cliff.b
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Posts posted by cliff.b
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47 minutes ago, johny said:
I always thought too advanced gives hotter running (even to melting pistons and sparkplugs) but thats probably over simplification and an expert view is required...
Just been doing some reading about this which suggests that both being too advanced or too retarded can lead to overheating, but in different ways.
Too advanced causing more heat in the combustion chamber due to higher pressures created, even though this may produce more power if not excessive.
Too retarded due to the exhaust valve opening before combustion has fully completed, leading to excessive heating of the valve and manifold.
I've become interested now so will see what else I can find on the subject.
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Just now, johny said:
uuuf now theres a subject!
Ok, or any commonly held wisdom (or even opinion) on the matter lol
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2 minutes ago, NonMember said:
They're always rich at low revs - particularly idle - by design, which makes the plug colour test practically useless unless you do the clean coast trick.
Ah, interesting. So could leaving the car to tick over for a while actually blacken the plugs?
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8 minutes ago, johny said:
Could be worth checking the distributor as well. There should be an advance/revs table listed somewhere and then with the vac disconnected and plugged you can use a timing light to check the degrees while an assistant increases the engine revs (ear plugs recommendable)....
Yes, I have replaced the distributor over the winter as well so was planning on checking everything again.
Is there any wisdom out there on the science of how ignition timing could affects combution?
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Ok, an unexpected lack of rain today has allowed some further testing.
So off for a drive, slower this time with more varied speed (revs in the 2 to 3k range). After a few miles I coasted to a stop and the plugs still looked very lean, so it would appear this is happening to some extent at lower revs.
So tried making half a turn richer, as Pete suggested, but then the exhaust smelt of petrol, it wouldn't tickover nicely and once on the move, it felt sluggish. Going back one flat improved things so back on the road again.
Stopped again after a few miles and plugs were as shown here.
Not as white as yesterday.
Didn't change anything and drove straight home, the last couple of miles in town traffic. Looked at plugs again and the same plug was like this
I have also remembered that a few months ago I took the plugs out and they were black, whereas the previous year they had looked perfect. So I reset the mixture again but I'm wondering now, is the problem that it's too rich at low revs and I am over weakening to compensate 🤔
Over the Winter I replaced the dash which meant removing the choke cable. If that is not adjusted correctly, could that make it rich at low revs/throttle openings but not affect the mixture much at other times?
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31 minutes ago, Pete Lewis said:
nope
heres some of the torque curves for 1500 the best is between 3k 4k then it drops a bit
many would not rev a 1500 as they are renowned for rociprocating failures
Interesting. The torque drops off quite suddenly after about 4000RPM so maybe the original issue I was investigating is normal. Even when accelerating hard I don't rev more than 5k and that's not very often. There's not really any point with this engine as it's all torque which in my later years I quite like. I only rev it that far so it will be at about 3k after I change up and pulling well.
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16 minutes ago, Pete Lewis said:
before you go opening the wallet get the basics sorted first
basic needles for a std 1500 are ABT or late ADN
a quick check of the spindle for wear is worthwhile
if you are not after utopia stick with the compromise
you dont need to spend £££s to go tootling around or even giviing it the beans
even worn parts can give acceptable settings with a bit of thought
it she basically runs fair dont jump into spending £££££s with little return
Pete
Do you know why they changed to ADN needles for later cars?
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19 minutes ago, Iain T said:
Cliff, as you've identified a problem I would first take a look at what needles are actually installed. If you've a modified engine it may be you need non standard needles.
Iain
Yes, it makes it difficult not knowing if the engine is standard but I can at least see what needles I actually have. But I still won't know if they are suitable for the engine 🤔
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35 minutes ago, johny said:
Must admit there was no doubt with the play in my spindles especially the one where I had installed an extra spring years ago to give the accelerator pedal more resistance😖
Ah yes, the law of unintended consequences. Caught out by that sort of thing many a time, but experience has taught me to try and think things through now. Not that it always works out lol
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15 minutes ago, johny said:
Dont know much about SUs but my Strombergs became difficult to set up and ran lean at higher revs. It took me too long to twig (so much so that Ive probably damaged my valve seats) that the spindles were worn but replacing them did the trick. There was quite a bit of movement (one carb more than the other) detectable on the car when a spindle end was rocked back n forth or up and down while new it would have been almost imperceptible...
It sounds a plausible explanation, but difficult to diagnose if you don't know what normal is.
I think, as suggested, I need to make some adjustments and test at different engine speeds to try and understand what is happening.
I can see me needing to strip them down though, which I have never done before, but I'm sure I will manage. Would just rather be driving though 😒
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23 minutes ago, johny said:
Another thing Ive just thought of is carb spindle wear - is there any play in them that is allowing air to be drawn in?
Can you determine that before you strip it down? Wiggling the spindle while on the car there is a slight movement side to side but I don't know what is normal
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Several questions so I will try and cover all of them.
When I bought the car last year it wasn't running and once I sorted the ignition side, it was running very rich. Black plugs & exhaust stank of petrol. I used a colourtune to get it somewhere close then kept checking the plugs until I was happy with the colour.
Waxstats were fitted but I removed them, applying the 1p fix, after which it was running weak, so I went through the above process again.
Ever since, it has all looked good when checking at home. Plugs look good, slight rise in revs then back to normal when lifting the pins or my personal test, removing the oil filler cap to get the same effect. There is zero smell or anything visible from the exhaust. If I hadn't carried out today's testing I would be none the wiser.
I haven't stripped the carbs yet so don't know what needles are fitted at the moment
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And by worn needles I was wondering if that would be making it too rich at lower revs and if I am over weakening it trying to compensate for that.
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3 minutes ago, johny said:
Not worn needles as they would tend to make it richer. Engine, intake and exhaust all standard I take it?
Unfortunately I don't know what's actually inside the engine as the person I bought it off didn't know.
Carbs & inlet manifold look standard but haven't dismantled yet.
Exhaust manifold is standard but the downpipe & rest of exhaust are non standard. 2" dia pipe and I think the silencer has been "modified" (evidence of cut open and welded)
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While generally, I feel my car is running well, with plenty of go at lower revs, it seems to be a bit flat around 4000RPM, picking up again approaching 5000. Not really a flat spot, just less urge, and exactly where I want it to be pulling well if overtaking in 3rd gear.
The plugs look ok but I decided to check the mixture out at higher revs by driving 10 miles or so at around 4k revs, coasting into a layby, and on removing the plugs, they were almost completely white.
I presume this shouldn't be the case and if so, am I right in thinking this is likely to be worn or incorrect needles?
Or is there anything else that might be causing this?
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My Spit had a 13" steering wheel when I got it and i was running the 175 front tyres at 26psi which was hard work.
I now have a 14" wheel and run the tyres at 29psi which has improved things a lot but still a good compromise for comfort & grip.
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3 hours ago, AlanT said:
I've just replaced my mad loud sports system with standard, sourced from Online Automotive. Very reasonable cost and all good.
Thanks. Did you find it online or call them?
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My Spit had a bolt which was very tight but coolant drained freely when I finally removed it.
I know they can get blocked with "crud" though.
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50 minutes ago, NonMember said:
But running cooler is not a benefit. The engine works best at the hotter end of the range it's happy with.
Quite possibly. I'm just sharing my observations that the car ran cooler with the mechanical fan.
Individual owners can decide for themselves if that is a good thing or not.
I really don't know 🙂
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6 minutes ago, Piglet said:
Going to drain and flush the rad today, add new coolant and see how she behaves!
Alex
Are you going to flush the block as well
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1 hour ago, Mjit said:
I think for most of our cars an electric fan set to 65°C is rather crazy and way too low a temp. I mean you're probably running a themostat that doesn't open until 82°C so you'd literally just be cooling the water sat in the radiator.
The Rovotec fan controller I had on my Spit. died during lockdown and I've replaced it with a simpler system with swappable, fixed-temp. switches. Their guide is to aim for a switch-on temp that's 12°C to 18°C hotter than the themostat opening temp. I seem to remember the set-up for the adjustable Rovotec controller was something similar - set 'stat to hottest setting, get it up to temp a the needle past the middle line, set 'stat to coldest setting, then when the needle drops to the middle line turn the 'stat hotter until the fan kicks out.
Yes, I only set it at that to find out the return temperature.
What I observed was that with the standard setup of a mechanical fan, the rad return temp was about 65C unless stationary after caning it when it rose to 75C.
That's what I usually set the thermostat at and with the mech fan removed the electric fans were coming on every time I slowed down for a roundabout, even after moderate driving.
I'm not suggesting that the car was overheating without the mech fan, as the temp gauge was still showing a reasonable reading, but hotter than it reads with the mech fan fitted.
So from what I have seen with my own car (Spitfire with wide rad), electric fans will stop a car overheating but it runs cooler with the mech fan fitted.
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As I explained previously, I refitted a mechanical fan but left the electric ones in place so although unplanned, I have both.
The thermostat probe for the electrics is in the radiator return pipe, set at 75C & now they only come on if I am stationary after "enthusiastic" driving. Before I refitted the mech fan the electrics would come on anytime I slowed down below about 30 so I assume at that point, the return temp was at least 75C. The temp gauge would rise to just over halfway.
I can adjust the thermostat from the driving seat so by turning it until the fans come on I can determine the temp in the radiator return pipe while on the move. So far, during normal driving, it stays at about 60 to 65C with the temp gauge just below halfway.
When I first fitted the electrics I experimented with different thermostat settings and at 65C, they were on almost continually, so I know this goes against conventional wisdom, but in my car, at least, it seems the mech fan gives a lower radiator return temp at any driving speed.
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18 minutes ago, clive said:
Yes, get a complete system including downpipe. Much less faffing will be involved.
Yes, probably the best chance of it all fitting properly, I guess 🤔
Spit seems to run weak at higher revs
in Fuel System
Posted
Yes, definitely useful as sounds, perhaps to a lesser extent, the sort of thing I am seeing.
Just as a matter of interest, how do you set your ignition timing? By ear, timing light, static with a bulb, meter, fag paper lol