No fast idle/Low compression on 1 & 3

[NYBo]

US Marine control box, flush mount, original to the boat. Among other problems, I find out that the fast idle setting on the control box doesn't advance the throttle at all. Is there an adjustment for this?

One of those other problems I discovered was that somewhere along the way, the throttle and shift cables got switched but the boat operated fine. How is this possible??

 

[Frank Acampora]

That's why you have no fast idle. The cable ends are specific to throttle and shift.

Go to the top of this forum and watch the videos. also read the sticky on synchronizing timing and carbs. Do a compression check on all cylinders

If (for whatever reason) The idle stop screw is in too far, then there will be no room to advance the throttle for fast idle. Correctly setting the carbs and timing then setting idle will solve the problem.

 

[NYBo]

Yeah, that also explained why the starter wouldn't engage when I tried to use fast idle- it was moving the shift mechanism instead of the throttle. :facepalm:
I'm still surprised I was able to use the boat with the cables switched.

Since the motor was running last, I've swapped out the trigger, CD modules, and stator chasing down a spark problem, so the timing is definitely in need of adjustment. I was dreading hearing I needed a new control box. Frank, thank you!!

 

[NYBo]

Do a compression check on all cylinders.

Carp. 50-125-50. I guess my next question is which is easier, swapping powerheads (assuming I have good compression in my spare motor) or the entire motor except the transom bracket (current motor has power T&T, spare does not).

 

[NYBo]

BTW, those numbers are with the motor stone cold since I can't get it started (no surprise there). The motor ran perfectly last year for about 1 1/2 hours. I idled down to wait for my turn to load at the launch ramp, and it died and couldn't be restarted. Seems strange to me that this would have led to the compression problem of two cylinders being at 50 with the one between them being at 125.

 

[Jiggz]

Try squirting some fuel oil mix into each low comp cylinder through the plug hole and test for compression again. If numbers are the same, remove head and inspect for leaks, gasket and rings. If problem is on gasket, it is much easier to replace that than swapping heads. Or if the piston rings have problems but cylinder is usable, then it will be better to replace piston and rings than swapping heads. Of course that is all my personal opinion.

 

[NYBo]

Thanks, Jiggz. I'll give it a shot and report back.

 

[NYBo]

Jiggz, how about SeaFoam instead of fuel mix?

 

[Jiggz]

Actually fuel/oil mix will be better since the purpose is to un-stick what could be a stuck ring. Seafoam has a tendency to de-lube and could do more harm than good for now.

 

[NYBo]

Thanks. I'll use fuel mix.

 

[NYBo]

No Title

Tried using fuel mix. No improvement so I pulled the head. It's a little hard to see in the pix, but there is a distortion at the edge of the 1 and 3 pistons at the 11:00 position. Also, there is some little hole in piston 2 at around the 1:00 position although this cylinder had 125 PSI compression. Everything looks suspiciously clean.

 

[Jiggz]

No Title

The ding on the two pistons is actually a result of broken damaged rings (got caught on the port lip). I'm not really sure about the little hole on #2 or if it is even a hole or could be a scar. Using a fine wire does it go through the piston? The next step is to assess the cylinders to see if they are still usable. Usually, scoring or gouging can result from the broken rings. The general test is to ran your finger nails through it and if it barely catches or better yet doesn't catch, then most likely the cylinders are still usable.

I can barely make it but it seems the "1" is stamped on the pistons signifying it is still the standard bore. If the cylinders are usable, the next step is remove the pistons and rods through the intake opening. Dismount the carb, remove the intake adapter and reed block. From here you can remove the two bolts holding the rod cap bearings. (Make sure you place a rag or white cloth to catch all parts. Do this before starting the work). You will need a 12 - point 1/4" socket with an extension to do this. Use your digital camera to have a reference to put things back together. Note the orientation of the rod and also the piston.

After piston removal, post pics of the cylinder if you are not sure if it is usable or not. I posted a dinged piston showing how the damage on the piston crown happened being pushed up by the broken rings which got caught on the ports. The most likely cause and as indicated by the clean piston crowns is lack of lubrication. Either the engine was ran without proper oil mix, lean fuel setting or overheated. My money is on improper fuel mix or lean fuel setting as indicated by the clean crowns.

 

[Jiggz]

Things to note if you decide to replace the pistons:
1. Place a rag or cloth below the carbs to cover the leg hole and catch falling parts and tools
2. Do not use magnet to pick up the roller bearings, instead use a geased stick or screwdriver
3. Some of the gaskets in the carb, intake adapter and reed block can be re-used if saved or undamaged.
4. The head gasket if not damaged can also be re-used
5. If cylinder is usable, hone it first and measure before ordering pistons. Highly recommend using Wiseco piston with their wrist bearing kits. You will need an hydraulic press to remove the old wrist pins but not on the new ones. You will reuse the piston rods and associated bearings.

 

[NYBo]

Not what I really wanted to hear but at least I've got a plan of action. Thanks again.

 

[NYBo]

UPDATE: Well, I have 125 PSI in all three cylinders, no piston work required. How? I switched to my spare motor, which was actually the one that came with the boat. I didn't want to mess with removing the power T&T from the bad motor, so I removed the tilt bolt (?) from the transom brackets and swapped the motors that way. Of course, I had to switch the T&T harness and relays to the other motor, in addition to several parts I had previously swapped. Imagine my joy when the motor started in less than 5 seconds! Now, to the river!!:whoo: