Another misfire - aargh!

[Badwolf]

15 hours ago, Pete Lewis said:

and  it may have a marmalade sandwich inside   

Pete

I loved that video. So simple but effective and clever.

[1969Mk3Spitfire]

Just had a great week meeting up with ex-work colleagues, rdv in Belfast. Rollercoaster downwind sleigh ride return to the Mull of Kintyre in 8 1/2 hours, a lot of fun surfing down the waves

…..and so back to my Spitfire.

I took it for a ride today and this included a 60 mph stretch of the A556. As I approached home the engine had an occasional hiccup. Removed the plugs and, no surprises, 1 and 4 looked good, 2 was sooty (I rarely remove No 3 as access is a pig).

I’ve fairly closely examined the choke linkages and at rest, the lever position of the rear carb is exerting more upward force to hold the jet in place. The forward carb choke lever exerts little upward force to hold the jet in place, albeit this is probably because the forward carb jet screw is set at least one full turn further “in” than its oppo to get the same pin-lift response. The forward carb choke return action is not as positive as the rear but this could be another red herring.

Currently, it’s taking about 10 miles to soot the plug sufficiently to cause a misfire and I’ve run out of ideas 😭

 

[Colin Lindsay]

Have you actually changed that one plug for a new replacement? It's one of the first things I'd have done, to rule out a defective plug even if the rest of the system is working fine.

[Wagger]

I would agree with Colin. Swap the plug and see if the problem is with the cylinder or the plug.

It is early days yet but my number two plug has not sooted up since setting the float levels on my SU's to 1/8th inch instead of 3/16ths. The old floats were non adjustable and gave 1/8th. The instructions with the new ones said 3/16ths. Various sources state 1/8th to 3/16th's.

There were blockage problems confusing the issue before changing the floats but I have done five runs now without having to clean number two and there has been no misfiring at all. Previously, number two cylinder would not fire on start up after every third run. However, I have also added I% two stroke oil to the fuel in case something was 'Gummed up'.  200ml in 10 litres of fuel.

I too, am guilty of doing more than one thing at a time when impatient. It pays not to do this, but to stay calm and do one thing at a time, Do as I say, not as I do!

As a result I have set floats, warmed up, adjusted carbs, added two stroke and then done a run, so the actual cure is unknown.

In this spell of fine weather use of the choke has not been necessary, so that could have been a cause of sooting. However, my jets are being returned when I shove the choke knob to the dashboard. It is really worth making sure that happens.

Fingers crossed for the next outing.

[1969Mk3Spitfire]

1 hour ago, Colin Lindsay said:

Have you actually changed that one plug for a new replacement? It's one of the first things I'd have done, to rule out a defective plug even if the rest of the system is working fine.

Indeed, it was the first thing I did, alas to no avail. Thanks for the suggestion, though.

[1969Mk3Spitfire]

2 hours ago, Wagger said:

I would agree with Colin. Swap the plug and see if the problem is with the cylinder or the plug.

It is early days yet but my number two plug has not sooted up since setting the float levels on my SU's to 1/8th inch instead of 3/16ths. The old floats were non adjustable and gave 1/8th. The instructions with the new ones said 3/16ths. Various sources state 1/8th to 3/16th's.

There were blockage problems confusing the issue before changing the floats but I have done five runs now without having to clean number two and there has been no misfiring at all. Previously, number two cylinder would not fire on start up after every third run. However, I have also added I% two stroke oil to the fuel in case something was 'Gummed up'.  200ml in 10 litres of fuel.

I too, am guilty of doing more than one thing at a time when impatient. It pays not to do this, but to stay calm and do one thing at a time, Do as I say, not as I do!

As a result I have set floats, warmed up, adjusted carbs, added two stroke and then done a run, so the actual cure is unknown.

In this spell of fine weather use of the choke has not been necessary, so that could have been a cause of sooting. However, my jets are being returned when I shove the choke knob to the dashboard. It is really worth making sure that happens.

Fingers crossed for the next outing.

I imagine that we are all guilty of tinkering with more than one thing, never truly knowing if/how/why we fixed an issue.

I don’t understand why it is one cylinder only. The two carbs differ in the position of the jet nut and the choke leverage mechanism to lift the jet (the latter could be a consequence of the former).

Messing about today, I managed to flip the inner choke spring and it took a lot of swearing and cursing to get it back in place. I still don’t fully understand the full working of the mechanism and the linkages between the two. 

Not sure about an air leak. Subjectively, acceleration is smooth and my past experience of carb wear and air leaks involves rough running.

Float chamber is a new thought. I’d need to get spare gaskets before going down this route and also to try to understand the relationship between float setting, one cylinder sooting and a misfire.

Does anyone have the number for “Triumph Anonymous” as I need help😭 

[Pete Lewis]

i would do a cam lobe lift check to ensure cly 2 is getting rocker lifting ok    a worn out lobe would give obscure problems 

 

[1969Mk3Spitfire]

15 hours ago, Pete Lewis said:

i would do a cam lobe lift check to ensure cly 2 is getting rocker lifting ok    a worn out lobe would give obscure problems 

 

That was an interesting exercise, not so easy to measure. Measured push rod movement at the tappet adjuster bolt.

Exhaust valves: 1=6.91mm, 2=6.99mm, 3=7.09mm, 4=7.18mm. Average 7.04mm

Inlet valves: 1=7.07mm, 2=6.95mm, 3=7.0mm, 4=7.19mm. Average 7.05mm

I suspect a good deal of measurement error but they all look consistent to me?

Not spotted before but I noticed No 3 cylinder inlet push rod is bent. If I can find another, presumably it’s just a simple swap and readjust the tappet?

Still nothing jumping out at me as being causal to the sooty plug issue.

People have mentioned running on a 2-stroke mix, what’s the consensus?

Next steps are to think about head overhaul and/or carb overhaul. Thoughts, costs?

 

 

[Pete Lewis]

valve lift is fine     it was just a nuts idea to  check off .

are we sure its just Soot or is there an oil mix coming to play ????

if you decelerate for a fair run and open up is there any smoke from the exhaust ???

whilst compressions may be fair  oil consumption may be the sooty culprit just on no 2

Pete

 

 

[Wagger]

It is worth running a two stroke mix for a short spell just to observe if it makes a difference. If you know that you have, say, 10 litres in the tank, just add 100ml of good two stroke to it. Take it for a good run and check the plug on return. Just done my sixth run, no misfiring but sciatica still prevents me from opening the bonnet to check the plug. The spring assist is missing. Why did I not fit one?

Well, I have had the bonnet catches unhitch and the bonnet rose on braking. Not on this Vitesse, yet.

My two stroke mowers and chain saws oiled plugs far less frequently than the four strokes. That was some thirty odd years ago though.

If you have a lathe, or know somebody who does, you could mount the pushrod and carefully straighten it. However, make sure that it is not cracked. It depends why it has become bent, poor storage during a rebuild, or bending in situ.

[Chilliman]

Not an answer to the source of your plug fowling problem but a suggestion to keep you running smoothly this year until you track down the underlying issue - valves, guides, carburation etc.

I was suffering quite badly with plug fowling to the point of misfire & poor starting which meant I was frequently swapping/cleaning plugs - not such a problem for me as I knew the reason why - I run rich on Webers and compete in sprint & hill climbs with lots of stop start & prolonged idling on occasions followed by high revs & then lots more idling.

In March this year I fitted a set of the Iridium spark plugs, I was a bit dubious as to whether I would see any real difference , in fact a good friend of mine referred to them as a case of the emperors new clothes, however I have been very impressed with the difference, the car starts & idles from cold straight away,no missing at all. The only downside is the cost as they are about four times the price of stock plugs........but if you want to keep her running this year & attack the cylinder head etc next winter as a winter project it may be worth you considering...

Good luck

John

[1969Mk3Spitfire]

1 hour ago, Chilliman said:

Not an answer to the source of your plug fowling problem but a suggestion to keep you running smoothly this year until you track down the underlying issue - valves, guides, carburation etc.

I was suffering quite badly with plug fowling to the point of misfire & poor starting which meant I was frequently swapping/cleaning plugs - not such a problem for me as I knew the reason why - I run rich on Webers and compete in sprint & hill climbs with lots of stop start & prolonged idling on occasions followed by high revs & then lots more idling.

In March this year I fitted a set of the Iridium spark plugs, I was a bit dubious as to whether I would see any real difference , in fact a good friend of mine referred to them as a case of the emperors new clothes, however I have been very impressed with the difference, the car starts & idles from cold straight away,no missing at all. The only downside is the cost as they are about four times the price of stock plugs........but if you want to keep her running this year & attack the cylinder head etc next winter as a winter project it may be worth you considering...

Good luck

John

Thanks, John, worth a try.

Do you have a favoured brand and know a equivalent part number to N9Y/BP5ES?

[Chilliman]

I always use NGK, - from the fitment tables it looks like the equivalent for your BP5ES are BPR5EIX...like you say worth a try.....👍

[Pete Lewis]

i dont fancy anything with an R (resistive) in the suffix 

it does reduce our low HT   and you need all you can get 

find some without an "R" 

 

[1969Mk3Spitfire]

Time to go back to basics.

The No 2 plug is sooty / dry. Not shiny and wet so I don't think it's oil (but can't be sure of anything with a 50+ year old engine). This is hydrocarbon so either an excess of fuel or insufficient air.

Setting the jet at "2 turns below the bridge" and using the pin method to assess mixture, the rear carb is pretty-much correct but the front carb (cylinders 1 and 2) needs at least one full turn lean.  I don't recall there being such a difference between the two when I first set-up the carbs 3 years ago, before the sooty plug issue manifested itself.

With clean/new plugs, the engine revs freely and pulls well, no flat spots so no evidence of an air leak.

What's the likelihood of a blockage within No 2 induction?

It's looking more and more likely that I have to start tearing down the top end. Does the Club sell a head gasket set?

I've been reading about a cylinder compression leak-down test.  I'm going to post within the Tools section but does anyone have any experience and care to comment about the value of such a test? 

[1969Mk3Spitfire]

A pal has suggested swapping the jet and needle (with or without piston) between the two carbs to see if this moves the sooty plug.

What does the forum think?

[Iain T]

I assume needle heights are at the same in both carbs? Fixing this would necessitate uneven jet depths. I set both jet depth and needle height with a micrometer. 

Have you synchronised both carbs?

Iain 

[Clive]

As the carb feeds 2 cylinders, that is irrelevent here.

I expect it is a faulty plug or oil.

[Pete Lewis]

there is a reason lurking why No2 soots   but not No1

it shares the same carb , manifold and the balance pipe as No1   so swapping carbs is of little help

soot is made from a slow unhealthy burn   that can be 

excess fuel   insufficient air   lack of ignition   

the only common denominator is for just No 2   the piston rings , valves , ignition 

carburation would be common to No1 as well ... its not 

Pete

[Badwolf]

14 minutes ago, clive said:

As the carb feeds 2 cylinders, that is irrelevent here.

I expect it is a faulty plug or oil.

Or Iginition cable, I would even have the distributor cap off to check the rotor contact inside and also the lead connection. Years gone by I had a dreadful misfire on all plugs. Checked everything, nothing obvious. Then an old skool mechanic said, start the engine in the dark, spray the dissy with a fine water mist and see what you see. The crack in the case was spectacular!!

 

[Pete Lewis]

we had a inspector who would put a damp hand over the dizzy and stop the engine 

a few tried to copy his antics and got a real belt up to the arm pit 

so in the dark is a safe option 

Pete

[Peter Truman]

Happened to a friends Sag on a club tour on a run down the snow fields got worse quickly couldn’t make the night stop.

Remembered an old fix asked the ladies who had some nail varnish & painted the inside of the cap with it fixed the problem and it was still going a year later but he by then carried a spare!

[1969Mk3Spitfire]

2 hours ago, Badwolf said:

Or Iginition cable, I would even have the distributor cap off to check the rotor contact inside and also the lead connection. Years gone by I had a dreadful misfire on all plugs. Checked everything, nothing obvious. Then an old skool mechanic said, start the engine in the dark, spray the dissy with a fine water mist and see what you see. The crack in the case was spectacular!!

 

When it first happened, I changed all of the ignition components but to no avail.

[Pete Lewis]

still think a colour tune will show that there is a firing problem  or a yellow burn 

can you borrow one ???

and never pick a colour tune when hot with the fingers they are silly hot !!!!

Pete

[Chris A]

4 minutes ago, Pete Lewis said:

and never pick a colour tune when hot with the fingers they are silly hot !!!!

And, how may I ask did you find that out. 🥵