1978 70hp evi runs poorly

[fireman57]

Model number 70873C. Picked it up cheap and had even compression when I bought it. 125 on all three cylinders. Got it home and fired it up. Ran rough so cleaned the carbs. When testing it on the water I could get it up to speed (5200 rpms) but ran rough. Pulled the plugs and had water on #2. Replaced and torqued new head gasket. Still had water in number 2. Replaced all exhaust gaskets and that cured the water problem. No scoring in any cylinder and compression is still around 125 on each cylinder. Still no hole shot and have to hit the primer to get up to speed. Tore down and soaked all carbs and blew them out. Still no change. Rebuilt with new kits, except the welch plugs, and still no change.There is one low speed jet that is about an 1/8th of an inch from screwing all the way in. Have replaced it but still won't screw all the way in. All passages are squeaky clean. Installed an inline fuel filter. Have spark on all three cylinders at low and high speed. Have checked the timing using Joe Reeves method and everything is linked and synced.
I know it is a long post but wanted everyone to know all that has been done. At my wit's end. Any suggestions would be appreciated.

 

[Joe Reeves]

Re: 1978 70hp evi runs poorly

Compression is good at 125 psi each cylinder.

With spark plugs removed, the spark should jump a wide 7/16" gap with a strong blue lightning like flame... a real SNAP! Does it.

Engine NOT running, spin prop and put engine into forward gear. Have someone slowly advance the throttle while you observe the timer base under the flywheel (spark advance). It should move smoothly from its retarded position all the way to the full spark advance position. If it sticks, find out why and correct that problem.

Spark plugs should be Champion QL77JC4 plugs gapped at either the original recommended gap of .040 or the 1990's revised recommended gap of .030. Try both gaps as one or the other may give improved performance at either idle or full throttle (It varies).

Note: Cranking engine over, especially in the dark, with no spark plugs installed will reveal any faulty coils that may be shorting to ground.

The slow speed jet that isn't "seating" may simply be due to a carburetor that has the jet threads machine slightly early. Make a note of the screwdriver shank when you insert the jet BUT before you start to screw it in and seat it. That statement is somewhat confusing as the threads of the jet are only about thre 1/8" you state. However, with that jet removed, look closely down that passageway to see if there is any foreign debris jammed in there.... also check to see that air passes thru that passageway properly.

The most overlooked item in cleaning/rebuilding a carburetor are the high speed jets. These (one to a carburetor) are located in a horizontal position, way in back of that float chamber drain screw/bolt that you see at the bottom front of the carburetor.... in the bottom center portion of the float chamber (they have 1/4x20 threads). Cleaning solvent really doesn't do a proper job on these jets so carefully clean them manually with a piece of single strand steel wire.

Now, your picture at the left of your post..... Is that Piano, a grill, or are you just a heavy smoker?

 

[fireman57]

Re: 1978 70hp evi runs poorly

Joe thanks again. This is the same boat that you had the thrust plates for the t/t. Again, really appreciate them.
Spark is a nice blue and easily jumps the distance.
Timer base works with the butterflies but have not done it in gear, only neutral. Will try it in gear but seems to move easily all the way to the stop.
Plugs are correct and new. Gapped at .40 but will try .30. I usually gap them at .30 if the boat does a lot of idling or trolling. This one is supposed to be going all the time as it is a small skit boat. 15.5 ft Aeroglass.
all the low speed jets are clean and have "scraped" and brushed but can't find anything in the threads or the end of the seat where the jet screws into. Just didn't know if it not being in the same amount would make a difference.
I have run small strands of wire through each of the high speed jets several times and sprayed cleaner through them. I am confident that there cannot be anything in there. Are the high speed jets removable? If they are I will drag them out and that way I can visually inspect them.
Also, how important is it to pop the welch plugs out and clean all of that. The reason I ask is because I ahve never had to do it before cleaning a carb. My understanding is that they are holes from casting and have a bb sitting on the hole and the plug seals it so it doesn't become an air leak. If that is not the case then I will pop them off clean and replace them.
Now for the fun part. We had an old piano that nobody wanted, even for free. No school or organization wanted it unless it was perfect condition. I ordered a new computer and was going to rearrange the small room in the basement where the piano was and there wouldn't be enough room with it in there. My buddy came over that day that the computer arrived so we rolled the piano to the back door and put a rope around it on some planks and drug it up the back steps, rocked it into the bed of the truck and rocked it back out on the burn pile. After a couple of barley sodas we decided to light it. The old shellac on it started easily and we took pictures and video of it while she burned. I use my favorite as an avatar. One great day it was too!

 

[fireman57]

Re: 1978 70hp evi runs poorly

bump

 

[Joe Reeves]

Re: 1978 70hp evi runs poorly

It is very seldom that I remove core plugs when cleaning/rebuilding a carburetor. However, to remove, I simply cave them in slightly with a shart center punch, enough to break thru so I can pry them out with a scribe, BUT the word is "CARE"! You absolutely do not want to go deep enough where you might damage the carburetor's passages.

The only thing under those core plugs are (usually) just small holes leading into drilled holes.... no lead shot (bb's) under them. The lead shot thing is a separate scenario.... just a small piece of a small lead fishing anchor to plug a exterior drilled hole.

The high speed jets are removable. They have 1/4x20 threads. Use a screwdriver that has a shank that is just perfect to fit in the threaded hole, just clears the threads, then file the end of the shank to look like the picture I am attaching here. You'll need a old (or new) extra high speed jet to get it perfect.

 

[fireman57]

Re: 1978 70hp evi runs poorly

Joe, the timer base is fully advanced against the stop at about 1/2 throttle. should I adjust the stop so there is more room to advance while it is getting more fuel?
The thing I don't get is the carbs are whistle clean, haven't done the welch plugs but did put fingernail polish on them so they are definitely sealed, and we can hit the primer and it will take off. It just screams fuel issue to be. The bottom jets have been removed (already made the tool) and they are squeaky clean. Pumping the primer bulb makes no diff so it's not the fuel pump. What am I missing?

 

[Joe Reeves]

Re: 1978 70hp evi runs poorly

Do not tinker with the timing. It can be set as follows.

Also.... pushing the key in operates a choke solenoid (Choke Butterflies), not a fuel primer solenoid. Having the rpms increase when you do that proves that fuel is not flowing thu the craburetors properly. To find the offending carburetor, at the speed when you would normally hit push the key in, stick two fingers into the carburetor throats instead. When the rpms increase, you've found the fouled carburetror.

(Timing At Cranking Speed 4?)
(J. Reeves)

NOTE: If your engine has the "Fast Start" feature", you must disconnect/eliminate that feature in order to use the following method. The "Fast Start" automatically advances the spark electronically when the engine first starts, dropping it to normal when the engine reaches a certain temperture.

The full spark advance can be adjusted at cranking speed,"without" have the engine running as follows.

To set the timing on that engine, have the s/plugs out, and have the throttle at full, set that timer base under the flywheel tight against the rubber stop on the end of the full spark timer advance stop screw (wire it against that stop if necessary).

Rig up a spark tester on the #1 cylinder plug wire. Hook up the timing light to the #1 plug wire. Crank the engine over and set the spark advance to 4? less than what the engine calls for.

It's a good idea to ground the other plug wires to avoid sparks that could ignite fuel that may shoot out of the plug holes. I've personally never grounded them out and have never encountered a problem (fire) but it could happen.

I don't know the full spark advance setting your engine calls for, but to pick a figure, say your engine calls for 28?, set the timing at 24?. The reasoning for the 4? difference is that when the engine is actually running, due to the nature of the solid state ignition componets, the engine gains the extra 4?.

If you set the engine to its true setting at cranking speed, when running it will advance beyond its limit by 4? which will set up pre-ignition causing guaranteed piston damage! You don't want that to take place.

No need to be concerned about the idle timing as that will take care of itself. The main concern is the full advance setting.

 

[fireman57]

Re: 1978 70hp evi runs poorly

using the fingers is how I found to get it up to speed the first time but after that I just figured cleaning the carbs would do it. I will get it out again and try it. The timing is spot on because I used you method to check it a month ago. I never really paid attention to the timer base to see when it does hit the stop when throttling it up. I'll look on one of my other boats and see when it hits the stop on them. Thanks again and I'll let you know what we find out.

 

[fireman57]

Re: 1978 70hp evi runs poorly

took it out and cold it runs the way it should. lost about 2000 rpms after a minute or so. Will check spark with timing light tomorrow and replace offending coil. Will swap with another on the water and make sure the problem follows.Will let you know the results. Thanks again.

 

[fireman57]

Re: 1978 70hp evi runs poorly

Well it did the same thing and the timing light showed good spark to each cylinder. We could idle for a while and it would take off and run again for a minute then drop back. Had to be running out of fuel. I have to tell you that you have to pump that bulb like a madman to keep three bowls full but that's what it is. A weak fuel pump. Should have one here Saturday. Joe, thanks for all your help again. Everything we did would eliminate something else and that is what I needed to get back on track. Sometimes I just get too close to a problem and can't find it. Thanks again and to everyone else on this board.