1987 chaparral 5.7 rough idle and bog under a load

[markmccartha78]

I have a 1987 chaparral with a 5.7 mercruiser I’ve replaced fuel pump and lines as well as carburetor ga a rough time starting once it starts it will idle ok put it in gear and it bogs and has no power could this be a air idle adjustment ? Please help

 

[dubs283]

could this be a air idle adjustment ?

Perhaps. Did you inspect/adjust the carburetor or just install it and run? Inspect contents/change fuel filter(s)?

May check fuel pump pressure/vacuum. New pumps can (rarely) be bad/fail. Have you verified if it's choking out on fuel or is it lack of fuel? When was the last full tune up?

 

[markmccartha78]

I bought a brand new carburetor that was supposed to be pre tuned and ready to go the boat was starting and idling fine I took it out and put it in the water idle just fine go to forward and start going and just falls on it’s face I tried to adjust the air idle screws thinking that was the problem now I am getting rough idling and still falls on it’s face I am just lost to know what it is

 

[dubs283]

I bought a brand new carburetor that was supposed to be pre tuned and ready to go...I tried to adjust the air idle screws thinking that was the problem now I am getting rough idling and still falls on it’s face I am just lost to know what it is

You should familiarize yourself with the proper carburetor setup procedures. No carburetor can be tuned to any engine on a bench, it must be finalized in the water with the engine running.

You need to figure out, as said, if the engine is getting too much or too little fuel from the carburetor. This is also a good time to inspect/replace ignition components. Have you verified the ignition timing?

 

[Blorton]

+1 on checking the timing

 

[Rick Stephens]

What carburetor and what was your source?

A number of years ago I bought a brand new Edelbrock 1409 carburetor for a 4.3. And as well, bought the Edelbrock 'calibration kit' for the 4.3L V6 motor. It was so far off it wouldn't run out of idle. Had to start from scratch on calibration, which isn't all bad as I learned every little detail on how that particular carburetor works.

Edelbrock as a carb manufacturer does a better job than IMHO anyone else on building usable manuals and white papers on how their stuff works and how to work on them. Most other manufacturers don't do as well. However, there is so much great specialty support from builders and aftermarket sources for all of those carburetors that the hardest part is finding a useable source. Your best resource there is going to be other users on this forum. They know where to look as we all had at one time or another learn how to fix our *whatever*. That's why this forum is golden. Lots and lots of users who had to crawl to the finish line to get their boat running. Been there, and done that.

Don't be afraid to start the process to learn calibrate your carburetor.

 

[Blorton]

...and just like that, my interest in getting a 1409 disappeared.

 

[Rick Stephens]

...and just like that, my interest in getting a 1409 disappeared.

Afraid of having to learn somethin? hehehe

 

[dubs283]

Edelbrock as a carb manufacturer does a better job than IMHO anyone else on building usable manuals and white papers on how their stuff works and how to work on them. Most other manufacturers don't do as well.

Edelbrock.....meh

Holly ftw

 

[Blorton]

Afraid of having to learn somethin? hehehe

Yes. And I'm a little funny about spending good money on parts if they aren't even going to be in the right ballpark to begin with. And that would be assuming I could get a "real" 1409 to begin with and not some converted model introducing yet more variables.

 

[Rick Stephens]

Yes. And I'm a little funny about spending good money on parts if they aren't even going to be in the right ballpark to begin with. And that would be assuming I could get a "real" 1409 to begin with and not some converted model introducing yet more variables.

Everyone else bought that kit had the same issue. Cool part is they refunded the cost and it wasn't hard to calibrate once read the manual and started at the beginning.

Note that the 1409 typically comes 'calibrated' roughly for a 5.0L, right in the middle of the suggested range of motors.

I doubt many or even any carburetor can come truly pre-calibrated - close, yeah. There's a lot of variables that add up over time with wear, overbore rebuilds, cam styles, gearing, etc. And too many new carbs are just not right at all. At the same time it is very costly to pay a professional to do the calibration - and said calibration has to be done step by step on the water, not just in the shop. Hence learning to do it yourself is a key way to do it right and save a little jack. That's the real reason this forum is here, not to tell you what part to buy but how to fix it yourself.

 

[markmccartha78]

I went back with a new stock oem carburetor Rochester Quadra jet for a 5.7 mercruiser. The motor idles alright just don’t do well when you get down on it. Secondary’s open an all but I think this carb doesn’t have many adjustments beside air idle screws the idle screw itself and that’s it. I don’t even know where I can check maximum vacuum at on the carb.

 

[Rick Stephens]

I went back with a new stock oem carburetor Rochester Quadra jet for a 5.7 mercruiser. The motor idles alright just don’t do well when you get down on it. Secondary’s open an all but I think this carb doesn’t have many adjustments beside air idle screws the idle screw itself and that’s it. I don’t even know where I can check maximum vacuum at on the carb.

Adjustment on a Roc is needles, jets and power valve. Those are all calibration parts.