HD8’s have idle screws. Fast idle screws [for choke setting] and mixture screws.
Normally, the idle on the HD8 is controlled by the large Volume screw at the back on the right above the mixture screws. The fast idle on the manual choke has nothing to do with the normal running other than at cold starting to hold the butterfly open slightly. On my car I don’t have these as have the electric choke.
My findings so far.
The short road test with a richer mixture did not show results.
The plugs were definitely brown going on black.
So l removed float lids and found that both were set very close to 1/2 inch. Also one arm had a wobble ( slightly bent arm), so l set both to 7/16. Also one of the brass plungers was not dropping as much as it should.
I set the main jets to .070, and it started with vigour! I will leave timing at 8 btdc for now.
So road test tomorrow.
Good night
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Well no luck with the tinkering, so back to the drawing board.
It is most noticeable at 3000 in any gear, and feels like a misfire but l can accelerate up to 5k no problem with no hesitation.
Tomorrow l will swop out my HT leads and distributor cap, from there l will change the plugs and rotor one piece at a time.
Replace cap/rotor as a unit: if that cures it, then you have localized it.
I had no end of problems with condensers on my Healey 100. Modern ones are just badly made. But mine would only start to fail when they got very hot. Now in the XK and Healey I have the 123 Bluetooth system. There was also a lot of rotor arms failing due to heat.
Your symptoms sound quite odd as you say 3,000 in any gear, so in some gears the advance will be coming in, but just free reving in first gear will be different to fourth gear.
I am no expert on electrics. But a couple of other things to check. Inside the distributor are little weights and springs that advance and retard. Try giving them some lubrication. If the new rotor and cap do not work, take plate off inside of distributor and check that one of the two little springs has not broken of become detached.
I disconnected the vacuum advance from the carb. And the surging / misfire disappeared.
So what that all about. ? Do l need a vacuum advance.
Car still has great acceleration.
Light throttle condition increases ign advance by means of increased vacuum / atmospheric pressure acting on the diaphragm of the adv / retard unit.
If you don’t experience hesitation when accelerating leave it disconnected., or connect it and back off the ign as per my advice, certainly adjusting the ign would have yealded a faster fix than pratting about with the carbs !!
Yes l will give it a go and see if you are correct, however l actually enjoy pratting about in my car and solving problems like so many others do also.
Cheers, and l thank you to all on this forum for all the valuable information l received.
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What is your recommendation for a ignition setting with the strobe light. Do you recommend a lower setting with higher compression as some of the books say ?
All for the pratting about fixing cars Morris, been doing it most of my adult life !
But when various solutions are proposed re a problem choosing the simple fix first might just pay off.
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Peter
I was deep into the carbs already so that’s the route i went first, just so happens I found the float levels were too low.
So what i understand is ,if I reconnect my distributor vacuum and then retard the ignition I will get the same results.
Yes ! turn the distributor anti clockwise approx the dia of a HT lead and test, if necessary go again but should not need more than two attempts. If you feel that the original static setting is best check for a advance / retard unit that has less total advance.
Hello John,
Bit of a delay, if you read the post from Jim re the DMBZ 6A this sums up my approach,
also if Morris posts his findings , this will inform.
Hello Morris, having been told off for making you “Pratting around” with the carbs, I wondered if you have found the cure for the problem.
Interestingly, I recently was down at one of the most well known Jaguar rolling road tuners, who tune race cars. They run the car on the rolling road and file the needles to the exact need for each car. They told me that none of the basic straight tapered needles are right and each one needs fine tuning by filing at some point. Not suggesting this would cure your problem, in case I get shot down in flames again but just an interesting experience I had watching the power and torque figures improve.
It is indeed a black art, one that requires fearsome amounts of time–and that rolling road–to master.
Weather been a bit lousy so no finality to my issue, however this is what I have found in the last few days.
Car idling at 600 rpm ,timing shows 8 deg , with Vacuum disconnected
Car idling at 800 rpm ,timing mark disappears with vac disconnected,
No difference if vacuum is re installed.
Will do road test and do what Peter suggested re turning Dist anti clockwise 1/4 inch. then see where timing marks end up.
Mk 10 [ or E type] 4.2 timing states 10 deg BTDC
I truly believe my issue is timing rather than fuel mixture, as plug color look very good.
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I agree your plugs look good, as I said righ5 at the beginning.
Have you worked out how much a 1/4 inch is in degrees around the circumference of the distributor. It sounds a lot of degrees of retarding? Every time I adjust the distributor and test on the strobe light, the slightest turn changes the degrees a lot.
I note you state a new vacuum unit in your first post Morris, might be worth checking the vacuum
unit advance figures for a 150 against those for a 4.2, say a series one XJ.
Clicked on the wrong name John.
Peter
Yes, it is a new unit for a 3.4 150, and l was wondering if l needed a different one for the 4.2, the distributor was stripped a year ago with springs & weights checked and all oiled, points are electronic.
Does anyone know if the E type and MK 10, 4.2 vac’s are the same. ?