Thanks Joel. I can never have too many books about Jags!!!
Dave
I didn’t have any time to work on the car over the weekend but I did get some photos of the carbs. I opened one up too. These cars were “rebuilt” a few months ago by a shop near me. The fuel tank and fuel pump were replaced with new at that time too. I think they’re just the basic CD175’s with no modifications at all. I don’t imagine these photos will help but here they are.
Morning,
There appears to be a large scuff mark on the piston. Is this on both and can you see if it aligns with any area in the body that would have caused it?
Thanks Les. I’ll check later this week.
Dave
David I don’t see your throttle stop screws in the last photo. I think from the camera angle they should be visible. Without them, no idle.
Anthony
I see them in this angled view. What did you do about adjusting them?
Nothing this past weekend. Last week I turned them in quite a bit. The revs with full choke were about 1500. I can pull the choke out about 1/4" before the engine quits. And when it quits, it drops off very quickly. Otherwise, the engine is running smoothly. Haven’t driven it yet.
Those screws do not adjust choke. They set your baseline idle. When you turn them in CW, do you see them moving the bracket they are pushing on?
I’m not trying to adjust the choke. I’m trying to keep it running with the choke off. The choke cables are working properly.
David, the screws I pointed out in your photo adjust your idle, you said you moved them. My question was, when you turn them in CW, do you see them moving the bracket they are pushing on?
Yes they do. The RPM increased when I screwed them in.
Did you observe that with the choke ON?
Yes, the engine only runs with the choke on. And it runs great. I’ve let it run up to temperature with no problem as long as the choke is almost fully set.
Try warming up the engine again with the choke on, turn those screws in so the RPM increases by at lease 500 to 1000, and start backing off the choke to see if it will idle.
Thanks Anthony. I was reluctant to run them in too much but I’ll try that next. Right now with the choke, the revs are about 1600RPM.
Dave
Those carbs look awfully dirty for having been rebuilt by a professional shop. I would start by giving them a good cleaning and make sure your needles are installed properly. Then put the pistons back in the carb bodies, raise them up and see if they drop at the same rate and end with a clunk. If they don’t you can try cleaning them some more or switching pistons and carburetors (they might have been switched previously). To initially set the idle screw, I would back them both all the way down and then turn them CW three full turns. This should get you in the ballpark.
Your initial thought that you are running too lean is probably correct. Using the choke, you are enriching the mixture to correct for that condition. Since the Stromberg’s mixture is not adjustable, something else is either allowing in too much air, or not allowing in enough fuel creating the lean state. The floats and needle valves are pretty easy to check. My bet is on the pistons sticking, or the needles sticking in the jets, just based on their less than clean appearance.
Thanks Bob. I get sick every time I think about how much money I wasted with that shop.
Dave, if you are reluctant to turning the screws in. Sit in the drivers seat and start the engine with the choke on. When it warms up, raise the RPM beyond 1600 (approx 2,500 give or take) by pressing the throttle slightly with your foot and hold it there. While holding it, start backing off the choke slowly and tell us what happens.
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Dave - that jet looks to me to be set very lean. From your photo:
The jet appears to be almost flush with the bridge. Usually one sees it about .100’ below the bridge and even that (from the factory) may be a bit lean. Some press them down to .125" (everything is adjustable if you have a hammer).
Here’s how mine looks (sorry, only had a side view):
A crude but effective way I use to measure is with a carpenter’s folding rule:
Looks to be about 3/32" or .100".
I now have adjustable jets which I highly recommend for fine tuning but yours may be able to get close by just being set-up correctly.