Carb trouble

ric · **Posted:** Fri Jul 27, 2012 2:59 pm

The holley marine carbs are standard car carbs with a return vent tube that costs $5. No other changes.

You're a good man for going out there with jets and PV's, I applaud you. When they leave the factory they're generically tuned. You can always squeeze a few hundred RPM's and better throttle response by tuning it. I gained almost 500rpms out of my 3.0 that allowed me to spin a bigger prop.

neutron · **Posted:** Fri Jul 27, 2012 3:48 pm

ric wrote:

You're a good man for going out there with jets and PV's, I applaud you. When they leave the factory they're generically tuned. You can always squeeze a few hundred RPM's and better throttle response by tuning it. I gained almost 500rpms out of my 3.0 that allowed me to spin a bigger prop.

it made a world of difference, problem was here in the Bay it was a little choppy and lots of boat traffic that day, you want to see steady hands and feet while bouncing over wakes. took about four times removing the bowl to get the right combo that made the biggest difference. went from a factory 69 main jet to a 73 and it was better on fuel overall and went like a sports car after. It would never jump out when push full throttle, it would always come up slow, after it tuned it you could wack it and it would scream from the get go.

BedlamX · **Posted:** Fri Jul 27, 2012 10:04 pm

Got the carb today will install tomorrow. The jets that were sent are 75 the Selok book calls for 70

The fired mechanic left me with a box of parts I assume this will take me longer than 30 minutes.

Question: does the gasket between the carb and the block need to be coated with anything or does it just go on.

The carb in the pic is original to the boat it still had the red paint from either Volvo or Fourwinns whom ever painted the engine.

I hope this solves the problems we are having.

neutron · **Posted:** Sat Jul 28, 2012 10:13 am

BedlamX wrote:

Got the carb today will install tomorrow. The jets that were sent are 75 the Selok book calls for 70

The fired mechanic left me with a box of parts I assume this will take me longer than 30 minutes.

Question: does the gasket between the carb and the block need to be coated with anything or does it just go on.

The carb in the pic is original to the boat it still had the red paint from either Volvo or Fourwinns whom ever painted the engine.

I hope this solves the problems we are having.

Just a thought you might want to consider going up a size or 2 possible on the main jets because if you are running 10% ethanol it will run slightly leaner than befere the days of 10%..... we see this at the motorcycle shop with carbs that cant "sniff" the exhaust and decide to lean out or richen the mixture automatically like a FI system can. most carb systems were set up before the days of ethanol.
you can run it with the stock set up and buzz around for a while then without letting it idle too long pull a plug from both sides and inspect to see if it is black with fuel or on the whiter(lean) side

ric · **Posted:** Sat Jul 28, 2012 11:21 am

If you run E10 pump gas I'd pick up 70,71,72,73,74 jets. I'd start off with a 72.

Grab a handful of plugs and start reading them as you try different jets.

http://www.angelfire.com/fl4/pontiacdud ... plugs.html

Once you get the jetting right you can borrow a timing light and advance the ignition a little. E10 pump gas with more timing and jetting will easily make 20hp over stock tune. Everyone hates on E10 but in the world of performance it's a big improvement over standard gas.

BedlamX · **Posted:** Sat Jul 28, 2012 12:02 pm

I have a feeling I should have let the professionals handle this. I have more questions:

The Old carb on the right and the new on the left. The part circled is my question what is it, why isnt it on the new carb.

This is the hose that connected to the old carb port. If the new carb doesnt have a port for this what do I do with it?

neutron · **Posted:** Sat Jul 28, 2012 12:19 pm

if everything else matches you can always swap the base plates, or you have to find another vacuum source for the PCV

ric · **Posted:** Sat Jul 28, 2012 12:34 pm

relax it's just a carb.

That hose is for the PVC... don't worry not a big deal. Just tape it to the air filter for the time being. 99.9999% of the time they have a fitting on the flame arrestor/air cleaner for that hose. To be on the carb is actually quite weird.

Nothing bad is going to happen with that disconnected. Most people in the car world actually get rid of it and put an air breather on the valve cover. The oil vapors that can get ingested can lower the overall effective octane rating of the fuel/air mixture.

You're almost done don't worry. You'll be on the water jammin out to tunes by mid afternoon

ric · **Posted:** Sat Jul 28, 2012 12:41 pm

With all that money you saved, pickup a KN air cleaner with the PVC hose adapter. Good for a few hps too.

This:
http://www.amazon.com/59-3264-Flame-Arr ... B000AP6RHU

Plus this:
http://www.amazon.com/K-N-85-1362-Vent- ... auto_img_b

BedlamX · **Posted:** Sat Jul 28, 2012 5:11 pm

I took the easy way out and just switched the plates. Got it in but no time to test it out. I used the 70 jet recommended by Seloc and left the power valve at 4.5 although the book says 2.5. I guess maybe tommorow I will have a chance to test it.

Thanks for the help.

neutron · **Posted:** Sat Jul 28, 2012 5:15 pm

that 4.5 might be a little strong I believe that one will open late. it will take more of a vacuum drop to open.
I forget which way the scale goes. I might have got it backwards though
good luck with the test

LouC · **Posted:** Sat Jul 28, 2012 6:30 pm

And the best thing besides saving a bit of money is the knowledge that you gained, the next time you have a carb issue you don't have to be totally dependent on shops that overcharge.
Gaining knowledge is one of the best things you can do in life but sometimes there is frustration that is just a part of it.

I learned not only how to rebuild carbs back in the 70s but also how they work, Bernoulli's Law.....pressure of a fluid (air here) drops as its velocity increases, you increase the air velocity in the carb venturi and the lower pressure in the venturi causes the atmospheric pressure in the carb bowl to push the gas through the jets into the venturi.

ric · **Posted:** Sat Jul 28, 2012 6:55 pm

Yup, the knowledge you're gaining from this is invaluable owning a boat with a carburetor. This won't be your last rodeo.

rpengr · **Posted:** Sun Jul 29, 2012 7:36 pm

BedlamX: Congratulations on finishing this job yourself. I had rebuilt the Rochester carburator on my OMC 4.3L a few times over the 18 years I owned it. And sometimes it just needed a new accelerator pump. Not expensive at all when you do it yourself. A week ago, I just rebuilt my first Holly (very similar to yours, except a 600cfm). I was impressed with how the carburator is designed, and everything went smoothly except that it took a long time to clean up the gasket surfaces because (apparently) it had been a long time since it was rebuilt, and I just used spray carb cleaner, not a more powerful dip cleaner.

As others have said, your new-found knowlege on this subject will pay off in the long run.

neutron wrote:

...when I was playing with different jets on my sundowner with that carb I went out with 5 different jet sizes and different PValves and changed them while on the water till i got the performance it should have. I got them all from Advanced Autoparts. they were dirt cheap

Neutron: How do you drain the bowl or capture the spilling gas as you open up the bowl out on the water. Or did you remove the carburator each time? And how did you get advanced autoparts to find the correct parts. They could not even find a bowl gasket for me when I brought in all the numbers off a Holley 600cfm.

neutron · **Posted:** Sun Jul 29, 2012 9:05 pm

We have absorbant "dyper" pads for oil spills at the dealership. I stuffed a piece under the bowl and just took the bowl off every time, its very easy. then took the pad and tossed it in an old small cooler.... no mess at all and no fumes

At the motorcycle shop that I also work at we have the luxury of using a dyno to test a result with air/fuel metering whether changing jets, needle position, adjustments, or simply changing a fuel map with a laptop.....On a boat you cant run on the hose to see the result you need to have it in the water. I got tired of going back and forth so I took it all with me out on the bay.

www.iFourWinns.com

Carb trouble

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