70hp all new igniton still bogs! quick help

[RaScLeS]

70hp merc 3cy from 1979, has new pack trigger stator and a working set of newer coils good gas and the carbs freshly cleaned. I cannot think of anyuthing else to do to get this to work. the power pack is grounded as it should be

the boat sometimes will take off to almost 4800rpm and die out from there, ive had the boat over 5000 before when it worked and held steady,

any help needed I cannot figure this out, it seems to run with 1 and 3 plug wire on as well as 1 and 2 wire on the same, as if both of those cylinders were getting a weak spark.

compression is all over 125psi

help

 

[Big flop]

Re: 70hp all new igniton still bogs! quick help

Does it have good spark during spark test?
Maybe time to look at the fuel system?

 

[CharlieB]

Re: 70hp all new igniton still bogs! quick help

Have you tried momentarily bumping the choke/enrichener or squeezing the primer bulb to see if either makes any difference? If yes then that shows a fuel restriction, fuel pump rebuild, old hoses, poor flowing connectors, fuel tank fitting or dip tube.

 

[RaScLeS]

Re: 70hp all new igniton still bogs! quick help

will try the choke and report back. I had it out in the morning and ran just fine for 20-30mins the best ever and I came home to dock it because it was low on gas. I went to use it later and it was no power. unheard of :S

 

[ajgraz]

Re: 70hp all new igniton still bogs! quick help

When you cleaned your carbs did you remove (as in totally unscrew and take off) the brass "T" and "L" inlet fittings on the bottom and top carbs (respectively)?

I had a lot of the same issues, did a carb cleaning, removed those fittings, and they were incredibly choked up with some dry, flaky crap that I must assume was dried-up varnish. Problems disappeared.

 

[RaScLeS]

Re: 70hp all new igniton still bogs! quick help

they were professionally cleaned im not sure exactly. only once I had the boat out in the exact state it sits right now, running smooth all across and hammer past 5grand.

RIGHT NOW it can be rev'd and blown up in neutral (runs on all 3 strong) but once in gear its dropping cylinders or flooding.

choking didnt help and I really need help!

 

[RaScLeS]

Re: 70hp all new igniton still bogs! quick help

bah well since everything checks out the only thing left is to re wire the main harness with new wires and connectors theres one red to brown, orange and black. even the starter wires were corroded bad and frayed so replace those aswell :S

I dont have much faith lol whos got any ideas what to do

edit: I havent blown any pistons yet after all this trouble testing it still 120psi across

 

[PHE]

Re: 70hp all new igniton still bogs! quick help

I have a 78 70hp that had a similar problem when I first got it three years ago. It would run fine at low RPM but would start missing around 3000 to 4000 RPM. Turned out to be the switch box dropping the first cylinder as RPM increased. Replaced it with an aftermarket for around $125, if I remember correctly, and it has run fine since.

A couple of other things worth mentioning. The floats on mine like to be level when removed and upside down. If set at the spec, it ran lean at max RPM. Also, the idle screws need to be set on the rich side to get a good hole shot. I also timed mine at 21 Deg BTC instead of the 23 spec so I can safely run regular gas.

 

[PHE]

Re: 70hp all new igniton still bogs! quick help

One more comment. I noticed that you mentioned that it can be "rev'd and blown up in neutral". Don't rev it past 1500RPM's in neutral or it will blown up.

Also, that motor doesn't have a good filter. Just a screen between the pump and carbs. You should check and see if the screen is clean. Also would be a good idea to put a real filter after the screen. A cheap Briggs and Stratton lawnmower filter works just fine. If there was junk in your fuel lines after the carbs were cleaned, they are probably dirty again.

Might also be a good idea to replace all the fuel lines. Alcohol in the new gas can desolve the lining in old lines. New fuel lines are design to resist alcohol.

 

[RaScLeS]

Re: 70hp all new igniton still bogs! quick help

thank you so much and welcome to the site !!! I was looking at the answer earlier today for 120$ on ebay, a new aftermarket pack. I will run by withmy mechanic what settings the carbs and timing is at. I need to buy a timing light anyway so I can also check myself.

lol I get angry with the engine its probably seen 3+k in neutral for a second and I really did not care if it popped.

so cold compression is between 120-125psi. full maintenance by mechanic (impeller carbs cleaned new trigger stator and varous tests)

I put all new wires on the merc, 14gauge wire was used and it started and worked the same....but some wires were all but one strand so this was needed. (wires replaced were only starter choke rectifier and merc switch wires)

I keep saying it but I guess ill give it another shot and order this pack? I have spare coils and 3....yes 3 dead packs. only one runs the motor now but has no power and is also garbage.

Im worried of frying the new pack but a 90day warranty on them (never heard of warranty on this till now) might put me at ease.

any other suggestions highly highly appretiated

for anyone reading THE NUMBER TWO PISTON DOES NOT SPARK. the motor runs freely on just one cylinder!!! top or bottom. strange mercs. and because no spark on 2 my lower carb is wet.

strange thing is two weeks ago I went to randomly mess with it and it started, ran perfect all the way till i shut it off at the dock 30-40minutes later. never got it to go again :facepalm:

 

[RaScLeS]

Re: 70hp all new igniton still bogs! quick help

I did a quick test of the rectifier since my tach stopped working :S could be from not disconnecting the battery ONE time....anyway

the rectifer showed I believe 2M ohms and open in reverse polarity bolted to the engine. off the engine I get open both ways. confused about the tach but more so getting the motor to run right. iffy on buying the new pack still

 

[PHE]

Re: 70hp all new igniton still bogs! quick help

I've read this site occasionally and found a lot of good info here. I thought I might as well try and help someone else out.

I found what caused my switchbox to go out before I put the new one on. The problem was in the connector from the controls on the motor side. Two wires had rubbed together until they were making contact. It was the wire to the starter soleniod and the wire to the kill terminal on the switchbox. Normally, when you turn the key switch off, the switch grounds the kill terminal and stops the motor. With the wires shorted, 12VDC was applied to the terminal whenever I hit the choke button. I've read that applying any voltage to this terminal will blow the switchbox. I wouldn't think that this has happened with yours, since it seems like a strange occurance for wires to short in a connector, but you might want to check the voltage on that wire before you connect it to the new box. Also, make sure all ground wires are clean and have good contact.

The rectifier really has four terminals, the fourth being ground to the block. The way to check it is with the meter set to diode mode. With the black meter lead on the battery terminal, you should get continuity from both stator terminals when touched with the red meter lead. Then put the red lead on the battery terminal and you should get no continuity from either stator terminal. To check the other two diodes, put the red lead on ground and you should get continuity to both stator terminals. Put the black lead on ground and you should not get any continuity to the stator terminals.

Another way to check if it is charging is to simply put the volt meter across the battery terminals, then start the motor. If the voltage slowly increases above 13VDC while it is idling, it is charging, although you could still have one leg of the rectifier bad.

Hope this helps.

 

[PHE]

Re: 70hp all new igniton still bogs! quick help

***

 

[ajgraz]

Re: 70hp all new igniton still bogs! quick help

PHE,

Not a strange occurrence. My 1978 70hp Merc had a short in the engine harness' connector that blew a switchbox. I bought another used harness off EBAY, it had the same short. I bought a third, same short. Finally I bypassed the connector and hardwired the control box harness to the engine harness.

 

[PHE]

Re: 70hp all new igniton still bogs! quick help

ajgraz,

Guess I wasn't alone with that problem and it was a design flaw. I used a dremel tool and pick to get into the connector. The two wires were very tightly wrapped before they potted it and gradually rubbed through due to the vibration. I was able to seperate them and re-pot it. I figured if I screwed it up with the dremel tool I could just hard wire it like you did. Glad I checked it all out before I blew new box.

 

[RaScLeS]

Re: 70hp all new igniton still bogs! quick help

well after tomorrow I will look into my mercury again testing the rectifier and other components.

I have a brand new switchbox on hand I will put in once sure everything checks out.

should I really get another set of plugs? The set in has an hour or less and same for the other 3 sets or so most likly. other then that gas is good all good hope when the throttle goes down it goes.... any more advice would help. Ill see the mercury manual on putting this in it has a warranty but with 3 packs set to the dead pile Im not sure this will work as it sits

 

[ajgraz]

Re: 70hp all new igniton still bogs! quick help

RasCleS,

Please let us know if the new switchbox (it is NEW, right, not used) fixes you up.

I think I have a bad switchbox again. Like you I've cleaned up the whole fuel system, I've DVA'd and VOM'd everything I can; yet my symptoms are exactly the same as PHE describes and very similar to yours, and IIRC the last time I swapped in a new switchbox many years ago it fixed the same set of issues I'm having now (again, like PHE describes).

 

[RaScLeS]

Re: 70hp all new igniton still bogs! quick help

to quickly respond I havent bolted it in only because im affraid of disappointment. but am doing so now.

the pack is a new aftermarket similar to the trigger and stator. 107$ was the price at like 280 retail.

currently going to test the rectifier with the above checks, take off the battery ground take off the switchbox and install the new one.

I am considering starting the motor so it starts easily on the new switchbox ( I can start it like a new engine on 2 cyl lol)

best luck to myself

 

[RaScLeS]

Re: 70hp all new igniton still bogs! quick help

Part started the motor on 2 cylinders smoked and ran bad. another 100+$ sent to the devil. any more suggestions ill take but that was it. purchased a merc poured hours of money and time into it new parts all around ready to go around the world youd think and I cant leave my dock. no old mercs for me.

all there is left is a problem in the harness itself. not sure how to address that but not really interested any thoughts post thanks

also my guess is i have two working packs since no difference in the most recent one and the new one. strange old mercs you beat me

 

[PHE]

Re: 70hp all new igniton still bogs! quick help

Sorry to hear that didn't fix it. After what I and ajgraz experienced with the harness shorts in the connector, I think you really should look at that. He mentioned having three shorted harnesses. Mine had a short between the wire going to the choke and the kill wire. This put 12VDC on a pin on the switchbox when I pressed the choke that is only supposed to float or be grounded, and it killed my box.

Not sure if you have an oscilloscope to look at the output of the switchbox to the coils, but you might be able to check the output with a DVM on AC. Compare each output to each coil when it is running and see if they are the same. This should tell you if the box is working. An oscilliscope is better, of course. Also check the resistance of the coils to see if they are all the same. I suppose you did check each plug wire with a timing light to verify that you really are running on 2 cylinders.

I wouldn't give up just yet, but back up and try to diagnose it a little more before buying any new parts.

Hope this helps.