Problem setting idle

[carmelowill]

Hello,

I'm experiencing an issue with my Jaguar E-Type Series 1. I’m trying to set the idle to 500-700 RPM, but I’m having trouble with the front carburetor that feeds cylinders 7 and 8. When I adjust the "slow running volume screw" (marked A in the service manual), this carb continues to draw air, regardless of how much I tighten the adjustment screw. Even when the screw is fully closed, this carb pulls in more air than the other two, which are adjusted out a turn. This makes it impossible to synchronize all three carbs and achieve the desired idle.

Does anyone have suggestions for troubleshooting this problem?

[abowie]

Firstly, consider that the front carb's butterfly may not be completely closing with the engine at idle.

If it is not fully closed you can completely tighten the slow idle screw and it will still pull air past the butterfly.

Check all 3 carbs, and ensure all the butterflies are fully closed at idle.

If this is not your problem, remove the slow idle screw completely. It has an o ring seal around it. See if this is leaking.

Alternatively the slow idle screws can corrode, interfering with their ability to seal. Inspect, clean +/- replace the screw as necessary.

If you've got here and not fixed it, try swapping idle screws around. If the problem goes with a particular screw that implies it's the problem. If the problem persists with the same carb this suggests a problem with that carb. The bottom of the port the screw goes in can get damaged. This is hard to fix.

[Allrand]

Cylinders 7&8 on a S1??

[40GT]

The front Carb has the Vacuum take off, is this leaking?.
It does sound like the butterfly isn't seating correctly though.

[malcolm]

Like Randall, I'd like to know where you found cylinders 7 & 8?

[caveman]

As mentioned in post #2, I had this same issue. My front idle bleed screw was all the way home and was incorrectly offset with over adjustment of the centre & rear carbs. The idle was lumpy and I always suspected the butterfly shaft seals as I could feel excess movement. I blocked the vacuum take off from top of font carb to no avail and replaced seals etc. This past winter I had Burlen replace the seals on all three carbs butterfly shafts and now the idle is spot on with air screws correctly set.
If you are confident, there’s some great setup information on this forum. I used Andrew Turvey’s (CMC) guide ‘Balancing SU and Stromberg Carburettors’ as a start point.

[caveman]

Aren’t there 9 cylinders on the S1.5 cars?