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View Full Version : Rough starting w/ 4160 Carb


James O'Keefe
06-29-2009, 09:24 PM
Hello - I have a 1993 205. I switched out the carb to a 4160 two years ago. It has always started rough, seems to be flooding now.

I crank without any shot of gas and it doesn't fire, then I try one, then two, pumps and still will not fire. then I have to hold it wide open for it to fire and it then it takes a second to clear it out, then takes 2 mins of rough low idle to warm up and then runs fine. It does seem to idle just a little bit rough when warm, but that might just be in my head. The mixture screws do not make a huge difference when I turn them in or out, not sure why? right now they are both at 1.5 turns out. idle is 6-700 rpm.

The carb has low hours, I always seafoam before and after storage and always run premium. Plugs, wires, dist, fuel filter and water separator all replaced about 2 years old too. Choke plate is closed when cold and if i just turn the key on will open in 1-2 minutes, not very gradual though, pretty much just goes from closed to open in a few seconds. I have also tried spraying cleaner around the base of carb while running to ensure there are not gasket leaks.

Is this possibly just a choke adjustment? Maybe a float adjustment? boat always runs/starts fine once warm...

Please help, thanks.

Commandohorn
06-30-2009, 04:29 PM
I'll take a stab because I just rebuilt my whole fuel system due to a bad tank of gas. I doubt it's the choke, sounds like it's doing it's thing. Easy to check though, before you start the first time, reach over and hold it closed while you turn the key. At idle there should be no visible gas dripping in the barrels. It is running on the idle circuit only. If you see gas you've got a carb problem, maybe a tiny clog in the idle circuit, those openings are tiny! To check and see if your accelerator pump is working just look down the primary (front) bowls while someone pumps the throttle, if you see a squirt then that's OK. Having to hold the throttle open to start is the classic fix for a flooded engine, and that is usually a float problem. The bowls come off easy for inspection/cleaning, I would do that as last resort. Hope this helps, I'm sure others will weigh in soon.

ROB
07-01-2009, 10:00 PM
Just put in a new 4160 750 CFM myself and took some time to fine tune the air/idle mixture. There are a couple of methods to achieve the proper mixture. One is with a vacuum gauge, the other on the water in gear. I know I've seen a thread somewhere here on the latter method. The vacuum gauge method can be found I believe on the holley website or on you tube. I would try this first. Be sure all of your vacuum ports are covered.

Cloaked
07-01-2009, 10:13 PM
Not the soultion but maybe an insight to an overlooked issue.

.

rkeune
07-08-2009, 12:09 AM
Hi James,
I had a similar problem with my Prostar 190 (4160 Holley). It sounds to me like your engine is getting a rich fuel mixture. A few things to check... How long has it been since the carb has been rebuilt? (not hours on the carb, but years since last rebuild/renew). Over time, the gaskets and diaphrams can begin to crack and leak. It can be a slow process, mine took about 1 1/2 seasons to finally stop working enough to require maintenance. I didn't notice it at first, but looking back at it I realized it happened slowly. During the rebuild is also a good time to check for correct float settings. Having the floats too high (too much fuel in the bowl) will cause problems like you describe. The adjustment methods are a bit different depending on if you have externally adjustable floats. (My 4160 carb did not.)

Once you know the gaskets and diaphrams are good, make sure the powervalve is torqued to the correct setting... (this is inside the carb on the metering plate between the front bowl and the throttle body, you have to have the carb apart to get to this). A leak here can make the mixture too rich. Also, make sure the linkage to the accelerator pump is set correctly. If it's not right, the pump remains slightly open at idle, again creating a too rich scenario.

I rebuilt my 4160 and the linkage to the accelerator pump was not right, causing hard starting , rough idling, no response from the mixture screws on the metering plate, and even a hiccup (or cough) when accelerating hard.

I'd be happy to clarify or post some pictures if need be. I hope this helps!
-Ralph

rholmes
07-08-2009, 10:18 AM
I'd be happy to clarify or post some pictures if need be. I hope this helps!
-Ralph


If you have the time to, go ahead and do it. That would be greatly helpful on this board with the number of questions there are about carbs. Maybe the mods would make it a sticky!