160 to 165 Mercruiser manifolds and backfiring

[Solitude 69]

I am new to this forum but have been operating and rebuilding boats almost my entire life. I operate on Lake Winnipesaukee in NH. I currently have a 1969 Mercruiser 160 inline 6 that is driving me crazy with backfiring under load around 3000 rpm but it is inconsistent. The engine has been pulled as part of a total restoration of the boat itself, a 1969 North American S-19. The lower end of the engine is rock solid with near perfect compression numbers so I had the head redone, installed new oil pump, water pump, rebuilt starter etc.. The engine starts with just a bump of the key and runs on water muffs like it was brand new. The big day for it's maiden voyage finally came and it jumped out of the water like it was brand new but shortly after running a few loops it started with a minor backfire and popping. It still had points and condenser ignition and as a troubleshooting step I put a hot jumper from the battery to the coil. The backfiring and popping stopped and it ran like a scalded dog! At least until the points burned up. I then converted it to Pertronix ignition. Next time to the lake at first it seemed like I solved it but eventually it came back again. I was now thinking a lean fuel condition. I've gone thru the fuel system, rebuilt the carb etc. and it is still happening. I'm now wondering about the intake manifold. It is original to the boat and now over 50 years old. If I wanted to replace it, you can't find any 160 manifolds anywhere but you can find the 165's (Barr Marine). Will the 165 manifold fit the 160 engine and if not, why not?

 

[dubs283]

No idea about the manifold. As far as runnability have you checked fuel pump pressure and vacuum at various load/rpm? Guessing by the ignition system swap the plugs, wires, cap, rotor, fuel filters, timing, etc was all done?

I know they rarely fail but is the coil new?

 

[Solitude 69]

Thanks for the reply Dubs, yes new cap at least twice, plugs, wires. With the Pertronix I put a new Flame Thrower coil in. At one point I noticed the coil getting very hot and thought it might be breaking down. I measured voltage at the + side of coil and was getting well over 14 volts (alternator recharging batt) and thought the high voltage may be causing the coil to overheat. I reinstalled one of the two ballast resistors and dropped that voltage to 11.8 volts. The Pertronix is designed to run at 12 volts. I later put another new Flame Thrower coil in, still backfires. I just installed an in-line fuel pressure gauge just before the carb and I'm getting 3.5-4.0 psi and steady from idle up to 2500 rpm on muffs. I haven't taken it back to the lake yet. I keep thinking back to the time when I put the hot jumper on it and it immediately stopped popping and ran great until the points burned up. Makes me think this is ignition/electrical not fuel or mechanical.

 

[achris]

If I wanted to replace it, you can't find any 160 manifolds anywhere but you can find the 165's (Barr Marine). Will the 165 manifold fit the 160 engine and if not, why not?

It appears to me that the 165 manifold (-58759) should fit the 160. It's basically the same engine.

 

[Solitude 69]

It appears to me that the 165 manifold (-58759) should fit the 160. It's basically the same engine.

Agreed, I'll bet it's the exact same cylinder head. I have reached out to Barr Marine about it. They used to offer a replacement manifold for the 160 but now only offer the 165.

 

[alldodge]

Backfire; Maybe valves not adjusted correctly

 

[Solitude 69]

Backfire; Maybe valves not adjusted correctly

As we speak I'm looking for the cheapest valve cover I can find so I can cut the top out of it and reset the valves. During this whole time I've been struggling with this problem there have been times when it ran perfectly for 30 minutes or so but eventually does it again. I guess I'm waiting for a cold to become pneumonia!

 

[alldodge]

As we speak I'm looking for the cheapest valve cover I can find so I can cut the top out of it and reset the valves. During this whole time I've been struggling with this problem there have been times when it ran perfectly for 30 minutes or so but eventually does it again. I guess I'm waiting for a cold to become pneumonia!

Not saying its your issue, but many have issue with finding zero lash and then the 3/4 turn. Zero is when there is no up/down movement with the push rod. You will be able to still turn the rod but there will be no up/down

For backfire on valve adjustment the valve would have to be to tight, so as it heats up and metal expands the valve isn't fully closed.

 

[Solitude 69]

Good point on that. I pulled the valve cover yesterday and I did notice one of the rocker arm nuts appeared to be tightened down more than the others with more threads showing thru the top of the nut. Could be different length on the stud but definitely going to reset the valves.

 

[kenny nunez]

Make sure that all the studs are the same height. If one is higher than the others it can be driven back down with a brass drift and a suitable hammer.
Then re adjust the rocker arm.

 

[Scott Danforth]

Did you service your ignition?
Set dwell with a meter

 

[achris]

Did you service your ignition?
Set dwell with a meter

What??!? You need special tools to set up points and carbs??? When did this happen?

Chris....

 

[dubs283]

When did this happen?

Before you (and i) were born

I have a cute story about my dwell meter acquisition, if you ask nicely I'll share

 

[dubs283]

OP: as mentioned you need to check/adjust valve lash. I kinda figured you did this already but my faux pas for assuming such.

FYI myself and others here have had issues with electronic ignition upgrades. Aftermarket sellers give all kinds of info/advice about external components regarding their products. Best is to stick with oem (points) ignition. It's the specific design your engine was manufactured for

 

[Bondo]

Before you (and i) were born

I have a cute story about my dwell meter acquisition, if you ask nicely I'll share

Ayuh,.... Will ya P l e a s e tell us yer story,..??..??

Myself, I had an ole analog dwell meter for years, til I loaned it out,.....
I since bought an Inova digital timin' light, that has a dwell mode included,....

 

[Scott Danforth]

I have the dwell meter my father had when he went to high school. It is older than I am.

The meter I had since I was in high school got damaged when the cables got pulled into the alternator belt 20 years ago

 

[alldodge]

I still have my dwell meter from back in the 70's

 

[achris]

When did this happen?

Before you (and i) were born

My comment was a subtle (apparently TOO subtle) 'dig' at people who complain about having to have special tools to work on 'electronic' engines (EFI etc).

I since bought an Inova digital timin' light, that has a dwell mode included,....

Same. I think I may still have my old analogy dwell/tach somewhere. Also from the 70s.

have a cute story about my dwell meter acquisition, if you ask nicely I'll share

Please, with a cherry on top, tell us your cute story.

I myself and others here have had issues with electronic ignition upgrades. Aftermarket sellers give all kinds of info/advice about external components regarding their products.

Back in the 80s I built a kit CDI for a points system in an old car. It worked so well that I built another for the boat. It retained the points, used them as the trigger, so in the unlikely event of failure switching back was very simple (I even put a switch on the side of the enclosure to make it that much easier). System worked remarkably well, and never did fail. And when I say 'built', that included winding the transformer and etching the board! There's still reference to it on the web, it was called 'Scorpio II ignition system'...

Chris...

 

[nola mike]

My comment was a subtle (apparently TOO subtle) 'dig' at people who complain about having to have special tools to work on 'electronic' engines (EFI etc).

Carb special tool: screwdriver, $1
Points special tool: dwell meter, free from your dad
EFI special tool: Rinda, $500 (plus adapters if you want to work on a different engine)

Yeah, pretty much the same thing

 

[Scott Danforth]

Back in the 80s I built a kit CDI for a points system in an old car. It worked so well that I built another for the boat. It retained the points, used them as the trigger, so in the unlikely event of failure switching back was very simple (I even put a switch on the side of the enclosure to make it that much easier). System worked remarkably well, and never did fail. And when I say 'built', that included winding the transformer and etching the board! There's still reference to it on the web, it was called 'Scorpio II ignition system'...

Chris...

I was burning and swapping e-proms in the 80's, sending ECM's to tuners in the 90's, I built a mega-squirt system about 20 years ago to replace a Holley DFI unit that was going south. Did an 032 motor sports EFI setup a few times. got tired of "specialty" low production hardware and having to buy different software and hardware for every other project

get the most pleasure out of digging something out of a barn or garage after 50 years and getting it running with a fingernail file and a screwdriver

regardless of what you are tuning or playing with. still need to be able to read the plugs, measure fuel pressure, use a mechanics stethoscope, and most importantly, feel how the engine is running and smell the exhaust. that slight shudder and acrid exhaust smell when you take off and are running rich. that slight raise in temperature and rattle when running lean. The un-mistakable sound of valve float and pistons hitting the valve heads at 8000 RPM just before the rods come out the side of the block as you coast across the lights on your best run ever.

@Solitude 69 , sorry, however it seams we have all hijacked your thread.

Back to topic.

your fuel pressure is good

the 160 and 165 motor are both a GM 250 cubic inch inline 6

the pertronix kits have been known to fry coils. just search pertronix here on iboats.

however the backfire and poping is either the motor running lean or the pertronix pickup shifted on the dizzy plate and you are now out of time.

your issue does sound like timing.

one thing to check. the inline motors tend to eat the distributor bushings. these little $8 bushings from NAPA wear out after a few years and the dizzy shaft flops around a bit. check if your shaft wiggles. if it does, its a 20 minute job to fix. just knock out the roll-pin in the dizzy gear, pull the gear, then pull the shaft out of the dizzy body and replace the bushings