Spark advance, throttle and timing

Redbarron%%

Chief Petty Officer
Joined
Dec 7, 2017
Messages
479
I have a 90 Hp Sport Jet that I have been working on finding an fixing water getting into the cylinders, ignition problems etc.
My current question is on getting the tower adjusted, the idle, full throttle and timing.
If I set the idle screw to 1/8" like it shown in the manual I cannot get full throttle.
It seems that the trigger link bottoms out on the trigger base before I get full travel.
I can get full throttle if I set the idle screw maybe 3/4" out and then I can set the timing to give 32 * at WOT and 8* at idle with the throttles opening to the mark at 100 %.
Now for my real question. With this set up as I advance the throttle from idle to 3000 rpm the timing goes from 8* to 30* and as I advance past 3000 it will go well past 30* and then as you go to WOT (100% ) the timing comes back to 30*.
Since the throttles are not 100% open at 3000 rpm and when the engine is at 100% the timing is at spec does this mean that there us supposed to be higher advance 3000 - 5000?
I hate to burn the pistons in this fresh engine because of too much advance in this range.
Does any one know if this is correct or why I can't get 100% throttle when the idle screw is set to the 1/8" as called for in the manual?
It looks like the linkage goes over center at about 4000 or so and the timing comes back down.
Thoughts?
I had never looked at the timing advance at this rpm until I put it in the water and advanced it slowly, worried when at 3000
the timing continued past the mark.
HELP!
 

Nordin

Commander
Joined
Jun 12, 2010
Messages
2,437
Redbarron look at the top of this forum there is a thread "carb and timing tutorial by Frank A.

BTW the importen thing when setting timing is the advance at WOT.
Set it to 30 dgr BTDC, then check the throttle butterfly at WOT.
If it does not open up to horizontal lengthen the throttle rod.

The time advance at idle will be what ever 3-8 dgr or more.
You set the idle screw at tower shaft so you get 7-800 rpm in gear in water.
Do not worry about if the screw is 1/8 or 3/4 out at idle.

About the timing come back at WOT, this normal on Chrysler and Force OB.
I think it is called "fuel save range".
 

Redbarron%%

Chief Petty Officer
Joined
Dec 7, 2017
Messages
479
Thanks for the info.
I had hoped that the higher advance was engineered in and normal.
This was the first time I looked at the advance as the throttle was advanced and I was surprised when it went well past the 30* mark.
I was hoping that the lower manifold pressure at part throttle the higher advance was correct and and there for better fuel economy.
The idle has to be higher for the sport jet since it needs it for cooling 1100 -1200 rpm.
Thanks for the reply
I have looked at the video several times, but it did not show about the advance curve.
 

Nordin

Commander
Joined
Jun 12, 2010
Messages
2,437
Oooh yes my mistake, did not notice it is a sport jet.
Then 1100-1200 rpm is correct.
 
Top