Calling the boat carb masters, lots of fuel still lean.
06-26-2021, 09:45 PM
#31
Registered
I have a Quickfuel 750 on my 10.3:1 383, it was getting an intermittent lean stumble. I mean bad, scared me like I was burning down the motor.
I believe the fuel was too hot and getting vaporized. I had too much fuel pressure, 7.5 to 7.9; and too much timing as well, 36 degrees.
The afr would go to the moon when it stuttered, and it happened at max torque around 3300 - 3500 rpm.
Well after that happening 3 times I had to correct things.
I did a full return fuel system, moved the lines away from the block, and used 3/8" metal line all the way through. To do it I had to drill out the Mercruiser fuel/water separator to 3/8 ID and use bigger fittings. It is undersized out of the box. BTW CP Performance sells a nice return fitting that you can use to put the fuel back in to the fill tube.
Also DO NOT do the .055 spark plug gaps that DUI recommends .035 or .038 will be the move there.
People will tell you they run all day on OE fuel lines, but the return system, 33 degrees timing, 6.25 lbs fuel pressure and .035 plug gaps seem to have fixed my issue. I never changed anything in the carburetor but jets and power valve.
AFR made it so much easier to understand and correct. I just installed the Innovate system last year. I had to use a 90 degree spacer to get the sensor out of the exhaust stream because it was ruining sensors at idle.
I believe the fuel was too hot and getting vaporized. I had too much fuel pressure, 7.5 to 7.9; and too much timing as well, 36 degrees.
The afr would go to the moon when it stuttered, and it happened at max torque around 3300 - 3500 rpm.
Well after that happening 3 times I had to correct things.
I did a full return fuel system, moved the lines away from the block, and used 3/8" metal line all the way through. To do it I had to drill out the Mercruiser fuel/water separator to 3/8 ID and use bigger fittings. It is undersized out of the box. BTW CP Performance sells a nice return fitting that you can use to put the fuel back in to the fill tube.
Also DO NOT do the .055 spark plug gaps that DUI recommends .035 or .038 will be the move there.
People will tell you they run all day on OE fuel lines, but the return system, 33 degrees timing, 6.25 lbs fuel pressure and .035 plug gaps seem to have fixed my issue. I never changed anything in the carburetor but jets and power valve.
AFR made it so much easier to understand and correct. I just installed the Innovate system last year. I had to use a 90 degree spacer to get the sensor out of the exhaust stream because it was ruining sensors at idle.
06-27-2021, 10:14 PM
#32
I have a Quickfuel 750 on my 10.3:1 383, it was getting an intermittent lean stumble. I mean bad, scared me like I was burning down the motor.
I believe the fuel was too hot and getting vaporized. I had too much fuel pressure, 7.5 to 7.9; and too much timing as well, 36 degrees.
The afr would go to the moon when it stuttered, and it happened at max torque around 3300 - 3500 rpm.
Well after that happening 3 times I had to correct things.
I did a full return fuel system, moved the lines away from the block, and used 3/8" metal line all the way through. To do it I had to drill out the Mercruiser fuel/water separator to 3/8 ID and use bigger fittings. It is undersized out of the box. BTW CP Performance sells a nice return fitting that you can use to put the fuel back in to the fill tube.
Also DO NOT do the .055 spark plug gaps that DUI recommends .035 or .038 will be the move there.
People will tell you they run all day on OE fuel lines, but the return system, 33 degrees timing, 6.25 lbs fuel pressure and .035 plug gaps seem to have fixed my issue. I never changed anything in the carburetor but jets and power valve.
AFR made it so much easier to understand and correct. I just installed the Innovate system last year. I had to use a 90 degree spacer to get the sensor out of the exhaust stream because it was ruining sensors at idle.
I believe the fuel was too hot and getting vaporized. I had too much fuel pressure, 7.5 to 7.9; and too much timing as well, 36 degrees.
The afr would go to the moon when it stuttered, and it happened at max torque around 3300 - 3500 rpm.
Well after that happening 3 times I had to correct things.
I did a full return fuel system, moved the lines away from the block, and used 3/8" metal line all the way through. To do it I had to drill out the Mercruiser fuel/water separator to 3/8 ID and use bigger fittings. It is undersized out of the box. BTW CP Performance sells a nice return fitting that you can use to put the fuel back in to the fill tube.
Also DO NOT do the .055 spark plug gaps that DUI recommends .035 or .038 will be the move there.
People will tell you they run all day on OE fuel lines, but the return system, 33 degrees timing, 6.25 lbs fuel pressure and .035 plug gaps seem to have fixed my issue. I never changed anything in the carburetor but jets and power valve.
AFR made it so much easier to understand and correct. I just installed the Innovate system last year. I had to use a 90 degree spacer to get the sensor out of the exhaust stream because it was ruining sensors at idle.
Charter Member
06-28-2021, 06:52 PM
#35
06-28-2021, 07:14 PM
#36
Was probably the chevamoco that was recently found and restored. It was at Epping.
Update on carb stuff. Needles were .097(got to many toys) now .110s. Thought I had checked, double checked there is no siphon valve on tank. Put jet extensions on secondaries just to make sure. Picking up fuel line and fitting tomorrow to hookup bypass regulator. Fuel will be on tap.
Update on carb stuff. Needles were .097(got to many toys) now .110s. Thought I had checked, double checked there is no siphon valve on tank. Put jet extensions on secondaries just to make sure. Picking up fuel line and fitting tomorrow to hookup bypass regulator. Fuel will be on tap.
07-05-2021, 11:31 PM
#38
Update after this weekend. Ran awesome right off the trailer. It was lean though. Jetted up still wasn't right. Plugs were to hot too.
Sunday morning went for a whole sale change. Heat range colder plugs, .035 gap
Went big on the carb, pluged middle emulsion (found out emulsions in blocks were not drilled consistent got .028s on the way to make them right) so now 2 emulsions, put stock 65 idle bleeds back in, still 31 high speeds, 71 primary with .053s with a 6.5 power valve, 84 secondary.......really made it a stock double pumper jetted up, 3500-3700 PV comes in.
Carbs awesome 👌 plugs look good. Still chasing a feed problem as it jumps and runs but about 8 seconds in to a WOT run it acts like it runs out of fuel. Got to be either the water separator or the fuel pickup.
If nothing going there, going to take a 750 brawler, and a 750VS holley see if they wake it up.
Was bouncing between 71-72 off the trailer on the gps just won't live long with white plugs.
Used a bunch of your guys advise. Thanks for the help.
I know....wide band.....just want to see if I can hit it old school reading the plugs....can say it close
Sunday morning went for a whole sale change. Heat range colder plugs, .035 gap
Went big on the carb, pluged middle emulsion (found out emulsions in blocks were not drilled consistent got .028s on the way to make them right) so now 2 emulsions, put stock 65 idle bleeds back in, still 31 high speeds, 71 primary with .053s with a 6.5 power valve, 84 secondary.......really made it a stock double pumper jetted up, 3500-3700 PV comes in.
Carbs awesome 👌 plugs look good. Still chasing a feed problem as it jumps and runs but about 8 seconds in to a WOT run it acts like it runs out of fuel. Got to be either the water separator or the fuel pickup.
If nothing going there, going to take a 750 brawler, and a 750VS holley see if they wake it up.
Was bouncing between 71-72 off the trailer on the gps just won't live long with white plugs.
Used a bunch of your guys advise. Thanks for the help.
I know....wide band.....just want to see if I can hit it old school reading the plugs....can say it close
07-06-2021, 09:03 AM
#39
Registered
iTrader: (2)
You are stubborn for sure. Order up a Willy's and throw that scabbed together carb on Yellow Bullet and let some mustang guy burn his motor down with it. Much cheaper than replacing just 1 piston. And while you are at it, INSTALL A WIDEBAND. I don't care how good you are, it is impossible to tell the difference between 11-1 and 14-1 all of the way through the power band by looking at a plug. I bet you don't time it by ear, why would you try to fuel it by ear?
Last edited by snapmorgan; 07-06-2021 at 09:06 AM.
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Smitty275 (07-06-2021)
07-07-2021, 12:14 AM
#40
You are stubborn for sure. Order up a Willy's and throw that scabbed together carb on Yellow Bullet and let some mustang guy burn his motor down with it. Much cheaper than replacing just 1 piston. And while you are at it, INSTALL A WIDEBAND. I don't care how good you are, it is impossible to tell the difference between 11-1 and 14-1 all of the way through the power band by looking at a plug. I bet you don't time it by ear, why would you try to fuel it by ear?
Nothing to do with weather my carb is scabed together (that carb if I bought some shinny bowls for it.....you couldnt tell it from a ultra xp with some j tubes by looking at it is running just fine....I can go through and thank the posts directly that really helped if needed....just went the a little off with it for a boat why I came to ask about holleys on boats in first place) what I know about carb tuning or anything else. If I am confident enough to to start making whole sale changes on my carb with out a wide band....maybe I have tuned a carb or more with a wide band (yes if you let the wide band teach and and not live or dye by it you will hear the motor when when it is lean or rich.....you can hear around a point or a little more depending on load with the wide bad hooked up....we can go through that to) 🤔 read the plugs with changes with a wide band. We can go through carb class if anyone is interested.
Things I didn't know that I found out might help some others an 89 baja 210 with a vortec 350 halfway hopped up will cruise on plane half way lean at 2200-3400 on 71 (think the 97 needels didn't help any of it) mains 34 idle feeds, but it needs a bunch of fuel WOT 10 in the PV an extra 3 in the secondaries so far....
