View Full Version : Engine noise under heavy acceleration

07-02-2010, 11:58 PM
1987 PS190 with a 350GM 795hrs.

Engine sounds like a loud, old lawnmower under heavy load from a stop ONLY. If I back off the throttle a little, it goes away immediately. If I don't back off, it will go away after about 5 seconds. If i am cruising at 5mph or more and go to WOT, it purrs perfectly. It idles well, starts up fine, and the power seems fine. But the noise is loud and noticeably from the engine.

Some things that MAY be related, though not sure how....
new edelbrock valve covers with new PCV valve and new breather were installed before it ran this year. Is it possible that an incorrect pcv or breather could do this? Boat has been making this noise all year.

I could use and would appreciate some suggestions on where to start. Thanks!

07-03-2010, 10:18 AM
I would check my timing and what octane are you running in fuel? What is the difference between old valve covers and new valve covers as to thickness and type of metal? I am just wondering if you are hearing something that has always been there now over valve cover or is this new.The hard acceleration description makes me think of lugging and fuel/valve chatter. Others may have a better answer cause I am not even sure where to start except timing/fuel.

07-03-2010, 10:54 AM
Thanks for the opinion. I'll check timing and run some new gas this week. The new valve covers are aluminum edelbrock, the old ones were the originals. The sound is very loud and wouldn't be covered up by a different valve cover, but i do have the old ones I could still swap out. I did put on new filler/breather cap and a new pcv, but I don't think that would matter, would it? I suppose i could have put a wrong pcv or breather cap if they are specific to the engine. I didn't think they were though, and i don't know if it would have this effect?

07-03-2010, 12:20 PM
Yes, definitely check your timing. I would be curious to learn if it was running to much advance, sort of what happens when the advance weight springs break. Of course I don't know if you have a vacuum/centrifugal distributor or not but your description of the symptoms sounds like something I have experienced before...

07-03-2010, 12:43 PM
no vacuum hose to the distributor, so i assume it's centrifugal. Is there a way to check the weights if it is? The points were swapped out with a mallory electrical unit before I bought it.

07-04-2010, 03:53 AM
Two ways.

One with a timing light. It will show more advance at a low RPM than it should.

Second, you can take the cap off the distributor and put an eyeball on the advance weight springs. They are under the breaker plate. Sometimes you can just make them out without actually having to remove the breaker plate assembly...

Of course you had the electronic conversion done so they would be under all that stuff :)

07-06-2010, 03:40 PM
just the timing off a bit. thanks! Runs good again!