Engine hesitancy/misfire

[martinbrowning]

Hi folks,
I have been trying to solve a problem with my S130 and run out of ideas. The problem started as a hesitancy and misfire on acceleration but backing off the throttle seemed to clear it. The problem got worse so that although the car would start and idle, after 10 minutes running it lost power and wouldn't respond to throttle, finally dying. Leaving the car for about an hour allowed me to start it again and so the cycle repeats.

Compression was down slightly on front two cylinders but nos 3 and 4 down below 100. I have replaced with new:
Both dellorto's (jetted and supplied by Paul Matty),coil,distributor,fuel pump,plugs and leads.

Finally gave in and removed the head,hoping to find something but,you've guessed it,nothing.
The pistons do move around slightly in their bores but I don't think that is the issue here. Engine probably done no more than 10-15K since total rebuild; head rebuilt by Miles Wilkins.

Any thoughts gladly received. I know that Lotus try your patience but this is getting beyond joke!!

Regards

Martin Browning

[twincamman]

have you replaced the gas cap recently???if so it may not be vented and causing a vacum lock situation ---- where the tanks vacum lock over comes the ability of the pump ---- if not check the fuel pump diaphram----then check your gas tank for a floater --then add some rubbing alcohol to the tank ---water may be in the gas - THEN go to electrics --then to mechanical ---[but you have by passed the other 2 ]--btw 'below a hundred IN A MOTOR THAT SHOULD HAVE 170 POUNDS COMPRESSION MAY BE A HINT ---orrr a piece of shmutz is fouling your needle and seat keeping it open causing flooding ----------------------[shmutz is a highly technical term so check the manual for clarification ]---ed

[miked]

Martin,

I am no expert but it does sound electrical (if you are not having fuel lock) . You say you have changed the Dizzy cap. Have you changed the rotor arm? I had some funny things happen when I had a coil that was too high voltage. It used to spank Dizzy caps and did a rotor arm. Same script as you have. Common factor was heat.

I know that the little metal rivot that holds the blade on the arm is very close to the inside part that goes on the shaft. It does not take much to track through.

Also what type of coil do you have. I caused my own problems with an Aldon Flame Thrower which was too high voltage. Actually beyond the Cap & Arm SAE rating.

The coil actually killed 3 caps before I took it off. I believe by opening plug gaps you also stress the cap and arm as the voltage has to rise further to jump the gap. Just my experience. Could be wrong!

Just noticed you changed the whole dizzy?

Mike

[ppnelan]

Assuming you've got sparks & air supply, could it be fuel starvation? When it 'dies', check whether there's fuel in the float chambers... and in the tank for that matter - it's often something simple!

Matthew

[miked]

Another thought.

Assuming you are on Mech fuel pump. Does it start straight on the key after the hour. If it does and you dont need to crank & Crank, then the fuel is in the carbs'.



I am off to the Pub in minute. Dont want you thinking I am sad on Sat night!


Mike

[redskatejbf]

I`m with Twicamman on this topic, I had a very small piece of insulation tape get into the fuel tank, it would intermittently block the fuel pickup pipe I would then get missing / hesitation and eventually full stop , leave the car for 30 mins. or so and of we go again until the next time.
You could have a build up of crud in the tank that may cause similar symtoms,
Regards John.

[martinbrowning]

Gentlemen,

Many thanks for your replies;they give me a few more thoughts/hings to check.
Looked at the valve clearances - inlets at about 4 thou,exhausts 10 thou. Is there anything odd in the movement of the pistons that I described (I can wiggle them in their bores).

Martin

[gjz30075]

Martin, nothing too unusual to be able to wiggle them in their bores. The stock piston clearances are something like .002/.003". That's all the way around the piston so you're really wiggling them about .006". You have to determine where the low compression is coming from, ie, rings or valves. Squirt some oil in the low compression bore and do another compression check. If the compression rises significantly, then it's rings. If not, then it's valves. Since valve clearances look good, they could be burnt.

[Tonyw]

Martin,

Low compression on a couple of cylinders will not usually cause the problem you describe, if your piston/rings are causing low compression you can usually expect the compression to be higher when hot, as stated a quirt of oil in the suspect bores will give the rings/pistons a false seal and compression will go up whereas if the valves are leaking it will not.

Even though you have new components I suspect you could have a faulty ignition system, I would not discount the carburettas but that would be my second choice after a full check on your ignition, timing, advance, earthing, you appear to have miss under load or is it a flat spot.....if it is a miss under load I believe it is almost certainly your ingition, do not forget to check the leads best done with an Ohm meter from the terminal inside the dizzy cap to the end of the plug lead where it fits to the plug, I assume you have changed plugs.

Good luck and keep us posted, if I were a betting man I would bet it is something really simple.

Tony W

[kstrutt11]

As the others have said, sounds like fuel starvation to me, After mine ran out of fuel it had similar problems, I blew back through the fuel line with an airline and it has been fine since.(I also fitted a filter before the pump which has susequently collected some muck in it), otherwise I would not rule out the new components as the quality of parts nowdays is often awful.

Other items I would check : is the coil matched to the vehicle ,ie have you fittted a ballasted coil to a vehicle which has been converted to 12V?, if it has a ballast resistor is it the right one?

Fuel pump it's self could have faulty internal valves.

Tank venting both pipes are in place and not blocked?


The low compression also looks an issue but would more likely be a result rather that cause of the running issue you mention, it might point to flooding on cyls 3 and 4 (bore/ ring wear) or valve damage if there has been fuel starvation this would also point to possible sticking / incorrect float level or fuel startvation (the front carb is fed first) as most the of the rest of the circuits in the carb are unique for each cyl.

If the bores all look much the same I would suggest you re grind the valves on cyl 3 & 4.

For your ref my +2s with 40k on the engine returns around 170 - 180 psi on each cyl.

P.S where are you? if you are near Chelmsford UK you coud try swaping over electrical parts with my car.


Kevin 73 +2S130.

[RotoFlexible]

Compression was down slightly on front two cylinders but nos 3 and 4 down below 100.

Martin,

What did 1 and 2 register? Assuming you are measuring correctly and consistently, <100 seems really low. I think you have to sort the compression before you worry about anything else.

[CBUEB1771]

Martin, nothing too unusual to be able to wiggle them in their bores. The stock piston clearances are something like .002/.003". That's all the way around the piston so you're really wiggling them about .006". You have to determine where the low compression is coming from, ie, rings or valves. Squirt some oil in the low compression bore and do another compression check. If the compression rises significantly, then it's rings. If not, then it's valves. Since valve clearances look good, they could be burnt.

The piston/cylinder bore clearance is measured at the bottom of the piston skirt, 90 degrees away from the axis of the gudgeon pin. The clearanceat the top of the piston is quite a bit larger. I agree that the pistons can be wiggled even when all is well.

[martinbrowning]

Hi again,

Many thanks to everybody who has offered advice; I am continuing to trace the cause of the problem. Because I have the head off I cannot recheck pressures etc as suggested.

Rotoflexible - I think that the pressures in the front two cylinders were about 140/150.

Kevin - thanks for the offer but I live in just outside Belfast

Like many "small Sunday morning jobs" I'm tempted to lift out the engine entirely for a rebuild and respray the engine bay whilst I have the opportunity. (Haven't told "her indoors" yet.............)

Kind regards

Martin B

[RotoFlexible]

Like many "small Sunday morning jobs" I'm tempted to lift out the engine entirely for a rebuild and respray the engine bay whilst I have the opportunity.

That's what I said - about 16 months, many thousands of dollars, and 100cc ago. Not to mention body removal, frame strip and repaint, adjustable ride height shocks all around, new front arms - the list goes on...

[garyeanderson]

Do it once, do it right and you will have many years of enjoyment before the "Lots Of Trouble, Usually Serious" bug bites again.