PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

[geddron1976]

Hi All,

I bought my 75 merc around 4 years ago and it has been a great engine.

However, last season i began to get some problems with the engine not idling correctly. It began to be a little troublesome to start from cold and when warm, it would only idle for 2-3 minutes before dying out.

A quick rise of throttle would keep it going and give you about another 2 minutes of idle. It would stall at low speeds when manouvering on to moorings etc, as i transferred the gears from forward to reverse to slow the boat to a stop when aproaching the harbour wall and resulted in some bruising to the bow of my boat.

I decided earlier this year to service the carbs and bought a repair/service kit.
I stripped and cleaned the carbs and replaced all the parts that came in the kit and then consulted the SELOC manual to rebuild and re install the carbs. when the carbs had been installed, the engine would not run at idle at all!

It will fire up at fast idle on the control box with some choke, but as soon as the engine drops below 1800rpm, it just dies.
I had a friend crank the motor whilst i adjusted the idle mixture screws to see if i could get it to even cough, but nothing.
I have bought a timing light to check the timing advance but as the seloc manual states that the engine should be at idle speed and in forward gear in the water before the link and sync and timing adjustments can be made.

So, how can i make the adjustments if the engine won't idle? GRRRRRRrrrrr!!!

I am beginning to suspect a crankshaft seal, but that may just be my mind running wild due to the frustration of wearing out the cranking motor hoping for ignition before the battery drains again!

Is there anyone out there that can help me sort this motor out without having to get a mortgage out to do it?
I'd really appreciate the benefits of your guys experience and also if anyone knows the spark advance settings i woudl be grateful as i have been told that the SELOC manual is quoting BS.. i would love to get a genuine mercury manual for this motor but i can't find one anywhere.

Thanks in advance for any help youl can give me..

Best regards

Paul AKA Geddron1976

 

[Chris1956]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

Paul, Idle timing is easily checked/set. Remove the 2, 3 and 4 spark plugs, install them into their wires and ground their bases to the block. Now advance the throttle until the carbs are ready to open, but still closed. Put a timing light on the #1 spark plug and crank the motor and read the timing. Push the throttle all the way forward to check max advance.

So you cleaned the carbs and adjusted the floats right? if so, set the idle mixture needes 1-1/2 turns out from lightly seated, and reinstall the spark plugs. The motor should start and idle in gear at 900 RPM or so. You need to adjust them for max idle speed and quality and then for correct richness.
Post back and let me know how you do.

 

[geddron1976]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

Paul, Idle timing is easily checked/set. Remove the 2, 3 and 4 spark plugs, install them into their wires and ground their bases to the block. Now advance the throttle until the carbs are ready to open, but still closed. Put a timing light on the #1 spark plug and crank the motor and read the timing. Push the throttle all the way forward to check max advance.

So you cleaned the carbs and adjusted the floats right? if so, set the idle mixture needes 1-1/2 turns out from lightly seated, and reinstall the spark plugs. The motor should start and idle in gear at 900 RPM or so. You need to adjust them for max idle speed and quality and then for correct richness.
Post back and let me know how you do.

Thanks for getting back to me so quickly, I am going to try what you have said.

before i do this can you confirm if this sounds correct as this is from a seloc manual and i am beginning to lose trust in the darn thing. It states that timing should read 3-4' BTDC at idle and max advance should read 23' BTDC. does this sound about right or should i shred the book?

 

[Wingedwheel]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

Just a thought, but you might want to do a compression test as well.

 

[Chris1956]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

I am not sure about the specs. They do use those specs on a distributor ign Merc 850, but you motor may be different. Also, the 23* Max advance might be better set to 21* with today's fuel.

I had thought ADI ignition would have idle spec of 4* ATDC. Your motor is ADI right?

 

[geddron1976]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

I am not sure about the specs. They do use those specs on a distributor ign Merc 850, but you motor may be different. Also, the 23* Max advance might be better set to 21* with today's fuel.

I had thought ADI ignition would have idle spec of 4* ATDC. Your motor is ADI right?

I'm not sure what ADI is chris? forgive my lack of technical knowledge.. The engine is running the thunderbolt V ignition system and has the 4 seperate coils, so if thats ADI, then yes! lol..

It does say in the SELOC manual that it is BTDC, but then i have read a lot of bad press about Seloc having misprints and bad information etc, so i just thought i'd check with someone.

I have run a compression test and all 4 cylinders are pushing out 135-140psi, so i'm pretty pleased with the compression, if only i could get it running again i'd be even happier! ha ha..

I am awaiting a second pair of hands to check the ignition timing but will let you know the results as soon as i can chris.

 

[Chris1956]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

yes, ADI is the 4 coil ignition system. It is Alternator Driven Ignition.

 

[geddron1976]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

yes, ADI is the 4 coil ignition system. It is Alternator Driven Ignition.

Ok, My friend has helped me with the timing and it is now reading at 4' BTDC on the primary pick up and around 23' at WOT.

I set the mixture screws at 1,3/4 turns out from lightly seated and turned it over and it tried to start but still failed.
I then tried moving the throttle to around half and choked it and it run up on 2 cylinders initially and then fired on 4 and sounded a little better than it had prior to the adjustment you advised chris.

However, I was checking out the carbs whilst my friend was cranking the motor and noticed that the bottom carb seems to be drawing fuel through the main jet whilst the throttle is closed to idle, also the top carb was dripping with fuel from what i believe is the bottom of the throttle body. the fuel was running down the link between the 2 carbs.

I then got my friend to crank the motor whilst i placed my hand over the carb openings to check the vacuum. I found that when i placed my hand over the bottom carb, the vacuum was very good and the engine actually fired up and ran until i removed my hand. the top carb, seemed to have hardly any vacuum but still when i placed my hand over the carb, it tried to fire up again???

I am REALLY confused with this now. the timing seems to be as close as damn it but the carbs are giving seriously strange results.. obviously the throttle body leaking is not going to help the cause, but do you think there is anything here that would suggest a crank shaft seal?

 

[geddron1976]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

Ok, My friend has helped me with the timing and it is now reading at 4' BTDC on the primary pick up and around 23' at WOT.

I set the mixture screws at 1,3/4 turns out from lightly seated and turned it over and it tried to start but still failed.
I then tried moving the throttle to around half and choked it and it run up on 2 cylinders initially and then fired on 4 and sounded a little better than it had prior to the adjustment you advised chris.

However, I was checking out the carbs whilst my friend was cranking the motor and noticed that the bottom carb seems to be drawing fuel through the main jet whilst the throttle is closed to idle, also the top carb was dripping with fuel from what i believe is the bottom of the throttle body. the fuel was running down the link between the 2 carbs.

I then got my friend to crank the motor whilst i placed my hand over the carb openings to check the vacuum. I found that when i placed my hand over the bottom carb, the vacuum was very good and the engine actually fired up and ran until i removed my hand. the top carb, seemed to have hardly any vacuum but still when i placed my hand over the carb, it tried to fire up again???

I am REALLY confused with this now. the timing seems to be as close as damn it but the carbs are giving seriously strange results.. obviously the throttle body leaking is not going to help the cause, but do you think there is anything here that would suggest a crank shaft seal?

just to correct that, the timing is at 4' ATDC at idle, 7-9 BTDC at primary pick up and 23' BTDC

 

[Chris1956]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

well it sounds like the next step is to fix the carbs. Make sure the idle jets are clean. They look to be on the face of the carb. I am not real familar with the center bowl carbs, so I cannot point out specific areas. Fuel leaking is usually due to bad floats or bad inlet needle and seat. it appears both are avail for your motor. You might replace them. make sure the carb-to-crankcase gaskets are good and seal well.

 

[geddron1976]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

well it sounds like the next step is to fix the carbs. Make sure the idle jets are clean. They look to be on the face of the carb. I am not real familar with the center bowl carbs, so I cannot point out specific areas. Fuel leaking is usually due to bad floats or bad inlet needle and seat. it appears both are avail for your motor. You might replace them. make sure the carb-to-crankcase gaskets are good and seal well.

carbs have been cleaned out and new gaskets fitted to the carb to engine joints. leak is definitley coming from the throttle shaft seal on the top carb.
i am going to order 2 carb repair kits, refurb the carbs and try again. I am hoping that the repair kits work as money is fast running out!
over here in the uk, the repair kits are around $165.00 for the 2 kits. I keep seeing the prices over there in the US and wish the UK would adopt your prices! they are seriously stealing from us english boat owners..

thanks again for your help

I will update as soon as possible and let you know the outcome of the repairs..

Best regards

 

[Chris1956]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

Paul, the fuel in the carb should never get high enough to leak out of the throttle shaft. This indicates a carb inlet needle/seat issue. I recommend you inspect, clean and be sure to set the float height correctly.

 

[geddron1976]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

Paul, the fuel in the carb should never get high enough to leak out of the throttle shaft. This indicates a carb inlet needle/seat issue. I recommend you inspect, clean and be sure to set the float height correctly.

I have stripped the carbs today and am just waiting for repair kits to arrive from the US.

I mentioned previously that the fuel was leaking from the throttle shaft. When i was stripping the carbs down the bowls were full of fuel, so i poured a little through the carb from the front (airbox side) as the fuel passed over the guide hole the the throttle shaft passes through, fuel began dripping out of the seal/washer/spring assembly at an alarming rate! I checked the seals and they are very loosely fitted. They appear to be a cup type rubber seal.

The thing that is troubling me at the moment is that whenever i have seen a seal that slides over a shaft of any sort, the middle of the seal usually has a small looped spring around it. For example, the main gearbox seal thats fitted to the selector shaft.
The seals fitted to the throttle shafts on this engine are simply rubber and without anything to support the seal against the shaft that they are supposed to be sealing. Is this normal or is it likely that someone has fitted the incorrect seals previously?

If this is the way these seals are then i believe that these ones are shot as when inspecting the lower carb, the seal on this also leaks fuel and appears to be lose fitting.

Fingers crossed when i get these repair kits in hand, it will breathe life back in to the old dog.. Can't say i'm too optimistic though as my luck kinda sucks recently!

 

[jimmbo]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

So much for boating being a recreation for relaxation

 

[Chris1956]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

Paul, You can look at the carb parts list, but I do not think you will see a seal for that area. They may have a brass bushing or just a naked aluminum hole. On a properly tuned carb, there will not be any fuel there to leak, so a seal is unnecessary.

 

[geddron1976]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

Paul, You can look at the carb parts list, but I do not think you will see a seal for that area. They may have a brass bushing or just a naked aluminum hole. On a properly tuned carb, there will not be any fuel there to leak, so a seal is unnecessary.

Hi chris, i've already looked at the parts list and also the carb. There is a throttle body seal which is situated on the bottom of each throttle shaft, this is then covered by a brass washer and then the throttle return spring.

Inside the carb, where the throttle shaft passes through the intake, you have the throttle butterfly plate. the shaft passes straight down through the intake and comes out the bottom of the carb, so as the fuel passes through the throttle butterfly, it is escaping down the shaft and leaking out the bottom.

When i removed the throttle shafts, the cup type rubber seal was not sealing against the shaft and subsequently the fuel was running out through the seal down the throttle shaft.
I have checked and reset the floats just to be sure, but i now have to wait for the parts/gaskets to arrive before i can complete the rebuild and reinstall them to the motor.

It makes sense now why i was finding small pools of fuel in the bottom tray ocassionally.

This obviously isn't helping the engine run right, so although it may not be the major cause of the problems i am having, at least fixing it should improve my chances of getting it right in the end.

 

[geddron1976]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

So much for boating being a recreation for relaxation

If i could spend as much time relaxing and fishing with my boat as i do fixing it, life would be great! unfortunately i seem to be working more hours so i can afford to fix and run it! can't beat the buzz when it's all working well though.

I only wish i had the money to buy a new e-tec evinrude, but then again there is a certain pleasure in knowing that i'm keeping an old dog going.. they don't make them like they used to. Ok so they use a bucket load of fuel but they have a certain character that gives them their charm!

fuel over here is now about $10 a gallon... unbelievable isn't it!

 

[treker]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

I would really check out your floats, specially the suspect one, You can do this with water cause if it is getting fuel leakage you are going to have to replace it anyway. Let them sit underwater for awhile, you may even see air bubles when you put it in the water

 

[geddron1976]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

I would really check out your floats, specially the suspect one, You can do this with water cause if it is getting fuel leakage you are going to have to replace it anyway. Let them sit underwater for awhile, you may even see air bubles when you put it in the water

thanks for the advice treker, i have already tested them in a bowl of fuel. I put the floats in the fuel and placed a weight on top to hold them down and when i took the weight off the top next morning, they shot straight to the surface and no fluid inside them. i'm pretty sure they are the originals but they are in great condition for their age.

`

 

[geddron1976]

Re: PLEASE HELP ME BEFORE I GO INSANE!!!!!! 1986 Mercury 75hp 4cylinder idle trouble

Can you believe i am still waiting for the throttle shaft seals to arrive? ordered them 2 weeks ago nearly and they haven't even left belgium yet! apparently they will arrive next wednesday!
fingers crossed the new seals will sort the problem or else i've been waiting around and will be back to square one again on wednesday!

does anyone know anywhere else that the seals can be bought from? i have looked around on the net, but because the seals don't have a a part number on them, it's almost impossibe to find an alternative supplier other than mercury.