16 replies to this topic

[Yorkshire Pete]

Please help I've ran out of ideas.

1994 Mayfair
1275cc
1/4 SU

So one day I turned right and she totally died on me in the middle of nowhere, finally I get home and start to try and find the problem I've checked to see if there was fuel and seems to be no problem then next was to check spark and same detail no problem, then the carb came off and checked and cleaned up a little again no problem, finally after all this I get her running with a lot of luck and nearly burning out the starter motor in the process, running 'lumpy' but thought nothing of it until after a day or two i turn right again and now back to square one without a clue once again!

Suggestions have been:

Coil
Electrics
Diaphragm?
Don't be tight and take it to a garage
And best one...... just don't turn right!!

Hopefully someone will know what this problem is or had a similar problems

Any help would be much appreciated thank you

[KernowCooper]

Your going to have to run through all the checks,like do you have spark when cranking and follow the system through checking voltage at the coil, visually check the condition of the rotor and cap and the condition of the ignition wiring, does it start if you pour a small cap of fuel into the carb intake?

What diaphram are you referring to ? fuel pump ?

[Yorkshire Pete]

Hi, I've done all the checks, there's spark on all cylinders, fuel into the carb and air flowing through the filter,
The diaphragm is the one on the dissy that's connected to the carb by a pipe (on mine it goes over the top of the engine) I thought it was part of the vacuum but been told the engine should work fine even if it's broken?!?
I have really hit a wall with this one a lot of coffee,head scratching and swearing has been put into this problem

[jaydee]

Start with the basics, static timing at 8 degs and fuel jet at initial position (It should be HIF38 carb so remove dashpot-piston assembly, set jet flush to the bridge, then mixture screw in 1/2 turn)

[blacktulip]

how do you know the fuel is actually getting into the intake? fuel in the carb does not confirm this. try pouring a cap of fresh fuel down the intake elbow and crank it over. if it starts up then the problem is that fuel isnt getting into the intake. usually a stuck float or blocked jet.

[gazza82]

The diaphragm is the one on the dissy that's connected to the carb by a pipe (on mine it goes over the top of the engine) I thought it was part of the vacuum but been told the engine should work fine even if it's broken?!?
 

it should start but it won't run right if the vacuum advance isn't working .

[ChopperHarris]

Elimination process, the easiest way
Fuel
Turn engine over with a squirt of Easy Start into the carb, engine runs for a few seconds and seems to run reasonably = fuel starvation
Ignition
Correct colour spark at all plugs?


Leaves the time the spark occurs
So Check firing order, timing OK?

Outside of poor compression etc that's all there is, being it was running OK before.
If you get these parameters correct, the engine will start when the car is stationary.
Regarding the intermittent fault, then the most likely source in a dodgy electrical connection...so as Kernow says, work from battery terminal connections forward

[Yorkshire Pete]

Guys thanks for the advice and patience looks like I've got a full weekend in front of me learning technical wording then applying it to the car.
I'll keep you all posted on the process and the turn out.
Thank you

[classicoop]

94 so electronic distributor?

I just had this same problem with an electroci dizzy. Had spark had fuel strong battery.

Turned out the connector on the ignition module (the one connected to the distributor) was corroded.

It would sometimes it would start with loooooong cranking sometimes not. Then not at all. Would get the occasional puff from carb or sometimes exhaust. When it did start it was lumpy until it was revved which wouldn't even rev sometimes.

Replaced the connector pins and cleaned up the module pins and distributor. Now 1 click start no misfire at any load.

My guess was inconsistent firing. Not spark blowout since coil seems to be doing just fine now.

[Yorkshire Pete]

Thank you might look into this first as it sounds just like my problem

[Yorkshire Pete]

Well the problem seems to be what classicoop said she started but running very sluggish so looks like instead of pratting about I'll just replace the whole lot.
Thanks to everyone that commented guess I've still got a lot to learn.

[Yorkshire Pete]

Ok ages since i messaged on here but problem fix(ish) now its miss firing and running really rich and any adjustment on the carb dosnt effect it at all

[gazza82]

Dirt in jet, bent needle or badly fitted stopping needle from seating? Sounds carb related so start there. Back off choke settings etc.

Edited by gazza82, 27 March 2016 - 04:08 PM.

[NiallLonsdale]

Could be timing maybe. Have you checked the rubber on each end of the tube connecting the distributor to the carb hasn't perished. Especially on the distributor side as it is right by the hot oil pipe which is perfect place to melt the rubber.....Small cracks in that can cause issues with the advance of the timing on the distributor. It's one of the reasons I'm fitting fully electronic ignition now, much simpler to diagnose, less mechanical stuff easier to swap bits and hold boot spares.

[NiallLonsdale]

Oh and if you look at the carb there is a pot with a black cap you can unscrew, if you unscrew and lift rod out there should be oil in the cylinder where the shaft (piston) connected to the black cap screw goes. 3 in 1 oil is suitable if that is low, the cylinder inside should move up if when you remove the black cap and put a very slight sideways pressure on the shaft (piston) as you pull it out of the cylinder. If that is stuck inside or doesn't have oil in it that can be an issue too. That I believe is like a buffer for excessive fuelling so without it the engine can get too much fuel when it's not needed and effectively....stall. See below explanation from wiki:

"To prevent erratic and sudden movements of the piston it is damped by light oil (20W Grade) in a dashpot, which requires periodic replenishment. The damping is asymmetrical: it heavily resists upwards movement of the piston. This serves as the equivalent of an "accelerator pump" on traditional carburettors by temporarily increasing the speed of air through the venturi, thus increasing the richness of the mixture.

SU carburettors do not have a conventional choke flap, which in a fixed-jet carburettor enriches the mixture for starting the engine from cold by restricting the air supply upstream of the venturi. Instead a mechanism lowers the jet assembly, which has the same effect as the needle rising in normal operation - namely increasing the supply of fuel so that the carburettor will now deliver an enriched mixture at all engine speeds and throttle positions. The 'choke' mechanism on an SU carburettor usually also incorporates a system for holding the throttle plate slightly open to raise the engine's idling speed and prevent stalling at low speeds due to the rich mixture."