my 1932 datsun replica build

This is abso-berkeleying-lutely the BEST news i have read on the forum this month.

Fantastic!! What a journey!

Awesome man, glad to see all the progress!

Sweet!!

Perseverance.

Good news: the car is running again!

Bad news:  It broke down two weekends ago on the way to our street rod club's weekly breakfast.  Apparently, those MSD electronic ignitions need to have electrons in order to ignite the gasoline.   Who'd have thought?  

We were on the way to breakfast, with the Mrs. driving in back of me in her car in case I had a problem.  (I'm expecting a newly legal project car to have some teething problems.)  After the meal, one of the guys jumped the car and we limped back home.  It took two more jumps from the Mrs.'s car before we made it back. 

Quite the adventure.  Here are pics.

Later in the week, a flatbed tow truck took the datsun back to our mechanic.  She had burned up an alternator, and did it again while at his shop.  I'm not sure what he changed to make the car break this habit, but I know that today I went to pick her up, and was able to drive her home.

Is anybody else having trouble seeing those two pictures of the wife jump starting my car? I uploaded them, so I doubt it is a website permission issue....

The picture with the following address is unavailable:

https://photos.app.goo.gl/1vaXfKZsuuHceQNY9

I haven't had a lot of success trying to link to my Google folders either.  With the current ability to directly upload pictures, linking really isn't required anymore.

In reply to jstein77 :

Okay, that makes sense. Here are the highly anticipated photos of me getting a jump start.

Today's drive was uneventful

Last weekend I made it to my first CFSRA breakfast with a street rod; ie we did not get stranded in route this time.  Most of the folk s were very accepting of my little built-from-trash car..... Lots of nice comments.

OTOH, there *were* issues during the drive:

1. The speedometer cable broke.  (It is now replaced.)
2. The brake light stopped working.  (A wire to the switch had come off.  It is now back where it belongs.)
3. The car idles nicely, and runs okay when it is revved up a bit, but in between those states it misses, chokes, backfires, and tries to die.  (I still don't know what's causing that.)

I'm planning to try taking it tomorrow to our monthly club meeting.  Wish me luck. Here is a photo of the new speedometer cable.

Is it carbureted? If so the spits and sputters could be the accelerator pump not working or not giving a big enough squirt. 

No accel pump on Hitachi SUs.

Could be the pistons in the carbs are dry or sticking, is there oil in the dashpots?

Toyman01 said:

Is it carbureted? If so the spits and sputters could be the accelerator pump not working or not giving a big enough squirt. 

Yes, carbureted.  We took the fuel injected maxima intake off.It has a 240Z intake with a pair of Mikuni SU carbs.

ShawnG said:

No accel pump on Hitachi SUs.

Could be the pistons in the carbs are dry or sticking, is there oil in the dashpots?

Yes, there should be oil; it was filled up two weeks ago and that stopped it from running pig rich and shooting flames when it backfiredI've been told to use transmission fluid in the dashpots.  Now I'm wondering if that's the problem.  The Z-parts site says they are using a mixture of motor oil and machine oil.  Do you think that this throttle problem could be an oil viscosity issue? 

FWIW, the black cap on one of the dash pots is broken.  Could that be causing the issue?

Everyone seems to have their own "mystery oil" formula for the dashpots. I think just having oil in them is the most important thing.

Every set I've rebuilt has gotten ATF and worked well, the two Brit car guys I hang out with say the same.

Lift the piston all the way up with your finger and let it drop, it should be nice and smooth in both directions. If it's sticking, that would be a problem. The ok at idle, ok once it gets to rpm thing tells me that the pistons might be moving too slow. Maybe a lighter oil like 3-in-1 or sewing machine oil might do it.

I'm no expert on SU carbs, just relaying what I know from rebuilding 4 or 5 sets now.

JoeyM said:

The car idles nicely, and runs okay when it is revved up a bit, but in between those states it misses, chokes, backfires, and tries to die.  (I still don't know what's causing that.)

Here's video showing the problem.

Well, I can't help with the carbs but it definitely sounds like it's running out of fuel in transition. 

ShawnG said:

Lift the piston all the way up with your finger and let it drop, it should be nice and smooth in both directions. If it's sticking, that would be a problem. The ok at idle, ok once it gets to rpm thing tells me that the pistons might be moving too slow. Maybe a lighter oil like 3-in-1 or sewing machine oil might do it.

I'm no expert on SU carbs, just relaying what I know from rebuilding 4 or 5 sets now.

OK, that seems plausible.  I know you're just going by my description of the issue.  I just uploaded a video of the problem occuring.  If you have time to look, you will see three attempts to rev it up.

1. Revving strongly to a higher RPM, with no problem
2. medium RPM (nearly dying), then backing off to idle
3. medium RPM (nearly dying), then revving past that point to where it runs well again.   

EDIT:. I know I need to read this thread.  Please suggest any others that you think would be helpful

https://grassrootsmotorsports.com/forum/grm/su-carb-help/48501/page1/

I'm going to say that the uncapped port on the manifold in the center of that video is a good place to start. 

If you had a backfire before you sorted the carbs, it may have blown that plug off somewhere and you didn't notice.

ShawnG said:

I'm going to say that the uncapped port on the manifold in the center of that video is a good place to start. 

That's actually a cap for a different size port that I'm using as plug; i.e. it is closed on one end and not a tube. 

Good suggestion, though, because it got me looking for other uncapped/unplugged things, and I found a  tube on each carb that needs to be closed off....those are where I will begin to focus my efforts.  

I don't know anything about those carbs, but just a thought ... Those tubes wouldn't be vents to atmosphere, I hope?    (Ask me how I know they need vents ... Or better yet lets not talk about it. !)

I had those same carbs on my L28 lemons engine.  Which port on the carbs did you find unplugged?  There's a vent on the fuel bowl of each carb, that shouldn't be plugged, but you can put a hose on it and run the hose somewhere safe in case the bowl overflows.

Do both dashpots drop at the same ish rate and drop completely? I had one that kept getting stuck before it came down all the way.  I had to adjust the dome a couple of times to get it centered, then both pistons behaved well.

Next thing is to look for vacuum leaks - see if it's pulling air in past the throttle shafts.

With the dashpots behaving and vacuum leaks fixed, it's time to balance the carbs.  I remember using a unisyn to check balance the carb and check idle mixture (idle should go up a little then settle.  If I remember correctly... If it dies, it's too rich, if it races too lean.  I don't remember how I adjusted the airflow.  Note, as you mess with idle mixture, airflow changes too.

03Panther said:

I don't know anything about those carbs, but just a thought ... Those tubes wouldn't be vents to atmosphere, I hope?    (Ask me how I know they need vents ... Or better yet lets not talk about it. !)

Oooh..Thank you!!!  I appreciate the heads up, and didn't know.....I'm better at pounding on metal until it resembles a car than I am at making a car move 

Brotus7 said:

I had those same carbs on my L28 lemons engine. 

Good, I need your advice.  This is all scary voodoo stuff to me.

Which port on the carbs did you find unplugged?  There's a vent on the fuel bowl of each carb, that shouldn't be plugged,

With my luck, that's probably the ones

but you can put a hose on it and run the hose somewhere safe in case the bowl overflows.

This is a good idea, since the carbs are directly above the exhaust manifold and pretty side pipe; there's lots of hot metal in that region

Do both dashpots drop at the same ish rate and drop completely? I had one that kept getting stuck before it came down all the way.  I had to adjust the dome a couple of times to get it centered, then both pistons behaved well.

Next thing is to look for vacuum leaks - see if it's pulling air in past the throttle shafts.

With the dashpots behaving and vacuum leaks fixed, it's time to balance the carbs.  I remember using a unisyn to check balance the carb and check idle mixture (idle should go up a little then settle.  If I remember correctly... If it dies, it's too rich, if it races too lean.  I don't remember how I adjusted the airflow.  Note, as you mess with idle mixture, airflow changes too.

Brotus7's advice sounds spot on. From your picture and his explanations, I assume those are vents.  

I started learning multi carb setups on bikes almost 40 years ago, but haven't worked much on them furin' cars! The smaller carbs on bikes helped me learn car carbs. Small carbs, multi or single, are less forgiving than getting a street car close enough, but I can "hear" the state of tune better on the small stuff. Twin SU's on an engine they didn't come on, would not be the be the best place to learn air fuel mix stuff on!  Course neither was 4 carbs on a CB 750F, but I was too young to know my limitations. I wouldn't have the nerve to tackle 'em today.  I'm older, a little bit wiser, but my brain ain't what she used ta be. Anybody that can build a car from scratch from appliances, has the nerve to learn what ya need to do most anything

Your welcome to pm me; well make some time to chat on the phone. I won't be much help, but I can explain what I learned back then!

I have made a poor attempt to find this info, but can't - what are the SUs off of?  British something?  Early Z?

Do you know the year of the carb donor?