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502 carb jetting help.
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
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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.
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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 ?
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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. |
Originally Posted by Thunderstruck
(Post 3101773)
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? |
Originally Posted by ezstriper
(Post 3102309)
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 ?
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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 .
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[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 |
If it basically has an off idle flat spot/bog, then you might need a bigger accelerator pump. Is the carb stock with the 30cc or the 50cc accelerator pump????
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Fixx
your way too far out on the idle mixture screws,,1/2 to 1 turn max..your stumble could be several reasons..first try to set the idle mixture correctly,start at 3/4 turn and turn the screws vary little at a time and let the engine calm bown..out is fat in is lein..if your idle screw is set to high then you will get a off idle stumble,set the idle with the secondary stop screw and leave the primary alone..
read this, http://www.candsspecialties.com/tuning1.html |
idle mixture screws,,1/2 to 1 turn max .i agree with mrfix.the jets set up sounds ok. let your motor idle take carb cleaner spray around the base of the carb to see if you have a leak and if the motor revs up the gasket is not seal . if thats ok i wounld check your timing put it at 34degrees at 3000rpm
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I see your getting a lot of info here and don't want to add any more confusion to your problem however I would seriously pull it off and pull your bowl covers and metering gaskets. I have pulled down brand new carbs with similar problems and found the metering block gasket was way off from where it was suppose to be. In a nutshell it (they) were blocking holes in the carb base. It's just a manufacturing quality issue. It happens. Just pay close attention when you pull the bowls for insepection. The gaskets can just sometimes shift during assm. from Holley or ???
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Carb thunderbolt V at 8 degrees???? I think my 1998 carb 500 hps had thunderbolt V ignitions. I think the ignitions had 20 degrees advance. At 34 degrees total advance, which is whate you need, you need to be at 14 not 8 at idle. Forget the purple/white wire deal. Put the boat in the water and run the rpms up to 3200 or so and set the timing at 34.
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I believe all the timing was in at 3000 rpm for the thunderbolt V so you should be OK at 3200-3500.
Why can't you rap the throttle out of gear??? Also, setting the idle screws while idling in gear is the best way to set the idle adjustment. Just enough fuel to keep it from dying in gear. You need to get down and start eliminating issues. It can't be ..... should not be in your vocabulary right now. |
Originally Posted by Thunderstruck
(Post 3103039)
Carb thunderbolt V at 8 degrees???? I think my 1998 carb 500 hps had thunderbolt V ignitions. I think the ignitions had 20 degrees advance. At 34 degrees total advance, which is whate you need, you need to be at 14 not 8 at idle. Forget the purple/white wire deal. Put the boat in the water and run the rpms up to 3200 or so and set the timing at 34.
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you probably have done so however also be sure both primary and secondary squirters are working well.
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Here is the TB V info as it different than the TB IV by alot. Its always changing advance so i dont think you can check the advance at at 3500 as depending on load it will chang itself. Thats why they want you to set base timing with wire grounded at 8 degrees....The knock sensor pulls and adds advance.
I have gotten alot of great ideas and info that i need to look into all of these ideas. See they tell u in the manual to set idle and mixture screw adjustments with the ECM in base timing mode with the wire grounded, is this rally necessary? in gear what should rpms be. General Description The Thunderbolt V ignition system has several spark control features that will be described following: D Idle Speed Spark Control D Acceleration Spark Advance D Mean-Best-Timing Spark Advance D Over-Speed Control (Rev-Limiter) D Knock Retard Spark Control NOTE: The Ski models do not have the Mean Best Timing feature. Idle Speed Spark Control The ignition module will control ignition timing to maintain a calibrated idle speed. This is accom- plished by making small spark advance adjustments. This feature is only active within a certain RPM range. This range may be slightly different from one engine model to another. The approximate range is 400-700 RPM. Acceleration Spark Advance This feature is active during acceleration only. When accelerating, the ignition module may add more spark advance to the “Base Spark Timing Curve”. The amount of spark advance added, is totally de- pendant on how fast RPM increases (how fast the throttle is moved). This feature is also active within a certain RPM range. This range may be slightly differ- ent from one engine model to another. The approxi- mate RPM range for this feature is 1200-4000 RPM. Within this range, the module can add approximately 10 degrees of spark advance to the base spark timing curve. Mean-Best-Timing (MBT) Spark Advance During light load cruising, the ignition module searches for the optimal ignition timing. This is also accomplished by small changes to the spark ad- vance. At a given RPM, the module will try to add a small amount of advance and wait to see if there is an RPM change. If RPM increases, it will try to in- crease timing more. The module will continue to ad- vance timing until it no longer gets an increase in RPM. Conversely, if it senses an RPM drop, it will start to retard some of the spark timing. The approxi- mate RPM range for this feature is 1200-4000 RPM. Within this range, the ignition module can add approximately 10-15 degrees of spark advance to the base spark timing curve. NOTE: The Audio Warning System is also connected into the ignition module circuit. If the audio warning system becomes activated by the closing of one of the audio warning system switches, the MBT feature is deactivated. Over-Speed Control The ignition module will prevent the engine speed from exceeding a preset limit by stopping the spark. This feature has an RPM range that varies from mod- el to model. The over-speed limit for a particular en- gine is set slightly higher than the top end of the RPM range for that model. For example, if the recom- mended range is 4600-5000 RPM, the over-speed limit would be set at 5100 RPM. When RPM reaches this limit, spark is turned-off until engine RPM drops down to a “Reset RPM”, which would be approxi- mately 4750 RPM for this example. At this point, spark comes back on. Knock Retard Spark Control The knock control feature helps provide protection from harmful detonation. Knock control is handled by the Knock Control Module. This module receives a signal from a sensor that is mounted on the engine block. The knock control module works in conjunc- tion with the ignition module to retard the timing if spark knock is present. |
Timing and Idle Adjustment
Procedures For Thunderbolt V Ignition Setting Base Ignition Timing 1. Connect timing light to number 1 spark plug. Connect timing light power supply leads (if applicable) to 12 volt source. 2. Connect a shop tachometer to engine. 3. Using a jumper wire, connect the ignition system timing lead “13” (PUR/WHT wire) to a good en- gine ground (–). This locks the ignition module into the “Base Timing Mode”. 4. Start engine and run at normal idle speed. Allow engine to reach normal operating temperature. 5. Aim timing light at timing tab, located on the tim- ing gear cover and crankshaft torsional damper. 6. Adjust timing using the conventional method. IMPORTANT: Be sure to disconnect the jumper wire from the ignition system test terminal before attempting to resume normal operations. If the jumper wire is left in place, the ignition module will operate in the “Base Timing Mode”. This means that the additional timing advance fea- tures would not function. 7. Make sure that the distributor has been tight- ened. Remove the jumper wire from the timing terminal. 1. Using a jumper wire, connect the ignition system timing lead “13” (PUR/WHT wire) to a good en- gine ground (–). This locks the ignition module into the “Base Timing Mode”. 2. Adjust idle mixture following the procedure in the appropriate engine service manual. 3. Remove the jumper wire from the timing terminal. Adjusting Engine Idle Speed This procedure should be done with boat in the water, drive unit in neutral and engine at normal operating temperature. Refer to the Operation and Mainte- nance Manual for the correct idle speed. 1. Disconnect the throttle cable from carburetor. IMPORTANT: In order to properly set idle speed, the ignition module MUST BE locked in the “Base Timing Mode”. This is necessary because of the “Idle Speed Control” feature that exists in the ignition module. See information on the previous pages about this feature. 2. Connect a shop tachometer to engine. 3. Using a jumper wire, connect the ignition system timing lead “13” (PUR/WHT wire) to a good en- gine ground (–). This locks the ignition module into the “Base Timing Mode”. 4. Start engine and allow it to reach normal operat- ing temperature. 5. Adjust idle speed to recommended RPM. 6. Stop engine. Readjust cable barrel and reinstall |
wow
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http://www.cpperformance.com/c-161-distributors.aspx here wt i did i got a msd with the box and set mine up .idles 650 in gear and timing at 34 she runs great tops at 5600rpm i took all merc stuff off . but that me . i got one more thing for you to check the is the float level . make shore it not to high that will make you run bad at a idle !!good luck
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Fixx
Originally Posted by ballon78
(Post 3103103)
Here is the TB V info as it different than the TB IV by alot. Its always changing advance so i dont think you can check the advance at at 3500 as depending on load it will chang itself. Thats why they want you to set base timing with wire grounded at 8 degrees....The knock sensor pulls and adds advance.
I have gotten alot of great ideas and info that i need to look into all of these ideas. See they tell u in the manual to set idle and mixture screw adjustments with the ECM in base timing mode with the wire grounded, is this rally necessary? in gear what should rpms be. General Description The Thunderbolt V ignition system has several spark control features that will be described following: D Idle Speed Spark Control D Acceleration Spark Advance D Mean-Best-Timing Spark Advance D Over-Speed Control (Rev-Limiter) D Knock Retard Spark Control NOTE: The Ski models do not have the Mean Best Timing feature. Idle Speed Spark Control The ignition module will control ignition timing to maintain a calibrated idle speed. This is accom- plished by making small spark advance adjustments. This feature is only active within a certain RPM range. This range may be slightly different from one engine model to another. The approximate range is 400-700 RPM. Acceleration Spark Advance This feature is active during acceleration only. When accelerating, the ignition module may add more spark advance to the “Base Spark Timing Curve”. The amount of spark advance added, is totally de- pendant on how fast RPM increases (how fast the throttle is moved). This feature is also active within a certain RPM range. This range may be slightly differ- ent from one engine model to another. The approxi- mate RPM range for this feature is 1200-4000 RPM. Within this range, the module can add approximately 10 degrees of spark advance to the base spark timing curve. Mean-Best-Timing (MBT) Spark Advance During light load cruising, the ignition module searches for the optimal ignition timing. This is also accomplished by small changes to the spark ad- vance. At a given RPM, the module will try to add a small amount of advance and wait to see if there is an RPM change. If RPM increases, it will try to in- crease timing more. The module will continue to ad- vance timing until it no longer gets an increase in RPM. Conversely, if it senses an RPM drop, it will start to retard some of the spark timing. The approxi- mate RPM range for this feature is 1200-4000 RPM. Within this range, the ignition module can add approximately 10-15 degrees of spark advance to the base spark timing curve. NOTE: The Audio Warning System is also connected into the ignition module circuit. If the audio warning system becomes activated by the closing of one of the audio warning system switches, the MBT feature is deactivated. Over-Speed Control The ignition module will prevent the engine speed from exceeding a preset limit by stopping the spark. This feature has an RPM range that varies from mod- el to model. The over-speed limit for a particular en- gine is set slightly higher than the top end of the RPM range for that model. For example, if the recom- mended range is 4600-5000 RPM, the over-speed limit would be set at 5100 RPM. When RPM reaches this limit, spark is turned-off until engine RPM drops down to a “Reset RPM”, which would be approxi- mately 4750 RPM for this example. At this point, spark comes back on. Knock Retard Spark Control The knock control feature helps provide protection from harmful detonation. Knock control is handled by the Knock Control Module. This module receives a signal from a sensor that is mounted on the engine block. The knock control module works in conjunc- tion with the ignition module to retard the timing if spark knock is present. so you installed a Holley on your boat now all that info is useless, set your timing procedure and go from their on the carburetor issues...you will need to do this by touch and feel of how the engine performs..i can go on and on about accelerator pump sizes,air bleeds,metering block modifications,accelerator pump cams,accelerator pump squatters but with out seeing it or hearing it run i would be here for hours trying to explain to you what to do. you may want to buy a Holley tuning book and read up on your carburetor to get the feel for what your trying to accomplish :) |
Originally Posted by getrdunn
(Post 3103163)
wow
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Originally Posted by bajabob
(Post 3103164)
http://www.cpperformance.com/c-161-distributors.aspx here wt i did i got a msd with the box and set mine up .idles 650 in gear and timing at 34 she runs great tops at 5600rpm i took all merc stuff off . but that me . i got one more thing for you to check the is the float level . make shore it not to high that will make you run bad at a idle !!good luck
I want reliababilty and won't run the msd stuff, everyone i know on here and around be carry an extra msd box, because its not if it will fail, but when. having a single engine i cant put, put home like twins can. |
Float levels are good, just below threads and only spill out when i rock boat with caps off...Im going to spend some time this weekend and try to dial it in better and look at a few thing that you folks have mentioned, I have lots of ideas now.
The thunderbolt V system was one my boat from new and so was a AFB carb, which wasnt ecm controlled.....basicly all i did was swap blocks and new carb. everything else is same. When i recheck timing and fuel screws, and idle should i do it all with the boat in gear? |
ok thats good floats fine. 1990 i install a msd box and it still works good for me i have msd install in my two cars gto and camaro. ok you wt to use the old stuff . you have to do the timing at a idle . i would set it at 14 not 8 let it warm up then put it gear and adjust your carb . good luck:drink::drink:
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with the flame arrester off, not running, ck to see if you a good accel pump shot when you open the throttle, you may have to change the cam position or the cam itself..also may have to up the shooter to get a better shot..Rob
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