First Datsun-1969 SRL31107911

[1969311]

Hello All,

I recently bought my first roadster, my Uncle registered it a month before I was born, and by the time I was nine I said someday I would own it, and just recently we made a deal. As beautiful as she is, has been sitting for a while.

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The fuel tank was rusted, but my uncle had a clean spare. I installed the new(er) tank, and drilled holes on the frame to secure the brackets ( no longer pulling down on the trunk ).

He said it had a rather nasty pinging sound and thus he never drove it, even after having the engine rebuilt. I changed the cap and rotor, but still it ran poorly, I did some research and discovered, thanks to you all, that smog roadsters had a different distributor advance curve, so I purchased a kit from Tom at eastcoastroadsters, and installed the EI dizzy. He had suggested that I replace the needles in the carb,to ADQ I believe. Soon! Recommendations?

The car was running with no pinging, but far to rich, so I have set out to learn the art of tuning the SU's there seem to be some fairly detailed write ups, but I am having trouble, as I cannot seem to get the carbs balanced properly.

I purchased a unisyn from datsunsports and have had a hard time getting the front carb to pull enough air to move the indicator. I have managed twice to achieve a good idle, balanced air flow, clean idle mixture, but have messed it up each time trying to set the proper idle speed (6-700?)

Preserverence is key!

The temp and fuel gauges were not functioning, and I had a look at the gauge voltage regulator under the dash and attempted the regrounding to see if that worked but it did not. I ordered an aftermarket voltage regulator (12<-->9V) and am hoping that that will fix the issue.

My overall goal is to have a very roadworthy car with some moderate performance enhancements to possibly take to the track occasionally. There is lots more to do , and I will add pictures when I can, just wanted to say thanks for all the information, there is clearly a lot of it here, I have wanted this car for almost 20 years, and am excited that we finally get to begin our journey together, thanks!

Chris from Smartsville, CA
1969 Datsun SRL311/U20/2000/SMOG/SU

[notoptoy]

Welcome and congratulations on the car - great story on the acquisition, cool that it goes back so far. On the carbs I would take a can of carb cleaner and spray it around the throttle shafts while running. I suspect you may have an air leak there making it very difficult to set the carbs. If the idle speed changes when you spray the carb spray around the throttle shafts then they are likely worn and you have a vacuum leak. It might be time for a new/used set of carbs.

[1969311]

notoptoy,

Thank you, I did spray some water around the plugs used to delete the smog system on the manifold, and around the carbs, I read this one on one of the older threads. I did not notice a significant change in the idle speed, I will retry with some carb cleaner. Is there a good source for new/used SU carbs?

I have an extra old set that came with the car but they are in pretty rough shape, I was thinking about sending two of them over to ztherapy, or purchasing a master rebuild kit with the RA needles. Any thoughts on either of these?

Also noticed after an initial attempt at tuning the carbs, that when the throttle was applied the rear carb thottle opened quicker than the front, someone had suggested a worn dashpot float and slide ( terms?).

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Thanks!

Chris from Smartsville, CA
1969 Datsun SRL311/U20/2000/SMOG/SU

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[devo]

Here is a $6 fix for the instrument voltage regulator. works very well. 8V is what you want to the fuel and temp gauges.

http://www.311s.org/pmwiki-311/pmwiki.p ... VoltRegFix

[spl310]

On the rear carb opening quicker, I would check to make sure that they both have oil of the same viscosity, and that the throttles are balanced before I started sweating worn dashpots.

[1969311]

SPL310,

Thank you for the reply, I had removed, cleaned, and changed the dashpot oil, and verified proper levels within the markings, I will keep trying to tune the carbs. I just really want to be cautious that I do not cause any damage in my experimentation, as my uncle spent a good chunk of change having the engine rebuilt before he parked it. I have been doing a lot of research prior to tweaking anything, and trying only one thing at a time to eliminate unnecessary variables.

Though I am pretty sure that the needles are still the original "smog" equipment, and may need replacing, it seems like needle selection is often vehicle specific, and from my research there doesn't seem to be a universal consensus with the selection, more of a trial and error system. I am seriously considering just purchasing a new set of SU's and sending the old two sets in for cores so someone else can have functioning carbs as well.

Thus far I have found remanufactured sets from:

datsunparts- Part # 1251 - $725/pair+core http://www.datsunparts.com/U20-Carburator
ztherapy- Part # ZT500 $680+core http://www.ztherapy.com
paltech1 - $695/pair new or $595/pair rebuild http://www.paltech1.com/id10.html

Thoughts on any of these? Others I may have missed?

More research on the horizon, eagerly looking forward to a run in the roadster in the hopefully not-to-distant-future!

Regards,

Chris from Smartsville, CA
1969 Datsun SRL311/U20/2000/SMOG/SU

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[1969311]

DEVO,

That is a slick fix for the Gauge VR, I will be doing that for sure, at least to verify that is the issue. Awesome, Thanks!

Regards,

Chris from Smartsville, CA
1969 Datsun SRL311/U20/2000/SMOG/SU

[JohnnyMac]

Welcome. I went with ZThreapy after not being able to balance my carbs and was very pleased with their product/service. I should have done it sooner, years sooner. Same thing with East Coast Roadster. If you aren't familiar with the Evil L and the death rattle, be sure to read about them here and inspect yours.

[1969311]

Thanks John,

I really appreciate the insight, this forum has saved me a whole lot of headaches already, I am so happy to have found this group. I will do some looking into the "Evil L" as I have a very limited exposure at this point, again thank you.

Regards,

Chris from Smartsville, CA
1969 Datsun SRL311/U20/2000/SMOG/SU

[spl310]

Keith Williams also does carbs. He is on the forum.

[1969311]

SPl310,

Thanks for the info, I ordered the parts for the $6 gauge voltage regulator fix recommended by DEVO, and will be waiting to do further tuning on the SU's until the gauges(fuel, temp) are fixed, I was tuning the carbs today and the coolant started seeping out the top rad cap.

Going to get a replacement cap and flush the cooling system, test for proper operation of the water pump and thermostat, then once the gauges are functioning and the cooling system gone through, I will move back tuning the carbs, would hate to have the head warp from overheating in the garage, haha.

Thanks again,

Chris

[Gregs672000]

Regarding the unbalanced air flow: make sure you understand your linkage and how the whole thing works together. As I recall (it has been a long time since i worked on SUs) I believe that each carb has its own throttle plate adjusting screw that is independent of the linkage. The rear carb is flowing more air because the throttle plate is open more. You said you can't get the front carb to flow enough air to read on the unisyn at idle. Look at the linkage to determine what impacts the position of that throttle plate, and what stops it from opening more. If it is not due to the position of the throttle plate, then it has to be pulling air from somewhere else other than the front of the carb in order for the unisyn to not read. If that's the case, you're looking for an intake leak... throttle shaft, gaskets, etc.

[1969311]

Gregs672000,

Thanks for the insight, I will be spending some more time with them once I have the cooling system and gauges in order, it sounds like an intake leak is most likely at this point, I will be sure to update as I discover the solutions.

Thanks again!

Chris

[S Allen]

That is a great story and it sounds like you are well on your way to having a solid runner. I grabbed one of your pictures and created an avatar for you. Good luck on your project and you have received some excellent advice so far.

S

[1969311]

S Allen,

Very cool, thank you for doing that. Actually traced the coolant issue to a bad cap, and the carb tuning issue was I was backing the idle adjusting screw out to far, and not watching the linkage enough, thanks Greg . Got the engine sounding really good, and went for a short drive last night at 11:40pm haha top dow and 36 degrees, but one of the biggest smiles I have had in a while.

Updates to come,

Chris