Hard starting Mercruiser 165

[kaliona]

Still battling my hard staring when warm issues. I thought it was the carb flooding, but after rebuilding carb, installing a phenolic spacer, and insulating the fuel line, I still get intermittent difficulty starting when warm. One other reason I'm ruling out the carb (after the aforementioned fixes), is that I can turn off the engine either after cruising a bit or idleing through a no wake zone, then IMMEDIATELY (within 2 seconds) try to restart and she just cranks and cranks. No way she could have flooded herself in 2 seconds. Which leads me to my question: Is it possible a bad ignition switch or faulty neutral cutoff switch can be causing my hard start problems? I've changed the coil recently. Points, cap, rotor, plugs all in good condition. I'm frustrated and grasping for any answers. Could it possibly be electrical? When she's running, she runs strong. No missing, no sputtering, quick throttle response, perfect. It's just starting her is hit and miss.

 

[johnkom]

You said, "points." So is it the in line 6 GM engine? Two barrel Rochester?

JK

 

[Bondo]

Which leads me to my question: Is it possible a bad ignition switch or faulty neutral cutoff switch can be causing my hard start problems?

Ayuh,..... With a test light, when it won't start, is there power at the coil's (+) terminal,..??

 

[kaliona]

It is a 1978 I6 with Rochester 2GC.

Bondo I haven't checked power at coil when hard start occurs. Well, I did once, but I didn't connect that problem with all my previous and ongoing hard start issues. One fishing trip, I had just idled out of the marina, hit the throttle to take off, and boat just died. So the engine was not really hot at that point. Turned key to start and it just cranked and cranked as if no fuel. Checked carb, was getting fuel. Then checked for spark at coil by grounding the coil wire, and had no spark. At that point I started wiggling wires and checking electrical connections. Checked under dist cap to make sure everything was ok. A few minutes later had my buddy crank while I checked for spark and to my surprise, got spark. Reconnected coil to distributor and she started right up. Not sure if that helps diagnose my hard start issues. But now I'm curious to see if I have no spark every time hard starts happens. Would that indicate bad wires somewhere in the harness.

 

[998cc]

Hi. I have a 78 GM 250 inline 6 in my Gulfstream and have no problems at all with starting hot or cold. It runs the stock Rochester 2 barrel carb and stock (points) distributor. Since your issue seems to be temperature related, I would focus on the devices/systems that can be affected by it.

1. Fuel boiling in the carb is a concern, but it seems you have addressed that. It seems a high float level could also be a factor when hot.
2. Is your automatic choke working properly?
3. Could the float clearance inside the carb be so close that expansion of the carb body causes it to bind? Very unlikely, but it?s a thought.
4. I have seen ignition coils that degrade considerably when they get hot.
5. Are your ignition points new or in good serviceable condition?
6. Condensers (Capacitors) can become sensitive to heat and could develop an internal resistance or open when hot.
7. Ignition resistors can intermittently open when hot. I have seen this one.

Obviously, you have to ring it out when the problem shows up. When it does, I would:

1. Immediately check the carb for fuel by removing the flame arrester and having someone operate the throttle while you observe the accelerator pump jets for squirting fuel.
2. Fuel yes, still won?t run? Check for spark.
3. Spark yes, still won?t run? Is the spark weak (thin or yellow), or strong (thick and blue)?
4. Weak spark: possibly bad points, corroded connections, bad ignition resistor, bad coil and/or condenser. The latter three devices can degrade when hot. Plug wires good? Correct plugs? Plugs sooty?
5. No spark: Shift interrupt cutout switch sticking open? Binding shift cable holding shift interrupt switch open?

Just a few thoughts.
998cc

 

[Scott Danforth]

IThen checked for spark at coil by grounding the coil wire, and had no spark.

that is not how you check. you get a test light and you go from ground (engine block) to the + side of the coil. if the light lights up, then you have power at the coil. from the sounds of it, you have an electrical problem. top suspects are bad condensor, bad connector or connections, bad ignition switch

 

[Fun Times]

Try connecting the ground side of your test lamp to the battery positive cable. Touch the negative side terminal of the coil while a helper cranks over the engine. The test lamp should blink repeatedly as the engine cranks. No blinking = bad module, pickup coil, points etc. Further testing is required to pinpoint the problem. Blink but no spark = bad ignition coil. Use a known working timing light connected to the high tension coil wire to cap to check for consistent flash then move timing light inductive pickup sensor to a few plug wires looking for a flash as the rotor turns.

 

[kaliona]

that is not how you check. you get a test light and you go from ground (engine block) to the + side of the coil. if the light lights up, then you have power at the coil. from the sounds of it, you have an electrical problem. top suspects are bad condensor, bad connector or connections, bad ignition switch

Yes, I realize that now :embarassed:. I'm going to get one of those HEI ignition tester to check for spark from the coil. Because the test light would only confirm I'm getting 12V to the coil, correct?

 

[harleyman1975]

I thought you had points? HEI is electronic ignition. If you have breakerless ignition then my misunderstanding. Test it like they guys told ya. Save your money for buying gas not parts/fancy gizmos. but that's just me.

 

[kaliona]

Shows you how much I know . Maybe I'm using the wrong terminology. I do have points and I was planning on getting some sort of spark tester (apparently not HEI type) to test for spark at the high tension lead. I will test as you guys suggest with the test light, but if I get 12 volts, I still need to test for spark, right?

 

[Fun Times]

but if I get 12 volts, I still need to test for spark, right?

Having good strong spark is just as important as having good 12v power in all the right places.
Yes you'll need to test for spark as well. The timing light trick I mentioned above just makes confirming that you have any spark at all easier at first glance...A spark tester helps confirm the spark is strong and the correct color should you need to go down that road with further diagnostics.

Bear in mind that it looks like you may have a resistance wire cutting down the 12v power to the coil.
http://www.mercruiserparts.com/selectSerailRange.asp?doc_nbr=165++GM+250+I/L6+1970-1978

 

[harleyman1975]

You gotta start some place so determine that you have power to the right places at the right time then look at whether the parts are working the way that they are supposed to. You can put the spark tester gizmo between the cap and wire or you can just put a spare plug on the end of the wire and ground it and look at how its sparking. either will work as long as you know what your looking for.

 

[kaliona]

Just wanted to put a close to my problem here in case anyone else might have the same symptoms I had. It was the starter solenoid that was bad. I wasn't getting consistent full battery voltage from the wire that runs from the starter solenoid to the coil (+) terminal. Sometimes only 5.7V and sometimes 10.9V while cranking. The contacts in the solenoid were worn and dirty. The starter armature, commutator, and brushes were all dirty, cruddy, and looked like a tired 1978 starter. I'm guessing the warm engine only made it harder for the starter to do it's thing. Replaced it with a new gear reduction starter and she fires up quicker than she ever has (on the driveway with muffs on anyway). Just have to take her out on the water and see what happens. But I'm certain that was the problem. Thanks again for everyone's input. It helped narrow down my problem.

 

[Silvertip]

You may have a bad condenser that breaks down. Coil may also become intermittent

 

[johnkom]

Thanks so much for the closure. So often we never hear the final outcome. As a shade tree mechanic all these stories help diagnose future issues. Thanks again.

JK

 

[harleyman1975]

Yes good luck to you! hope its fixed!