Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
21
IIRC, the early Stranglebergs had needles that went straight down the center of the jet, but with emission controls came needles that leaned against one side of the jet because that resulted in more consistent metering. Either way, obviously you want the bottom end of that damper pot to be oil-tight, and since that’s where the needle is located, whatever the attachment scheme it needs to be sealed.
With either SU’s or Stranglebergs, it’s not terribly difficult to just rip the top off the carb – in situ – and look at how the needle is attached to the slide and figure out how to seal it up if necessary.
That’s a good explanation, and I agree with your final assessment.
I recently experimented with accelerator pump discharge nozzles on a V8 equipped with a Holley. My theory was that going to a smaller discharge nozzle should make it more responsive, just up to the point where it becomes too lean.
I went to smaller and smaller nozzles, and the car DID become progressively more responsive. But, I was able to get all the way down to the smallest discharge nozzle available without even a hint of lean behavior, even when taking readings around town with an AF meter shoved up the tail pipe…small V8, small carb, lightweight car.
Using that same logic, thinner oil should make the car more responsive, but you might struggle to find oil that is too thin.
I’m curious why no one seems to be suggesting the damper oil from SU. It isn’t expensive, and it seems the manufacturer’s provided solution would be a good one.
SUZenith damper oil, or Penrite, it is made for the job: …as to cost?? one small $9 bottle on my shelf has been topping up my SU’s for about 4 years…and is now half full. So I am at the exorbitant cost of $2 per year. I may expire before I open the 2nd bottle I purchased at the same time.
Nick
1 Like
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
27
In a discussion of EFI fuelling maps, someone recently pointed out that there shouldn’t be any acceleration enrichment once you’re significantly off idle. For example, at 2000 rpm half throttle and full throttle look the same to the engine, they’re both effectively full throttle since the butterfly is not effectively restricting airflow into the manifold. Hence, why would you have any accelerator enrichment going from half throttle to full throttle at 2000 rpm? It’d just make it briefly rich, wouldn’t it?
The problem with the SU’s and Stranglebergs is that when the oil gets a bit low, it’s the damping near idle you lose first.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
28
There’s got to be more to this story. The good people at Holley don’t just routinely provide waaay too much acceleration enrichment, do they? And presumably neither do the good folks at SU or Zenith. Why do these things always seem to run rich when stomped?
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
29
Wait a minute. Nozzles? Don’t those only affect the spray pattern and not the quantity of fuel sprayed? Maybe slowing the quantity down a bit so the spray takes longer. Don’t you have to revise the linkage somehow to actually adjust the quantity of fuel sprayed?
20 years ago I sold a very worn out (200,000 miles) car with an auto box. I had some ATF left over from a 5litre can, used to replace the auto gearbox oil. At current rates of usage I have about 1,200 years supply left.
It’s an interaction between the nozzle size, and the linkage cam that operates the pump diaphragm.
If you stomped on the accelerator and held it down, you would eventually evacuate the entire volume of the diaphragm. With a big nozzle size, that would happen more quickly than with a smaller nozzle size. So, in my mind, you would get a greater level of enrichment earlier with a bigger nozzle.
The linkage cams adjust the amount of diaphragm compression you get for a given throttle position, so that become a fine tuning tool for bringing in more or less spray at different times.
That’s how it’s been explained to me, and how Holley seems to explain it here…
I use gear oil in my dampers, which may have 1/4 million miles on them. I believe them to be worn internally. It definitely helps, but gear oil is not as heavy as you think - it’s not 90 weight as compared to 30 weight engine oil - like 3 times as heavy.
I have used mortorcycle fork oil, 20 wt for years. Reasonably priced and readaly available.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
37
Does the weight of the car make any difference? I understood that the enrichment is only to compensate for the fact that the airflow increases more quickly than the fuel flow when the throttle is suddenly opened.
Like @L.Lynn, I use whatever oil I have handy, usually 30 weight. I fill to the miniscus and push the damper back in. Wish all the maintenance was this easy!
