[ihc] Scott Machalk and his high rev

[Joel M Brodsky <jmbrodsky@xxxxxxxxxxxx>]

Hey Scott!

      Glad you're back!  It's been a while no?  Last I remember, was seeing
you in Tulare back in....whoa!  '98!?

      I hope some of this helps:

      I vote for timing too early and a vacuum leak.  Make sure it's timed
off cyl no. 8, and start somewhere between 0 and 5 deg BTDC.  If it's more
than that you're asking for difficulty.  An IH engine, in my experience,
will idle anywhere from 30 before to 15 after so try and start in the
middle and go from there.  The mileage will usually suffer, but the
backfires should go away.  Make sure the plug wires are routed
1-8-4-3-6-5-7-2 from the distributor cap.  If they are 'keyed' off, ie. 1
on 8, 8 on 4, 4 on 3, etc, then the timing will be wrong and you may be
cross-firing some cyls so early that they are backfiring through the carb.
The fact that you get compression on all the cylinders is a sign that the
backfire is due only to an ignition spark when the valve is closing, but
I'm not sure if this should occur more often at high or low RPM, but like I
said, I'd set the timing to 0 then work from there.

      In my experience, the vacuum leak is usually the culprit when the
engine speeds up, then slows down and seems to do this like there's a ghost
pushing the pedal.  All these problems are with/during the idle correct?
Check all your vacuum connections, and I would start by leaving the vacuum
advance disconnected and plugged, thus avoiding any vacuum advance issues.
Also, try and set the timing under about 1000 rpm.  Any higher than that
you might have some mechanical ignition advance in there too.  Also, pull
the vacuum line to the brake booster and plug that as it comes off the
carb/manifold as that is often a source of huge vacuum leaks.

      So, if you already took care of the usuals, plugs, wires, cap, rotor,
then the rest is fiddling.  Also,make sure the jets are all clear in the
idle circuits in the carb.  I've seen more than my fair share of 'new' or
'rebuilt' carbs with plugged or dirty passages.  A healthy dose of carb
cleaner from the attached straw through every little hole (wear safety
glasses and make sure the idle screws are removed) should do wonders.  Be
careful when cleaning the carb passages.  When spraying carb cleaner in
there it will most likely go out the orifice that directs the stream
straight to your eyes, your friend/buddy/wife/GF, or your trucks' new
paint/interior, usually in that order, so make sure you're in an open area
when you spray it out and wear eye protection.  Also, I like to use a piece
of stripped 22GA wire to poke around through the holes in the carb to make
sure it's all clear.  Usually the copper is soft enough not to damage the
holes.  Don't use a drill or a welding torch cleaner as it will often
resize the carb opening.

      Also, for some reason, I've had good luck at starting the idle screws
at 3 turns each from fully closed.  There is an ongoing debate with the
mechanics of/in history about whether or not these screws control fuel or
air.  Everything I've read says that these are called Idle Air Bleed
Adjustments, so why does the truck quit when you turn them in?  I don't
know, but I start at 3 turns out from fully turned in (lightly) and then
usually I turn them in, until the engine just begins to run poorly, then
back them off about 1/4 turn.  I've heard this called a lean-roll-off
adjustment, but call it what you will.  I'd say, that as a rule of thumb,
if they are turned in to any more than about 1.5 turns or out to any more
than 5 turns, then you have some other problem in that carburetor, or there
is an air leak.  Make sure the baseplate gaskets are sealing too.  A
Propane hand torch, unlit, but hissing propane can sometimes help you find
vacuum leaks as the idle speed goes up a bit with propane, but if you
haven't done this before, you might endanger yourself more than help.  You
might want to stick with spraying WD-40 or other flammable lubricant around
fitting and joints to check for vacuum leaks.

      Good luck, and lets us know how it goes!

JoelB