Get the black off!!!!!!

[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??????????

[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.

[spectras only]

Your engine maybe running a bit too cold ?

[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

[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>

[Boater Bill]

What are you running on top of your carb?

[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....

[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

[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??????????

[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!

[Tinkerboater]

I didn't mention it before but 13 inches vac. seems quite high for your motor. Buy another one of good quality and test it again. I think your power valves are open. Try the 3.5 power valves. And only drag cars run without power valves or pulling trucks. without power valves you have to put huge main jets in to feed all the fuel that would be going thru the power valves.

[Thunderbutt]

Tinker, I have two 750 Holleys on my boat and have never had power valves they have been blocked off for 30 years. Originally posted by Tinkerboater:
I didn't mention it before but 13 inches vac. seems quite high for your motor. Buy another one of good quality and test it again. I think your power valves are open. Try the 3.5 power valves. And only drag cars run without power valves or pulling trucks. without power valves you have to put huge main jets in to feed all the fuel that would be going thru the power valves.

[2prop]

Hey guys I have the same problem, with a mpi engine, and I do idle alot,, at the end of the day it seems as if the transom was in a fire all sooty looking ,, is it too rich ?? any help is greatly welcomed!!

[Tinkerboater]

With an mpi engine it is just computer calibration nothing else. With the power valves blocked off you will have problems of being too rich in the midrange. Yes you can get it to work but it is a lot more work. Kind of like dialing in the midrange of a QUADRAJET.

[spectras only]

2Prop ,is this your 29 scarab? Do you have raw water cooling ,or fresh?

[TripleDigits HTM]

Hey, thx for all the good suggestions...I'm on my way to Havasu this weekend to try them out.....

[Fat Chance]

Originally posted by Tinkerboater:
With an mpi engine it is just computer calibration nothing else.
Tinkerboater, I too have a 502MPI with a black transom at days end. I installed a K&N/Adj. fuel pressure reg. and had Teague set fuel pressure. You say there is a computer calibration that can be done? Is it tweaking ignition or fuel supply?? Tell me more. please!
Thanks,
Scott

[Snafu]

Family and performance boating Magazine has an artcile this month. If the temperature sensor does not reach a temp. of 160 the computer will stay in cold start mode and run rich.
Great Magazine I highly recommend. At $2.00 an issue the motor you save may be your own!!!

[lghtnin33]

hey snafu you are right that mag has some good info! but anyone in my view that is running an untuned carb can be better suited to a TBI injection. they are fully tunable with a dial of enrichment at idle to full go at the upper end with the turn of a knob. and as far as the black stuff on the transom, dont idle around as much, drive as fast as you can away from it http://free.***boat.net/ubb/smile.gif run that thing, thats why you opted for the hp. if you dont believe the whole intake/exhaust reversion thing with the GM cams, then you will have to look around some more.

[locogringo]

If you go to Havasu, email me when you'll be out there. I have a spray that works better than anything else ever tried. I'll give YOU a bottle!

[1faster]

Hey HTM, I have had this same problem with the same carb. It turned out to be that there are 4 small jets on top of the carb, that you can remove without removing the carb. Pull them out and clean thoroughly, and then blow with some carb cleaner (carefully) through the orifices. Re-install jets and VIOLA! Runs like new!