75hp stinger 1975 need help. Bogging down.

[Brabbtiger22]

I'm very familiar with this engine yet I'm stumped. To bring you up to speed know the this: I have replaced the fuel lines, bulb, and connectors. Compression checked and perfect. Spark plugs new and coils are working. Giving spark. I have taken apart the carbs like 5-8 times cleaning and seeing if I missed anything. Finally ordered the entire rebuild kit and did that. The primer bulb holds pressure after filling the carb chambers. I have had to adjust the floats quite a few times to make sure it's right. Yet I'm still experiencing my problem. The problem is when I go to crank the engine cold i have to relaly hold the key over about 10 seconds for it to finally crank. Once cranked it will idle just fine. Next problem is the main problem. When I put it in gear it almost wants to stall unless I throddle up to give it gas a bit. The boat is a 19ft bass boat and the motor does have a fin above the prop to help it plane out easier. If I were to quickly throddle up it will bog and cut off. If I slowly bring it up to speed very slowwwwwwwwly.. with the throddle the engine sort of catches like the right amount of mixture and it's like here we go on a roller coaster and it will slowly take off. Once it gets going I'll be up to 37mph and can go wherever just fine. Now let's say I have to bring it back down to idle going under a bridge I have to do this all over again slowly or it will bog down. Side note: I noticed after running the engine for awhile if I cut it off and crank eithin 10 minutes it cranks right up on the dime. No heavy key turning... But if it sits for about an hour off it's hard to start back up. It will want to spit and hissss trying to catch. Even with the prime bulb stiff and in upright position. I eventually get it to crank by turning over the engine alot with the key and playing with the coke at the motor. Cranks better when not choked as much. Flaps have to be open by 1/3 or so if that helps. The gas tank is a 22 gallon aluminum inside tank that has a vent external. If there's anything I'm missing please let me know. I'm stumped and tire of dealing with this same problem for over a year now.

 

[Brabbtiger22]

It's a Johnson! "Stinger"

 

[jimmbo]

How did you adjust the floats? Did you remove the cover plugs to get at all the fuel passages for cleaning? What were the initial settings for the Idle mix screws? Are the carbs all synced together and re they synced to the timing correctly? While you say the compression is good, there is also crankcase compression to consider. With the flywheel off check for signs of oil at the upper crankshaft seal. Oil getting out means air is getting in and leaning the top cylinder. Is the fuel pump diaphragm free of leaks and is the fuel filter clear?

 

[racerone]

Take the starter apart for inspection.---Open slow speed mixture screws 1/4 turn.----And often the " carburetor " problems turn out to be something else.

 

[Brabbtiger22]

Fuel filter and pump are new with no leaks. I did remove the cover plugs during the rebuild and nothing was clogging it up. Hammered the new plates back in after cleaning it out anyway. I took a detailed look around the block of the motor for any oil leaks and did not see any signs of any leaking from main gaskets! I also replaced the hoses going to all carbs and each are getting gas! Bowls are filling up . I believe on this motor you can adjust the low screws (idle) when i got the motor these we're both screwed all the way in. Note I just cranked the engine up on the dime first try by adjusting the throddle more to the start position (as in giving it gas). I back off and the idle is fine. No bumping or thumping. Now is the question of what could be causing it to bogg down to cutting off getting out of the hole. The tank is well ventilated I know that much

 

[racerone]

Sorry---Some 75 hp models did use adjustable low speed jets.----The parts book for a 1975 model shows a non adjustable " fixed " jet for low speed mixture.

 

[Brabbtiger22]

Also how hot is the engine suppose to be on the outside while at idle with the water hooked up on the foot? I have a thermo reader gun that says 146-154 degrees F. I replaced the impeller last year and praying I don't have to again lol.

 

[racerone]

What is " perfect compression " in numbers ?----Temperature sounds fine.

 

[Keyboardman]

I have a '76 Stinger. A bunch of these engines would develop a bogging down problem. There is a Johnson Technical Service Bulletin I have about it. The fix is re jetting the carbs and drilling some precise holes in the body and pick up tube. OR, do like I did and get a set of later year carbs that already had the factory changes. This is presuming that your timing base is not sticking or the wires coming from it aren't preventing it to fully advance before the throttle is advanced.

 

[Brabbtiger22]

Yes I read about the jet problem last year! A few people mentioned the Jets were drilled too small factory wise in this year model. As far as the compression I did that a good few months back it was 125-130 psi on all . It's definitely a fuel to air mixture problem of some sort. I didn't mention this above but last year I had to take the carburetor front casing off just to increase the airflow. It wouldn't get out of the hole bogging down. I can also say if I take the hood off the engine without that carb protector case on as well ....and throddle forward it will get out of the hole real fast. I can post a pic of the casing I'm taking about

 

[Brabbtiger22]

[No message]

 

[fireman57]

If it runs good without the hood on then you probably have an exhaust leak.

 

[Keyboardman]

Did you check out the timing base advance not sticking?

 

[Brabbtiger22]

How would I be able to check for an exhaust leak? My plan is to check the timing base tomorrow. What exactly should I look for? That could be a problem. I know it being an old engine once sat for 13 years alot of things were sticking. I greased up almost everything!

 

[Brabbtiger22]

I'm not too familiar with the timing base , but there has always been one thing under the fly wheel that tends to stick. It's connected to the throttle . I'll show a pic. This could be the problem, but if so please share how in the world to get it to uncease. I have marine crease and plenty of wd40 hehe.

 

[Brabbtiger22]

[No message]

 

[spybot]

To fix a sticky timer base. You need to pull the fly wheel then gain access to the base. It is them a case of freeing it up.

 

[Keyboardman]

As you advance the throttle from idle, the timing base moves forward toward the black stopper until it contacts it Before the butterflys in the carbs start to really open up. Have an assistant slowly move the throttle lever forward and see if that is happening. One thing to check is the metal retaining tab that holds the big black bundle of wires that come from under the flywheel. Bend it out of the way from the wires. The wires can get stiff and the white metal tab can hold the timing base from fully advancing. This happened on my engine. If the timing base is sticking, you can try to squirt some WD 40 up in there but, removing the flywheel is the better way of getting to it.

 

[fireman57]

Running better with the cover off is pretty much the check for an exhaust leak. With it running carefully visually inspect the base of the engine where it joins the midsection and see if you can find a little smoke or hear a spitting sound. It is usually the base gasket that leaks.

 

[fireman57]

I have had two of these engines and both needed rejetted per the bulletin. If you do a search on here you should find it. It didn't totally cure the problem but helped at least 90%. Also, before I did that work I used to have to bump the primer as it started out of the hole.