470 Timing

[Bikestdy]

Hello all,
I have a 1985 4Winns 170 Horizon with a Merc 470. My issue is when timing is set to spec (8*) with a timing light, it barely runs and chokes and sputters and backfires when the throttle is goosed. When I turn the distributor to where it runs good, the dampener mark is probably about 4" away from the front cover timing marks and it runs great and idles smooth, has good power. Just trying to figure out why it runs terrible on the marks.

I thought missing key on the dampener, so I removed the dampener and the key is in place. Points are properly gaped. plug gap is good. When set to 0* on the marks #1 is at top dead center (pulled plug and verified socket extension in cylinder).

 

[dubs283]

Choke open fully? Is the firing order correct? Have you investigated fuel supply?

 

[Bikestdy]

Choke is fully open. Firing order is correct. And I don't believe it to be a fuel issue, because when it is set far advanced then it runs perfect, idles smooth, good power, no issues.
I didn't try to get a reading of how much advance it has,I can try and do that as my timing light allows for that. I can maybe post a video too.

 

[Scott Danforth]

Make sure your damper ring didn't slip. Use a piston stop and degree wheel to verify

Also, you need to set dwell before timing

 

[Bikestdy]

As I already said
When set to 0* on the marks #1 is at top dead center (pulled plug and verified with socket extension in cylinder).

And dwell was properly set at 28.

 

[dubs283]

I think at this point you try a different timing light. Sounds like the one you have is advance, gives rpm reading, etc?

 

[Bikestdy]

I was looking a bit and found an article that said a very lean mixture can be a reason for lots of spark advance due to it's slow burn. So I need to look into the tune next.

However now, last week on vacation it failed me on the first day, after a little over an hour of running, it suddenly started going through a quart of oil in about 10 minutes and has an excessive amount of blow-by. None of the local marinas near there would even look at it (they all said they didn't want to work on something that old and parts are hard to get), so I had no boat on vacation. So now I'm home and need to look into that as well. Hopefully in next couple weeks I'll find time to look into it. I'm suspecting a head gasket, and praying it isn't rings.

 

[ScottinAZ]

sounds like a leakdown test is in order to see where the issues are. With any luck running lean didnt cause any major issues

 

[Scott Danforth]

running lean will eat pistons

too much spark advance will eat pistons