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Good news & good luck! I'm suddenly experiencing a slightly sticky throttle & do you think I can find where it's binding SMH!
When I just took mine apart I found a couple of issues with the throttle, firstly where it pivots on the inlet manifold was sticking so I cleaned it up and gave it a good dolop of grease. The second is where the carb linkage joins the throttle linkage (the ball joint which you screw up from the underside, this was slightly at an angle so I turned it round and it was much smoother.
LOL! If only it were that simple. I want it to reliably return to slow idle with new standard return springs. My restoration guy had fitted a piggy back spring to restrict throttle movement while transport company was moving the car from Johannesburg to Cape Town. Since removing that I have a slight issue.
Stupid question, have you tried slackening off the throttle connection to the carb spindle to check if the return issue lies before or after that point ?
You can rotate the lever for the connection of the spindle return spring to increase the pressure of the stock spring on the linkage at that point.
I have also seen more than one connection point for the return spring bracket that fixes at the oil filter, depending on that position also increases/decreases spring pressure. (which bolt the spring bracket fits on).
With what I will call the pedal linkage disconnected the carbs settle perfectly ~ so no binding butterflies or anything like that. That said the pedal linkage on it's own does not seem bad but obviously has too much drag. The only answer to me is to systematically start at the pedal & ensure each point is free & lubricated. I will also try increasing spring tension as well so thanks for that reminder that I'd overlooked. I'm sure Jaguar selected return spring tension/rate carefully to prevent undue wear on the carb spindles. We have been sparse with any external lubrication on the car which I am steadily rectifying due to my guy's workshop being rather dusty. Inside doors etc. all mechanisms are plastered with long life polyurea synthetic grease.
My spanner man (who is now 1300Km away) says just drive the car ~ it will loosen up with use. That aint good enough for me and I need to get the car through roadworthy.
With what I will call the pedal linkage disconnected the carbs settle perfectly ~ so no binding butterflies or anything like that. That said the pedal linkage on it's own does not seem bad but obviously has too much drag. The only answer to me is to systematically start at the pedal & ensure each point is free & lubricated. I will also try increasing spring tension as well so thanks for that reminder that I'd overlooked. I'm sure Jaguar selected return spring tension/rate carefully to prevent undue wear on the carb spindles. We have been sparse with any external lubrication on the car which I am steadily rectifying due to my guy's workshop being rather dusty. Inside doors etc. all mechanisms are plastered with long life polyurea synthetic grease.
My spanner man (who is now 1300Km away) says just drive the car ~ it will loosen up with use. That aint good enough for me and I need to get the car through roadworthy.
Do you have both throttle return springs fitted? There should be one from the front carb to a bracket bolted to the bottom of the front carb (a Y shaped bracket) and then the one from the level between the two carbs down to the oil filter housing?
Sorry Homer, hijacked your thread a little on this subject. Glyn, you will be dead right re too much spring tension, the two springs do counteract each other in that respect to a point as one acts on the throttle linkage directly and the one on the spindle is opposing the force from the throttle linkage, obviously you would want minimum required tension to zero the linkage. Teaching Granny to suck eggs here of course Glyn.
The pedal linkage spring can be over tensioned a fair bit as the stop and fulcrum should not pass the tension through to the spindle. As you say if you go through the linkage ensuring all is lubricated and free then apply minimum spring force to ensure proper return, if you need any advice on the best lubrication, I do know a good tribologist !
Does anyone here know exactly which bolt on the oil filter that the return spring bracket should attach to, I have not found a definitive answer to this as yet.
Do you have both throttle return springs fitted? There should be one from the front carb to a bracket bolted to the bottom of the front carb (a Y shaped bracket) and then the one from the level between the two carbs down to the oil filter housing?
Sorry Homer, hijacked your thread a little on this subject. Glyn, you will be dead right re too much spring tension, the two springs do counteract each other in that respect to a point as one acts on the throttle linkage directly and the one on the spindle is opposing the force from the throttle linkage, obviously you would want minimum required tension to zero the linkage. Teaching Granny to suck eggs here of course Glyn.
The pedal linkage spring can be over tensioned a fair bit as the stop and fulcrum should not pass the tension through to the spindle. As you say if you go through the linkage ensuring all is lubricated and free then apply minimum spring force to ensure proper return, if you need any advice on the best lubrication, I do know a good tribologist !
Does anyone here know exactly which bolt on the oil filter that the return spring bracket should attach to, I have not found a definitive answer to this as yet.
This is where we have the long spring bracket mounted to the oil filter housing at present (rusty old float spring at that time ~ now new & somewhat tensioned.) I guess the bracket could be moved to increase tension.
Mine is connected lower, there were 2 brackets for the float bowl overflow tubes on the top 2 bolts and I forgot where the bracket was mounted for the spring,
The spring on yours appears to have very little tension in the picture as it looks quite closed, but that could be my eyesight.
That pic was before the engine was finished and fitted. It now has a single bracket holding the 2 drain tubes which I understood to be original. I think I should move the bracket to a lower bolt. These springs are pretty lightweight. The manuals are unclear as to which bolt the bracket goes on. The old spring was slack. Not your eyesight.
Last edited by Glyn M Ruck; Jan 14, 2019 at 01:16 AM.
Checked the S Type parts manual tonight to see if I had screwed up. Spring bracket shown in my own engine pic above is correct for S Type & Siamesed drain pipes through one clip also correct. I guess running changes over time. Of course they don't show on which bolt each is mounted.
Just to report back & not further mess up Homer's thread. Shortened long spring slightly instead of moving bracket. Adjusted fulcrum lever clamp on butterfly shaft, found a split pin not turned back properly catching, adjusted link rod, did a rough jet setting, balance & idle mixture. Checked timing. Lubricated everything. Result ~ nice stable idle at 500RPM. Slowly grasping SU constant depression carbs after being a twin sidedraught Weber & Dellorto man. (Rods & pistons weight equalised, crank & flywheel with clutch balanced.) Proper tune up will take place once car is registered & on the road officially.
