105 distributor advance incorrect???

[Glenn NZ]

Hi, on my 1974 105hp (converted to pointless distributor), Im having some timing issues...any thoughts??
When opening the throttle, the timing advances until near full throttle, where it then slightly retards. It is the linkage that goes "over center" and pulls the dist back, where the timing screw adjustment is.
thanks

 

[Frank Acampora]

Re: 105 distributor advance incorrect???

Glenn: Short story---That is 100% correct. The timing will retard about 2 degrees at full throttle. Just set it to 32 or 30 BTDC at full throttle.

Long story---This is very common on ALL engines, both marine and automotive. Typically they will retard a degree or two and (in the case of older auto engines) the carb will get a little richer.

Because air is the limiting factor in an engine, it can only ingest so much, going slightly rich at full throttle ensures that ALL the air is burned. Excess fuel to a degree, will cause less power loss that too little fuel. Excess fuel coupled with the retarded timing help to prevent detonation and engine damage.

 

[Glenn NZ]

Re: 105 distributor advance incorrect???

Many thanks Frank!

The motor is burning 45-50 litres per hour at 5000 rpm (12 US gallons), when it did use around 25 litres prior to the install of the pointless distributor. The timing appeared to be way off & I discovered that the throttle was partly on to counter this, to make it run. Havnt tested it yet, but stripped the carbys down etc.
What sort of fuel consumption would be normal anybody??

Thanks

 

[Glenn NZ]

Re: 105 distributor advance incorrect???

Hi Frank, I have just checked the dist retarding when approaching full throttle. Mine retards 6 degrees? how does that shape up??

(the spare 120hp engine I have, does not seem to have any retard approaching full throttle?)
Thanks

 

[Frank Acampora]

Re: 105 distributor advance incorrect???

Well, Glenn, I never actually measured it, I just guesstimated a couple of degrees.

Depending upon the orientation of the plastic threaded blocks it can be different as the tower goes over center.

Newer non distributor models do not do this, at least not very much at all.

At any rate if you are at 32 or 30 BTDC at WOT, the timing is correct and since you will have slightly more advance at partial throttle in cruise mode, fuel economy should be better.

Your fuel consumption is a tad high, I would expect more like 25 litres per hour at WOT.If anything, I would have expected just a small decrease in fuel consumption with the electronic distributor at cruise because of more precise timing. At WOT, I would expect slightly worse fuel mileage because of greater power produced--but not to the degree you have experienced.

 

[Glenn NZ]

Re: 105 distributor advance incorrect???

Thanks for the info Frank! Just didnt want any detonation at cruise speeds etc.

I think the fuel consumption was high due to the carbys being a mile out & timing also way out. Will see how it goes at the weekend, should be back to the 25 ltr mark, as its sounding much better running in the back yard.

Cheers