Carburetor Help?... I think...

[Sherony]

I am not sure if I have a carb tuning issue or not. Any advice would be very appreciated.

The vehicle is a 69 IIA. 2.25 Petrol with Weber 34 ICH. I rebuilt the carb about 6 months ago, and I drive the truck almost everyday, avg. 30 miles a week. She always starts right up and runs like a dream.

I know my brake booster is bad. When depressing the brake pedal, the booster hisses and the RPMs rise by about 800 - 1k.

Another known issue is a plume of gray smoke that is emitted from the muffler when starting the truck. The truck never smokes besides this one cloud when starting.

Pulling the choke reduces the RPMs. From what I understand, a choke is supposed to increase the RPM by cutting the airflow, thus increasing the Fuel/Air ratio.

The truck idles beautifully as soon as i start it. It takes an absurdly long time to get up to operating temp, but when it does, the idle is about 600-700 RPM higher than when starting a cold engine.

To me, it sounds like this carb is running rich. I believe that the RPMs are reduced by the choke because it is almost flooding the engine. Part of me feels like leaving it alone, because the truck always starts and always gets me where I'm going, but I want to get it perfect.

I plan on ordering my new brake booster from RN soon, and I wanted to get this community's input on what would cause my irregularities so I can purchase any needed parts to get my Rover perfect.

Thanks in advance.

[SafeAirOne]

Here's a view from somebody who doesn't own a carburettor:

The dark smoke on startup is evidence of too much fuel in the induction system for whatever reason. If it clears right away, I'd suspect carb fuel leakage after shutdown or just a plain too-rich mixture.

Good on you for replacing your your brake booster. It is bad and it could kill your engine (not permanently, of course) while you're braking, though the vacuum leak appears to be bringing your fuel/air ratio within the correct range when you hit the brakes right now.

Pulling the choke on an already-rich mixture will cause a further reduction in engine RPMs. The normal increase in RPM associated with the choke usage you usually experience is generally not mixture-related, but rather accomplished through mechanical means. Specifically, a cam on the end of the choke actuator opens the throttle a bit to supply more fuel to the induction air, as if you were stepping on the accelerator pedal slightly. In fact, sometimes you can feel the accelerator pedal drop slightly when you fully actuate the choke.

I think you're on the right track in saying that your mixture is too rich, for whatever reason, be it fuel leakage or improper carb adjustment or incorrect jetting. I'd remedy this before you have spark plug and lubrication/cylinder wall/ring problems.

Again, take this for what it's worth from somebody who thinks that proper engines use injector pumps and burn fuel that costs over $4.00 a gallon. ;)

[Billy5]

I have a weber also. Are you sure the plume is not oil? It could be the valve stem seals leaking. Mine does the same thing, although not every time. The choke will increase rpms if its cold, but when warm, the truck should run rough and be sluggish. It is possible your choke maybe stuck. As for the booster, I had the original in mine. I had a rough idle ( not major) and could not figure it out. Take a pair of vice grips and clamp the hose to the booster, and see how the engine reacts. If your booster is bad, then tuning the carb isn't going to help much. You will be tuning it to an already lean condition. Fix the booster first. Hope that helps.
Billy

[Sherony]

After a tear down that went much deeper than anticipated, I have been back on the road for a few weeks. Amongst the ridiculous amount of new parts I have installed was the brake booster (along with every other component in the braking system), and the idle issues are gone. I tried to tune the carb to the best of my ability, but I am still having some issues. First, I can adjust the idle mixture screw all the way in, the truck still seems to run rich. If the mixture screw is all the way in, it should kill fuel to the carb, correct? I have since backed the idle screw out 1 turn for my own sanity. I get a small plume of black smoke when I start the truck every time.

Not sure if it is related, but the vehicle has a strange problem after driving at sustained speeds for more than 10 minutes and coming to a stop at a light, the vehicle will surge when trying to accelerate. It will idle fine, but touch the accelerator, and it bogs down. Slug through the rough, pulsing acceleration (with a few backfires) for 2-3 minutes, and everything is back up to par. Is this another issue from the truck running rich?

My only thought on a fix at this point is to take the carb apart and lower the float. I'm assuming this is possible based on the one other automotive carburetor I have rebuilt. Does the carb need new jets perhaps? If so, any recommendations to get the best A/F ratio in the Midwest (St. Louis)?

[albersj51]

Have you verified your timing is correct? I know when mine (when it was running) backfired the timing was off.

[Billy5]

I agree with timing. But also check Pierce Manifolds website. He has tuning instructions for all webers I think. If I remember right, first turn idle adjustment screw until just touches the stop. Then turn one full turn in. The mixture screw turn all the way in until it stops, but don't force it. Then back out two turns. Start the truck and turn the mix screw in until the truck runs better. You are lokng for leanest idle here.

[Sherony]

I have had no issues with the truck running. It starts and idles just fine. I did the mixture screw out two turns then in to lean it out, but it still runs rich. Timing is a new animal to me, but I know I have a timing light and enough manuals to figure it out. I will explore that next. Would poor timing cause it to only bog down after driving a sustained speeds? I can drive it around town for hours without a problem, but a country road or the highway makes it want to die when I finally come to a stop.

[JimCT]

the vacuum leak in the brake booster is the source of all the problems. Touch nothing till that is fixed



I have had no issues with the truck running. It starts and idles just fine. I did the mixture screw out two turns then in to lean it out, but it still runs rich. Timing is a new animal to me, but I know I have a timing light and enough manuals to figure it out. I will explore that next. Would poor timing cause it to only bog down after driving a sustained speeds? I can drive it around town for hours without a problem, but a country road or the highway makes it want to die when I finally come to a stop.

[Billy5]

Just to make sure, Jim is right you did fix the booster? If not then everything else comes second. But, all adjustments to my knowledge should be made after driving around, engine up to operating temp. THings set at cold will not be the same when warm. Timing isn't difficult, most do it by ear. But again, I had the same issues until i found the booster problem. Then and only then did I go after all else. Once the booster was replaced, I started from scratch with the carb etc. The bogging down could be that the engine cannot take all the fuel you giving it, pretty much choking it until rpms increase. Also, age of engine matters as well. By the book is for new, as these age and miles, we need to adjust as such.

[Sherony]

The booster has been replaced with a new one from our hosts, and the new one works wonderfully. I did my adjustments after a 20 minute cruise, and the truck was at operating temperature. With the idle screw turned all the way in, it was still running rich.

Thank you all for the help. I do appreciate it.

[stomper]

Is this truck new to you? Where did it come from? If it was re-jetted for higher altitude, you may need to rejet for your current altitude. I would recheck everything else in the carb to make sure you didn't mess something else up first.

[Sherony]

I have had the truck for a little over a year, and it has been in this area for 4-5 years and in Kansas before that. I have no idea what I could have messed up in the carb. It was a very simple rebuild, but I had never worked with a weber single barrel before this one. My PO seems to have taken decent care of this truck. It suffered a little neglect here and there, but overall I haven't found anything ridiculous. I doubt it was jetted for high altitude, but there is no way for me to know.

I will see if I can check the timing tonight when I head out to the garage.

[albersj51]

You can check the jetting by pulling the main jet out and reading the numbers stamped into it (if you have good eyes). I forget the correct one for sea level, but a quick google search will yield the answer...or look at expeditionlandrover.info, I believe TAW discusses the jet size.