Engine stumble when adjusting trim

[1979 Quartermasters]

Hey people. Tested my boat last weekend with new carb, 1409 Edelbrock ( as discussed in another thread at length) and it ran flawlessly. No flat spots, stumble or beats missed. Only thing is, when cruising, if I adjust the trim, the engine stumbles and my gauges freak out. Is this related, or another issue. I did wire the electric choke from a purple wire and a black wire that were laying on the intake taped up.

Thanks,

Ken

 

[scoflaw]

I'd be looking at the health of the battery and the charging system

 

[Bt Doctur]

and all the cable connections

 

[alldodge]

Go to the starter post, remove the wires, clean and reinstall, do the same at the battery and the ground. The trim pump is connected to the starter post

 

[Bondo]

Ayuh,..... Clean the Ground connections, from the battery post, all the way to the ignition, 'n trim pump,.....

 

[1979 Quartermasters]

Will do! Thats awesome you guys all agree.

Thanks.

 

[1979 Quartermasters]

Well, after cleaning and testing many electrical connections, still stumbles and misses and backfires at higher RPMs. So, I was thinking, what has changed. Only thing is the carb. Now this doesn't act like a carb issue, so I unplugged the wires on the choke and the old girl was back. Hit WOT easily and running all through the RPMs with no issues. Also the trim was not interfering with motor. I would like to have the choke, so how would I correct this issue. I believe the power for the choke comes from the coil.

Thanks,

Ken

 

[alldodge]

Think you still have a bad connection, and maybe inside the 10 pin motor plug. Removing wires off the choke reduces the current draw a very small amount. The amount is probably just enough to keep the voltage high enough to keep the coil firing. The coil and everything else on the motor gets its power from the purple wire coming from the Key

 

[Lou C]

That may be your problem (wiring the electric choke to the coil). In fact for some electric auto chokes it specifically says in the instructions not to wire to the coil, because it may not be a 12V source and can lower the voltage to the coil and cause some of the problems you had. You might try wiring the choke open so it does not close and disconnect the wiring and try it again. If it does not act up then that's your answer. I recently installed a Holley 4160 on my engine but wired the coil positive to the AC tap (P terminal) on the Mando alternator. The choke works great and it does not affect the ignition at all.

For the choke you need a 12V source that gets power only when the engine is running, not when the key is on and engine off, or when everything is off.

 

[alldodge]

not when the key is on

Just a point of clarification; Most boat keys have 3 positions, OFF/ON/START. So the key on mentioned position would have a 4th position known as ACC (Accessory)

 

[1979 Quartermasters]

Well guys, thought I had it fixed. Ran great for two days, then when coming home from fishing it started missing around 3200 RPM, then gradually got worse. You guys still think its a ground issue, or could it be a coil?

 

[alldodge]

Well guys, thought I had it fixed. Ran great for two days, then when coming home from fishing it started missing around 3200 RPM, then gradually got worse. You guys still think its a ground issue, or could it be a coil?

If you were not adjusting the trim, and this was happening just running, then it could be fuel or electrical.

I would check fuel pressure

 

[scoflaw]

What's your charging voltage at ? Trim motors can pull volts down by quite a bit. Your batteries could be tired also

 

[1979 Quartermasters]

Battery is 12.6 and. charging at 14.6

 

[1979 Quartermasters]

Still having this problem. Had battery tested and its 100%. Something I noticed today, is that the trim gauge usually goes to the half way point of the gauge where the limit cuts in. I'm noticing it only 1/3 of the way now. Could this be a symptom of the problem. Today It ran nicely for a couple of runs. When I shut it off and restart it, it begins to run poorly. Firstly with a small miss you can barely feel, then it becomes worse as you try to get back to the dock.
Hope I can find this problem soon.

Ken.

 

[1979 Quartermasters]

Could this be the coil? How would I test it. Still wondering if that trim limit change could be part of this.

Ken

 

[alldodge]

Doubt its the coil, but may be a tach starting to go. Also doubt its the trim gauge, it just gets 12V on one side and a resistor mounted on the gimbal to provide a reading. If it was shorting out it would probaly blow the 20 fuse and all the gauges would go out

 

[1979 Quartermasters]

I guess I'll keep looking for a bad connection.

Thanks

Ken

 

[1979 Quartermasters]

Hey Guys,

It has been suggested to me that maybe the trim senders are culprit. How would I test these to make sure they're not the problem.
Didn't get a chance to work on it last weekend, but I would like to solve this issue. Have starter connections and trim connections to clean. Did battery, main ground on block, ignition switch and coil. Hope I find it soon.

Ken

 

[alldodge]

You can take the trim limit and gauge sender out of the mix by disconnecting them. Unplug the gauge sender, and take the limit leads going to it and connect them together. Could also unplug the limit and just use the trailer up to bring drive up for trimming