omc bb goes pop pop ?

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Hello
1987 460 omc while on plane. At 3500 rps once in awhile maybe 2 times today the motor would go pop pop and then keep on going just fine. Had a new f/w separator this year .the only repair I did besides plugs/points /timing cap and roter ,was the exhaust riser gasket . Manifold, risers and manifold look to be in good shape since it was a fresh water boat with no real rust of salt build up any ideas ? also new carb last year thank you JD

 

[mkast]

Re: omc bb goes pop pop ?

Popping through the carburetor is usually associated with a lean fuel condition.

 

[HT32BSX115]

Re: omc bb goes pop pop ?

You may also be slightly out of time or have a burned valve.

When is the last time you removed the risers and checked/replaced the riser gaskets?

 

[rusty bolts]

Re: omc bb goes pop pop ?

Port riser gasket was replaced 2006 stabord side last week / it does not pop all the time had it out one night and it ran fine /it runs good top out at 4300 rpms. boat 23 gradywhite gulfstreem 5600 pounds / ran good last year. I was thinking maybe water leaking by the riser or water in gas? I will go down and look at plugs/change fw sep .The boat is running a bit cooler this year about 140 new water pump installed ,also will re check timing thanks JD

 

[rusty bolts]

Re: omc 460 bb goes pop pop ?

Re: omc 460 bb goes pop pop ?

Bubba It has to run a while on plane 10 15 min or longer . I does not happen when i start it up . Also when i had it out yesterday it was running fine then i had to make a turn while on plane , while in the turn it poped once ,then was fine ,maybe like you said starving for gas ,Maybe the sharp turn made it happen ? I will change the filter and dump out the gas in a glass jar to see if water is in it ? I wonder what has changed from only a few months on dry dock

 

[rusty bolts]

Re: omc bb goes pop pop ?

Thanks, tried running both tanks,inspeced inside /outside of tanks last winter looked good maye a little startron would be in order Ita time to go down to the water and try my luck an fixing it thanks JD

 

[rusty bolts]

Re: omc bb goes pop pop ?

Worked on motor today ,change f/ w sep ,tighten carburetor nuts , all plugs looked good except 2 on the starboard side center ? would a leaking riser gasket let water in to the cylinder? plugs had a slight rust color but it may have been before I changed the riser gasket? I was also thinking since I have to take it apart I will change the manifold gasket . I think I have 2 issues hear . I will run the boat tomorrow an check the new plugs to see if they are wet Any ideas ? Thanks

 

[HT32BSX115]

Re: omc bb goes pop pop ?

Worked on motor today ,change f/ w sep ,tighten carburetor nuts , all plugs looked good except 2 on the starboard side center ? would a leaking riser gasket let water in to the cylinder? plugs had a slight rust color but it may have been before I changed the riser gasket? I was also thinking since I have to take it apart I will change the manifold gasket . I think I have 2 issues hear . I will run the boat tomorrow an check the new plugs to see if they are wet Any ideas ? Thanks

Yes it could leak.

I'm sure it would not cause backfiring though when running since the water would be quickly pushed out the exhaust.

Water would only run back into an open exhaust valve once you shut it down and it would probably hydrolock briefly when you tried to restart it.

My 460 did that very same thing before I tore it down. I discovered that my riser gaskets had been leaking for quite some time. a small amount of water would run back into the engine. Although I still had pretty good compression, if it sat more than a couple hours or so (or over night) the water would leak past the rings and it would start normally.

Since it was a small amount of water, if I ran it for a few hours afterward, all the water would pretty much evaporate out of the oil.

The risers drain fairly quickly when you shut it down so not a lot of water will leak back.

I had another problem that could possibly cause your problem. My camshaft had several flat lobes. The valves were opening but not very far. That's why it didn't show up on the compression check. ( I didn't see it until I removed the intake manifold and could look at some of the cam-lobes)

It wouldn't turn any more than about 4200rpm at WOT.

Manifold gaskets won't make any difference at all since there's path for water to the engine from the manifold except at the riser connection.


Also, I found that I had vacuum leaks at the intake manifold. the gasket was in pretty bad shape.

replacing it didn't make any difference though.

I did fix the problem. but not by fixing the 460..... see my signature.



Cheers,


Rick

 

[rusty bolts]

Re: omc bb goes pop pop ?

UPDATE
reset points adjusted timing a bit /added startron good . i ran hard for a bout 1 hour or so no pop
today took out went fishing. ran good but on commiing off plain it went pop ,rest of the day ran fine?
2 middle starbord side plugs looked good but had a slight white chalk ?on them/ were not wet .could it be also a manifold leak ? any ideas ? thanks

 

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