Mercruiser carburation problem?

[JohnJR]

I have a 1989 Rinker Captiva 206 with a Mercruiser 5.0LX Alpha 1 drive with 600 hours in the clock. It's the 230 hp model with a Rochester Q-jet carb. Here's my problem. The boat starts fine and runs well until it's fully warmed up. Then it will start to load up at idle and stall as throttle is insreased. I've checked the obvious things; choke, fuel pump and filters. I suspect it's the carb and will attempt to rebuild it myself using the Sierra rebuild kit. Is there something else I shouid try prior to doing this? Once rebuilt, how much adjusting and fine tuning will be necessary? I'm told that even a new or remanufactured carb will require the same amount of fiddling. Thanks in advance for the help.

 

[wingnit]

Re: Mercruiser carburation problem?

How long has this boat been sitting? <br /><br />Rebuilding Q-jets can be a chore. Most of them are what is called vacuum secondary... meaning the motor idles on the front two barrels on the carb and as you accelerate the secondaries (back 2 barrels) open based on vacuum. Before you rebuild the carb, there are a few things I would check. <br /><br />1) Check to be sure that there are no leaks. Listen for leaks. <br />2) Check for fuel leaks around all the gasket areas and around the accelerator pump.<br />3)Check to make sure that the bolts to the intake manifold are tight. Loose bolts will create a vacuum leak and cause the motor to hesitate.<br />4) Tighten all screws that hold the top of the carb onto the body. Loose bolts will create a vacuum leak and cause the motor to hesitate.<br />5) A worn accelerator pump will cause hesitation. Replacing the accelerator pump requires disassembly of the carb.<br />6) Q-Jets are notorious for leaking around the throttle linkage and at the base of the body. On the base of the body there are two plugs (molded in) that will leak over time. If they are leaking it will cause rough idling, hesitation and stalling.<br />7) A high float level will also cause rough idling, hesitation and stalling.<br /><br />Check all of the above and then get back to us.<br /><br /><br /><br />------------------<br />Mark<br /><br />Thought for the day..... If everything seems to be going well, you have<br />obviously overlooked something.

 

[wingnit]

Re: Mercruiser carburation problem?

John,<br />In my last post, 1) I meant to say listen for vacuum leaks.<br /><br />------------------<br />Mark<br /><br />Thought for the day..... If everything seems to be going well, you have<br />obviously overlooked something.

 

[wingnit]

Re: Mercruiser carburation problem?

Hey John,<br />When the motor is warmed up is the choke all the way open?<br /><br />------------------<br />Mark<br /><br />Thought for the day..... If everything seems to be going well, you have<br />obviously overlooked something.

 

[JohnJR]

Re: Mercruiser carburation problem?

Wingnit, thanks for the replies, yes the choke is fully open when warm. I'll check the items you suggest first.<br />JJR

 

[crazyray]

Re: Mercruiser carburation problem?

engine loads up after warm up..... what do the plugs look like......a can of WD-40 with one of those red straws is a excellent tool to find hard to locate vacumn leaks... make sure the metering rods are not sticking open and also another problem with these carbs is that the float will absorb gas over time and level will rise.....would give adjusting a shot first before I rebuilt it.....

 

[clanton]

Re: Mercruiser carburation problem?

I would go for the MERC ,or AC Delco kit. The parts and gaskets will fit.

 

[fone_man]

Re: Mercruiser carburation problem?

Rochester Quad... Great Carbs... Easiest one out there to rebuild...<br /><br />I agree with float getting heavy... the only thing that I hated about them was their floats plus your is going on 12 years old now!!! They are a composite plastic which after time absorb the gas... and get heavy... after you tear down, you let air out & is light again, put it back in because you think ok... absorbs gas again... same problem. <br /><br />DO NOT & I stress DO NOT put the same type float back in... make an investment & get Brass Float... when was the last time you saw metal absorb anything!!!<br /><br />Sierra kit should be fine, I have used all types... shouldn't have any problems after rebuild. Do not waste any extra money on buying a rebuild carb unless your core is damaged.<br /><br />You can actually buy kit, remove top of carb while on engine, set new float to specs, install new airhorn gasket, run both idle screws in until they bottom out, them back out 2 full turns, fire it up & adjust both idle screws to obtain smooth idle & the turn back in 1/4 turn... you should be up running and gunning again.<br /><br />Any questions,give me a holler at fone_man@bellsouth.net but remember to post on iboats board also for the rest of the members.<br /><br />fone_man

 

[ODDD1]

Re: Mercruiser carburation problem?

Jonh, before a rebuild is finished, the "fine tuning" is the MOST important part of the job...if your gonna bother to go through the trouble, shouldn't work right when you are done?<br />the one thing you should look at before you pull the carb off....is gasoline dripping out of the booster venturis when the engine is idling? if it is and not when engine is turned off, the idle air bleeds need to be drilled..mercruiser service manual covers the procedure....the booster venturis must not drip when endine is idling, or it will load up...<br />what ever you do, do NOT put a different carb on...almost all replacements i have seen are a pathetic excuse for a marine carb....

 

[JohnJR]

Re: Mercruiser carburation problem?

To ODDD1, I haven't pulled the carb yet so I can check for dripping. I'm not exactly sure what you mean by the booster veturis. Are they the smaller round components in the middle carb bores? Are they in both the primary and secondary barrels? I have a Clymer manual (not with me now) that does have an exploded view, but I'm not sure how much detail it has regarding the idle air bleeds. Are suggesting that they could be clogged? Thanks again for everyone's suggestions.<br />JJR

 

[ODDD1]

Re: Mercruiser carburation problem?

John, you are right on about what the booster venturis are......are in the primary bores only....the fix i was recommending is because they werent setup right to start with....i dont know what clymers say about this....i had their manuals for autos/motorcycles years back an burned em all in disgust.....if your idle speed is low enough {800 in neutral} and are dripping, idle mix screws can be turned out 7 or 8 turnsbefore prob desists....after the "adjustment"of the air bleeds, the mix screws will run at 1 1/2 to 2 turns without dripping......