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Sput...Sput...Sputtering?

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TR4A_IRS

TR4A_IRS

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So, the weather was actually nice this Memorial Day weekend. I was pretty tied up with home improvement projects, but I did get the car out for a spin on Saturday.

The car was running very well at idle and under constant throttle. However, whenever I gave the car more than about 1/2 throttle, she sputtered. If I just kept my foot in the throttle, the engine would eventually start behaving normally. If I let up on the throttle when it sputtered, the engine would get back to normal more quickly. The behaviour (spelling for our English friends among us) was more pronounced when going up hills.

Vacuum advance?

I am pretty clueless when it comes to carburettors.
 
Not likely vacuum advance, IMO, but I'm not sure what it is from your description. First thing I'd check would be the oil level in the dampers. If you unscrew and lift the plunger slightly, you should be able to feel definite resistance when you push it back in.

Which carbs do you have? I believe 4As came with either ZS (early) or SU HS6 (later) carbs. If you have the ZS, the next thing I would check is the diaphragms, as even a tiny pinhole can cause problems.

Then I'd look a fuel delivery, perhaps a clogged fuel filter, or the ethanol in our gas has gotten to the diaphragm in your fuel pump.
 
The carbs are HS6s. I guess I could replace the fuel filter and see if that helps. I am using one of the clear types and it doesn't look clogged, but it is worth $1.49 to find out if it solves the problem.

I will also check the dashpot oil level. I always find this task difficult, as it seems to be something done more by feel than reading a dipstick etc.

I appreciate the suggestions.
 
TR4A_IRS said:
I always find this task difficult, as it seems to be something done more by feel than reading a dipstick etc.
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If you would prefer to read a dipstick, just look at the plunger. If the oil level is above the top of the brass piston, there is enough oil. But since unlike crankcase oil, this oil stays clean, I find it hard to see. The resistance method is easier for me.

Or, you could just remove the plunger and fill to the top of the inner sleeve. It won't hold that level, the excess oil will slowly leak out, but in doing so it lubricates the guide rod for the venturi piston. The TR3 manual says to do this every 6000 miles (but I think the later manuals don't).
 
I wouldn't rule out ignition either. An engine can have a pretty bad miss and still idle near acceptable. Can also run at higher rpms once you get there. But acceleration and uphill load will reveal the problem more noticeably.

Also, if you have been working on it at all, verify that the plug wires are connected correctly (1342) probbaly not the problem, but wouldn't be the first time.
 
tdskip said:
Is it possible to overfill the dashpots even? Won't it just spill out via the top if you put too much in?
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Too much will make the engine run badly (way too rich) until the excess oil can be forced out the vent. The volume of the 'chamber' goes down as the venturi piston rises and the oil takes a relatively long time to run through the vent hole. But you can solve that by lifting the piston all the way to the top after inserting the plunger, so any excess is already forced out before you start the engine.

However the excess winds up in the intake, so you can expect some smoke with this method.
 
So next you are going to tell me that whacking the carbs with a hammer is probably a bad tuning technique as well....LOL.

Thanks Randall.
 
Geo Hahn said:
I wouldn't rule out ignition either. An engine can have a pretty bad miss and still idle near acceptable. Can also run at higher rpms once you get there. But acceleration and uphill load will reveal the problem more noticeably.

Also, if you have been working on it at all, verify that the plug wires are connected correctly (1342) probbaly not the problem, but wouldn't be the first time.
Click to expand...

Thankfully, I haven't been working on the car over the winter. I doubt it is ignition, as I am using a pertronix unit. Aren't these things pretty binary - either they work or they don't, unlike traditional points?
 
TR4A_IRS said:
I doubt it is ignition, as I am using a pertronix unit. Aren't these things pretty binary - either they work or they don't, unlike traditional points?
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I've certainly heard from others with strange problems eventually traced to the Pertronix.

And the Pertronix only replaces one small part of the ignition system. More throttle means higher cylinder pressure which makes it harder for the spark to jump the gap. So anything that isn't quite up to snuff (coil, rotor, distributor cap, wires, plugs) can cause a problem that only shows up under heavy throttle.
 
I had a similar problem recently after rebuilding the distributor and fiddling with the timing. Turned out that I hadn't clipped one side of the distributor cap on!
Silly, but it shows that an electrical problem can have these symptoms.
Although it does sound as though there is not enough fuel getting through on high demand. Also the fuel can quickly go off if the car isn't used for a few months, but that would likely show up with difficult starting.
Probably worth pulling the plugs to see if there are any clues there - gap size, colour, etc. Also the HT leads could be shorting out or have corrosion on their ends.

PS we spell behaviour properly here in Scotland too!!!
grin.gif
:laugh: Sorry, I couldn't resist that one!!
 
NickMorgan said:
PS we spell behaviour properly here in Scotland too!!!
grin.gif
:laugh: Sorry, I couldn't resist that one!!
Click to expand...

:laugh:

I almost didn't start this thread because I expected it would turn out like it has so far - i.e. you have got to check everything. Why couldn't one of you just given me a simple one-step solution!?
 
TR4A_IRS said:
I almost didn't start this thread because I expected it would turn out like it has so far - i.e. you have got to check everything. Why couldn't one of you just given me a simple one-step solution!?
Click to expand...
Well, I'd have said check the carburetor diaphragms first. :devilgrin:

But I say that from personal experience in years past with my GT6+, where once a year, almost like clockwork, I'd have similar symptoms...that I tracked to a torn diaphragm.

Hint for short-term repair: If you find a small tear and don't have a new diaphragm handy, try a small piece of plastic electrical tape!
 
TR4A_IRS said:
I almost didn't start this thread because I expected it would turn out like it has so far - i.e. you have got to check everything.
Click to expand...
Well now you're finally getting the hang of this Ian!
It's either fuel or electrics!

BTW, my votes on an ignition problem, pertronix, coil, wires, cap, rotor etc.
 
Maybe cause some chuckles here...but check for play at the rivet connection on your coil...any play will create engine havoc. Fix...slight tap on a screwdriver with a hammer. (Zen and the art of motorcycle maintenance)
 
tdskip said:
Ian - any update?
Click to expand...

Nope, and it will probably be a few weeks before I have any. Kid #1 has a birthday party this weekend and I am usually too tired by the time the kids are in bed to work on the car - not to mention that I can't run the car after they go to bed because of all the racket!

I am going to do the right thing though. I will start with the plugs to see how the car has been running, and then start going down the list of typical things and then some of the more oddball things suggested here until I am sure I have everything in good working order.

I know many folks are leaning towards ignition, but it feels like a carburetion problem to me. I don't know if that makes sense, but the behaviour seems to come and go smoothly, and my past experience with ignition problems is that they were more binary in the way they felt. But, I will do my best to put my preconceptions aside and approach this like an old British car mechanic - very methodically.

Aw, heck, who am I kidding - I am just going to drive the darn thing until it gets better or worse. Half of my driveability issues in the past solved themselves if I just drove the car more often...
 
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