Quadrajet idle problems, please help...

I have twin inboard 305's with rochester 4bbl carbs.

The starbord engine runs great. It will run at about 800 rpm, warm. It will shift at 1000-1100 rpm without stalling. It runs smooth up to and above 3000rpms.

The problem carb. is on the port engine. Once the engine is started, I have to keep the engine running between 1000-1100 rpms or the engine will stall. I have to keep the engine at 1600-1700 when trying to shift or the engine will stall.

I removed the carb., cleaned, replaced all gaskets. I wanted to make sure the low idle circuit was not clogged. I re-installed the carb and it runs the same. Once the engine warmed up, I was running it at 1000 rpms (the minimal without stalling) and looked into the top. The fuel was spraying from the two holes in the top, center of each bore (I think the primaries).

When compared to the other carb, also running at 1000 rpm's, The fuel definitely was coming throught the low idle circuit and had minimal(very, very little) fuel coming from the two holes in the top.

Other info about the troubled carb: The choke is opening all the way when warm. I sprayed carb cleaner around the intake, hoping to check for leaks, I did not notice any surges or stumbles. When trying to adjust the idle screws, The engine did not change until the screws were, almost all the way in, or many turns out.

Thanks for any help

 

Scott, I still think you have carb problems.

One thing you may consider is when you did the carb work you may have failed to get the carb cleaned out completely. The only time I have good luck going through a carb is when it has been completely torn down, soaked over night in a strong carb cleaner and blown through every circuit with pressurized air. This is the only way I have found to properly get one cleaned out. I have tried building carbs without this process and ended up with the same problems only to have the problems go away after taking the carb apart and cleaning it out again. One foot note here: Be advised that marine carbs often have special coatings on certain parts. Good quality soaking cleaners can remove these coatings! Be sure only to soak the uncoated parts of the carburator. It has been my experience that the parts that need the soaking, ie. throttle body, circuit plates, venturis, ect. are not coated. However things that can rust like; throttle blades, choke valves, throttle shafts and so on will be coated to protect them from corrosion. You can tell the parts are coated if they are a different color than the rest of the carb. My advise is to have a good carb guy rebuild the carb for you. A marine carb guy is even better. If you can't find one (join the club) and you want to do it yourself, GET A MANUAL, make sure you take your time, do it in a clean enviroment, and clean the carb out very well. Organize your parts, and follow any directions you may have to the letter. Take the time to do it right and you will have good results.

 

Float Level?

Sunk Float?

Leaking into the centre well (the plugs in the carb base leak into the cavity in the centre of the throttle bores)?

 

You may have either a weak or damaged spring in the piston that opens the fuel needles. Also the needles may be bent, binding or be the wrong type. Q-Jets have a humongous amount of possible combinations and parts for any required service.

 

thank you for your replies.

Note:

I did not soak the carb overnite and blow out the passages. I will do this.

I will check the float level and see if the plugs in the base may be leaking.

is this right?......If the piston spring is weak, it will open easier with vacuum, therefore allowing gas to flow when it shouldn't.

I took the boat out this morning and it runs fine. Just the idle circuit is not working well. I got 22 miles off shore in 3-5's and one of my shafts(drive shaft) broke clean, right where the key way is, where it slides into the trans. I had to come back, thank goodness with a following sea, at around 6knts.

Thanks for all of the input

 

Scott, Your prop shaft broke? You may want to look at shaft alignment. I went through a problem with my old inboard due to bad alignment. My prop strut was bent causing the prop shaft to rub where it exits the bottom of the hull. It was not a big deal fix, but I did have to haul the boat. And I have a 100 ton press at work. I straightened the strut, aligned everything, and happy days. Let me know if you want the full skinny. (all the info)
Drew

 

drew,

The shaft broke right where it goes into the flange at the back ot the motor. The ocean was rough, but we were only doing about 6-7 knots. It must have been cracked already.

I had repacked the stuffing box about a week ago. During the change, I noticed that the previous owner (state of Ohio, Wildlife) must have over tightened the nut, which overheated the shaft. It was blue in color, with signs of light grooving. I was wondering if the overheating may have warped the shaft. I noticed some vibration, but nothing violent.

I am going to trailer the boat tomorrow. I have been reading alot of information on the web about shaft alignment.

I will inspect the motor mounts and the ange at which it goes through the bearing under the boat.

Any tips will help. Thanks

 

I doubt that heating caused by an overtightened packing nut would have caused the shaft to warp. I would take a cutting torch to get one to bend. If the blue color of the shaft was caused by heat than the shaft indeed did get hot, but not hot enough to cause warping. Think of it this way, ever see a chrome exhaust pipe on a motorcycle turn blue? Think they bend? Prop shafts are made out of tougher stuff. I think it is more likely that the shaft broke due to fatigue after running out of alignment for a long period. Couple that with possible hull flexing in rough seas and snap! I have a friend that had to have his transmission rebuilt recently because of bad alignment. I would check your transmission's output shaft for endplay while you have the shaft out. You should not be able to feel any movement up and down in the output shaft. A good indication would be if the output seal is leaking. I don't mean to freak you out, but check it anyway. Mine was out of alignment for a good while and so far I have not had any trans problems. Also, its a good idea to go ahead and replace the strut bushing while you have it apart. If you do have an alignment issue there will be wear in the bushing.

 

I pulled the boat today:

1. I removed the flange, zinc, propeller and pulled the shaft. The key way at the transmission end showed signs of wear. The key was bent slightly to one side. This could have been when the shaft spun and broke.

2. noticed some mis-alignment through the strut (not up and down but left to right). I looked at the gaps.

3. From what I have been reading......with a one inch shaft it should only stick pass the strut 1/2"......It is sticking passed 2.5".

4. one bolt is missing from the motor mount. Several lag bolts, that hold the motor mounts were loose. when I tried tightening, they seemed to strip.

5. where the rudder shaft comes through the bottom of the hull, The outer shaft has play and the caulk is loose. I must have some leaks.

6. Where the strut is bolted through the hull, water was dripping, well after the boat was pulled from the water. It must be leaking as well.


My plan, And I NEED INPUT, PLEASE.

1. I am getting a new shaft made tomorrow..... Aquamet 22

2. will check transmission end play. ????????what do I need to replace if there is play?

3. motor mount plan.........I think I should remove the lag screws, twist the mounts to the side, drill out the old holes, glue in a wooden dowel, drill pilot hole, use new and longer lags for the motor mounts, replace missing motor mount nut. ??????? Am I doing the right thing?

4. replace the strut bearing.

5. ?????? Not sure what to do about the strut...... I think I need to pull my gas tanks, remove the strut, clean, seal and remount...

6. ??????? rudders ....... I should also remove the rudders, clean, seal and remount


Any tips would help.......


thanks Rob

 

Scott, Have a shaft made of the correct length. If I were you I would repack your shaft logs and rudder through-hulls while you have the boat out of the water. I would check, remove and reseal any hull penetrations. While you are at it, inspect the hull for soft spots, damage, blistering, or any condition that may need to be corrected. Get all of the under water stuff fixed before you go back in the water. I say this because I have to have my boat professionally hauled and I have no trailer. If you have a trailer, obviously you can take you time getting some of this done and still use the boat after you make repairs. The point is, do a complete inspection and perform any needed repairs that concern you. Remove and visually inspect the prop strut. Look for any damage or bending. Retain any shims you may find under the strut, you may need them later. If the shims are made of wood and rotting or soft, make new ones when you get to the alignment process. The strut does not have to be perfectly striaght. Only as striaght as possible. I eyeballed mine using a press to straighten it. The transmission is tougher. If you fiind any endplay in the shaft I would pull the trans and have a pro look at it. Trans problems may require opening it up and that kind of work is best left to a professional. I have more to follow. I will get some more information together.

 

I took the shaft to a reputable machine shop. I am getting an aquamet 22 shaft cut to the proper length.

I am contemplating pulling the engine so I can get to the engine mounts properly or coating the holes with CPES then epoxy and inserting the lags throught the mounts. I also think the mounts should be a "c" or "L" shape so they can be through bolted.

looks like I'll be pulling the tanks to get to the strut mount and rudder mount to re-move and re-mount.


thanks, rob

 

I also noticed that the two engines have drastically different engine mount hieghts. about an inch different at the adjustment screws.


rob

 

you know, in every case of twin engines with quadarjet that I know of (including mine), why does the port engine always have the problems?