Rpms go wild above 2000rpm?

Bryanttttt

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Hey guys,

New here. Appreciate the help..
Picked up a 1986 Bayliner Trophy cuddy with an inboard Volvo Penta AQ125 (I believe).
Everything works perfect up until I try to go over 2000 rpm. Then the RPM gauge goes bonkers.

I went through all the effort of trying to locate a bad connection etc... Ended up running a new signal wire to the ignition coil and direct connections to the battery.
​No difference.

​​Installed a new tachometer, no difference.

Replaced the ignition coil, no difference.

So due to not being sure where my rpms were, I didn't really push the boat beyond the wacky zone. I've taken it out multiple times just slowly (about 7mph) with zero issue.
I'm now at the point I want to take it out to the islands and need to make sure this is resolved and I can also push the engine.
When I tested it, I would push the boat further into the zone where gauge goes bonkers without feeling any difference in the engine.
Wasn't until today that I replaced ignition coil that I feel like I can feel the engine running differently when over 2000ish.

Any suggestions as to what to look for?
From. What I know, previous owner replaced the alternator and spark plugs shortly before I bought it from him.
 

alldodge

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Howdy
Check the power and ground on the tach, could be its loose
Connect a handheld meter to the tach at both the ground and 12V connections. Try to see if voltage is changing
 

Bryanttttt

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Howdy
Check the power and ground on the tach, could be its loose
Connect a handheld meter to the tach at both the ground and 12V connections. Try to see if voltage is changing

Definitely not power and ground as I ran brand new + - and signal wires to eliminate that as potential part of the problem. Also new tach.
I'll try voltmeter anyway, at what level would I see change? Entire volts or in the decimals?
 

Scott Danforth

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did you service the points and condenser?
 

alldodge

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Since you replaced +- then disregard voltage, was wonder if it was bouncing

The distributor module is a switch which grounds the - side of the coil and then opens it. This ON/OFF switching is what the tach reads and displays the value. Something is wrong with the signal so I would be looking at the distributor module.
 

Bryanttttt

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Since you replaced +- then disregard voltage, was wonder if it was bouncing

The distributor module is a switch which grounds the - side of the coil and then opens it. This ON/OFF switching is what the tach reads and displays the value. Something is wrong with the signal so I would be looking at the distributor module.

Got it. Can that also affect performance at higher Rpms if it's not working properly?
​​​​Don't know much about how these Thing work
 

GA_Boater

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Does the boat slow down when the RPMs spike? Does the motor rev up or just the gauge?
 

Scott Danforth

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Not really sure what that is, so I'm gonna say no lol. Could u elaborate please? 😁

your motor still has a points ignition. if you have arcing in your points, or your points are worn out, you will get bouncing..... which will break up the ignition and give you an erratic tach signal.
 

Bryanttttt

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Does the boat slow down when the RPMs spike? Does the motor rev up or just the gauge?

When I use it on the water, there's no noticeable difference. But I also haven't pushed the boat very far into the zone where it goes haywire, nor for very long.
When I ran it on land, I felt a slight shutter but it wasn't crazy
 

Bryanttttt

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your motor still has a points ignition. if you have arcing in your points, or your points are worn out, you will get bouncing..... which will break up the ignition and give you an erratic tach signal.

Ok! So what's the solution? New distributor?
 

Scott Danforth

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Ok! So what's the solution? New distributor?

you open the factory service manual...... you then follow the process on replacing the $15 point kit (your cost if you buy the parts).

you service the points. if you dont know how to file points, gap points, verify dwell, and set timing. there is a sticky at the top of the forum. if after that you dont feel comfortable doing the work. take it into a mechanic and pay $120 labor and $50 for the point kit.

points get serviced every year.
 

Bryanttttt

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you open the factory service manual...... you then follow the process on replacing the $15 point kit (your cost if you buy the parts).

you service the points. if you dont know how to file points, gap points, verify dwell, and set timing. there is a sticky at the top of the forum. if after that you dont feel comfortable doing the work. take it into a mechanic and pay $120 labor and $50 for the point kit.

points get serviced every year.

Watched a couple YouTube videos, correct me if I'm wrong. Attached picture, the cables go to the condenser right?
I don't see the points thing that I see in other pictures and videos. Is it under that?
 

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Scott Danforth

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Looks like an early pertronix conversion

I never had luck with them. Time to troubleshoot with a DVM and dwell meter
 

Bryanttttt

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Looks like an early pertronix conversion

I never had luck with them. Time to troubleshoot with a DVM and dwell meter

You're right. I shoved phone in side angle I can't see by sticking my head against it and it looks like it says pertronix
 

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Scott Danforth

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pull the instructions for the pertronix from their web site. verify the gap between the pickup the the magnet trigger. that could be the reason your tach is going flaky and your engine isnt running right above 2500
 

alldodge

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Watched a couple YouTube videos, correct me if I'm wrong. Attached picture, the cables go to the condenser right?
I don't see the points thing that I see in other pictures and videos. Is it under that?

Finding the electronic pickup makes more sense why it was happening. Couldn't get my head around points doing it

The prior owner modified the pickup to install. There are several manufactures which make pickup coils, Petronix, Mallory, Sierra
 

Scott Danforth

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Finding the electronic pickup makes more sense why it was happening. Couldn't get my head around points doing it

usually point bounce on worn points with burned point contacts will cause the ignition to break up at low RPMs.
 
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