape on it & tightened it back down. I was beginning to worry I was looking at having stuff machined or finding some sort of gushy gasket to help even out the mated surfaces. Feels like I'm chasing gremlins.

 

 

It's not likely in your case since you said it ran fine and then it didn't, but it may be worth a shot to check the gasket surface on both the head and the intake manifold. For some reason, in the past decade or so it has become industry standard to clean off old gasket material and RTV with a Scotch-Brite Roloc disc on a air grinder. The results of this method often leaves surfaces wavy enough to surf on. If you have done this to your intake or head it is a possibility that the gasket has lost it's seal and is leaking.

 

Depending on how bad the surface are, you can clean them up with a block of alunimum wrapped in 220 grit emery paper (or wet sandpaper). Lubricate the cutting with WD40. It may take a few minutes on each surface, but it can be restored.

 

Also, most people don't but I actually torque the bolts and studs that hold the intake and carb on. I have seen a lot of them over-torqued and warped or cracked as a result.

 

Have you tried pulling the PCV hose off and plugging the valve with your finger while it's idling? If it gets better, this may be your problem. Another source of vacuum leaks that often gets overlooked is the vacuum advance unit inside the distributor. They do go bad over time.

 

 

Vacuum advance shouldn't affect it. It's a port just above the throttle plate, so little to no vacuum sensed at idle. As the throttle opens the plate rises up to and above the port sending vacuum to the distributor. This is so that there is no advance at idle and effectively you are running on your static 12 degrees advance set with a gun.

 

Totally an emissions thing imposed on all cars from the late '60s. Before this distributors ran manifold vacuum, about 18 in hg. (at idle) and why it was always stated to disconnect the hose and plug it when timing these engines. Engines like lots of advance at low throttle opening and idle even more so. Next time you are timing your distributor set to 12 degrees and note the idle. Now advance the distributor and notice the idle jumps up and runs smoother and faster than at 12. Having no vacuum advance at idle is effectively running the engine retarded. It is no good for idle quality but it does reduce emissions dramatically..

 

 

 

UPDATE: Still chasing gremlins it seems : (

 

PLEASE FORGIVE ME IF WHAT I'M ABOUT TO WRITE IS CONFUSING…I'LL TRY MY BEST TO BE DESCRIPTIVE , IF NOT SOMEWHAT CLEAR : )

 

(I value & respect the advice I've been offered & don't want to put anyone off because I'm a newbie trying desperately to understand the car I love).

 

So, I checked everything you guys threw out there (thanks again) & my mechanic friend & I checked the surfaces & everything was trued up & not warped. (cool). We then cleaned everything up real nice & installed a Remflex gasket that's guaranteed to stop any leaks, etc. Put everything back together & started her up and took her for a spin. She was zippy & sounded pretty good but when we attempted to take a steep hill, she became gutless again & wanted to die. We had to climb using only 1st gear to make it up.

 

(We ran short on time yesterday so we didn't get a chance to check for leaks again or adjust timing after the new gasket install but we're going to hit it again next Monday.)

 

At one point during this whole issue (several weeks ago) he raised the float level to what was recommended (by Weber?) when rebuilding the carb. He said it looked like someone had gone through it already 'cos it looked pretty good all the way 'round. We had played with different jetting going large, then small as he was trying to figure out my problems.

 

When we 1st dropped this other motor/trans in (L16/A87 closed chamber/5 speed) back in March, my Datsun buddy got it timed & dialed in pretty good but thought the idle was a bit high & it was running either rich or lean (can't remember 'cos it's been back & forth) but I was able to zip up a decent hill/grade in 4th gear w/o issue. I drove it around for a few weeks, & suddenly she started acting fussy…dieseling, not wanting to stay running without the choke pulled about half way, etc. I took it into a dealership where a real Datsun enthusiast works to have him go over everything & adjust valves, etc. Seemed to be o-k-a-y but he didn't take it up a hill. My issues seemed to continue & he's real expensive so I went with a guy who comes out to the house & who's been working on my mom's '65 mustang. He's a Master Mechanic & affordable but not much experience with Datsuns. He's more a VW Baja dude but really patient & curious to learn what's going on with my car. He spent hours helping me out yesterday & didn't charge me a dime 'cos we haven't figured it out yet. 

 

Ok, so next week we'll check timing, any additional leaks, adjust float level (?) & then what? Any ideas? I need help & am dying to just drive my wagon (hopefully to the Eagle Rock Show!).

 

Anything anyone has to offer up for ideas or to share similar experiences would be most-appreciated.

 

Thanks!

[Doctor510]

Sounds like 2 two possibilities:

 

1  timing chain has stretched and the cam is so retarded you loose power, check the cam timing

 

2  Total timing is way off, should be 34-36* BTDC, leave the idle timing setting alone after you set the total timiing

[Stoffregen Motorsports]

Is it heat related? I mean if yo got in it and fired it up and immediately took off up that steep incline, would it be any better? If yes, then vapor lock or ??? If no then on to the next possibilities.

 

Does your new mechanic know how to check cam timing (the right way with a dial indicator) ? Has he checked initial and total ignition timing? Does he know the difference? Has anyone verified TDC (by removing a spark plug and bringing the #1 piston all the way up and checking it against the timing poiinter) ?

 

What sparks plugs are you using? Should be NGK B6ES or equivilent. Do not use spark plugs with a projected tip (NGK BP6ES would have a projected tip, hence the P) until you get this situation figured out.

[Angela]

Just wanted to thank everyone who took the time to comment or give advice for my 'Goon's gremlin issues. My mobile mechanic finally gave up so I took it back to my Datsun enthusiast mechanic that costs an arm & a leg. He discovered someone (previous owner of this newer L16 I just put in) had drilled a hole in the carb for whatever reason (better performance at high RPMs ?) Anyway, he soldered the hole & made adjustments that've helped but he says I need to just get SSS Dual Su's to replace the Weber 32/36. Today I was tinkering on my car with my other Datsun buddy & found the fuel pump was failing. We found a small hole in the diaphragm & replaced it with a spare from his horde. Haven't tested her going up hill yet but I'm hoping to soon. She runs pretty good now but there's some uneven idling that still concerns me.

 

Anyone out there in the community have any leads on finding SSS Dual SU's with a 220 intake? I'll be going to the Eagle Rock show to search for some but just scouring any leads I can at this point.

 

Also, any advice on weather or not I should keep the stock, never rebuilt L16 with stock Hitachi carb, & 4 speed transmission etc? I was thinking I should hold onto it "just in case" but it is taking up space in my folk's garage & I doubt I'd ever go back to a 4 speed & still not sure about the engine. Pro's? Con's? Advice welcome : )

[datzenmike]

Fuel filter or lines clogged? Can't supply enough fuel in high demand situations like climbing hills?

[Stoffregen Motorsports]

This is a common misconception, that SU's are somehow better than a DGV. Actually, a two barrel downdraft Weber outperforms SU's in all aspects. Idle is better, tuning is easier, CFM ratings are higher for better wide open throttle performance.

 

If you're concerned that the DGV is the problem, it would be easier and cheaper to buy a new DGV and bolt it to the manifold you are using now.

 

Where in CA are you? I'm near Sac and would be willing to help.

[Angela]

Ahhhh thank you so much. I'm in central California in Atascadero/San Luis Obispo. Any & all help is very welcome.

Thx!

Angela

[Doctor510]

Disconnect the vacuum line at the unit and plug it.  If the diaphragm is broken it will leak.

[Stoffregen Motorsports]

Ahhhh thank you so much. I'm in central California in Atascadero/San Luis Obispo. Any & all help is very welcome.

Thx!

Angela

Hmmmm...

 

I'm an easy 4 1/2 hour drive from you.