17 replies to this topic

[James_1]

Hi, I am currently pulling my hair out over a Mini Scamp I am working on. The car has an A+ 998cc engine with an HS4 carb and a 59D dizzy but with a non-balast coil and ignition system.

The background is that the car was used to run around on a farm for a few years before it decided not to start one day and it was pushed into a barn and left. 3 months ago someone had a go at getting it going and decided to remove the head. That was as far as they got and it then sat until a few days ago. Then I came in and have done the following to the car:

• Cleaned up all the gasket faces and rebuilt the engine with new gaskets
• Cleaned all the crud out of the dashpot and fuel bowl and relaced the rubber o ring on the fuel line to the jet which now doesnt leak and does allow fuel through
• Put new service bits in the dizzy and set the points
• Set the tappets and checked for compression in all pistons
• Fitted a new coil and HT leads as the old coil wasn't working and the old HT leads had massive resistance (15 ohms plus)
• Given it a full service
• New battery
• New fuel

The engine spins over fine and has good earths, there is fuel getting into the carb and from the carb into the engine (I can see it with the dashpot removed and the choke pumped, and it is replenished quickly - the jet isn't blocked). There is a good spark and the HT leads are in the correct order. All four pistons have good compression and I can find no vacuum leaks. The vacuum advance and crank case breather outlets on the carb have been tested both connected and blocked.



Now for the problem:

The engine will spin over and fire and on occasion, without logical explination, burst into life for any peroid of time ranging from 5 seconds to 5 minutes. When running it requires throttle to keep it going and does not respond to choke. It will not idle. It will then cut out and refuse to restart. When initially put back together it would start quiet easily but this has got worse over the last few days. The carb settings were not changed from when it was running reliably and adjusting the timing does not help.

Everything has been checked and double checked. The fuel pump does pump fuel into the bowl and will squirt fuel over a metre when operated manually of the car.

My main concern is that I know the engine was run for some time before it stopped with little oil in it so I am thinking that the cam lobe that runs the pump may have worn which is hindering the operation of the pump and I am looking into fitted an electric pump as a last resort. I am completely out of ideas so please help!!!

Thanks!

James

Edited by James_1, 02 September 2011 - 08:01 PM.

[James_1]

Sorry, just to clarify when I say rebuilt I mean I lapped in the valves and rebuilt the head and reassembled, I don't mean a full engine rebuild.

[minimender]

Try squirting some fuel into the inlet to eliminate fuel starvation, you can use a kitchen spray with petrol in it
(I have had a car running like this with no carb on it)
Could be the dashpot piston sticking, or a slightly bent needle
It might be worth checking the tappets again, just check that each one has free play using the rule of nine, you dont have to undo them all again.

out of ideas for the moment but it has to be something that you have 'mended'

[James_1]

Thanks, I'm putting a new needle in tomorrow as it didn't look as straight as I'd like it to and I'll redo all the tappets again just for good measure. I've tried squirting fuel in like that but to no avail. I'll give those two a go and I'll recheck the fuel line from the pump to the tank while I'm at it as that is orginal.

I agree, it is almost certainly something I've messed with - unless it's the gremlin that stopped the thing going in the first place...

[bmcecosse]

I agree - likely to be a fuel feed problem - but not the cam lobe worn away!

[James_1]

Okay thanks, just to play devils advocate, if a replaced needle (like for like) and correct tappets didn't solve it (the dashpot isn't sticking) is there anything else to look at?

Edited by James_1, 02 September 2011 - 09:41 PM.

[minimender]

Okay thanks, just to play devils advocate, if a replaced needle (like for like) and correct tappets didn't solve it (the dashpot isn't sticking) is there anything else to look at?

Maybe a Corsa

[dklawson]

• Cleaned all the crud out of the dashpot and fuel bowl and relaced the rubber o ring on the fuel line to the jet which now doesnt leak and does allow fuel through

there is fuel getting into the carb and from the carb into the engine (I can see it with the dashpot removed and the choke pumped, and it is replenished quickly - the jet isn't blocked).


The fuel pump does pump fuel into the bowl and will squirt fuel over a metre when operated manually of the car.

I am thinking that the cam lobe that runs the pump may have worn which is hindering the operation of the pump and I am looking into fitted an electric pump as a last resort.

For the record, resistance type HT leads often have in excess of 8000 Ohms of resistance (end to end). They are used with "regular" plugs without resistance. You can also use low resistance (like solid core) wires that have almost no resistance. They are used with resistance spark plugs.

In one place you say that you can see fuel in the jet and something about pumping the choke and fuel being replenished. What does that mean? With the choke pushed in the jet should be "high" and you should see fuel in the jet but NOT coming out of the jet (unless the engine is running). With the choke knob pulled out the jet is lowered and the fuel will appear higher in the jet and/or maybe above the top of the jet tube.

You said the engine does not respond to the choke but you were confident there were no vacuum leaks. That implies that the carb is not adjusted properly. It could be that the choke is not adjusted correctly or that a problem with the float valve is allowing too much fuel into the engine (flooding).

I always recommend that people go through the ignition system and adjust the valves before working on the fuel system. In your case, at least check over your previous work and make sure nothing has changed with the ignition components. If nothing is found, work through the carb adjustments from scratch. The first of those adjustments should be to check the float valve, replacing it if necessary and making sure the float is the correct height. And... if you do not have fuel filters fitted, install one before the carb.

As for the electric pump, your test to date say that the pump can move fuel very adequately. I would not invest in a new pump until you have completely ruled out ignition and carb adjustments.

[James_1]

In one place you say that you can see fuel in the jet and something about pumping the choke and fuel being replenished. What does that mean? With the choke pushed in the jet should be "high" and you should see fuel in the jet but NOT coming out of the jet (unless the engine is running). With the choke knob pulled out the jet is lowered and the fuel will appear higher in the jet and/or maybe above the top of the jet tube.

By this I mean that when the choke is pulled out with the dashpot removed the fuel instantly fills the space above the jet. I made a point of this because this was not happening when I first started trying. This was down to the rubber o ring on the jet pipe having corroded and partially blocked the hole in the fuel bowl, which has been replaced.

I changed the HT leads because I had a set of unused ones which made a big improvement and got the engine to fire. They have a resistance of between 6k and 8k ohms.

I will definiatly check the float valve setting and ensure that the engine isn't being flooded with too much fuel when running. I have a new fuel filter fitted in line between the pump and carb.

As for the fuel pump I am confident to rule out the possibility that it is at fault.

[Tommyboy12]

The fuel filter should be between the tank and the pump really.

[Dan]

Set the carb to the initial position and adjust the cables and stops to their proper positions. Initial position is two turns rich from the jet being flush with the carb bridge. It's all in the better manuals, or you can search here for initial position because it's been fully described here a few times. Don't assume that the carb settings were right before, it could have been adjusted to compensate for any number of problems that you have now fixed.

Is there a spacer behind the fuel pump?

[leroy26]

stoopid question time, wheres the carb bridge?

[Dan]

Check your thread, but it's the raised bar sitting in the base of the carb choke that the jet bore passes through.

[James_1]

Well it now runs like a beaut.

When I arrived I carried the following checks:
Fuel
Tappets
Spark plug gaps
Points
All were fine.

The first thing I changed was the needle and piston - I had to do this because on close inspection the needle was sticking out of the piston at a funny angle. I don't know if it's bent or just seated incorrectly because no amount of pursation would convice it to seperate from the piston - not something I've come across before but nevermind, I had a spare.

With that changed the dashpot seemed to lift and fall slightly easier so I attempted to fire it up. This was successful and the engine burst into life, idled happy, revved and then died, and refused to restart.

Overfuelling was then checked. The float level appeared to be a bit high and there was a small pool of fuel below the dashpot. The float was a late type nylon unit which I replaced with a known item from a carb that had been untouched since being removed from a car. This solved the flooding but still no running engine.

With the fuel system running perfecting, without any doubts, I came to the conclusion that it had to be ignition. I knew the points were good and new, the coil was good and tested, as were the plugs and HT leads so it had to be LT. I'd already rewired the LT circuitry so it had to be inside the dizzy. This left the nice new condensor so I removed it thinking it must of failed. This revealed a short caused by the connector that came with it. With this cut off and the wire soldered onto the points it fired up on the first turn without choke (2 turns on the mixture screw). 5 minutes of tuning got it warmed up and running perfectly.
Well it now runs like a beaut.

When I arrived I carried the following checks:
Fuel
Tappets
Spark plug gaps
Points
All were fine.

The first thing I changed was the needle and piston - I had to do this because on close inspection the needle was sticking out of the piston at a funny angle. I don't know if it's bent or just seated incorrectly because no amount of persuasion would convince it to separate from the piston - not something I've come across before but never mind, I had a spare.

With that changed the dashpot seemed to lift and fall slightly easier so I attempted to fire it up. This was successful and the engine burst into life, idled happy, revved and then died, and refused to restart.

Over fuelling was then checked. The float level appeared to be a bit high and there was a small pool of fuel below the dashpot. The float was a late type nylon unit which I replaced with a known item from a carb that had been untouched since being removed from a car. This solved the flooding but still no running engine.

With the fuel system running perfecting, without any doubts, I came to the conclusion that it had to be ignition. I knew the points were good and new, the coil was good and tested, as were the plugs and HT leads so it had to be LT. I'd already rewired the LT circuitry so it had to be inside the dizzy. This left the nice new condenser so I removed it thinking it must of failed. This revealed a short caused by the connector that came with it. With this cut off and the wire soldered onto the points it fired up on the first turn without choke (2 turns on the mixture screw). 5 minutes of tuning got it warmed up and running perfectly.

Without specifically looking for a short it was invisible so I guess the moral of the story is to never trust anything purchaced new.

[100ev8]

Okay thanks, just to play devils advocate, if a replaced needle (like for like) and correct tappets didn't solve it (the dashpot isn't sticking) is there anything else to look at?

Maybe a Corsa

pmsl