Bogging down during fast acceleration

[irideflatland]

So this is probably not related to my overheating issue so I'm making a new thread...
'72 120HP Mercruiser

Anytime we accelerate quickly (wakeboarders) it will bog down for a second and then go. Every single time. Doesn't matter what RPM we are at, as long as we try to accelerate quickly it will bog for a second. Slow acceleration works fine. If we throw the shifter all the way forward sometimes it will bog so much that it dies.

A few weeks ago the shop replaced my accelerator pump and possibly rebuilt the carb? (They charged me for a carb kit).

Now if I have it in idle and I move the choke up really fast, it revs right up with no problems. But when it's in gear and I accelerate quickly, it bogs.

Any ideas? Timing maybe?

 

[PuddleJumper]

Re: Bogging down during fast acceleration

Sounds like accelerator pump. With engine off, look in carb and actuate throttle. If gas stream/spray isn't strong then new accel pump needed.

 

[irideflatland]

Re: Bogging down during fast acceleration

Sounds like accelerator pump. With engine off, look in carb and actuate throttle. If gas stream/spray isn't strong then new accel pump needed.

That's what I thought after reading some other threads. But the shop changed it just a few weeks ago. It was actually dying when putting it into gear before, but after the shop changed the pump, that was fixed. I'm waiting for a friend to help me out so I can look at the gas stream though.

 

[irideflatland]

Re: Bogging down during fast acceleration

Took it to the shop, and they said the carb was all gunked up again (3 weeks after the rebuilt it). They clean out my gas tank and said there was a bunch of rust stuff in it, so that was making dirty gas which clogged the carb.

 

[bruceb58]

Re: Bogging down during fast acceleration

That's actually pretty normal. You can't just slam the throttle open and expect instant engine response. It is the accelerator pump's job to help the situation by squirting some fuel but you have a major vacuum drop at that moment and therefore a lean condition for a little bit. Better to advance throttle smoothly.

Even after you get your carb rebuilt, you may have a similar problem.

After you get you carb and tank cleaned, you really should buy a good water seperating filter to go between your tank and your carb. Will help keep your carb from getting clogged up with water/debris from your tank in the future.

 

[full stringer]

Re: Bogging down during fast acceleration

check your timing anyway my boat used to do that and i found the timing was set wrong from the previous owner almost 5 degrees off whew!!! after i adjusted my points and timing it ran bitchen

 

[SeanMcl]

Re: Bogging down during fast acceleration

That's actually pretty normal. You can't just slam the throttle open and expect instant engine response.

Not trying to start anything here, but I a properly tuned motor doesn't bog when you hit the throttle. If you the average guy notices it, something is wrong.

I'm talking about a noticeable *drop* in power when the throttle is moved quickly to maximum, which is what I think the OP is talking about. He also mentions that sometimes the motor will die, which is not normal either.

I'd look at the accelerator pump and proper fuel level in the fuel bowl, as well as timing. Then ask the shop how all the tank gunk got past the fuel filter and into the carb. I wonder if they really rebuilt it the first time or just hot tanked it. In any case, carry a spare filter if your gas tank is known to be full of crud.

 

[bruceb58]

Re: Bogging down during fast acceleration

Not trying to start anything here, but I a properly tuned motor doesn't bog when you hit the throttle. If you the average guy notices it, something is wrong.

Every carburetted boat I have ever had has done this. It is what they have the accelerator pump there. Depends on HOW fast you open up the throttle. I agree there is probably something else wrong because it dies sometimes but there will always be some bogging down when you open the throttle quickly.

 

[irideflatland]

Re: Bogging down during fast acceleration

Well I took it out today right after I got it from the shop, and it's running absolutely perfectly. No hesitation at all if I go from 1000 RPMs to WOT as fast as I can...

 

[-JR-]

Re: Bogging down during fast acceleration

what kind of carb was it ?

 

[irideflatland]

Re: Bogging down during fast acceleration

what kind of carb was it ?

No idea
They did say that it was a pain to clean it and they had an old one laying around so they just swapped it in. They didn't charge for parts, probably because I paid for parts 3 weeks ago...