4.3 with q-jet

[JasonB]

Helping a friend work the bugs out of his boat that seems to run way rich. The engine is new (used to be a 175hp or so Mercruiser 4.3, 1991 vintage I think). Replaced with a 4.3 balance shaft motor with a 4bbl cast intake and remanufactured q-jet. Does anyone know what Mercruiser used in this combo for jets, rods, and hangers so I can use that as a starting reference?

Thanks.

 

[achris]

Re: 4.3 with q-jet

Merc never used the Q-jet on the Gen II V6s. (Balance shaft engines)

If you want information on the Q-jet used by Merc you need to reference the previous series (non-balance shaft engines). Here is a link to the manual for those engines. You'll find the carb information in section 5.

https://docs.google.com/open?id=0B1TAvwZ3TjhfNWFyczBmVUE4Wlk

Chris.......

 

[makonnen]

Re: 4.3 with q-jet

Lets back up a step ...

What are the indications that its running "way rich?"

Under what throttle / load conditions are we talking about?

 

[JasonB]

Re: 4.3 with q-jet

As I understand, it won't idle (land or water), black smoke, and poor power, and fuel smell but no known leaks. We're starting on paper before digging in too far to make sure he has the basic platform right as this setup has never run correctly.

 

[makonnen]

Re: 4.3 with q-jet

Hmmm... sounds like a fun diagnosis. Here's what I have in mind:

- Your first goal should be just to get it to idle correctly then go from there

- The first step in any diagnosis is to do all the simple easy stuff first... so:

- Is the choke stuck on?

- Look down the carb while keeping the engine running, fuel pouring in from venturis?

- Use you finger and push open the secondaries, any fuel pouring in there (have to do this fast)

- Check tune up conditions - plugs, wires, cap, rotor

- Do the spark plugs give you any clues?

- Do you have a major vacuum leak?

- The firing order correct?

- Plug wires correct?

- Plug boot plugged in correctly?

And getting a little more involved:

- Wind in the idle screws all the way, then back them out 3 to 3.5 turns, does it idle now?

- Disconnect fuel pump, get a can of carb cleaner, will engine run while spraying carb cleaner down the throat?

- Power valve spring stuck and holding needles out of the jets?

- Secondary needles being held out of the jets?

- Incorrect or bent linkage rod between primry throttle plates and secondary throttle plates?

- Obviously the manifold has been changed... could the distributor be off a tooth or two?

- Someone mix up the firing order?

- Carb float sunk? Stuck? Missing? Incorrectly adjusted?

- All spark plugs firing correctly? Got a dead plug or two?

If you think of it, how about get us a video?