Hi All!

I have a 69 Jag E type with a freshly rebuilt 4.2 (300 miles) and freshly rebuilt triple Su Carbs along with a 123 Dizzy set on #2 currently. The carbs have been set per the manual and the engine runs very smoothly, the choke also works as it should. The only issue is the vehicle surges (hiccups) while driving. I cannot see any rhyme or reason as to when it does this as it is sporadic. I cannot go past the 2k rpm due to still breaking in the engine. I've verified the fuel pump is well grounded and its specific for su's.
My hope is someone will be able to help resolve this annoying issue.

Things to note: when pushing up on the carb pistons the idle actually decreases which per the book means its too lean. Only thing is I've already got the jet pretty far turned in. The floats were also set to the book at 7/16, and I used a sychrometer to sync all three. I don't really believe the issue is due to this, but someone out there knows more than me, so shoot.

 

First question on this modified car---what type of air cleaner system are you using---is it stock or?

 

3 K&N filters

 

The factory air filter set was well tuned for the carbs. While this may not be the issue many times odd running behavior has been resolved by returning to stock. If you are having these issues at 2000 RPM it will be worse later at WOT. If you have the jets almost fully dropped and are still lean are you sure you have the correct needles?

 

Running UE needles. Btw, the "surging" is not constant. Only happens sometimes. It feels like there is no fuel delivery or spark for a split second, then back to running smooth

 

Well that sounds more like loss of power than surging. I would start by checking all of my electrical connections and esp. the ign. switch..

 

I recently finished retrofitting triple SU's to my 68 and I will tell you my experience. Following exactly the SU repair manual, I set the tip of each jet even with the carb bridge, then lowered them 2.5 turns. The manual says to keep the position of the 3 jets matched so I marked the screws as an aid. As George said, the stock air cleaner worked better than any aftermarket product I tried and all further adjustments had the sir cleaner in place. After tuning for smoothest idle, I too encountered surging when cruising with light throttle and misfiring on deceleration with engine braking. It took several tries to get the best balance between idling and running, In my setup, backing out about 1/2 turn from the initial setting got the best results. Final adjustments were very touchy using 1/8 turn steps. Timing ended up at 9 degrees btdc. Adding vacuum advance (in 68 it was not used) made the whole process somewhat easier so I stuck with modifying the original dizzy. I am happy with that choice. Your problem may be different but I could not help noticing your description sounded just like mine. Good luck.

 

Thanks for sharing your experience. When you say "backing out about 1/2 turn from initial setting do you mean lowering or raising the jet? Initial setting is 2.5 turns down from the bridge. I've found at 2.5 turns my car will not stay running. Closest to 2.5 turns I've been able to keep it running at is 3.25 turns and my synchrometer is registering around 11-12 to keep the idle smooth and around 850 rpm.... I was also just thinking about something I may have missed when setting the timing - Should the Vacuum line to the dizzy be removed while setting 10 btdc at idle?

On a side note, what's the easiest way to remove the tachometer? I can relatively easily get to one of the securing nuts but the other... I have a kit to "repair" the tach's jumpyness to accommodate the 123 dizzy.

 

Backing out meant making the mixture leaner. Ended up about 2 turns down from the bridge. Your results are a surprise, I think the initial 2-1/2 turns was meant to be too rich to insure the engine would start. Maybe you should look for a vacuum leak. Squirting some starter fluid around all connections usually works. I had a few.

Assuming you have the vacuum advance line connected to the port on the front carb, there is no effect at idle. I set mine to 9 degrees just because gas octane is much lower now than then. No secret to removing the tach, just stretching and squirming.

 

Hi All!
"I have a 69 Jag E type with a freshly rebuilt 4.2 (300 miles) and freshly rebuilt triple Su Carbs along with a 123 Dizzy set on #2 currently. The carbs have been set per the manual and the engine runs very smoothly, the choke also works as it should. The only issue is the vehicle surges (hiccups) while driving."

Just to separate ignition from fuel. Set 123 to "0" curve and set 10 degrees static advance with vacuum disconnected. Once your engine is fully broken in, you can try different curves. IMO 34 degrees at 3000 RPM is too much for stock cams, compression & 91 octane fuel. See 123 tech sheet attached. Did you upgrade the coil and ignition wires to be compatible with electronic distributor?
Rgds
David

 

Had a very similar problem on my 1969 Roadster. Found that in the banjo on top of the fuel tank had some gelatin stuff in there. Removed it and the surging/cutting in and out stopped. Also there was no screen on the pickup tube.