SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: Riverlife_ on July 01, 2014, 04:51:27 PM
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BBC w/ Victor Jr intake & Holley 750 double pumper
So after re-jetting my carb to
76 primaries & 80 secondaries this is what my plugs look like, the big stutter I had is mostly gone but I still have to give it like a 1-2 pump to get it going from a dig.
Plugs have one lake day on them running it pretty hard
They look a little light still to me but I am not to sure & would like some more experienced guys to help me out.
Pics 1&2 are from #8
Pics 3&4 are from #3
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Is this a fresh engine?, to be honest, the only way to really read plugs on a gasoline engine is to put some real hard pulls on the engine and "click it", then by using an otoscope to look deep into the plug shell at the base of the porcelain insulator for the color ring. Or even better, dyno tune the engine with headers with O2 sensors in each header tube, the load put on an engine on the dyno is real close to how a jet boat will load the engine. So if a "tune" is ironed out, it usually can be left alone in the boat. On one of the pic's I see a few dark peppered specs, this may be an indicator of detonation, this may be carbon that was rattled loose from a piston top, but I dont know your compression ratio. A 750, mechanical secondary is enough for that eng CID, and those jets are pretty much what that model came with out of the box, along with 6.5 power valves. Is your ignition strong enough?. Getting a jet boat to pull out onto a plane is a pretty good load on everything. How quick does your ign. advance come it? I have initial set at 16 and total is in at 1,800rpm and 20 deg. of spread in the weights put my total at 36 deg. Has anything in your combo been changed recently?..there are some unknown variables for me to really let loose on some possible solutions.
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The motor is fresh, >10hrs I'm running a msd billet HEI with a 65k coil, these plugs are brand new, I had the carb jetted to stock 70/76 I think was oem and with the Victor jr, I change them both at the same time from a lower rise old intake and a vac sec 750 to this set up after I changed everything intake/carb I was having issues with it wanting to die if I stabbed it with one swift press but if I pumped it I could get it going, so I assumed not enough fuel and I bumped the jets to 76/80's with 6.5 PV and new plugs gapped at .38 and it improved a lot but still has a small sputter it's all still useable just not as smooth as I know it can be, so I was thinking it might need a little more fuel I have no black smoke or soot whatsoever
Also my timing is close to yours
14 initial with 22 advance total of 36 I'm by 2k ish
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