Mercruiser 2.5 120hp ignition help

[Erik-G-C]

I am brand new to working on boats and need some help. I am not new to mechanics however. I am an ASE certified master tech with 26 years experience so I can understand whatever it is you tell me. No that that's out of the way.
So my uncle bought a nice boat for next to nothing but didn't run well at all. Was supposedly a rebuilt 3.0 130. Definitely had mechanical issues. Dismantled it to find that it is actually a 2.5L. It was definitely rebuilt by someone who has no idea what they are doing. Was bored .060 over but only had .0007 wall clearance and the skirts were all damaged. Fast forward and I rebuilt the engine with all new correct marine parts. It also had an automotive water pump with a steel impeller that was basically a pizza cutter at this point.. lol. Put a brand new carb on it. We could not find one with the correct baseplate bolt pattern so bought a new one from a reputable company and I milled out a custom adapter.
It has the Delco electronic ignitin system on it. Not sure if it is from the 3.0 that the valve cover and other parts are from or if some halfwitt used an automotive distributor.
It now runs well, sort of. If I set base timing to 8° BTDC it starts and runs fantastic at low rpm. Will not rev at all. If I advance the distributor it will rev past 5000 RPM under a load and runs great until it's time to idle. Then it runs rough and when trying to start the engine it is clearly experiencing premonition and kicking back on the starter.
My experience is with cars and trucks and with them the electronic distributors on these iron dukes have a timing curve which is controlled by the ECM.
My question here is: what controls the timing advance on these marine engines? From what I've been able to find it seems this curve is built into the ignition module. I can only assume to timing curve is based on RPM. If that's the case and this thing has an automotive distributor this may be my issue. Everything I've found on the electronic distributors is on the 3.0. Did the 2.5 ever come with the electronic ignition? If I do have the wrong ignition module, what part number would I need to put in thos boat to fix my timing curve? I would love to take my family out on the water soon so any help you can give would be extremely appreciated.
Thanks in advance
Erik

 

[Scott Danforth]

The Delco voyager base timing is something like -2

 

[ROY WILLIAMS]

I am brand new to working on boats and need some help. I am not new to mechanics however. I am an ASE certified master tech with 26 years experience so I can understand whatever it is you tell me. No that that's out of the way.
So my uncle bought a nice boat for next to nothing but didn't run well at all. Was supposedly a rebuilt 3.0 130. Definitely had mechanical issues. Dismantled it to find that it is actually a 2.5L. It was definitely rebuilt by someone who has no idea what they are doing. Was bored .060 over but only had .0007 wall clearance and the skirts were all damaged. Fast forward and I rebuilt the engine with all new correct marine parts. It also had an automotive water pump with a steel impeller that was basically a pizza cutter at this point.. lol. Put a brand new carb on it. We could not find one with the correct baseplate bolt pattern so bought a new one from a reputable company and I milled out a custom adapter.
It has the Delco electronic ignitin system on it. Not sure if it is from the 3.0 that the valve cover and other parts are from or if some halfwitt used an automotive distributor.
It now runs well, sort of. If I set base timing to 8° BTDC it starts and runs fantastic at low rpm. Will not rev at all. If I advance the distributor it will rev past 5000 RPM under a load and runs great until it's time to idle. Then it runs rough and when trying to start the engine it is clearly experiencing premonition and kicking back on the starter.
My experience is with cars and trucks and with them the electronic distributors on these iron dukes have a timing curve which is controlled by the ECM.
My question here is: what controls the timing advance on these marine engines? From what I've been able to find it seems this curve is built into the ignition module. I can only assume to timing curve is based on RPM. If that's the case and this thing has an automotive distributor this may be my issue. Everything I've found on the electronic distributors is on the 3.0. Did the 2.5 ever come with the electronic ignition? If I do have the wrong ignition module, what part number would I need to put in thos boat to fix my timing curve? I would love to take my family out on the water soon so any help you can give would be extremely appreciated.
Thanks in advance
Erik

did the 153cu in engine . 4cyl ...what is the engine year ? ignition points or the electronic distributors ? the water pump is steel ? also that variation is the engine parts .

 

[Scott06]

Sounds like the module is not advancing. Is it stuck in base mode ? Delco est is a good system needs to be locked in base mode to set initial timing.

instructions are here https://marineengines4less.com/images/companies/1/EST Ignition Instructions - ME4L.pdf?1431462059320

 

[dubs283]

The 2.5 and 3.0 liter engines mercruiser used in oem setups were never marketed by GM for automotive use. The engines were designed and built for marine and industrial use only. AFAIK the 2.5 liter displacement engine never used an electronic ignition as it was phased out of use by mercruiser in the late 1970's

I would guess a Delco electronic ignition system as used in many 3.0 liter applications would work to get the engine running, but unknown of it would work properly as the 2.5 liter engine was designed to use a conventional ignition.

The timing spec of -2 degrees or 2 degrees ATDC is for a much later model 3.0 liter and does not apply to the 2.5. My guess is the original spec for idle timing on the 2.5 is 6 degrees BTDC.

Based on your provided info I would have to agree with afore mentioned thought that the timing isn't advancing and is possibly stuck in base mode/service mode. There is a procedure outlined in the manual(s) for the 3.0 liter for setting base timing with the Delco electronic ignition.

At this point I would suggest locating/acquiring an original distributor with conventional ignition (timing advance controlled by springs and weights) rather than electronic because the engine was designed to use a conventional ignition

 

[Erik-G-C]

did the 153cu in engine . 4cyl ...what is the engine year ? ignition points or the electronic distributors ? the water pump is steel ? also that variation is the engine parts .

Most of this is in my post. Valve cover says 130. No idea what year. It is badged as a 3.0 but upon disassemble found it to be a 2.5. Had a steel impeller pump. Replaced it with a correct marine pump. No idea what you mean by variation but it has .060 oversize pistons, marine head, marine cam for a 3.0 mercruiser.
My main question is did the 2.5 ever have electronic ignition? Looks like the answer is no. The ignition system on the engine must be from the 3.0 that the head and top end parts are off of. I can only assume the 2.5 block came out of a S10.

 

[Erik-G-C]

The 2.5 and 3.0 liter engines mercruiser used in oem setups were never marketed by GM for automotive use. The engines were designed and built for marine and industrial use only. AFAIK the 2.5 liter displacement engine never used an electronic ignition as it was phased out of use by mercruiser in the late 1970's

I would guess a Delco electronic ignition system as used in many 3.0 liter applications would work to get the engine running, but unknown of it would work properly as the 2.5 liter engine was designed to use a conventional ignition.

The timing spec of -2 degrees or 2 degrees ATDC is for a much later model 3.0 liter and does not apply to the 2.5. My guess is the original spec for idle timing on the 2.5 is 6 degrees BTDC.

Based on your provided info I would have to agree with afore mentioned thought that the timing isn't advancing and is possibly stuck in base mode/service mode. There is a procedure outlined in the manual(s) for the 3.0 liter for setting base timing with the Delco electronic ignition.

At this point I would suggest locating/acquiring an original distributor with conventional ignition (timing advance controlled by springs and weights) rather than electronic because the engine was designed to use a conventional ignition

I understand what you are saying, but the blocknis definitely a basic iron duke 2.5. I'm pretty sure mercruiser didn't have special castings. Probably different machining specs. Maybe more zink to resist corrosion.
None the less, all the marine parts are on it now.
It has a 3.0 marine cam and head and everything is marine spec on it now. The one think I don't know about is the ignition system. So if the 2.5 never came with electronic ignition it either has a 3.0 distributor and ignition system or a GM HEI distributor from a car or truck.
So what I really need to know is what the part number is for the marine ignition module for the electronic ignition 3.0.
Or, is there an upgraded ignition system that controls timing and has hotter spark that will drop into this thing?

 

[Erik-G-C]

The 2.5 and 3.0 liter engines mercruiser used in oem setups were never marketed by GM for automotive use. The engines were designed and built for marine and industrial use only. AFAIK the 2.5 liter displacement engine never used an electronic ignition as it was phased out of use by mercruiser in the late 1970's

I would guess a Delco electronic ignition system as used in many 3.0 liter applications would work to get the engine running, but unknown of it would work properly as the 2.5 liter engine was designed to use a conventional ignition.

The timing spec of -2 degrees or 2 degrees ATDC is for a much later model 3.0 liter and does not apply to the 2.5. My guess is the original spec for idle timing on the 2.5 is 6 degrees BTDC.

Based on your provided info I would have to agree with afore mentioned thought that the timing isn't advancing and is possibly stuck in base mode/service mode. There is a procedure outlined in the manual(s) for the 3.0 liter for setting base timing with the Delco electronic ignition.

At this point I would suggest locating/acquiring an original distributor with conventional ignition (timing advance controlled by springs and weights) rather than electronic because the engine was designed to use a conventional ignition

There is no way I'm going back to points ignition. There is no reason an electronic ignition won't work. I think I just need to find out what ignition module to put in it

 

[Scott06]

Most of this is in my post. Valve cover says 130. No idea what year. It is badged as a 3.0 but upon disassemble found it to be a 2.5. Had a steel impeller pump. Replaced it with a correct marine pump. No idea what you mean by variation but it has .060 oversize pistons, marine head, marine cam for a 3.0 mercruiser.
My main question is did the 2.5 ever have electronic ignition? Looks like the answer is no. The ignition system on the engine must be from the 3.0 that the head and top end parts are off of. I can only assume the 2.5 block came out of a S10.

different 2.5 in an S10 than this engine. The S10 used the pontiac made Iron Duke 151 cu in engine.

The 2.5 Mercrusier is the 153 cu in chevy 4 cylinder that debuted in the Chevy II in 1962... and ceased passenger car production in North America in 1970...

the 2.5 /3.0 mercs were industrial GM motors after that never used in cars or trucks, had a common lineage with Chevy straight 6 - 230 cu in/250 cu in

The Delco EST is a very good marine ignition system if I were you I would figure out what isnt working like the module and make it work. Both Merc and Volvo Penta used it on many chevy based engines.

With and advance light should be able to see how much it is advancing, if at all. If it doesn't advance would get a new module. If it does advance you should be able find out the timing curve for a 2.5 and get it to match total advance. Would think if you start at a total of 24 degrees at 2800 or so, you can try it out and bump up the total in degree increments until it runs ok idle to WOT

I'll see if I can find the advance curve for a 2.5 when I get home this evening.

some details towards bottom of this article on diff between iron duke and chevy 4/6 engines merc used

The Little Engines That Could, Part 4: Chevy II 153 Four - Six Minus Two Equals Roughly Unpopular - Curbside Classic

(first posted 10/14/2016) Welcome to Part 4 of this ever-expansive dive into the depths of automotive history, exploring various times when relatively small displacement engines were used to power mainstream […]

www.curbsideclassic.com

 

[ROY WILLIAMS]

Most of this is in my post. Valve cover says 130. No idea what year. It is badged as a 3.0 but upon disassemble found it to be a 2.5. Had a steel impeller pump. Replaced it with a correct marine pump. No idea what you mean by variation but it has .060 oversize pistons, marine head, marine cam for a 3.0 mercruiser.
My main question is did the 2.5 ever have electronic ignition? Looks like the answer is no. The ignition system on the engine must be from the 3.0 that the head and top end parts are off of. I can only assume the 2.5 block came out of a S10.

the GM S10 engine is internal parts , then updated of the marine components . 130cu in ..... did the valve cover of that picture number ...
I did my MERC 470 I changed the ignition points to the PERTRONIX 1146A
https://pertronixbrands.com/products/pertronix-1146a-ignitor-delco-4-cyl-cw I did it 20 yrs ago .... I did engine is , high power of those 20kv of that spark plugs ...
so the engine is of that model , serial number and the motor manual ...

 

[Scott Danforth]

There is no way I'm going back to points ignition. There is no reason an electronic ignition won't work. I think I just need to find out what ignition module to put in it

if you are using the delco voyager, your base timing is -2 degrees. regardless of 2.5 or 3.0

 

[Erik-G-C]

different 2.5 in an S10 than this engine. The S10 used the pontiac made Iron Duke 151 cu in engine.

The 2.5 Mercrusier is the 153 cu in chevy 4 cylinder that debuted in the Chevy II in 1962... and ceased passenger car production in North America in 1970...

the 2.5 /3.0 mercs were industrial GM motors after that never used in cars or trucks, had a common lineage with Chevy straight 6 - 230 cu in/250 cu in

The Delco EST is a very good marine ignition system if I were you I would figure out what isnt working like the module and make it work. Both Merc and Volvo Penta used it on many chevy based engines.

With and advance light should be able to see how much it is advancing, if at all. If it doesn't advance would get a new module. If it does advance you should be able find out the timing curve for a 2.5 and get it to match total advance. Would think if you start at a total of 24 degrees at 2800 or so, you can try it out and bump up the total in degree increments until it runs ok idle to WOT

I'll see if I can find the advance curve for a 2.5 when I get home this evening.

some details towards bottom of this article on diff between iron duke and chevy 4/6 engines merc used

The Little Engines That Could, Part 4: Chevy II 153 Four - Six Minus Two Equals Roughly Unpopular - Curbside Classic

(first posted 10/14/2016) Welcome to Part 4 of this ever-expansive dive into the depths of automotive history, exploring various times when relatively small displacement engines were used to power mainstream […]

www.curbsideclassic.com

I knew there were some differences. Thanks. I'm still not convinced this is a marine block but everything is done.
The timing jumps all over the place. Looking at the ignition module it has no numbers on it and looks to be generic. I ordered the Sierra ignition module for the 3.0. I'll get it installed and timed and see what happens

 

[Erik-G-C]

the GM S10 engine is internal parts , then updated of the marine components . 130cu in ..... did the valve cover of that picture number ...
I did my MERC 470 I changed the ignition points to the PERTRONIX 1146A
https://pertronixbrands.com/products/pertronix-1146a-ignitor-delco-4-cyl-cw I did it 20 yrs ago .... I did engine is , high power of those 20kv of that spark plugs ...
so the engine is of that model , serial number and the motor manual ...

Not to be rude, but I have no idea what you are trying to say here

 

[ROY WILLIAMS]

Not to be rude, but I have no idea what you are trying to say here

did you do the engine model # serial # of the GM ? did the year engine ?
I was of my auto manuals around 1970-1980s ...