74 MERC RPM amp SPEED

"Hi I purchesed a 1984 kencraf

"Hi I purchesed a 1984 kencraft Buxton inboard with a 2001 7.4 merc. the guy I bought the boat from removed the small block and installed the 7.4
I have replaced the full tanks and all hoses,vents and fittings, and the floor. oh yea he also removed the factory carb and replaced it with a holly 650? marine carb. before I did anything to the boat I ran it. it would only run at about 1800 rpm. at the dock it would rev up to 4000+ we messed with the carb linkege a little wd40, and then we tested again. this time 4000+ however now after all the work. back to 1900- 2000 rpm. I installed new cap rotor plugs. tested we were at 3000+ but all of a sudden it would drop out and almost stall. I would bring back the throttle and it would idle. then we could bring it back up to speed. oh yea my friend adjusted the needle screws to only 1/4 turn out. he did this as the boat sucked up 20 gal of gas in just a few hours of testing. I think the set screws may have had something to do with the dropping out. I have adjusted to 1 1/2 out I have also installed new wires today. I have noticed this evening that the coil is sparking to each post intermittently. I did not use any grease on the wires. as they said it was to aid in removing wires only. the speed of the boat is about 15 knots. I will test tomorrow with new wires. any thoughts on what happens when you pull out the small block and install a 7.4 as far as the prop is concerned. when I was getting 4000+ rpm after about 3500 rpm the prop would cavitate. this boat has a small tunnel like a pennyan. thanks for any help Billy"

"lots of questions. maybe I ca

"lots of questions. maybe I can help with a couple. idle adjustment screws are just that. idle adjustment. don't think you can alter full throttle by messing with them. clean top of coil of all oil and grease. the new wires will probably help. if the carb has a choke, check it. cavitation problem would be below the boat."

Thanks Scott
it was not the

Thanks Scott
it was not the idle adjustment he adjusted it was the needle screws. any way I put them out at about 1 1/2 turns. I am sorry I know this is a long winded problem. but I have been working on this boat since may. if you don't know what type of boat it is. it is like a c-hawk or parker it has a pilot house. also somebody has told me to check the magnets in the distributer. something else I need to learn about. I did look at the magnets but that told me nothing.

"one more question on the dist

"one more question on the distributor cap there is a brass 90 degree elbow, what is this for? at this time I don't see any thing hooked up to it. is it for vacuum? thanks Billy"

Hi again I think I answered my

Hi again I think I answered my own question about the brass elbow. I think it is a vent?
Thanks Billy

"yes, it's a vent. more on

"yes, it's a vent. more on the carb. the screws are for idle mixture. high speed is not adjustable.does it have adjustable floats? you can identify by a screw and locknut on top of float bowl. re: coil. every time you see a spark, a cylinder did not fire. double check that this has stopped. did the new wires help?"

"Use the attachment below.

"Use the attachment below.

Select the boat type and fill in the items as it states. That will tell you what prop should be on it. If the prop is cavatating, for what ever reason, it will lose thrust.

<center><table border=1><tr><td>http://www.marineengine.com/discus/icons/mime_msexcel.gif""" align=left alt=""application/vnd.ms-excel"">prop finder
[url=""][b]Copy of Boat_Speed_Finder-79780.xls[/b][/url] (22.5 k)</td></tr></table></center>"

"the new wires did not stop th

"the new wires did not stop the sparking at the coil. I replaced the coil today, and that has stoped the sparking. I still can only reach about 3000 rpm. I think that maybe when my friend was with me on a sea trial he was moving the distributor back and fourth. this may have been what allowed the increase to 4000+ rpm. as I said in a previous post when that happened the prop cavatated at about 3500 rpm. so now I am thinking maybe the spark was advanced. and maybe timed at 8 btdc with the current prop it will only reach 3000 rpm. or maybe the distributor is bad. I will call a prop shop and see what they think. the boat used to have a small block. this motor was installed three years ago with a 1-1 transmission and never tested. I truly thank you for you're time and help I am all ears. I hope I am posting right I am new here. Thanks Billy"

"have the timing checked. you

"have the timing checked. you could do serious damage running with it wrong. I'm sure your freind meant well, but keep him away from it. check your prop carefully. if it has dings, or damage on the leading edge, this could cause cavitation. also anything on the hull directly in front of the prop could affect it."

"Hi Scott
Thank you once agai

"Hi Scott
Thank you once again for you're time and wisdom.
ok I do have Thunderbolt IV so I can set the timing were it should be. I checked the flame/air filter to day and it was dirty. I cleaned it good
went for test ride with timing set 8deg btdc no difference, I even moved the timing around some could not get the rpm up to that 4000 mark. wot 3200-3250rpm only 17.5 - 17.8 knots, motor is working to hard, bot going to slow.
remember I just bought the boat from a guy who pulled the small block out and put in the 454. oh yea he put in a 1 - 1 trans. so I dont know what the boat should do, nor does he. but we did get it to 4000 rpm once however I have had other 25' pilot house boats with a lot less hp 225 (outboards)
that went almost 40MPH. I have one more thing to try. I pulled out the inline gas filter today, I will replace with a new one tomorrow. funny you mention the prop having nicks or dings. I jumped in the water over the weekend, and one of the blades felt a little riped up plus the boat is vibrating. I could not see, water to murky. so maybe you have a good point maybe I had some growth on the bottom, the boat sat in the water for two years. but the bottom feels smooth with few barnicals. I am a diver I need to bring the boat to clear water pull the prop, and run home on 15 hp merc. If I put in the new inline gas filter and there is no change in rpm. I will go to a prop shop and see if they can make sense of the low speed and rpm.any other thoughts
thanks Billy"

"Clean the hull; a few barnacl

"Clean the hull; a few barnacles cause more drag than you know. Since the prop is dinged, don't get it repaired until you know if you are changing or keeping it. Finally, have the shaft inspected for straightness due to vibration which is most likely due to the prop. Also discuss the gear ratio with someone knowledgeable about the engine and gear ratio combination; perhaps the boat mfg. or engine mfg.
You may need to change gearing to accommodate the larger engine."

Was the 7.4 a marine engine?

Was the 7.4 a marine engine? If not the cam will not be right for a marine application. Just a thought.

Jack