Chevy 175 hp, 4.3 I/O question!

[mako]

Working on a 1991 4.3 Chevy with a OMC outdrive. Starts up fine but idles rough and when I rev it up I get a popping sound, and some backfiring through the carburetor. Changed the plugs, distributor cap, and rotor, and tried adjusting the timing. But still the same. Any ideas what is causing this? Thanks!!

 

[12Footer]

Re: Chevy 175 hp, 4.3 I/O question!

Check (or replace) all vacumm hoses, and in particular, the vacumm advance hose to the distributor,if so equipped.. Listen for a hiss.<br />You may have a timing chain that has jumped a tooth. It definately sounds like timing.<br />When the tensioner cam gets stuck,or the chain wears beyond the tensioner's ability to keep it taught, this happens.

 

[SeaBear]

Re: Chevy 175 hp, 4.3 I/O question!

Check the carb to manifold gasket - if you have had the carb off and replaced it without renewing the gasket it will do this! I know cos' it happened to me!

 

[mako]

Re: Chevy 175 hp, 4.3 I/O question!

Thanks for the input. Cant see anything wrong with any vacuum hoses. I just took this boat over from my friend and I know the carb hasn't been off since he owned it, which is about 5 years. <br />How difficult is it to do a timing chain on this motor? And does it look like this is the definate problem? Also their is a minor lifter tapping noise. Could this be related?<br /><br /> Thanks!

 

[Dhold]

Re: Chevy 175 hp, 4.3 I/O question!

The tapping could be related to the retarded timing. Something else it may be is that the harmonic balancer slipped. You may think you have it timed perfectly with a light, but in fact, it may be way off. Not too long ago, a stump hit my prop shearing two blades (Good boaters never hit stumps, stumps hit them!), and I thought sure I twisted the crank. As it turned out, it twisted the balancer. I retimed by ear, and it runs great! Has any stumps jumped in front of your friend?

 

[mako]

Re: Chevy 175 hp, 4.3 I/O question!

Solved the problem. Had a sticky lifter. Ran some Motor Medic through the oil and it got a bit better. Ended up taking the valve cover off and shot some Marvel Mystery Oil into the push rod also put a couple turns on the adjustment bolt. Running like new now. I think I'll end up replacing the lifters but I'm on vacation till the 23'rd and want to enjoy the boat.

 

[norman158]

Re: Chevy 175 hp, 4.3 I/O question!

if your going to replace the lifters do the camshaft too chevy is great for flat cams