Krumbsnatcher

I know Thrillseeker had a similiar post a while back, but i checked it and no follow-up on the answer, so here is another one.

My buddies 38' fountain's port 525sc with an intercooler runs fine till it reaches 4500 RPM it will then start to sputter and kick back and pop a bit and she is tapped out while the other motor will run to 5000 no problem, you can feel in the boat that the motor is tapped out and is running rough, you back it down and it runs fine.

It is hard to tell and diagnose in the waves offshore, but you can definitely tell there is a HP problem.

Here is what we have done. We all ready replaced the MSD boxes. We are planning on switching the rev limiters, then if that fails I guess we will switch the carbs.


Changed the fuel filter, checked the pressure everything is ok.

Any ideas, would be helpful. Its now perfect Southern California Boating weather and this happens.

THRILLSEEKER

I am still haunted by this friggin problem, I have changed: carbs, coils, ignition modules, checked fuel pressure, throttle linkage, jumped 12v directly to coil from battery, tried different timing settings, bla bla bla I am going to change the electronic pickups (or whatever they are called) inside the distributor tonight and try to run tomorrow. My motor has the exact same symptoms as krumbsnatcher is describing The only other thing that I think could possibly be wrong is drive allignment, but I would guess that if the drive was out of line then I would have probs from idle up through 4k.

Krumbsnatcher, you may want to try some of the things that I posted above....let me know what you find out

Biggus

iTrader: (1)

Just a wild stab in the dark....but, weak valve springs would give you the same symptoms.

Krumbsnatcher

Biggus

I also have that in the back of my mind, the springs can not keep the valve alignment or worse yet maybe fractured somewhat. I am not an expert but i do know that this is a symptom at higher RPM's.

If all else fails we will pull the valve cover and check the head.

Biggus

iTrader: (1)

Weak valve springs make a very effective mechanical rev limiter

Good luck,

Kurt

HiPerf2000

iTrader: (2)

exactly what i was thinking......look for obvious electrical/fuel problems first, and if that does not cure the problem, it's usually in the valve train. Good luck.

THRILLSEEKER

Would replacing a worn cam and lifters. and using the same valve springs cause the springs to weaken Also how do you tell if the springs are weak??

Gary Anderson

If it's backfiring, I would check fuel first. Everything from the pickup through the carb.
BTW, Valve springs can be tested using a compressor that mounts on the rocker arm stud. I think the 525s should be around 135 lbs on the seat.
Gary

Scott

Thrillseeker

"how do you tell if the springs are weak"

It will have the symptoms you have. The real way to tell is to check them with a spring tool,meter or whatever it's called for the proper open and closed pressures per spec.

I had a feeling when I first heard that motor acting up that it was a bit more than what you hoped it would be For the price of springs and with the new cam and lifters they should of been replaced although I have a feeling your problem has something to do with the cam install and cam timing. This is just a guess and I hope I am wrong but something to think about.

You better get to work didn't you sign up for a Poker Run this weekend?

THRILLSEEKER

Scott, yup I am going to the poker run this weekend, It is running a lot better that it was when you heard it, the timing was way off I am still leaning on electrical problems because, once in a while it will run great, sometimes I can get 3k rpms, this weekend I was getting 4500 and the motor sounded great I pulled into PIB and it sputtered and died and wouldnt start. when we left, hours later, it fired right up and ran 4500 clear back to the ramp I have given some thought to the cam timing thing, I am posotive that I did it right. I was also told by a few other guys that if the cam wasnt timed right then the motor would hardly even start.

BTW, any of you guys know what valve pressures should be on a sbc, it has the old angled plug heads if that matters