Liberator21

Does this setup have a sputter switch? I've seen those out of adjustment cause exactly what he's talking about as well as stalling.

stinger390

Whats a sputter switch? Is it part of the thunderbolt IV module or distributor sensor? ( I switched modules without change)

Had to order wires today. Coming in tomorrow.

I set the balancer at TDC for #1 today and checked the rotors fireing position and it was fine ( advanced of course but perfect when I rotated the distributor to line up the rotor with the #1 plug wire.)

Tried disconnecting tach / sync, no change. This problem is ever so slightly better after installing a new distributor gear. It used to happen around 1000 RPM now it starts at 1200. The new gear must have tightened some tolerances. It must be somthing like Gary said, loose chain or bad sprocket or both. If that is it, it must be getting slack in this problem RPM range, and tightening above that so it runs smooth.

(you would think a guy rebuilding the engines would install a new chain and sprocket set for the lousy $100.00 or less that they cost.) I would like to think he did.

I'll try the new plug wires, but I'm not thinking that is it. They can't hurt though.

The gear set does not seem hard to change except for getting the balancer on and off. I have never done it, but by the book it looks pretty straight forward. I assume you need a special tool for the balancer on and off though.

What about the valve adjustment tolerances being too tight or too loose? Could that cause problems like this?

formula31

Just theorizing now, but Ive alwasy felt that the oil pump puts enough of a load on the cam gears and timing set to keep them in contact, loaded and not subject to backlash. Especially cold. Could be wrong. I cant see how anything in the valves would cause ignition issues like this.

I think by sputter switch lib21 was referring to the shift cutout switch on alphas.

Liberator21

That's exactly what I was referring to. On the Merc's I've always heard it referred to as a sputter switch. On the OMC's it's the shift assist. When activated, it scatters the spark to drop engine rpm to aid in shifting into and out of gear (at least on OMC's anyway). I've replaced a few on Mercruiser setups. The usual complaint is the engine stalling when shifting into gear.

phughes69

Did you check the dist gear to dist housing gap? Maybe the shaft is moving up and down from excessive play causing the timing to move back and forth. What kind of wires are you using? spiral core or solid core?

stinger390

Clearance on dist gear is less than .010". The wires are Silicone surpression 8mm wires. (gray) Unsure of core soild or spiral but if they were replaced, and knowing the mechanic who put it together, they most likely came from Advance auto parts or Napa. (I did find lots of small cracks in the wires I replaced yesterday so I can't believe they were new this year. Not knowing mych about the different types of wires, both Napa and Advance auto wires could be just fine anyway. When I started working on the engines myself I found the plug wires bundled together and wire tied tightly together in several locations so I cut them free.

I replaced port engine wires yesterday with Moroso blue max spiral core silicone surpression 8mm wires. They seem a big difference on that engine. I ordered a set for the starboard engine (problem engine) and they should be in this morning.
Maybe it will make a difference. I have a hard time believing the mechanic did not replace the timing set when he rebuilt the engines, but anything is possible.

LAKESIDE RESTORATIONS

Just a thought did you check your kill & ign switches??? If the ign switch is worn internally it could cause some grief. Also this is a long shot but did you check for a vaccum leak at the manifold or carb base?? It can give you a bit@h of a stumble off idle if its a small one.. Again, just some other thoughts.. Jamie

stinger390

New rebuilt carbs, 7psi fuel pressure, no problems with carbs. Timing mark is jumping around when this happens.....must be ignition. Spark is also erratic in this problem zone.

Kill switches are disconnected ( I have not got that far yet to hook them up.) I'll check key switches, anything is worth a shot at this point. No neutral safety switches either.

phughes69

years ago my boss was having trouble with the fuel injection system in the race car he owned. The car had a lot of misfiring a high RPM. We finally traced it down to the spark plug wires being to close to the MAP sensor wires. The wires were giving off enough EMI to give the computer a bad MAP signal. We moved the MAP sensor and plug wires away from each other, and the problem was solved. The small crack in the ignition wires you found could be bleeding off enough energy to influence something in the distributor or the wires connecting it.

stinger390

Here is a thought....

I have not messed with the plug wires at all on this engine, or checked them for the correct cap / plug position. What would happen if 1 wire was misplaced on the cap, especially if close in the fireing order?

What if say 5 was on 7 and 7 was on 5 or something on the distributor or plug end? Would it run but stumble at times? When the advance module kicks in would it advance enough to perhaps correct the spark being misplaced?

I did replace the cap but did it one wire at a time without tracing the plug wires to their plugs. I know this is a long shot, and I will certainly check tomorrow, but I'm wondering what the symptoms would be. (stumbling, hard to start etc) It is certainly harder to start than the port engine.

I think I'm fishing but why not throw the wild thoughts out there.