Datsun L16 running fine with no vacuum advance, but not when plugged in

[DirtnastyDatty]

Hello, so I've been trying to trouble shoot this for weeks and thought it was a vacuum leak, replaced carb spacers, problem persisted, ECT. But when the vacuum advance isn't connected, the engine runs just fine and doesn't seem like it wants to cut out in high rpms if I hold it there in neutral, when it's plugged it, it does exactly that, kinda sounds like it's running out of gas but it ain't, timing is advanced 10 degrees, done with generic timing light and scale on engine. Is it okay to run without vacuum advance? And any possible solutions? Thanks

[Doctor510]

Just plug the carb end of the vacuum line and check your total timing.  Leave the vacc adv unit alone, do not remove it cuz the breaker plate could move.

[datzenmike]

If running 10 degrees more timing of course it will act up when connected. You're way too advanced and then when vacuum advance is added it probably starts pinging. If you mean timing is set at 10 degrees try reducing it 2 degrees at a time till the problem goes away. I think old L16 is 6 degrees?

 

Things that can cause pinging...

 

Wrong plug make or heat range. NGK only on Datsuns!

Engine running tooooo hot

Wrong gas, poor gas. Try different brand or higher octane

Static timing too high, lower it.

Carb flooding, or rich causing carbon build up

Compression too high for the gas used.

 

 

 

Yes you can run without vacuum advance but it will affect part throttle performance and mileage.

 

 

All this shit was touched on in your other post on exactly the same thing......

 

You never answered what plugs you are using. Timing was suggested at 5 degrees. Follow through on suggestions so they can be eliminated and you can move on.

[DirtnastyDatty]

Well I tried the other suggestions and nothing seemed to work, will swap to ngk's but i retarded the timing and the problem still persisted, installed new carb plates because the others were leaking from a crack. Regapped the plugs as they were .040 and over, cleaned the distributor, leaned out fuel idle screw and that seemed to help, but I'll try higher octane as well. Also, this is unrelated but when I took off my valve cover soon could access the carb bolts and noticed my timing chain is pretty loose, I know they can usually be loose and tighten up with oil pressure but it just seemed a little more loose than average, is it bad to run it that way? (When I manually mess with the crank the chain slaps on the drivers side)

[datzenmike]

Plugs should be NGK B6ES and gaped to 0.032" for a stock L16 with points.

 

The fuel mixture screw only affects idle. Has no effect above idle

 

Retarded the timing to ... what? The '73 FSM says 5 degrees BTDC.

 

I'm going to assume that the timing chain is fine they usually are. If you don't know anything about the L series timing chain it may appear loose yet be totally fine. The test for looseness is to set to TDC and check the V notch on the back of the cam sprocket's relation to the horizontal etch mark above it. When the two are out of position and an adjustment fails to set it right... then the chain and or sprockets are considered loose or worn and need replacement. Remember that the engine turns clockwise and the chain on the right side as viewed from the front will always be tight. If you are moving the crank back and forth and getting the chain to slap the guide this is something that would never happen when running. Any looseness is always gathered on the left side as viewed from the front.

[racerx]

Well I tried the other suggestions and nothing seemed to work, will swap to ngk's but i retarded the timing and the problem still persisted, installed new carb plates because the others were leaking from a crack. Regapped the plugs as they were .040 and over, cleaned the distributor, leaned out fuel idle screw and that seemed to help, but I'll try higher octane as well. Also, this is unrelated but when I took off my valve cover soon could access the carb bolts and noticed my timing chain is pretty loose, I know they can usually be loose and tighten up with oil pressure but it just seemed a little more loose than average, is it bad to run it that way? (When I manually mess with the crank the chain slaps on the drivers side)

...why higher octane, running mine on 89 and no pungs, as mike said too,much gap on your plugs and when u say loose more than avg. Based on what?

[Doctor510]

Hello, so I've been trying to trouble shoot this for weeks and thought it was a vacuum leak, replaced carb spacers, problem persisted, ECT. But when the vacuum advance isn't connected, the engine runs just fine and doesn't seem like it wants to cut out in high rpms if I hold it there in neutral, when it's plugged it, it does exactly that, kinda sounds like it's running out of gas but it ain't, timing is advanced 10 degrees, done with generic timing light and scale on engine. Is it okay to run without vacuum advance? And any possible solutions? Thanks

Might be a vacuum leak via the diaphragm in the vac adv unit, maybe that's why it runs better unhooked.

[Cheetahking]

If running 10 degrees more timing of course it will act up when connected. You're way too advanced and then when vacuum advance is added it probably starts pinging. If you mean timing is set at 10 degrees try reducing it 2 degrees at a time till the problem goes away. I think old L16 is 6 degrees?

 

 

 

I would guess he is stating that timing at idle is set at 10 degrees BTDC - which is correct for stock 510 with dual points.  If SSS distributor (single points) - it will have a shorter mech advance on the cam and timing at idle is 14 Degrees BTDC.  

 

It makes sense to deal with the vacuum advance as it is a repeatable, changeable item that is affecting performance.  If you can suck on the hose for the diaphragm and it doesn't leak - the diaphragm is probably OK.  I imagine it is leaking and creating a vacuum leak like Doctor mentioned.  When you disconnect the line, are you plugging it - or leaving it open - when the engine is running well?

[datzenmike]

• Cars:Datsun 620 pickup

Well from the info supplied in the original post, it's an L16 from a 620. If this was another car it should have be mentioned again, and also the problem with double posting.

 

Vacuum advance is never from the intake directly. It's from a port on the side of the carb just above the throttle plate. At idle it 'feels' ordinary ambient air pressure present above the throttle plate, but as the throttle plate rises up to and above the port, more and more vacuum is sensed. There is no need to plug this ported vacuum source as first... there is none at idle and second it isn't a direct manifold leak.

 

It won't hurt to disconnect the hose from the port just in case the idle setting is too high and the throttle plate is at the port and some vacuum leaking into the line. This is why there is no mention of removing the vacuum advance hose when setting the timing. If this was an earlier 60s engine they will say this as the vacuum advance is directly from the intake. In the late 60s it was decided to switch to ported vacuum to retard the ignition at idle to reduce emissions.

 

Dual points are strictly a way of providing 4 to 6 degrees of retard under certain conditions to reduce emissions above idle.  

 

Yes, if you take the distributor cap off you can watch the rotor points plate advance (clockwise) if you suck on the hose. If you place your tongue over the end, the rotor should not return until you release it.

[Cheetahking]

I missed that - and the other post - my bad.  I have always assumed that distributors have probably been messed with/replaced etc. until I know otherwise (which is why its always good to know what your timing is all in rather than just at idle.