Problems with 1972

[irideflatland]

Just bought a 1972 Crestliner with a 120hp Mercruiser IO 4 cylinder last weekend. It's my first boat so I'm completely clueless about it.

We've taken it out 3 times so far. First 2 times were alright, but when you open the throttle up too much it will make a popcorn popping sound. And if you open the throttle all the way, there be random huge loud bangs, and the power will kind of cut out for a split second.

So we just kept it at about half throttle and it was fine, until the last time we took it out. It starts fine, but when you drop the choke it will die. So we have to play with the choke and throw it into gear and mess around with it until it is running fine. Once it is running in gear, it is good.

So I'm probably going to just take it to a shop, but I was wondering if anyone has any ideas how much this might cost, or if there are any easy things I can check first?

Thanks

 

[havasuboatman]

Re: Problems with 1972

The popping and back firing is due to a lean fuel mixture at WOT. In this case i would suspect the carb, but first, if your boat is equipped with a water seperating fuel filter, remove it and dump it into a clear container and see if it's got a bunch of water in it.
Water or not, don't reuse the filter.

 

[Bondo]

Re: Problems with 1972

or if there are any easy things I can check first?

Ayuh,... As noted, CLEAN the fuel delivery System....
That,+ a Full complete Tune Up might do it, although I suspect the Carb needs rebuilding or replacing...

 

[irideflatland]

Re: Problems with 1972

Thanks for the help. I ended up taking it to a boat shop, and they said the accelerator pump or something was bad... so they ordered a carb kit and did whatever with that, and they changed the thermostat. It ended up being like $330.

The guy came out and talked to me, and said I needed to change the fuel filter ASAP, because there was a lot of water in the gas, and he said I need to use 91 octane instead of 87 with ethanol.

I had to order a filter since they didn't have any. We took it out yesterday before I got the filter, and it runs perfectly, except at WOT. It still backfires and the power backs off.

I got the filter today, so I put that on. Also put on a new gas line since the old one was kinked. I poured the old gas from the filter into a mason jar and let it sit for a few hours, but I didn't see any water separate from the gas.

So my new question: Should I drive the boat until all the old gas is gone, and then fill it with 91? Or should I start adding 91 to dilute the old stuff?

 

[starsnstripers]

Re: Problems with 1972

Do a tune up and timing now.

 

[cr2k]

Re: Problems with 1972

I suspect there may a timing issue too.

 

[red85k100rs]

Re: Problems with 1972

So my new question: Should I drive the boat until all the old gas is gone, and then fill it with 91? Or should I start adding 91 to dilute the old stuff?

Maybe some octane boost

 

[bomar76]

Re: Problems with 1972

Maybe some octane boost

Octane boost isn't what it claims to be.
The label says boosts octane up to 2 point or whatever.
That doesn't mean it will take it from 87 to 89.
When they say points they mean TENTHS of points, like from 87.0 to 87.2.
You need to dump gallons of it into a tank to have any result.
It's just another example of snake oil in a can.

 

[irideflatland]

Re: Problems with 1972

Took it out yesterday to run out the old gas, but didn't stay out long enough to do that.

I ran really nice though, got it up to 5000rpms for a little bit with no problems. Then towards the end of the night it started backfiring a few times when we were around 4000rpms, and losing a bit of power.

The new fuel line and fuel filter helped out sooo much though, so I think after I run out the old gas and put good new gas in, it will be fine.

Is the timing easy to do or would I need to take it back to the shop?

 

[bigskiohio]

Re: Problems with 1972

5000 to much rpm should be 3900 - 4300 tops. keep reving to 5000 and you will killit eventually.