Misfiring while cruising

[Mark Maras]

How long are you planning on letting it idle? Also, how long do you normally have to let it idle in traffic?

[jalexquijano]

Heavy stop and go traffic 5 minutes per stop light

[Mark Maras]

 How long are you going to let it idle? 

[jalexquijano]

What about long idling bumper to bumper? Shouldnt these car stand these situations?

[AK260]

 A big improvement. No more fouled #4. I don't have an answer to why #s 2, 5, &6 have a slight rusty color on them. I wouldn't worry about it for now. Does anyone have a guess? I'd drive it for a while and check them again.

Great to hear, well done. [emoji106]

Imho those plugs look on the hot side, look at this ...




If those colours were on the same bank of 3 cyls I would have said carbs, but since they are not, I'm tending towards valve clearances.

Now, two questions:

1. Have you adjusted your valve lash clearances? They determine how much / little or consistently across the cyls your valves open and shut and their timing relative to each other. I find my engine (a highly modified L28 but with a mild cam of 270 degrees and .46" lift) reacts very strongly to well adjusted valve clearances. It's more noticeable on a modified engine but the principle is the same for yours.

2. As for your idle, are you running a working vacuum advance? Have you checked it is actually working? Your mix at idle or part throttle will be lean and will require more timing for it to burn well. Mine has a base timing of 17 degrees (higher than stock due to cam) and vacuum advance adds 12 degrees at idle. But as soon as I go on the throttle and open the carb butterflies, the manifold vac drops and timing goes back to 17 + mechanical advance as the revs rise to a total of 34 degrees (without Vac! With vac connected, add 12 degrees to that).

A lean mix without sufficient timing will burn hotter. With vac advance, you will find your idle will improve and engine temp at idle or cruise will drop noticeably. Also the cruising to on-power responsiveness improves (not to mention gas mileage).

Think of it this way, imagine you have two plates full of gun powder on the floor, one packed with dense gun powder (rich) and one sparsely packed (lean). On the rich one, the gun powder particles are touching, on the lean one there is air between them. Then you light both from the centre - the plate with the denser gun powder burns faster towards the edge.

Now imagine you had a fixed amount of time of say 1 second for them to burn before you dump the contents into the trash can. The fully burnt / rich plate dumps hot soot. The lean plate is still combusting and finishes it's burn in the trash can, burning the edges of the bin as it goes in (and that is the edges of your exhaust valves in an engine).

Next time around, you light the lean plate half a second ahead of the rich plate. This time, both finish their burn before you dump them. The principle in your engine is exactly the same and your exhaust / header temps will drop with more vac timing at idle.

Hope that helps, good luck!

BTW, where are you able to do 100mph without getting a blue light escort!? Are you in Germany!? (Joke!) Or a test track?