i have a 35 gtr that has been modded to a 45. it has 160 hrs on it. had 4 guys and lots of crap and wouldnt get on plane. kept pushing it and got in some shallows and finaly got it on plane. ran high-4400 rpm( usualy runs 4200) for 45 min up river but we stayed on plane and made it. on the trip back would not get on plane at all. seemed to be just clutch slipping. prop was wore pretty bad so we stopped n changed it. no diffrence. took it easy after that. unloaded everybody and would get on plane then but is taking 400yds to get there. rpms jump right up to 4-4500 then slowly build speed. went out today with one guy and gear and will get on plane but still taking forever.
any thoughts or am i correct in the clutch?

never had one of these clutches "slip". Im not saying its not....just normally they go poo. What I have seen time and time again is an engine with bad/leaky valves causing the exact problem that your describing.

Well I have iron mountain heads with less than 8 hrs on them. Wouldn't have thought that but ill check compression and see

If it's jumping up to 4500 rpm's it's not the valves it's your Clutch. You've got the power but no push

A persons natural instinct is to trim the engine up to take off allowing the propellor to cavitate and allow the engine to turn up high rpms. The prop could be mostly out the water (no resistance) the way to check it would be to put the prop in a bind (trim all the way down pushing the bank) and see what happens.

A person that's mechanically inclined could troubleshoot this instantly....most here aren't and this very problem has been brought up more times than none and has been traced back to valve issues each time!

Well just thoughts cuz I'm on here for ideas and advice from ones who have already fought these problems.
i have it trimmed down to take off n tried lots of different things trim wise. No difference. Revs right up but seems to slip. Sounds like it holds power to prop till about 2500-3000 rpm/ right where it trys plane out.
I'm going looking for a compression gauge tomorrow ...

Again, I doubt your clutch is slipping.....in fact, I'm pretty confident that it is NOT slipping! Unless someone performed work on your engine and installed something wrong, your clutch IS NOT slipping!!!!! What kind of boat is the engine on? Is it the correct transom height and angle? I would start looking else where for the problem..... Could very well be your boat!

Is it possible that the belt could be loose slipping on the gears or maybe a gear is stripped, i don't see a clutch slipping either but then again weirder things have happened with this things!

If the belt is slipping you'll know it! The sound of a slipping belt resembles that of a crescent wrench in a gear box! Only way for the gear to slip is if the engine was worked on by someone and the key wasn't installed upon reassembly!

i agree with garret i am a mechanic and if the engine is tacking up to 4500 and running strong why would the vavles have a problem. i dont think it would be the clutch tho becuase if your clutch had been slipping it would have started smoking after a trying to get on the wave a few times. i would check your keyways and be sure the "new" prop your running is the right size be cause i have seen 12x10 stamp but are a 12x11 or 12x9

My Mechanic (below) states that it is either the Clutch or the Valves.. Shes Never Wrong !!engine.jpg

If it is the clutch that is slipping please don't post that it was that. Say it was the valves. The holidays are coming up and we don't want any one to have a medical meltdown.

Clutch is possible but not with those sympthons mine went out at 10hrs started slipping than made some noise so I just ran it till it went out all together brought it to gatortail said clutch was fried good thing they make warranties

well the compression checked at 115-125 left to right. and the clutch isnt blue like it has been hot. now what?

Have you checked your valve lash clearance?

Did he also do a leak down test, or just a compression check? You can have a good compression check and still have a leakin valve.

gota get a feeler gauge tomorrow and replace the o ring on the compression gauge cuz its broke and leaking keeping me from doing a leak down test. sucks cuz i have all the tools in storage at my parents but i moved last fall 3 hrs north and aint got crap here! and its 24 deg outside and im working on it in the driveway

well it looks like its leaking valves!! never would have started there. valves were at .008-.014 and adjusted them down to .004-.006. know this isnt whats causes them to leak only if they were to tight and not sealing. compression is still at 115-130 and bleeds off within 1min-1:30 when i shut it off and roll it to TDC. not sure that is the proper way to do a leak down but seemed right to me?

Did you hold da throttle open while doin dis?

I have a buddy that just had to replace the clutch on his prodrive. His motor did the same thing. I was in it when it happened. Clutch cost around 200. His motor would run fine and then it would get the rpms but would not plane. Then he got in there by himself and it would get on plane but it took forever. Good luck.