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7&8 plugs rich, 1-6 all good

 
Old 10-06-2018, 06:47 PM
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Default 7&8 plugs rich, 1-6 all good

combo:
4.080 bore L92
Wiesco flat tops
K1 rods
stock crank
L92 heads
LG G6X3 cam
comp 921 springs
TR6 plugs @ .035
L92 Vic jr
BLP 650 (870cfm) carb (74 jets squared, .031 squirters)
Daytona Smart spark


problem is 7&8 are extreamly rich, yet 1-6 are good. Compression is good. Iíve swapped 6&8 coil packs and wires, same problem.

I warmed the motor up. Put new plugs in 6&8, ran the motor 6000rm WOT for 1 minute and here are the results.

Anyone have any ideas? First pic is of #8 plug after a 30 minute ride at about 3500rpm. Second pic is after the 1 minute test.


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Old 10-07-2018, 07:03 AM
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How is your PCV plumbed?
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Old 10-07-2018, 03:13 PM
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Originally Posted by Pop N Wood View Post
How is your PCV plumbed?

using the vac from the prop and using a catch can.


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Old 10-07-2018, 03:42 PM
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Old 10-07-2018, 03:58 PM
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There is no actual vacuum behind a prop, as there is an unlimited supply of air to replace what's pulled thru the prop. There IS, however, a DRAFT of air, which could draw crank vapors from a breather IF it's arranged right. The way the pic shows, there is no real way vapors are being pulled from the crankcase. I would come up with a more positive way of pulling vapors from the engine than what you have.
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Old 10-07-2018, 04:52 PM
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Originally Posted by G Atsma View Post
There is no actual vacuum behind a prop, as there is an unlimited supply of air to replace what's pulled thru the prop. There IS, however, a DRAFT of air, which could draw crank vapors from a breather IF it's arranged right. The way the pic shows, there is no real way vapors are being pulled from the crankcase. I would come up with a more positive way of pulling vapors from the engine than what you have.

well it does pull vapors and moisture out quite well the way it is setup.
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Old 10-08-2018, 05:55 AM
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OK so no chance the PCV is sucking oil back into the intake.

The reason I ask is that almost looks like oil fouling. I've had old engines with bad valve seals and it is usually the downhill plugs that foul first. My other thought is some sort of fuel leak into the manifold running down hill into the rear cylinders.

This is really out there but if you have enough draft to draw a suction on the catch can do you suppose it could be drawing fuel up through the carb vents? Don't suppose you have a wideband on that rig.
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Old 10-08-2018, 02:01 PM
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Just fixed one that looked exactly like that. 7and 8 fouled out and the rest looked good. It was both coil harnesses were flipped over backwards. The motor ran great you could not even tell there was anything wrong. I'm talking about the 2 harnesses that plug directly into the coils. Something quick and easy to check. Otherwise do a leak down. And check your rear float level.

Last edited by TTur1996; 02-19-2019 at 03:19 AM.
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Old 10-08-2018, 02:40 PM
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Originally Posted by Pop N Wood View Post

This is really out there but if you have enough draft to draw a suction on the catch can do you suppose it could be drawing fuel up through the carb vents? Don't suppose you have a wideband on that rig.
Ive actually been running it with a scoop for that exact reason. If you run it with no air cleaner, you can actually watch the fuel come out of the carb.

I did tune it with a wideband, just kinda difficult with the exhaust setup.

Took the carb back to BLP this morning, lots of head scratching. Gonna ditch the scoop for a large air cleaner when I get the carb back
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Old 10-08-2018, 02:46 PM
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Originally Posted by TTur1996 View Post
Just fixed one that looked exactly like that. 6 and 8 fouled out and the rest looked good. It was both coil harnesses were flipped over backwards. The motor ran great you could not even tell there was anything wrong. I'm talking about the 2 harnesses that plug directly into the coils. Something quick and easy to check. Otherwise do a leak down. And check your rear float level.
I made sure all the harnesses were in correct. I actually have another set of jumper harnesses on order.

Iím running jet extensions in the back (mains) and the float level is just barely visible is the glass.

I figured the boat was always *** down in the water, but no one else has the problems I do
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Old 02-13-2019, 10:41 PM
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I was having the same issue with 7 and 8 being fouled while the other six plugs were spot on. If your carb is on the engine the usual direction- check the secondary transfer slots. If too much of the slot is exposed the vacuum signal could be pulling fuel on the transfer ckt. when it shouldnít be. Also make sure your idle screws are even on all four corners. In my case, the secondary transfer slots were too long and those two cylinders were getting flooded. I replaced the baseplate on the carb and itís been golden since. Good luck and hopefully you find or have found the issue!
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