CC247

I changed from stock exhaust to emi/ss, had the motor running real good at 3000 rpm's. Then at about 5-6 hrs the exhaust manifold gaskets started leaking(felpros). I changed them to the copper type. Run the boat up to 4000 rpms and wouldn't go any higher. I could back off the throttle and no changes. Feels like it was fuel starving. I came off plane and the motor backfired a couple times out the carb. Also sounded like no oil up top valves noisey. Shut off and checked oil ok. Restarted after 5 mins and no noise now missing and exhaust gaskets blown again. Could I have a really lean carb because of emi's? Could it get hot enough to cook exhaust gaskets and make my valves tick like a sewing machine? The season is almost over and I'd like to run again.

deboatmon

That almost sounds like you've plumbed the water incorrectly at the manifold or there's a water flow issue. I would consider it unlikely that EMI manifolds would change air/fuel mix enough to create that condition. Maybe it's entirely possible, but I might look elswhere. If you were already running close on your air/fuel mix maybe it is the manifolds.

CC247

Just got off the phone with EMI. Seems I was close to begin with. They state with a carb setup you should jet up 4 sizes. I ran her lean up around 4K because I had more throttle,just no more go. I pulled 2 plugs and the centers were gone. EMI also states not to use gaskets. huh? Well I'm game, I'm gonna up the jets,pull the gaskets,and new plugs.

hillbilly24

4 sizes up on the jets sounds a little much if all you did was the exhuast, but it's much safer to go too fat and find out it's rich then to do it the other way as you have just learned. The no gasket thing is a new one on me and I think you might want to call them back to confirm that one. Copper exhuast gaskets aren't very well suited for water cooled marin exhuast, they need alot of heat to seal an the manifolds just don't get hot enough. Was the center strap missing off the plugs or the elctrode ? if it was the strap then you may have more problems yet, they don't typically melt away tottaly they get hot and break off where the conect to the body of the plug and you are left with the strap banging around in the clyinder and you would be amazed at what havoc that little piece of metal can create.

articfriends

iTrader: (1)

Ive never tried to run manifolds in a marine application without gaskets BUT I have done it in automotive applications. I once installed a gale banks exhaust kit on a 94 chevy 454 dually,the instructions said to clean all old gasket off the port surfaces and bolt the header directly to head w/no gasket. The headers had a 5/8" thick port flange that was blanchard ground,they never leaked.
Did your plugs lose the centers on the cylinders closest to the exhaust leak? If the rest look lean then you were overall lean which i find hard to believe but anythings possible,Smitty

CC247

All the plugs were complete just porcellin broken away. Ground straps were all good. All plugs were white,lean across the board. I'm going 4 sizes up on the jets to be safe,then back off from there. The copper gaskets were leaking everywhere, maybe because of no heat. The gaskets came off blue in color. I'm trying the no gaskets, 3rd time has to be the charm.

hillbilly24

I still have to diasagree with the no gasket thing, aluminum against Iron just aint gonna seal, a blanchard ground steel header is one thing but an aluminum manifold is another.

East Coast B

What motor are you running? I'm interested to learn the outcome of the rejetting, if in fact it is a problem.... I've been thinking about new exhaust systems... Good Luck!

CC247

Hillbilly-so far so good on the no gaskets, I just used a little red silicone.
ECB-It's a warmed up 460 Ford. The little time I have been testing from 2500-3800 rpms is alot more umph. No wot yet. Also on plane time is alot quicker by seat of my pants. The manifolds have that nice 60's style cam crackle at idle. I went up 4 sizes on jets, can't give anymore results till next week,going to NHIS now. Thanks to everyone for the insight.

East Coast B

Glad to hear all is well so far!!!! What other mods above stock do you have in the motor??