1970 Bayliner Mercrusier 120HP

[Celtichawk]

So this past monday I was out and I believe it happened before too just never really seemed to care. Well a little more often my engine decided to back fire/pop on me mainly when I throttle up and run high throttle. Just at a idle speed 5 mph coming into the channel bouy area doesnt seem to be a issue. Open throttle it likes to pop/backfire. I have not changed anything such as plugs, wiring, fuel filter, timing adjustment, etc... since I got boat from previous owner.

The best thing I have done so far is sea foam in the gas prior to fuel up and running. I might need to aslo remove the carburetor Rochester 2jet and clean/rebuild?

Any case could you shed some light what some things to look for for this issue?

 

[RogersJetboat454]

Re: 1970 Bayliner Mercrusier 120HP

I have not changed anything such as plugs, wiring, fuel filter, timing adjustment, etc... since I got boat from previous owner.

OK...
So how long ago was that?

Check the compression of the engine. If you have a valve sealing issue, you may be getting popping through the intake.
Check the condition of your plugs. Check the condition of the points. Check the timing and dwell. Toss in a new fuel filter for good measure. When you open the throttle up, are you getting a good jet of fuel squirt through the ventures from the accelerator pump?

 

[Celtichawk]

Re: 1970 Bayliner Mercrusier 120HP

OK...
So how long ago was that?

Check the compression of the engine. If you have a valve sealing issue, you may be getting popping through the intake.
Check the condition of your plugs. Check the condition of the points. Check the timing and dwell. Toss in a new fuel filter for good measure. When you open the throttle up, are you getting a good jet of fuel squirt through the ventures from the accelerator pump?

Thanks I will do all that and we go from there, I had a feeling without doing any of that it would be hard to diagnose. Start small work way up. Keep you guys posted and again thanks.

 

[Celtichawk]

Re: 1970 Bayliner Mercrusier 120HP

OK...
So how long ago was that?

Answer: June 24 on Monday is when I really noticed it doing it, again it was only when I throttled up and ran it a little higher speeds.

 

[RogersJetboat454]

Re: 1970 Bayliner Mercrusier 120HP

Answer: June 24 on Monday is when I really noticed it doing it, again it was only when I throttled up and ran it a little higher speeds.

Let me rephrase...

How long have you owned the boat?

 

[Watermann]

Re: 1970 Bayliner Mercrusier 120HP

It's time for a tune up and some preventive maintenance I would imagine. The poor ole iron duke is in need of some love it sounds like.

 

[RogersJetboat454]

Re: 1970 Bayliner Mercrusier 120HP

The poor ole iron duke is in need of some love it sounds like.

The "Iron Duke" was the 2.5L Pontiac cross-flow engine from the 80's.
The 2.5L in this gentleman's boat is GM corporate, nothing in common with the Pontiac besides the displacement.

 

[Watermann]

Re: 1970 Bayliner Mercrusier 120HP

The "Iron Duke" was the 2.5L Pontiac cross-flow engine from the 80's.
The 2.5L in this gentleman's boat is GM corporate, nothing in common with the Pontiac besides the displacement.

So that helps with his problems alright. Ah yeah the nickname argument for the GM 2.5 for the rear wheel drives S10's, mercs, Chev II or is it the the FWD Pontiac. Who gets that damn nickname is the source of debate on every forum guess this one is no different.

 

[RogersJetboat454]

Re: 1970 Bayliner Mercrusier 120HP

So that helps with his problems alright. Ah yeah the nickname argument for the GM 2.5 for the rear wheel drives S10's, mercs, Chev II or is it the the FWD Pontiac. Who gets that damn nickname is the source of debate on every forum guess this one is no different.

It helps him if he doesn't assume that the 2.5L he has in his boat is the same as the Pontiac "Iron Duke"/ "Crossflow"/ "Tech4", and goes off to a boneyard seeking one to replace what he has, only to find out it's not the same beast.