78 Chrysler 105 runs 3 seconds...backfires and dies

[SSSuper83]

Just picked up a really nice 78 Conqueror with a 105. Before purchase, we started it in a barrel and it ran great.

Get it home and all cleaned up, and it starts, but runs for 2 to 3 seconds and backfires HARD. Kills it instantly. Suspected bad fuel, pumped and cleaned entire fuel system, refueled with sta bil and fresh oil and gas. No change.

Definitely seems to me to be ignition related. This has the Motorola CD and breakerless distributor. Engine has approx 40 hours on bare block rebuild with shop receipts to prove it. What I am asking here is where do you guys think I should start...

Has surface gap plugs, and original wires. Doesn't appear anything is grounding out. Made new rubber mounts for the CD box as they were dry and falling apart. Boat was on Lake Michigan twice in the last couple years since rebuild. Does the photoelectric eye that triggers the ignition possibly be at fault here? Any way to clean them? Or test the CD unit? Does this sound like a problem related to the archaic electronics and if so, I have read about the conversions people have done here and that's also possible.

Just don't want to waste time chasing the wrong thing first as here in Chicago, boating season is about a month long now haha!

 

[Frank Acampora]

Running then backfiring and stopping USUALLY is a fuel problem. That is why I recommend removing, disassembling and cleaning the carbs. However, the Motorola ignition, while usually reliable can fail in some puzzling ways. I have had a couple go by losing an internal transistor and putting out constant spark. The electric eye has no known test. The only thing to do to test it is to replace with a known good one.

One simple test for your black box: Remove and ground the top plug. Turn the flywheel by hand with the ignition on. The plug should only fire once as you pass its firing point. If it fires multiple times--BZZZZZT-- the CD unit is bad. Also examine where the ignition wires pass under the flywheel. Often they will rise and touch the flywheel rubbing off the insulation. Then, when the vibration from starting or running makes the touch again. they short and stop the engine. The circuit breaker will pop and need to be reset

The Conquerer is a nice boat with a cult following. There is one show on the history channel called "Flipping Ships" The guy has a boat restoration business called "Boats Have Souls" He has a restored Conquerer BUT horrors of horrors--he has a Mercury on the back!

 

[batman99]

If backfiring / spitting gas backwards "out the carbs", then remove / inspect factory read leafs while its carbs are being cleaned. I installed CCM fibre reed leafs (available on ebay) on my previous Force 120 engine - during its last carb cleaning task. Their plastic reed leafs and threadlock glue (for their screws) worked great. Hope this helps...

 

[SSSuper83]

Thanks guys. I will admit, Frank, that I was in a hurry and did not completely disassemble the carbs. One split choke plate spring was broken, installed a new one on top carb fixed that but I knew it wasn't a contributor to the problem. I will pull both off and clean. I just did the same thing to my Yami sled last fall and it made a world of difference. I was in a bit of a hurry Memorial Day weekend and time to pull back.

Frank mine is a 16 footer with all original interior fabric. Last owner had all the old fabric off and reinstalled new wood and foam under the front bolsters and rear bench. Then reattached everything. Hull is beautiful.

I will pull both carbs off and rebuild. Cheapest and easiest way to start. I will post pics of this boat as soon as I can. I get compliments on it at gas pumps on land. Never expected that.

Thanks again. I will report back shortly.

 

[SSSuper83]

And I will do my damnedest to keep the great white hope on the back!

 

[SSSuper83]

Frank, the complete carb cleaning did the trick. Starts and idles without sounding like it's going to launch a piston into the neighbors house.

I noticed on the factory tach it's idling around 1200. Needs to be at around 800 from what I have read. Should I try to work the idle out with mixture screws before I adjust any linkage here? I manually backed off the roller cam for the throttle and it came down quite a bit. Any tips on lubing the contact points and should there be a return spring anywhere to return the engine to idle?

I am ecstatic that she runs. Now the OCD in me wants it to be perfect.

 

[Nordin]

If it idle 1200 rpm on muffs in the drivway........ thats correct. It will be 700-800 rpm in water.
Air/fuel mixscrew set about 1-1 1/8 turn out from seated. The idle might be a bit rough then if it is set 3/4 or leaner. BUT leave it at 1-1 1/8 if not........you might melt pistons.

 

[Frank Acampora]

Watch my video on the top of the page on synchronizing carbs and timing. Unless you set everything back to a zero point you will never get a good idle. Start with setting the roller and cam so the roller just touches the cam at the line at a tangent with the carbs fully closed. Then set the cam using the ball link so that the carb butterflies are horizontal at wide open throttle.

Next, set timing at wide open throttle to 30 degrees BTDC. With the Motorola ignition you can do this simply by turning the flywheel by hand and watching the top plug spark. A timing light is not necessary.

Start with the carb low speed needles set to 1 1/4 turns out. Under no circumstances go leaner than 3/4 turn out from lightly seated.no matter how it idles.

Idle speed is set in the water in forward gear to 700-750 RPM. Idle speed is regulated by the idle stop screw on the bottom of the timing tower. Screw in to raise idle, out to lower it

 

[SSSuper83]

Just wanted to update as I got her in the water yesterday. What a great running boat. Just have to get back used to what an old outboard likes since I have had stern drives for years. This old motor has legs for sure...it's a bit sluggish on the low end but barely noticeable. Once you get into that timing curve though...WOW it pulls like a freight train! It really surprised me. Thanks for all your advice on fuel system, etc.

I can't believe also how good it's manners are around the dock. No dying, shifting problems, etc. Previous owner knew what he was doing with the rebuild and the set up of everything that's for sure. Gotta give him the credit.

Now one thing...this boat has an original temperature gauge. Chrysler labeled. It isn't working though and I'm sure it's something simple. I'd like to get going ASAP as it's just more insurance. Also tach reads about 1000 rpm high...I know for a fact that it's not buried at 6 grand at 20 mph and half throttle. Any connections on the engine I should look at to double check?

I'm so impressed with this thing it's not even funny. And no less than 4 people complimented me on it, land and sea!

 

[Frank Acampora]

On top of the head will be a sending unit. This unit goes to ground and its resistance varies with temperature. The gauge is attached to the switched 12 volt source at the switch ("I" or "A" terminal.) The other wire goes through the loom to the engine terminal board and then to the sending unit. As resistance decreases with heat, more voltage flows through the gauge and it reads higher. Look for corrosion on all the wire connections. If all that is good, remove the gauge and test momentarily with 12 volts. It should go off scale.

As far as the tachometer, it is a 12 pole tach and if not Chrysler it should have a switch on the back. Be certain the switch is set to 4. I have not seen too many Chrysler tachs and am not certain how they account for different pulse rates. If Chrysler, you may need to use the purple wire off the voltage regulator for signal.

 

[SSSuper83]

It's a Chrysler tach Frank. I will peek under the dash tomorrow to take a look as I have a trip planned sat and want both to function properly. I know the ignition was replaced recently and I assume that's what you meant by one wire running to the switch.

I have a lot of work to do tomorrow as far as cleaning so thank you AGAIN for the advice and I'm sure we will get her sorted out. Your a treasure trove of info Frank. Much appreciated. Once I figure out how to resize iPhone pics I will be posting them.

 

[Frank Acampora]

NO! The tach will have one wire from power terminal attached to the "I" or "A" terminal on the switch, a ground wire, and a signal wire from the engine. I have seen Chrysler tachs with only two wires, a black and white and I suspect these are for magneto ignition engines. I have never used either one.I always use Teleflex tachs.