Mercruiser 140 Points to Delco EST results in low RPM at WOT

[me78569]

I've been banging my head on the wall trying to figure out how to solve my low RPM at WOT issue that happened after I replaced the points with a Delco Est ignition.

I've got a 84 crestliner with a merc 140, serial A330922, the boat got a replacement 140 to replace the blown up older 370 that was in it before I owned it.

Boat 2 years ago ran good all season, it would do ~4400 rpm at WOT and do a gps verified 42 +- mph all day long on the river. the season ended and the next spring I decided to do some preventive maintenance on the boat. I don't know the first thing about Points so I went ahead and replaced the points with a Delco EST ignition conversion kit from this seller on Ebay. https://www.ebay.com/itm/293047598226?hash=item443aff7c92:g:GFYAAOSwPPtcslXp I think it is the OEM setup for later year 3.0's so it should be good is what I thought.

I went through the directions and set everything up to a T. Base timing set at 1* , the timing advance is working to put timing at ~24 * at high rpm, but now the motor hits a wall at ~3600 rpm when in the water. My speed has dropped to match the lack in RPMS so I am trusting my rpm gauge being correct in the loss of rpm.

I ran the boat all last year like this and it runs good other than that. I have a slight lul in power off idle, but I think that is related to the carb power valve not being set right after rebuild I did trying to sort the RPM issue.


I have searched more than I care to admit and done a couple things so far like,

1. checked for the exhaust flapper being stuck in the exhaust
2. rewired the delco coil to have a full 12v and verified it has 13.8 v when running.
3. verified timing at idle and speed using a timing light
4. messed with base timing to try and get more timing up top ( didn't help)
5. full carb rebuild
6. new fuel pump
7. new plugs
8. bypassed the 1 way valve in the tank
9. new fuel filter.
10. checked compression, all at between 130 and 140

My plugs look like they have carbon fouling, but I am not sure if it is related or not. Can anyone offer any suggestions on what to check to try and gain back the RPM's that I lost? to me it feels like a lack of timing issue up top, but I can't really explain how it gets up to 3600 rpm and then just sits there. It will sit at that rpm at WOT all day long without any issue, but something is wrong.

 

[achris]

I suspect the timing curves are different. Once I get back to access of the pdf I'll post the curves.

Chris....

 

[Scott06]

Are you putting it in base mode when you set the 1 d BTDC? And you have verified the 24 degrees all in timing with a light or you mean it should supply 24 degrees total advance? Have you checked the strength of the spark with a spark gap tester?

Try with tach disconnected. Wondering if tach made for points is messing up the EST? I'm assuming the old fuel filter was clean?

Did you measure fuel pressure at 3600 rpm under load ? May be reaching but a flat cam lobe would work a new fuel pump just as bad as the old one...

 

[alldodge]

Re-check firing order 1-3-4-2

 

[nola mike]

Re-check firing order 1-3-4-2

Always a good idea, but feel like this wouldn't be subtle on a 3.0. have you checked total timing with a light? 24' total sounds low (though I don't know the specs)

 

[alldodge]

Always a good idea, but feel like this wouldn't be subtle on a 3.0. have you checked total timing with a light? 24' total sounds low (though I don't know the specs)

Timing curve shows about 22 to 24 total

 

[me78569]

Are you putting it in base mode when you set the 1 d BTDC? And you have verified the 24 degrees all in timing with a light or you mean it should supply 24 degrees total advance? Have you checked the strength of the spark with a spark gap tester?

Try with tach disconnected. Wondering if tach made for points is messing up the EST? I'm assuming the old fuel filter was clean?

Did you measure fuel pressure at 3600 rpm under load ? May be reaching but a flat cam lobe would work a new fuel pump just as bad as the old one...

I am putting it into base mode then setting timing at 1* btdc, then it jumps to 12-12 at idle when I take it out of base mode, then it goes to 24* as rpms rise.


I will try disconnecting the tach. I have not measured fuel pressure, but I would figure I would have good power until the bowl emptied if i was running into a lack of fuel pressure, maybe not though. the old fuel pump did in fact die %100 which is why I replaced it.


double and triple checked the firing order.

 

[Scott06]

I am putting it into base mode then setting timing at 1* btdc, then it jumps to 12-12 at idle when I take it out of base mode, then it goes to 24* as rpms rise.


I will try disconnecting the tach. I have not measured fuel pressure, but I would figure I would have good power until the bowl emptied if i was running into a lack of fuel pressure, maybe not though. the old fuel pump did in fact die %100 which is why I replaced it.


double and triple checked the firing order.

you are setting the base timing correctly, and total is correct, unless balancer has slipped so it is not indicating TDC correctly anymore.

would also think fuel is ok based on your comments just thinking a sanity check as we may be running out of options .

did the plunger for the power valve mive smoothly when you had the carb apart?

 

[nola mike]

My next step is checking for consistent spark at each cylinder. Timing light on each lead, make sure you're not dropping occasionally. Also, assuming you have good fuel/checked filters etc. Water/old fuel is always suspect. At some point I might go old school and put a vacuum gauge on there.
Also, may be getting tunnel vision with the EST conversion. Not sure how much of a pita it would be to put the points back in for troubleshooting purposes. Lastly, in the grasping at straws department, hull weight (water weight)/bottom growth can be a consideration

 

[achris]

I think I have found your problem. Your engine is specéd for a total advance of 36 degrees, not 23, that is for the later 140s...

You've removed 13 degrees of advance out of the engine, little wonder it's only making 3600rpm.

 

[me78569]

that's what my thought was. So the old advance has a range of 8* to 36*? I am assuming the new delco can't do that as to get a total of 36* of timing I would need to set my base timing at ~12* and that would idle at ~24*?

Thoughts on a solution? am I just gonna have to go back to points and change to the other method of electric ignition / learn how points works?

 

[alldodge]

Agree setting it at 8*
https://forums.iboats.com/threads/converting-to-delco-est-ignition.184784/

 

[Lou C]

There isn’t much to how points work. You set the gap with a feeler gauge and verify with a dwell meter. Then check base timing and idle speed. You can also inspect the centrifugal weights & springs under the points plate and lube them with a bit of oil. An advance timing light can be used to verify the total timing advance. You replace the points & condenser when the contact surfaces of the points get pitted & burned or the engine just won’t run right even when dwell & timing are correct. I have em on my engine and thought of converting but am used to points so I haven’t. Just like the cars I grew up with in the 70s.
Thought of using the Petronix system which has been around a long time but heard of random problems with those too. The Delco EST of course is an option but the advance curve must match your engine specs which is what happened in this case.

 

[me78569]

Agree setting it at 8*
https://forums.iboats.com/threads/converting-to-delco-est-ignition.184784/

Ill give that a try and see how it does.

There isn’t much to how points work. You set the gap with a feeler gauge and verify with a dwell meter. Then check base timing and idle speed. You can also inspect the centrifugal weights & springs under the points plate and lube them with a bit of oil. An advance timing light can be used to verify the total timing advance. You replace the points & condenser when the contact surfaces of the points get pitted & burned or the engine just won’t run right even when dwell & timing are correct. I have em on my engine abs thought of converting but am used to points so I haven’t. Just like the cars I grew up with in the 70s.

I am sure I can get it figured out I just dont really want to learn another 1 off skill, but I will if I have to. Life is already to busy haha

 

[Lou C]

If you ever buy a classic car it’s a useful skill to have. Here’s a data point for you:
I drove cars with points from 1972-1980, had exactly one breakdown due to points. 1965 VW Bug with a points distributor easily fixed by the side of the road with simple tools & a feeler gauge. The electronic module for the GM Delco HEI failed twice on our ‘75 Olds. Also an easy repair.
On the boat I never had a breakdown due to points but have a spare set in a plastic bag with a clean feeler gauge of the right size just in case.

 

[nola mike]

I think I have found your problem. Your engine is specéd for a total advance of 36 degrees, not 23, that is for the later 140s...

You've removed 13 degrees of advance out of the engine, little wonder it's only making 3600rpm.

View attachment 358365

What's the difference in the engines to account for that?
Also looks like it would need 12' initial as OP said originally... Wonder if that would start/idle like crap.

 

[me78569]

Less Compression would be my guess.

 

[Scott06]

that's what my thought was. So the old advance has a range of 8* to 36*? I am assuming the new delco can't do that as to get a total of 36* of timing I would need to set my base timing at ~12* and that would idle at ~24*?

Thoughts on a solution? am I just gonna have to go back to points and change to the other method of electric ignition / learn how points works?

Give it a try the merc thunderbolt 4 & 5 for V6 and V8 use 8 and 10 degrees base timing and has a similar advance at idle. I would think 8 or 10 degrees would get you close enough to the factory advance it should run well at WOT.

Would set it to 8 run it and see if you have detonation then bump it up two degrees, maybe 2 more after that ...

 

[alldodge]

What's the difference in the engines to account for that?

I would think cam

 

[me78569]

will do, thanks for the help on this, Thought it might be a lack of timing, but good to see the spec agree's