carb, linkage, throttle question (with pic)

[gonelong]

Problem:
Motor starts easily, idles nicely, moves into gear ok, dies if any throttle is supplied.

Not sure if carb butterflies should open close with manual manipulation of the throttle with motor not running, keys not in ignition. From reading some of the threads here, I get the feeling they should be opening/closing under these conditions. Based on that, I have the following questions.

Setup
I have a 1977 Mercury 500 50HP with Thunderbolt Ingnition. In the attached picture you can see I have labeled a few of the parts 1-2-3-4 and A-B-C.

Using the throttle control, I engage the motor (not running) and can see the linkage that puts the motor into gear. Pushing the throttle down a bit more I can see #1 rotate, which causes #2 to pivot backwards, which causes #3 to pull back, which causes #4 to rotate. Between #3 and #4 I can see the Actuator Plate turn. What I don't see, is the butterflys of either of the carbs move all at. The plastic piece noted as #4 connects both the carbs.

Question 1: Should this action be opening the butterflys? I think it should.

Above and to the right of the "A" is a little knob that can be manipulated manually up and down to cause the butterflys on both carbs to open and close by moving the plastic arm noted by the "C".

Question 2: I am just missing a linkage or piece that should connect between "B" and "C" which would allow the butterflies to open/close as the throttle is manipulated?

Question 3: Is the solenoid labed as "B" there to work with the manual control of the carbs noted by "A" or is this a "powered" piece?

Any and all suggestions welcomed.

Notes:
* I don't believe it a fuel problem
* I haven't rebuilt the carbs yet (want to be sure the butterfly control is or is not an issue first)

 

[tashasdaddy]

Re: carb, linkage, throttle question (with pic)

A/ is the manual choke, B/ is the choke solenoid, that is activated from the controller. C/ is the link rod to the choke butter flys, and these are not controlled by the throttle linkage. the throttle butterflys are behind the choke butter flys. i really think you need a manual, before adjusting this stuff, or it will that an $80 an hour mech, 3 hours or more, to figure out what you did.

 

[Smig]

Re: carb, linkage, throttle question (with pic)

Gonelong,
In another thread you mentioned that you have a manual - take a look at the section on timing and synchronizing your carbs. That may help you understand the sequence of operations. You should also look carefully at Clams' 'link & sync' post in the FAQ.

Be careful - I don't want to sound alarmist but, you are treading into melted piston territory, so make sure you understand what you are doing BEFORE you change or disassemble anything more! There is more than enough info. in your manual and here in these forums to get you going...

Smig

PS: A few weeks after your bleeder hose issue, mine ruptured - what a pain to replace!

 

[gonelong]

Re: carb, linkage, throttle question (with pic)

When I figure out what one thing does, it makes it a bit easier to understand what the piece beside it is doing. I realize I have a **TON** to learn before I begin tweaking in here, but thanks for the warning nontheless.

I wasn't kidding when I said I was a COMPLETE novice in this area. I haven't ever even worked on a lawnmower.

I started reading a bit about the Link and synch [http://forums.iboats.com/showthread.php?t=168855] on the FAQ section and I leafed through the manual a bit last night, but couldn't figure out exactly what these butterflys were for. Really, my largest problem is determining what each piece is. I am really thinking about buying a manual that is specific to my motor.

If I am getting your drift, these butterfly valves are only for the manual choke, and should likely be completely closed during operation?

If you could confirm this, then my next step is to rebuild the carbs. I wasn't going to go through that process until I was certain what was up with these butterly valves. If these are supposed to be closed, then I am almost certainly having an issue with my carbs being dirty.

PS: A few weeks after your bleeder hose issue, mine ruptured - what a pain to replace!

Doh!

GL

 

[j_martin]

Re: carb, linkage, throttle question (with pic)

Carbs work like this (grossly simplified)

Air comes in, through choke (butterfly) valve.
Air goes through mixing area, where various metering things add some fuel to it.
Air goes through throttle valve, which limits the amount of all this that happens. (another buterfly valve).


The choke valve is normally completely open, except when you want to have a little extra vacuum in the mixing area to pull in more fuel. (manual choke)

The Throttle valve is normally closed at idle, and is opened at the right time and sequence by the timing (throttle) linkage, which also affects spark timing.

hope it helps
John

 

[gonelong]

Re: carb, linkage, throttle question (with pic)

Carbs work like this (grossly simplified)

Air comes in, through choke (butterfly) valve.
Air goes through mixing area, where various metering things add some fuel to it.
Air goes through throttle valve, which limits the amount of all this that happens. (another buterfly valve).

The choke valve is normally completely open, except when you want to have a little extra vacuum in the mixing area to pull in more fuel. (manual choke)

The Throttle valve is normally closed at idle, and is opened at the right time and sequence by the timing (throttle) linkage, which also affects spark timing.

hope it helps
John

That does help John, and when you put it in very simple terms such as this some of what I read before make a a bit more sense to me. I'll read some more tonight ... thank you.

http://www.mercruiserparts.com/show_image.asp?ivar=IMAGES/MERMAR/74962/14.png

If I get what you are saying and I have put it all together ... then #34 (throttle shaft) in this diagram will turn #39 (throttle shutter) to allow more fuel into the carb(s). When I give the engine more throttle, #34 is the arm that rotates in place (I think). This would be hooked to both carbs such that it will open both the same amount at the same time. (makes sense to me)

If all this is true, then I want to leave the choke butterflys completely open (laying flat). - Under what condition smight one consider closing the choke butterflies and to what degree?

I think it is most likely that my carbs are gummed up since the #34 arm rotates freely when throttle is applied. While I may have a timing issue to work on, I am almost positive I have a carb issue to take care of first.

I have some deep creep I can try this weekend to see if I can free up the carbs at all while I wait to get in a carb rebuild kit.

Thanks to all three of you.

GL

 

[Smig]

Re: carb, linkage, throttle question (with pic)

I wasn't kidding when I said I was a COMPLETE novice in this area. I haven't ever even worked on a lawnmower.

Same here - I had never even changed a spark plug! However these motors are so simple, they are a great way to learn. Plus there is a huge community here that can help out. YES! buy the appropriate manual!! I use two - a Clymer and the OEM. You can find them on ebay or various old mercury websites.

Also, be sure to buy a few things from iboats (those carb kits for example) just to let the business folks know that you appreciate these forums.

Smig

 

[Smig]

Re: carb, linkage, throttle question (with pic)

Under what condition smight one consider closing the choke butterflies and to what degree?

The pro's will know more, but the only time I use the choke is when starting the engine. If the engine is warm, then sometime I don't even have to use the choke. The choke button on your controller is all or nothing - when you press it, the butterflys close, when you release it, they open.

I've never used the manual choke, so I'm no help there.

Smig

 

[gonelong]

Re: carb, linkage, throttle question (with pic)

The pro's will know more, but the only time I use the choke is when starting the engine. If the engine is warm, then sometime I don't even have to use the choke. The choke button on your controller is all or nothing - when you press it, the butterflys close, when you release it, they open.

I've never used the manual choke, so I'm no help there.

Smig

Good info to have, thanks. I think its possible that the manual choke is there in case you have to start the engine with the pull-string? (Mine has one) Its in the right spot for that.

That might be interesting to try sometime just to see if I can get is started that way.

GL

 

[tashasdaddy]

Re: carb, linkage, throttle question (with pic)

you're starting to get it. i'm not the merc person, i'm more of the johnson/evinrude guy. give it try to start it with the rope, you need to know how. try doing it on a 1350 inline 6.

 

[Smig]

Re: carb, linkage, throttle question (with pic)

... try doing it on a 1350 inline 6.

There's a thread somewhere with people's experiences pull-starting big motors...take a look - makes you appreciate an electric starter!!

TD makes a good point, better to learn in the driveway than with a 'boat load' of people watching (and snickering:redface

 

[mississippiriverrat]

Re: carb, linkage, throttle question (with pic)

Just to put my 2 cents in if your are looking at the choke butterflys the should be open when you are running or you will flood out your motor with to much fuel. use the manual choke to open them then use your choke on the key switch to start the motor.Not a expert on the yet but do understand how they work pretty good.

 

[j_martin]

Re: carb, linkage, throttle question (with pic)

Different motors have different specs for when things happen. Some just advance the timing for a bit to speed up, then pick up the throttle valves and start to open them. Some pick up the throttle valves immediately. That pick up point is a specification.

Get the book and take the time to understand the linkage and syncronization adjustments. (link'n'sync)

In my experience, people tinkering with outboards without knowing exactly what the design was for that particular motor get this sequence so far out of wack it'll never run right until it's put back where it should be.

hope it helps
John

 

[gonelong]

Re: carb, linkage, throttle question (with pic)

Different motors have different specs for when things happen. Some just advance the timing for a bit to speed up, then pick up the throttle valves and start to open them. Some pick up the throttle valves immediately. That pick up point is a specification.

Get the book and take the time to understand the linkage and syncronization adjustments. (link'n'sync)

In my experience, people tinkering with outboards without knowing exactly what the design was for that particular motor get this sequence so far out of wack it'll never run right until it's put back where it should be.

hope it helps
John

Thanks John, that is exactly what I am trying to do ... I haven't even pulled the toolbox off the shelf yet. I am trying to gather a bit of information such that I can understand what is happening and why.

My first time through the manual looking at the info for the carb and link-n-sych proved to be information overload for me. I didn't have time to study it, I only had time to take a peak at it. My manual is also a one-size-fits-all type, I'd like to find one specific to my motor. Nonetheless, I'll be curling up with the manual on Saturday evening to see what I can figure out from it. A few helpful souls here have given me enough of a push that I think I'll pick up what is going on with a careful read.

I'll probably have more questions next week.

GL

 

[Smig]

Re: carb, linkage, throttle question (with pic)

After looking at the book, go see the real thing. Learn how to properly disconnect the throttle cable so you can sit there and watch what happens as you move the throttle arm. It will make all the difference...

Last spring I did just what you are doing now - it is fun to learn what is really happening under that black hood!

Smig

 

[gonelong]

Re: carb, linkage, throttle question (with pic)

After looking at the book, go see the real thing. Learn how to properly disconnect the throttle cable so you can sit there and watch what happens as you move the throttle arm. It will make all the difference...

Last spring I did just what you are doing now - it is fun to learn what is really happening under that black hood!

Smig

That is the plan. I had the Mrs. move the throttle around a bit as I peaked under it last night. (She's a trooper) I think that'll help when I go back to read the manual.

The biggest problem I was having was matching up the parts/part names with what the manual referenced them by. Cam? What the heck is a cam and what does it look like? After a bit of peaking around I found it and figured out what it was doing. The illustrations in the manual are much more helpful once you can identify the parts.

GL

 

[gonelong]

Re: carb, linkage, throttle question (with pic)

Had a chance to leaf through the manual this weekend, but not to study it.

Took the boat out on Sunday morning to do a bit of bass fishing (hey, gotta have your priorities straight) ... awesome morning here in Ohio and had a great morning of fishing with my neighbor.

I sprayed 3/4 of a can of deep creep into every nook and cranny that I could reach in each of the carbs on Saturday night. Sunday morning, same issue, motor fires up no problem, dies instantly when throttle is advance.

Next steps:
1) Check compression
2) Rebuild Carbs
3) Link-n-synch

Thanks for everyone's assistance up to this point. It'll probably be a few weeks before I get the time to get to step #2 so I'll let this thread die and put up a new one when I have questions.

GL

 

[gonelong]

Re: carb, linkage, throttle question (with pic)

Also, be sure to buy a few things from iboats (those carb kits for example) just to let the business folks know that you appreciate these forums.

Smig

I checked.

Unless I am missing it, I don't see that they sell a carb kit for my year/model.

If I have missed it and anyone could point it out to me I'd likely purchase it from here.

GL

 

[gonelong]

Re: carb, linkage, throttle question (with pic)

OK, I finally found a place that can order "diaphram kits", they have the gaskets, etc in them. $9.00 or so apiece.

Is this the "rebuild kit" people talk about, or does that also include floats, jets, etc?

GL

 

[Smig]

Re: carb, linkage, throttle question (with pic)

Try this carb kit: Sierra Kit 18-7007

http://www.iboats.com/mall/partfind...gd_poid=112062&gd_row=28&**********=556290768