I'm running a 35 GTR with a 42mm mikuni carb. The boat is an Xpress 1650 DB. I bought the rig used, and I'm having issues with it idling for 30 seconds to a minute, then dying unless i give it some throttle. It doesn't die at full throttle.

I had the carb cleaned by a motor cycle mechanic, replaced the fuel pump, replaced all the fuel lines, the in-line fuel filter, and the bulb. It's still trying to die at idle, and I can't get the boat out of the hole (it's only turning 1400 to 1500 rpms in the water with just a couple of guys and very little equipment). It revs up out of water, but seems to puke a little black smoke. I can't tell how many RPMs it is turning out of the water, because my tach goes bonkers when I rev up the engine, but it sounds like it's turning quite a few RPMs.

Why would it bog down and only turn 1400 RPMs under water? I'm running the 3 blade prop, and I also have a big blade. They both run about the same. I wouldn't think that a 1650 would be too much boat for a 35 HP engine.

Any ideas?

It could be a popped head gasket or a flat cam. You can set the valves and look at the pushrods. If there is a white line half way down the pushrods thats a dead giveaway for a popped headgasket. Make sure all the rockers have full travel. Beyond that its time for a leakdown

I just wonder if it tossed a pushrod and an intake valve isnt opening on one side. Checked the valve lash?

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I'll need help with checking the valve lash. That's beyond my knowledge when it comes to these things. I have done a compression check and hot 120 on both cylinders. I've heard they call for up to 150, but this was a $40 compression checker from O'reilly. So I don't know how exact it is, but the cylinders were consistent.

Do you agree that a 1650 semi-V shouldn't be too much boat for a 35 GTR? Is the 3 blade the right prop for this setup?

It’s not a great boat for it, but that’s not the issue here.

As for compression, doesn’t really matter which is why leakdown test keeps being referenced.

Pull rocker covers, and follow nick willey’s YouTube video for setting valve lash (Willey fast)


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Valve lash, check to make sure both plugs fire, then do the leakdown. And that cost 25 dollars more than my compression tester. As long as you hold the throttle open, itll be close enough. But lash and leakdown and spark are more important for this problem.

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#GhostBoat
#Whoneedsphysicsihaveamudmotor

Send it get checked out. Have them clean and tube carb, do a leak down test and adjust valve lash. They will almost certainly find you some more HP.

Ok. So I adjusted the valve lash using Willey Fast's YouTube video. I got one of those cheap $30 leakdown testers off Amazon. It wasn't showing the correct intake pressure from the compressor, so I didnt lend too much credence to what it read on how much leak I had. What I was able to do is listen to the heads under pressure.

On the non-fuel pump side I heard a fairly faint hissing from the cylinder, and a definite, but not too loud hiss from the carb. The other side had a definite and unmistakable leak from the cylinder. I even saw what appeared to be a piece of gasket in next to the pushrods.

So I'm going to assume I have a popped head gasket on the fuel pump side (the side with the oil fill cap). Does this appear to be the source of all my problems, or might I have multiple issues?

I'm going to assume that pretty much no motor is completely leak free with no hissing or pressure loss at all.

Fix the head gasket that you know is popped, may as well do the other while you're at it to check and make sure both cylinders look ok (just dove into one about 3 weeks ago that the cylinders had some fairly deep grooves in). Once that's done, do a leakdown with the pushrods removed, make sure all sounds better, then put the pushrods in and set valve lash. See how that works out for you.

#CFFITR
#GhostBoat
#Whoneedsphysicsihaveamudmotor

Also, I checked spark with an in-line spark tester. The spark was constant on the side away from the oil cap, and an inconsistent spark on the side with what appears to be a head gasket leak. Is this because of the head gasket issue, or do I have another possible problem on top of the head gasket (bad coil as well?)