Volvo 501b timing questions

[jim.bresee]

(1st post seems to have failed! Trying again..)

Patient is a 1993 Volvo 501b.

Boat is a Larson 200sei.

Problems:
1. stumble or miss at WOT
2. Idle wanders

What's been done:

1. Motor is a reman with about 100 hours on it.
2. Carb was just rebuilt (it's a Holley 4 barrel, but given how hard it was to find a rebuild kit, it's not a common variant).
3. Plugs, cap and rotor just replaced.
4. Plug wires replaced last year.
5. Carb fuel filters are new.
6. Water seperating fuel filter replaced end of last season.

specs call for 20 degress BTDC @ 3000 RPM. It also calls for 8 degrees BTDC initial timing.

Visually, it looks like the timing is at 12 BTDC at idle (750rpm).

Questions:

1. I understand and can see how to pull the timing back to 8 BTDC. I don't see how to measure 20 degrees at 3000 rpm.

2. I set the idle mixture according to the manual - 1.25 turns out on both left and right mixture screws. Does idle mixture make a difference at full throttle, or do these settings only impact idle?

3. Any thoughts on why the idle wanders by 25-50rpm?

Thanks for your thoughts,
Jim

 

[Don S]

Re: Volvo 501b timing questions

The 1 and a quarter turns on the idle mixture screws are only a starting point. Final adjustment is done to obtain best idle while the engine is idling.

Most people just use an advance type timing light to measure the advance, you can also do the math and calculate where the mark should be on the balancer and mark it yourself, then check it with the engine running using the timing light.

 

[jim.bresee]

Re: Volvo 501b timing questions

Hi Don,
Thanks for your reply. I did further tweak the idle mixture to obtain the best idle after the initial setting.

I have an inductive timing light, but it does not have the advance feature. What does that do?

Also, I'm not understand what math needs to be done to calculate where to create the timing mark. Are you just measuring the distance between the hash marks on the timing cover and extrapolating that to the 20 degree location?

Thanks again for your help,
Jim