Motor wants too much advance

[Tkisner]

I have decided to bring my 75 Westy to a bus guru because it has never run right. So this question is purely because I am pretty confused, and would like some help wrapping my head around what may be happening.

It is a later hydraulic lifer 2.0, progressive carb (will be changed to duals), SVDA. The bus was running hot under conditions I would not consider extreme. Highway driving going 50-55 mostly flat. I pulled the plugs it was detonating slightly (light gray color). I fattened up the idle and basically idled home in 4th gear and the motor ran cool.

I also checked the timing when I checked the plugs. With vacuum hose plugged at 7-8 btdc the engine ran ok. It occasionally backfired out the exhaust. However, if I advanced it to say 12-14 it ran much much smoother and picked up idle RPM. At 28* max advance same thing happened. The motor smoothed out in the 32-34* range. Everyone says that is too much for a bus so I wanted to ask why this motor runs better with a setting that most deem harmful?

Like I said earlier I am going to have a pro get all of this squared away. I also have a wideband o2 that I bought for a different project that I am going to put in so I can keep better track of my AFR. Any input would be appreciated.

[telford dorr]

The first thing to do is to verify that the timing scale is accurate. Seems that scales vary - either made wrong (aftermarket), bent, or something. Basically, you need to check that TDC is really TDC.
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[Tkisner]

[Tom Powell]

ACVW engines are detuned for longevity. It's a touring vehicle not a dragster that gets a few miles out of a well tuned engine. Keep it cool and you'll keep it long.

Aloha
tp

[airschooled]

Is your 28° max advance with the vacuum hose on or off? It should be hose off… 35°-40° hose ON is not out of the question on a Type 4 engine.

Robbie
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[busdaddy]

You should also elaborate on your distributor, SVDA covers a wide range of good German as well as shitty Chinese dostributors.
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[Wasted youth]

Let's see a picture of your vacuum hose relationship on the Progressive carburetor to the vacuum can on your distributor.

[Tkisner]