Header double walls

+1 on Ed´s comment.

DGA wrote: I pulled the plug wire off #3 while idling and it does make a difference, yes. But I noticed that plugs #1 and #4 were leaner than the other two. And the idle won't go under 1500. The vacuum hoses for the EGR valves, or whatever that system is on top of the cam cover, goes to both of those cylinders, so I removed the hoses and capped the nipples. Big change with the idle speed, now is under 1000, maybe 700. So that system was causing a vacuum leak. So, should I just remove the whole thing and make blanker plates for the cam cover, is it ok to do it that way or?

Good Fortune!

On the large fours with needle bearing cranks, there's not quite so much danger from low oil pressure at ultra-low idle. Because the oil pressure is minimal anyhow, and the needle bearings and cam journals just need a some oil bath as opposed to significant pressure required by surface-to-surface crank bearings in the smaller engines such as KZ650.

In any event, would set the idle per factory specs.

When an idling large four engine sounds like it's digesting nails, a tune-up (including valve clearances and carb sync) may significantly reduce the noise at idle and produce a smooth idle.

A strong, smooth and steady pull-away from idle depends on perfect pilot circuits in the carbs.





Good Fortune!

The vac leak from the clean air system into cyl 2-3 would be expected to have caused leaner instead of richer plug readings.

Would expect an ignition-related weaker combustion in #3 to also manifest in #2, as both are in the same secondary loop.
Whereas a carb-related weakened combustion in #2 would not impact #3.

The richer plug readings in both cyl 2-3 indicates an ign issue in the secondary loop, or issues in both carbs #2 and #3.

Good Fortune!

Perhaps leakage of high tension voltage through old, hard, cracked worn-out spark plug wires.

For fun, could spray water mist over plug wires while engine is idling in a dark garage, and possibly enjoy a fireworks show.

Good Fortune!

The idle was a problem at 1500, after I took the vacuum hoses off that run the EGR system and capped the nipples, THEN the idle, without me touching the adjuster, went to 700. I am not trying to make it idle at that speed, was just saying that it was the vacuum leak. Those cylinders were showing lean with that leak. Plug wires are new and #3 did drop the idle speed when I pulled it, and it was cracking when I pulled it.

OK, a question from this if I could ask, Could a problem with the egr reeds or whatever is in there make the cylinder 3 run cooler, something to do with the original problem this thread was for?