Merc 120 (2.5L) Timing/Fuel/Iginition Help

[chewy7097h]

I have a 1987 Merc 120 - 2.5L. I bought the boat about two months ago. So far, I have rebuilt the carb, replaced the coil, wires, points, cap, condensor, plugs, metal fuel line (old one had the beginnings of a kink near the carb) and fuel filters (one on the pump and the strainer in the carb during the rebuild). The engine will not run properly unless I set the timing to between 32 and 38 degrees btdc. If I set it back to 8 degrees btdc, it will bog, hesitate, and try to stall as soon as I give it some throttle away from the ramp. With the timing at 32-38 degrees btdc, it runs normally, save for a small hesitation which I can almost eliminate with minute changes to the timing (through trial and error on the water).

As a side note, the mechanical advance was not functional when I got the boat either - the springs had disintegrated. I have since replaced the springs and weights and the mechanical advance is working properly.

I was originally thinking fuel, but it seems to me that a fuel delivery problem could not be masked by advancing the timing.

Any pointers would be sincerely appreciated!

 

[Haut Medoc]

Re: Merc 120 (2.5L) Timing/Fuel/Iginition Help

Welcome to iboats.......
Are you sure you have your ignition wires in the right spot?....
IE, when doing initial timing, did you bring the #1 cylinder to TDC by checking for compression when that cylinder approaches TDC?......
& then make sure the rotor is pointing at the #1 post on the dist cap?....
You should be able to do the same thing on the #4 cylinder......
Do you have a timing light with the advanced feature?......
I don't see how an engine can run advanced 32* at idle & then advance normally......
That 32* should be the total advance near or at WOT....​

 

[chewy7097h]

Re: Merc 120 (2.5L) Timing/Fuel/Iginition Help

Thanks for the quick reply. I do have a timing light with the advance feature.

I have verified that the plug wires are in the correct order on the cap, and I have verified that the rotor is indeed pointing at the number one post on the cap when the pointer is at "0" on the timing marks.

 

[Haut Medoc]

Re: Merc 120 (2.5L) Timing/Fuel/Iginition Help

I bumped this for Don S & Robolt to look at.....​

 

[chewy7097h]

Re: Merc 120 (2.5L) Timing/Fuel/Iginition Help

Thanks - appreciate it. I took her out today and had a thought. I'm not going to do anything with my thought until Don S or Robolt offer their input, but here it is. I had to replace the springs on the mechanical advance. In order to do this, I had to buy and advance curve kit. It had three sets of springs and new weights. I currently have the heaviest springs on it, as these seemed to offer the best results performance wise. I also put the new weights in. When I say that the heaviest springs offered the best performance, this was with the timing set at OVER 30 degrees advance. I wonder if I should set it back to 8 degrees advanced with the lightest springs and see how it performs...

Either way - let's see what Don s and Robolt have to say.

Thanks again for your help (and persistence!).

Matt

 

[JustJason]

Re: Merc 120 (2.5L) Timing/Fuel/Iginition Help

a. your wires are in the wrong spot
b. your spinning a 11 thousand 500 rpm idle to need 38 degrees of advance
c. your timing light is broken or has an advance built into it that you do not have set at zero.
d. you have the light hooked up to #4 instead of #1. (if its showing a 30+ advance at idle rpm (600rpm or so) )
e. pretty much most maring engines, because of the load, have a slight hesitation or "blip" from when you throw the throttle down till it takes off... so that may or may not be normal depending on the duration of it.
f. Timing Timing Timing..... before fuel!!!!!!!!!!!!!! timing makes more of a difference than anything!!!!!!!!! always touch/feel/look at timing before you even think about fuel.
g. the distributor shaft is off by 1 tooth or more.
e..... reset timing manually by pulling distro shaft and pulling plugs and spinning numero uno pistoneous maximus up to TDC compression stroke. then re-align distro shaft so the rotor points at what is supposed to be #1 on the cap. (it should be right on it... not a little before or a little after... but dead center on the nub of the cap for #1)

Really you should just start with E... and go on from there.....

 

[chewy7097h]

Re: Merc 120 (2.5L) Timing/Fuel/Iginition Help

CaptJason - Here's some answers to what you posted:
A: Wires are in the correct spots and correct order
B: Idle is set at 600 +/- when idling, in gear, on the lake
C: Already tried another timing light, same result. Advance set to 0
D: I am hooking up to the first (front of the engine) plug wire
E: If I give the throttle a strong push, it will stall - can't be normal
F: That's what I figured, hence my post here
G: If the shaft were off a tooth, it seems as though I could compensate for this, to a degree (no pun intended) by turning the distributor. It seems that by using a timing light - when it indicated 8 degrees advanced, that means the number one cylinder is firing 8 degrees before TDC, regardless of the position of the distributor.
H (or E2): Did that already, which is how I verified where to position the number one plug wire...

Could it be that she jumped time (as in timing chain / belt)?

 

[Bt Doctur]

Re: Merc 120 (2.5L) Timing/Fuel/Iginition Help

Your reading something wrong somewhere. I don`t think it would crank at 30 deg.adv. cam is gear driven off the crank not chain. I`d set #1 at TDC and see if the mark on the crank is at "0".If not paint a mark there and recheck the timing. weights and springs in a dist set the time and total amount of advance that is available. they do nothing at idle speed.

 

[chewy7097h]

Re: Merc 120 (2.5L) Timing/Fuel/Iginition Help

I've been using the timing mark as in indicator for TDC. How do I find TDC without using the mark? This seems like one of those times where "close enough" doesn't cut it... At the same time - this would raise another question - what would cause the mark to be off 30 degrees?

The engine does indeed run at 8 degrees, but I got nothing over 2000 rpm or so (save for silence after the engine stalls). With the engine idling, if I advance the distributor from 8 degrees the idle increases up until I get around the mid 30's (checked with timing light). From this point, I get great top end performance, but real boggy at the low RPM's.

 

[JustJason]

Re: Merc 120 (2.5L) Timing/Fuel/Iginition Help

E=MC2....
MerCruis Redeux...
How to set base timing manually......

1. disconnect ignition coil and tape wire or do whatever you have to do so they don't ground out.
2. Look at the distro cap and where #1 is paint a mark on the rim of the shaft (where the cap meets the shaft) (i use white out... works ok)
3. Remove distro shaft, wires, plugs.
4. hook up a remote starter button
5. put thumb lightly over #1 cyl and "bump" starter until you feel compression
6. this part is a pita because of the motor mount on the 2.5... not letting you put a wrench on the harmonic balancer.... however.... after you verify that #1 is on compression stroke, stick a screwdriver down the spark plug hole, and slowly turn the balancer/main pulley by hand or with a wrench (in fact just disconnect the remote starter button at this point so you don't accidently hit it) until #1 piston is at exactly TDC COMPRESSION stroke... go slow... if you pass TDC then you have to spin the pulley twice around to get the piston back up there... don't spin the pulley backwards, you'll be fighting, and eventually will ruin the water pump.
7. look at the timing mark on the balancer, it should be lined up with the timing indicator on the timing cover... if it's not, paint a mark on the balancer (with white out)...
7a... if its doesn't line up by a little,
1. you are not exactly at tdc
2. you have a bent crankshaft.
3. the timing indicator is bent.
4. the key is broken and the hub on the balancer has spun
7b... if it doesn't line up by a lot
1. spun hub on the balancer....
2. your at TDC exhaust stroke and not compression
3. your skkaaarewwed
8. after you get #1 on tdc compression, reinstall the distro shaft so the rotor points to the mark that you made in step 2.... you will have to back the rotor up a bit as it will twist when you install it. The important thing is that it lines up with the mark you made when the distro shaft is seated.
9. being off by 1 tooth will throw your timing off wildly, and you will not be able to read it accurately.
10. good luck!!!!
11. Not everything is a 12 step program!!!