Carb not opening at WOT?????

[wil7483]

OK, I need your help. I'm not a mechanic and I don't fully understand the workings of the internal combustion engine but I am mechanically inclined so I'll try anything once. I went out today to try to adjust my rocker arms to rid the engine of what I thought was lifter noise. After I completed it and got the engine all back together I was able to see a bit of an improvement but the noise isn't totally gone yet. However the engine is running smoother than it was before the adjustments.

Anyway, I then removed the carbs flame arrestor and watched the carb as I gave the engine gas. I never went over 2000 rpms but I did notice that the throttle plates weren't open fully. Or at least what I think are the throttle plates. Also, the choke has a crack in it so is that something that NEEDS to be replaced for optimum performance? I am still trying to get the engine to turn at 4200-4600 rpm's with the 19p prop. The best I can get with the 19p is 4050. With the 17p I get 4300, and with a 15p I am able to get 4600 easily but top speed is only in the 35mph range.

When I turned the engine off and placed the remote control in the WOT position I still do not see the throttle plates opening. Maybe I'm looking at the wrong thing so please help me out on this. Thanks in advance guys.

Here is a video of the engine running. I haven't gotten the idle right yet so that is why it sounds like that. Right now it is idling at about 550 rpm's. I would like to get it to idle at 700 rpm's.

 

[WizeOne]

Re: Carb not opening at WOT?????

The throttle plates should be virtually vertical. I cannot see them in your pictures, only the top choke plate. It is all the way open.

To check, disconnect the throttle cable at the carb arm and rotate it all the way open. If it moves further than it does with the cable connected then you need to adjust the cable ram. The adjustment 'knob' is at the rear of the black plastic ram, back underneath your spark arrestor. Just dial it out until the hole matches the throttle arm in the full open position, then reconnect the ram to the carb bracket.

After doing that make sure that when you move the throttle to neutral, that the carb arm moves all the way back to the idle stop.

If by cracked choke, you mean the plastic choke cover, that will not cause a running issue and should not even affect the choke operation. Maybe you can glue it back together as the cap provides protection for the thermostat spring inside. It is also the rotation of that cap that adusts the choke.

In your vid, the engine sounds like it is idling a bit slow. Use the idle adjustment screw, on the carb throttle shaft bracket, that I mentioned before to dial the idle up to 600 or 650. I wouldn't go all the way to 700. That's geting a bit too fast for shifting.

 

[coastalcruiser]

Re: Carb not opening at WOT?????

Regarding your valve noise, I had a mechanic friend adjust my valves years ago while the engine was running and after he finished it purred. This is on a porsche. I think I read on here you can make a splash guard in order to do that...just a thought.

 

[180shabah]

Re: Carb not opening at WOT?????

As mentioned, the throttle blades are not visible in your pictures. Your choke plate (the one that is vertical in the pics) is fully open. If you look down through either barrel, past the choke, venturi, etc. you will see the throttle blades. With the engine off and choke open you should be able to see them open fully when the throttle handle is pushed all the way forward.

I think what you are expecting to open is the large plate covering the two rear barrels. This is not connected to the throttle linkage, it gets "sucked" open as the engine demands more air. You will not see this without a load on the engine, which means you'll probably never actually see it at all.

 

[WizeOne]

Re: Carb not opening at WOT?????

I think what you are expecting to open is the large plate covering the two rear barrels. This is not connected to the throttle linkage, it gets "sucked" open as the engine demands more air. You will not see this without a load on the engine, which means you'll probably never actually see it at all.

I think those must be the heralded vacumm operated secondary 'air doors' on the Edelcrock carbs. Yes, the lower secondary throttle plates open via mechanical linkage, but no air/fuel will flow until conditions allow those top 'doors' to open.

Just push your throttle lever wide open and if the primary plates are near or totally vertical, you are good to go. If not, then follow my proceedure above.

 

[wil7483]

Re: Carb not opening at WOT?????

You guys are all right, I was expecting those large plates covering the rear barrels to open. OK, I will go back outside and recheck it and look down the barrel and see if it opens vertically in the WOT position. Thanks.

 

[wil7483]

Re: Carb not opening at WOT?????

Just by the looks of the carb. a can of carb cleaner used on all the butterfiles and linkages would not hurt a thing.

What you are looking at is left over paint that hasn't faded off. The carb was rebuilt about 5 months ago and it sat in a vat of industrial strength cleaner over night before the rebuild. Not that crap you get at Autozone but some real heavy duty stuff that comes in a 55 gallon drum. The carb is clean as it is going to get.

I did go ahead and spray the flame arrestor with an entire can of carb cleaner to ensure that it is sucking in as much air as possible and little dirt. I then blew it out with compressed air. So now I will get the manual back out and try to adjust the carb to get the idle correct.

 

[Glastron_V210]

Re: Carb not opening at WOT?????

You have a Rochester Quadrajet dude.

It's billed as the closest thing to fuel injection in a carb. If you Google it you will see many explanations, but here goes:

The front two are the idle/primary side of the carb. They work for the vast majority of throttle settings. There is a 'power valve' in this side of the carb. It uses vaccuum created by the engine countered against a spring to determine the load and allow the right amount of fuel to enter the engine.

When the engine demand elcipses the primary's capability, the secondary (Rears) start to open, again via vaccuum. So, they have little to do with throttle setting like some other carbs. They have to do with the CFM being demanded by the engine. As they open, the hanger (In the middle of the secondary plates) rises, pulling metering rods out of the secondary jets, allow ing more fuel to enter for the increase in airflow.


What should happen is this:


From idle, goto WOT. Watch the carb. Usually around 3500rpm the secondaries will start to open due to CFM demand. They may never open all the way, it depends on what the engine wants. There is an adjustment on the carb to determine when the secondaries open, and you can tune the jets, power volve spring, secondary plates opening, secondary metering rod shapes, etc, etc. That's why this carb could be used on a mild straight 6 and a heavily modded 350.


Chay

 

[wil7483]

Re: Carb not opening at WOT?????

Thanks everyone, I went out today and readjusted all of the rocker arms and lifters again today. I eventually found my stethoscope and was able to pinpoint the noise to a loose exhaust flapper. I will take the exhaust elbow off later and see if there is anything I can do to tighten that up and get rid of that noise. Hopefully tomorrow I can get the boat in the water and see if my adjustments make any difference in her performance. Thanks again for all the help and explanations about the carb.

 

[Bondo]

Re: Carb not opening at WOT?????

and was able to pinpoint the noise to a loose exhaust flapper. I will take the exhaust elbow off later and see if there is anything I can do to tighten that up and get rid of that noise.

Ayuh,... You've gotta Replace them... The rubber has been Burnt off...

 

[MikDee]

Re: Carb not opening at WOT?????

That engine doesn't sound right, like it's not hitting on all 8! How did you adjust the valves? Engine off, or engine on?

Here's how I do it, messy, but thorough, and secure.

With the engine warm & idling, take off one valve cover, and slowly, loosen each lifter, (one at a time) until it clicks, (then snug it down slowly in 1/4 turn increments), till the clicking stops (this is zero lash), then slowly snug it down 1/2 a turn more, (in 1/4 turn increments), and you're done, move on to do each lifter on that side,

Then put your valve cover on, & move to the other side of the engine, remove that valve cover, and do the remaining lifters as I described.

 

[wil7483]

Re: Carb not opening at WOT?????

That engine doesn't sound right, like it's not hitting on all 8! How did you adjust the valves? Engine off, or engine on?

In the video it is idleing too low at about 500 rpm. I have adjusted the idle now to 700 rpm and it sounds a lot better. I adjusted them with the engine off. I rechecked the exhaust flappers and they are fine so I don't know where that noise is coming from.

In my initial video the 1st time I started the engine you can hear it also and it wasn't in the boat yet. Any ideas?

 

[MikDee]

Re: Carb not opening at WOT?????

In the video it is idleing too low at about 500 rpm. I have adjusted the idle now to 700 rpm and it sounds a lot better. I adjusted them with the engine off.

The rpm has nothing to do with it, I'm saying it still does not sound right to me, at any rpm on the video!

If you adjusted them with the engine off, did you follow the procedure in the Merc manual? If not, then you may have done it wrong.

If you are sure you are on TDC on the crank, and Cyl #1 (by looking at the rotor under the distributor cap) being as the engine runs at this time, you can adjust certain intake, & exhaust valves at this time.

Then, if you crank the engine over 1 turn clockwise, you will be at TDC of Cyl # 6, and you can then adjust the rest of the valves

Here it is in detail from the service manual:


5.0l / 305 cid / 5.7l / 350 cid ENGINES SERVICE MANUAL NUMBER 24
Page 3A-24 90-861327--1 OCTOBER 1999
Valve Adjustment
Engine Stopped
With valve cover removed, adjust valves when lifter is on low part of camshaft lobe.
1. Crank engine with starter or turn over in normal direction of rotation until mark on torsional
damper lines up with center ?0? mark on timing tab. Ensure engine is in No. 1 firing
position by placing fingers on No. 1 valve as mark on torsional damper comes near ?0?
mark on timing mark. If valves move as mark comes up to timing tab, engine is in No.
6 firing position and should be turned over one more time to reach No. 1 position.
72328
2. Adjust the following valves:
MCM and MIE Left-Hand (Standard) Rotation Engines
Exhaust - 1-3-4-8 Intake - 1-2-5-7
3. Loosen adjusting nut until lash is felt at push rod, and then tighten adjusting nut until all
lash is removed. Lash can be checked by moving push rod up and down while tightening
adjusting nut until all play is removed.
72300 I personally just twist the push rod, back, & forth, until it is snug, after much experience, this works best for me
4. Hydraulic lifters can be adjusted by tightening adjustment nut an additional one turn (360
degrees). I just tighten them down 1/2 on small block Chevys, again after much experience, this also works best for me No other adjustment is required.
5. Crank engine one revolution until pointer ?0? mark and torsional damper mark are again
in alignment. This is No.6 firing position. With engine in this position, the following valves
may be adjusted as previously outlined.
MCM and MIE Left-hand (Standard) Rotation Engines
Exhaust - 2-5-6-7 Intake - 3-4-6-8

 

[MikDee]

Re: Carb not opening at WOT?????

That engine doesn't sound right, like it's not hitting on all 8! How did you adjust the valves? Engine off, or engine on?

Here's how I do it, messy, but thorough, and secure.

With the engine warm & idling, take off one valve cover, and slowly, loosen each lifter, (one at a time) until it clicks, (then snug it down slowly in 1/4 turn increments), till the clicking stops (this is zero lash), then slowly snug it down 1/2 a turn more, (in 1/4 turn increments), and you're done, move on to do each lifter on that side,

Then put your valve cover on, & move to the other side of the engine, remove that valve cover, and do the remaining lifters as I described.

By the way, Rapido marine adjusts the valves on their small block Chevy's, just like this with the engine running, I believe it is the most accurate way

 

[wil7483]

Re: Carb not opening at WOT?????

Yes, I followed the procedure in the manual.

 

[wil7483]

Re: Carb not opening at WOT?????

The rpm has nothing to do with it, I'm saying it still does not sound right to me, at any rpm on the video!

So what does it sound like and how do I rectify it.

 

[MikDee]

Re: Carb not opening at WOT?????

So what does it sound like and how do I rectify it.

It sounds fine to me, out of the boat, what did you change?

The noise sounds like a bad lifter, but it could be a broken valve spring? This could happen if your valves were adjusted too tight, and you revved the motor too much, that's why I like to adjust the valves with the engine running, (there's no need to find TDC for both #1, and #6 then).
If it is a broken valve spring, unless you can identify which one, you'd have to loosen your rocker arm, and try to turn the spring, there will be no spring pressure on it, and you'll be able to turn a broken valve spring on it's base.

 

[wil7483]

Re: Carb not opening at WOT?????

It sounds fine to me, out of the boat, what did you change?

The noise sounds like a bad lifter, but it could be a broken valve spring? This could happen if your valves were adjusted too tight, and you revved the motor too much, that's why I like to adjust the valves with the engine running, (there's no need to find TDC for both #1, and #6 then).
If it is a broken valve spring, unless you can identify which one, you'd have to loosen your rocker arm, and try to turn the spring, there will be no spring pressure on it, and you'll be able to turn a broken valve spring on it's base.

The only difference out of the boat is the idle was high (900rpm) and she was out of time (12 BTDC). I guess I will take that valve cover off again and check the springs. Tomorrow I will go to junk yard and get a set of valve covers that I can cut open and use to do the adjustments with the engine running and not get oil all over the place.

 

[MikDee]

Re: Carb not opening at WOT?????

The only difference out of the boat is the idle was high (900rpm) and she was out of time (12 BTDC). I guess I will take that valve cover off again and check the springs. Tomorrow I will go to junk yard and get a set of valve covers that I can cut open and use to do the adjustments with the engine running and not get oil all over the place.

If you do the running valve adjustment, you should be able to find the lifter that is making noise, then you can examine what is wrong. They make a set of little clips to put on the rocker arms, to divert the oil spray, they're usually not that expensive. I've even used spring clip type wooden closepins, I think they even make a miniature version of these you can use. Normally, every engine I've done, some of the pushrods will squirt oil, some will just dribble, it is not hard to do, just a little bit messy, you usually lose some oil, but I've never lost more then 1/3- 1/2 a quart. Once you do this procedure, you will understand more of how your engine works, and you'll be sure of what you've got! Then afterwards, be proud of yourself for doing it right, most accurately, and once, and for all!

This is even more annoying doing it with soild lifters, & a feeler gauge, Been there, Done that

 

[coastalcruiser]

Re: Carb not opening at WOT?????

hey Wil7483,
there are some photos of those valve clips and cut out covers, also might be some good info.
http://www.hotrodders.com/forum/best-way-adjusting-valves-sbc-132599.html