15 replies to this topic

[maddogmcg]

I have recently aquired a self built car ,constructed wih an a series engine ( donor vehicle either an austin 1100 or a mini estate as traced from engine number ) and am having trouble with getting it started .

I have replaced the dizzy cap ,points , rotor arm , HT leads and plugs .

The car is POSITIVE earth !! it ran when stored 20 years ago so the wiring must be ok ,the engine has a dynamo and voltage regulator . It also has what i think may be a Mk 1 mini ignition switch and floor start

The wiring has very little resemblance to a standard mini in as much as the colours cannot be compared to a the standard wiring loom .

When i crank the engine i do get a spark but it is very small and the carb blows petrol vapour out and inevitably the engine wont start .

I am asking if anyone has any idea where i can find info on this early +ve earth system . Or any advice on how to check the ignition system ,the only part i havnt had chance to change yet id the points capacitor ( i had all the other parts in my spares stock ) could this be the problem ?

Any advice gratefully welcomed

Cheers Maddog

[Dan]

A Mk1 manual will have information about positive earth Minis. I believe all Mk1s and most Mk2s were positive earth. Certainly I have wiring diagrams up to 1967 that relate to positive earth cars and many Mk2 diagrams that do also. If you can come up with a model that you think it might have been based on I could send you a scan of one.

[Ethel]

It being +ve earth shouldn't make any difference to the ignition. The only thing is the coil, the primary and secondary windings share the +ve LT terminal on -ve earth systems. So I think that means you should still connect the points to the -ve terminal and the ignition switch fed to the +ve, if the coil is a later one marked for -ve earth cars.

or the short answer - try swapping the LT wires over if it ain't sparking

[dklawson]

Ethel, positive earth coils are hooked up differently. While they'll work "either way", the spark is about 20% weaker if the coil is wired backwards.

Early coils were designed for positive earth applications and as such, they had low-tension terminal markings to match.

Look at your coil. If its terminals are marked SW and CB, AND you are sure you have got the battery's positive terminal hooked to the chassis, connect the coil as follows:
Run a wire from the ignition SWitch to the "SW" coil terminal.
Run a wire from the Contact Breakers in the dizzy to the "CB" coil terminal.

If you are running positive earth BUT the coil is later (or German) it will have terminals marked + and - (or 15 & 1)
Again, if your battery is hooked up for positive earth and you have a later coil, connect as follows:
Run a wire from the ignition SWitch to the "-" ( or 1) coil terminal.
Run a wire from the Contact Breakers in the dizzy to the "+" ( or 15) coil terminal.

Again, these connections are for positive earth only. The coil connections are reversed on Negative earth application.

With the wiring sorted or confirmed, be sure to go through all the basics of a tune up before trying again in earnest to start the engine. You said the car/engine was placed in storage 20 years ago. Do not expect it to start without opening the carb float bowls and cleaning them, the carb jet tube, and the carb needle. Also, you'll need to make sure the carb float valve is working properly. All of these carb parts will gum up and glue themselves together with varnish if the carb was not run dry prior to storage.

Likewise, though the ignition may have been working 20 years ago, the plug wires are likely to have dry rotted and the condenser may or may not be working correctly. As a minimum, fit a new condenser, adjust the points, and adjust the static timing. If the plug wires are at all cracked, replace them.

[Ethel]

I've had a ponder 'n the only way I can think of that might cause that 20% spark reduction is feeding the secondary winding via the primary so it acts as a resistor. Am I missing something, as that seems to confirm my suggestion that the common LT terminal should be connected to the ignition switch regardless of polarity. I think you're saying the same in your answer Doug, though more clearly than me?

I can't figure what the effect of discharging the HT voltage of the plugs against the polarity of the LT circuits would be though

[dklawson]

Ethel, this is one I don't pretend to completely understand.

On an Austin-Healey forum I used to visit I made the mistake of saying coil polarity didn't matter. Several of those guys were on me like "white on rice" and cited many references that documented the reduced coil capacity when the coil is hooked up backwards. Again I don't pretend to understand it. The easiest way to remember which coil terminal goes where is with later coils marked + and - and to make sure that those coil terminals are in effect connected to the corresponding battery terminals. (Coil (+) to battery (+) via the ignition points on a positive earth car, Coil (-) to battery (-) via the ignition points on a negative earth car).

As a footnote to this, when you read articles on changing a car from positive to negative earth you will find switching the coil low tension wires mentioned specifically. This is not because the coil won't work, it's because if you fail to switch the wires the coil will fire "weaker".

Google revealed the following articles:
http://www.xvo73.dia...com/ht/coil.htm (an article about coil polarity on an MG-TD)
http://www.tpub.com/...0-14P-1_545.htm
(an article regarding International Harvester gas engine equipment)
There are of course lots of others.

Suffice it to say, I don't think the ignition system alone is the issue with this particular non-starting problem.

[maddogmcg]

thanks guys for the replies i am not sure of the history of the model the engine came out of as i stated either an austin 1100 or a mini estate according to the engine number ,the owner said the engine came out of a mini van ! but who can say if this engine had already been replaced in the van .
I have cleaned the float bowl and put in some new fuel , i will clean the jet this weekend , the electric fuel pump works fine so petrol is getting to the carb and being used ( you can see the petrol pumping thro the inline filter ) also getting a condensor and will fit it this weekend .

Thanks Again Maddog

[mk1leg]

Silly question?? but has to be asked .....have you drained old petrol out and put in fresh 4 star and not unleaded..........if unleaded you will have to put some octane booster in the petrol as ulleaded was not around when this car was built........hope this helps....................

and have you put battery in correctly +ve earth straped..............

[dklawson]

Mk1leg, is your cautionary message aimed at raising the octane of the fuel or at adding a lead substitute to protect the valve seats?

For getting an engine started, lower octane fuel actually works "better" than high octane. The surprising reason is that low octane fuel is slightly easier to ignite and burns relatively quickly compared to high octane that is formulated to burn slowly and evenly/smoothly. However, any tank of 20 year old fuel is likely to be more of a problem than a benefit.

[mk1leg]

Mk1leg, is your cautionary message aimed at raising the octane of the fuel or at adding a lead substitute to protect the valve seats?

For getting an engine started, lower octane fuel actually works "better" than high octane. The surprising reason is that low octane fuel is slightly easier to ignite and burns relatively quickly compared to high octane that is formulated to burn slowly and evenly/smoothly. However, any tank of 20 year old fuel is likely to be more of a problem than a benefit.

well an older engine will not start with UNLEADED fuel or you will F**K up valve seats

[Ethel]

1 tank full of unleaded won't be enough to allow the valve seats to erode. nor ar you likely to have any detonation issues with a cold engine in the first few minutes of start up. If you want some assurance that the ignition is ok slop a drop or two of fresh petrol down the carb's throat and try to start it off that.

[dklawson]

well an older engine will not start with UNLEADED fuel or you will F**K up valve seats

I'm sorry, but that is not true. An old engine will start and run fine on unleaded.

As Ethel said, over time you will erode the valve seats by running unleaded gas in an engine built for leaded gas. The effect is slow, not immediate.

The reason I asked the question of you in the first place was that I wasn't sure if you were concerned about running the octane booster to improve the quality of the burn, or if you were thinking the octane booster would protect the valve seats. Common misconceptions are that octane boosters protect the valve seats and that lead substitutes raise the octane of the fuel. Most of these products do one or the other, not both.

[maddogmcg]

yes i have of course emptied the 20 year old four star out and drained the system ( i believe 4 star to be rare nowadays so im gonna put it on e bay he he ) .
i have put new unleaded in with octane booster , the same stuff i use in my 1988 mini .

put a new condensor on it today and it still wont start ,im wondering if it need a new fuse box as it has now started with some strange electrical issues namely one of the unlabeled toggle switches has now begun to activate the starter motor !!!! as well as the original floor start switch . I am always a bit flummoxed when it comes to electrical problems . But have cured weird electrical problems in older minis by fitting a new fuse box and cleaning up the connectors .
and whenever i have paid an electrician to fix an electrical problem with one of my minis it always seems to be ' bad connections ' ,so i will try that path before getting the auto electrician in
I have found an old haynes manual that covers from 1959 to 69 with the + ve earth diagrams in .

thanks again for the info guys

Maddog

[Phaeton]

Is it possible for you to ditch the existing wiring just for th purpose of getting it started? I have in the past used jump leads & wires remote from the car to start an engine, then once proved start faulting the vehicle. Another one, lots of people don't like it & say cars get addicted to it (tosh) but use a squirt of easistart or derivative just to prove the ignition is kay.

Alan...

[maddogmcg]

Phaeton my can of easy start is on the bench at the ready lol

cheers maddog