1974 Chrysler 90 HP Magnapower - Starts then stalls

[theterminator93]

Hi everyone, first-time poster here. Stumbled across the site while looking for information regarding what can be done with an old outboard my uncle has been having trouble with, but doesn't have much time to work on. I'm a Ford EFI guy myself, so these old-school setups with carbs - especially marine engines - are a little foreign to me, but I think I'm a quick study and piston engines aren't anything new to me.

The engine in question is, as I'm told, a '74 Chrysler Magnapower 90, 3 cylinder, 2 stroke. The engine was almost always used at least annually up until a few years ago; attached to what looks like a Chrysler Bass Hunter (based on photos I Googled of Chrysler boats from that era) it ran pretty well from what I recall too. I haven't yet examined the engine personally, but I have been told it will start and run for a few seconds then die. My uncle tells me that he thinks the problem is with the magneto/coil and he is fairly certain it's an electrical issue.

I have done some reading here where I can about this motor in particular and about some similar issues on other engines; I'm seeing lots of references to points and CD units etc. but the terms are somewhat foreign to me. I assume points are contacts in the distributor that transfer current to the specific spark plug to fire it as it rotates, and the CD I understand is a capacitance discharge (coil?).

At this point I'm doing research to try and be as helpful as I can when the time comes for me to head over to my uncle's place to help out with the boat so I'm not totally useless to him. I'm at two points:
1) Anyone have a good read for me so I can get acquainted with the design of these motors, basic terminology etc.?
2) Are there any suggestions/troubleshooting steps to help narrow down this issue I can suggest when I have the motor in front of me? Common issues etc.?

Many thanks for reading - and thank you in advance to any who reply.

PS - if anyone can shed insight into what the boat actually is, I'd appreciate it as well.
Photo at http://i60.photobucket.com/albums/h30/theterminator93/Vacation_07/IMG_0690.jpg

 

[Frank Acampora]

The points are inside the distributor. They should be set to ,014 open on a high lobe.The points do not actually cause a spark. Instead they signal (when open) the CD unit to dump the capacitors into the coil. It is actually a well choreographed dance: The points signal the CD box, It dumps voltage into the coil. Almost instantaneously the coil steps up the voltage and sends it to the distributor. The rotor is at the correct terminal on the distributor cap to let the spark jump the correct spark plug. The usual mode of failure on the CD units is complete. If the engine starts and runs for a few seconds the problem is almost certainly not the CD unit. Probably not the coil either.

Clean and reset the points. Then clean the carbs. Check the complete fuel system from tank to carbs.

Now, some of these engines can be fussy if not started correctly: Pull out the silver knob and advance the throttle handle as far as it will go. When cold,push in the key and hold it while cranking to choke the engine. Once the engine starts, back off the throttle but not all the way. let the engine warm-up for a minute or so before you put the control handle in neutral position. Push in the silver button to allow the engine to shift normally.

A properly tuned engine will, when warm, start in the neutral position simply by turning the key. No fast idle or choking is necessary.

 

[theterminator93]

Thanks for the response Frank. I've been doing a little research here and there about things to do to the engine, along with watching a few videos (including one of yours on YouTube) to try and familiarize myself with how basic maintenance is done on these engines. I feel a lot more confident poking around now that I know what most of the components are on the sides of the engine and how to adjust them. Based on the information I've gathered, I've come up with a little list of maintenance items I'd like to address:

1) Remove and clean spark plugs
2) Check and realign throttle linkages if necessary
3) Disassemble and clean carburetors; check floats and pins
4) Disassemble and clean the distributor; clean/reset the points
5) Check timing and adjust if necessary
6) Check fuel lines for debris or fatigue, replace if necessary and possibly add an in-line filter

If the reason the engine won't run is in any way linked to basic maintenance, hopefully all of this will clear that up without the need to try and track down replacement parts. Hopefully I will have an opportunity to start tearing into this over the weekend.

 

[theterminator93]

Ancient thread, I know, but it has really taken me three years for me to finally remember to (and get around to) going over to my uncle's place to tear into this thing. I wanted to provide an update for posterity and to document the apparent fix.

Removed and cleaned the carbs, checked the floats and pins
Reset/readjusted choke mechanism and throttle butterfly valves
Cleaned distributor cap and rotor
Reset timing

Spark was good on all three plugs. Aside from an intermittent starter solenoid, it still didn't want to start. Suspecting a rich AF mixture (when choked it wouldn't fire at all - without choke it would sputter before dying), I raised the idle screw a bit and it fired up. It starts at idle right away when warm now.

I've got some reading to do about methods to adjust the mixture properly, and reset the idle, but it runs now and I feel like I've gotten over the biggest hurdle.

 

[jerryjerry05]

Glad i's fixed.