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Sometimes these engines won't start unless the enrichment carb is operating correctly. Prior to pulling the head I would suggest depressing the gas pedal to open the butterflys, spraying some starter fluid into the carbs, letting off the gas pedal and then try firing it up. Having a helper would make this a little easier. Also, you could do this yourself under the hood by operating the throttle mechanism, spraying and then pushing the remote starter button. Be sure in have the key turned on.
The other possibity is that the timing is way off. The #6 cylinder is at the front of the car.. I saw where a guy on Youtube had assumed the #6 was at the rear and set his timing accordingly. Car wouldn't start for love or money...
Good Luck !
Schmitty
Sometimes these engines won't start unless the enrichment carb is operating correctly. Prior to pulling the head I would suggest depressing the gas pedal to open the butterflys, spraying some starter fluid into the carbs, letting off the gas pedal and then try firing it up. Having a helper would make this a little easier. Also, you could do this yourself under the hood by operating the throttle mechanism, spraying and then pushing the remote starter button. Be sure in have the key turned on.
The other possibity is that the timing is way off. The #6 cylinder is at the front of the car.. I saw where a guy on Youtube had assumed the #6 was at the rear and set his timing accordingly. Car wouldn't start for love or money...
Good Luck !
Schmitty
I’ll pull the cam covers off and check again…
Thanks for the tips.
Let's assume valve timing is correct, because otherwise your efforts to start may have had expensive results!
So, suggest you begin with the following . . .
You have verified fuel at carbs. Even so, use starter spray test.
How did you test for spark? With engine at rest or cranking?
If not, lift #5 plug, re-attach lead and ground, then crank. Repetitive sparking? Refit #5 plug.
Even with low compression on one cylinder, engine should start, or at least attempt to start, especially with ether based starter spray.
If not . . . most likely "no start" is caused by incorrect dizzy timing, perhaps out by 180 degrees. Oil pump / dizzy drive?
If not . . . suspect possible failure of points capacitor, as even "new" replacements could be 50+ years old.
Cheers and best wishes,
Last edited by cat_as_trophy; Mar 12, 2026 at 04:51 PM.
You have verified fuel at carbs. Even so, use starter spray test.
How did you test for spark? With engine at rest or cranking?
If not, lift #5 plug, re-attach lead and ground, then crank. Repetitive sparking? Refit #5 plug.
Even with low compression on one cylinder, engine should start, or at least attempt to start, especially with ether based starter spray.
If not . . . most likely "no start" is caused by incorrect timing, perhaps out by 180 degrees. Oil pump / dizzy drive?
If not . . . suspect possible failure of points capacitor, as even "new" replacements could be 50+ years old.
Cheers and best wishes,
pulled the #6 spark plug and left it on the lead. Turned over and got spark.. #1 was covered in clean oil when I pulled them all for the compression testing. 2-6 smelled of gas. And if I crank. Rest. Crank it will backfire.
First I would check the valve clearances, as perhaps the low compression reading is caused by a tight valve, This could be caused by the valve bedding in when spinning over and re-shimming will prevent the valve or seat being damaged.
It's then easy enough to check the ignition timing by taking the distributor cap off to see which plug lead the rotor arm is pointing at when the rear cylinder, (no. 1) is at top dead centre with its valves on the heels of the cams - the compression stroke. The rotor arm should be pointing at the HT lead that goes to this cylinder, usually the cap connection that's nearest the rear cylinder. It's then easy enough to follow the sequence of 1 5 3 6 2 4 through the cylinders in the direction of the distributor's rotation and ensure the leads are all plugged into their correct position in the cap and on the plugs. Hopefully this is where the problem is and it's an easy fix.
I'm sorry if I'm telling you how to suck eggs but we have no idea how much you know or what your experience is. I made this error many years ago when I wasn't aware that Jaguar numbered their cylinders from the back, and not the front like Ford and BMC.
First I would check the valve clearances, as perhaps the low compression reading is caused by a tight valve, This could be caused by the valve bedding in when spinning over and re-shimming will prevent the valve or seat being damaged.
It's then easy enough to check the ignition timing by taking the distributor cap off to see which plug lead the rotor arm is pointing at when the rear cylinder, (no. 1) is at top dead centre with its valves on the heels of the cams - the compression stroke. The rotor arm should be pointing at the HT lead that goes to this cylinder, usually the cap connection that's nearest the rear cylinder. It's then easy enough to follow the sequence of 1 5 3 6 2 4 through the cylinders in the direction of the distributor's rotation and ensure the leads are all plugged into their correct position in the cap and on the plugs. Hopefully this is where the problem is and it's an easy fix.
I'm sorry if I'm telling you how to suck eggs but we have no idea how much you know or what your experience is. I made this error many years ago when I wasn't aware that Jaguar numbered their cylinders from the back, and not the front like Ford and BMC.
Ray, in Cold and Windy UK.
my knowledge level is : triumph spitfires = yes, XK series = not a clue.
the car came to me with a block and pistons, but other than that, an empty engine bay… I’ve had to source everything and none of the wires match the wiring diagram color code.
the block was decked and had performance pistons, the head is skimmed, polished and pressure tested before I re added the hardware.
The spitfire will start (rough) with the dizzy out of timing, and I can turn the dizzy with the light gun attached to set the timing.
the jag seems to be a different kettle of fish.
and my hands are so big I find it so hard to adjust the pinch bolt to allow the dizzy to be adjusted then retightened without moving the dizzy again - seems like I need a grandson (haven’t been issued yet)
Apart from timing being way off, the only thing that I can think of that could give the exhaust backfire is a big leak into the intake manifold. But with that, you'd probably get some brief life from the engine with a good spray of starter fluid.
This is your bench mark for timing. If you pull the distributer with number six piston at top dead center then this is the position where the shaft for the distributer drive should be. Note that the alignment grooves are BELLOW the center not above. My engine came back from the machine shop with it in the above position which would have put my timing 180 degrees out. We caught it in time before putting the oil pan on. Talked to a very experienced Jaguar restorer about the machine shop mistake. He said it can easily happen, so I wasn't too mad at the shop.
Last edited by Felixbobcat; Mar 13, 2026 at 11:37 AM.
Reason: wrong info
This is your bench mark for timing. If you pull the distributer with number six piston at top dead center then this is the position where the shaft for the distributer drive should be. Note that the alignment grooves are BELLOW the center not above. My engine came back from the machine shop with it in the above position which would have put my timing 180 degrees out. We caught it in time before putting the oil pan on. Talked to a very experienced Jaguar restorer about the machine shop mistake. He said it can easily happen, so I wasn't too mad at the shop.
Thank you… I’ll report back.. I’ve so much to do this weekend but I’ll try to find time
Let me try this approach, I think you're overwhelming yourself.
Start with the cam timing, and answer my questions.
Did you use the cam timing tool to set the cams, see photo ?
Were pistons 1 and 6 at TDC (top dead centre) when both cams were put in place using the tool ?
Correct me if I'm wrong, but weren't you the one having trouble getting the timing chain over the sprocket gear, if this is so, then I'm pretty sure you have the cam timing correct.
It was gone over quite thoroughly in that other thread.
Please answer my questions, if you don't I (we) can't help you.
I will say this though, I think you have your distributor wired wrong, remember that on a Jag engine, the distributor rotor turns counter-clockwise, but don't worry about that for now, we have to get the cam timing issue of the table first.
Answer my questions.
As for the low compression on #5, I don't think the valve is bent from the cam timing being out, bent valves from a cam timing issue usually would have ZERO compression and would effect more then one valve and compression number.
Lets deal with one thing at a time.
Let me try this approach, I think you're overwhelming yourself.
Start with the cam timing, and answer my questions.
Did you use the cam timing tool to set the cams, see photo ?
Were pistons 1 and 6 at TDC (top dead centre) when both cams in place using the tool ?
Correct me if I'm wrong, but weren't you the one having trouble getting the timing chain over the sprocket gear, if this is so, then I'm pretty sure you have the cam timing correct.
It was gone over quite thoroughly in that other thread.
Please answer my questions, if you don't I (we) can't help you.
I will say this though, I think you have your distributor wired wrong, remember that on a Jag engine, the distributor rotor turns counter-clockwise, but don't worry about that for now, we have to get the cam timing issue of the table first.
Answer my questions.
As for the low compression on #5, I don't think the valve is bent from the cam timing being out, bent valves from a cam timing issue usually would have ZERO compression and would effect more then one valve and compression number.
Lets deal with one thing at a time.
Yeah that was me, I will test the distributor tooth position asap - you are correct, between work, immigration, kids, and 2 other projects I have overwhelmed myself.
Im 98% sure #1 was at TDC when i used the tool, but i have a TBI so i cannot rely on my memory.
I am also sure #5 is venting through the carbs on turn over... but this could be the valve not seating properly?
A lot of confusion on when to use # 1 cyl. or #6 cyl. TDC when putting the engine back together: When checking for TDC on #6 compression stoke you can look in oil service cap and see exhaust cam lobe position.
If using #1 cyl. you can take spark plug out and your finger in the hole can feel pressure on compression stroke coming up to TDC.
If your distributor timing is out it will be 180* out, as it was at TDC on exhaust stroke.
I did this on cylinder head change and after much too much fussing move spark plug wires on distributor cap 180* from book. I drove that way for 6 months before correcting the original error.
Move wires 180* if it starts and run you have found the problem.
Rgds
David
Last edited by David84XJ6; Mar 13, 2026 at 03:53 PM.
The first hint is in the OPs thread title of a "rebuild". Perhaps that involved re-meshing the distributor drive? If so, it is so easy to get things out of phase, because there are TWO TDCs in every 4 stroke engine . . . one on compression/ignition and one on exhaust. As David has advised, you can test this without removing anything other than oil cap, dizzy cap and (possibly) a spark plug, A possible 180 degree shift in ignition timing is far more likely than a 180 shift in valve timing . . . the latter would have already returned you a very second hand bunch of pistons and valves!
I truly believe that your #5 low compression (not "no compression") is a red herring, not to be ignored, but it's probably an unseated valve.that is either tight or poorly lapped, but not a cause for "no start".
I have made the same potentially fatal error when it comes to mis-timing the distributor to the correct TDC and timing chain sprockets. Despite my self-reassurances, and only nailed after the engine was all buttoned up, my red face lasted for days . . . but I only did it once! You do it and you learn from it, so that makes any shop forever mindful to double check. In my book, any worthwhile engineering shop should NOT get this wrong.
The checks I advocated way back in this thread and summarized by David since, are a necessary pathway in any total rebuild. My only reservation is to fix it immediately . . . not wait David's six months with mis-directed HT leads! LOL
Yeah that was me, I will test the distributor tooth position asap - you are correct, between work, immigration, kids, and 2 other projects I have overwhelmed myself.
Im 98% sure #1 was at TDC when i used the tool, but i have a TBI so i cannot rely on my memory.
I am also sure #5 is venting through the carbs on turn over... but this could be the valve not seating properly?
It's easy enough to check with a feeler gauge to see if there's enough clearance on both the intake and exhaust valves on number 5 with the cam covers off.
It could be as simple as a shim being too thick.
The first hint is in the OPs thread title of a "rebuild". Perhaps that involved re-meshing the distributor drive? If so, it is so easy to get things out of phase, because there are TWO TDCs in every 4 stroke engine . . . one on compression/ignition and one on exhaust. As David has advised, you can test this without removing anything other than oil cap, dizzy cap and (possibly) a spark plug, A possible 180 degree shift in ignition timing is far more likely than a 180 shift in valve timing . . . the latter would have already returned you a very second hand bunch of pistons and valves!
I truly believe that your #5 low compression (not "no compression") is a red herring, not to be ignored, but it's probably an unseated valve.that is either tight or poorly lapped, but not a cause for "no start".
I have made the same potentially fatal error when it comes to mis-timing the distributor to the correct TDC and timing chain sprockets. Despite my self-reassurances, and only nailed after the engine was all buttoned up, my red face lasted for days . . . but I only did it once! You do it and you learn from it, so that makes any shop forever mindful to double check. In my book, any worthwhile engineering shop should NOT get this wrong.
The checks I advocated way back in this thread and summarized by David since, are a necessary pathway in any total rebuild. My only reservation is to fix it immediately . . . not wait David's six months with mis-directed HT leads! LOL
Rebuilt engine won’t atart
