1979 70HP Mercury Thunderbolt Cold Start Problems

[whitnes10]

Hey,

I have a 1979 Mercury Thunderbolt 70hp engine. Been working pretty smooth all summer, but lately have had problems with the "cold start." Today, I spend about 1 hour trying to turn it over, finally turned over after a lot of persistence. After that, started up every time for the rest of the day (once warm).

Earlier in the summer I checked compression in all 3 cylinders and they were all within 140 - 150, although that doesn't mean something could have changed since, I don't think it is compression related. I have taken out the plugs and am going to try getting 3 new ones for next weekend and see how that checks out.

What do you guys think some simple things I could check for?

Thanks!

 

[aussieflash]

Re: 1979 70HP Mercury Thunderbolt Cold Start Problems

Check your choke is working correctly.

 

[ajgraz]

Re: 1979 70HP Mercury Thunderbolt Cold Start Problems

New plugs (or even cleaning off your old ones) might well help. Always helps with the cold start on my 78 70hp Merc.

 

[whitnes10]

Re: 1979 70HP Mercury Thunderbolt Cold Start Problems

Yeah I have tried cleaning the plugs, no luck there. That's why I'm going to get 3 new ones. I'm thinking it could have something to do the the coils possibly, hopefully nothing to expensive whatever it is...

 

[whitnes10]

I have the same engine and here is my issue I'm having. It's all about the cold start and yesterday I couldn't get it started from a cold start. When I turned the key, the starter engaged with the flywheel but turned it very slowly and couldn't get it to start. I checked some things: battery, cables, electric choke, but everything there seemed fine. I tried to start it with jumper cables going from the battery to the starter but the same thing kept happening. This had been a problem all summer but I previously had been able to get it started, and once started every time after that it would start perfectly. This time I just couldn't get it going. I took the starter off the motor, but now I don't really know where to go from here.

Any suggestions will help! Thanks!

 

[hotrod53]

My 1977 Thunderbolt starts flawlessly.... I pump the primer ball 15 times, press the choke, put the enricher bar straight up, and it fires right up. I can tell you that if you have a weak battery or the motor spins slow, it won't start. I almost killed my battery last weekend using the livewell, it turned over slowly and I would have expected it to start, no go.

I'm doubting your coil hypothesis, I can't see 3 coils going bad at once.... oh, and coils are $55 each, I had 1 go bad a couple of years ago. If you have a plug wire come off, the coil will eat itself. Are you using center fire plugs?

Don't let ripping into the starter scare you, it's easy. You will however have to make a chincy little tool out of sheetmetal to get the brushes back in. I have a template out of a manual that I can send you if you need it. You need to clean out the worn brush crap and lubricate the bushings. Does your starter gear disengage prematurely? This is a sign of low starter RPM.

 

[GA_Boater]

whitenes10 here the info from the new topic you started - Seems you still have the same problem. Since you restarted this one, the new topic has been deleted. GA_B

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So my engine had been working great all season thus far. The only thing I had been noticing is that it really struggled to get started from a cold start, but once I got it going for the first time it always started up no problem. Yesterday I could not get it going from a cold start (had not had it running for about 2 weeks). When I turned the key, it the starter would engage with the fly wheel, but it would turn it quite slowly and just didn't have enough power to get it going.

Things I checked:
Battery - checked out and even tried my car battery
Electric Choke - Works
Cables and grounds - nothing seemed to be abnormal though I know that there are some wires that need to be updated.

*I also disconnected the battery and tried the jumper cable technique to start it that way, but again it engaged and turned the flywheel, just was too slow to get it started.

I took and currently have the starter off my engine to inspect but I don't really know what I'm doing from this point on.

Please if you have any suggestions, anything will help! Even if there is something else I can check on my engine. Am I pinpointing my issue to the right spot?

 

[whitnes10]

No my starter doesn't disengage until it turn the key off or until it wears the battery too much. It just literally does not turn the flywheel fast enough. So you are thinking a simple cleaning of the starter could fix the problem or do you think I'll have to possibly replace the brushes or something?

 

[hotrod53]

It sounds like you narrowed down the problem. If it won't start while jumped right onto the starter, you pretty much eliminated everything else.

I would pull the starter apart and clean it real good, it may be full of worn brush dust. You can replace the brushes if they look worn out, clean the armature with some steel wool, lubricate the bushings, and try it again. If that doesn't speed up your starter, sounds like you're due for a new one. I know that my motor won't even fire if it isn't turning over quick enough.

 

[whitnes10]

So I currently have my starter pulled apart. If one of my four carbon brushes was stuck and the spring wasn't pushing it up into place, would that be my problem? The other three brushes had full movement but that one I mentioned was stuck down.