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BBC running lean

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lean running
4K views 13 replies 8 participants last post by  Sweat 
#1 ·
I was heading to the local sand bar and ran my Taylor SJ jet boat with a 505 maybe three or four miles and I noticed that the engine temp was moving up. It normally runs around 180 on the temp gauge and when it shut down it was at 220. It died on me while running about 3k RPMS and I had flames coming out of the headers. Had a buddy pull me to the sand bar and let it sit for a few hours and it fired right up when I was ready to leave. I haven't pulled a plug yet but I did notice in the exaust that it was a white looking color. My fuel pressure when I started it back up was around 7.5 pounds. Just wondering what I should do or look at first. The carb is a Proform 1050 and the floats are out of adjustment but the sight bowl is full and needs to be adjusted back down. Could something like the air idle screw being out of wack cause this or what?
I upgraded from a Holley mechanical pump to an aeromotive electrical pump with a regulator and run new 1/2 plumbing from the tank to the carb. I made it back to the trailer and the temp was just above 180 and the motor sounded good but not the same, almost like it was missing or something.
 
#3 ·
I pulled the plugs last night and they look lean. I also pulled the inline fuel filter and it was about70% blocked so i'm thinking that may be where my problem come from. I also turned the fuel pressure up to 9 pounds. I'm going to do a compression test tonight when I get home.
 
#5 ·
Am I correct in thinking that just because it has pressure doesn't mean it has flow? I have two fuel pressure gauges, one before the fuel filter and one after. Also, where can I buy a good but cheap compression tester? I think autozone has some for 30 bucks but not sure if they are worth a darn.
 
#6 ·
Correct, pressure and flow are proportional to each other. Reduced flow (clogged filter screen) = increased pressure before clog, increase flow = reduced pressure. You need to run the carb at the manufacturer's recommended pressure and check for restrictions like clogged fuel filters first.
 
#8 ·
Until he runs a compression check nothing is going to help. The missing after the cool down and the flames out the exhaust tell me this is not going to be pretty. Not hoping for the worst by all means but until I hear about compression and plug readings, top end tune don't mean dick. Now if the compression readings come up good then you can look at fuel distribution issues. Mark
 
#9 ·
I was heading to the local sand bar and ran my Taylor SJ jet boat with a 505 maybe three or four miles and I noticed that the engine temp was moving up. It normally runs around 180 on the temp gauge and when it shut down it was at 220. It died on me while running about 3k RPMS and I had flames coming out of the headers. Had a buddy pull me to the sand bar and let it sit for a few hours and it fired right up when I was ready to leave. I haven't pulled a plug yet but I did notice in the exaust that it was a white looking color. My fuel pressure when I started it back up was around 7.5 pounds. Just wondering what I should do or look at first. The carb is a Proform 1050 and the floats are out of adjustment but the sight bowl is full and needs to be adjusted back down. Could something like the air idle screw being out of wack cause this or what?
I upgraded from a Holley mechanical pump to an aeromotive electrical pump with a regulator and run new 1/2 plumbing from the tank to the carb. I made it back to the trailer and the temp was just above 180 and the motor sounded good but not the same, almost like it was missing or something.
Was what i changed to red always that way when you started or you noticed it after it quit and flames out the headers? You mention your filter was plugged, i'm wondering if you may have stuck the floats and flooded the engine with fuel, leading to a bunch of fuel in exhaust that lit off. an overly rich engine can look lean (basically a clean plug) on the plugs.
 
#10 ·
I ran a compression check and all 8 cylinders were at 195psi give or take a pound here and there. The plugs looked like they were lean but it's hard to tell because I ran it back about 2 miles to the trailer at around 3k rpms. I also checked the floats again just by turing the key on and the back is a bit high, maybe 3/4 of the way up the sight glass. The front look good, about 1/2 up the sight glass. Which brings me to another question, should I set the floats with the boat being level out of the water? That makes sense because when i'm running, the boat should be about level in the water. Or how do you guys set yours? Again, the carb is a proform 1050.
 
#11 ·
Glad to hear the compression is up on all eight! Now what did you find on the fuel filters. I was thinking that you leaned down enough to melt a piston but with the compression being good now you search other areas. The heating up issue could be caused by a lean issue or a water pressure problem. Good luck and I hope for the best for you!!! M
 
#12 ·
Over the winter, I changed all the fuel lines to -8, from the tank to the carb and installed a new electric fuel pump. I did a lot of cutting on the fuel lines and was sure that I got rid of the rubber but I was wrong. When I said the inline filter was about 70% blocked, all the material I seen was rubber :bangmyhead:


I think I will hook a water hose to the water system to check for anything that may be clogging up the inlet tube.
 
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