carb rebuild questions

[vipzach]

Re: carb rebuild questions

Well, the throttle not springing back was bothering me, so I pulled the carb off and realized that I had the choke lever hooked up wrong. I corrected it and after putting it back together, the whole thing would spring back, like I thought it should.

Put it back on the boat and it still idles around 3000 rpm (in the neutral position)and runs rough.

Any ideas? What other info can I provide that will help you guys help me?

 

[fishrdan]

Re: carb rebuild questions

3000RPM? Sounds like the carb butter fly valves are not closing off all the way. Check and make sure the throttle lever (on the carb) is touching the stop screw, it should be.

How are you adjusting idle? Mercarb's have 1 idle mixture screw and then the idle speed screw. The manual will give you initial settings, but then you have to adjust them after the engine is running, get the engine to idle smoothly at the correct RPM, 700RPM or so.

Also, just spraying carb won't clean a really dirty carb. They need to be soaked in a bucket of carb cleaner like Berryman's Chem-dip. Just make sure not to put any plastic or gaskets in to the bucket of cleaner as it will eat those parts.

How far did you tear down the carb, everything removed and down to the bare casting (well except for the choke, butterfly's and throttle shaft)?

 

[vipzach]

Re: carb rebuild questions

3000RPM? Sounds like the carb butter fly valves are not closing off all the way. Check and make sure the throttle lever (on the carb) is touching the stop screw, it should be.

I don't think it is touching. Is the same screw that adjusts the idle speed?

How are you adjusting idle? Mercarb's have 1 idle mixture screw and then the idle speed screw. The manual will give you initial settings, but then you have to adjust them after the engine is running, get the engine to idle smoothly at the correct RPM, 700RPM or so.

With the boat running, I can back the idle speed screw all the way off and the rpm does not change.

Also, just spraying carb won't clean a really dirty carb. They need to be soaked in a bucket of carb cleaner like Berryman's Chem-dip. Just make sure not to put any plastic or gaskets in to the bucket of cleaner as it will eat those parts.

I didn't just spray the carb. It sat in a bucket of berryman's chem-dip carburetor cleaner for 1.5 hours, after I took it all apart. After I took it out, I used compressed air in the orifices, then the spray cleaner, then air again.

How far did you tear down the carb, everything removed and down to the bare casting (well except for the choke, butterfly's and throttle shaft)?

I took it completely apart, other than butterfly's.

My answers to each question are in red.

Thank you

 

[Monte1961]

Re: carb rebuild questions

Ok 1.5 hours is not enough soak-time! Soak it overnight. Theres something obviously not right!!!!! will send you a pm Zach.

 

[fishrdan]

Re: carb rebuild questions

^ agree soak over night

If the idle mixture screw has no affect on the idle quality, something is not right. The engine should stumble/die when it's turned in too far, then drop RMP and run bad when turned out too far. When the carb butterflies are too far open (IE 3000RPM) the idle circuit is not operating, so that's why you can turn the screw in-out without anything happening.

Is the base gasket different, thick compared to thin, and could this be causing the throttle to stay open too far. Other than that it sounds like something is not connected/adjusted properly, not allowing the throttle and butterflies to close all the way. Look down the throttle bores (engine off) and see how far it's closing, it should be darn near completely closed.

 

[vipzach]

Re: carb rebuild questions

^ agree soak over night

If the idle mixture screw has no affect on the idle quality, something is not right. The engine should stumble/die when it's turned in too far, then drop RMP and run bad when turned out too far. When the carb butterflies are too far open (IE 3000RPM) the idle circuit is not operating, so that's why you can turn the screw in-out without anything happening.

Is the base gasket different, thick compared to thin, and could this be causing the throttle to stay open too far. Other than that it sounds like something is not connected/adjusted properly, not allowing the throttle and butterflies to close all the way. Look down the throttle bores (engine off) and see how far it's closing, it should be darn near completely closed.

The idle speed screw has no effect on the rpm.

I will describe this as best I can. With the linkage off, I can fully close the butterfly. The rod that sticks out of the side, with the threads and flat sides, the flat side is up when the butterfly is fully closed. When I pulled the carb off, that flat side was approximately 1/8 of a turn open.

Does that make sense at all?

 

[vipzach]

Re: carb rebuild questions

Carb is back apart and setting in the berrymans bucket. This time it will be over night.

 

[Pete104]

Re: carb rebuild questions

OK! Now you put it back together, AFTER you blow every little hole/orifice (even BIG orifice) with compressed air. Blow in & out plus !!! On the venturi cluster are 4 brass tubes. 2 big 2 small, make sure that they are clear. Use your mouth to pull & push air thru them. Only way to know. & where they go in the casting, blow more cleaner thru it. Put it together the way you took it apart. Double check your float level from where it was from where you started. You said you changed it earlier. Put it where it seems like it should be. The line on the float should be level when the "float chamber" is full. Put the carb back on the engine with the thin gasket. Hook up everything EXCEPT the linkage! Do not connect the throttle cable!

Start it up & check back!

 

[fishrdan]

Re: carb rebuild questions

I can fully close the butterfly.

Are you talking about the choke plate on top of the carb, or the 2 butterfly valves attached to the throttle shaft on the bottom of the carb?

If starting the engine with the throttle cable (linkage) disconnected, put a bungee cord on the carb throttle to hold it closed, so it doesn't stick open and make the engine run away. The throttle cable/linkage should line up with the carb's throttle and hold the carb closed at idle. Actually, the cable/linkage should be applying a tiny bit of pressure to hold the carb's throttle closed.

 

[vipzach]

Re: carb rebuild questions

Are you talking about the choke plate on top of the carb, or the 2 butterfly valves attached to the throttle shaft on the bottom of the carb?

If starting the engine with the throttle cable (linkage) disconnected, put a bungee cord on the carb throttle to hold it closed, so it doesn't stick open and make the engine run away. The throttle cable/linkage should line up with the carb's throttle and hold the carb closed at idle. Actually, the cable/linkage should be applying a tiny bit of pressure to hold the carb's throttle closed.

I was talking about the butterflys on the bottom of the carb. When the carb was completely put together, the butterfly's were not fully closed. I am about ready to start putting it back together after soaking over night.Should the butterly's be completely shut? If they are not, do I need to bend the pump rod, so that they are completely closed?

In the mercruiser manual, it tells you how to measure and says "see specification" but I can't find where the specification is located.

 

[Pete104]

Re: carb rebuild questions

As long as you STILL have it apart, without any linkage connected! Bare carb, no nothing! Where are the "throttle plates"?

 

[vipzach]

Re: carb rebuild questions

It is still apart. By throttle plates, are you referring to the butterflies in the throttle body, the bottom part of the carb? If so, I can easily open or close them.

 

[Pete104]

Re: carb rebuild questions

Do they close? You should not be able to see Hardly any LIGHT thru them!

 

[Pete104]

Re: carb rebuild questions

When you "open" them straight up & down, are they true? I'm refering the plates if you didn't know!

 

[vipzach]

Re: carb rebuild questions

Do they close? You should not be able to see Hardly any LIGHT thru them!

Before I took it back apart, I shined a light up from the bottom and you could see a lot of light coming through both sides of the plates!

This is why I was wondering if I needed to bend the pump rod a little. I was wondering if that is why the idle screw had no affect on the idle speed.

 

[vipzach]

Re: carb rebuild questions

When you "open" them straight up & down, are they true? I'm refering the plates if you didn't know!

Yes, I would say they are true.

 

[Pete104]

Re: carb rebuild questions

Either they are "bent" or you have installed linkage improperly. You have a mess. It doesn't take much to get 3grand out of a motor with "no load" on it!
Did someone force the throttle back to idle or force it open, after you reinstalled the carb?

 

[vipzach]

Re: carb rebuild questions

Either they are "bent" or you have installed linkage improperly. You have a mess. It doesn't take much to get 3grand out of a motor with "no load" on it!
Did someone force the throttle back to idle or force it open, after you reinstalled the carb?

The butterflies aren't bent and I put the linkage back on, like it came off. Nobody else has touched the boat and I didn't force anything.

 

[Pete104]

Re: carb rebuild questions

I don't what to tell you! Except to keep asking you "what did you change"?
The description you gave, about idling @ 3000, & the screw was even touching the cam! Are you positive you don't have rods switched?

 

[Pete104]

Re: carb rebuild questions

That would be the accel pump rod switched with choke rod!