64 replies to this topic

[1984mini25]

998, hs4 carb, standard air filer, cast manifold and peashooter, 64md dizzy and 12v electronic coil (been running since 07)

 

So far I’ve tried, full carb rebuild including float valve, jet (hs4 waxstat) throttle disk and spindle (couldn’t find any one to entertain replacing the bushes, but then didn’t seem worn) and needle (AAU fitted, to replace the slightly worn ADL that was fitted/originally tuned with, but is slight closer to the AAC needle fitted as standard below 3k).

 

8mm performance silicone hat leads, dizzy cap and rotor arm cleaned as they aren’t that old. And several sets of spark plugs (ngkbpr6es) As if it tune the carb with the lifting pin the plugs end up so black they are only fit for the bin, but if I tune it to the colour tune I’m stuck with the misfiring issue.

Mechanical fuel pump replaced 2019, but it only did 300 miles between mots for all of last year.

 

I thought I’d test the coil (GCL 143) as it getting on for 12 years old (replaced in 2009). From what I’ve found it should have a primary resistance of around 0.9ohms and secondary resistance of between 5 and 15k. I got 1.2ohms on the primary and 5.2k on the secondary.

 

So I took a punt and bought a brand new GCL 143 coil, Fresh out the box it tested. 1.6ohms on the primary and 4.6k on the secondary, worse than my old one. I’ve since fitted it and it’s made no difference, it’s still misfiring below 2k (idles fine all day long) until it’s warmed up enough to be driven. Other than the misfiring and the works when it wants to speedo, which is a spate issue, it drives great for a standard 998 providing you ignore it’s got a 4^th gear (no pull in 4^th with a 2.9 diff). Just it’s starting to be a bit of a pita and going through sets of plugs.  

 

 

So is it my coil/s? (Can’t send the other one back) or something else?

 

 

 

[cal844]

Refit the ADL needle and see how it goes, make sure you only make one change at any time.

Then try the old coil

[1984mini25]

Will do.

 

Although I did refit the ADL needle when I rebuilt the carb, But even with the choke out fully if you tried to rev it before it warmed up the engine would bog/die, there’d be a metallic clonk witch I assume was from the dashpot piston falling in the carb and then the engine would suddenly race back into life.

 

So I fitted the AAU needle as it was the only spare one I have that was new, the ADL one being slightly worn along with the old jet.

And I did try using this…  https://www.classicm...hnical/needles  to see if they were a close match to consider using until I could source a new ADL needle.

[ACDodd]

Is there a ballast resistor in line with the coil? What year is the car?

Ac

Edited by ACDodd, 03 August 2021 - 05:20 PM.

[1984mini25]

No Ballast resit wire (the pink one) as that was removed from the loom when the electronic dizzy and coil were originally fitted. And the coil is fed 12v from no1 of the fuse box.

 

And as I had the multimeter out testing the coil I did also check. The coil voltage while running is 13v and the battery voltage is 12.8v (new battery only a few weeks old as the old one went flat from being sat for too long) and 14.1v while running (so that could rule out it being the alternator).

[cal844]

What oil is in the carb dashpot?
Did you refit the spring?

It sounds like the wrong grade of oil is used in the dashpot from what was used previously

[1984mini25]

I can’t remember what time and if it coincided with the misfiring, but I have switched from 20w50 to 5w30 in the squirty oil can, as I’m tripping over half used bottles of the stuff (buy 5l but only need 3.5l) and have run out of 20/50.

 

Still been using 20/50 in the mini and it hasn’t needed topping up for a while (you wait, I’ll find a huge puddle of oil under the mini now)

 

 

And the spring was refitted, although I'll check when i swap the needles back over. 

[cal844]

I can’t remember what time and if it coincided with the misfiring, but I have switched from 20w50 to 5w30 in the squirty oil can, as I’m tripping over half used bottles of the stuff (buy 5l but only need 3.5l) and have run out of 20/50.

Still been using 20/50 in the mini and it hasn’t needed topping up for a while (you wait, I’ll find a huge puddle of oil under the mini now)


And the spring was refitted, although I'll check when i swap the needles back over.

Bingo! Changing the oil weight in the dashpot has changed dashpot speed. Change back to 20w50 and it'll be fixed

[1984mini25]

 

I can’t remember what time and if it coincided with the misfiring, but I have switched from 20w50 to 5w30 in the squirty oil can, as I’m tripping over half used bottles of the stuff (buy 5l but only need 3.5l) and have run out of 20/50.

Still been using 20/50 in the mini and it hasn’t needed topping up for a while (you wait, I’ll find a huge puddle of oil under the mini now)


And the spring was refitted, although I'll check when i swap the needles back over.

Bingo! Changing the oil weight in the dashpot has changed dashpot speed. Change back to 20w50 and it'll be fixed

 

 

 

It’s a mini, it’s never that simple. 

 

I have just tried…

 

Refitted the original (or one it was tuned with) ADL needle and emptied and refilled the carb with 20w/50.

 

Jump in and turn the key, starts up, set the choke to 1500 rpm, but even go near the throttle and its pop, pop, pop, pop, dies. 

 

Check spark plugs and they were black (same as it’s done to 3 sets of plugs now). Wire brushed/cleaned them and refitted, swapped the coil over form the new one back to the old one. 

 

Jump in for start number two. Same as before, the popping/misfiring is still there, but not as bad and if it’s left to idle below 1500rpm with the choke (dies instantly without) the rev counter is jumping slightly and there’s a rhythmic pop, pop, pop from the exhaust. 

[cal844]

Has it improved or got worse?

But yes changing from 10w40 to 20w50 did cure my issue was similar.

When you changed the plug leads etc did you move or remove the dizzy from its position? Check the coil positive supply wire and also the wiring to the dizzy module for breaks, which might cause the issue you are having.

Or go to a local supplier for a replacement coil, I've had that before too...

We fitted a clutch, built the car back up and the car would misfire under load in 4th gear only... We changed the carb, dizzy 2 or three times and even made a new wire to the coil.... Changed the coil for another new item from another supplier and it ran perfect.

We will find the issue on your car

Edited by cal844, 04 August 2021 - 04:07 PM.

[1984mini25]

It got worse.

 

Before I could ether rev it for a bit or let it warm up on the choke at 1500rpm and then be able to drive off. It’s been doing it for quite a while, but thanks to various lockdowns (only run up in the garage every few weeks) and limited use it’s become more of an issue with it getting more regular use again (or trying to) and the flat spot on initial acceleration when warm going up or down the gears.

 

Example being, slowing down for a roundabout, pop it in to second/, looks clear go to get on the load pedal and there’s a few second delay till anything happens. Or accelerating through the gears (within the speed limits) like 30mph in 2^nd at 3k, pop it into 3^rd (2k at 30mph) back on the load pedal and a slight hesitation before picking up again (I can get away with using 4^th at 1.5k at 30mph but only on the flat). Which has been a more recent thing (within the last few weeks) since the carb rebuild but before the first post above.

 

 

Now it just doesn’t want to know. As, as soon as you try and rev or give it any throttle it just pops a few times and then just dies/stalls. So before it was an inconvenience but drivable once it had warmed up/run for a bit, now it isn’t/doesn’t want to know.

 

I have tried earlier/later in the day purely as I haven’t lost anything in trying.

 

I can’t work out if it was the start of the issues or not, but I thought I’d give replacing the new 8mm silicon ht leads (in original spec lime green) back to a standard used set I had lying around.

 

It was a little reluctant to idle even on the choke, so had to turn the idle up a bit until it had warmed up, but it was idling and revving up better. And once warmed up I did rechecked the timing (seamed right/hadn’t moved) and had a play with the colour tune (ritchened it up buy 3 flats for a medium blue flame) it still had a rhythmic pop from the exhaust on tick over and some pops from the exhaust (standard peashooter) if revved hard on the overrun. (Some people would pay a lot of money for that)

 

But the test will be what it behaves like from cold and if it’s at all driveable, I’ll then be able to head off out for a fresh tank of fuel and a long ish run.

 

And as for the local supplier option. I only have Halfords, eurocarparts, GFS or and independent to choose from, the latter tends to source non-consumables and car parts through eurocarparts with their mark-up added on top.

But the problem with that is all (if they had the bits in the first place) only go by the reg, witch being and 84 on an A plate wouldn’t of had this 12v electronic ignition as standard (yes I know the ignition isn’t ‘correct’ for a 998) so what the computer system says is the correct part, isn’t.

Edited by 1984mini25, 04 August 2021 - 08:20 PM.

[sonscar]

Backyard fitter here,pops from inlet are too weak and pops from exhaust are too rich(generalisation I know).Popping from exhaust,burned valve.Rev counter flutter low tension circuit including coil,wiring,ignitor,earths in dissy(small wire connecting backplate).In my experience once the plugs have been wet they are scrap(opinions here will differ).Just a few thoughts,Steve..

[1984mini25]

Well I’ve started it up from cold.

 

It was still reluctant to rev (just pop, pop, pop) and idle on the choke. So I richened up the mixture another 2 and half flats and increased/screwed in the idle a bit more.

 

While the air filter housing was off to adjust the idle witch had dropped off (starts to get really unhappy/rattily if it tries to idle below 500 rpm, but normally have it set to 900rpm) if I choked off half the carb with my hand and revved it seemed soo much better/happier, hence richening up the mixture.

 

It seemed happier once it had warmed up, although it’s probably a bit richer now compared to yesterday even though I used the colourtune. But pulling the plugs back out they were all as clean as they were when I’d last brushed them off (they were sooty the last time).

 

And just out of curiosity I checked the resistance of my new silicone ht leads I’d just removed and a random spare standard lead.

 

The silicone ones were ranging from 1.3 to 1.6k and the spare standard lead 25k.

 

Could those of made a difference? As the plugs I’m using are the ngk BPR6ES with the resistors.

[ACDodd]

I think you may need the part throttle fueling section on the needle tweaked a little to get rid of a possible lean misfire. Check the exhaust gas readings at the problematic speeds to determine what is happening.

Ac

[1984mini25]

Random question.

 

On a healthy engine with a single breather on tappet cover connected to carb, what should happen if either the vacuum advance pipe is removed from the dizzy, or the oil filler cap removed while the engine is running/idling?

 

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