1997 mercruiser 4.3 LX fuel / ignition issues??

[bman440440]

ok to give everyone the back story my engine was running good until I started getting rod knock(water in the oil from cracked riser spacer) last trip... well I knew it was time for a rebuild so I pulled it and sent it off to (a very trusted) a shop and had it rebuilt... no major issues... had them do more than it needed... complete valve job, new standard bore pistons and rings, cylinders honed, new cam, lifters and bearings... yadda yadda yadda... get it back in the boat and go to start the break in process and it was a little hard to start... I did prime the oil system (40 PSI for 90 seconds) before starting... no biggie... but here is what it is doing now... its backfiring threw the carb when under load and is not making any power and will not go over 2000 RPM... I did set the timing at 10 degrees... but it runs rough (in neutral) at any thing below 1200 and wants to die at 800... I checked the compression 185-186 across the board... also I did not mess with the carb because it was running great before I rebuilt it... I took the intake and carb off as one unit so not to mess with anything... one thing that is not new is cap / rotor and plug wires and coil... have any of you guy's out there dealt with something like this before? any help would be great!! thanks!!
Brian

 

[bman440440]

oops I just realized that my compression reading should say 165-166

 

[bman440440]

oops I just realized that my compression reading should say 165-166

 

[Jcris]

I would have gone through that carb also. This could be a fueling issue

 

[bman440440]

I would have gone through that carb also. This could be a fueling issue

I was sorta thinking about that but it ran so perfect before... I was careful when I disassembled it and set it and the intake manifold (never separated the 2 from each other) on the shelf making sure not to mess with it... but I suppose that it could still be the problem

 

[alldodge]

Is your firing order correct?
1-6-5-4-3-2

 

[bman440440]

Is your firing order correct?
1-6-5-4-3-2

holy crap that might be it...I think I messed up and set it up as counter clockwise rotation on the distributor

 

[achris]

Messed up firing order would explain your problem.

 

[Jcris]

did you check the firing order?

 

[Pete_a]

Kudos alldodge, when reading i thought timing first before i saw he checked it. Sounds like a misfire

 

[bman440440]

problem SOLVED!!!!!!!!!!!!!!!!!!!!!!!!!!! i did set the firing order for counter clockwise rotor travel :stupid:

 

[Pete_a]

Enjoy the new motor, glad it was easy fix

 

[bman440440]

Enjoy the new motor, glad it was easy fix

thanks and yes it was.... wheew!!

 

[bman440440]

took it out on a test run on the water today... it runs GREAT!!!! lovin' it!!

 

[bman440440]

UPDATE: after the new floscan install I have now confirmed my fuel burn #'s!! at low cruse of 23-25 MPH 4.6 MPG and normal cruse of 32-35 MPH 5.0 MPG and at WOT (54 ish MPH) 3.25 MPG... gotta love that!!!!

here is a video of it screaming along

https://youtube.com/embed/g8ncFoCen8Q?rel=0

 

[alldodge]

The youtube link isn't a link

Your Miles Per Gallon seems a bit high even for a V6. The average V6 burns 16 to 18 GPH at cruse speeds. So doing 32 to 35 MPH would put the MPG at 2 to 1.78 @ 32 MPH and 2.18 to 1.94 @ 35 MPH.

The link is working now

 

[achris]

Here?s a little graph I did after putting the new engine in?..
It'?s in litres (1 US Gallon =3.78 litres) and nautical miles (1nm = 1.15 statute miles), but just a little converting runs the numbers like this?..

Cruising (~3000rpm @ 21knots/24mph) uses 1.2nm/litre = 0.833nm/l = 3.6 miles/US gallon?
Full throttle (5100rpm @ 40knots/46mph) uses 1.5nm/litre = 0.75nm/l = 3.2miles/US gallon?
Best fuel speed is at 27 knots (3350rpm) and returns 4 miles/US gallon?

 

[bman440440]

The youtube link isn't a link

Your Miles Per Gallon seems a bit high even for a V6. The average V6 burns 16 to 18 GPH at cruse speeds. So doing 32 to 35 MPH would put the MPG at 2 to 1.78 @ 32 MPH and 2.18 to 1.94 @ 35 MPH.

The link is working now

not to bash but... I don't know what "average" v6 your talking about at WOT I'm burning 16 GPH verified by my floscan... even the mercruiser web site backs those #'s ---> http://www.boat-fuel-economy.com/mercury-mercruiser-4.3-262-190-fuel-consumption-us-gallons

next time I take the boat out I will get some pic's backing my #'s up :smile-new:

 

[bman440440]

Here’s a little graph I did after putting the new engine in…..
It'’s in litres (1 US Gallon =3.78 litres) and nautical miles (1nm = 1.15 statute miles), but just a little converting runs the numbers like this…..

Cruising (~3000rpm @ 21knots/24mph) uses 1.2nm/litre = 0.833nm/l = 3.6 miles/US gallon…
Full throttle (5100rpm @ 40knots/46mph) uses 1.5nm/litre = 0.75nm/l = 3.2miles/US gallon…
Best fuel speed is at 27 knots (3350rpm) and returns 4 miles/US gallon…

is your chart based on your boat? I do believe that your 4.3 MPI has a base WOT usage of 18 GPH... and I would think that your boat is a MUCH heavier boat than mine... but a very nice one though!!

 

[achris]

Yes, that's on my boat. And yes again, heavy boat with a very deep Vee. (Hence the bump in consumption as it climbs over the hill).... I know I burn about 63 litres per hour at WOT with that prop (just banging on the rev limiter). 63 litres is 16.64 US gallons.

I intend (one day) to do the numbers with the other props I have. An 18" Alpha4 4 blade Al, a 19" Vengeance 3bld SS and a 19" Black Max 3 bld Al.... The 19" SS gives me 4600rpm WOT, which is the 'right' prop, but I prefer the 17". It pushes the revs up a bit for the same boat speed and keeps the engine in the power band even when the weather gets up a bit and I have to pull back. It also makes the whole boats free better, and more 'driveable'... More responsive to the throttle and less of a lazy old dog...

From comparisions I have done I know the 'miles per gallon' are going to be pretty close to that of the 17" SS...

I run a Navman Fuel2100 for flow readings.

Chris......