GT750 oil pump question

[tz375]

The late-model rod-link arm has an alignment mark to adjust the pump when the throttle is closed.
So the throttle-closed pump setting will be correct when using either the CV or early-model carbs.

The early-model cable-link arm has an alignment mark to adjust the pump at part throttle.
You can only set this correctly with early-model carbs because its based on carb slide position.

So as I understand it, in Lane’s case the pump it correct at closed throttle.
The late-model rod-link arm is shorter & its rotation results in a shorter linear distance.
The throttle rotation conversion to linear distance is for the early-model cable-link arm.
Because of the short arm, Lane’s pump reaches 100% flow a bit earlier.

I currently have the same setup & adjustment as Lane.
Its working for Lane.
I don’t know if switching arms will make much of a difference in the real world.

You are correct.

[jabcb]

Here are three pics of the oil pump.
When you open the throttle, the actuator arm/shaft rotates counterclockwise from A -> B -> C.
The positions are:
A) actuator arm resting against the stop, has noticeable resistance when you turn the actuator shaft with your fingers
B) cam position where the actuator shaft starts to turn freely with your fingers
C) cam position where the actuator shaft stops turning freely with your fingers
The actuator shaft turns freely between B & C.

The actuator arm shown in the pic is a late-model arm that was modified to connect to the early-model throttle cables.

Its easy to figure out the correct assembly if you removed the actuator arm:
1) find positions B & C
2) mark the shaft so you can confirm the assembly is correct (I used a dab of paint)
3) assemble the pump so that you get position A

Position A


Position B


Position C

[chopwhatyagot]

Thanks for the post fellas, i was able to figure out my problem by reading this, my oil pump was 180 out. I moved the shaft and now she is burning clean and brown with no piston wash.

[rngdng]

Great thread!



Lane

[Suzukidave]

Easy test to see if the arm on the pump isnt 180 out , with the pump off the motor move the arm from the idle to the full on position . The drive shaft in the bottom of the pump will move up into the pump a bit as you swing the arm from idle to full .

[Suzukidave]

Its been a while sense i have check a pump but i am pretty sure if the arm is on the pump correctly ... when you move the arm through from min to max positions the shaft in the bottom will move up into the body of the pump a bit .

[jabcb]

Reposting the pics moved from Photobucket to Flickr…

Per this reference, the GT750 oil pumps were effectively the same, except the actuator/lever arm had two different designs depending on the type of carbs.
http://www.pinkpossum.com/GT750/Oilpump.htm" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

The pump adjustment also depends on the type of carb.
The following are from the GT750 service manual.

GT750 oil pump output spec:
GT750_OilPump_Spec by jabcb, on Flickr

Early-model (72-73) GT750 oil pump adjustment with throttle open as shown:
GT750_OilPump_72-73_Adjustment by jabcb, on Flickr

Late-model (74-77) GT750 oil pump adjustment with throttle closed:
GT750_OilPump_74-77_Adjustment by jabcb, on Flickr

If you look closely at the two different actuator/lever arms designs, you can see the adjustment alignment marks are in different locations. The arms may also have different effective lengths.

[jabcb]

Here are three pics of the oil pump.
When you open the throttle, the actuator arm/shaft rotates counterclockwise from A -> B -> C.
The positions are:
A) actuator arm resting against the stop, has noticeable resistance when you turn the actuator shaft with your fingers
B) cam position where the actuator shaft starts to turn freely with your fingers
C) cam position where the actuator shaft stops turning freely with your fingers
The actuator shaft turns freely between B & C.

The actuator arm shown in the pic is a late-model arm that was modified to connect to the early-model throttle cables.

Its easy to figure out the correct assembly if you removed the actuator arm:
1) find positions B & C
2) mark the shaft so you can confirm the assembly is correct (I used a dab of paint)
3) assemble the pump so that you get position A

Position A
GT750_OilPumpPosition-A by jabcb, on Flickr

Position B
GT750_OilPumpPosition-B by jabcb, on Flickr

Position C
GT750_OilPumpPosition-C by jabcb, on Flickr