Dollar-bill Test

[john r. lebetski]

Could be ignition or idle mixture setting. Could be 18436572 pattern with header lengths exaggerating the effect. If it's not an actual missfire and
there are no ticks or knocks I would drive it. Remember that 3-5 and 4-6 are not true header pulses as the heads have one port and headers have 2.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[john r. lebetski]

I'd also listen for a miss and feel for a miss. You may think the sky is falling when it isn't. Though all pulses are 90 degrees apart, they do not
all alternate banks but 8/4 and 5/7 are clumped on same side banks. Mine runs perfectly and pulses do not feel even with hand over tail pipe.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[Matt Colie]

Corey,

You can't see the cross-over from any intake port. If it still has a working choke stove, then that port is open.

I would not put too much stock in your dollar bill test with a long exhaust system like most coaches have installed. A system that long and screwy is
bound to have some reversion at idle. Did you ever run a 2-stroke with an expansion chamber?

I don't put a whole lot of stock in compression tests either. But in your case, if any exhaust valve was so badly seated as to cause that reversion
you are seeing, there would be no compression left in some cylinder.

Drive it and enjoy it.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

 

[Jim Hupy]

What Matt said! More'n likely a spark plug, or a wire that leads to it, or
in the case of the GMC, crossfiring plug wires where they run beside each
other. Or, it could be carbon tracking inside the distributor cap, a crack
in the coil, or a faulty rotor. Last, but certainly not least likely, is
too large a spark plug gap. Keep it to .045". NO LARGER THAN THAT.
Lastly, look into the carb, and vacuum lines and that means all of them,
including the factory cruise control.
Jim Hupy
Salem, Oregon

On Sat, Feb 29, 2020, 7:29 AM Matt Colie via Gmclist <

> Corey,
>
> You can't see the cross-over from any intake port. If it still has a
> working choke stove, then that port is open.
>
> I would not put too much stock in your dollar bill test with a long
> exhaust system like most coaches have installed. A system that long and
> screwy is
> bound to have some reversion at idle. Did you ever run a 2-stroke with an
> expansion chamber?
>
> I don't put a whole lot of stock in compression tests either. But in your
> case, if any exhaust valve was so badly seated as to cause that reversion
> you are seeing, there would be no compression left in some cylinder.
>
> Drive it and enjoy it.
>
> Matt
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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>

 

[Matt Colie]

> I though of my error after I posted yesterday. I did not see the blocked crossover because the carb was off... it was when I had the choke stove
> plate off... trying to figure out why the choke was not pulling off when it should. Figured it out! Will probably get an electric choke soon

Corey,

Thanks for the clarification.
Get the electric choke heater real soon.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit