Last shot to diagnose bogging problem!

[ntheyer]

Re: Last shot to diagnose bogging problem!

Power valve feels good. No obstruction, no stickiness. Float level and drop look ok. I found another post stating float level with the upper carb body upside down with the float on the upside should be set to 21/32" with the gasket on.<br /><br />Float drop is 1 3/4" with the gasket on.<br /><br />I am assuming this is measured from the body of the carb to the center line on the float at the end of the float. If that is true, it looks correct. I will take the carb to a marine shop tomorrow to get their opinion.<br /><br />Any other ideas folks?

 

[ntheyer]

Re: Last shot to diagnose bogging problem!

Update for everyone... I am very embarrased and frankly ashamed for this.. Turns out the carburator was wrong all along. It was a Rochester 2GC, which came with the boat, but it was the automotive version we suppose (marine mechaninc and I). In all of his 30 years, he had never seen one like mine before. Problem was I had it rebuilt by another person at the beginning and I never knew differently. So I always assumed the carb was good, even when messing with different main jets. Long story short, The mechaninc basically made me a new carb out of a new carb body and it works perfectly. The boat runs like a champ other than I think a vaccum leak at low throttle from reusing the carb base gasket. I will order a new one. Up at high RPM, it runs like a strong champ up to 4400 RPM with the three blade 17 pitch 15" diameter prop on the 17' boat. I think that it right.<br /><br />Once again, thanks for everyone's help. I'll be around reading posts. Now everyone knows a question to the next person should be, Is it a MARINE Rochester 2GC carb??? The mechanic said that is why you should never use automotive anything parts in a boat. They're just not quite the same.<br /><br />Thanks again.

 

[Mile-High Mariner]

Re: Last shot to diagnose bogging problem!

Okay, Nick - I'm going to pick up this thread for the sake of my own problem, similar to yours, but I have a stock '92 Mercruiser 3.0L Alpha One from prop to pulleys. Carb is the OEM MerCarb (9562) and the system is fresh from a 100-hr service. I have fresh plugs, cap and rotor, newer wires and a new ignition module. Engine revs in neutral very nicely right up to ~4600; if I push the throttle all the way, though, the engine bogs as if it's choking. Pulling the throttle back restores high rpm and smoother operation. I can engage the drive and idle out of the NWZ, right through low troll up to about 1500 rpm; with any further advance in throttle, it bogs, maxing at ~1800 rpm. Any further throttle advance in engaged mode will result in the same bogging behavior. I'm perched on the edge of a carb rebuild, just because I don't know when it was last performed, and rejetting for the altitude at which I routinely operate (~7000 msl), but the lugging does not seem to be jet-related. I think it may be accelerator pump-related, but wouldn't it prevent it from revving to >4000 in neutral, or does the vacuum generation in neutral differ from that while under load? Thanks in advance for your input!

 

[ron7000]

Re: Last shot to diagnose bogging problem!

yes vacuum generated in neutral differs from when motor is in gear under load.<br /><br />search on my username in this forum. I did small writeup on common carb problem with the 3.0.<br /><br />Most likely related to float level. Raise your float level a little. That's only if the motor runs great except for a bog around 1500-2000 rpm and gets up to 4000+ rpm wide open throttle. This is with easy to moderate acceleration, not jamming the throttle from idle to wide open.<br />If it bogs out and you don't get over 2000 rpm, then it can be a number of things which you will require the carb to be cleaned out and maybe require a new power valve.<br /><br />Do you know what main jets you're running? If the boat was sold originally in your area, then most likely it was jetted for that altitude but should be verified anyway.

 

[Mile-High Mariner]

Re: Last shot to diagnose bogging problem!

Ron:<br /><br />Thanks for the rapid response! I brought my boat ('92 Stingray 556ZP) here from Texas (~650 msl), so it most likely is equipped with the factory standard 1.45 jetting for sea-level operation. I'm considering dropping to 1.40s or even 1.35s, but I don't want to get too tight on the jets.<br /><br />So you agree that I'd benefit from a rebuild? I plan to clean out, replace acc. pump, gaskets and float. Any other suggestions? I'll get to your writeup here presently.....

 

[Mile-High Mariner]

Re: Last shot to diagnose bogging problem!

Incidentally, a review of compressions tonight revealed ~150 in cyl. 1,3 and 4 with only ~60 in cyl.#2. I'm going to check the rockers first, but I'm thinking valve seats. Motor has 1060 hrs on it, according to the Hobbs. I have some other curious observations, but I'll reserve them for later.

 

[retodd]

Re: Last shot to diagnose bogging problem!

Most likely you need one of three things: an accelerator pump adjustable lever if over-fueling on acceleration; if running rich all the time throughout the band you may need a modified venturi cluster; or if flooding in hard corners or rough water, you need the three-piece inlet needle and seat part that allows fuel into the carb. The carb on your engine is a Mercarb, an evolution of the Rochester two-barrel. That unit when installed on the 3L, had a 4cc accelerator pump. Mercury installed the same pump on its 4.3L and 5L engines which worked fine but it's far too rich for the 3L. Mercury has an adjustable accelerator pump linkage that you can purchase. The linkage has three position holes and each hole changes the amount of fuel that's discharged through the accelerator pump by a 1/2cc, so you can reduce the fuel flow by 1cc from one extreme to another. For 3L engines that bog on acceleration there was a Mercury bulletin on a modified venturi cluster. This part installs with three screws. You need to establish which venturi cluster you currently have before ordering.<br />Steve Auger, Mercury Marine <br />No I am not Steve Auger, but i found this on another thread and have the same troubles...retodd