Sputtering/Chopper effect...

[NC Rover]

So for the love of me, I cannot get rid of the sputtering when it idles. It sounds like a helicopter. I've adjusted all the valves and checked them twice. They are perfect. I've adjusted the timing I don't know how many times trying to get it right. The carb is a Weber two-barral. It only has a screw for the idle. There is no screw for air mixture as I have taken it off and inspected it carefully.

Any suggestions on what to check next? I just replaced the whole exaust as well and that didn't help it.

[swaschka]

is it a perfectly repeating miss? If it is, determine which cylinder it is and work backwards through the system til you reach the common or shared portion of the system using known working components. IE: Once you know it is one cylinder replace things connected to that cylinder you know work on others such as plug, plug wire... well you run out pretty quick on these motors, but look at the cap internals etc. If it is not a perfectly repeating miss then go the other way. Vacuum leaks, faulty ign components. Replace with what you have you know works or systematically pull and check what is on the truck. Perfectly repeating misses are rarely caused by shared system components such as timing, fuel, air. Vice versa for random missing. Good luck. FYI my last series truck drove me to work every day for 5 years. Hardly ever did not have some intermittent miss or pop. Don't try to make it run like a Tundra, you'll go bald.

[NC Rover]

Yeah its pretty much the same repeating miss. I've replaced all the plugs, plug wires, cap, rotor...adjusted valves. I'm not sure but maybe the problem could be with the distributor. The carb may need fine tuning but I'm not a pro at tuning a carb. I've got the idle adjusted right. Its pretty frustrating. I'm not trying to get it to run perfectly smooth...but its annoying b/c it sputters along and never has full power.

[sven]

Which weber model # do you have?

[singingcamel]

Hows the compression?

[Jeff Aronson]

Sputtering

If you have another set of points, swap them out and gap them correctly, Make certain you don't have any distributor shaft wobble or you'll never get accurate timing or a smooth idle.

Singing Camel suggests you might have an "inside the cylinder" problem and it's well worth examining.

An easy way - start the car and then, using plastic pliers or insulated handle pliers, remove each spark plug cap. The engine running should degrade until you plug it back in. Try each cylinder in turn. If the engine note does not change, or changes hardly at all, on one cylinder, there's your problem. It could be a simple thing, like a bad plug, or more complex, like a poor valve adjustment [they do need to be adjusted every 15K or so], or worse, a burned valve. A compression test would tell you a lot more.

Another thing to try is to take a can of WD40, PB Blaster, or similar stuff, and spray around the carb body, the throttle shaft into the body of the carb, and when the engine is cold, the intake manifold. You may have a vacuum leak, which would cause similar symptoms. The intake manifold bolts onto the exhaust manifold, and as a unit, to the engine. So the gasket between the block and the manifold is really important and it can fail over time. You might just find that you have loose bolts which are letting air in; the carb is adjusting the constantly shifting amount of air.

The only Weber I'm familiar with is the single barrel so I can't be of great help. In general, Webers are reliable carbs but they can wear at the carb body area. I get about 100,000 miles per carb using the Weber, and find it easy to install and tune.

Good luck!

Jeff

[Tim Smith]

Helicopter sound? I bet you had a spark plug come loose.

[Bostonian1976]

is this sound just from the tailpipe? Mine has always sounded like this from the tailpipe (not that mine is a great example!)

[Eric W S]

Another thing to try is to take a can of WD40, PB Blaster, or similar stuff, and spray around the carb body, the throttle shaft into the body of the carb, and when the engine is cold, the intake manifold. You may have a vacuum leak, which would cause similar symptoms. The intake manifold bolts onto the exhaust manifold, and as a unit, to the engine. So the gasket between the block and the manifold is really important and it can fail over time. You might just find that you have loose bolts which are letting air in; the carb is adjusting the constantly shifting amount of air.

Carb Cleaner! Other aerosols like starting fluid can do bad things to the internals of your engine.

Find a local garage and see if they have a smoke machine. They will be able to tell you pretty quick if it is a vacuum leak.

Vacuum gauge works well to time the engine as well and you can tell a myriad of things about the internals as well. Google it.

EwS

[Rineheitzgabot]

I think that it would be okay to use the WD40 or PB blaster, as they are not nearly as flammable as ether. Additionally, the amount being deposited in the engine (only if there was a leak) would not be enough to cause damage.

[Eric W S]

I think that it would be okay to use the WD40 or PB blaster, as they are not nearly as flammable as ether. Additionally, the amount being deposited in the engine (only if there was a leak) would not be enough to cause damage.

Even a little bit of the wrong aerosol can cause a bad hotspot or even damage the piston/walls. Hence the cautionary advice.

My old mechanic had to order a new block for someone trying the same technique with PB Blaster.

Easiest way to do it is to have the engine smoked for 50 bucks and have the shop tell you what is leaking. No petroleum products gunking up the bay and you can move on to the next issue without standing around hosing your truck down...

Spraying is shade tree IMO...

[Jeff Aronson]

Sputtering

As one who constantly finds that the PB Blaster or WD40 can still feels quite full when the aerosol propellant runs out, I can't believe that there is enough propellant to cause damage. I've used this method on a lot of engines and did not make it up. A mechanic who's still in business showed it to me.

Carb cleaner has a propellant in it, too, or of course it would not come out of the can. I find that engine idle diminishes when carb cleaner is first sprayed into a carb. The opposite occurs when I use PB Blaster or WE 40. So if I want the rpm to increase when a petroleum product is sucked into a vacuum leak, I would stick with these products. This is not a long process; so not much is being taken into the engine.

I don't doubt that your mechanic had to replace a damaged block, but it's just not been my experience with over 20 different needy British cars that this diagnostic method has caused any damage.

Jeff

[Rineheitzgabot]

As one who constantly finds that the PB Blaster or WD40 can still feels quite full when the aerosol propellant runs out, I can't believe that there is enough propellant to cause damage. I've used this method on a lot of engines and did not make it up. A mechanic who's still in business showed it to me.

Carb cleaner has a propellant in it, too, or of course it would not come out of the can. I find that engine idle diminishes when carb cleaner is first sprayed into a carb. The opposite occurs when I use PB Blaster or WE 40. So if I want the rpm to increase when a petroleum product is sucked into a vacuum leak, I would stick with these products. This is not a long process; so not much is being taken into the engine.

I don't doubt that your mechanic had to replace a damaged block, but it's just not been my experience with over 20 different needy British cars that this diagnostic method has caused any damage.

Jeff

I agree with Jeff.

Additionally, this method costs less than $3, rather than an instant $50+.

For the past 15 years, I have been exposed to hundreds of diesel engines where ether was used (cautiously) to get them started, and not once have I seen problems caused by it. I realize that we are not talking about ether, and it is not a safe way of starting a motor, but I use the ether example because ether is much more volatile than less-refined petroleum products (which Jeff pointed out, actually make the engine miss, more than it accelerates combustion-propellent or not).

Besides that, who hasn't pulled a small block out of an old chevy using a hoist and an oak tree? Shade tree mechanics rock!

[Eric W S]

I think it's similar to smoking. Some people get cancer others don't. To each their own I suppose. I'd rather pay the shop, order the parts from our host and move on to the next fun project knowing that one problem has been fixed.

[Jeff Aronson]

Sputtering

Eric, I understand your point. I, too, would prefer to "do the least harm" in trying to fix something. The smoke machine would do the trick, but the local mechanic on this island doesn't have one. Autoweek reports that one brand costs $745 list - that's just too much for me.

Most of the time I'm stuck with diagnosing and repairing a problem in the open air. A can of PB Blaster - something that will serve multiple purposes - is a good thing to have with me.

Of course, the best solution is maintaining my car properly. When I bother to check on gaskets, tighten nuts and bolts and do tuneups around oil changes, I tend to have fewer running issues altogether. I only wish I practiced what I preached more often .

Jeff