What might cause a dry Carb?

Doc

Doc

Liquid Addiction
Staff member
Not sure if it's a Rochester carb or not.
Was talking to someone else about this earlier this evening. The subject of a new or rebuilt carb came up. Would I be better off replacing the carb or rebuilding it?
What are the advantages either way.
Any idea on the cost of new or rebuilt carbs?
I don't know of a shop around that would rebuild it. What kind of shop would you look for?
 
Doc

Doc

Liquid Addiction
Staff member
Found carbs here:
http://bpi.ebasicpower.com/c/MER7A-IB/Carburetors+for+Mercruiser+Inboards

[FONT=Arial, Helvetica, Sans-serif]Carburetor, 4 Barrel, Mercruiser 454 V8 with Spring Choke
Part Number: CPIMC31
Weight: 11
Price: $329.00
Quantity in Basket: none
[/FONT] [FONT=Arial, Helvetica, Sans-serif] Remanufactured Marine Carburetor for Mercruiser 330-340 HP GM 7.4L Big Block V8 with remote choke
Rochester 4 BBL 4MV Remote choke
MIE 330 Serial # : 4623115-5889913 MIE 340 7.4L Serial # 5889914-D715493 Mfg. # 1347-8288A1 OEM # : 17080560 [/FONT]
 
waybomb

waybomb

I'd rather be blown
I bet your local marina could rebuild it for 125 or less if you remove it. I usually do my own stuff, but a few years ago, my Carver was having carb issues. Not having the time to go out get the rebuild kits, get my bucket of hydroseal, rags, parts bucket, etc, I had my kid remove both engines' carbs and bring them over to the marina next door. 200 bucks later, my hands were still clean, my clothes were not stinky, and the carbs were back to like-new.
 
bdavis

bdavis

New member
Doc said:
UPDATE: We had great weather here for the 2008 Memorial day weekend and I was able to run the Baja Friday, Saturday, Sunday and Monday. I had to prime the carb every day but Monday.
Got to talking to a local marine mechanic (retired) and after describing the problem to him and some of the possible solutions he eliminated the anti siphon valve saying that if that were the issue then when there was a call for lots of fuel it would fail causing hesitation and possible engine dying. I can run at half or full throttle without issue.

He said it sounded like a carb issue. This was Sunday. I just so happened to have brought some STP carb cleaner with me to add to the gas that same day. So I added the treatment and I still had the problem, but not as often. Monday all was well most of the day but just idling she started coughing and then died. I was able to start her back up and by pumping I was able to keep her running. This did not work (pumping vigorously) prior to adding the STP. I shut off and drifted a while and later it started up just fine. After taking off it started hesitating again but giving it more gas kept her running. Like I said earlier, until the STP was added I was not able to save the stall no matter how much I pumped the throttle.

....So, I'm thinking we are on to something. I plan to pick up some gum out and spray it into the carb later this week. But I'm looking for other ideas if you all have any of what else I might need to do to fix this issue.

TIA!!!!!
edit to add:
The majority of the time when it coughs and dies I am at idle or just starting to take off. Once up and running I've never experienced the coughing / dying out issue.
Click to expand...

Sounds like you're going through the same problems as me. My 40hp yamaha ran excellent last year being only a month old. It was fogged before being stored for the winter. I put new plugs in it, a can of fuel cleaner to the gas etc. but she still won't idle for long and bogs down when accelerating. All I have to do right now to get it up to speed is quickly back off the throttle and nail it again and it'll get up and go. I could see a problem like this hapenning on an oldr motor but this thing is new. Getting furstrated.........any ideas???
 
Doc

Doc

Liquid Addiction
Staff member
Sounds a bit different than my issue Brian. Feel free to start a fresh thread to talk about the issue. It might be noticed more in a thread of it's own.

New rebuilt carb runs around 300. Taking the carb out and having the mechanic rebuild it costs 100 (parts and labor). So I'm off to remove the carb and deliver it to the boat repair shop.
Wish me luck.
 
Doc

Doc

Liquid Addiction
Staff member
Got the carb reinstalled today. All is good so far. I only tested the boat at the dock, but should be able to give it a real test tomorrow.
The weather forecast is good for tomorrow but ify for Saturday, so we're going to get in some boating tomorrow for sure. :thumb: :D
 
Crums

Crums

Wakeboarder Extraordinaire
Glad to here you got it back together and it. We're going to try to get down early enough to get in the water before dark, but you know how it goes. We'll give you a call on our way. Good luck with it, call us if you need a tow in and I'll take off from work early(haha).
 
Doc

Doc

Liquid Addiction
Staff member
The carb didn't fix the problem.

If I start up and rev at 1500 to 2k for a little bit, no problem. If I start up and go straight to idle and then take off sometimes it works, sometimes it falls on it's nose. If I pump vigorously I can prolong it but eventually it dies. A squirt of gas to the carb and I'm back in business.

What are your thoughts on what might cause this?
 
Bt Doctur

Bt Doctur

Super Moderator
Staff member
Doc, try running on a outboard tank to eliminate a tank/fuel delivery issue.
Let us know the results.
 
Doc

Doc

Liquid Addiction
Staff member
Bt Doctur said:
Doc, try running on a outboard tank to eliminate a tank/fuel delivery issue.
Let us know the results.
Click to expand...

I've considered that but am not comfortable with how I could accomplish that.

In talking about the issue I know how we can change out the anti siphon valve at the gas tank ... but local logic says that if it was the anti siphon ball it would likely interrupt the flow of gas when demand for gas increased. I can be cruising at 3000 rpm and go full throttle without incident. No hesitation or cough or anything. She runs as expected.

Would / could a fuel pump problem possibly be the issue?

One suggestion was to make up a line w/ gauge that would show fuel pressure reading. This is also over my head ...
 
Doc

Doc

Liquid Addiction
Staff member
I'm leaning towards fuel pump or maybe the anti siphon ball.

Care to take a guess which you think it might be?
 
waybomb

waybomb

I'd rather be blown
They're both relatively cheap. Go for the easiest first.

Here's another thought. How hard is it to replace the fuel lines from the tank to the pump? Ive heard of the alcohol in gas these days damaging hoses. I've heard of at least one guy that leaned out his engine because of a collapsed hose, alegedly made spongy by the alcohol in the fuel.
 
Doc

Doc

Liquid Addiction
Staff member
I've heard of another possibility, and actually this happened to another owner of a Baja just like mine. Carb leak down.
I thought rebuilding the carb would have fixed the carb leak down issue but now I'm not so sure of that.
Have any of you heard of this problem? Does it sounds like a potential culprit for my issues?
 
waybomb

waybomb

I'd rather be blown
Doc said:
I've heard of another possibility, and actually this happened to another owner of a Baja just like mine. Carb leak down.
I thought rebuilding the carb would have fixed the carb leak down issue but now I'm not so sure of that.
Have any of you heard of this problem? Does it sounds like a potential culprit for my issues?
Click to expand...

See post 20. The rebuilder should have corrected the issue is your carb is of the type from that vintage.
 
Doc

Doc

Liquid Addiction
Staff member
You're right Fred. I just got off the phone with the shop where I had the carb rebuilt. He checked the fuel pressure and it was 2 to 3 pounds max. He replaced the fuel pump and now it's reading 7 to 8 pounds constant. :thumb:
I think we are back in business for our little go fast. I plan to give her a good test run this weekend. :thumb: Now if only the weather will cooperate for a change. :D
 
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