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Blow back through one carburetor on twin clyinder Evinrude

M

maverick1942

Member
I have purchased a 1976 Evinru

I have purchased a 1976 Evinrude 55 HP Mod: 55673E Serial E0004750. I have disassembled and cleaned both carbs and have good spark. Engine starts easily and idles. When attempting to adjust carbs I noticed I had some blow back on the top carb. I can put my hand over the bottom carb and engine will die. Put my hand over top carb and it makes little difference and engine keeps on running. I sprayed some Seafoam into clyinders and spayed carbs with engine running. I still have blow back on top carb. Any idea what my problem is?}
 
"Follow up: Thanks Joe Reeves

"Follow up: Thanks Joe Reeves for your reply to my post. I removed intake manifold and inspected leaf valve assemblies and found nothing wrong. Manifold gasket was a mess and had probally been reused and leaking. Cleaned gasket surfaces and installed new gaskets. I reversed position of leak valve assemblies on reinstallation. Started engine and noted blow back problem had been corrected. However, engine is still running on bottom clyinder. I can take the plug wire off of top clyinder and it makes no difference. Carbs have been rebuilt and I have spark to both clyinders. I pulled plugs and put my thumbs over plug hole while spinning engine, appears that compression is about equal. I do not have a compession guage.Any new ideas?"
 
"Thanks Morten for your reply

"Thanks Morten for your reply to my posting. As near as I can tell it looks as if both clyinders are firing at the same time. I pulled the plugs, held them both to ground with plug wires attached and cranked engine with electric starter, looks as if both were firing at the same time."
 
"Another update--1625 Eastern

"Another update--1625 Eastern Time. I did some more tests. I put top plug wire on bottom clyinder and tried to start engine. All it would do is backfire. My thinking was that if both coils were firing at the same time, engine should still run as before. I borrowed a compression gauge. Top Clyinder has 150 lbs of compression and lower checked 160 lbs compression. I am not a mechanic and this is the first outboard I have ever worked on so all I know is what little I have learned from the service manual that I have purchased for this motor. Thanks again for any advice you can give me."
 
"That means You have most prob

"That means You have most probably lost ignition on one cylinder!
Top cylinder is fireing both at the same time, bottom may be 'dead'.
Most often it is a defective power pack, but measure output from stator, trigger and power pack.
A manual will in this case be handy!"
 
"Thanks Morten for your guidan

"Thanks Morten for your guidance. I used an ohm meter to test the ignition coils. charge coils, and sensor coils. All checked good. I swapped ignition coil position and bingo. It still ran on the same clyinder. I think the power pack has to be bad. Do you agree? Thanks again to you Morten, Joe, and marineengine.com for providing this message board. It is a blessing to get technical assistance without it costing an arm and a leg. Us old guys that live on a pension can not afford to go to a dealer for repairs. Thanks"
 
If you swapped the output wire

If you swapped the output wires from the pack and the same coil still fires then it would seem that it is the coil.Both outputs are good but one coil will not fire.
 
"If both coils fired originall

"If both coils fired originally, it is not likely a defective coil!
To be sure it is the pack, swap the outputs from the power pack and run a cranking test (NOT START), then the the double fireing should change to the other cylinder."
 
"You stated that your compress

"You stated that your compression was 160 and 150 correct? Was the 150 on the cylinder that is also blowing out the fuel? We have found over the years that the earlier 2 cylinder 50's 55's 60's are much less receptive to compression variances, sometimes as little as a 5lb difference is enough to require a rebuild on them."
 
"A small comment to Michael co

"A small comment to Michael comment above.
This goes in general for all the older cross engines, and the reason is the location of the upper piston ring which is very close to the piston top.
Cross engines in general are more vulnerable to burn the piston top edge at the exhaust port which again gives a very early warning, slightly comp difference, that the piston is dammaged and soon the ring would be gone. As a general rule I allways stripped off the head to check the conditions.
However should I recommend every one on this board to strip the heads every time I would probably quite soon loose credability.
As a general rule for the old loopers I recommend to completely dismantle the powerhead and reseal every 10 years. Doing this the engine would probably last for ever!"
 
PS:
Was a bit too quick: repl

PS:
Was a bit too quick: replace loopers with cross engines when it comes to reseal every 10 years.
 
"Thanks gentlemen for your rep

"Thanks gentlemen for your replies. Michael, while I have engine out of the water I will pull the head and inspect clyinders. not-a-student, I not only swapped wires in power pack, I swapped coil positions and the bottom clyinder was still the only one firing correctly. Also checked coils with ohm meter. Coils ok. Morten, I will swap the wires in the power pack as you suggest to make sure the problem is the power pack. Also, I do not understand some of the trade language y'all are using. What is a cross engine and what is a looper? If I had to guess, I would say a looper is a piston ring. Does reseal stand for rebuild? Don't laugh guys, I know I am a dummy!"
 
"Thanks gentlemen for your rep

"Thanks gentlemen for your replies. Michael, while I have engine out of the water I will pull the head and inspect clyinders and yes, the 150 lb clyinder is the one that was blowing but it stopped blowing after I replaced intake manifold gasket. not-a-student, I not only swapped wires in power pack, I swapped coil positions and the bottom clyinder was still the only one firing correctly. Also checked coils with ohm meter. Coils ok. Morten, I will swap the wires in the power pack as you suggest to make sure the problem is the power pack. Also, I do not understand some of the trade language y'all are using. What is a cross engine and what is a looper? If I had to guess, I would say a looper is a piston ring. Does reseal stand for rebuild? Don't laugh guys, I know I am a dummy!"
 
When I test I leave the coils

When I test I leave the coils where they are and switch the wires to them that come from the pack. If the same coil still fires then the powerpack is OK.
 
"In a 'cross' engine t

"In a 'cross' engine the fuel/air mix enters the cylinder, is pushed upwards to the combustion chamber in the head by a potrusion on the piston top, gets ignited and passes straight out through the exhaust port on the oposite side of the intake ports.
In a 'looper' engine the mix enters the cylinder, passes over the piston tops, hits the cylinder wall on the other side, makes a 'loop' up and back and gets ignited by the spark and emerges out the exhaust ports(s) still opposite the intake ports. Pistons in theese engines are flat on top or slightly convex."
 
"Update: I still have the sam

"Update: I still have the same problem. The engine is running on the bottom clyinder. I ordered a new power pac and one coil from marineengine.com I installed them today. No help, engine is still running on bottom clyinder. I replaced one coil because one of my old ones had a crack in the coating over the winding. It tested good on my ohm meter but I didn't like the look of that big crack. What next can I do?"
 
Do You still have double spark

Do You still have double spark?
Do You have the possibility to post a pic of the sparks?
 
"Yes, both coils are firing.

"Yes, both coils are firing. I can not tell if both are firing at the same time. I do not have a needle point spark checker but I do have a digital camera. I will see if I can find a couple guys to help me set up for the picture and I will post it."
 
"let us go back to square &#39

"let us go back to square 'one'.
1:You have an engne that starts, idles and runs obviously without any significant problems?
2: For some reasons You wanted to adjust the carbs?
Was this done the correct way?
With reference to below pic, here is roughly the procedure.
Start the engine, let it run at lowest possible idle. Loosen screw '15' so both carbs are completely closed. If engine stops, advance ignition, but DO NOT open the carbs!
Start with both needle mix screws '30' about 2,5 turns out from seated and adjust to max rpm is obtained without adjusting ignition, but try to keep the rpm below 700. When max rpm is obtained, open the mix screws another 1/3-1/2 turn.
Stop the engine and adjust the cam.follower and tighten screw '15' so the carbs starts opening when the follower is at the mark on the cam.
Put back the silencer box and be sure gaskets are ok.
Unhook the throtle cable from the engine and adjust the idle adjust screw (Not mix screw!), engine in gear, boat not tied to the dock - idle around 750.
Do a test run. If engine hessitates at acc, You may have to open the needle '30' anothe 1/8-1/4 turn.
53741.gif
"
 
"Reply to Morten.The answer to

"Reply to Morten.The answer to your first question is no. Engine starts easily but is running on one clyinder, the bottom one. Take top plug wire off and it makes no difference. Take bottom plug wire off and engine dies.I have stated this in the posts above. Question 2, the only reason I tried adjusting the carbs is because of top clyinder not firing properly. By reading above posts you can see what has been done and what has been checked. Thank you for the info on proper carb adjustment for this engine. I am in the process of checking the wiring for any problems. This engine is 30 years old so I might find just about anything. Thank you for your replys to my posts. I hope we can figure out what the problem is with this engine. I bought it and it is no good to me if don't run, however, that said, I do not give up easily and I will keep trying. At one point, we even changed carb positions, top on the bottom and bottom carb in the top position. Same thing, still runs on bottom clyinder. Swaped coil positions, same thing. Replaced power pac and one coil, still runs on bottom clyinder. Mercy sakes, this one is a real brain teaser, Roger Beep."
 
"This leaves ut at the moment,

"This leaves ut at the moment, after change of PP that You have ignition on both cylinders, hopefully not at the same time. If You have reasonable compression (stated above) You must lack fuel, unless a faulty cylinder/piston.
Time for a clean/rebuild of the carbs (might as well take both). Note the small gasket '39' in the pick above. If that is defective, carb sucks air and nt fuel. It is important that that starts 'sealing' before the bigger one '37'."
 
Have you inspected the outside

Have you inspected the outside of the top crankcase??These motors have a history of breaking a piece off the piston and then in turn a piece out of the block. No crankcase compression means no operation of the cylinder.
 
"That kind of happenings are n

"That kind of happenings are normally caused by big end failure on the con rod, meaning no piston movement and no compression! Here we obviously have a reasonable, however reduced compression reading on the 'problem' cylinder."
 
You can have a hole in the cra

You can have a hole in the crankcase caused by a piece breaking off the piston.No crankcase compression but perfect cylinder compression.At any rate finding the problem on this motor should really be easy.
 
"Thanks Gentlemen for your hel

"Thanks Gentlemen for your help. I am spending the winter in Florida and do not have my tools with me. I will be going to NC the first week of Feb. and pickup enough of my tools to tear this engine down. I will report back my findings to this message board when I find the cause of my problem. Not-a-student, you may be right about the hole. Will let you know in February. Thanks again guys."
 
"In reviewing all of the above

"In reviewing all of the above, I see reference to testing the ignition (spark) but apparently by simply using the spark plugs? If so, this is no test as spark will jump the very small plug gap when the plug is in open air BUT it may not jump that gap when under compression.

The spark must be a strong blue lightning like flame.... a real SNAP!

To test the spark properly, you must use a 7/16" gap at cranking speed with the spark plugs removed. You can easily make such a spark tester as follows:

Spark Tester - Home Made
(J. Reeves)

A spark tester can be made with a piece of 1x4 or 1x6, drive a couple nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:


..........X1..........X2

.................X..(grd)

..........X3..........X4

The compression mentioned (10psi difference), low reading on top cylinder, would indiate to me that either the engine has been run with a fouled top carburetor (cylinder running lean), or the ignition being weak on that cylinder.

Let us know about the spark, with it being tested with the 7/16" gap."
 
Thanks Joe for the info. I wil

Thanks Joe for the info. I will build a spark tester today and get back to you with the results. Question? I put new spark plugs in motor. Engine starts easy but is running on bottom clyinder only. After several starts I can pull top plug and it is dry as a bone. Shouldn't it be wet if upper clyinder is functioning properly?
 
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