stinger390

Why though will it run fine above 1600 RPM? Smooth as silk above that, and perfectly smooth idle.

Grn / Red wires are connected correctly. Ground is connected nice and tight to an intake bolt. Rotor is tight on the driveshaft, cap is new. No apparent play in the rotor shaft. Tight as can be.

If it were wires why would all of them be a problem in the trouble RPM range? (all of them have a wierd spark pattern when this happens.) I put my light on every wire on the cap except the coil.

When this happens, the timing mark is going crazy on the timing tab and promptly smooths out at full idle and above 1600 RPM.

This is freaky.

stinger390

Would an incorrect distributor drive gear cause this problem, or would that be throughout the entire rpm range? I think the mechanic used comp cams, and possibly the stock dist drive gears from the thunderbolt distributors but I'm not sure, and can't get an answer to my request for cam information from the guy who put these engines together. Nothing like trying to work in the dark.

stinger390

Found the distributor drive gear extermely worn. Replaced gear with a new one from Mercruiser. Now the same problem starts at 1200 RPM instead of 900 - 1000 RPM.

I took the boat out again and now my WOT RPM is 4100 like the left engine, instead of the 4500 that it was. Timing mark is still jumping around on the right engine until 1600 RPM. Both engines set at 12 degrees base and 32 degrees full advance.

I'm starting to feel like I am spinning my wheels, and getting nowhere fast. I have wasted more good days on this thing and the only positive move forward is ruling one thing after another out. With how worn that gear was I thought that was it.

If the timing chain jumped a tooth or was not set correctly could this problem happen or would it run crappy all the time? I also have been re-installing the distributor on marks that I made from the start. If the distributor was installed from the beginning off slightly and I keep putting it back in the same place could that cause this? How about plug wires cross fireing? Could that cause the timing marks to jump? These are 8mm wires, how likely is cross fireing on thicker wires like this?

The last thing I am thinking is cam gear worn, but that seems unlikely since I think it was new a few months ago. (from what I was told) Comp cams.

I feel like I need to work this out before I put the boat away or it will bother me all winter, and time is running out fast.

Griff

If the dist gear was that badly worn, then I would guess the cam gear is also bad.

stinger390

I think the dist. gear was so worn from previous use. I think when the engine got assemballed a new cam was put in without the dist. drive gear getting changed. The gear on the left engine looked fine and looked like it had been changed.

Isn't the dist. gear supposed to wear out way before the cam gear?

When this problem came on initially it came very quickly. On power up at 1.5 hours (of dock time setup) it was a good and smooth transition all the way up on power. We idled down and picked it up again...no problem. Then again, and all of a sudden the power would stumble from 1000 to about 1600 rpm.

I have not worried about it at first because I thought it was carburation and it always cleared out and ran fine. I just changed carbs for other reasons, and the problem is still there. Now I find it is ignition and am concerned, even though it still clears up religiously at 1600 rpm.

When this happens the tach also drops several hundred rpm and is slow to show higher until the problem clears out, but I figure that is happening because the timing signal is getting so far off for it to read correctly.

formula31

The tach issue has lit a light in my old brain. I know this is far fetched but get a good voltmeter and read whats going on with the 12 vdc on that engine at those rpms. I wonder if the battery or wiring is suspect and the alternator isnt supplying enough in that rpm range? I would check voltage at a few spots, on both sides of the round plug and right at the battery too.

stinger390

I'll check it.

Battery's are new (2) interstate deep cycle group 29's and I run in the "all" position on the switch. Voltmeter on the dash is showing 14 + all the time but it is worth the check for sure.

I'm also going to get new wires today. I think the guy put new ones on, but I'm not sure. There are a few small cracks in spots on some of the wires but they are all pliable and seem to be making good connections, but at this point, it seems to be the last simple thing I have not replaced. I'm also going to get some good spacers and make sure none of the wires touch at all anywhere.

If none of this works, I'm putting it away and will deal with it in april (or let someone else fix it) and give my brain a rest. I'm trying to learn and do things myself which is part of the reason I wanted one of these boats, but I am an amature, and I'm sure this could have been fixed long ago by a pro. I like to tinker, but I am fast reaching my limits of ability, knowledge, and patience.

Gary Anderson

Is the timing mark jumping around or just missing?
If missing, try disconnecting the tach and or kill switch. You may have a short in the "grey wire" circuit.
If it's jumping around, I'm guessing a bad timing chain or gear.
Gary

stinger390

Mark is jumping around very intermintently at full idle, and if it does jump it is not by much.

Crack the throttle even slightly and the mark shifts back to 8-10 degrees and sometimes forward to 14-16 degrees (base is 12)

Open the throttle a little more and the mark shifts back and fourth from about 8 degrees to 14 degrees and the engine starts to run rough and the spark starts going crazy on the timing light on all plug wires.

Open the throttle past about 16 - 1700 RPM and the mark starts advancing normally and the engine smooths out and seems to run fine all the way up. Timing light clipped to all plug wires shows a smooth spark after that.

There is a definete break point in the crappy running. From extremely rough and chugging to like a crack and all is well. Much more noticable under load than not.

Gary Anderson

One other possibility, the TBolt module controls advance by sensing the coil discharge frquency. If you have bad wires/plugs/cap/coil, this can cause a high reading on your tach. Try pulling a plug wire (ungrounded) and your tach will read high.
This may be causing the TBolt to intermittantly cause an advance.
Still betting on bad timing chain/gear.
Gary