Fixing up dad's old 69 SRL
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- Gregs672000
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Re: Fixing up dad's old 69 SRL
After years of messing with jets and every version/make of carb, my answer to all issues carb related: EFI! Not very helpful here through...
It's been years since I messed with SUs, but my understanding is the dash pot oil viscosity has an impact as it helps to control the speed in which the piston raises up from the increased vacuum. I believe a thicker oil will reduce the lean spike as it slows down the rise speed, keeping it from suddenly leaning out. Experts will have to pipe in here. This may be the same idea behind the springs.
Good idea on the wideband... I find them invaluable and have had one for years. My engine is high compression with a high lift cam and for whatever reason is very sensitive to minor changes in throttle position. I'm still working on getting my enrichment settings to respond appropriately to those little changes so I don't see/feel lean spikes, and that is with FULL control over things and data logging to pinpoint it... you may struggle some with that cam and SUs...
BTW, as I'm sure you know power is found in the ignition timing... you're the kind of owner that might be interested in the Megajolt controller I have sitting in my tool box unless you ever decide to go with a 123 dizzy... it's just the controller, not everything you would need to convert to a crank-fired system, but with your obvious skills you would have no problem modifying the necessary parts (uses Ford EDIS components and a modified crank pully). It's not doing me any good in my tool box, so let me know if you're ever interested. I'll be honest though, a 123 dizzy would be much easier if a little less accurate.
It's been years since I messed with SUs, but my understanding is the dash pot oil viscosity has an impact as it helps to control the speed in which the piston raises up from the increased vacuum. I believe a thicker oil will reduce the lean spike as it slows down the rise speed, keeping it from suddenly leaning out. Experts will have to pipe in here. This may be the same idea behind the springs.
Good idea on the wideband... I find them invaluable and have had one for years. My engine is high compression with a high lift cam and for whatever reason is very sensitive to minor changes in throttle position. I'm still working on getting my enrichment settings to respond appropriately to those little changes so I don't see/feel lean spikes, and that is with FULL control over things and data logging to pinpoint it... you may struggle some with that cam and SUs...
BTW, as I'm sure you know power is found in the ignition timing... you're the kind of owner that might be interested in the Megajolt controller I have sitting in my tool box unless you ever decide to go with a 123 dizzy... it's just the controller, not everything you would need to convert to a crank-fired system, but with your obvious skills you would have no problem modifying the necessary parts (uses Ford EDIS components and a modified crank pully). It's not doing me any good in my tool box, so let me know if you're ever interested. I'll be honest though, a 123 dizzy would be much easier if a little less accurate.
Greg Burrows
'67 2000 #588
Tacoma, WA
'67 2000 #588
Tacoma, WA
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Re: Fixing up dad's old 69 SRL
Thanks for the offer Greg! I might take you up on it in the future, I want to build another engine and will go down that rabbit hole when the time comes. For now I just wanted to get the original carbs working around the neighborhood.
The dashpot oil effects the transient loads, not the steady state. I tried 30wt oil, that made it too rich under accel, ATF was just right.
The steady state cruising is still lean, its fine when you put your foot into it but once the piston has come up to position it leans out.
I used a rod in the dashpot to check where on the RA needle my lean spot is, and its right at the 3rd "station" about 1/4" down the needle. I might try to modify some of these RA needles because they are readily available and cheap if I mess up. Adding some sort of air bleed is my last resort, I havent played with the piston weight yet but I figure that would effect the whole range of vacuum operation, which brings me to another thought...
The original nissan needle is good at idle and full throttle but lean in vacuum, so switching back to the nissan needle and weighting the pistons is another option I might try?
The dashpot oil effects the transient loads, not the steady state. I tried 30wt oil, that made it too rich under accel, ATF was just right.
The steady state cruising is still lean, its fine when you put your foot into it but once the piston has come up to position it leans out.
I used a rod in the dashpot to check where on the RA needle my lean spot is, and its right at the 3rd "station" about 1/4" down the needle. I might try to modify some of these RA needles because they are readily available and cheap if I mess up. Adding some sort of air bleed is my last resort, I havent played with the piston weight yet but I figure that would effect the whole range of vacuum operation, which brings me to another thought...
The original nissan needle is good at idle and full throttle but lean in vacuum, so switching back to the nissan needle and weighting the pistons is another option I might try?
Seattle, WA
1969 SRL311
1972 PL510
1969 SRL311
1972 PL510
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Re: Fixing up dad's old 69 SRL
chased my tail a bit more today, tried nissan N17 needle with weighted slides but the weights only make a small difference to the midrange leanspot.
I figured needles are cheap so went and sanded off .002" about 1/4" down the RA needles, it seemed to do the trick?, looped it around the neighborhood and no more dead spot!!, full throttle was perfect!, cruise was actually a little rich now (12-13:1). Then it started leaning out randomly by the time I got back home, and I noticed I only had a 1/4 tank of fuel. Took it to the gas station and filled up and leaving it started randomly going full rich in cruise (10:1) and full throttle leans out and completely bogs lean(19:1), its all over the place, unpredictable.
popped the hood and noticed some boiling fuel in the fuel filter
I think what I have is a fuel delivery issue?? I'm going to order a new set of RA needles to compare against my modified set. Then im going to check for restrictions in the fuel supply, I am using an electric pump with two new filters, pre and post pump, Maybe its too much filter is blocking the pump? Or maybe I just vapor locked it, I might try rerouting the fuel hose away from the hot fan or putting a fire sleeve on it.
I remember in the past this car ran fine with RA needles, so I should have considered that more before modifying needles to chase a tuning issue I think, but I feel a bit of progress was made nonetheless, I let the car cool down and took it for another quick drive and it seemed to drive good again...
Its getting there, but I dont quite trust it to leave the neighborhood yet!
I figured needles are cheap so went and sanded off .002" about 1/4" down the RA needles, it seemed to do the trick?, looped it around the neighborhood and no more dead spot!!, full throttle was perfect!, cruise was actually a little rich now (12-13:1). Then it started leaning out randomly by the time I got back home, and I noticed I only had a 1/4 tank of fuel. Took it to the gas station and filled up and leaving it started randomly going full rich in cruise (10:1) and full throttle leans out and completely bogs lean(19:1), its all over the place, unpredictable.
popped the hood and noticed some boiling fuel in the fuel filter
I think what I have is a fuel delivery issue?? I'm going to order a new set of RA needles to compare against my modified set. Then im going to check for restrictions in the fuel supply, I am using an electric pump with two new filters, pre and post pump, Maybe its too much filter is blocking the pump? Or maybe I just vapor locked it, I might try rerouting the fuel hose away from the hot fan or putting a fire sleeve on it.
I remember in the past this car ran fine with RA needles, so I should have considered that more before modifying needles to chase a tuning issue I think, but I feel a bit of progress was made nonetheless, I let the car cool down and took it for another quick drive and it seemed to drive good again...
Its getting there, but I dont quite trust it to leave the neighborhood yet!
Seattle, WA
1969 SRL311
1972 PL510
1969 SRL311
1972 PL510
- Gregs672000
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Re: Fixing up dad's old 69 SRL
Ya never know what fiddling around you do now may be an answer some time down the road for you or someone else eh?
Greg Burrows
'67 2000 #588
Tacoma, WA
'67 2000 #588
Tacoma, WA
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Re: Fixing up dad's old 69 SRL
quick update to this thread
The car is running well now. I did have multiple issues.
the vapor lock symptoms and inconsistent running was actually a bad fuel pump, carbs were sucking fuel from the tank on gravity and manifold vacuum alone.
once I replace the fuel pump it was running much richer and now it is consistent and doesn't stall out .
my u20 has smog deleted, two inch exhaust with factory su carbs with a larger aftermarket cam and the stock air filter. now that the car was running consistently I had to find the right needle.
RA needle was too rich everywhere
RV needle still too rich (9:1)
RB needle close, runs ok idle 14:1, cruise 13:1, full throttle 9:1
KW needle 14:1 idle, 17:1 just off idle, 14:1 cruise, 11.5:1 full throttle.
Nissan needle 14:1 idle full lean everywhere else
it's amazing what such small needle size changes can make to the AFR! just .0005" makes a difference. the KW needle is not perfect but it is very drivable and I think I'm going to call it good there. I think if I build another u20 I'm going to fit mikuni rs40 carburetors, much easier to tune when you have pilot and main Jets...
also my big electric fan was causing the idle to drop down a lot because the camshaft is very sensitive idling. to fix that I installed a vacuum switching valve that switches the distributor from ported to manifold vacuum when the fan kicks on and that acts like a simple little fast idle that works well with the fan.
The car is running well now. I did have multiple issues.
the vapor lock symptoms and inconsistent running was actually a bad fuel pump, carbs were sucking fuel from the tank on gravity and manifold vacuum alone.
once I replace the fuel pump it was running much richer and now it is consistent and doesn't stall out .
my u20 has smog deleted, two inch exhaust with factory su carbs with a larger aftermarket cam and the stock air filter. now that the car was running consistently I had to find the right needle.
RA needle was too rich everywhere
RV needle still too rich (9:1)
RB needle close, runs ok idle 14:1, cruise 13:1, full throttle 9:1
KW needle 14:1 idle, 17:1 just off idle, 14:1 cruise, 11.5:1 full throttle.
Nissan needle 14:1 idle full lean everywhere else
it's amazing what such small needle size changes can make to the AFR! just .0005" makes a difference. the KW needle is not perfect but it is very drivable and I think I'm going to call it good there. I think if I build another u20 I'm going to fit mikuni rs40 carburetors, much easier to tune when you have pilot and main Jets...
also my big electric fan was causing the idle to drop down a lot because the camshaft is very sensitive idling. to fix that I installed a vacuum switching valve that switches the distributor from ported to manifold vacuum when the fan kicks on and that acts like a simple little fast idle that works well with the fan.
Seattle, WA
1969 SRL311
1972 PL510
1969 SRL311
1972 PL510
- Gregs672000
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Re: Fixing up dad's old 69 SRL
Nicely done, the KW looks like the ticket... can't do much better than that given the system! If you ever do a dyno run I'd love to see how that cam profile works for you. Let us know how and where it makes power. Congrats!
Greg Burrows
'67 2000 #588
Tacoma, WA
'67 2000 #588
Tacoma, WA
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Re: Fixing up dad's old 69 SRL
FYI, I had my Su Carbs rebuilt when I did my Restoration on my 1969 2000 and Tom who did the rebuilt for me, told me to use Auto Transmission Fluid in the reservoir its the right Viscosity. I've been using it for 14 years and no problem.
- spl310
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Re: Fixing up dad's old 69 SRL
Most people don't realize that changing the oil can help tune responsiveness
"Wow, a Roadster!" Stuart Little
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1967.5 2000
1967.5 2000
1964 1500
1964 1500
1967.5 1600
1968 chassis
2006 Acura MDX
2013 Volkswagen Jetta TDI wagon
1995 F350 Powerstroke!
More...
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Re: Fixing up dad's old 69 SRL
Roadster update!
What really helped with the response was changing to a softer vacuum advance spring that would more quickly add timing when opening the throttle.
Here's a little video of me testing some carb response.
https://www.youtube.com/watch?v=-5IrSKi0DXQ
switched to needle "KW2" and installed a new air filter, just bought a round filter for a truck for 15$ from local autoparts store, and it fit up ok once i removed the metal grating.
Restored the old snugtop hardtop. removed the old weatherstrip and painted satin black
For the snugtop glass gasketing I found Trim-Lok LK1179-25 to be a suitable replacement with LK723C-25 chrome insert.
For around the door window I am testing out Trim-Lok X2123HT-25, the triangle shape provides a positive seal against the glass while still allowing the door to be opened without rolling down the glass.
BIG THANKS to SIN CITY DATSUNS for selling quality stainless reproduction top clamp sets!! Happy to have those!!
For the bottom of the hardop I am using dense "1 Inch Wide X 3/4 Inch Thick, Adhesive Foam" with 3mm thick polyester FELT tape protecting the top from rubbing where it contacts the body. The car also have self-healing XPEL Ultimate PPF film on the rear deck area to protect where the felt rubs.
https://www.amazon.com/gp/product/B07M83PYPR/
https://www.amazon.com/dp/B09T5789V7
Overall been driving and enjoying it more, it seems to be reliable.
What really helped with the response was changing to a softer vacuum advance spring that would more quickly add timing when opening the throttle.
Here's a little video of me testing some carb response.
https://www.youtube.com/watch?v=-5IrSKi0DXQ
switched to needle "KW2" and installed a new air filter, just bought a round filter for a truck for 15$ from local autoparts store, and it fit up ok once i removed the metal grating.
Restored the old snugtop hardtop. removed the old weatherstrip and painted satin black
For the snugtop glass gasketing I found Trim-Lok LK1179-25 to be a suitable replacement with LK723C-25 chrome insert.
For around the door window I am testing out Trim-Lok X2123HT-25, the triangle shape provides a positive seal against the glass while still allowing the door to be opened without rolling down the glass.
BIG THANKS to SIN CITY DATSUNS for selling quality stainless reproduction top clamp sets!! Happy to have those!!
For the bottom of the hardop I am using dense "1 Inch Wide X 3/4 Inch Thick, Adhesive Foam" with 3mm thick polyester FELT tape protecting the top from rubbing where it contacts the body. The car also have self-healing XPEL Ultimate PPF film on the rear deck area to protect where the felt rubs.
https://www.amazon.com/gp/product/B07M83PYPR/
https://www.amazon.com/dp/B09T5789V7
Overall been driving and enjoying it more, it seems to be reliable.
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Last edited by akara on Sun Nov 05, 2023 3:14 pm, edited 1 time in total.
Seattle, WA
1969 SRL311
1972 PL510
1969 SRL311
1972 PL510
-
- Roadster Nut
- Posts: 46
- Joined: Sat Oct 04, 2014 12:24 am
Re: Fixing up dad's old 69 SRL
some closeups
triangle gasket in the door window
felt under the hardtop
foam gasketing inside under hardtop
triangle gasket in the door window
felt under the hardtop
foam gasketing inside under hardtop
You do not have the required permissions to view the files attached to this post.
Seattle, WA
1969 SRL311
1972 PL510
1969 SRL311
1972 PL510
- Gregs672000
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- tig
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Re: Fixing up dad's old 69 SRL
This thread inspires. Love the quality of your work!
Peggy '69 SRL-311 Penny '69 SRL-311 Minerva: S54 powered '85 528i Vlad: '87 Zinno 535is Maytag: '87 Alpine 528e '88 Veneziablau 911 Uglina: '78 FJ40
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Re: Fixing up dad's old 69 SRL
How in the world did you put the white paint on the knobs???
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Re: Fixing up dad's old 69 SRL
A very small brush and some alcohol on a rag to wipe off the excess, for the HVAC letters i soaked some paint into a paper towel and dabbed it on.
Seattle, WA
1969 SRL311
1972 PL510
1969 SRL311
1972 PL510