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Discussion Starter #1
my friend has a carribean 19' with a 454 bb and jacuzzi. motor is mostly stock with a mild cam. we broke in the cam at 2200 rpm and then took it 4 a test run at lake elsinore. made it 3 laps around before it started backfireing out of the carb and losing rpm n power. we replaced the gm hei cap and rotor for a tried and true accel cap, coil, and rotor. when we launched at the river(lost lake) it ran great for a half mile up river before the same problem returned. by the way, he is not much of a lead foot, more of a cruising guy. i appreciate any help.
 

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Living in a cage of fear
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Your cam has flat lobes. hate to say it.
You will find loose rockers and flat lobes.
 

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Some guy
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my friend has a carribean 19' with a 454 bb and jacuzzi. motor is mostly stock with a mild cam. we broke in the cam at 2200 rpm and then took it 4 a test run at lake elsinore. made it 3 laps around before it started backfireing out of the carb and losing rpm n power. we replaced the gm hei cap and rotor for a tried and true accel cap, coil, and rotor. when we launched at the river(lost lake) it ran great for a half mile up river before the same problem returned. by the way, he is not much of a lead foot, more of a cruising guy. i appreciate any help.
What's the status of the fuel filter? Been checked or changed recently or with the new engine?

The fact that you stated it ran well both times before having the problem leads me to believe it's not a valve train problem, but certainly check that out to make sure.
 

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Discussion Starter #6
brand new fuel filter, fuel/water seperator, put on motor before the test run. by the way, whats the best method for checking for a flat cam?
 

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Discussion Starter #7
i just checked with him and he said that all but the wiring is new. we did however go thru the wiring just to double check and it all seems to be savy.
 

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Some guy
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brand new fuel filter, fuel/water seperator, put on motor before the test run. by the way, whats the best method for checking for a flat cam?
If you are sure the carb is not starving for fuel, you can pull valve covers and check the valve lash. If you have one or more that are way loose, and the polylocks didn't just back off or something, that would indicated a cam lobe went away.
 

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Does it clear out after it sits a few minutes.. If so it may be a venting problem.. Or a collapsing fuel line!
 

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Discussion Starter #10
we did let it sit and cool 4 a bit before returning to the trailer and it didnt make a difference, but i will confer with him to make sure since i wasnt 100% sober at the time. im trying to get him on here to help with the tech. give me a few and i will get back with you all. by the way, thanks for the help so far!
 

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Did it run good before you changed the HEI to Accel?
Water in your fuel could also make this happen. Idles great then sputters at the top.
In the Kachina I have I get a fair amount of water in the tanks just plowing through the wakes. I ed to stop & drain the separator a few time a day to keep from sputtering.
 

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Discussion Starter #12
thank's for you help guys my name is john and i'm the owner of the angry big block. the only info e-roc forgot was that the day we took it for it'stest run the valves were too tight and no oil got to the upper valve trian. after fixing that it seemed to run great out of the water but the morning it went back in it only ran for about a mile and it wouldn't pull above 4200 rpm with my foot to the floor. the motor setup is 9:1 compresion rv cam performer intake holly 650 vacume secondary carb with wet log exhaust.
 

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What brand of EOS (engine oil supplement) did you run to break the cam in? If you didn't use any at all, you have a flat cam. Even the truck oils don't quite have enough zinc and other minerals for proper scuffing of the cam during break-in.

If there is no supplement in the oil for break-in of a flat tappet cam (non-roller), it is pretty much 100% failure rate.
 

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Winded Walrus
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i used a some slick 50 but forgot to put in any break in lube but iv'e never used it before and all my other motors have ran fine but this is my first jet boat motor
 

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Winded Walrus
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the thing that's realy got me stumped is it runs like a striped assed ape on the hose but it falls apart as soon as it hits the water?
 

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I would also check the carb. If the secondary float level is low/dry, as soon as you drain the bowl, you have a massive lean condition. Throw a double pumper on and take it out. A few more cfm wouldn't hurt either.
 

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i used a some slick 50 but forgot to put in any break in lube but iv'e never used it before and all my other motors have ran fine but this is my first jet boat motor
Slick 50 is not a break in additive. Odds are your cam is hosed. Time to pull valve covers and look for signs of a flat (or going that way) cam.
 

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my friend has a carribean 19' with a 454 bb and jacuzzi. motor is mostly stock with a mild cam. we broke in the cam at 2200 rpm and then took it 4 a test run at lake elsinore. made it 3 laps around before it started backfireing out of the carb and losing rpm n power. we replaced the gm hei cap and rotor for a tried and true accel cap, coil, and rotor. when we launched at the river(lost lake) it ran great for a half mile up river before the same problem returned. by the way, he is not much of a lead foot, more of a cruising guy. i appreciate any help.



My guess is it's fuel related. Leaning out will cause it to backfire out the carb. If it were the cam, it wouldn't have magically fixed itself after the first run. I fought the same problem on my ski centurian, and finally put a fuel pressure gauge on it at the carb. I thought it was spark also. Sure enough, after a bit of running, the fuel pressure would suddenly drop, and she'd pop through the carb. New fuel lines, vent line and pump, and she's as good as new.


Darrell.
 
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