Erratic Engine

[esray]

Dear All,

Roy has been running perfectly for ages, but recently he cut out, would restart, run perfectly for a short distance, then cut out again.

Now he starts first time, runs perfectly for thirty seconds to a minute, revs up of his own accord and then stalls!

I have rebuilt the fuel pump with the kit (full of crap but working fine now), stripped down the carburettor (HIF6) and all appears fine; timing is spot on.

STUMPED - PLEASE HELP :!: :!: :?:

Ray

 

[JVY]

Are you absolutely sure it's a fuel problem and not an ignition problem? Sudden stalling after a short warm up is typical of coil, condenser, rotor arm or similar ignition problem. The thing that seems odd is the revving up. What sort of increase to you get in engine rpm before it stalls? Is the revving up very rapid or more gradual? First thing that I would quickly check is the advance/retard mechanism in the distributor?

 

[Geordie Jim]

If the revs increase before a sudden stop it's a sure sign of fuel starvation.
As the mixture weakens, the revs increase until it's too weak to run.

Jim.

 

[cdnp6]

I had a similar problem after rebuilding a fuel pump that the car wouldn't run until I cleaned and lubed the fuel pump rocker arm parts. Worth a try.

 

[esray]

Are you absolutely sure it's a fuel problem and not an ignition problem? Sudden stalling after a short warm up is typical of coil, condenser, rotor arm or similar ignition problem. The thing that seems odd is the revving up. What sort of increase to you get in engine rpm before it stalls? Is the revving up very rapid or more gradual? First thing that I would quickly check is the advance/retard mechanism in the distributor?

JVY,thanks for your reply.

I have Powerspark electronic ignition fitted. Having said that, I did have a problem with the advance/retard. Instead of the vacuum advancing the distributor base-plate, the whole vacuum unit was being 'sucked out'. I cured this by gluing the splined 'bolt' (with the knurled nut at its other end) back into the unit with industrial strength glue; tested the vacuum and it appears to work perfectly?

It runs perfectly for a short period, then the revs suddenly increase (not alarmingly) and then fall away again, sometimes recovers but eventually stalls. From the exhaust end, the period of risen revs feels like best setting, with the initial lower revs being somewhat 'blowy'.

I am with you regarding igniton versus carburation - I am constantly examining both - I have repeatedly checked the timing with a strobe and it is spot on; of course, having said that, I do realise that the timing could be going out at higher revs - But if so, how on earth do I solve that?

It sort of 'feels' like carburation. The appears to hunt. I have checked the float position and it is correct, so I do not think the float chamber is holding insufficient fuel - I understand the system relies on oversupply from the pump? I have used a colourtune, but obviously it is difficult to be sure about the mixture given the short running time available. Also, the symptons have changed; previously, it would start and run beautifully for perhaps 500 metres, then cut out; now it stalls much more quickly.

It is very difficult to diagnose when the symptons keep changing!!

 

[esray]

I had a similar problem after rebuilding a fuel pump that the car wouldn't run until I cleaned and lubed the fuel pump rocker arm parts. Worth a try.

cdnp6 - Thanks.

I'll give it a try!

 

[esray]

If the revs increase before a sudden stop it's a sure sign of fuel starvation.
As the mixture weakens, the revs increase until it's too weak to run.

Jim.

Thanks, Jim.

Perhaps I should re-check the pump and the float chamber?

 

[JVY]

One other obvious/easy thing to check for is air leaks. E.g. if the engine is cutting out completely, I wonder if you could have a leak on the inlet manifold. The TCs have a reputation for the rubber O-rings that seal between the carb adapters and manifold leaking but if yours is an SC, going by the manual, instead you have gaskets either side of the adapter plate that connects the carb to the inlet manifold. You could try the old trick of spraying WD40 around the adapter (or anywhere else you suspect a leak). You should notice a change in engine idle if there is a leak?

 

[esray]

Dear All,

According to my strobe, the engine starts retarded (left of the timing mark), retards further as the engine revs of its own accord, then advances (to the right) to bang on the mark as it stalls; it does this with the vacuum pipe connected and disconnected?

Any ideas, please :?:

Ray

 

[harveyp6]

There are marks on the pulley for 10 degrees either side of TDC, so what is the timing according to those when it starts, and as the engine RPM rises?

Have you checked that the timing pointer lines up with the TDC mark on the pulley when number one piston is at TDC?

 

[esray]

There are marks on the pulley for 10 degrees either side of TDC, so what is the timing according to those when it starts, and as the engine RPM rises?

Have you checked that the timing pointer lines up with the TDC mark on the pulley when number one piston is at TDC?

Hello Harvey - Trust you are well!

Timing pointer lines up with the timing mark when number one at TDC - Rotor arm at number one plug lead. Cannot really see marks other than the timing mark (which has served me perfectly okay to date). Is it distributor turned clockwise or anti-clockwise to advance, please?

Ray

 

[harveyp6]

You need to disregard this, because we've all just realised it's a 4 pot now haven't we..... Do come in Budge.....

 

[esray]

Is it distributor turned clockwise or anti-clockwise to advance, please?

Ray

Clean up the crank pulley so that you can see all the marks. The rotor arm turns clockwise, so you turn the distributor body anti-clockwise to advance the timing.

Harvey,

I'll clean up the pulley in better light tomorrow - Even though the car has run perfectly with the clearly visible 9 degrees retarded timing mark previously. The timing is moving right across the 10 degs advanced to 10 degs retard and as it does so it revs up as it retards, tries to stall, recovers as it hits its timing mark then repeats the process; it is rhythmically advancing and retarding, revving and then falling away - All of its own accord. If I throttle up it stalls immediately. I can sometimes overcome this throttle up stall this by enriching the mixture, but my plugs are already sooty!

Harvey, faulty carburation could not affect the timing, could it? The problem here is definitely distributor isn't it?

 

[harveyp6]

Harvey, faulty carburation could not affect the timing, could it? The problem here is definitely distributor isn't it?

All things affect others, but you need to do things in the correct order, so, dwell first (if points fitted) followed by the timing, moving on to the carbs last. Obviously you may find on occasions that you need to tickle up the carbs a bit just to get it running at a settled idle so you can check the timing, but the final carb setting should be done afterwards. The only times I've had engines that won't run correctly at the correct timing is where the camchain has jumped a tooth or two. So clean up the timing marks on the pulley, and then if the pointer is accurate set the timing to 8BTDC, and then watch the timing marks as you rev the engine so you can see the mechanical advance working.

 

[DaveHerns]

I did have a problem with the advance/retard. Instead of the vacuum advancing the distributor base-plate, the whole vacuum unit was being 'sucked out'.

I think somethings wrong in the distributor if the timing is floating this much

 

[harveyp6]

.

 

[esray]

I did have a problem with the advance/retard. Instead of the vacuum advancing the distributor base-plate, the whole vacuum unit was being 'sucked out'.

I think somethings wrong in the distributor if the timing is floating this much

If it still has points either points without a peg fitted when they should have the peg, or points with the peg on, but the peg not engaged with the arm on the vac unit.

Harvey, no points - Powerspark distributor. Is there still this 'peg'? I have had the vacuum unit out - to glue the splined 'bolt' back in place. I hooked the spring back over the peg - Is this the peg to which you refer, please?

Ray

 

[harveyp6]

Powerspark distributor. Is there still this 'peg'? I have had the vacuum unit out - to glue the splined 'bolt' back in place. I hooked the spring back over the peg - Is this the peg to which you refer, please?

See my later posts.

 

[chrisyork]

I agree with Harvey. Before you go any further you need to confirm whether the vacuum advance and the centrifugal advance are working. No matter how many times you've taken them apart that says nothing about whether they work.

To verify the function of the vacuum advance. With the distributor cap off, disconnect the vacuum pipe to the advance unit at the inlet manifold end. Suck on this end. You should see the baseplate rotate within the distributor. If it doesn't, then check that the baseplate isn't seized solid within the distributor. If free then bin the complete vacuum unit and buy a new one.

To verify the function of the centrifugal advance. With the distributor cap off. Twist the rotor arm clockwise. Does it spring back to its original position when you let g? Is there any rotational free movement when it is at the rest position before you feel the spring resistance? If any of these are faulty you need to strip the baseplate out of the distributor and find out what is going on with the fly weights and the springs.

Once these two functions are verified, only then can you move on to discuss the timing.

Chris

 

[esray]

Harvey, Chris, thank you for your patience and persistence.

The vacuum does rotate the baseplete (in a CLOCKWISE direction) when 'sucked'! Chris, the rotor arm (which rotates in an anti-clockwise direction when the engine is turned over) does spring back, with no slack movement when twisted in an ANTI-CLOCKWISE direction?

Ray