I have a '06 GTR 35. Motor has 65 hrs. on it. Motor is stock. I do have a new single crossover exhaust on the motor. I can achieve 4250 or 4300 RPM's out of water. I have installed a brand new big blade prop with less than 2 hrs. of deep water running time on it. The boat will only run 20-21 m.p.h. pushing a 2011 1751 Excel SWV with no hooks in it. Boat has only been in water 4 times. When I start motor and let it run for a while to warm up I then throttle up and there seems to be some rough running/backfiring at around 3200-4000 out of water. I have checked valve clearances twice and am at a solid .005 on all valves. When in water I can only achieve 3100-3200 rpms and the aforementioned speeds in deep water. I can trim up and boat slows down and of course rpms will go higher then. With prop half in water like everyone says to run it I am at about 20-21 mph. Have changed the fuel line, changed to brand new primer ball. Have good gas in tank, half of fuel filter is full. Can squeeze primer ball and put a gas a little higher in filter. Motor does not seem to be affected by this OOW or in Water. I have read about fuel pumps, I have read about rounded cam lobes, I have read about burnt valves. We have checked the compression and I let it turn over 10 times. I got 180 per cylinder. I have not performed a leak down test on it yet. I am sure there is a thread about it I will have to read on recommended procedure for it.

I just bought a brand new '11 stock carb and am gonna install it on this motor in case my carb was dirty or underperforming (got good deal) thanks MMT. This motor did seem to have set before I bought it. Gas was stale and found a dirt dauber nest in air cleaner housing. To me this was indication motor had not been run in a while.

I was just wanting some input on where you all would go next with troubleshooting this motor if the carb doesn't allow it to run higher RPMS and better speeds in the water. I feel like its either not getting enough fuel or it could be a valve issue. When I run it out of water its not real smooth or stable at higher RPM's, however, it will get there. That has me worried about the cam. I would take it to someone if I lived near a dealer, however, I live near Owensboro, Kentucky and don't know of anyone who is recommended in this area. Thanks in advance for any help on this issue.

Sorry its long and I still forgot to post some info. Plugs are new, I found one plug boot that was cracked. I went to small engine shop and got some new really thick plug boots and they seem to be better. I will do the water spray test. Thanks will post results..

will try to check the deflection on the valves tommorrow. Thanks 50hp

Something is robbing your RPM. The backfiring rough spot at a specific RPM indicates coils not firing or valves not opening properly. As 50hp posted you can try to isolate the issue to the wiring harness by removing the cowling and disconnecting the spade connectors to the coils. Note- you will not be able to turn the motor off with the switch and will have to choke it or remove the plug wires to kill it. If those wires are chaffed anywhere and grounding to the motor, its grounding the coils causing them not to fire.

just food for thought, with only 65 hours, i wouldnt think it would be a cam rounded down, you may need adjustment on the carb or the jets cleaned or a kit in it since it seems to only run rough at higher rpms

as for a rpms in the water, another thing to look at if the other suggestions that you have already received do not help and it is not a carb issue is to look at the pitch on your prop, i have ran bass boats for over 15 years and we always get the props tweaked on pitch to adjust the rpms to the exact spot that we want the motor to run, less pitch= higher rpms, i usually dont hear much about owners of MM getting props repitched to make their motor perform at its peak but on bass boats we do it all the time.

if you get the motor to running smoothly like it should and you still have issues with rpm while at wot, i would check the prop out and get it worked on to improve your rpms.

the heavier the boat is the less pitch you would normally turn

Well got the new stock carb put on today and what a difference it made. I still have not got leak down done yet. Waiting on a leak down kit I bought off Ebay. The motor runs like a new one. Very responsive and no backfiring. It will go right up to the governor and sit there smoothly as long as I don't overrev it. I will try to put it in the water tommorrow. I think the issues are solved. It must have been a problem with the main jet on the carb. It only was affecting it at higher fuel flows. Good News is right now it looks as if there are no more issues. Will get gps speeds on deep water and run it on the mighty ohio tommorrow. Thanks for all input I will post results of 1751 swv excel and 35 gtr speeds.

bigritter70