I have a 35 GTR, 8-10 years old and has performance cam and heads ordered from Calen that we installed last spring.

Been having some trouble lately and trying to diagnose. The other day as soon as I left the ramp and came up to full throttle the engine would sputter/bogg a bit, RPM’s would drop, and then it would pick back up to 3800RPM’s while at full throttle. It would run fine for awhile and then drop RPM’s again, then pick back up. Seemed to do it more often if I trimmed motor down(under load). Pulled to the bank. At idle, not under load, no problems with top RPM’s around 4100.

Next morning motor wouldn’t start, backfired a lot, had to get towed in.

Once home checked plugs and they were black. Replaced with new plugs.
Thought maybe bad gas. Dumped tank, replaced in line fuel filter, put in new fuel, took out carb, took apart, sprayed out everything put back together (float wasn’t stuck). Walla, fires up, good! Max RPM’s at idle (or with clutch engaged) at around 4100 RPM’s. Thought I had it fixed, maybe clogged carb was it.... In the meantime, ordered new carb gaskets and plug screw for the bowl so I could get rid of the solenoid (as maybe that was the problem).

Took boat to lake this morning to test out in water under load. Engine again ran fine around 4100RPM at idle, but back to bogging a bit at full throttle and only getting 3600RPMs. Same deal as what was going on last time on the water. Shit!

Back to the garage. Motor starts up fine. Pulled plugs, they look clean. Pulled valve covers and checked lash and rods. One side at .006, other at .007/.008. Set that side to .006. Rods looked fine. Replaced covers. Started fine and at first got back to around 4100RPMs at idle. Held it there for a bit to check in line fuel filter for air bubbles (looked fine). Turned engine off. Started again, now at idle, full throttle RPM’s max out at 3400!

WTF!

Maybe firing on one cylinder? So at idle pulled spark plug boot off plug to see if it shut off. Motor still continues to run, but boggs/idles rougher with the boot pulled from the plug. Did the same for the other plug side. Same thing.
My carb parts should be here early next week. But I’m beginning to think that isn’t the issue.
HELP!

Have you checked for and eliminated any air leaks?

Make sure all your hose, filter, and tank connections are good. No cracks in fuel line. Gaskets on carb and intake are good.

You can use carb cleaner to check for leaks at the intake and carb. Spray short , direct puffs where air could be sucked in and see if your idle increases. Avoid spraying anything on the exhaust.

Pull the valve covers and make sure the rockers are moving "equally" as much as each other. Do a leak down test and compression test. it sounds like a weak engine from the description. Either worn camshaft or Severely leaking valves causing a lack of compression.

Sorry, been waiting on a few parts and have been working on things. Replaced all all fuel lines (both to and from carb and fuel pump) and everything else associated with the fuel lines, except the tank itself. New gaskets for the carb, and took off fuel solenoid from carb bowl and replaced with just the bolt. Clean out the carb again for the 3rd time. Also replaced spark plug boots with NGK boots.

I figured out that the screw that clamps down the throttle cable had slipped and moved throttle cable to get my out of water max RPM's back to 4300ish. SO... that problem solved. Adjusted by idle RPM's to 1300ish via the screw hole drilled in the front of the Briggs plastic front plate.

Checked the valves again and they are fine at .006. Rockers seem to be fine as well.

Put the boat in lake again this morning. In gear under load only getting 3100-3200 RPM. Again once in awhile it sputters at full throttle a bit and drops some RPM's before recovering. Same ole issue. Max RPM's not under load still at 4300...

What should I concentrate on next to fix the issue?

DAM feels like I'm chasing gremlins trying to fix this motor...

I compression tested the motor today. Jamie B decked head, and performance cam. Both side were at 170. So that's good.

I ran all new fuel line (got rid of the water separator), took apart the carb again and cleaned it all up.

I took off the front crowling and inspected the coils/wire. The wire between the coils had been rubbing and pushed up against the pipes. The left side coil wire, if your looking at the front of the motor, was bent back quite a bit and the rubber was removed. Electrical taped everything off. Thought I might have solved my problem. Set coil gaps at .006.

Motor really hard to start now. When I do get it to crank and try to give it a little throttle I can vaguely hear a slight "tick" and then it loses RPMS on the tach..

Bad coils, or diodes...? Starting to lean that way....Any insight would be great!

Unplug the wires. If it runs fine with the coil wires disconnected, it's either a pinched wire or the diodes.

Bought a couple inline spark plug coil testers hoping I would see a miss when I hear a slight "tick". No go, light fires without skipping a beat.

Motor still tough to start. Only way I can get it to start is hold down throttle, pull out choke and turn key over. Fires right up then.

Give it gas and I hear the tick and it dumps a couple hundred RPM's, throws a bit of smoke or a quick second, then rebounds RPM wise until the next "tick"

Someone mentioned a bad CAM. Had already threw away my old oil filter, so wasn't able to check it for shavings. I pulled the valve covers again and checked movement on the valves when I spun the prop to see if maybe one wasn't moving as much (screwed up cam) and they all had equal amounts of travel.

Any more ideas....Running out of things to check. I'll try pulling the wires off the coils tommorow, but wouldn't that show up as a slight interruption in spark on the inline plug tester when it "ticks" and drops a few hundred RPM's?

Thanks!

Should add that when I get motor running and pull the plug wire on one side it kills the engine. When I pull the other side there is no change.

Diode.

Go on parts tree and get a new diode wiring harness, or go to RadioShack or some electric store and get a new diode and wire it up.