have new holley 800 dp on new 502 mag 435hp motor. seems aweful rich right off idle at 1200=1300 rpm when im headway speed for 20-30 mins to get out in ocean, when i start to bring up on plane it stumples and coughs if i dont feather the throthle up very slowly. think my front jets are to big for the stock 502?

Any rejetting ideas? Runs perfect at 2500 and above, just seems like it really loading up down low.

i check the power vale and wt size jets do you have in the carb ??????? your motor should idle 650 to 700 rpm

Accelerator pump shot too big on the primaries??


Power valve leaking is also a possibility. Do you have a 6.5" PV in the primary?? What is the idle vacuum??

Also, is the motor loading up at idle and the idle is causing the stumble? Does the motor wind up crisply when you rap it out of gear? Maybe adjust the idle circuits down with the motor in gear, warmed up, until the motor dies then back up 1/8 turn on each circuit so you know you are very lean at idle and try again.

What timing are you running at idle and what is the total advance?

Power valve is probably opening up too early and making it load up.

sounds more lean than rich, jets have little effect just bringing on plane, accel pump/power valve issues seem like to me, you see black smoke when this happens ? what temp is engine ? timing ?

Its a Brand New Out of box 800 DP 9022 carb so dont even know what size jets and powervalve are. its idleing much higher like 800, doesn't seem to like o idle real low at 650-700. Have adjusted the mixture screws a few times, think they are at 2 turn now. i have Tunderbolt V so, i think i can only set my timing to the 8 degrees as they say in book after i ground the ECM wire. Some times my idle hangs at 1000-1100 and i have to blimp the throthle to know it down.

The TB V ignitions have Idle control function in the ecm that changes the timing at idle for what ever reason, and i think that is what is happening besides the rich condition.

If i put in gear, and get on throthle it will cut out and backfire sometimes, i have to be real smooth gettinng the throthle then above 2500 i can hammer it hard with out any problem.

Cant rap it out of gear, dont think PV is leaking as it brand new...10 hours on motor. Havent chaecked vacum. what should it be at.

145 degrees water temp, Thunderbolt V so its set at 8 degree's when wire is grounded. new carb, no black smoke, boat runs awesome just have to ease into throthle till it comes out of stumble.

here wt you got to do!!!take the carb apart and see wt jets and power vales are in it !!!till then you are you are pissing in the wind. when your motor back fires that when the power vale blows. you need to check them!!and did you look at any plugs see what color they are that would help to .

[QUOTE=bajabob;3102334]here wt you got to do!!!take the carb apart and see wt jets and power vales are in it !!!till then you are you are pissing in the wind. when your motor back fires that when the power vale blows. you need to check them!!and did you look at any plugs see what color they are that would help to .[/QUOTE
Here is specs from holley:

9022 800 jets (F)72,(R)87 Powervalve 6.5 style4150 Marine

Plugs look great after i had a few hours on them, looked perfect color but thats alot of 3500-5000 run time.

Has been running like this since i install new carb and motor so i dont thing the powervalve are blown. Didnt backfire til after it was already running like this. Holley has fixed the backfiring/ powervalve blowing out issue years ago from all I have read but, i could be wrong...They have a check ball valve or something so it doesn't blow the valve out...

thanks