Datsun Roadster Forum-311s.org

Yeah, Rear carb looks to be starving !

The S bend of the tank is 1/8 " new with calcium build up less ,I removed mine and cleaned the tank found a sock filter/Screen that fits on pickup tube , but best to run a upward U line on the back of interior underneath so in a crash ,& fuel line gets cut, it doesn't keep siphoning out the gas under it

JacobWisdom wrote: ↑Wed Mar 20, 2024 12:40 pm In the meantime unless someone with authority tells me it won't work, I'm going to try the 2L needles to see if I can at least get it to run through the full power band under load.

Going to address this question first , this will not work properly unfortunately,
Notwithstanding the fact that their profile and therefore fueling characteristics are totally different just for the simple reason that they are different size and length.

This is the Internet, so you will encounter a wide range of opinions. Take these as you wish, but here are some facts to use as a baseline:

• A 1600 38mm SU carburetor, while not the first choice for performance applications, can function adequately on a stroker engine and will run to 5500 rpm+ without issues if it is in good condition.

• Most stock SU 1600 carburetors tend to run rich and fat at idle and then lean out significantly starting at the upper mid-range. This issue is amplified with a stroker motor if stock needles are used.

• A stock mechanical fuel pump in good condition will provide adequate fuel for a stroker engine.

One thing I've learned about these cars is that whatever you think the problem might be, it's probably timing-related, and I've found this to be true in 90% of cases. Even though you've eliminated potential timing issues by replacing ignition components, I would still double-check. Make sure the TDC (Top Dead Center) mark is actually correct.

Next, I suggest installing an O2 sensor to monitor what's happening with the fuel mixture. If it goes way lean, then you have some guidance. It's easy to go on a wild goose chase with the SU, replacing parts that might improve things temporarily until the problem starts again.

I went through this with 'Mrs. Blue' (a high compression, cammed 1600), until I installed a wideband O2 sensor. It turned out I was running low 11s AFR (air-fuel ratio) at idle and leaning out past 16 at anything over 4000 rpm. It ran okay but never great. Once I understood what was happening, I found the perfect needle for it, and now it runs like a champ.

For anyone struggling with SU carburetors, I recommend reaching out to Keith Williams. He's one of the best with SUs and helped me figure them out. You can find him here memberlist.php?mode=viewprofile&u=331

Datrock wrote: ↑Sat Mar 23, 2024 11:27 am I noticed in your photo of the engine compartment that you have the fuel return valve installed on the inlet to the front carb, it needs to be installed at the rear carb. Not saying this is the answer to the problem but it should help by moving it to the correct place.

You're a legend! Great eye

I was out of the country the last few days but returned yesterday and immediately checked your suspicion. You were were of course right, not only that the regulator was on the wrong carb but turns out the regulating parts were missing entirely inside...so fuel was completely flowing through the system and not building any pressure. I scavenged the parts from a spare carb, sync'd, adjusted AFR then sync'd again. Took her out for a spin and she hauls as high up into the power band as I push it. I don't have confidence in the stock tach (should I?) so I didn't run much past 5k, but there was no sound of leaning out on decel

Pjackb wrote: ↑Mon Mar 25, 2024 4:46 pm

JacobWisdom wrote: ↑Wed Mar 20, 2024 12:40 pm In the meantime unless someone with authority tells me it won't work, I'm going to try the 2L needles to see if I can at least get it to run through the full power band under load.

Going to address this question first , this will not work properly unfortunately,
Notwithstanding the fact that their profile and therefore fueling characteristics are totally different just for the simple reason that they are different size and length.

Thank you for answering this question. Since you said so, I swapped the stock needle back in while rectifying the return regulator



I have to assume it was configured with the return line blocked off on the black/midnight purple car...which is maybe why the location of the gutted regulator was irrelevant

"Took her out for a spin and she hauls as high up into the power band as I push it."

Victory!

Wow, what a great team effort by this group. The cumulative knowledge here is just awesome. Well done everyone!

I just went back and looked at the photos of your car and I noticed two things:

1. What wheels are those? I don't think I've ever seen them before and I like their 60's retro vibe.

2. It appears that you are missing two lug studs on the driver's side rear. Please make sure you replace those before driving around with all your newfound high-RPM power.

Edit: I'll bet Alvin has 20 photos of wheels just like that, and knows the brand, model, and what years they were produced.

funkaholik wrote: ↑Tue Mar 26, 2024 12:22 pm I just went back and looked at the photos of your car and I noticed two things:

1. What wheels are those? I don't think I've ever seen them before and I like their 60's retro vibe.

2. It appears that you are missing two lug studs on the driver's side rear. Please make sure you replace those before driving around with all your newfound high-RPM power.

Edit: I'll bet Alvin has 20 photos of wheels just like that, and knows the brand, model, and what years they were produced.

That's a good catch on the wheel studs/lug nuts ... I went back and looked at the pic and I'm only seeing one!
Hopefully just an older pic...

funkaholik wrote: ↑Tue Mar 26, 2024 12:22 pm I just went back and looked at the photos of your car and I noticed two things:

1. What wheels are those? I don't think I've ever seen them before and I like their 60's retro vibe.

2. It appears that you are missing two lug studs on the driver's side rear. Please make sure you replace those before driving around with all your newfound high-RPM power.

Edit: I'll bet Alvin has 20 photos of wheels just like that, and knows the brand, model, and what years they were produced.

Good catch, they are actually just hub caps and the missing studs are little spin on deals (see attached). I'm not sure what they are off of, I tried looking for them online but was not successful. I have seen similar but no exact match...I may be selling them.

The tires are 185/65R14 - I believe the wheels are stock size

Those came on the 1st 810
F10 had a close copy too

Aha. You are all good then. Those are cool-looking hubcaps. I thought maybe they were some exotic magnesium wheels from the 60's.