Mercruiser 5.0 losing RPM

V

vetting

Petty Officer 2nd Class
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If you determine its the carb and you cant rebuild it yourself, it might also be a good time to upgraded to an Edelbrock 1409 marine carb. Ouch...just looked up the current pricing $500. They were only 300ish when I put mine on a 5.7 a few years ago.
 
79Invader

79Invader

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vetting said:
If you determine its the carb and you cant rebuild it yourself, it might also be a good time to upgraded to an Edelbrock 1409 marine carb. Ouch...just looked up the current pricing $500. They were only 300ish when I put mine on a 5.7 a few years ago.
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Ouch, that is expensive. What kind of upgrade does it offer? Power gains? Reliability? An Eldebrock sticker on the transom? Lol
 
Bondo

Bondo

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79Invader said:
Ouch, that is expensive. What kind of upgrade does it offer? Power gains? Reliability? An Eldebrock sticker on the transom? Lol
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It’s a four barrel that’s all I know about it.
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Ayuh,....... I think in 1990, they were still usin' the Quadra-Jet carb,.......

Shortly later they went to the Merc/ Weber AFB, which is a carbon copy of the Edlebrock carb,.....

Rebuild the carb ya got,...... No performance gains to be had,...... They're both good 4bbl.s,.....
 
79Invader

79Invader

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Rick Stephens said:
Ask away here on rebuild tips. Lots and lots of experience from the old guys (like me)
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Thanks Rick. I'm going to go ahead and order the rebuild kit since it should be done regardless if that's my problem or not. I will start a new thread for carb rebuild questions when I get to that bridge.
 
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rad1026

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People freak out about the Quadrajet but with a little reading and knowledge its not a bad rebuild and there is no reason it can't be reliable. Clean out all the idle tubes, learn how to set the float and definitely replace the choke pull off diaphragm as that controls the opening speed of the secondary throttle flaps. You have to go by your carb number but this is probably it.

https://cliffshighperformance.com/Q...uadrajet-parts/quadrajet-67-70-choke-pull-off
 
79Invader

79Invader

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alldodge said:
Most Q-jets do have a filter at the carb, would check yours but don't have a serial number
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where is the serial number? Shouldn’t it be an “18-“ number? Only number I’m finding is 17080565. Then a 1399 below that.
 
79Invader

79Invader

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alldodge said:
Think your motor is a reman, and would explain the number. Merc number are one number, one letter and 6 more numbers 0B123456. Remans are just numbers.
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I found the engine serial number. 0C752996.
 
79Invader

79Invader

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So I foolishly disconnected the wire that runs from the coil to the distributor from the coil. Cranked the engine to look at fuel flow. There was spark at the coil so I stopped cranking. Put the wire back on and now no spark. Thought I fried the coil so I ran down to the parts store and got another one. Still no spark. Now what did I fry? :mad:
 
alldodge

alldodge

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Which wire was removed from the coil (main tension lead, 12V, distributor or tachometer)?
 
alldodge

alldodge

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Might have blown the pickup or module.

Run thru the guide to figure out what happened. Works same for TB4 or TB5

TBV Troubleshooting.jpg
 
79Invader

79Invader

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Learned how the TB IV and V systems work, very simple and easy to understand. Seems like a great system if you don't have an idiot (like me) working on it (lol). Blown pickup is 95% the culprit, which makes sense since I'm sure the spark from the coil found it's way to ground through that sensor... inside of the dizzy looked terrible, and had to break the rotor to get it off. So all new cap rotor and sensor. Get her fired up then I'm going to rebuild the carb, seems like the most logical thing to so since it quickly filled up a sandwich bag with gas while cranking for less than 10 seconds. Thanks for your input everyone, I'm loving these forums!!
 
79Invader

79Invader

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Chris, great post you wrote, I read all of it last night while learning. I wasn’t being sarcastic in saying it’s easy to understand, it really is easy to understand, and your thread helped quite a bit.
 
achris

achris

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79Invader said:
Chris, great post you wrote, I read all of it last night while learning. I wasn’t being sarcastic in saying it’s easy to understand, it really is easy to understand, and your thread helped quite a bit.
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Oh, I quite agree. It's not a difficult system. The intricacies are in the way the program works, and getting one's head around the fact that a pulse initiates the spark for the NEXT cylinder. But at a mechanic/repairer level, one of the easier systems to work with.

Pretty much, the module and sensor replace points.

Chris........
 
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