Spark plugs

[JamesG]

Just working through my engine, trying to get it working. Have cleaned carburettors (Dellorto FRD 32E), swapped out bent push rod, reset tappets, fitted new distributer arm, checked compression (no1 190 psi, no2 200 psi, 3 195 psi, 4 177 psi) and checked spark on all plugs. Currently it will fire, occasionally run for a couple of seconds then stop.
On checking spark plugs, the front 2 are fairly clean, but nos 3 & 4 are dry and sooty, which i thought would normally suggest a rich mixture. But why would the front and back differ when the come from the same carb?
Any suggestions welcome.

[Forumadmin]

Check the firing order.
Check you have fresh petrol.
Does it run if you give it throttle?
Any difference if you give it choke? Maybe you do not have chokes!!
Check for leaks on carb adapter gaskets.

[JamesG]

Thanks for that.
Firing order 1 4 3 2
I had drained the tank and fuelled with V Power
Have tried both half throttle and pumping throttle when running but still dies.
Have fitted temporary arrangement of two separate choke cables, starting on 3/4 choke.

Will inspect for air leaks this week.
I have ordered new plugs (NGK BP6HS) to eliminate those.

Also worth mentioning - I get an occasional backfire when trying to start, which can be quite spectacular with flame out of the carb air intake. Valves should be good, based on compression test, so could be my timing is way out.

Enjoying the challenge!

[Keith Clements]

Could be valve timing.
There should be12 deg btdc mark on flywheel which is when inlet valve should start opening.

[PJGD]

Note that the correct firing order is 1-4-2-3, not the 1-4-3-2 that you are indicating.

If you have the plug leads on wrong (and don't forget that the distributer rotates counter-clockwise), then that will cause you problems. . .

[JamesG]

Thanks for spotting that. Have checked, and it is my short term memory, and not the actual firing order that is at fault.
Actual firing order 1 4 2 3.

[Keith Clements]

Also make sure you have adjusted the tappets correctly as per the instruction in a Jowett Patient
viewtopic.php?p=43335#p43335

[JamesG]

No I inlet opening

So I have stuck on the timing chart so that tdc is at the vertical position (there is a paint mark on the pulley which confirms this) and at the point the inlet pushrod starts to go tight looks to be about 12/13 degrees before it should be.
I know the car was modified for hill climbing, and tuned engines may have a greater valve overlap, but it still seems more likely that the timing is out. I will try to check inlet / exhaust opening/ closing angles to fully check.

[Keith Clements]

Check tdc by using plastic wire in plug hole.
Then check on flywheel at 3 4 and 1 2 cylinders.
Then work out 12 before tdc.
A mark should be on flywheel but may have been removed by lightening.
I doubt any modified cam would vary much from that.
Note exact adjustment requires dial gauge on rocker to acheive 12 thou of lift without the 3 thou clearance normally there.

[nigel jarrett]

What caused the push rods to bend and have they bent again since you tried to start the engine ?

[JamesG]

Nigel - no idea what caused the bent rods - bent when I bought the car. Not so bent that they did not operate, but bent enough that it was not possible to get a consistent tappet gap. Replacements have, as yet, stayed straight.

Keith - many thanks for the advice.
I had used a probe to identify tdc, but difficult to judge exactly, so I used an endoscope and marked tdc from that.
I have now set the tappets and ignition timing following the guidance in the post you listed.
The engine on my car is set a long way back, so difficult to access the flywheel, but I have copied your timing disc and fixed it on the pulley and will take all readings from that.
Next step is to put a dial gauge on the rockers - I hope to do that tomorrow.

[JamesG]

Hopefully I understood correctly. Set the tappet on no 1 inlet so no gap, then rotated until I had 12 thou lift on a dial guage. Difficult to be precise within a couple of degrees, but it is about 13 before tdc. Not the 12 specified, but I assumed close enough not to be an issue.
Reset tappets and put back together.
Fitted new plug leads and plugs.

And SHE WORKS.

a bit rough, noisy and smokey, but a good starting point to refine from.

[Keith Clements]

You did not say that you adjusted the valve timing by moving the position of the peg in the camshaft timing wheel. Did you?

[JamesG]

No, I thought it was so close as it was that I would leave it. Very difficult, even with an endoscope, to be completely accurate about tdc as there is so little movement. This was my best estimate of tdc

You can see that my mark (that I initally put on using a probe) is maybe 2 degrees before tdc viewed by the endoscope
The 12 thou on the dial gauge came here

So I thought it looked as if 12 thou of lift came around 13degrees before tdc. Is the peg adjustment as granular as 1 degree?

[Keith Clements]

The start of the ramp on the cam is at a point where acceleration starts and as you observed occurs rapidly.
It is a while since I did the adjustment but getting to within one degree is probably difficult. Philip may be able to work it out from the engineering drawings!
In my experience I would do the measurement and adjustment a few times before I was happy. Wear in the timing gear would make the adjustment alter on all lobes and as we know each lobe can also wear differently. Also Philip's work on the bending of the cam reported here will also have an effect, particularly as wear occurs in the camshaft bearings.