OMC 3.0L hard re-startf

[inthedirtagain]

I'm troubleshooting a hot re-start issue with my 1984 Invader 181BR. It has the 140hp 3.0L and the model 400 sterndrive. I've only had the boat in the water twice, so bear with me as I learn this I/O thing. Been an OB guy on my last 2 boats. When cold, the engine starts relatively easily, but I do need to pump the throttle a couple times. It starts, then dies, starts, then dies. Eventually, it will fire up and steady out after a minute or two.

We took it out on the 4th for our first time kneeboarding and tubing with it. I learned not to shut it off because it seemed like the battery was getting weaker upon cranking and cranking. I have verified the condition of the points by checking the dwell. My service manual states I should be between 32-34, and I'm right there. Plugs are new, but I haven't pulled them to see if I'm running rich or lean. Upon de-winterizing early this spring, I set the timing at the recommended 4 deg BTDC, as the valve cover sticker and manual indicate. While there, I also checked the compression (dry) and cylinders 1,2 & 4 were hitting 120-ish psi, while #3 was around 110. This was dry, so compression may have improved with proper ring sealing after warm-up and decent lubrication. Also, my throttle doesn't want to hit a fast idle without engaging the drive. Its got some slop to it and I'm not sure how to clear that up. I've noticed that the factory tach reads a little low compared to my shop tach, about 2-300rpm off. This makes me feel better because the factory tach was reading 4000rpm @ WOT (30-ish mph). I was expecting a little closer to 40mph, but don't care. As long as I can pull the family around. We rarely run it flat-out. Prop is in decent shape and 15p.

So here's where I'm at and feel free to make any suggestions. I've bumped the timing up a few degrees hoping for a little better low-end response. Plus, I've heard the retarded timing can hinder warm re-starts. At some point, I'd like to get the throttle slop taken care of so that I can warm the engine up a little faster in neutral. Right now, I can't get a fast-idle to happen. My book is not clear on the forward controls. I've cleaned the flame arrestor and verified that the choke plate is open 100% when warm. In the morning, I'll check to see that its closed when cold. I'm also going to check the float height inside the carb. Am I missing anything else?

PS.....there is no hesitation when advancing the throttle and pulling a skier up. It idles and runs out nice, with no lean bog.

 

[vinnie1234]

I don't think valve adjustment is your problem, but it does affect the setup of the carb, as more or less valve clearance changes the breathing characteristic. If I was going to fuss with the carb, I would do this first regardless if it helps the problem.

There is a procedure in the manual for setting them, but I find the best way is to adjust with the engine running. Once you have the valves adjusted (whatever method you choose), you can re check compression. you will (should) see a difference. At this point I would look to adjusting the carb, but not before. here is what you do:

~~(Put some rags around the top of the engine, but not on the manifold...this might get a little messy.)
Warm the engine, then shut it down.
Remove the valve cover.
Start the engine.
Back off the adjuster nut on the first valve on the first cylinder slowly until you hear it start to make a ticking noise.
Turn the adjuster back in very slowly until the tick goes away.
Repeat the process for all of the other valves.
Shut off the engine.
Turn each of the adjuster nuts 1/4 turn clockwise.
Put your valve cover back on.
Clean up the mess.

This will change the way the engine idles and it will change the torque curve of the engine. (assuming that an adjustment was needed). You are now ready to play with your carb.

 

[inthedirtagain]

Appreciate the advice, although if I'm going to do a valve adjustment, I'm going to do it by the specs. I've heard of your suggested methodology before, but I'd rather take the time to set the proper gap and rotate the engine by hand to do so. As a former diesel mechanic, I'm not afraid of turning wrenches or tearing into an engine.

That being said, I am planning on repeating my compression test on a warmed engine. If the results dont change, I'll plan on checking valve lash. We've had it out several times since the original post, and with each adjustment, I'm getting closer to how I feel this engine should perform. I found that my choke was not operational, so that has been corrected. The bump in timing took a little off the top end, but gave me more bottom, which is what I expected. I'm more concerned with the bottom end of the rpm range and getting a good tug for the skier than I am running WOT. I appreciate the suggestion. That was one I hadn't considered.

 

[vinnie1234]

Glad to hear your getting closer. The only word of caution I can offer about setting in accordance with the manual, is that if there is any lifter collapse your valves will be maladjusted using the factory method. The procedure described above compensates for that. Good luck!

 

[Scott Danforth]

a hot restart would not be a valve issue. its most likely either fuel or spark.

you already stated you have a battery or electrical connection issue. fix that first. clean all the connections and have the battery tested.
You already stated you have a throttle control issue. I would also fix that.

then check your points, condenser, cap and rotor. replace as required. I would recommend a pertronix module vs points, however that is my opinion. I have had a bad condenser which would give fits when warm. motor would buck, miss, and backfire, sometimes not starting.

then check your fuel. pull the flame arrestor off and see if there is fuel pooling in the carb. if so, you have a leaking needle and seat. if you advance the trottle, do you see the two streams of fuel being squirted. if not, you have an accelerator pump issue.

make sure that the throttle linkage at the carb is in working order. I remember having to repair this twice.

My 1984 OMC 3.0 / 400 stringer would push my 17' boat at 42mph. I was running a 19p Solas stainless prop at 4600RPM Hole shot required someone at the bow. for watersports I ran a 17p

 

[southkogs]

Have you checked your throttle cable to make sure it's working properly? Sometimes they get a little loose or "off" and it effects your operation including idle. Sometimes you wind up looking all over the place for some major problem and it's the stupid cable connection ... er .... well ... I mean, that happens to other people. Not me, y'know?

 

[vinnie1234]

I think you guys may have misunderstood my post. I am not saying that valve adjustment is the issue. I hope that isn't the message that was taken from my post. If I had to guess I would put my money on fuel mixture.

Having said that, maladjusted valves cause a reduction in vacuum during startup due to increased duration from low clearance. The low clearance is caused because - as the valves wear the stem moves closer to the rocker arm. This increases the duration of valves opening, which benefits breathing at high RPM, but inhibits breathing at low RPM, as there is less time for a pressure variance to form between the combustion chamber and the manifold.
Here is why setting up the valves first, makes sense in this case:

The variance in compression that was mentioned would most likely smooth out (and probably increase), providing for a smoother idle once the carbs are sorted. I have seen changes in excess of 20 to 30 psi on a compression test after a proper valve adjustment. In addition the change in manifold vacuum will effect carb settings. If you adjust the valves first, the finished product will be better and closer to factory settings, once the real issue has been solved.

Besides, higher compression and better manifold vacuum sure cant hurt anything.

After setting the valve clearance, I would remove the carb, disassemble, clean and reassemble. You can check all parts at that time, repair as needed and re-set the carb to factory settings. Then you will either have fixed, the problem, or at the very least eliminated fuel as a cause, AND performed a regular maintenance job and improved your performance overall.

 

[inthedirtagain]

I appreciate the efforts to help fix the hot-restart issue. We had it out on the lake the other day and I got the chance to do a re-start scenario. Seems that a slight bump in timing did indeed help the restart. When the kids were in the water, I would shut down so they could safely board. It wasn't an on-off-on situation, but rather, I would let the engine remain off for a minute or two. I would think this would give plenty of time to boil fuel if it were a true vapor-lock situation. In my case, the engine would fire up quickly. I now have a slight bog when moving from in-gear idle to full throttle (think "hit it!") as I attempt to pull up a skier. My guess is that I need to go a tad richer on the pilot circuit. With the family out of town today, I'm going to work on it some more, including: WOT blade position, pump accelerator advancement, float levels, and another compression check. Thanks again for the help.

 

[inthedirtagain]

After a proper warm-up, I did another compression test and hit 135-140 psi in each cylinder. I rechecked the throttle blades and the carb is indeed hitting WOT. The bog is still persistant, but I'm also getting pretty low on fuel, so I'm hoping that a good fuel system cleaner will help out. The idle jets were set exactly where they needed to be, so no help there. If a fuel system cleaner doesn't fix it, I'm guessing a carb rebuild or accelerator pump replacement is in order. Still want to get it out on the lake with my shop tach to see if the dash is truly reading 2-300 rpm off. I would have thought that a 15p prop would spin higher than 4-4200 rpm. The engine doesn't seem to be tired. Mechanical advance on the distributor is smooth, but I don't see a timing mark on the crank pully. Can someone post a pick of theirs?