305 carb issues

[sean6721]

hi everyone im new to the forum and a first time boat owner.im in love with the water and always wanted a boat so I purchaced one. its a 1992 searay 220 with a 305, very clean boat. anyway it has a quadrajet on it and its acting up. boat wasn't ran for a year or so. when I got it I drained the old gas added new gas, changed fuel filter and plugs. took it out on the water and idle through low rpm ran fine. 3/4 to full throttle it had a lag. pulled the cover off carb and noticed the big air flaps(don't know the exact wording for them) were not opening like they are supposed to. turned around came home and rebuilt the carb. took it back in the water and it ran 100 times better but still those flaps are not opening and has the lag and will not reach WOT. when I open them with my hand they boat takes right off like it should and runs great but then they don't close either, I have to close them by hand. im mechanically inclined as I have built handful of motors from sled harlels and bigblocks. I wanna say its a vacume leak but I have no idea where it would be leaking from. id also like to know where abouts the mixture screws should be, I had them started at 1 1/2 each one. im getting frustrated and about ready to say f it and just buy a rebuilt one off ebay. and suggestions will help wether its messing with the old carb or just putting a rebuilt one on it, thanks in advance

 

[alldodge]

Re: 305 carb issues

hi everyone im new to the forum and a first time boat owner.im in love with the water and always wanted a boat so I purchaced one. its a 1992 searay 220 with a 305, very clean boat. anyway it has a quadrajet on it and its acting up. boat wasn't ran for a year or so. when I got it I drained the old gas added new gas, changed fuel filter and plugs. took it out on the water and idle through low rpm ran fine. 3/4 to full throttle it had a lag. pulled the cover off carb and noticed the big air flaps(don't know the exact wording for them) were not opening like they are supposed to. turned around came home and rebuilt the carb. took it back in the water and it ran 100 times better but still those flaps are not opening and has the lag and will not reach WOT. when I open them with my hand they boat takes right off like it should and runs great but then they don't close either, I have to close them by hand. im mechanically inclined as I have built handful of motors from sled harlels and bigblocks. I wanna say its a vacume leak but I have no idea where it would be leaking from. id also like to know where abouts the mixture screws should be, I had them started at 1 1/2 each one. im getting frustrated and about ready to say f it and just buy a rebuilt one off ebay. and suggestions will help wether its messing with the old carb or just putting a rebuilt one on it, thanks in advance

:welcome: to iboats

The vacuum diaphragm appears to not be working, and probably binds to keep the carb from closing when throttling down. It's a Rochester Q-jet and are fairly simple and work very well. Need to fix the linkage and probably replace the diaphragm or fix the line going to it.

http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=816596&ivar=images/COMMON/38512.png&inbr=1014&bnbr=140&bdesc=CARBURETOR%28ROCHESTER+%2D+4+BARREL%29

 

[sean6721]

Re: 305 carb issues

when I push in the arm on the diaphram and hold my finger over the hole it holds the arm in until I let my finger off the hole then the arm comes back out, seems to be working.

 

[wrench 3]

Re: 305 carb issues

The only vacuum diaphragm on a quadrajet is usually the vacuum choke brake. The air flaps on the secondarys are sucked open by the air flow. The linkage running forward is to lock them closed when the choke is on. There's a spring in the center that closes them. Either the pivot shaft is sticking, or the metering rods are binding. You can remove the metering rods by removing the really small philips screw from the center of the flaps.

 

[alldodge]

Re: 305 carb issues

when I push in the arm on the diaphram and hold my finger over the hole it holds the arm in until I let my finger off the hole then the arm comes back out, seems to be working.

In that case see if the port going to the diaphragm is drawing a vacuum when the engine is running at idle. If the port is drawing a vacuum then it should be in the linkage. The Q-jet when throttled up causes the vacuum to be reduced to a level where the diaphragm releases. Once released, the throttle linkage opens the secondary's. Unless the vacuum diaphragm releases the secondary's are not allowed to open

 

[sean6721]

Re: 305 carb issues

The only vacuum diaphragm on a quadrajet is usually the vacuum choke brake. The air flaps on the secondarys are sucked open by the air flow. The linkage running forward is to lock them closed when the choke is on. There's a spring in the center that closes them. Either the pivot shaft is sticking, or the metering rods are binding. You can remove the metering rods by removing the really small philips screw from the center of the flaps.

so your saying the diaphragm has nothing to do with the air flaps and only the choke? the choke is working like it should. so should I move to something else and eliminate the diaphragm?

 

[wrench 3]

Re: 305 carb issues

so your saying the diaphragm has nothing to do with the air flaps and only the choke? the choke is working like it should. so should I move to something else and eliminate the diaphragm?

AllDobge could be rite that the diaphragm could help keep the plates closed, but it wouldn't stop it from opening and closing by hand.

 

[Walt T]

Re: 305 carb issues

Secondary restrictor flaps are adjustable. Small screw changes tension on the spring. However I doubt your motor will pull enough air to open them much. If you make the restrictor flaps too loose then you'll have a bog when you accelerate. You can test by wiring the flaps open, then accelerate slowly to wot, then if it doesnt go any faster or feels the same then the flaps arent the problem. Diaphragm is not related to the flaps

 

[sean6721]

Re: 305 carb issues

Secondary restrictor flaps are adjustable. Small screw changes tension on the spring. However I doubt your motor will pull enough air to open them much. If you make the restrictor flaps too loose then you'll have a bog when you accelerate. You can test by wiring the flaps open, then accelerate slowly to wot, then if it doesnt go any faster or feels the same then the flaps arent the problem. Diaphragm is not related to the flaps

This is the carb thst came on this motor from what I've found so the motor should suck enough air to open them or they wouldn't of matched the carb to the motor right?? I kinda tested it like you said, with carb hooked up like normal I open the throttle slowly starts excellent in like it should. U can see the flaps start to open. A lil over half throttle it bogs and won't reach top speed or maximum rpms (the flaps won't open any more). Then from a moving slow start when it is running good at low rpms I manually open the flaps ease on the throttle (not hammer it) and it takes right off like it should reaches 4300 rpms (max on carb cover says 4200) and reached speed of 35 mph with 3 people in boat and a not so good bent prop. When I ease back off the throttle back down to idle the flaps that I manually opened I have to manually close because they are stuck open. I hope this explanation helps understand what is going on

 

[alldodge]

Re: 305 carb issues

The vacuum diaphragm is what should close the flaps. Wonder if something is misaligned and causing not to open as well as close. The pic below shows the linkage to the flaps



Here is a great link for adjustment
THE Q-JET

 

[MikDee]

Re: 305 carb issues

I like my Quadrajets, but hate this choke pulloff setup. I've had more problems on cars with the secondary's not opening because of this!
I guess it's an extremely sensitive setting? but when those secondary's open, it's pure joy being pushed back into your seat as those large air valves open & lift the metering rods out of the high speed jets, as it does it's thing!

You do have the metering rods hanging on their hangers on carb top, in between the Air Valves? Right?

 

[sean6721]

Re: 305 carb issues

Alldodge mine has the block choke on it and the linkage in that pic looks nothing like mine. And mikdee yes they are hanging as they should. Boating season is here and this is the only thing holding me back. Should I just buy a rebuilt q-jet on ebay or a 1409 eld. Carb?? This is the first q-jet I've ever worked with and Ist stumping me

 

[alldodge]

Re: 305 carb issues

Alldodge mine has the block choke on it and the linkage in that pic looks nothing like mine. And mikdee yes they are hanging as they should. Boating season is here and this is the only thing holding me back. Should I just buy a rebuilt q-jet on ebay or a 1409 eld. Carb?? This is the first q-jet I've ever worked with and Ist stumping me

I would recommend the 1409

 

[sean6721]

Re: 305 carb issues

Would the 1409 (marine 600 cfm) already be jetted for the boat, simply bolt it on and tune it and good to go?? Would I need a adapter plate?? I know I would need a new gas line

 

[wrench 3]

Re: 305 carb issues

AllDobge could be rite that the diaphragm could help keep the plates closed, but it wouldn't stop it from opening and closing by hand.

I forgot to say that if the engine is off, The plates should close by themselves if opened by hand.

 

[MikDee]

Re: 305 carb issues

Alldodge mine has the block choke on it and the linkage in that pic looks nothing like mine. And mikdee yes they are hanging as they should. Boating season is here and this is the only thing holding me back. Should I just buy a rebuilt q-jet on ebay or a 1409 eld. Carb?? This is the first q-jet I've ever worked with and Ist stumping me

Qjets are a great carb, if set up right! Why spend a ton of money on a new different carb, if yours can be set up to work right? Are the secondary butterflys on the bottom of the carb opening fully with the linkage as well? Are there any vacuum leaks, or a possible poor fitting of the carb mounting gasket, or could it be the wrong carb mounting gasket? The Air valves should be loose enough to drop back into place with gravity, and no vacuum on them.

 

[MBAKER]

Re: 305 carb issues

Did you set the tension on the air door (flap) when you rebuilt the carb?

The air door opening is based on air demand and velocity, if the engine does not need more air then it wont open. Thats why the same Qjet carb can be used on V6 to big blocks, it self regulates its size to the airflow requirements. I would not be surprised that on a 305 it might only slightly open even at WOT.


The 1409 is a good carb as well and you could run it out of the box and be very close on setup. Its prob a little rich but thats far better than a little lean. Operates much the same as the Qjet in that it only opens the secondary air door on demand.

 

[sean6721]

Re: 305 carb issues

Yes the bottom butterflys are opening like they should and new gaskets inside and out. I don't know if there is a vacume leak. How would I tell if there is one? I read that it leaks from where the throttle linkage bolts on.


I didn't adjust the flaps when I rebuilt it. Seemed to be lose enough from the get go. It doesn't make sence, the motor must need the air but won't open the flaps enough. When I open them by hand it runs like a champ. I'm confused as I have never worked on a q-jet before

 

[sean6721]

Re: 305 carb issues

Also the rebuild kit came with 2 base gaskets, I used the one the was more open under the carb. There was another 1 that had 4 barrels openenings

 

[alldodge]

Re: 305 carb issues

My take away from what your saying is:

Everything is great except lack of full power
The 4 barrels open all the way
The flaps are not opening all the way
When flaps are manually opened all the way you get more power, but they hang
The flaps have to be manually closed if opened by hand
The vacuum pot which keeps the flaps from opening at idle will not close the flaps if manually opened during WOT

My take away is:
You need to work on the linkage and get it working correctly. If the linkage was working correctly your boat would run great. Need some pics of your carb so we can see what the possible problem might be.