How to tell what carb I need?!?

Lou C

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It’s a 2 bbl carb right now. But there are empty bolt holes on the manifold which makes me think someone put an adapter on there but I have no clue
not its not that is a 4bbl Quadrajet!
look at the first pic I posted....
 

Timangas

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Yes, the 1988 350Mag was fitted with a Q-jet carb.
Cool thanks! My original worry was it was only hitting about 3500 WOT and a buddy was saying it was the wrong carb but obviously he don’t know lol
Who ever told you that is a 2 bbl is wrong. Thatis a 4 bbl Rochester Quadrajet. good news is properly rebuilt and set up it is a very good carb, dont get fooled by the quadrajunk, quadra bog or other comments you may see.
start with the basics check compression, look-at what comes out of the fuel filter, check ignition components and timing, especially total advance
not its not that is a 4bbl Quadrajet!
look at the first pic I posted....
Yup you’re right! My original worry was it’s only hitting 3500 wot. It doesn’t bog or stutter so I’m a little scared to tare into the carb this close before boating season here in ks never working in carbs before. Might let her ride thru the season and try to work on it next winter...idk tho what would you suggest?
 

nola mike

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Cool thanks! My original worry was it was only hitting about 3500 WOT and a buddy was saying it was the wrong carb but obviously he don’t know lol


Yup you’re right! My original worry was it’s only hitting 3500 wot. It doesn’t bog or stutter so I’m a little scared to tare into the carb this close before boating season here in ks never working in carbs before. Might let her ride thru the season and try to work on it next winter...idk tho what would you suggest?
Suggest that you do what Chris suggested to determine the cause of your low WOT, especially compression test, plugs, other ignition stuff depending on your setup. Also verify that your tach reading is correct. 3500 RPM WOT means something is seriously wrong with your setup, and you have potential to screw it up more if not corrected.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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In addition to going thru the carb, make sure your compression is good. 140-150 psi good.

Also, other things that will prevent the motor from spooling up:
Wrong prop or gear ratio
Improper throttle cable adjustment
Carrying 1000# of water in the hull
Wrong timing
Worn cam
Flappers dropped in the y-pipe
 

Lou C

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In addition to all the other good suggestions the anti siphon valve if corroded or partly obstructed it will cause fuel starvation and low WOT rpms
 

Timangas

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Suggest that you do what Chris suggested to determine the cause of your low WOT, especially compression test, plugs, other ignition stuff depending on your setup. Also verify that your tach reading is correct. 3500 RPM WOT means something is seriously wrong with your setup, and you have potential to screw it up more if not corrected.
I’ve got a compression tester so I’ll do that in the morning as well as check the plugs. When I bought it it came with the msd ignition box which the guy I bought it from has bypassed. Tried looking up how to hook it back up but can’t find anything for that old. How would I verify the odometer is correct? It is a different motor from the boat so maybe that’s my problem? I guess it could be the throttle linkage because I did adjust it so it would idle but seems to be idling high what rpm should it be idling at?
 

achris

More fish than mountain goat
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I’ve got a compression tester so I’ll do that in the morning as well as check the plugs. When I bought it it came with the msd ignition box which the guy I bought it from has bypassed.
If the MSD box is bypassed, what system is running the engine?
.. Tried looking up how to hook it back up but can’t find anything for that old....
How do you know its age? and can you give us more details on the system? (Like a model number, or some way to identify it)
...How would I verify the odometer is correct? ...
Boat's generally run by engine hours, not odometers. Most boats don't have odometers (I've not seen one, but they may exist)...
... It is a different motor from the boat so maybe that’s my problem?...
Boat manufacturers don't make engines, they ONLY make boats. They ALL buy engines in from marine engine suppliers, like Mercruiser, Volvo, etc. Being not the original engine is NEVER the problem.
...I guess it could be the throttle linkage because I did adjust it so it would idle but seems to be idling high what rpm should it be idling at?
There is a correct procedure for adjusting idle. I suggest you get a hold of Merc service manual #9 and have a good read. In the meantime, the idle is 650-700rpm, in forward gear, in the water, unrestrained (ie, not tied to a jetty!).

The next thing you should be doing is opening the throttle fully and removing the flame arrester (looks like an air filter) and looking at the throttle plates (you'll have to push the secondary air flaps open with your finger) and making sure the throttle plates ARE fully open. And do it with the engine NOT running. (Yes, I have seen people try to do it with the engine screaming its box off. 🤦)

Chris......
 

Timangas

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If the MSD box is bypassed, what system is running the engine?

How do you know its age? and can you give us more details on the system? (Like a model number, or some way to identify it)

Boat's generally run by engine hours, not odometers. Most boats don't have odometers (I've not seen one, but they may exist)...

Boat manufacturers don't make engines, they ONLY make boats. They ALL buy engines in from marine engine suppliers, like Mercruiser, Volvo, etc. Being not the original engine is NEVER the problem.

There is a correct procedure for adjusting idle. I suggest you get a hold of Merc service manual #9 and have a good read. In the meantime, the idle is 650-700rpm, in forward gear, in the water, unrestrained (ie, not tied to a jetty!).

The next thing you should be doing is opening the throttle fully and removing the flame arrester (looks like an air filter) and looking at the throttle plates (you'll have to push the secondary air flaps open with your finger) and making sure the throttle plates ARE fully open. And do it with the engine NOT running. (Yes, I have seen people try to do it with the engine screaming its box off. 🤦)

Chris......
Currently power is ran straight to the coil then to the distributor.

I found the serial number on the block and looked it up. Came back as a 1988 350 mag

sorry I meant tachometer not odometer 😬. Was wondering since it is a different motor than original possibly the new motor is sending the tach reading that the original tach isn’t reading right?
I included some pics of the carb at full throttle. The secondary flaps are open but I’m not sure if they’re open all the way.
I’ll look into merc service manual #9. I have a feeling my throttle cable isn’t set right back at the motor. Everything was unhooked when I got it and I just got everything hooked up good enough for it to run. It doesn’t sputter or die but just not getting more than 3500 or so rpm at WOT. Is there any instructions you can point me to to hook back up the msd ignition?
 

Timangas

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Pics of the carb and msd box
 

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nola mike

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That carb looks like it's open. So that msd isn't hooked to anything? I don't think that's marine rated. Where does the negative wire off the coil go? One should be your tach, one may be to your shift interrupt switch, and one should be to whatever is controlling your ignition. If it goes straight to the distributor then you either have points or there's an ignition control module somewhere around there
 

Scott Danforth

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MSD = My Spark Disappeared

I would remove the MSD crap and go back to a stock mercruiser ignition system or a delco voyager.
 

Timangas

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That carb looks like it's open. So that msd isn't hooked to anything? I don't think that's marine rated. Where does the negative wire off the coil go? One should be your tach, one may be to your shift interrupt switch, and one should be to whatever is controlling your ignition. If it goes straight to the distributor then you either have points or there's an ignition control module somewhere around there
Looks like it’s going straight to the distributor right? Yea the msd is completely bypassed
 

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achris

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Lift the distributor cap and show us a photo of what's inside....
 
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