Sporadic inability to start and sometimes restart engine

[Good Trout To You Sir]

Hoping someone can shed light on what has become a recurring problem: unpredictable inability to start cold motor AND sometimes the inability to restart the motor after a break of 15 minutes after use. This is a 2.5HP (E3RC). Problem has become more frequent and more serious coincident with a Seafoam decarb. This motor utilizes a small fuel primer in lieu of choke mechanism. On Saturday after 40 min of operation at variable speeds punctuated by brief stops and restarts, motor refused to turn over after a 20 min break. Here's what I know:
Compression reasonably good -- "wet" compression in cold cylinders about 120 psi. Top and bottom readings differ by less than 5-8 psi.
Just changed plugs - they are proper plugs with proper gap. Good spark.
Fuel primer built into carb is difficult to "feel" for correct operation. Either I overpressurized the entire fuel system or just the carb fuel primer b/c I smelled fuel and could see it dripping out of the cowling. Removal of vacuum tube from the small port on carb top to redirect primer stream directly into carb throat enabled a restart. After I had it restarted I kept it WOT to make my run back to the dock. During WOT, motor seemed to function normally.
Does motor likely suffer from fuel system blockage, air system blockage, air leak, or something else?
How can I rule out possible causes to isolate the issue?
Thanks!

 

[flyingscott]

Could be a leak check the primer assembly.

 

[Tim Frank]

What is your definition of "good spark"?
What do you mean by "refused to turn over"? It would not start, or was seized and would not turn over?

When you say Seafoam decarb, did you mix Seafoam in with the fuel or spray into the carb throat. If the former, the Seafoam may have dissolved/dislodged some debris that is messing up the carb operation.

 

[GA_Boater]

Why did you use Seafoam? How did the motor run before you dosed it?

What Tim asked - How did you treat with Seafoam and what is good spark?

 

[Tim Frank]

Just changed plugs - they are proper plugs with proper gap.

Since you aren't telling us....might as well ask...what plugs , what gap?

 

[Good Trout To You Sir]

Thanks for replies. Not ignoring questions. Just checked forum for first time today. Answers:
New spark plugs: QL86C. Gapped to 0.03.
"Refused to turn over" intended to convey idea that motor would not attempt to start running. Mechanical works never seized.
Seafoam mixed with gas/oil in ratio recommended in engine FAQ post. Why Seafoam? Motor seemed to have lost some power at WOT. Probably incorrect, but I thought it could not hurt. Lots of hours on this motor.
From time to time in the past - and always unpredictably - motor has had instances where it runs fine after short or long running spurts - and then it's VERY difficult to restart.
To rule out blockage of carb port that receives the small primer stream, OK to insert very small wire or cake tester or will that likely cause damage? Thanks.

 

[garbageguy]

Besides the other things to check - Fuel tank vent blockage? Anti-siphon valve good?

 

[tomhath]

Sometimes a warm start (ran then cooled down for a while) makes motors, especially 2-cycle, hard to start.

I always try starting a warm motor without choke/primer first, then half choke, then full. They are easy to flood when warm. Keep experimenting - every motor has its own preference.

 

[Tim Frank]

What is your definition of "good spark"?
.

i.e. How do you test?

 

[Good Trout To You Sir]

Spark test was subjective: grounding plugs and pulling recoil starter at dusk. I was focused on blockage or excess of air or fuel. The most recent event was cured (eventually) when I directed a few drops from primer to the carb throat. Then the motor started and stayed running. Do you believe the ignition system is at issue?

 

[flyingscott]

Use spray carb cleaner to clean out the primer nipple. If you use wire be careful not to break it off.

 

[oldboat1]

A simple tester will allow you to measure spark (determines ignition strength):

You should see about a half inch spark with that motor if the power pack and coils are doing their job. Additionally, see if the motor is running too hot (technically 160F or hotter). Look for an operating temp. of about 130-140F, depending on lake temps.

 

[Tim Frank]

^^^ Exactly.
Really quick and easy test and then you can rule out ignition as the problem. Usually my first troubleshooting step as it eliminates so many items.

It does sound as though a carb R&R with thorough cleaning is in your future.

 

[Good Trout To You Sir]

To the guys with decades of experience with these 2-stroke OMCs, to which online illustrated "how to" sites can you refer me for the PROPER way to remove, disassemble, clean, reassemble, reinstall and tune (slow speed) the carb?
On tuning: carb kits seem to come with insufficient packing material for the slow speed needle. Parts diagram for my motor indicates 3 cork-style packings and 1 nylon style. My nylon packing ring is and always has been missing since I acquired the motor. Since I have a high number of hours on this motor previous to the most recent trouble, unclear to me that missing nylon ring would be at issue. Thoughts?
Oldboat1: Thank you for picture of recommended spark tester.
Re: engine operating temperature and cooling: Is there any recommended form of liquid I could pressurize and push through the system from water tube bottom that may dissolve or dislodge any particulates that may be in cooling passages? I'm thinking vinegar, vinegar/water or some marketed solution.......would such an application cause any damage? I'm trying to resurrect a late '90s 4HP and would like to use a method like this preemptively.
Operating conditions are almost exclusively saltwater. Chesapeake Bay and it estuaries. Water temps can reach into the 80s during summer.
Thanks to all on your time and input!

 

[oldboat1]

I spent a number of years fishing the bay and the Magothy. I'm pretty sure regular fresh water flushing was the routine recommendation. You might try a product like Salt Away, though -- and I would try the vinegar treatment in a barrel (cheaper, and likely effective). Some summers are "saltier" than others in the creeks and rivers, but don't think I heard of that making much difference in maintenance.