Logo
FULL SITE MENU

Need help with Mercruiser 165 hp inline 6

R

rb21654

New member
I have a mid 70's 19 foot Fiberform boat with a inline 6 Mercruiser 165 hp engine. Took boat out of storage and was going to change oil and flush weatherization fluid. Started engine and had let it idle for about 15 minutes. Idled just fine.

I went to advance throttle and rev it up a little and after about 30 seconds at a little higher rpm engine quit. Tried to start it up again and it would start but then quit running. Tried starting it several times and every time it would start but not run. So I took a spark checker and connected it inline to all spark plugs and spark plug wires and would get spark on all plugs initially at start up but then would loose spark.

Don't think it is a fuel problem because when I advance throttle I can see fuel being squirted into throat of carburetor. This engine is equipped with a Mallory 540 Breakerless ignition system. I have checked all connection and they appear to be good.

Any help would be much appreciated.
 
Start w/a visual inspection of the ignition components...look under the dist. cap; it may have moisture in it. Check all of the wire connections fo corrosion and tightness. Does the Mallory 540 ignition still use the mechanical advance? Inspect it also. Pull the spark plugs; replace if needed.
 
guyjg, thanks for your responce

Prior to starting this thread I did do a visual inspection of the wiring, distributor and cap.
Found quit a bit of rust on the mechanical advance components. Also a lot of rust dust in cap. Cleaned all rust from mechanical advance components and cleaned cap. I reinstalled cap and still same problem. I get initial spark on start up and then lose spark while engine is still rotating from initial start.

Spark plugs and wires are new. They were replaced last year prior to winterizing and storing for winter. Was wondering if I have and ignition switch problem? Mallory 540 ignition system has two wires from control box that goes to sensor wires coming from distributor, a red wire that hooks to + terminal on coil, a green wire that goes to – terminal on coil and a black wire that goes to ground. All seem to be tight and no corrosion. Have not checked gap between high point of cam and sensor. Paperwork for system says it should be .008 gap. Have not checked voltage at + terminal of coil to see if I have voltage after releasing switch from start mode. Will maybe do this tonight.

Don’t understand why I would get the initial spark at start up and then loose spark after it starts.
 
disconnect the tach lead to the neg side of coil. Also find the shift interupter swich, one wire should also be going to the neg side of the coil. disconnect this also.

Now retry and see if you loose spark. If there is a cable/cable adjustment issue you could be activating the shift interupter. If the tach is bad it could short out the ignition.
 
If the engine harness is original, checked for the reduced B+ (8-9VDC)on the "+" side of the coil...if if is present during cranking but not with the key in the "RUN" position, check the resistance wire.
 
Check the weights, they moving freely. Wobble in the shaft maybe.

The points gaped correctly ? Rusted maybe a couple of pulls with fine sandpaper maybe.

You cleaned the wire connections on the coil etc.

The main ground wire cleaned. I ran a ground wire from my coil to the block.

Me i would run a switched wire straight to the pos side of the battery and pos side of the coil. Called a jumper.

Flip the switch you got power straight to the coil, how's it running now.

Turn off keyswitch flip the jumper switch and the power is off to the coil. This is just for testing purposes.

However i have known people who left it on and have the switch at the helm.

Not that i recommended it just sayin.

Disconnect the battery follow the cables clean as you go, and pull the main barrel plug and see if it's corroded inside.

Merc didn't use a resistance wire. Omc did.

Post back !
 
Last edited:
Here's what I came up with for the 540.
Does this look like your ignition distributor???

This uses electronic triggering..... whether Photo-eye or VR, I'm not sure, but the three wires (red, green and brown) tell us this.


Since you mention Mallory offering a gap dimension, this is very likely VR (variable reluctor).

DO NOT use a metalic feeler gauge to check the gap between the sensor and reluctor points/tips.


rb21654 said:
Don’t understand why I would get the initial spark at start up and then loose spark after it starts.
Click to expand...

Look to see if this uses a "Start-by-pass" circuit.
The SBP circuit provides full 12 volts during cranking only, and lets go imediately upon starter motor disengagement.
If the normal ignition circuit is faulty, this may explain your issue.

Could be a bad ignition switch... could be a bad ignition circuit.
Pull the engine harness/hull harness connector apart. Your ignition circuit is in this harness connector.




.
 
Last edited:
RB21654 the reason you are getting Spark at Startup then NO Spark, is because on Startup there is a direct wire that sends FULL 12V to the Coil to aid in startup through the Wires going to/from the starter this is to give a boost to the coil while the battery is under load and Voltages are low, then when you release the key the coil gets 9V through the resistor wire coming from the altenator if I'm not too mistaken. Some after market electronic ignition systems let you run direct 12V from the key-on position to the ignition system. That's what I did with my pertronix, need to make sure if the engine is off, the key is off else you can burn out the coil ( i think ).
 
Last edited:
Thanks everyone for all the advise. I will check these things out. My job is taking me out of town for a couple of weeks so won't be able to check these things out till I get back. When I resolve the problem I will re-post and let everyone know what I found out, again thanks for all your help.
 
mallory 540-2.JPGWas able to get back to working on my boat. Checked all the things everyone suggested and all check normal. Knowing the Mallory 540 ignition control is outdated and Mallory does not sale them any more, was able to find a new one on ebay. Bought it and put it in this weekend, and engine runs fine. Starts every time, idles good and throttle's up fine without dying. Thanks to everyone who commented to this thread. Off to do some fishing.
 
Back
Top