View Full Version : Carb & rebuild shop problems (Holley 4bbl)

04-19-2006, 07:02 PM
Hi all,
On my 2000 Moomba I have the Vortec 350 with the stock Holley Carb (4150 style), Holley P/N 75021-1. I had a minor leak from the accelerator pump and thought it would be a good idea to get it rebuilt, rather than just replace the accelerator pump (see earlier discussions). Boy, was I mistaken.

I brought the carb to a well known local rebuilder. They claimed it would be no problem to restore marine carbs and that they've done many before. I gave them my specs, from Holley (600 CFM, 68 Primaries, 66 Secondaries, 2.5 Power Valve, WHITE Secondary Springs) - they ignored them and even claimed it was a 700cfm, despite Holley confirming it was a 600.

I got the carb back and it ran extremely rich, to the point where it wouldn't get above 3,000 RPM, then the plugs fowled and it quit running after 10 minutes. I double checked timing, etc. The engine ran PERFECT prior to the carb rebuild and nothing changed, yet the carb rebuilders claimed it must be my fault. Only after having their mechanic come out and verify (which I had to pay for), did they take it back.

Second time around, I got the carb back and it still runs very rich.

My question: is there something unique to this *Marine* carburetor that requires a unique metering plate gasket or something that the carb shop is consistently doing wrong because they are treating it like a automotive carb? It seems strange they would rebuild it twice and it would have the same problem both times. Particularly considering it ran absolutely wonderful before the rebuild?

I should mention I checked the float level to be even with the sight threads and even lowered that -- and tried leaning out the idle air-bleed screws (although the problem was in the full-throttle spectrum, not just idle). The choke plate is 100% open too.

Thank you in advance for any suggestions,

04-20-2006, 09:33 AM
Do you have a friend with a similar boat you can examine?

Can you buy a rebuilt Carb from the dealer or a boat repair shop?

At WOT 3,000 RPM fouled plugs could still be an air issue, not a fuel issue (not enough air to burn the correct amount of fuel). How is the choke hooked up, can you add air if you disconnect it and try that?

Do you have a vacuum gage to be sure your lines are solid? A little cut wear or burn can really mess up a carb. I always started with replacing ALL the lines. That worked more than half the time.

Floats are often blamed but rarely the root problem until after they are fixed, then they are a well, pain.


04-20-2006, 12:16 PM
Thank you, Smoke Dog.

1. No friends with ski boats (if I did, I think I would get rid of this nightmare and pay them for co-use of theirs -- I'm beginning to realize I wasn't meant to own a boat).

2. Yes, I'm thinking about buying the Edelbrock marine carb, which is only $290 at Summit, if this continues going South.

3. Interesting, I hadn't considered this. I don't understand what you mean about adding air by disconnecting the choke. In my 4150-style Holley, the choke is the electrically-connected circule that opens the choke horn (which is open, btw). Can you give me more detail on what to do with this to follow your instructions?

4. I will buy a vacuum gauge, although I have to reiterate -- the engine ran fine prior to having it rebuilt. I had it rebuilt, put the rebuilt carb on the engine, and it immediately ran terrible. The problem is not outside the carb itself. With that said, I am still happy to test the vacuum lines if you can tell me how and where I go about inserting the vacuum guage?

5. I've checked the floats and needle/seat and they seem to be fine. The floats barely drop fuel over the sight threads and the engine is running (I've now adjusted it to be just below the threads) and when pressurized, no fuel is released when closed (so I don't believe it's a stuck PV or floats). They did the pressure test before returning it to me.

Thanks again Smoke -- if you can elaborate on the choke-air and vacuum technique, I'll do that immediately and let you know.


04-20-2006, 03:13 PM
Just back with a big a$$ blister on my foot. I better not be laid up. Everyone I know in training is wounded one way or another.

Im used to mechanical chokes and have never worked on electric. Can you cut the power to this and run without the choke wide open and see how it runs once warmed up? Is the choke opening at higher RPMs?

Are you sure you have all the vacuum lines connected and connected correctly? Im great for focus on the easy.


Checking vacuum is not my strong suit. Id ask the auto parts dealer, they should know what you need. You can crack a tube pulling it off and have that as your problem now.


04-20-2006, 08:00 PM
Hi Smoke,
The choke plate is wide, wide, wide open -- and is always open because I have the choke set not to close unless extremely cold. The choke definitely isn't restricting any air movement, that's for sure. This may be one of the few things I can say definitively, since the choke horn is the stuck right up there in front of everything!

As far as I know, the only vacuum used on this carb is the one used for the secondaries. I am absolutely positive I have all vacuums connected (and capped), however. I spoke to a mechanic friend and he said that a vacuum leak won't cause it to run rich but would cause it not to run at all, or barely run if a vacuum were completely disconnected.

I ordered the marine kit for this carb and I'm rebuilding it myself tomorrow. At least this way I'll know for sure what parts are being used. I'm also going to document all the parts and list them here on the site, to save others this hassle in the future.


04-20-2006, 11:36 PM
Well, wish I could have helped. I hate Carbs.

04-22-2006, 01:10 PM

Sorry to hear about your problems with the carb. That said, I had a similiar problem with my 2000 Kamberra. It turn out to be that the 2.5 power valve was to small, it takes just 2.5 inches of vacuum to open it. Where I live, elavation is about 1600 to 2500 feet, the power valve was open all the time causing the motor to run rich. A friend of mine helped me stroke the motor and when we did we found that I had a bunch of gas in the oil from the carb running rich.

So he ask to look at the carb. He took one look at the power valve, pulled it out and threw it away, replacing it with a 6.5 valve. My boat never ran rich or dirtied the transom as it had in the past. My friend also builds motors that he runs in old style v-drive flat bottom race boats, so I trust his knowledge on this point. Hope that this helps with the carb. One other point to maybe check as far as the top end rpms could be the timing. Good luck and don't give up, sound like you will get it figured out, keep us posted on the progress.