3.7 Carb issue...surprise, right?

JSavage

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May 14, 2009
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44
Hey guys and gals,

Ok, I'm up to my neck in my 3.7 again. This time, I'm chasing a throttle issue.

When I start it up, I idle for a bit, it gets rough, then wants to stall. So, I hit it with a hammer (not really... I just flick the choke plate closed) and start it again. SHe's still a touch rough but it'll hold idle... until I crack the throttle. Once I start to open the throttle, it makes a narsty sucking sound (similar to the sound of the cash leaving my wallet) and dies. It'll start right up again but does that EVERY time.

Now, if I goose it a bit and drop my throttle back to where I want it, it's fine... well fine meaning it tries to die for a second but picks up.

Alright, now for what I've done...

I rebuilt the carb last year, but when I did, I couldn't get the choke plate or rod out, due to stripping the screw heads. I got new screws and got the old ones out. So, I cleaned the junk off the plate, cleaned the edges, cleaned the rod and got that all back together. I hope that's going to be smooth again.

I also put some length in the AP rod. My brain was telling me the throttle plates were opening before the fuel was being shot in. Might have been a bad move? Didn't really solve the problem.

Ummm... I think that's all that I did. It's off the boat right now and it's raining, so if I need to do something else, it's a good time. I hate pulling that carb out.. I drop a nut every time (not a euphemism).

Thanks in advance.

It occurs to me that I was having an issue last year coming back to idle. It might have been stalling when I came back down too fast. Could have been the year before though.
 
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JSavage

Seaman Apprentice
Joined
May 14, 2009
Messages
44
Re: #.7 Carb issue...surprise, right?

Re: #.7 Carb issue...surprise, right?

No one has any thoughts?
 
Joined
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Re: #.7 Carb issue...surprise, right?

Re: #.7 Carb issue...surprise, right?

I looked at your previous posts, and it was already 2-years ago on the rebuild, unless you did it again and did't post anything:
http://forums.iboats.com/showthread.php?t=414614&p=2775406#post2775406

Almost seems like there's some crap in the carb effecting your idle. Maybe in your rebuilding you missed some junk in there in the idle passages, or has it ran well since the last rebuild and is having problems again?

Here is the list of things to check for "runs poor at idle"
 

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JSavage

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Re: #.7 Carb issue...surprise, right?

Re: #.7 Carb issue...surprise, right?

Wow. I guess it was 2 years ago. I'm not sure I ever really solved the problem. As I saw Bondo say on another thread, a professional with the right tools has a 50/50 shot at getting a rebuild right; while I'm pretty handy, I'm no marine tech. As I recall, I had it in the water twice last year. I've been in school full time for 3 years and hardly have time to use it OR fix it.

I guess I might be getting a rebuild kit today. Napa gets $37 for it... worth it if it cures the problem.
 
Joined
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Re: #.7 Carb issue...surprise, right?

Re: #.7 Carb issue...surprise, right?

Have a look at these videos by Alpheus on Rebuilding the carb. Even thou you've already done it, there may be something in these that you've missed and didn't realize.

It's worth the time to check out:

http://forums.iboats.com/showthread.php?t=362542

While I was on that thread I scrolled down the posts in it and BT Doctor posted a TSB on rough Idle, might be worth checking on:
http://www.boatfix.com/merc/Bullet/84/84_04.pdf
 

JSavage

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Joined
May 14, 2009
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44
Re: #.7 Carb issue...surprise, right?

Re: #.7 Carb issue...surprise, right?

Thanks, Eric. I saw those videos, but didn't watch them as I have the 3.7, not the LX (2bbl Mercarb). I DO, however, prompt me to seek out video of a mercarb rebuild. I'll post what I find.
 

JSavage

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Joined
May 14, 2009
Messages
44
Re: #.7 Carb issue...surprise, right?

Re: #.7 Carb issue...surprise, right?

Mkay. I ripped it open and found a mountain of crap inside. Idle passage is probably plugged full along with everything else. Here's to a good cleaning.

I Soooo hate this 10% ethanol fuel.
 

JSavage

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Joined
May 14, 2009
Messages
44
Re: #.7 Carb issue...surprise, right?

Re: #.7 Carb issue...surprise, right?

We could REALLY stand to have some good drawings of the passages in these carbs. I figured out that there are 3-4 fuel outlets that control idle. I eventually figured out which ones fed where and where they got their supply from and which ones were joined. Come to find out by plugging the little slotted outlets in the throttle body and forcing some carb cleaner through a syringe into the hole that feeds them results in a flood of crap coming out by the idle fuel valve.

More or less the same in the venturi cluster, not in regards to figuring out the passages but back flushing with carb cleaner produced much crud.

I'm now advocating for the use of syringes in a clean and rebuild. Fluid is denser than air and will push a great deal more junk out. Likewise, you can see where it comes out and thus, can mentally map the passages. I have access to many different sizes and volumes as a Nursing Student, but the one I used the most I got at the grocery store. Has a big, fat needle for injecting juices into meat but I used it without the needle and just pluged it into the various holes. It has MANY times the volume of a medical syringe and really allows it to move a lot of debris.

I'm letting it soak for a couple of hours and then going to flush again. ONLY when it flushes clean will I blow it clear and reassemble.

I found a nice pair of rebuild videos on Youtube. I'll post them with my conclusion summary.
 
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