4.3 v6 dies after reving

[biteme12]

I have a 1986 Chaparral V6 4.3 MerCruiser, Thunderbolt IV 175 hp..

Serial B579723
Carborater is a two barrel McM 175 3304-9565

Working on the boat I replaced the head gaskets, intake gaskets, riser gaskets, and adjusted valve trains, by taking the slack out of the push rods, then turning the nut one complete turn. Have the timing set 8 degrees. The boat will start up and idol ok. No problem starts right up, after revving the engine it will rev as long as you keep the rpms up then it will die, back off the throttle.
I took the linkage off the carborator started the boat, and manually gave the boat gas, by revving up it still dies..

Please advice

 

[littletoes]

Re: 4.3 v6 dies after reving

Timing??? Tach/Dwell? Then carb adjustment? Its supposed to idle at 600 rpm's, no? My points gap needed to be 19 thou, but wouldn't run right till 20 thou.....just a thought, but your carb might be way out too.....

 

[Cpt D]

Re: 4.3 v6 dies after reving

You might want to adjust your valves with engine running. I usually only tighten half a turn when push rod is snug. You might be too tight with your adjustment.

 

[biteme12]

Re: 4.3 v6 dies after reving

On my distributor i don't have points.As for the push rods i read conflicting opinions about the adjustments some say torque the nuts at 20 pounds other say 1/2 turn some say 1 turn. The lifters don't make noise.

 

[Cpt D]

Re: 4.3 v6 dies after reving

If too tight, the lifters won't make noise. Best method for adjustment is while engine is running. I bet you have valves not closing all the way.

 

[biteme12]

Re: 4.3 v6 dies after reving

If the valves are not closing all the way, then why does the motor sound real strong when I rev the motor.The problem is a soon as I throttle back it dies.Also the choke does not work.Any one have a picture of the same carb I have.But the motor starts up fine when cold.Looks like some one put two screws in the manifold where there should be some kind of choke parts.

 

[BAproject]

Re: 4.3 v6 dies after reving

Dumb though.....shift interrupter switch out of alignment?

 

[biteme12]

Re: 4.3 v6 dies after reving

I dont think so because i disconnected the throttle linkage and manually gave the carb gas and it still dies

 

[Cpt D]

Re: 4.3 v6 dies after reving

Your valve adjustment is very easy to check and worth while. Yes a motor with a few valves adjusted a little tight will rev up just fine (until valves get burnt) and not idle.

 

[biteme12]

Re: 4.3 v6 dies after reving

So is the proper way to adjust the valve is while the motor running.If so what is the procedure in doing this.

 

[biteme12]

Re: 4.3 v6 dies after reving

anyone

 

[biteme12]

Re: 4.3 v6 dies after reving

help

 

[Danny Mc]

Re: 4.3 v6 dies after reving

To adjust valves with eng warm and idling, slowly loosen the rocker nut till valve clatters, then slowly tighten nut till clatter stops, then slowly tighten 1/2 turn ,stop, go to next one till all are done. Key word is "slowly" to do this.

 

[Cpt D]

Re: 4.3 v6 dies after reving

If you don't want the oil mess in your bilge, just back each rocker arm back a quarter to half a turn and try starting again. If it idles fine, you found the problem. Most books say to adjust them just like you did, never worked for me. A little loose doesn't hurt anything, a little tight burns valves.

 

[biteme12]

Re: 4.3 v6 dies after reving

Ok today I ll try what Danny Mc said to adjust my valves.I hope it works.

 

[biteme12]

Re: 4.3 v6 dies after reving

Didn't get time to work on the boat today.Have to wait for tomorrow, and keep hoping it will run right.

 

[biteme12]

Re: 4.3 v6 dies after reving

OK tried with motor running ran a little better but still died when backing off the throttle just not as fast.Is there a way to adjust the valves with the motor not running by turning the motor over by hand and adjusting each valve when they are both closed.

 

[biteme12]

Re: 4.3 v6 dies after reving

help ?????

 

[Cpt D]

Re: 4.3 v6 dies after reving

Adjusting as Danny noted will be the easiest way for you to do it and the most accurate. If you do want to adjust them while not running the motor, follow the sequence the manual states and only go half a turn instead of a full turn. You are bringing each cylinder to TDC to adjust valves?

 

[Cpt D]

Re: 4.3 v6 dies after reving

Another thing I just thought of. How long did you run it with valves not adjusted right? If too long you might already have some burnt valves. Are you sure you adjusted them right with the motor running? You might want to do a compression check.