Must push in key to allow acceleration - or it dies

Hi guys,

First post ever! Struggling with a 1990 70hp outboard. I bought it 15 years ago and it has always been reliably unreliable. I had a marine mechanic rebuild all carbs. It ran ok but still had the following issue:
When I first start it cold, I can put it in gear and smoothly add power and it will accelerate nicely. But after it is warmed up, and I kill it then start it again, (like when I drive to the marina to get gas) it starts fine, but when I put it in gear and add throttle, it will bog and die unless I simultaneously push the key in (primer solenoid). I recently replaced fuel pump, fuel tank, fuel line, bulb primer, and changed plugs. Now the problem seems to be getting worse. My first thought is carbs given that after changing fuel pump it got worse - clogged float jet? Given that when I push the key in, it will save it from dying, the primer solenoid sounds like it is working ok?

I would like my wife and son to be able to drive this reliably but as it stands, I am the only person who can keep it running. I guess on a positive note, nobody's can steal it! BTW - I converted it to a tiki bar. Pics attached. Enjoy!

I don't know *THIS* engine, but I've rebuilt plenty of others; ultimately these are simple devices: Spark, Gas & Air.....that's all it takes.

If pushing in the key (i.e. closing the choke) makes it run, then this almost certainly has to be a fuel starvation problem. Think about it: what is "choke"? It's closing off air to dump a fuel-rich mix into the intake. With the choke off (open), you're getting too much air, not enough fuel (wrong stoichiometry). If the stoichiometric ratio is off even a little bit, your engine...indeed ANY engine....will run like crap. Or not at all....

Could be a number of things: clogged-up high-speed ports, possibly a needle issue, etc. But whatever it is, I'll bet my boat you have a carb issue. Just because it was "rebuilt" doesn't mean it was rebuilt *properly*. Have to pop the disks & clean ALL the ducts, which a lot of "pros" don't bother doing.

EDIT: Love the Tiki look......but your pontoons look VERY low in the water to my eye. Having had a pontoon boat in the family, I know they leak over time and really need to be drained (and just as often had un-noticed leaks welded). You might want to have that looked at.

There are no flappers or choke plates on these carburetors !!------The electric primer ( AKA choke ) puts fuel directly into the engine.---This fuel bypasses the carburetors.---This clearly points to fuel delivery issues.----------Perhaps low speed needles need adjustment if carburetors have them.-----------Also I recommend a compression test whenever there are stalling issues.---------These motors have a history of problems with scoring of the #2 cylinder.

AND--it is vitally important that the carburetors are properly synchronized with the spark advance. If they open too soon, you can just about count on it hesitating or conking out completely when you give it some throttle. Such a simple thing, but it must be done by the book.

Add 1/4 turn rich (counterclockwise) on the slow needles and see if it improves?

If this has been an ongoing issue is it possible the engine was jetted for higher altitudes? What color are the spark plugs? Those carbs have the intermediate jets (air jets) putting smaller jets will richen up the intermediate circuits up when you throttle up. If the plugs are powdery white your running lean and need to fix it before you toast the pistons and cylinders.

Thank you! I agree. My first step was to pull off the drain plug of each bowl and pull out the jet. (Not sure if I am using correct term) but the middle carb jet was all tore up. It was tough to remove because it looked like the flat head groove was tore off half way and it was partially blocked as well. I actually put it back so I could take a tiki cruise and it ran better but not great after clearing the blockage. I will probably start there by replacing just those jets and see if it corrects the issue before I rebuild all three carbs.

The pontoons are fine. Just too small! The issue is that I widened the deck by 2 1/2 feet with steel and the roof frame is out of steel. I would have loved to done it all in aluminum, just resource and skill limited! Just too heavy!!! The instability is part of the whole tiki (and rum) experience! ��

Will keep you updated. Thanks again!

fdrgator said:

AND--it is vitally important that the carburetors are properly synchronized with the spark advance. If they open too soon, you can just about count on it hesitating or conking out completely when you give it some throttle. Such a simple thing, but it must be done by the book.

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Thanks! I will look into this as well!! I'm a YouTube mechanic. Gotta search this one!

kimcrwbr1 said:

If this has been an ongoing issue is it possible the engine was jetted for higher altitudes? What color are the spark plugs? Those carbs have the intermediate jets (air jets) putting smaller jets will richen up the intermediate circuits up when you throttle up. If the plugs are powdery white your running lean and need to fix it before you toast the pistons and cylinders.

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Thank you! When I removed the old plugs, they actually looked pretty good for having not changed them in 10 years and the boat sitting in the water the entire time. I bypassed the VRO and mix

Ok. The proper term is orifice plug that was all tore up. So it may be possible that there is a piece of metal inside that #2 carb given nothing came out when I remove the drain.

The orifice plug has a calibrated hole to measure fuel flow.-----If nothing came out when you removed the drain then you may have blockage at the float valve.----Needs to be resolved as no fuel means no oil going to # 2 cylinder.----Compression test may be a wise thing to do.

As "tdkehoe" states, Orifice is the correct terminology... BUT... that definition alone takes in "all" sizes and types. If you're speaking of the one that lies horizontal in the bottom center of the float chamber, that would be the "High Speed Jet Orifice".

The jets will become tore up due to being removed with a ordinary screwdriver. It requires a screwdriver that has a shank the size of which will just clear the 1/4x20 threads of the drain screw hole... with its tip machined as pictured below.

racerone said:

The orifice plug has a calibrated hole to measure fuel flow.-----If nothing came out when you removed the drain then you may have blockage at the float valve.----Needs to be resolved as no fuel means no oil going to # 2 cylinder.----Compression test may be a wise thing to do.

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Will do! Thanks!

I just grind a wider tip screwdriver to barely fit inside the threads. The are tight be sure and install them just as tight.