I’ve been rather annoyed by this problem for several months now. I bought car back in julyish and the mechanic rebuilt the carbs from scratch. I believe he charged around 2k for the carbs alone. Anyways, I took it back to him at one point because the cold idle was running around 1200 rpm and he lowered it. I’ve had it back for a while and would rather not take it back to him if this is a simple fix.
Problem: When cold, with choke on, the engine starts easily, and runs for ~10 seconds at ~1200 rpm, then drops to a slower idle. Then the engine begins to rumble as if it is running on less cylinders. I feel like the choke on one of the carbs (3) is set malfunctioning and it is starving those cylinders.
After writing this all out I realized its probably best to just take it back to the mechanic. But I’ll ask anyways, I need to learn this car eventually.
Here is a picture of the car, who doesn’t have a name yet.
I LOVE THAT COLOR!!!
First off its an old car with carbs…The car must be fully warmed up, then put the choke down all the way.
once 180 you should be fine, if not your a hair lean…turn jet mixture down a half turn, big difference…
Good luck…
I LOVE THAT COLOR…
As you move the choke lever from Cold Start to Warm Start on the choke lever, you are effectively going from full choke (enrichment) to no choke. Try moving the lever down in small increments and see if the shaking is affected/lessened.
Agreed. Anything with carburetors will NOT perform properly until everything is warmed up. The whole system is out of balance. Hot spots in the combustion chambers. Cold air in too many places. Mixture is wrong, right, middling, wrongish until the engine will idle with the enrichment fully off.
Then, don’t push things until the oil in the shocks is properly distributed.
In below 40F weather I start out after about 30 seconds of idle. As the engine warms I progressively reduce the choke. I sometimes get a bit of a misfire until the temp gauge needle is near the end of the lower solid section, the start of the “NORMAL” section.
It’s hard to diagnose from a distance but you may not be getting “full choke” when the dash lever is all the way up. It might be good to take it back to your mechanic and leave it with him overnight so he can perform a cold start.
Typically you start these cars on full choke, and unless it’s quite cold out (near freezing) after about 10 seconds it will start to run rough and slow down because it is too rich at that point. If you lower the choke a bit it should run better. Keep your foot on the throttle as you do this to maintain the 1200 rpm and slowly lower the choke until it runs smoothly Then take your foot off the accelerator. It will probably stall. increase choke, and restart etc.
When the car is not running have somebody in the car to operate the choke. The parts you need to look at is the mechanism on the left side of the carb body slightly behind the butterfly shaft. There is a small bracket screwed to a bronze vertical shaft that goes into a pylon like structure on the carb. On the other end of the bracket is a spring loaded screw. This screw regulates the fast idle when the choke is on. It screws down onto a paddle shaped piece that is a lever on the throttle shaft. With no choke on, the bottom of the screw should be almost (but not actually), touching the paddle on all three carbs. Get your friend to start raising the choke lever. You should see all three of the brackets with the screw descend equally. The screw will make contact with the paddle and start to open the butterfly - this is fast idle. At the same time you will also see another spring loaded screw located on the left side of the carb towards the front of the carb but at the bottom of the carb slowly rise. This is the mechanism that lowers the jet and enriches the mixture. If all this is working and synchronized your choke is working ok but might need some adjustment…
Without more info your problem seems to me to be one of excessive richness caused by keeping the choke on in too high a position. If not report back.
Also for carbs…
After the car starts, push the choke in about 1/3 of the way (give or take, depending…)
Then push it in the rest of the way in 30-60 seconds, depending on outside temperature. The youngsters (say, 50 or below) have forgotten how chokes and carburetors work. Or never learned…
As for the name, sometimes it takes a long time for it to appear. My “new” car 2014 Volt, bright candy apple red, took about a year to give me her name (Yakut), Arabic for “ruby”.
LLoyd
Trying to be happy by accumulating possessions is like trying to satisfy hunger by taping sandwiches all over your body.
Roger Corless, Buddhist scholar
Your goal is to make sure the oil pump gets oil pumped to “everything”. I usually give it 30 seconds before revving.
LLoyd
Trying to be happy by accumulating possessions is like trying to satisfy hunger by taping sandwiches all over your body.
Roger Corless, Buddhist scholar
Back again. I called the mechanic to tell him the choke felt like it was missing an entire carb. He didn’t seem too enthusiastic to fix it. He said if you’ve been using regular pump gas (91 octane) then the ethanol has gummed up the jets and they are sticking. I paid $2500 to have the carbs rebuilt about 500 miles ago.
When she’s hot she runs like a champ, but that cold full choke is nasty. He told me to try and find 100 octane which is apparently hard to find on tap in southern CA. I meandered my way over to the airport and ran into a mechanic I knew. He let me onto the field to take a pic. Unfortunately I can’t just buy Avgas from a pump. I’ve got a few numbers to try calling.
p.s. I believe we use a very low ethanol blend in southern CA. I never ever see E85 at the pump. Just 87, 89, 91. I really don’t want to believe that 500 miles of this fuel buggered the carbs.
These cars run fine on 91 octane, 10% ethanol pump gas.
Setting up the carbs is a long and fiddly process but once it’s done properly your car will run well for many years (I haven’t touched my triple SU’s in over ten years).
Take your car to another mechanic (preferably someone with gray hair) who appreciates the finer points of SU carbs. There must be a dozen such old-timers in Southern California.
The fine art of juggling a manual choke is something those of us of a certain age had to refine when we first ventured onto the open roads with our own vehicles. All my motorcycles had manual chokes on carburettors. All my cars had until the 1990s - I always owned second hand cars usually over ten years old.
My children have never used a manual choke in any car. It has to be explained to them. I don’t think SWMBO would cope well with a manual choke, the art of using one long since forgotten.
I never warm the engine up before driving off. I alway drive off with a cold engine, and push the choke down until the engine stutters, then up a smidge. Drive a few more yards and back off again, until the engine runs cleanly with no choke. Given the naturally rich mixture the XK engine needs this is never more than a few hundred yards even in the coldest winter days (we have very few days close to freezing in Southern Blighty these days), and during the summer driving season the choke is down to fast idle only before I engage second gear.
Usually, by the time I get to the first junction (about 1 mile) the engine is warm enough to idle on no choke. Idle is 600 rpm when cool, 750-800 when hot.
First click on the choke control detent is fast idle and no enrichment. 700 rpm cool, 1000 rpm hot.
The throttle and choke controls on my car are similar to, and different from all other SU carbie’d XK engines. Similar to in that the mechanical controls began life the same. Different from because after over 200,000 miles a unique history of often careless owners has left an equally unique pattern of wear.
Like the cab settings….Bahaaaaaaa
Well I thought it was funny
If the car runs fine hot
Remove the air cleaner look under the carbs make sure all three are in sync when you pull up on the cable
That’s all from what I hear
It’s hard to adjust the choke linkage on the S1 4.2 setup. And I find that for some reason, they tend not to hold adjustment. When you pull the lever, you’re actually setting the jet on the center carb, this is tied to the front and rear carbs by bellcranks. Due to wear or stretch or whatever, there always seems to be more choke on the center than the end carbs. To adjust them you need to remove the tiny washers and pins on the bellcranks and lengthen or shorten the rods. There’s very little room in there for your hands, and you may have to remove the center carb to make the adjustment. So I can understand your mechanic’s reluctance, but it shouldn’t require a rebuild.
Frankly, to get the engine started, the choke does not have to be exactly equal on each carburetor: what does have to be kind of done correctly is to make sure that the levers that operate the high idle are relatively in sync.
