1999 Mercruiser 5.7 deiseling after carb rebuild

[jlanka]

Title says it all. Engine is deiseling when I shut it down. This started happening after I took the carb off and brought it to a local shop to rebuild.

Can't be bad gas because I have twins and the other one is fine.

Is there a carb adjustment I can make to stop this?

It may have actually reversed the impeller in my water pump (saw this in another thread) because I started it up and the serp belt started squealing and eventually burned through. Water pump was hard to turn by hand after this happened.

 

[Another retired guy]

Re: 1999 Mercruiser 5.7 deiseling after carb rebuild

For a gas engine to diesel requires extreme heat. Maybe carbon build up in the combustion chambers coupled with an overlean mixture following the carb rebuild?? The carbon glows red hot and keeps igniting the fuel.
I've seen this on an old car motor!

 

[Don S]

Re: 1999 Mercruiser 5.7 deiseling after carb rebuild

Is there a carb adjustment I can make to stop this?

Idle speed over 750 will cause it to diesel, you also need to adjust the idle mixture after warming the engine up.

As far as the pump, take it apart and look.

View attachment Engine Dieseling or Running on single page.pdf

 

[jlanka]

Re: 1999 Mercruiser 5.7 deiseling after carb rebuild

Actually high idle speed sounds like a good candidate. It IS idling too high. I will adjust that right away. Thanks!

I took apart the pump and sure enough the impeller was shredded. Replacing that too.

What about bad timing? Could that cause dieseling?

 

[Don S]

Re: 1999 Mercruiser 5.7 deiseling after carb rebuild

It could if it was off far enough. Get the rpms down and check it. Don't forget, It is a Thunderbolt V ignition, so you do have to put it in base timing mode to set timing as well as adjust idle mixture.

 

[jlanka]

Re: 1999 Mercruiser 5.7 deiseling after carb rebuild

one more question, shop manual is ordered but in the meantime is there a diagram of the adjustments (specifically idle speed) on the 2BBL carb on that engine? Thanks in advance if anyone has a link or pic.

 

[Don S]

Re: 1999 Mercruiser 5.7 deiseling after carb rebuild

Here's a link to download the OEM service manual for your engine. http://www.4shared.com/office/JOT2vS2W/24__GM_V8_50-57_98-01.html?

 

[jlanka]

Re: 1999 Mercruiser 5.7 deiseling after carb rebuild

thanks. I didn't realize it was available for download.