Hard to start when cold...1930 Triumph Super 7 (850cc) side valve 6v positive earth.

[Rata Road]

Hi guys I have a hard starting issue with my car, its a 1930 Triumph Super 7 (850cc) side valve 6v positive earth.

Its starts perfect when warm but stubborn and sometimes wont start when cold. My gut feeling it is the carby/fuel system, The carby is getting fuel correctly from the gravity fuel tank.

It has advance retard on the steering wheel, Ive tried all sorts of starting systems/methods with no luck yet.

It has a good oversize 6v battery that winds over quickly but has a 12v coil (was like this when I got it).

What I would like to know if the 12v coil good be the issue? I dont want to buy a new 6v coil unless it would fix it. I dont want to change the system to 12v, the 12v bulbs dont worry me but then the generator wont be any use.

Your thoughts on the coil or any way to test to see if the coil is working correctly when its cold.

 

Thanks

[keithb7]

Compression test first.  Next steps to be determined from the test results. 

[Bloo]

1 minute ago, Rata Road said:

What I would like to know if the 12v coil good be the issue? I dont want to buy a new 6v coil unless it would fix it.

 

Is there a number and brand on the coil and can you look it up and see what cars it was intended for? On a majority of US cars with 12v systems, a ballast resistor, sometimes a wire you can't see, was used. The coil would run on a lesser voltage during normal operation, probably 7 or 8 volts, and then get sent everything the battery had only during cranking. A lot of US 12v coils should work fine because the 7 or 8 volts they expect is about the same as the 7.2-7.6v a 6v car probably has when it is running and charging. If the coil turns out to be applicable for stock replacement on any 1960s or later major brand US cars, there is a good chance you don't need to change it.

 

During one of the periods when you can't get it to start, see if you have a nice hot spark or not.

 

 

[TerryB]

Can you look at the spark plug, removed from engine of course, and observe the quality of the spark when turning over the cold engine? Also if you are handy with a Volt/Amps/Ohm meter you should be able to read the resistance of the ignition coil.  A true 12v that does not require an external ballast resistor will measure about 3 ohms and a 6v coil will measure about half that amount.

 

Edit- As noted above there are 12V coils whose internal resistance is low enough to operate on 6V.  This assumption is based on your 6v battery voltage not dropping too low during cranking at startup.  You may want to check your battery cables to ensure they are clean and tightly connected.  

 

Edited July 31, 2022 by TerryB (see edit history)

[Rusty_OToole]

It may be the coil. Most cars are set up so they get a hotter spark when starting. I recommend a Bosch blue coil. This used to be a popular accessory for air cooled VWs and dune buggies. They are 6 volt, work with points ignition, and do not require a separate resistor (they have one built in). You can often find them at swap meets for a few bucks and anyone who used to mess with VWs probably has a couple kicking around. Just be sure it is the 6 volt version.

https://vwparts.aircooled.net/6V-Bosch-Blue-Coil-US-Version-00-016-p/00-016us.htm

 

If you want to get technical, many 6 volt cars came with a 4 volt coil. When you give one a full 6 volts you get a hotter spark, even if the battery is a bit weak and power drawn down by turning the starter, if you get 4 volts the car will start. Then you add resistance while the engine is running so you don't burn out the coil. This resistance can be from a separate ballast  resistor or internal, build into the coil.

 

On 12 volt cars they did the same trick, using a 6 volt coil. That is why a coil off a 12 volt car will run fine on a 6 volt car but may be hard to start.

 

PS a stock coil off a 6 volt VW should work, and not require a separate resistor. In fact any coil off a 6 volt car or tractor or motorcycle if you use the stock ballast resistor.

 

In the meantime you could try cleaning the spark plugs and gapping them a little closer than stock. If they are supposed to be .025 try .015. If it starts easier that tells you the spark is weak.

Edited July 31, 2022 by Rusty_OToole (see edit history)

[Ronnie]

I would give it a sniff of starting fluid while trying to start it when cold. If it tries to run it's a fuel problem.

[Terry Bond]

Should not be that much different that my 1935 Morris Eight to start.  Don't know what kind of carb you have, but sometimes I would need to use the little button on top of the SU carb to fill the float bowl, and usually a little choke but it would start up pretty good.  Check your carb float level and also the needle valve to ensure nothing is out of adjustment or stuck that might prevent the bowl from maintaining proper level.  With a gravity feed fuel system I've also seen people install aftermarket filers that can cause a problem.  Some filters have a ball-check valve in them to prevent back-flow.  If you have a newer fuel filer in-line someplace take it out and try starting the car.  With manual advance and retard, you should fully retard the spark when starting cold - just like my Model T Ford. Just a few extra things to look at before you start just replacing parts.

Terry

[28 Chrysler]

Check your choke to make sure it got full movement. A small vacuum leak ?

[Rata Road]

Thanks guys some great suggestions there and I've learnt a lot.

I tried the plug out test and it has spark, I tried changing to another coil, same issue then while I had a plug out I squirted a bit of petrol in one hole, replaced the plug and hit the starter button and it fired up. So I guess it is the carby. Its a Solex carby, updraft and virtually impossible to get easy start into it so that didn't help with the fault find.

Thanks so much for your ideas everybody.

[jdome]

British sports cars I've owned in the past had SU carbs with oil bath Dampers. Solex may be similar. Hard starting and/or rough running could be an indication of low oil. Hopefully you have an owner's or shop manual for your specific car. If not, one of those General Repair Manuals For Foreign Cars will have information on the care & feeding of SU Carbs. Typically a downdraft or side draft will have a dome on top of the carb with a filler cap at the top center of the dome. The cap may be a hex bolt or it may be a twist knob you can unscrew by hand. The oil bath will be on the underside of a true up draft and the filler cap may not be obvious to find. There should be a stub dipstick under the cap with fill level marks. DO NOT use anything other than what is recommended in your manual. SU Carb oil has the consistency of brake fluid and is sold in brake fluid size cans. it shouldn't take more than a couple tablespoons  or so to top off a car your size. Should be available at your local auto parts store or foreign parts specialty store. Checking the carb fluid level of a car of your vintage should be as routine as checking the other fluid levels.

 

NOTE:  I had to edit this post because I had my Jaugar SU Carbs confused with Solex carbs. It was many years ago that I owned these cars. I Believe that Solex carbs may have similar oil fill requirements. Check your manual to confirm.

Edited August 2, 2022 by jdome (see edit history)

[Rata Road]

Thanks Jdome but no the Solex doesnt have a oil damper like the SU's. I have done a bit of work with the SU on my 70 Mini and I like them to work on they are so simple.

Thanks for your time

[zepher]

Interesting car.

How about some more pictures?

Good luck sorting your carb.

[8E45E]

How old is the distributor cap & rotor?

 

I'd change them out if they are ancient.

 

Craig

[Rata Road]

Well guys I have solved the issue very easily. I have a habit on all my old cars of turning off the fuel and running the carby dry before I turn the ign off etc. With several cars you never know when you will drive it again so it avoids stale fuel glueing up the carby.

For 3 days in a row I couldn't start it no matter wheat until on the 4th day i poured fuel down a spark plug hole.

The fix - I simply turn the key off when its running and then turn the fuel off i.e. leave the carby bowl fill. The next day it starts after a few winds? I'm happy.

Here is a couple of more pics.

I have also bought a 1928 Triumph Sport which I will collect in a few weeks. Its lovely wee open car.

Thanks again for your input guys