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89 convincor 251

R

rupes

New member
I just picked up a convincor 251 with a 454 mated with a bravo 1. The motor was said to have been done about 25 hours ago and it dynod at 410 hp. Now my issue is the motor is only reading 3750 on the tach at wot. I'm running at 23 mirage and have an 850 dp holley.
 
That carb seems a little big to me, but I don't think that accounts for the 1000rpms or so that you are missing. There are a bunch of things it could be really. If I were you, I would start with a complete tune up. New plugs, wires, cap and rotor. Then check and set the timing. That's all stuff thats pretty cheap and easy to do and you are starting fresh and eliminating possible small problems. Plus reading the old plugs you take out could tell you what is going on, how the motor was running.
 
corey331 said:
That carb seems a little big to me, but I don't think that accounts for the 1000rpms or so that you are missing. There are a bunch of things it could be really. If I were you, I would start with a complete tune up. New plugs, wires, cap and rotor. Then check and set the timing. That's all stuff thats pretty cheap and easy to do and you are starting fresh and eliminating possible small problems. Plus reading the old plugs you take out could tell you what is going on, how the motor was running.
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Welcome to the forum. What Corey said here is a good place to start. You are not over propped but double check that. If it were a 27 pitch or near you would be down on rpms. Good luck and let s know how it goes.
 
Welcome to the Obsession! Yes, checking the timing would be the best place to start. Does it run smooth other than the low RPM? I would make sure that Base timing is set properly (Should be 8 degrees BTDC) and then make sure that the distributor is giving full advance at higher rpm's. (Depending on heads/compression somewhere 30-34 degrees at WOT)
 
Check compression first. If its good, then go through all the tuning suggested above. That 850 DP seems a little on the large side, was it the carb used when it was dynoed?
 
rupes said:
Of course I'm trimmed up.
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Sorry if that seemed dumb. You never introduced yourself or history.
You will be surprised how many guys get a boat and don't know how to use it. So not knowing I always start with the basics.
Hope you get it right.
 
The motor runs strong and I'm seeing 60-61mph at said 3700 rpm. U checked the carb and it's opening up all the way at wot. I'll do a compression test today when I get to the shop and investigate my plugs while I'm there. As far as the tach being accurate I'm not sure. It seems to be reading close to what my ears are hearing. I don't have a spare tach kicking around so I'll pick one up at Napa today.
 
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