Merc 470 stalls when you gun it

[Stings]

I have a 1979 merc 470 with a 4bbl Rochester quadrajet carb. just got it used this season. I had to replace the coil,solenoid, plugs, oil, all 3 fuel filters, and gas and reground the starter for other reasons besides the reason im posting a question here. the points looked new so I got a set to keep on board. the problem now is when I try to give it allot of gas it will stall from take off but if I open it up slowly I can get up in rpms. but it will act like it wants to stall out once the 4bbl opens up and it seems to be just dumping gas in it and it runs slugish. im not sure if it should have allot of gas pumping in it like that or not, I can live with out the top speed but the slow take off is driving me crazy. I used carb cleaner. im not sure if its a timing issue or a carb problem. what is the correct timing settings for this motor. does it sound more like a carb issue? any help would be great

 

[Bondo]

Re: Merc 470 stalls when you gun it

Hi Stings,<br />Welcome to iboats.....<br />

what is the correct timing settings for this motor.

8*BTC<br />

does it sound more like a carb issue?

No Doubt in My mind......<br />A Rebuild,+ Tuning, Might bring that Q-Jet back............<br />Maybe Not........<br />Carb Kit from NAPA is about $25.00........(#18-7077)

 

[Stings]

Re: Merc 470 stalls when you gun it

is this something anyone can do? im a machinist with mechanical abilites but i saw a diagram of one and it looks intimidating. would i be able to just take the top off and clean what i can get at or is there more to it after the top comes off?

 

[rattana]

Re: Merc 470 stalls when you gun it

A carb kit has a picture of an exploded view of the carb. While it does look daunting with 100 pieces or more pieces, it really isn't that bad. Ensure that it is the right kit for your carb and you will find it goes together quite easily. Every piece will be associated with a number on the diagram. I always follow the numbers one at a time both disassembling as well as reassembling. You will omit one or two steps as some carbs don't have all the components. That will be staright forward as you go about it. The kit will have parts for a couple different carbs so look at the parts carefully to use the right replacement parts. A wrong gasket could block off a port and cause poor running.<br />Make sure you have a large area (tabletop in your shop) so you can spread everything out. I found there are a few things you have to pay attention to. One is that it has to be cleaned properly, varnish inside the carb is more than likely what cause the carb problems in the first place so you have to clean it all out. A good carb cleaner will clean it up. Blow everything out with compressed air when you have it disassembled. <br />Float setting and accelerator pump setting are another. Check the settings of these two things before you disassemble the carb and make a note of it. If there are big discreptancies from the actual and what the kit suggests, make sure you have the right specs from the sheet.<br />Remember take your time and follow the instructions and you will be fine.

 

[Stings]

Re: Merc 470 stalls when you gun it

ok i got the carb rebuilt from a pro and it still seems to have the same problem so i had it rechecked from another shop and it still does the same thing but now it will stall when i am at idle speed after about 30 seconds and it wont restart unless i pump the gas twice and then its good at idle for another 30 seconds. it will run fine with the muffs on in the driveway but the lake its a diffrent story. the 20 seconds of run time is good then it starts to act up for 10 seconds then it dies. if anyone has any advice on what i should try next please feel free to let me know. one more thing. what other carbs could i use on this engine. i know a guy with a 350 that has a 4bbl on it that he would be willing to give me in trade for computer work, he also has other carbs from other boats but im just not sure what will fit. is their a list of carbs that will fit a 470?

 

[rattana]

Re: Merc 470 stalls when you gun it

Three things I would check to try and narrow it down are;<br />1) What is the voltage at the positive side of the coil when the key is in the run position, does the voltage drop off when it starts to act up.<br />2) What is the vacuum reading when the engine is running. You would have to connect a gauge to get a reading.<br />3) What is the fuel pressure going to the carb.

 

[Northern Eclipse]

Re: Merc 470 stalls when you gun it

There is a good chance you have a blockage in the exhaust, such as the exhaust shutter coming apart and dropping down the pipe, will run on muffs but as soon as your in the water you get a extra bit of back pressure from the exhaust port being submerged and chokes the motor, to check for this you'll need to loosen the 4 clamps on the rubber exhaust boot between the elbow and down pipe, remove boot and see if the shutter is intact, it should look like a rubber butterfly and only open in a downward direction, if you only see a metal shaft across the pipe then the other piece have dropped down and need to be fished out, this may not be your problem but is seems its a good chance.

 

[Stings]

Re: Merc 470 stalls when you gun it

as soon as the weather clears up ill be able to check all that stuff out. thanks for all the advice, i would be lost with out it. i have been looking online for my carb to research it and see if maybe there is something that the tecs working on it might not know about it. this is the part # right off my carb 7045220 the only info i can find for it is all about a 75 0r 76 GM truck. could i have bought the boat with a carb ment for a car?<br /><br />1975 7045220 350 A GM TRUCK G10 VAN/SPORT VAN<br /><br />1975 7045220 454 ALL GM TRUCK C10

 

[MattSD170]

Re: Merc 470 stalls when you gun it

I had the same problem with the same engine. I did the same things and when i hit the throttle, a huge hestiation. After a new carb, tons of new fuel line componests and new coils, i learned that is was a sticky exhaust valve. they are poor valve guides and collect carbon. A valve job is nessecary. The head is a ford 460. and easy to take off. My machinist honed them out as well. To bandaid the problem, use marvins mystery oil in the oil. It lossened my up after a while, but change your oil after you run and let it sit.

 

[Stings]

Re: Merc 470 stalls when you gun it

boats up for sale now, i don't need the problems that a 470 gives. I'm more in to fishing then fixing