7.5 HP intermittent miss at WOT

[huntin dawg]

Hi Gents,
I finally got my 1973 7.5 HP out for its first full test run after it's rehabilitation. She runs great except for an intermittent skip/miss at WOT. It pushes my little jon boat at 16 MPH which is pretty impressive.

Any ideas why it misses at WOT?

Thanks,
HD

 

[verado7]

Re: 7.5 HP intermittent miss at WOT

only way to know for sure is to test the ignition with a dva and or you can check the resistance on the stator - check plug wires - sounds like switchbox or stator though .

 

[huntin dawg]

Re: 7.5 HP intermittent miss at WOT

What is a dva? I haven't done any ignition work.

HD

 

[CDI Tech Support]

Re: 7.5 HP intermittent miss at WOT

What is a dva? I haven't done any ignition work.

DVA Explained

DVA is a highly accurate measurement. But you must have a digital meter with a DVA Adapter attached.

This should be our troubleshooting guide for your engine:

Mercury 1 and 2 Cylinder - 336-4516

If not, obtain the ignition part#, then check here:

CDI Troubleshooting Guide

Since the problem is occurring at high speed, it could be that the high-speed coil is breaking down. Check resistance from Blue to Yellow. It should read from 170-180 ohms.

If you find that it's out of spec, we suggest replacing both the high-speed coil & low-speed coil at the same time while you have the ignition apart.

If it's within spec, the ignition itself could be in need of repair. We offer Repair & Return for the 336-4516 ignition.

Again, if this isn't the correct ignition, obtain your ignition part# (or serial#), then check our troubleshooting guide page for the correct guide.

 

[huntin dawg]

Re: 7.5 HP intermittent miss at WOT

Thanks for all of the input.

The miss is very intermittent and only when at absolute WOT. If I back off just a tiny bit it stops missing. Could it possibly be a synchronization problem?

HD

 

[CDI Tech Support]

Re: 7.5 HP intermittent miss at WOT

Thanks for all of the input.

The miss is very intermittent and only when at absolute WOT. If I back off just a tiny bit it stops missing. Could it possibly be a synchronization problem?

HD

You would need to confer with a qualified marine mechanic.

 

[huntin dawg]

Re: 7.5 HP intermittent miss at WOT

Synchronization was the problem. All it took was about 1 1/2 turns of the max advance screw to fix it. I'm sure glad I didn't buy new coils.

HD

 

[CDI Tech Support]

Re: 7.5 HP intermittent miss at WOT

Synchronization was the problem. All it took was about 1 1/2 turns of the max advance screw to fix it. I'm sure glad I didn't buy new coils.

HD

That's why we always suggest taking it to a qualified marine mechanic to have all mechanics checked prior to any ignition checks or changes.

Our troubleshooting guides/procedures are assuming all mechanical checks have been exhausted.