Big Twin 40 HP bogs at high rpms, carburetor is clean!

[sms986]

So thanks to a lot of patience and help from you guys on the forum, I have my 1963 big Twin up and running, sort of. I got it all together and took it out on my boat (longshaft transom) because the carpet on the boat I am restoring had not yet dried. The engine started fine, but it vibrated pretty strong at low RPM's. May be normal on an old motor, but it was much more "violent" than the vibrations from my 87 seahorse 9.9. Anyway, the other thing I noticed was that there was fuel leaking from the fuel filter. It was between a drip and a stream. So I left it choked for a bit to warm it up and shut the choke off. On the trailer, I ran it at full throttle for a few seconds at a time and it did just fine. Took it off the trailer and it didn't move very well (short shaft motor long shaft transom.) So I decided that when the carpet dried on the other boat I'd take it out again. That day was today, and today sucked. I started off same as the other day, choked it and let it run for a bit then shut the choke off. I started to play with the lowspeed fuel screw, closing it entirely and working it open. It would shut the motor off when closed, but when I started to open it I noticed no difference in performance, rpm, sound as I unscrewed it until it was practically out (9+turns). So I set it to about 1 turn out and put it in gear. I slowly cracked the throttle and it would get to the point where the throttle plate itself started to open, maybe a little further, and then bog down. I'd say about 3/4-7/8 throttle. When I backed off the throttle, I could keep the engine running fine. But every time I went past that mark it would begin to bog and eventually die out if the throttle was left all the way open. When I choked it, I could pull the throttle all the way out. No problem. I could even choke it, throttle out the whole way, and then turn the choke off and it would run for 2-3 seconds without choke at full throttle before bogging down.
Things I changed between the two runs: fuel filter diaphram and fuel line replacement, changed gas tanks, fresh gas mixed 25:1. I did notice that when squeezing the primer bulb, it never got to hard to the point it does on my other motor. I also noticed fuel leaking out of the inlet of the carburetor Venturi when priming, as if the needle did not shut. Note this.
Things I checked after second run: the needle seated fully when I turned the carb upside down and blew into the fuel inlet. Carburetor is IMMACULATELY CLEAN. Fuel filter and pump assembly is clean.
Note, the primer bulb is brand new.
Compression checked out at 90 psi in both cylinders before the initial start.
Fat blue spark in both cylinders as well.
I'm at a loss. I don't think the bulb is collapsing because the gas tank cap has a small hole in it where the vent is. I will check this. Also, the fuel lines have an inner membrane which I read on another post ended up collasping. It doesn't make sense to me that I can go up to 7/8 throttle before they collasping though. I have scoured the internet for a possible solution because I am at a loss and I am tired of making petty orders for one or two parts at a time, only to find that I need another part later on. The only things I've found other than the membrane collapse situation are "cleaned the carb, works great" or "primer bulb was collapsing." Any suggestions? Possible vacuum hose leak somewhere? Something more in depth? I am at a loss with this thing and walleye comes in in 3 weeks. Thanks in advance.

 

[racerone]

Check the fuel pump diaphragm.-----Check high speed jet in the BOTTOM of float bowl.----Does spark jump a gap of 1/4". yes or no.

 

[sms986]

Where is this high speed jet in the bottom of the float bowl? There is a jet that threads into the carb from the float bowl into the main venturi. There is also a channel in the bottom of the bowl that directs fuel into said jet, but I do not see a jet in the bottom of the float bowl. Fuel pump diaphram has been replaced and I checked it after I ran the motor to make sure it was not torn on installation. No fuel leaks from that area anymore. Spark jumps a 1/4" gap no problem, and plugs are gapped correctly.

 

[oldboat1]

http://ww2.iboats.com/Carburetor-Group/dm/cart_id.576929291--session_id.913441306--view_id.1550173

#64 is the nozzle — small holes have to be unblocked, and gasket #56 has to be in place for fuel feed to work. The h.s. jet at the bottom of the bowl is #60, behind the screw or bolt. It’s number 67D for the ’63 carb (diagram in the link is for a ’68). 67D means .067” orifice. It’s possible your h.s. jet is missing.

btw, plug gap is .03 inch. A 1/4” spark is obviously .25 inch. In order to test for 1/4” spark, you need an adjustable spark tester — test is for magneto strength/output required for proper ignition.

Chances are your problem is the not on the low speed side (top of carb), but check to make sure the assembly of the needle and related parts is correct. The needle adjustment is very sensitive when the carb is working correctly (1/8 turn will make a difference).

 

[jimmbo]

You say the engine runs ok until you advance the throttle to the point where the carb starts to open, then it bogs and/or dies. That sounds like as mentioned earlier a plugged main fuel circuit, or a low fuel level in the float bowl, a carb to timing sync issue, Can't rule out ignition cut out on one cylinder either.

 

[sms986]

Oldboat1, it appears that my high speed jet is indeed missing and has been since the motor was purchased because I did not remove/see it. I don't recall seeing threads for it either. I'll pop it open and check. It does seem possible that if this high speed jet functions as the name says, it's flooding the engine out at high rpms, but that still doesn't answer to the fact that it peaks in rmp when the choke is in. I do have an ignition spark tester that I used to test the spark. Also have two new coils.

 

[sms986]

So this high speed jet, is there a brass plug that needs to be popped out before removing it, or does it simply screw in behind the drain plug? If so, I indeed do not have one.

 

[sms986]

Also, jimmbo, the carb-ignition timing possibility. I see that there are two points where this can be adjusted. 1, where the cam and roller are. I have this adjusted to where the throttle plate just begins to open when the timing marks on the cam align with the mark on the carb. 2, there is that arm that extends from the carburetor, underneath the flywheel, to the arm that rotates and turns the armature plate. There is a stopper on this arm, and the manual has no mention of this. Should this be adjusted?

 

[racerone]

Carefull when you adjust that stopper.----There is usually 3/16" gap at idle when it is correct.

 

[F_R]

That "stopper" thing is the fuel saver thing. It should do absolutely nothing till the throttle/spark advance reaches full advance (up against the projection on top of the cylinder block). THEN contact is made with the stopper thing and further throttle advance opens the carburetor fully. It should be in the book.

If you truly do not have a high speed jet/orifice plug in there, well there ya go. No wonder it won't run at high speed.

I noted you said it will run at full throttle on the trailer. NEVER, EVER do that. If it were running correctly, you would have scattered engine parts all over the place.

 

[Crosbyman]

if you are looking for part #60 better to take out the flashlight... I totally missed mine when working on my 6hp carb

the cover plug comes out but the orifice plug is screwed in at the back of the cavity


tiny thing way inside the cavity

very delicate and you need a properly sized screwdriver or tool to take it out better yet try some carb cleaner and blowback some air


try taking of the gaz cap off for a run ...that small vent hole may be crudded up

 

[sms986]

So I got a high speed jet, installed it, recleaned the entire fuel system, and took it down to the river to test it. Aaaaand now the starter motor is bad. At this point I am going to cut my losses and dump this motor in the scrapyard. I know that once I get the starter motor replaced something else will go wrong and I will spend another chunk of money on it.

 

[oldboat1]

Have a beer or two first. May find that the cable ends need to be cleaned up (sandpaper until they shine) -- or wire ends somewhere else in the starting circuit. Or the starter may just need to be opened up and cleaned.

A "bench" test for the starter is to jump directly from a known good battery (from your truck is fine) -- red cable to the stud on the body of the starter, negative/black cable to the base or mounting bracket. Try it initially with the plugs removed.

 

[racerone]

These are / were fine reliable motors in their day.----You need to understand how they work and how easy they are to maintain.-------But there are new motors available were all you do is push the button to make them run.----Computer does all the thinking for you.

 

[sms986]

Oldboat1, unfortunately all of the wires are new. I redid the entire wiring harness, including a new starter solenoid. All of the connections are clean. When I start it up, it clicks. I can feel the click in the solenoid but nothing in the starter. The starter motor does nothing. I tried bench testing it as well. I left the motor grounded to the block and hooked the negative terminal on a new fully charged battery to the ground on the block. I took a hot wire from the positive terminal and tapped itiheld it the starter motor post. No spark, no movement, nothing. Unfortunately I think it is the motor. I am going to tear it apart and try to clean it but I don't know what comes next if it doesn't work.
Racerone, I don't have any doubt/lack of confidence in the old Johnson/rude motors. I have an 87 seahorse that runs like it's brand new. Haven't even changed the plugs in it. Never had to do any repair work/tuning either. Just mix the gas right and change the gear lube every few years. This motor however, is a nightmare. It seems like every functional part has either gone bad it is ready to go bad. I've rebuilt the carb, replaced both plug wires, coils, condensors and points, all wiring, armature plate, flywheel, water pump, rebuilt the enginee and more. Now that it's about ready to go the starter motor goes bad. It's just one thing after another. I have built many, many different engines over the years and I've never had this kind of trouble. This is my first outboard and I can't imagine it's that much harder. It just seems like the previous owner threw a handful of sand in the carb then dragged it a few miles down the road. Everything that can go bad has gone bad.

 

[Crosbyman]

ok the starter crapped out but is then engine running did you try the battery to starter suggestion maybe the selenoid or something else is bad....

patience brings joy... don't give up on it or......if you really want to scap it an AOMCI member r could pick it up...



put up a post on AOMCI and the motor will disappear

 

[jimmbo]

So I got a high speed jet, installed it, recleaned the entire fuel system, and took it down to the river to test it. Aaaaand now the starter motor is bad. At this point I am going to cut my losses and dump this motor in the scrapyard. I know that once I get the starter motor replaced something else will go wrong and I will spend another chunk of money on it.

So why not just use the recoil to start it?

 

[sms986]

Even the recoil starter is broken... Figured I would replace it once I got the engine rebuilt but since then I've spent every dime I'm willing to spend on this thing to fix something else. If I ever get this thing running the recoil starter will be replaced before taking it out on the water as a safety measure if nothing else. I've tried justhooking the starter directly to the battery, but I get nothing. I've tried multiple batteries as well.

 

[sms986]

So, after "a few" beers and a vacation I got back to the motor. Found a used starter and got it all home up. Had the boat out for the past few days with no major issues. However, I noticed two off things about this motor. It idles fine for days, but as soon as it's put into gear it seems to misfire or something, dropping the rpm down, after which it will slowlt climb back up again. It does this about every 3-4 seconds. It isn't the cut out switch because I have both wires coming from the motor wired directly to the starter switch, bypassing the cutout. This was recommended by a guy at the local boat shop because it wouldn't kill the engine before when the ignition was turned off. Doesn't affect the running of the motor at all, just seems strange. Also, I have the lowspeed issue screw adjusted to where the idle is highest and performance is smoothest. However, this spot is only 1/2 turn out from closed, if that. Again, doesn't aftect performance, I just don't want to be tricked into starving the engine at idle. It does seem to idle higher than my 9.9 Johnson.

 

[F_R]

You won't starve it at idle. If too lean, it will sneeze and quit.