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Thread: Get the black off!!!!!!

  1. #1
    TripleDigits HTM
    Seeking input for a re-occuring problem...By the end of the day, the back of my boat is black from carbon/un-burnt fuel build up...I currently have a roller 540, 1040cfm Holley, at 36degrees timing, 642hp, MSD ignition, 13inches of vacuum with 5.5 powervalve's....I've bumped up the timing, lowered the carb jets to 80's, and put in hotter plugs...I currently run 91oct pump gas...The last thing I haven't tried was running a 3/1 mix of pump gas to AV gas....Any suggestions??????????

  2. #2
    Tinkerboater
    At some point in your rpm range you are running rich. Has your engine ever backfired? If so than one possibility is a blown power valve. With a 4 barrel carb you have to adjust each level. idle, main jets, power valve.Do this with the primaries then with the secondaries.

  3. #3
    spectras only
    Your engine maybe running a bit too cold ?

  4. #4
    Havasu Hangin'
    Depending on the soot (splashed vs soaked at the water line), I'd look closely at your idle (and off-idle) mixture.
    Mine used to get black, but only when the transom is in the water. Do you idle at partial throttle? Like TB said, might be a powervalve.
    Simple Green works well to get it off.
    http://www.planetsmilies.com/smilies/happy/happy25.gif

  5. #5
    lghtnin33
    try a holley projection, only way to go ,it will dump the fuel you will need when you need it unless you are all out race then carb is the only way to go. i have one and it will make me too rich before too lean which in my book is a good thing give it a try http://free.***boat.net/ubb/smile.gif once i got it tuned from idle to WOL the black stuff stopped except initial throttle responce one puff of smoke and it settled right in to the groove>

  6. #6
    Boater Bill
    What are you running on top of your carb?

  7. #7
    TripleDigits HTM
    I eliminated the powervalves initially, it loaded really heavy during 0 to take off, and occasionally would pop...Put the powervalves back in, ran much better, but still loads..The blackness is all over the back of the boat, not just at the water line and it all occurrs during idle..I thought about the whole engine running too cool, thats how the AV gas came into play, it burns hotter......As far as on top of the carburetor, I just have a chrome, standard breather/filter....

  8. #8
    lghtnin33
    have you ever checked your air/fuel ratio at idle vs.WOT with an O2 sensor? may need to lean the primaries and enrichen the secondaries.especially with a roller cam with large overlap.(dont know what your cam spec.s are) meaning the cylinders are being over scavenged at idle with rich mixture. (excessive raw fuel through intake valve=unburnt petro, black stuff). just a thought http://free.***boat.net/ubb/smile.gif

  9. #9
    Thunderbutt
    Take your timing to 40. I wouldn't do the av gas yet. make sure your carb. and hoses are compatible to av gas, What is your compresson? Maybe you have a float sticking. Check your acelerator pumps. Are you filing spark plugs? Make a run at 6M shut it off and check the plugs. It is better to run a little fat then it is to lean. Originally posted by TripleDigits HTM:
    Seeking input for a re-occuring problem...By the end of the day, the back of my boat is black from carbon/un-burnt fuel build up...I currently have a roller 540, 1040cfm Holley, at 36degrees timing, 642hp, MSD ignition, 13inches of vacuum with 5.5 powervalve's....I've bumped up the timing, lowered the carb jets to 80's, and put in hotter plugs...I currently run 91oct pump gas...The last thing I haven't tried was running a 3/1 mix of pump gas to AV gas....Any suggestions??????????

  10. #10
    Boater Bill
    Hard to tune at a computer but it sounds like you've done some right things to lean it out(jets/pwr valves). I will suggest however you look at your air filter. I K&N'd mine and it helped the black plague and have heard it helped others, but my boat is way diff than yours. I would disagree that av gas runs hotter, todays pump gas runs pretty hot. You didn't mention what water temp you're running at and the previous suggestion is a good one. I also like the tip on checking floats/float levels and would add you may have a needle sticking. Another thing to look at is your ign if you are running a MSD box 'cause they do have problems at times, also make sure your advance is working properly. Thunderbutt - don't you think 40 degrees total advance is VERY agressive with todays gas? Good luck!

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