starting diesels while working throttle

[Ray IN]

I have never tried working the throttle back and forth when starting a 4020 or other similar diesel. But I saw a long-
time JD mechanic hop on one and pump the throttle while cranking, as if it was his normal practice. Sure enough, when
I tried it on mine, they fired up a lot quicker than normal. What is going on when you do this, and is it common
practice for most?

 

[Dieseltech]

I'd say it's just coincidence, once the throttle on Roosa or CAV pumps are just above idle any more will not change anything, as the metering valve is already open. There's no accelerator pump either on diesel engines like some carbs have. Inline Bosch and Denso pumps have starting springs to move the rack to full fuel start position when the stop lever is moved to run position, throttle lever setting makes no difference at starting if the governor is working correctly. There are some pumps that will not start best at idle, American Bosch Model 100 as used on IH and AC tractors. M100 has an excess fuel cylinder that limits the full load fuel setting when running, with no oil pressure it allows further fuel stop travel for starting. BUT it only helps when throttle is above idle setting by 1/4 or more. Those should never be started at idle.

 

[David G]

My buddy does that too on 4020, think it is psychological.

 

[Ray]

I've heard of turning the steering wheel back and forth fast to relieve hydraulic pressure for an easier start,but never the throttle.

 

[Tx Jim]

(quoted from post at 23:17:42 03/08/17) My buddy does that too on 4020, think it is psychological.

DITTO

 

[Ray IN]

Thanks--that is kind of what I thought

 

[Mike M]

Isn't there some models you are to go to full throttle and then back down to set an aneroid ? Models like a 4430 ? or some of the bigger older ones ?

 

[Dieseltech]

The early aneroid pumps with the 'rat trap" linkage was set with the throttle pulled back to idle, otherwise it would not disconnect the aneroid when needed for more cold start rack travel. The oil cylinder cutout works much better. There are some Bosch RSV governors that use an electric solenoid on the cutout shaft too.

 

[JDEM]

It does not do anything on a Stanadyne rotary-distributor pump. Not unless there is something wrong with the pump and the governor and metering-valve linkage inside the pump sticks. Throttle-lever movement on a gas engine is important when the carb has an accelerator-pump (not all tractor carbs have one). No such thing in a rotary diesel fuel injection pump.

You remind me of something funny I saw happen. Back when the GM 6.2 diesels were common and having awful glow-plug problems. I saw many a "mechanic" pump the gas pedal trying to make them start Needless to say, it did not work.

 

[Tx Jim]

(quoted from post at 07:43:07 03/09/17) Isn't there some models you are to go to full throttle and then back down to set an aneroid ? Models like a 4430 ? or some of the bigger older ones ?

I was taught moving throttle to WOT then back to idle after stopping engine when engine oil was at operating temp help set rack inside Bosch pump on 4430's for easier starting in cold weather

 

[oakley21550]

That is correct on relieving hydraulic pressure by turning steering wheel to relieve pressure. Can do this instead of fixing problem which is supposed to be fairly simple O ring or something. Have seen fix on here a
long time ago. My 4020 gasser starts MUCH easier, especially when cold.

 

[oakley21550]

Posted 1/2/14 by El Rey