Engine Stop running after about 3 minutes

[jbcollier]

RD Enterprises will have the needles: B2AR (Lotus part #36S6180)

Moss has the major overhaul kit:

https://mossmotors.com/master-rebuild-kit-genuine-zenith-stromberg?assoc=81812

You will also need the adjustment tool:

https://mossmotors.com/triumph-tr6-250/fuel-intake-emissions/tool-carb-adjusting

And a sync tool:

https://mossmotors.com/triumph-tr6-250/fuel-intake-emissions/meter-carburetor-flow-sk

And to chase down two used dashpots with adjustable needles from a wrecked TR6 or TR7.

[jrnicl5]

Hello Jbcollier,

Yes, I’m in the US, Texas. I plan to keep the car. I am now evaluating the cost of rebuilding the carbs and with the constant adjustments of the strombergs. Would it be better to transition to what you suggested with the Mikuni kit. The cost is higher but low maintenance down the road and more power.


Your thoughts on this

[jbcollier]

Properly rebuilt and modified (air-compensator and decell-valve disabled) Strombergs are very reliable carbs.  Mikunis will give better performance if you build a performance oriented engine.  Your engine is (probably) stock and of unknown condition.  I would overhaul what you have so you can drive it and make decisions from there.  You can always sell them later if you decide to upgrade things.

Now, let's look at your carbs closely to see what they actually need.  Start with grabbing the throttle shafts and seeing if you can move them sideways or up and down.  Pull and push hard.  Any movement?

[Richard48Y]

I watched your video.
To my ear the engine changed tone slightly, twice before it quit.
Stop was sudden, seems more like a switch than fuel starvation.
Have you watched the tachometer while it is running?
Is the RPM steady or fluctuating, does it decrease in steps before stopping?
If the car has sat so long rebuilding the carbs is a very good idea but I will not be shocked if that fails to cure the issue.
My old S.E.A. analyzer is very large and heavy so not portable.
But there are modern O'Scope versions that run on a lap-top.
The software is not cheap but good tuning shops should have it.
Maybe you can get a Tuner to look at your ignition system as it runs and fails.
Would it be too difficult to just return the ignition system to stock as a test?

[EuropaTC]

To my ear the engine changed tone slightly, twice before it quit.
Stop was sudden, seems more like a switch than fuel starvation.
Have you watched the tachometer while it is running?
Is the RPM steady or fluctuating, does it decrease in steps before stopping?

I've also watched it a couple of times now. I don't pick up a massive change in engine note but the idle sounds quite fast compared to my car so it's harder to pick out. I'd need to see the rev counter I think.

I must admit I was strongly on the fuel starvation option but I'd also agree that the cut-out was much quicker than I expected from running out of fuel, it's more like the ignition was turned off. With that in mind I think I'd also revisit the electrics and make 100% sure that there's a strong spark immediately after the engine cuts out because that's simpler than rebuilding the carbs.

I use inline testers such as the one in the attachment, very simple to plug in and check there's a good spark. You might have a spark that's simply not strong enough to ignite under compression but good enough to flash on a plug in the air.

Would it be too difficult to just return the ignition system to stock as a test?

That's got to be an option, the old fashioned CB points, condenser & coil might not be desirable from a long term maintenance viewpoint but it is very simple and easy to install.

Brian

[4129R]

I must admit I was strongly on the fuel starvation option but I'd also agree that the cut-out was much quicker than I expected from running out of fuel, it's more like the ignition was turned off. With that in mind I think I'd also revisit the electrics and make 100% sure that there's a strong spark immediately after the engine cuts out because that's simpler than rebuilding the carbs.

I use inline testers such as the one in the attachment, very simple to plug in and check there's a good spark. You might have a spark that's simply not strong enough to ignite under compression but good enough to flash on a plug in the air.

Brian

If you attached a timing strobe to the HT leads, and watched the timing light, if the spark stopped, wouldn't the timing strobe also stop at the same time?

If it stops suddenly after about 3 minutes, using a timing strobe might tell you if the spark just stops and cuts the engine. Ditto the rev counter. Maybe after all the rev counter is the easier option to watch.

[EuropaTC]

If you attached a timing strobe to the HT leads, and watched the timing light, if the spark stopped, wouldn't the timing strobe also stop at the same time?

If it stops suddenly after about 3 minutes, using a timing strobe might tell you if the spark just stops and cuts the engine. Ditto the rev counter. Maybe after all the rev counter is the easier option to watch.

Yep, the theory works but I doubt I could tell if the spark had stopped because there was no fuel so the engine stopped, or the spark died first with fuel still in the carbs. It's a fairly abrupt stop in the video and did almost sound like the ignition was switched off.

The spark tester idea is based on the fact that from earlier comments he said he'd got to wait a while before it would restart or it would fire up for a short while with an ether spray. I would stick one of these testers in line and immediately after it cut out, spin the motor and see what sort of spark there is - none/weak/strong. If there is a good spark with the plug under compression, I'd move back to fuel as a candidate. A weak or no spark, I'd be tempted to pull the electronic ignition and fit points to get it running.

Brian

[Richard48Y]

An oscilloscope will present a waveform that may be observed in real time.
If the issue is electrical the waveform will alter as the system fails.
The waveform may be read to see which component of the ignition cycle is failing.
This works regardless of ignition type although non-standard ignitions may require a more skilled operator to interpret the pattern.

EDIT: New scopes start at only about $100.00, good ones about $700.00
https://www.picoauto.com/products/automotive-oscilloscope-kit/overview
Not sure what town you are in but any large city should have a Tuner shop.
These days even the local Garage should have a scope and many are portable.
Since my old console version is not portable I am going to look for a used lap-top version for my own use.

[jrnicl5]

Thanks for all your replies.

I uploaded another video where you can hear me starting the engine and later one it will stop on its own. The tach is not connected I believe as it is not showing any rev for now. I could not record it though. Will have to deal with it after.

I have a long list of testing as per your advice to go through.  I will rebuild the carbs too. By the way, I'm in Texas.


Also, during the video, you will notice the idle decreasing close to the end. It's because at one point I adjusted the idle as it was too high. 

https://drive.google.com/file/d/1Q0NeCFn0vLhIURsWtYJLRY84tT7NpS_T/view?usp=sharing

[jrnicl5]

Hello Richard48Y,

I don’t have the parts to return the ignition system to stock.

jbcollier,

The throttle shaft seems to be fine. Thanks for the references for the rebuild kit and tools.
I will definitely rebuild it to eliminate any issues with the carb. Parts will be ordered today.

[jbcollier]

If the throttle shafts are good, then you just need a minor overhaul kit, and the jets, needles, used adjustable dash pots, and tool.

The overhaul kit is much cheaper:

https://mossmotors.com/rebuild-kit-genuine-zenith-stromberg-for-2-carburetors?assoc=81813

Still need the fixed jets:

https://mossmotors.com/jet-pressed-into-carb-body

[Pfreen]

Not to to state the obvious, but ignition switches can become intermittent.  I know from experience and it is not the most obvious problem.
Your video to me indicates to me he ignition cuts out.

[Richard48Y]

Easily checked via a "Hot" wire from the battery.

[4129R]

Easily checked via a "Hot" wire from the battery.

But take care not to let that wire get into the rotating bits, is easily removed to cut the engine, and is preferably fused to prevent shorting to earth and causing an electrical wire melting problem.

Loose wires around the engine worry me and they can easily get into places they shouldn't be.

[jrnicl5]

Is the following the right jet needle? should I replace it too?

https://mossmotors.com/jet-needle-bag