25hp johnson runs in reverse & neutral, bogs down in forward

I just bought a 14' alumacraft MV Jon with an early 80s 25hp pull start johnson. The motor starts fine, and works great in reverse and neutral. It will putz around fine in forward, but once you crack it open to get on pad the motor will bog down after about three seconds and if you don't pull back on the throttle it will kill the engine. It will start right up again, but the same problem is always replicated. I had a buddy who's a small engine mechanic clean the carb and it looked good. We pulled the plugs and tested compression and everything was ok. Anyone have any idea what could cause this? :roll:

thanks in advance

Marty

Does it have the adjustable carb adjuster on the front. It could be running to lean or rich under load.

I'd bet a cold beer that one of your float needles is sticking. Pull carbs or carb. Remove bowl, see if you can get needle to stick by rolling carb around. I have had this happen to me. Carbs look good but one needle hangs closed or mostly closed. Enough to fill bowl runs fine at low power but can't keep up under power and drains bowl (bog) couple seconds and will refill bowl.

Might only be getting spark to one cylinder. Get a spark tester and test em out.
When you "crack open the throttle" choke it and see if that keeps it from stalling out. If so then you probably have a fuel issue.

+2 on the fuel issue.Try pumping your primer ball when in forward.

My bet is the power pack...probably only running on one cylinder. Mine did that and choking helped a little but teplaced the power pack and had a new feeling motor. Check your spark first...its easier than taking off the carb.

However you want to go about it. Sure sounds like fuel. Not that it can't be electrical. Depending on how the fuel lines are ran to the carbs. If you can isolate them blow in fuel line w mouth with empty bowls should flow free.

In the original post I said that a buddy had already taken off the carb and cleaned it. Didn't look that bad. After reading the first few posts I took the boat out again this after noon after dumping a bottle of seafoam in the fuel tank for the heck of it. The engine again bogged down and would kill when I had it in forward and gave it WOT. I then restarted the engine and tried pumping the bulb while going WOT. This definitely helped and I was able to get the boat up on plane, although it started to bog again and I could not maintain WOT. The bulb pumping helped, so that seems like a fuel issue. One buddy said he thought the fuel pump was suspect. Another one thought it might be the stator. I am bringing it to an outboard mechanic tomorrow, but if I can't get it fixed for $100 or less I am going to sell the motor as is to a shop. I have a new 25hp yam 2 stroke that I am going to be putting on the boat either way. (well it's a 2009 yam)

I would say fuel pump. The fuel pump diaphragm is either rotten or streched out there cheep to fix.

Those old rubber tipped needles are prone to sticking. Cheap to replace. They can look fine and cause headaches.

Source a fuel pump kit and rebuild the fuel pump. Your pumping the bulb takes the place of the fuel pump and supplies the fuel where the fuel pump may not be able to. Now, depending on the failure inside the pump, you may have to disassemble the carb again and clean out the bowl, jet, and idle pick-up tube. Alcohol extended gasolines will dissolve some of the gasket material in the pumps and guess where that goes......right into the carb. The worst material in the pump is the reddish gasket material, visible from the outside. Not all pumps were manufactured with this material. Regardless of what material is visible, rebuild the pump.

Fuel pump diaphram is busted....I would bet 2 cents on it lol...yeah I'm cheap.

Bufford

Ok well I recant the powerpack solution...but would check the spark for poops and heehaws.
Could be as simple as an air leak in the line from the tank fitting or the motor fuel line fitting. Hope things work out. If the shop doesn't give you what you think is fair lemme know...I'm always in the market for an easy fixin motor.

Let us know what you find. Fuel pump diaphragm sure won't hurt to replace. Kind of difficult to troubleshoot from behind a desk but if it still has the same symptoms change the needles and seats.