Author Topic: Carburetor for a 350 (Read 15192 times)

Shrom CVX-18 · « **on:** July 21, 2011, 06:42:32 PM »

Some of you guys that have been following my threads know I put a 350 in my boat recently. I bought a Quadrajet 4brrl carb and have been running it with that. It is not running at its best. I think it may be because the carb needs rebuilt? I am contemplating on getting a new carb that will give me better performance. I am looking for any ideas on the best carb to get.

The only thing done to this 350 is that it is bored .040 over. So that makes it a 358? Before I dropped it in I took it apart to look at the internals. Pulled the cam. (looks to be a stock replacement) Crank was beautiful, it was ground .010 under.

Or should I just turn it in to a 383 stroker in a couple years? I have done a inline six stroker in my wrangler years back and was vary happy with the performance. So I'm kinda leaning towards the stroker idea. But would still like to either rebuild the carb I have or get a new one.

Rosscoe · « **Reply #1 on:** July 21, 2011, 08:15:14 PM »

Well from what I have been told, Quadrajets are actually pretty good carbs. I recently had one rebuilt and basically it is new. About 100.00 cheaper then the "new/rebuilt" one I bought on line and that one didnt fit and I had to ship it back. That is why I decided to have the one I took off rebuilt.

OleRed · « **Reply #2 on:** July 21, 2011, 10:36:24 PM »

Mercruiser has been running the quadrojet for a Lot of years on the Chevy's, nothing wrong with them in my opinion, but with use and age, there are a couple things that go wrong with them, as with most other carbs, they have their quirks. one of the most common problems with an old quadrojet carb is that the throttle shaft wears into the main body causing a rough idle and a "bog" on exceleration, another thing is the lead plugs in the throttle body begin to leak the gas out of the carb into the intake. They often have a "bog" in full power because the vacumn piston that operates the secondary metering jets gets worn.
I prefer the old style afb carter carbs myself, and the the new style Edlebrock carbs is a chip off that old block, best bang for the buck in my opinion, you can order one for your application already jetted for performance, economy, or general use, runs great right out of the box. The Holly is a good carb also, I'm not going to Knock them, but you do have to set them up for the performance you want out of your engine, they will run hard, or they will get you some great ecomomy, but you have to set them up for what you want out of them, just bolt-em-on and go usually don't get best performance.

Myself .. again, in my opinion, the Edlbrock combo with the Performer manifols is the cat's meow ... did I spell that right ?

Rich_V174SS · « **Reply #3 on:** July 22, 2011, 06:49:36 AM »

I have a Quadrajet on my 3.7 liter 4 cylinder in the V174. I have two of them actually. The one that I got with the engine had a leaning out problem at full throttle, even after rebuilding it twice. I bought the second one from ebay for $105, rebuilt that and now my engine seems happier.

Quote

They often have a "bog" in full power because the vacumn piston that operates the secondary metering jets gets worn.

There's a vacuum piston on the primary metering rods, the secondary rods pull mechanically with the opening of the air shutter over the secondaries.

I just picked up a book from Amazon.com that explains everything about the Rochester Q-jet, see the link below:

http://www.amazon.com/Rebuild-Modify-Rochester-Quadrajet-Carburetors/dp/1932494189/ref=sr_1_1?ie=UTF8&qid=1311335784&sr=8-1

OleRed · « **Reply #4 on:** July 22, 2011, 09:17:30 AM »

Quote

There's a vacuum piston on the primary metering rods, the secondary rods pull mechanically with the opening of the air shutter over the secondaries.

Ooops .. my bad Rich, you are right. Correct me if I'm wrong about this, but one of the things that make the quadrojet such a universile carb is that secondary metering design, depending on the vacumn demand for the secondaries, by the throttle plates, that (shutter) acts like a varible venturi, only allowing it to open enough to provide enough air and gas to
flow through the secondaries that the motor requites. Although the tension on the stutter is pre-set by the mgf for it's application, you can change it, to open sooner or later, I have done that to get rid of a "bog" on the hole shot.

For some reason I still get a grin on my face when I see a GM carb on a Ford motor ...

n0ukf · « **Reply #5 on:** July 22, 2011, 10:29:25 AM »

A neighbor (4 miles away) up here mentioned he's having carb trouble with a Thermoquad on his V185. I invited him here but have seen no new members here yet since that invite. I've never heard anything good about those carbs, all the mechanics around here hate them.

Hyperacme · « **Reply #6 on:** July 22, 2011, 10:36:24 AM »

Have him email me if he would like to sign up ... hyperacme@gmail.com

New member accounts are shut down because of the large amount of spammers signing up.

Eric_Michael · « **Reply #7 on:** July 22, 2011, 10:48:34 AM »

In my experience, Edelbrock carbs have been really solid right out of the box.

My situations were similar, although automotive in nature: Tired Q-jets causing odd problems. I could have re-worked the Q-jets, but I took the easy way out. A few bills for a new Edelbrock, a few minutes to bolt it up, and the problems all went away.

Although I kept them, I probably could have E-bay'ed the old carbs and offset my expenses a bit. That probably would have taken me close to a net-zero cost relative to the expenses associated with rebuilding the Q-jets.

-Eric

Rich_V174SS · « **Reply #8 on:** July 22, 2011, 02:42:12 PM »

Quote

Correct me if I'm wrong about this, but one of the things that make the quadrojet such a universile carb is that secondary metering design, depending on the vacumn demand for the secondaries, by the throttle plates, that (shutter) acts like a varible venturi, only allowing it to open enough to provide enough air and gas to
flow through the secondaries that the motor requites. Although the tension on the stutter is pre-set by the mgf for it's application, you can change it, to open sooner or later, I have done that to get rid of a "bog" on the hole shot.

Yes, the shutter has a cam on it that raises the metering rods out of the jets as the shutter opens, its tension can be adjusted by loosening or tightening the tension spring. So far I haven't done any "tricks" to my carb to enhance performance, it's basically stock.

Rosscoe · « **Reply #9 on:** July 23, 2011, 08:05:16 AM »

Rich I am looking at what I think is your main wiring harness with the plug....looks brand new. Were you able to find a replacement or was it just in that good of condition?

Shrom CVX-18 · « **Reply #10 on:** July 23, 2011, 08:43:36 AM »

Thanks guys sorry I haven't responded. I am at the lake now and have bad internet service here. But when i get back Monday I'll will give more details on what my how my boat is performing. See what you guys think.

Rich_V174SS · « **Reply #11 on:** July 23, 2011, 04:15:18 PM »

Quote from: Rosscoe on July 23, 2011, 08:05:16 AM

Rich I am looking at what I think is your main wiring harness with the plug....looks brand new. Were you able to find a replacement or was it just in that good of condition?

Believe it or not that wire harness came from the 1988 donor boat that was so gracious to sacrifice its parts for my boat. Those parts included the inner & outer transom assembly, XD trim rams, trim pump and hoses, main wire harness and steering cable. I don't think it's an OEM Mercury harness because it had all sorts of pre-molded connectors at the control panel end to connect to the gauges and stuff that were used in the other boat. I cut all that stuff off and put ring terminals on the wire ends to connect to my gauges.

Shrom CVX-18 · « **Reply #12 on:** July 23, 2011, 08:01:17 PM »

Quote from: Rich_V174SS on July 22, 2011, 02:42:12 PM

Quote
Correct me if I'm wrong about this, but one of the things that make the quadrojet such a universile carb is that secondary metering design, depending on the vacumn demand for the secondaries, by the throttle plates, that (shutter) acts like a varible venturi, only allowing it to open enough to provide enough air and gas to
flow through the secondaries that the motor requites. Although the tension on the stutter is pre-set by the mgf for it's application, you can change it, to open sooner or later, I have done that to get rid of a "bog" on the hole shot.

Yes, the shutter has a cam on it that raises the metering rods out of the jets as the shutter opens, its tension can be adjusted by loosening or tightening the tension spring. So far I haven't done any "tricks" to my carb to enhance performance, it's basically stock.

you guys saying about a adjustment to get ride of the "bog" that is what mine is doing. Ot is bogging out when you give it full throttle, then it straightened it self out. Where is that adjustment spring located on these carbs? Also you guys that recommend the edlbrok carbs. What model do you recommend. Where is the best place to get these carbs?

Jerry · « **Reply #13 on:** July 23, 2011, 09:54:39 PM »

It may just be the accelerator pump. You can buy that without buying the whole kit for a couple bucks.

OleRed · « **Reply #14 on:** July 23, 2011, 10:30:07 PM »

two things Schrom, the Edlbrock carbs are available everywhere, online, Oriely's, NAPA, and you can get one for the engine and purpose you want to run, and it will work just fine right out of the box. One of the most frequent problems people have is over carborating a motor, the 350 Chevy, stock configuration, developing 260 /300 hp only requires 570 cfm carb to run efficiently, the 600 cfm Edlebrock I'm running, actually on Barb's boat, is the #1406 carb, and there is hardly any difference in the marine application, just a little neopreme plug to close off the vacumv port for the power brake drum.
http://www.edelbrock.com/automotive_new/mc/carbs_acc/performer.shtml
Secondly, it takes a little thinking to adjust those secondaries, and that may not be your problem anyway .. you may need to check your timing with a degree wheel, or a timing tape on the harmonic balancer, with the thunderbolt ignition it needs to be running @ 32 to 34 degrees total advance @ 2000 rpm, check that fiirst, then, at an idle 600 / 800 rpm, set the idle screws forward till you hear the motor labor just a bit, thenback up the screws 1/4 turn, one at a time, that should give you a nice smooth idle. If it still "bogs" on a full throttle hole shot, then you may need to adjust the secondary thingy's. There is a slight spring with a tensioner on starbord side of the carb, and it's up side down, but if you set the tention a little tighter, so the flapper don't just fly open on a hole shot, that usualy takes out the bog ... Like I said .. it's a thinking thing ,, and that is getting more difficult for me the older I get. Good Luck ! but you may find out by messing with that you can really wake that carb up. I know a lot of folks will tell ya those carbs ain't worth a nickle, but Chevy has been running then since 1961 or so .. I really don't remember. but a Long time, and they have been using them on 4 cylinders, 6 cylingers, 8 cylinders, and I think the marine motors used them until 1996 ... so, go figure. and Yes, I prefer the old style Afb /Avs carbs to the quadrojet because I think I get a little more performance out of them, and better economy in a boat, not the same as a quadrojet, in a car, the quadrojet will get more milage, but not in a boat, it's a different bird, and I'm going to argue that point with anyone .. it don't make much sense to me, but it's a fact.

MarkS · « **Reply #15 on:** July 24, 2011, 03:15:16 AM »

Used to LOVE the sound of the quadrajet kicking it on the old man's Olds Vista Cruiser..........

If you do decide to go with the Edlebrock, Summit Racing has them on sale and a $25 rebate Shrom;
http://www.summitracing.com/parts/EDL-1406/?rtype=10

Rich_V174SS · « **Reply #16 on:** July 24, 2011, 07:21:39 AM »

That's not a Q-Jet though, that's their version of a Weber carb. Webers were also used by Mercruiser on some of their engines.

Shrom CVX-18 · « **Reply #17 on:** July 24, 2011, 08:17:16 PM »

You guys have been a big help. I am going to try a little more with this carb and see where I get. I have tried adjusting it many times. And just feel like im getting know where. But I'll keep trying these tips, you guys have bin giving me. I'm am a young buck still learning the tricks. Honestly I'm getting tired of the problems I have been having. I just had to replace the shift cable to the outdrive last week. And now I found that I am leaking trim pump oil in the bilge.

Rosscoe · « **Reply #18 on:** July 25, 2011, 08:22:38 PM »

Things can certainly get frustrating...I hear ya, but hopefully, you knock these things off, one at a time.

Shrom CVX-18 · « **Reply #19 on:** July 26, 2011, 06:19:19 PM »

Quote from: Rosscoe on July 25, 2011, 08:22:38 PM

Things can certainly get frustrating...I hear ya, but hopefully, you knock these things off, one at a time.

Thanks, yeah I just got back from the lake. Boat ran half decent. However I have a few more things to add to the list of bad luck. When I replaced the shift cable to the out drive, It did not seal at the transom correctly. Water drips in the boat.(at a slow rate, but still needs fixed) The intake gasket right near the distributor is leaking...So that being said. No more rushing around. I am going to most likely pull the engine again and tear her down and paint it this time. Do things more meticulously, I'm taking this as a sign. Maybe I just need to take the rest of the season and work on the boat. Hopefully have everything done for a good season next year and hopefully many more.
Will probably chose a new color for the engine then your normal black. Something to catch the eye when I open the hatch. After the oily mess this season, I want to take care of that and have my engine spotless! Maybe upgrade a few parts...