1988 Mercruiser 165 4 cyl wont start

[Neverenoughboating]

Hey guys, I'm lost. I'm a automotive mechanic by trade. Bought this boat as a fixer upper. I had the engine running but rough. Changed out the carb, ran perfect. Shut it off, now it wont start. Pulled a plug to check for spark and it starts with the plug out of the engine. Have spark and fuel. Compressions seems equal across the 4 cylinders. New pertronix electric ignition, new plugs, new battery, new starter, newly rebuilt carb. I'm got about 11v at the coil, gave it a new 12v hot wire just in case and didn't effect it. I'm lost, any ideas?

 

[alldodge]

Pulled a plug to check for spark and it starts with the plug out of the engine.

What is the compression ?
When it was running, did you set the timing (4 BTDC)?
Firing order 1,3,4,2

 

[Scott Danforth]

did you service the points?

what is the compression? equal across all means nothing without numbers

the lower voltage is because with points you need a ballast resistor or you burn out the points.

 

[Neverenoughboating]

Compression is
1- 122 2-130 3-120 4-120

 

[alldodge]

Compression numbers are good enough and should run

How was the timing?

Wonder where those 470 Dudes are when we need them

 

[Neverenoughboating]

Timing was good. It ran perfect(once) after I put a rebuilt carburetor on. Shut it down to let it cool and hasn't started since.(except with one plug pulled out completely) my only thoughts is it's a defective rebuilt starter. Maybe it's not spinning the motor fast enough?

 

[alldodge]

Could be, but maybe check the ignition

https://itstillruns.com/do-test-pertronix-ignition-7993715.html

 

[Neverenoughboating]

So now I've been messing with everything for 2 days now. I've found that I can get it started and running at mid throttle but then when I try and get it back to idle it dies. I'm a new school mechanic with computers and injectors and suck. Carburetors make no sense to me. What do I have to mess with on this mercarb 2 barrel to get it to start/run at idle

 

[alldodge]

In that case the idle jets are probably clogged up, so it needs to be taken apart and cleaned. Need some fine wire and feed it thru the idle circuits

 

[Scott Danforth]

service the points (in the stickies) prior to doing anything. most likely your gap is off, so your dwell is off, so your timing is off.

file the points, gap the points, verify the dwell, set the timing (and you dont even need the motor to be running to do that)

if you dont understand the principles of a simple carburetor, then can not call yourself a mechanic, as the theory is still part of the first few days in the courses taught on the Otto cycle, long before they get to computers, injectors, etc.

 

[Neverenoughboating]

Ok I clearly understand the principals of a carburetor. Air and fuel mix in a venturi to go into the motor blah blah blah. I get it. Adjustments wise to fine tune it, no clue. And they do not teach carburetora in schools anymore mainly because you don't see them much anymore. I've been a mechanic for over 12 years now. Ford master certified technician so sure I'm not a mechanic. But anyways, don't have points, changed them over to electronic ignition. And the carburetor is clean and clear. Just rebuilt. I'm having trouble getting this thing to idle smooth at anything lower then 1000 rpms. Spec calls for 500-700 I believe.

 

[alldodge]

And the carburetor is clean and clear. Just rebuilt. I'm having trouble getting this thing to idle smooth at anything lower then 1000 rpms.

Trying to be nice, but its not clean and clear, if it was and the idle circuits were clear and then the mixer screws could be adjusted to bring the idle into spec

 

[Scott Danforth]

assuming the carb is clean (not idling below 1000 RPM is number 1 symptom of a plugged idle circuit passage)

with the boat in the water

use a propane torch (unlit) and with the spark arrestor off, lean out the idle fuel mix screws until the RPM's increase just slightly (about 25-50 RPM) when you introduce the slight bit of propane. This is to run the carb just a tad lean which will straighten out when you add the spark arrestor back on. to check, with the spark arrestor on, the carb should richen up and drop about 25 RPM when you add propane to the outside of the spark arrestor

then with it in the water in gear and in open water, adjust the idle speed setting to the 600-650 RPM make sure the throttle cable isnt hanging it up.

however if it wont idle smooth below 1000 RPM, pull the carb back off and chase the idle circuit with a small fine wire or fishing line. if the carb is clean and clear, you should be able to get it to smoothly idle down to 500 RPM