ford 351 older 1984 Nautique
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=410
Printed Date: November-21-2024 at 10:50pm
Topic: ford 351 older 1984 Nautique
Posted By: Guests
Subject: ford 351 older 1984 Nautique
Date Posted: May-26-2004 at 2:56pm
After I get over 4000 RPM's she begins to lunge, if I pull back the throttle, all is well. Actually everything is fine but the very top end... it seems like timing, but how do you time at top end? I timed with a gun at low RPM, stablized and runs great.. but at the higher end, I am not sure why it is still off.
Any clues?
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Replies:
Posted By: tommer12
Date Posted: May-26-2004 at 2:57pm
Posted By: reidp
Date Posted: May-26-2004 at 3:32pm
By "lunge", do you mean bogs down quickly and looses power intermittently(sp) until you pull back on the throttle? If that's the case, my 1970 Mustang always does this as soon as my fuel filter fills up with the miniscule debri from the old fuel tank I've failed to replace / repair. The fuel flow is insufficient for higher rpm, as it's fine until somewhere in that rpm neighborhood you mentioned, but a quick filter clean and I'm back in business.
-Reid
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ReidP
/diaries/details.asp?ID=231&yrstart=1971&yrend=1975 - 1973 Mustang
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Posted By: tommer12
Date Posted: May-26-2004 at 4:13pm
I replaced my Fuel and Water seperator. But I will have to look into the filter... I didnt think about that. I don't think I have ever replaced that old filter. I did replace the carb a year or so ago.
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Posted By: 64 Skier
Date Posted: May-27-2004 at 1:00am
You can plot a "Timing" curve for the higher RPM's if you still want to dig into that. Typically, you plug the vacuum advance and set timing at idle. Then hook-up the advance and run up the RPM's and record again. You can do this every 500 RPM till your satisfied. The timing should continue to change, albeit in smaller increments as RPM increases.
I'm not familiar or know of any adjustable vacuum advance, but the MSD's mechanical advance can be adjusted...typically for high compression racing appliactions. You change springs for different curves. I read where a high compression engine will advance quickly and max out at 2500 RPM, whereas a street machine with vacuum advance will continue to advance up to 4500 RPM???
Unless you've changed compression you'll be OK, but this exercise will allow you to see if you are not getting proper advance at higher RPM's.
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64 Skier
66" HO VTX and 67" HO Triumph
http://www.correctcraftfan.com/diaries/details.asp?ID=1071&sort=&pagenum=3&yrstart=1971&yrend=1975 - 71CC
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Posted By: nms1991
Date Posted: May-31-2004 at 8:46pm
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most marine distributors donot have vacumme advance systems they only have mechanical systems, so no need to plug off the vacumme line to check for base idle timing. to check you timing advance put boat into nuetral so you can free rev the engine and check the timing at 3600 rpm and it should be at 30degrees btc on a stock 351 engine but do not keep it there too long because it could cause a lean condition because of the carb function with only 1/4 to 1/8 throttle to acheive this. If you rebuild the carb try a different accelerator nozzle like a #31 instead of a #25 it could cure the problem with the lean bog.
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Posted By: nms1991
Date Posted: May-31-2004 at 8:54pm
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also i forgot to have you check you pickup in the tank for a plugged screen. the screen sometimes are hidden up inside of the tube and you have to dissassemble the tube to find them.
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Posted By: tommer12
Date Posted: June-01-2004 at 10:34pm
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It seems to have happened when I went to a larger carb... 480 to 650.... the strange thing is that i had it running at top RPM just fine, but then over the next 50 hours, it goes on and off from this strange sputter
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Posted By: 64 Skier
Date Posted: June-02-2004 at 8:50am
I assumed when you said Older you had a vacuum advance like both my older boats. I even see there's an old CC on E-Bay with vacuum advance. Sorry if that doesn't apply to your motor.
The timing plot's the same concept independent of Advance Mechanism. The SBF's like at 30-35 degrees total advance.
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64 Skier
66" HO VTX and 67" HO Triumph
http://www.correctcraftfan.com/diaries/details.asp?ID=1071&sort=&pagenum=3&yrstart=1971&yrend=1975 - 71CC
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Posted By: tommer12
Date Posted: June-15-2004 at 7:46am
It is mechanical advance, but I think with talking to my mechanic, that it is "lean" on the top end... not getting enough gas, which leads me to:
a. jets are slightly plugged.
b. filter is dirty
c. tank is dirty
So this weekend, I am going to take a look. I have also heard this working...
take the flame arrestor off the carb. With the boat idled, bring the RPM's to 2500-3000... take your hand or something to plug the carb so it starves for air... the vaccums will try suck any air it can, in turn possibly pulling any dirt out. let it stale out ....
84 2001 (for sale here!)
92' SNOB... ahh.. something a little newer!
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