16 replies to this topic

[mini670]

Well I have encountered another problem with my fresh engine build. GOt a couple of questions please guys.

It was running not too bad when i started it a few days ago, it started first time everytime and only had a very slight misfire. The misfire could be seen on the timing light, it would miss a flash every few revs.

The last two days it has not started, turning it over it had made 'chuff' sound about every 4 revs and on this chuff sound the starter struggled. Sometimes it would backfire through the carb. So i got thinking about a sticking valve? (also i took the dashpot off and it had some petrol inside, and the piston was stained with black soot)

Today after a bit of messing about i got it started. Im unsure which bit i messed with enabled it to start, but changed to non resistive plugs (as i have resisitive caps), swapped ignition coil triggers around, tightened manifolds. Pulling ht leads off one at a time doesnt seem to make a difference.

.

Now say i have a sticking valve, air leak or running lean would the timing still show as a constant flash, or would the slowing down of the trigger wheel on a misfire cause the spark to miss too?

 

heres a video of it running rather rough tonight. ohh its a 266 cam too, so nothing too lumpy really. Any help appreciated.

http://s98.photobuck...7f8cfc.mp4.html

 

 

 

[dean]

I would say its your coil pack breaking down. I had a Ford KA which uses the same coil packs and that started to mis fires once. Went though the same process. Leads. Spark Etc etc.

And it ended up being the coil.

When it started it was not too bad but slowly got worse.

Well that's my guess

Edited by dean, 04 September 2013 - 10:01 PM.

[mini670]

Cheers, ill see if i can get hold of a spare coil.

I did measure the resistance across both coils and they are both within 5K ohms of each other. I dont know what happens as they break down but if they are they are going at the same rate.

[jaydee]

Looks like its the coil pack going wrong

[mini670]

Ok i have got it running again. The low tension wires to the coil were the wrong way around, i have also adjusted the carb with the lifting pin method.

 

At idle it still seems to misfire slightly. With the light on the pulley it shows 10 degrees, but frequently it looks as if the mark jumps to somewhere like 20degrees.

I tried another coil pack yesterday and it made no difference. The vacuum gauge flickers around also then steadies out at 1700rpm+ and the misfire seems to disappear, from what i read it could be worn guides.

 

If it is somehow missing due to guides, would this cause the engine to temporarily slow and give the above effect on the timing light?

[mini670]

here is a video of it running.

 

http://s98.photobuck...629e65.mp4.html

[jaydee]

What CO at idle?

[mini670]

Have no way of telling co at minute. Will this show worn guides? Cheers

[jaydee]

Why worn guides, is it burning oil at start up?

[Ethel]

Where's the gauge & MAP tapped into the manifold? The original dizzy tapping is designed to shield the dizzy from full manifold vacuum at idle so you get a less advance and a smoother idle. Your vac gauge & MAP sensor are likely to be a lot more sensitive. Though you could set zero load advance at idle rpm to fix that bit.

 

I guess all sorts of weird things are possible with wasted spark & misfires. 

[mini670]

The MJ is connected to the original distributor tapping (after butterfly on HIF44).

I did however make a test may with 10deg all over to check. This map still makes this misfire happen.

Checked all wires, tried another coil pack, another set of HT leads, non resistive plugs, checked sensor resistance (273 ohms).

Hoping to try another VR sensor soon, this is the only other thing i can think off bar a new MJ or EDIS unit.

Cheers

[jaydee]

A slightly broken idle is normal with a 266, you have to look into fuel mixture to iron out the lumpiness before 1700 rpm

[mini670]

Would this cause the stutter on the timing light also?
I have a new vr sensor on order too.

[jaydee]

Yes, its normal but it must clear out at about 1200-1500 rpm, 1700 sounds a bit too high. Check tappets clearance, try 16 thou.

[Ethel]

You could have another look at the routing & shielding on your vr cabling. it seems odd that it'd only misbehave when it's got the easiest (slowest) operating conditions.