I have completed the conversion to triple SU carbs on my 68 and have been quite pleased but have 2 questions.

When travelling or decelerating at low to moderate speeds with the throttles closed or cracked, the engine surges slightly, nothing dramatic but noticeable. I have adjusted timing and idle mixture and can make the problem worse but cannot eliminate it. Currently timing is back to 9 degrees static. I have checked the centrifugal advance and it is in spec. Any thoughts?

Second, unrelated to the above, the 68 distributor has no vacuum advance. I am not sure if adding it (123IGN) will make a noticeable difference in running or performance. Once again, any thoughts?

 

Your correct, find a vacuum advance distributor. New or old.
Petronix has one as well.
DO NOT US A SERIES TWO.....ITS A VACCUUM RETARD!
Good luck
gtjoey1314

 

Actually Joey the early S2 cars relied on mechanical advance--no advance and no retard. It was not until the last version (long ret. air filter) that a retard unit was fitted.

 

I agree , I don't know if he has a strobe machine , better off getting something new
imo
gtjoey1314
ps it's a different car with triples!

 

Yes Joey, I have used a timing light to check the centrifugal advance and found it to be close to spec. Still hoping to find someone who has added vacuum advance and can report on the results.

 

I had the triples on my 1970, I had a vacuum advance.
The linkage is freed up ? you had to switch to the longer throttle linkage as well.
So did you do anything else?
Lightened flywheel, 5 speed?
Did you use stock air cleaner? or racing shorties?
All will throw off the intake.
Good luck
GTJOEY1314

 

Bill, just for kicks is your brake booster hose from the firewall AWAY from the throttle linkage?The hose next to the peddlebox.
GTJOEY1314

 

Joey, yes the hose is clear. I have also checked for vacuum leaks using starting fluid spray. But, after you mentioned air cleaners, I swapped my ITG filter for the original and found a significant improvement, much easier to tune. This was a surprise that I am having trouble understanding. Once the current weather cold blast subsides, I will try some test drives to see if all is well.

 

Whats ITG ?
Air flow plays a huge roll with su's they respond so mch better but once set they are bullet proof.
You air mixture is important and that's why I said it.
Your getting there,also retighten your carb bolts to the manifold with the gasket!
good luck
gtjoey1314

 

Greetings Bill & Joey. May I add another area you might look at . . . damper fluid atop the SU air pistons. Many assume using engine oil, but in colder climes (our Blue Mts during cold winters) this can prove too viscous. It is possible that both acceleration and throttle over-run deceleration may be improved by using a lighter fluid for damping. ATF was our choice, whether cold or hot.

Not surprised at your comments of performance improvements. Even earlier than '68, the US (CAN also?) E-Types were strangled compared to ROW cars. You may be surprised to find somewhat tamer valve timing specs than the higher lift, longer overlap cams that we got and which may be available at not onerous cost from UK. Not sure about your CRs. Here, all appeared to be top spec 9:1 whether in 3.8L or 4.2L, but that would be a far more expensive upgrade and harder to justify unless a bottom end engine rebuild was required.

Cheers,

Ken

 

Cat, I agree, Bill is on the right page, it just takes time.
When I switched to triples, I redid the throttle linkage and return springs three or 4 times , Its not a new car, you need time, but he will get it. Ive used atf/dextron for 25 years plus on the dampers. More forgiving in the cold.
Again you and I are true drivers, most make a change and drive 50 feet and put the car away.
Never gets to temp and everything is always off.
One of my hero's Denis Jenkins always said it best.....
I'm too busy driving my E TYPE to notice all its short falls!
Once bill stretches out the linkage and springs,tweeks the air intake,all will be fine....
GTJOEY1314

 

Good conversation guys. Cat, so far the testing has been at late summer temps (global climate change?) and I have observed the piston movement. I use 20W but will recheck this as it gets colder. For info, CR is 9.0 and valve clearances are .004/.006. Joey, you are right, with this linkage it is tough to get complete throttle closure, full throttle opening and smooth pedal pressure. But patience paid off.

 

Had a senior moment and closed last reply without soliciting thoughts on the value of adding vacuum advance.

 

Hello again Bill & Joey. I will resist buying into the question of "adding" vacuum advance, nor of any method of "retarding" for one simple reason . . . none of ours came equipped with what you have described. I am being super careful here because most of my experience was on our E-Types and similar, which were all Series1, both 3.8L and early 4.2L.

That said, ours had a combination of mechanical advance on the rotor shaft based on CF, but also vacuum advance on the points plate based on applied vacuum drawn from intake manifold. Perhaps these differences arise from differing market specs as referred to earlier?

Good-oh with that 9:1 CR, but the valve timing I referred to is about the lift, duration and overlap as result of profile of the cams - not clearances. Your clearances, BTW, of .004 inlet & .006 exhaust are spot on factory spec, whereas our competition engines all called for safer .006/.008 inlet & .008/.010 exhaust. It may be of interest that we built all our road engines with .006/.008, there being no added wear or noise issues while marginally wider clearances offered greater safety against valve bounce or unseating at higher RPM.

May I congratulate both of you for this interesting thread. I do agree that, when tuning triple 2" SUs, it is relatively easy to arrive at a workable setup . . . especially if care is taken with seating of needles, float levels, air piston spring matching, and linkages. Beyond that, experimenting with alternate needle profiles to best match your local conditions (air temps, altitude) and use of a quality manometer or stethoscope, can lead to a time consuming quest for perfection. But hey, fellas, time and patience are commodities that are the bread & butter of DIY enthusiasts.

So . . . keep at it and keep us posted. Congrats on your progress and huge thanks for the enjoyment you bring to those of us following your achievements.
Best wishes,

Ken

 

To the both of you as well.....
please look at my co driver in this picture, he drove and created our cars brand new!
no computers no wind tunnels and of course no laptop computers!
so at a young 97 just think, our cars are over 50plus years old!
a little leaking a little farting a little slower off the line!
it sounds like us!
so enjoy the ride my friends and take it all in stride!
God bless Norman Dewis, this guy is going to out live me!

 

Doubt many of you will go for this though... (as a side note you can get a Chevy engine to fit in an XKE).

 

I like it but.....It takes all the pain and suffering which comes with original ownership.
You also put Castrol 20/50 out of business......bahhahhhh
gtjoey1314

 

I've had the SUs, Strombergs, and Side Draft Webbers (45CFM which I had on the '64). I'm in the process of pulling the double pumper on this thing and putting on a Holly Sniper EFI. I've become a huge fan of just turning the key to start the damn things. The drama of chokes and ugly cold starts got really old over the years. (And I bought the car with the Chevy in it).