SwedeSpeed - Volvo Performance Forum banner
1 - 13 of 13 Posts

·
Registered
Joined
·
49 Posts
Discussion Starter · #1 ·
Hello

Has anyone tried using a spacer? I've not seen them on volvos before but I have on several triumphs with SU's.

I always thought I understood the basic mechanics of how SU carbs worked and as I prepare to get rid of the previous owners Weber and install a nice set of Z Therapy SU's, I called Joe in New York to get the correct B20 needles. My mechanic told me that even at 7,000 feet (where I live), the needles are stock for the engine and that the automatic rising and falling of the piston will compensate for the elevation. He stated that the only adjustment is for idle and thats done with the mixture jet under the carb to get a richer or leaner flow. This floored me; why then are different needles sold? Who is correct? The needles I got with the carbs from sea level were KD. Joe stated that at my elevation, I needed to start with a ZH. Any thoughts?

Thanks

Mark
Flagstaff, AZ
 

·
Registered
Joined
·
7,614 Posts
I'm gonna guess that guy has more knowledge on the subject than any of us here.

All I can say is that when I bought my 122 I was able to dial it in for 5000 here in town with no problems or weird mixture. When I would take it to 8000-9000 feet on a day trip into the hills, it ran fine the whole time and I never needed to adjust anything. It even appeared to start the same.

I'm guessing you really only need different needles for different displacement and cams.

I did just google high altitude SU tuning and one local triumph club says they don't consider "high altitude" needles (which are just a lean needle) unless the car lives above 8000 feet all the time. My guess is you'd only need that to make sure you don't run out of jet adjustment.
 

·
Super Moderator
Joined
·
9,305 Posts
I agree that KD will be way too rich for you, I find them way too rich at sea level. ZH has always been problematic for me however, too lean. I swear by SM - perfect mixture. But the key to the right needle is the overall profile, so it meters more fuel at each flow rate. And that varies by multiple engine parameters.

What do you mean by "spacer insulator"? The hex adjuster on the bottom sets the base (idle) mixture, but there is no other adjustment, the needle does all that. If you have the wrong oil in the dashpot, or a bad spring/sticky chamber, those will affect the needle by under- or over-allowing it to rise. And balancing the two carbs across the linkage, and making sure the valves are perfect, will affect things too. So I agree that you can't simply shim something.
 

·
Registered
Joined
·
49 Posts
Discussion Starter · #6 ·
The spacer/insulator I'm referring to are the extra piece of wood or metal (not sure their composition) that some add to make the carb farther from the manifold.
 

·
Super Moderator
Joined
·
9,305 Posts
Oh, that spacer is phenolic/plastic, and it's for thermal isolation. It has no effect on mixture. It's kind of important though, the car will run a little inconsistently without it, especially when hot.
 

·
Super Moderator
Joined
·
9,305 Posts
They were not there in the earlier models, I'm not sure what year they appeared. The manifold may have changed slightly, longer studs for sure. There's also a heat shield that might or might not be present.

It's a non-essential part, if that's what you're concerned about. How many threads are showing outside the nuts where the carbs attach?
 

·
Registered
Joined
·
49 Posts
Discussion Starter · #10 ·
Not sure on the threads, I'm trying to put a '67 B20 back to original SU's from a Weber conversion an wondering if I should buy the insulators?
 

·
Super Moderator
Joined
·
9,305 Posts
Just remember, the SU carb is a masterfully elegant design, with basically one moving part (the dashpot). After choosing your needle, everything else (butterfly, jets, float, linkages, intake valves) are the adjustment tools you have at your disposal.
 
1 - 13 of 13 Posts
Top