850 mighty demon carb tuning?
+ Reply to Thread
Page 1 of 2 1 2 LastLast
Results 1 to 14 of 21

Thread:
850 mighty demon carb tuning?

  1. #1
    Senior Member hotbo's Avatar
    Join Date
    Feb 2008
    Location
    lake Ouachita AR
    Posts
    4,677

    Default 850 mighty demon carb tuning?

    okay fellas here is my questions

    the motor i built for my uncles lp is doing great

    it has a rpm air gap and a 1inch open spacer.
    850 mighty demon{not my choice but does good nevertheless}

    okay here is the problem.i ran it hard this evening.pulled plugs #1 is to rich-#2 is bout right all the rest are way to lean,almost scarey lean.

    what should i do.if i jet it up well thats gonna hurt the #1 more and take #2 from bout right to worse.


    ????????????should i do away with open spacer,put 4 hole spacer or what,any help i will be thankful

    demon carbs suck imo but im stuck with this one b/c he loves it,lol!!!!!

  2. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  3. #2
    Senior Member ol guy's Avatar
    Join Date
    Mar 2008
    Location
    Lake Elsinore Ca
    Posts
    3,814

    Default

    Quote Originally Posted by hotbo View Post
    okay fellas here is my questions

    the motor i built for my uncles lp is doing great

    it has a rpm air gap and a 1inch open spacer.
    850 mighty demon{not my choice but does good nevertheless}

    okay here is the problem.i ran it hard this evening.pulled plugs #1 is to rich-#2 is bout right all the rest are way to lean,almost scarey lean.

    what should i do.if i jet it up well thats gonna hurt the #1 more and take #2 from bout right to worse.


    ????????????should i do away with open spacer,put 4 hole spacer or what,any help i will be thankful

    demon carbs suck imo but im stuck with this one b/c he loves it,lol!!!!!
    After reading the post, what kind of idle time before shut down and do you have a feul pressure gauge and pressure readings thru the day. M

  4. #3
    Senior Member hotbo's Avatar
    Join Date
    Feb 2008
    Location
    lake Ouachita AR
    Posts
    4,677

    Default

    Quote Originally Posted by ol guy View Post
    After reading the post, what kind of idle time before shut down and do you have a feul pressure gauge and pressure readings thru the day. M

    5-6 psi with stock fuel pump idle time thru no wake zone back to the boat ramp,run the boat about 1 hour off and on 2 wot passes the rest of the time was cruising 3-4 grand.turned a a/b agressor impeller 5100 rpm max speed 65.2 in a taylor lp 21 foot heavy as hell boat,does that help cutting impeller and adding some more timing to try and make it gain some speed and turn more rpms,but im afraid to do anything till i get the carb tuned in some more,

  5. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  6. #4
    Senior Member ol guy's Avatar
    Join Date
    Mar 2008
    Location
    Lake Elsinore Ca
    Posts
    3,814

    Default

    Hotbro, Take the boat out with a plug socket and make a good pass. Slow down asap let cool alittle the pull the four corners of plugs on the motor,(or if you have time pull all the plugs and take a visual) It really is amazing how fast the color of a plug will change with 3 to 5 minutes idle time. Depending on mixture screw settings, manifold and timing. Might tell you another story. Lite tan plugs mean good feul to air ratio, If cyclinders come up up still black run a combustion check and see if things are close. Even is perfect 15% is acceptable. Good Luck M

  7. #5
    jetboataholic HawaiianJet's Avatar
    Join Date
    Mar 2008
    Location
    Lexington, KY
    Posts
    2,798

    Exclamation Here's your fix!

    DuaneHTP told me to use this under mine. I haven't done it yet because I don't have the money, but my engine hasn't been run yet, so I can't tell you anything about them. But, Duane told me that this solved that problem on the dyno runs.

    http://www.highvelocityheads.com/ss.htm

    Duane is the guy to talk to about the Demons!
    HJ

    ***FOR SALE*** 1978 19' Full Stringer Hawaiian Molokai Jet Boat w/ Berkeley 12JC-AB and Chevy 440 Tall Deck ***FOR SALE***

    Quote Originally Posted by mako shark mark View Post
    Oh yeah, Forgot to mention that the hull is a special mixture of speedcote, herculiner and rain-x, all blended together- good for another 8 mph top end.

  8. #6
    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
    Join Date
    Dec 2007
    Location
    Newton Ks.
    Posts
    6,834

    Default

    Buy a Holley.




    Now, any mixture reading with cruising time or idle time on them are not really worth a damn.Dragstuf.com How To Read Plugs
    "As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron."
    H.L. Mencken

    OBAMA: Some people deserve this.
    The rest of us are being dragged along kicking and screaming.

  9. #7
    Cantard 71hallett's Avatar
    Join Date
    Mar 2008
    Location
    snow bank
    Posts
    5,017

    Default

    Quote Originally Posted by ol guy View Post
    Hotbro, Take the boat out with a plug socket and make a good pass. Slow down asap let cool alittle the pull the four corners of plugs on the motor,(or if you have time pull all the plugs and take a visual) It really is amazing how fast the color of a plug will change with 3 to 5 minutes idle time. Depending on mixture screw settings, manifold and timing. Might tell you another story. Lite tan plugs mean good feul to air ratio, If cyclinders come up up still black run a combustion check and see if things are close. Even is perfect 15% is acceptable. Good Luck M
    x2
    Quote Originally Posted by gn7 View Post
    It would be a balmy 85* in Steel's shop if he would move a little faster

  10. #8
    Wishin I was at the lake! Brian's Avatar
    Join Date
    Dec 2007
    Location
    Cave Creek, AZ
    Posts
    547

    Default

    They call it "plug chop" for a reason!

    If you want a reading for a particular condition, run it at that condition and shut it down asap (even coasting to a stop), then read plugs. Don't idle back to the ramp and then expect a good reading...

  11. #9
    Boat Nut sleekcrafter's Avatar
    Join Date
    Dec 2007
    Location
    South Elgin, Il.
    Posts
    5,131

    Default

    Quote Originally Posted by HawaiianJet View Post
    DuaneHTP told me to use this under mine. I haven't done it yet because I don't have the money, but my engine hasn't been run yet, so I can't tell you anything about them. But, Duane told me that this solved that problem on the dyno runs.

    http://www.highvelocityheads.com/ss.htm

    Duane is the guy to talk to about the Demons!
    Duane dislikes the Demon's, Super Suckers do help!


    The problem lies with BG claiming their carbs are a much bigger CFM than the stated model. Like an 850 flows 900 plus CFM, too big of carb, results in loss of draw thru the veturies. This results in lean conditions with BG carbs.

  12. #10
    Senior Member
    Join Date
    Dec 2007
    Location
    New Jersey
    Posts
    307

    Default

    Will the Super Sucker help a holley on a single plane manifold? What does it actually do?

    Doug

  13. #11
    Senior Member hotbo's Avatar
    Join Date
    Feb 2008
    Location
    lake Ouachita AR
    Posts
    4,677

    Default

    okay my question is 4-hole spacer gonna be better than the open spacer or just do away with the spacer all together

    i know how to read plugs and to really get a good reading yes you are suppose to make a cruise run with no idle time or wot pass then kill.


    by just lookin at a plug you think you may be reading it but in reality you need to look inside the thing towards th bottom of the electrode not just the outer part.anyway just trying to find a happy meduim

  14. #12
    cfm
    cfm is offline
    Banned
    Join Date
    Jan 2008
    Posts
    1,263

    Default

    hotboat - what kind of intake ? I forget. Yeh, getting old and too many motors to keep track of.

    And yes, the BG's typically flow way more when flowed dry. So, when going by same train of thought with standard Holley's, this can through you off.

    Any pepper on the inside porcelian ?

  15. #13
    cfm
    cfm is offline
    Banned
    Join Date
    Jan 2008
    Posts
    1,263

    Default

    Is this the motor in question ?
    "heres what i have a 9.1 781 heads 2.19-1.88 valves comp 294 solid,248-595 110-106 "

    What cid ? What intake ? Does that stae you have 9.1:1 compression ?

    =============
    Sorry, your different threads and different motor builds have me confused on which engine you are talking about.

    Can't follow and remember everything.

    Thanks.

  16. #14
    Senior Member hotbo's Avatar
    Join Date
    Feb 2008
    Location
    lake Ouachita AR
    Posts
    4,677

    Default

    Quote Originally Posted by cfm View Post
    Is this the motor in question ?
    "heres what i have a 9.1 781 heads 2.19-1.88 valves comp 294 solid,248-595 110-106 "

    What cid ? What intake ? Does that stae you have 9.1:1 compression ?

    =============
    Sorry, your different threads and different motor builds have me confused on which engine you are talking about.

    Can't follow and remember everything.

    Thanks.
    my uncles mill,9.5-1 flat top .100 over bore bbc 475 c.i. closed chamber oval ports,2.19-1.88 valves.comp hyd roller.242-248-296-302-566-566,112-110.
    performer rpm air gap-850 mighty demon.i put a 1 inch open spacer under it.

    #1 is too rich for me-#2 about right light tan.all the rest to lean to me.little black around the begining of the threads,the porcelian look almost as white as they did coming out of the box.tried to look down inside as best as i can.but hard to see.notmuch if any color down inside on the porcelian.sorry spelling sucks.

    wondering if it would help or hurt by doing away with the open spacer.

+ Reply to Thread
Page 1 of 2 1 2 LastLast

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Please select your insurance company (Optional)

Log-in

Tags for this Thread

Digg This Thread

Posting Permissions

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
  •  
 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95