Is this a misfire?

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I have a 1989 Chevy 5.7 liter 350 on my boat and at idle speeds it makes a tink like sound and a thud at the same time. Also the motor shakes a tad when this occurs also. Opinions? It also has a rich gasoline smell to it too and is hard to restart when hot unless you give it some throttle. On a cold start it fires right up within like 2 seconds. It doesn't seem to do this until about 15 minutes in once it's warmed up. It also has a bit of vibration when this occurs and feels sluggish.
 
Carb or Injected? Betcha it is carbed, Possibly fouled plugs running rich, bad plug wires, The usual '70s car stuff
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Originally Posted by andyd
Carb or Injected? Betcha it is carbed, Possibly fouled plugs running rich, bad plug wires, The usual '70s car stuff
grin2.gif



It's Carbureted. Also I did put new plugs in and it worked good for like one or two boat trips, then the vibration and misfire came back.
 
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If you have the engine cover off and hear a snapping noise like sparks jumping where they're not supposed to... That's likely exactly what is happening.
 
Definitely a full tuneup is needed. Check the timing as well including the distributor. For some reason I'm thinking that is where the issue is but a full tuneup should expose that if that's the case.
 
Originally Posted by mk378
If you have the engine cover off and hear a snapping noise like sparks jumping where they're not supposed to... That's likely exactly what is happening.


Watch for sparks jumping , where they are not suppose to , at night .

If you have 1 bad plug wire , by a set and replace them all . Do not forget to check the coil wire , if it has a separate coil ( is the coil OK ? ) .

Is the distributor electronic or points & condenser ? Check the distributor cap and rotor .

Any electronic sensors / controls on it ?

Check all vacuum lines / sensors / devices .

As preventive maintenance check the fuel filter .
 
How often is a tuneup supposed to be done on these older engines? I know it's a boat, but on a car of this vintage aren't wires, plugs, and a new distributor cap like a 30,000 mile item?
 
Originally Posted by motor_oil_madman
How often is a tuneup supposed to be done on these older engines? I know it's a boat, but on a car of this vintage aren't wires, plugs, and a new distributor cap like a 30,000 mile item?




That sounds close but stuff will happen. I remember a lot of stories about not being able to get good quality parts back then. Points and rotors for example just didn't hold up. Plugs and wires are usually good for the distance.

On a boat you would have to go by hours. I'm guessing this is used on saltwater? There are a number of things that should be done annually. Check your cooling system as well as your zincs. If you haul it out on a annual basis then this should be standard procedure.
 
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