Datsun Roadster Forum-311s.org

One more quick updates... So i checked for spark, that is fine. I also bought new plugs, gapped them and installed. still no combustion. Not even a putter. At this point I have the carbs set to 2.5turns from full lean, checked timing again against the crank, checked spark, wire order again, I am really at a loss for what to do.

I understand your frustration. I have been there before too with old motorcycles. I like to keep things simple, and here is a thought process I typically go through for such situations.

Does it have good compression? This can tell you a lot about the condition of the valves, pistons, rings and cam timing and whether it is getting air
Does it have spark?
Is the spark occurring at the correct time? I often set the timing statically to start with and then use a timing light once it is running to fine tune the timing.
Is it getting fuel? If it will fire on starting fluid, but won’t continue to run, it has a fuel issue.
Is it getting the correct mixture of fuel and air? (Vacuum leaks, carburetor set-up, etc.)
Is it flooding? Are the spark plugs wet with fuel?
Are the plugs fouled with oil? (bigger deal on 2-strokes, not so much our cars)

I hope this is somewhat helpful.
Steve

If you crank any motor for ten seconds and it doesn't start the plugs should have gas on them. Otherwise it is not getting any gas. The soot could be from running too rich prior to an interruption of the fuel supply.

A short shot of starting fluid will tell you if it's fuel. Just a quick hit, don't try to run it on the stuff as it will wash the oil off pistons. But that will tell you if it's fuel.

Anybody nearby who can take a look?

Ether has been know to do a lot worse than just wash oil from the cylinder walls, especially in high compression engines.

Thanks guys for the guidance! To answer some questions:

1. it does have good compression, tested it when I started having these issues.
2. It does have spark, I have an in-line light that flashes when there is a spark signal. Super handy.
3. I now have some doubts... Ill try starting fluid tonight. The gas is a bit old but I figured if it ran several times already on this tank, the fuel is good enough. Ill also check the little hoses connecting the float bowl to the jet it may have gotten kinked or clogged?
4. I have the carbs/intake manifold cranked down as hard as I can, at this point, I worry about stripping something if i go tighter.
5. as of the last time it ran, the plugs showed lean condition. checking the plugs after cranking a while does not show flooding which points back to fuel.
6. no oil on plugs.

A few notes about fuel, I know the pump is good, i have two filters in line before the pump and my pressure regulator reads 3psi. So I am fairly confident about fuel flow up to the carburetor.

Ill try after work today and report back.

oh and spark timing is at least good enough for the engine to run. its not like the engine has not yet run, it does but just not for long.

The fact that it doesn't run long hints at the floats and needle valve in the fuel bowl may need some attention

a bit of discussion on the SU carbs to consider, (apologies if you already know this)
1) The fuel bowl float allows fuel in by actuating a needle valve, float needs to be set correctly and free to move to engage needle vale. The needle in the valve also should move in and out easily
2) As the jet nozzle lowers (with the mixture knob) more fuel flows from the bowl to the jet (makes mixture richer) - the fuel level is uniform across the fuel bowl and the jet.
3) The jets should move easily up and down. When you pull the choke cable, you will be pulling the jet nozzle down, letting more fuel in. You should be able to pull the jet nozzle down with you hand (car not running) and it should pop back up on its own, if not it may need to be cleaned and lightly lubricated. A spray of carb cleaner and WD40 should help free it up.
4) One way to check fuel bowl level is to remove the dome on ONE carb, remove the piston and needle (carefully) and observe a small puddle of fuel at the jet nozzle opening. If not present, try lowering the jet with mixture knob, if you can't get the fuel puddle, then the float in fuel bowl is incorrectly set or needle valve is blocked. Pistons and domes are matched set so only look at one carb at a time so that you don't mix them up.

Other things to look at while dome and piston are out is wear on the piston needle (shiny marks) and an oblong hole in jet nozzle (vs. round hole). These can cause poor engine performance and make it hard to tune/dial in.

Thanks for that, Ill take a look today as well, The carbs were rebuilt about 2 years ago (<5k miles) by ztherapy. So I would be shocked to see wear but it never hurts to check. my only concern is I dont have any spare gaskets for the float bowl so a bit hesitant to crack one open...Ill save that for last resort if all the other tests you mentioned fail.

Agree that there should be no wear or tear on your rebuilt carbs. Best guess is some contaminate from the old fuel might be hanging something up...

Why not take a video of the engine starting post to yt
Spark dies with compression

redroadster wrote: Mon Mar 08, 2021 6:17 pm Why not take a video of the engine starting post to yt
Spark dies with compression

Ill take some video if I can.

Okay, so tonight, i did a lot.

To start with, I bought some fresh gas and starter fluid. Using just starter fluid, the engine turned over and ran for a few seconds. Good sign! So I dismantled the carbs, each separately and checked for fuel which looked good, pushing down the jet showed a bit of fuel bubbling up. I set the jets at 3 full turns from full lean. Then I did a cold start, i was not able to film this but it started pretty much immediately. I was able to adjust the carbs so it idled although rather high, anything below 1500rpm and it would want to stall. Once warm, I went ahead and set the timing to 16degrees BTDC. You can see all this in this video.

Datsun 1600 Cold Start Video

After that, I turned the engine off and tried to start again.... Nothing. I had to set the phone down to operate the throttle, getting it to stumble a bit but not start.

Datsun 1600 Warm Start Attempt Video

After this, I pulled the plugs to see if I was possibly in a flooded condition in the cylinders.

Cylinder 1


Cylinder 3

OH! Don't mind the temp/fuel, they are known bad gauges. I believe my fuel sender is bad as I already replaced the temp sender and they will work and stop working intermittently. Today, I guess they didn't feel like working. Also, all the dried coolant on the tower is due to not tightening the thermostat tower down enough. It is water tight now but have not had a chance to clean everything up.

Good stuff, you are getting close. On the restart, it sounds like the timing is off. I am thinking 16 BTDC at 1500 rpm is probably retarded at idle as the timing advance is likely on at that rpm. two thoughts, 1) disconnect the vacuum line from the distributor advance diaphragm and see what happens on restart. Set the idle timing (16 BTDC) at 750 rpm if you can with the vacuum advance disconnected. Also, when you get it started again, use the timing light to observe the crank timing marks when you blip the throttle to see how far it advances (read the marks on the damper, not the dial on the light - set the light dial to 0) 2) If cranking and no fire, try the starting fluid again...my WAG is there is vapor lock somewhere (being in Denver) but it looks like you have all the lines covered. Do you have a fuel return line connected? I doubt that it's vapor lock but the only other thing I can think of.

The high idle may be a vacuum leak somewhere - make sure all unused vacuum ports are plugged. You can spray gasket interfaces with carb cleaner to see if the engine reacts. I know you said everything was tight...

This is one of the best technical write ups on the311s site from Keith Williams and touches on timing, a lot on carbs and some valve settings - suggest you read through it and it might help you diagnose:
http://311s.org/pmwiki-311/pmwiki.php?n ... sNewSuTech