1958 Mark 78 backfiring when starting

[gwmark78]

Hello,<br />My Mark 78 ran just fine last year-no problems. <br />Put the boat in a few weeks ago and will not start- try's a few times and then starts backfiring through the exaust. Checked plug wires, replaced plugs,pulled dist cap and had about 1 teaspoon of water in it. I puzzled over how the water got in there' but cleaned and dried out. Motor started right up. Went back to the lake 2 weeks later and now backfiring again. Dist cap was dry this time. MY plug wires are correct, new spark plugs,new gas. I have not messed with timimg or points. I did do a gap check on points when drying out the cap-ok. I could not visually find any carbon paths or cracks in the cap. I have spark on all 6. I did do a individual spark/start test on each cylinder with the other 5 disconnected. 1,2,4,5,6 all fired normally and wanted to start. #3 backfired right off. Compression cold was 110 on all. I know this sounds like a timing issue, but how can it just change from one day to the next? Sure could use some help on this one- Thanks.

 

[Chinewalker]

Re: 1958 Mark 78 backfiring when starting

Hi Mark,<br /> Just a shot in the dark - is the timing belt loose on the cogs? Could it be jumping off a tooth or two?<br />- Scott

 

[gwmark78]

Re: 1958 Mark 78 backfiring when starting

Scott,<br />I did check the belt and all looked ok and my reasoning for not rechecking timing is it cannot just go in and out of time-?? Thanks for the reply.

 

[heybaylor]

Re: 1958 Mark 78 backfiring when starting

Mark , just another shot in the dark..but years ago , sorry many years ago ..I fought , and fought a timing ,spark problem ..worked most of the time ,<br />but sometime just wouldnt run /start .<br />.<br />cut to the chase !!!<br /><br />the housing on the distributer ..had a fine-line crack ..couldnt see it ..but caused the same as u describe.."condensation , and or bad luck was in the "dist housing . drove me nuts ..as I still am today.

 

[gwmark78]

Re: 1958 Mark 78 backfiring when starting

Heybaylor,<br />You're confiriming my suspicions that my problem is in the cap or the distributer. Just curious, how did you finally find it? I'm not quite sure how to trouble shoot this other than visual. Any thoughts would be appreciated, Thanks

 

[heybaylor]

Re: 1958 Mark 78 backfiring when starting

I replaced the dist case , and dist cap ..to be honest in desperation <br />..<br />it would run all day on the "hose "<br />but in the water ..sometimes did, sometimes didnt<br /><br />I never did see with the eyeball anything wrong ..<br />But problem went away ..

 

[Clams Canino]

Re: 1958 Mark 78 backfiring when starting

Time to get the manual and go through the distributor inch by inch. Sounds like it's in there somewhere.<br /><br />-W

 

[gwmark78]

Re: 1958 Mark 78 backfiring when starting

Hello Clams,<br />Well, another weekend in Montana and no fishing! I think I'll bring a new cap with me and like you said, inch by inch look at everthing possible. Thanks

 

[technostingray]

Re: 1958 Mark 78 backfiring when starting

Boing. Keep us up to date on your progess and what you learn.

 

[technostingray]

Re: 1958 Mark 78 backfiring when starting

Ok, Mark, 'fess up. You had it in reverse.

 

[Clams Canino]

Re: 1958 Mark 78 backfiring when starting

Not just the cap / but clean and set the points too.<br /><br />-W

 

[gwmark78]

Re: 1958 Mark 78 backfiring when starting

Techno'<br />Cap should be here today- so I guess it's going to be working on the old merc over the 4th weekend. It does backfire just as good in reverse though!

 

[gwmark78]

Re: 1958 Mark 78 backfiring when starting

Clams,<br />I figured I needed to clean and get the dwell and sync plate out and reset points-I'm really hoping it's the cap because I did have the points dead on ..I thought. Thanks

 

[technostingray]

Re: 1958 Mark 78 backfiring when starting

As a side not to this, we found that the mercury switch had been by passed and re-routed to a switch on the dash. which one is ohyeah ;D

 

[Clams Canino]

Re: 1958 Mark 78 backfiring when starting

If you just touch the points up with a light abrasive you won;t need to reset them the long way. I'm just thinking a film of corrosion is keeping them unhappy. <br /><br />Also, make sure the battery isn't overcharging. that will cause the condensers to break down and do just what you're saying also.<br /><br />Unless the old cap is cracked or broken, a good trip through the dishwasher will usually take care of it.<br /><br />-W<br /><br /><br />-W

 

[gwmark78]

Re: 1958 Mark 78 backfiring when starting

Clams,<br />Last trip to the lake I did clean with #600 wet/ dry and then matchbook wipe. I did check gap with 'feeler' and was tight .007 which the manual says to start with on #1 set of points. But you brought up something else I have been wondering about-the condensers and the overcharging issue. If I understand you correctly, my condensers could be shot if the system was/is overcharging? Until I can get this bugger running, I cannot check it. Thanks

 

[heybaylor]

Re: 1958 Mark 78 backfiring when starting

check your condensers with a ohmmeter

 

[gwmark78]

Re: 1958 Mark 78 backfiring when starting

Heybaylor,<br />I can check for resistance, but how about for "breakdown"? Thanks

 

[heybaylor]

Re: 1958 Mark 78 backfiring when starting

well I used to "charge them up" and let em sit for a hour or so , then check for "storage !!<br />your welcome

 

[heybaylor]

Re: 1958 Mark 78 backfiring when starting

LOL, matter of fact we used to charge them up ,and leave them on the desk in the shop .<br />then some curious soul would pick it up and check for "storage for me ..zap.!! it was a good one