70s Chrysler 16hp outboard funny runner

[EJD83]

Picked up a 70s Chrysler 15hp ob engine. Smokes heavy at idle and runs rough in low range and skips mid range to run like heavy open throttle if i roll into the throttle to keep it running. It's either running rough at low range or tries to take off...no nice transition between the two. Where should i start to look?

 

[440roadrunner]

My first thought is carb gummed up and way out of adjustment. Personally, on any "new" (ley acquired) engine, a thorough tune up and compression / leak down check is adviseable.

 

[jerryjerry05]

Sounds like it's sucking air somewhere?
Do the starting fluid test: start the motor, spray SF around the intake side, if spraying makes a difference? then it's sucking air somewhere.
Possible the fuel pumps diaphragm needs eplaced?
Excess smoke: the motors been setting and the gas/oil that's been setting or introduced into the motor, the gas has evaporated and the old oil is being burned and show up in excess smoke.
Once it's ran for a while the smoke will slow down(some).

 

[topgun3690]

If unknown when the impeller was last changed you might want to do that first.....if it goes then anything else you do won't matter....found out the hard way a long time ago.

 

[EJD83]

Ok ill probably start with the carb clean and then leak down check since I can do that without firing it. What is the proper procedure for leak down on these engines and what result should I be looking for?

 

[Samu_el]

I redid my 1980 Sea King 15 Horsepower with the impeller, fuel pump, and cleaned carb. Mine’s does that hesitation and then jumps to heavy throttle too. I think that they must all run like that. I bought a carburetor from allstrand marine I think and it was supposedly new or rebuilt. It looked clean upon arrival and I shakes it hearing the needle rattle around so It seemed good to me. It didn’t help. Currently I am running my original carb just in case that new one isn’t giving me the right 15 horses. The original carb’s needle is a bit worn and rounded but no difference I can see between the carbs by performance. I took my boat out today and it ran flawlessly except for that throttle hiccup jump you speak of but I live with it. 17-18 mph is my top speed on a 10.8 inflatable HydroForce boat

 

[jerryjerry05]

Don't worry about a leakdown, just do a compression test.

 

[EJD83]

I pulled the carb (tillotson co-10b) off. The only thing I wasn't sure about was what the diagram calls a bypass tube (merc/ quik # FO15522). It seemed odd to me...the bottom end was squeezed half shut and the top end extended past and was more or less squeezed against the narrow diameter end of the idle adjustment screw. Anybody familiar with that and its function and if that might explain anything related to original post?

Edit: meant to mention that the engine is a 152h8d.

 

[jerryjerry05]

Don't remove the tube.
That description of the tube is normal.
Just make sure it's clear.

 

[EJD83]

Don't remove the tube.
That description of the tube is normal.
Just make sure it's clear.

Wellll....I already removed it assuming something was wrong with it since it wasn't cylindrical at the bottom (looked half shut). Now it's completely squeezed shut, of course. I removed the main nozzle to get a good look at it and pretty much as soon as I started turning the flathead screwdriver the slotted end of the nozzle broke. Did Imake a rookie mistake?

 

[EJD83]

Thanks for the tips so far all and I apologize for potentially killing an exceedingly rare piece of the Chrysler OB family, all in pure rookie haste. Lesson learned. I haven't been able to find replacements for the main nozzle or the tube...all websites I've searched show them as no longer available. Does anyone have any suggestions on where to go from here?

 

[Nordin]

Try Franz Marine service