Fuel Problem? Ignition?

[chautauquasun]

So I finally got her in the water. The rebuild is great and it looks great. Took her out on her maiden voyage and she ran great. Still have some trouble with the carb with it stalling at low rpm and when it is cold. Took her back to the dock then went out for another run and started to have a strange problem. The boat started to surge like I was pushing the throttle back and forth in a cycle at low to mid rpm. Seem to happen around 20 mph...it didnt seem to affect the performance a lot but the you could hear the engine surging in and out in a perfect cycle. It didnt do it a low rpm 5-10 mph and it didnt seem as bad or was non-existent at faster speeds. The engine wasn't hot and all the guages read where they should be. Same thing the next day. The first time out no problem, second time out when it was warmed up same problem again.

The boat is a hot rod on water and I think she is telling me she likes to go fast...but I kind of need it to run well at slower speeds.

Any ideas? Does it sound like a fuel issue...maybe the pump or choke? Or does it sound more like an ignition issue. I did not change the points or condenser this year.

Any help would be much appreciated. Its good to be back on here again!!!!!

Thank you.

Dan

[Hematoma]

Whens the last time you checked the carb spacer gasket? you might have a vacuum leak around it. When its cold it's tight but when it warms up it starts sucking past the gasket? Just a thought. Get you some wd40 and run the motor at idle, spray all the gasket areas on the carb and listen for a change in the idle.

[chautauquasun]

thanks for the info. I will give that a try...but wouldnt I be having vacuum problems at all speeds? Also a little piece of info I left off...it smells like it is running extremely rich. could that be due to a vacuum leak as well? Whats the best way to tune the carb to stop it from running so rich.

thanks!

[Hematoma]

thanks for the info. I will give that a try...but wouldnt I be having vacuum problems at all speeds? Also a little piece of info I left off...it smells like it is running extremely rich. could that be due to a vacuum leak as well? Whats the best way to tune the carb to stop it from running so rich.

thanks!No it would run lean if anything. It's hard to say sitting on the other end of a computer lol. I would check the easy things first. Try running it with the cover up and the arrestor off, see if you can see some kinda fluctuation in the spray pattern.

[michael hunter]

Check the power valve and float level. If the carb hasn't been rebuilt lately its probably time.

[chautauquasun]

I had it rebuilt last year. Ran pretty well but not great after the rebuild. big problem I am having now is it stalling while idling waiting the the skiier to get ready. That is a real pain...just as the skiier says go the boat dies then you have to try and get it restarted and take off before the skiier gets messed up.

A little frustrating but I know it is fixable. I have never tuned a carb so I am a little worried about starting to twist screws and really mess it up.

[Sunapee Sunsport]

Try backing out the carb adjsment crews 1/4 turn - 1/2 turn each. Sounds like the carb rebuild shop pre set adjustment for you to lean.
Do you run a gas addditive? I add both startron starbright allong with lucas fuel treatment upper cylinder lube with each fill up.

[Hematoma]

I had it rebuilt last year. Ran pretty well but not great after the rebuild. big problem I am having now is it stalling while idling waiting the the skiier to get ready. That is a real pain...just as the skiier says go the boat dies then you have to try and get it restarted and take off before the skiier gets messed up.

A little frustrating but I know it is fixable. I have never tuned a carb so I am a little worried about starting to twist screws and really mess it up.Have you had any backfire thru the carb? The old style powervalves where notorious for blowing out during a carb belch. The new styles have a blowout preventer. If its got a pin hole in it it will leak fuel and cause a rich condition like you say. They are really easy to change.

[chautauquasun]

I have had just one back fire this year...dont recall any last year. Does it take just one to blow the power valve?

[rludtke]

Yes. Holley is adamant on their documentation that backfires will not damage the current powervalves, which may or may not be true. But it is true for the older style powervalves, and I don't know how to tell the difference, but the new style entered production in 1992.

According to Holley (http://www.holley.com/data/TechService/Technical/power_valves.pdf), there is an easy test you can perform to determine if the powervalve is bad.

[Hematoma]

I have had just one back fire this year...dont recall any last year. Does it take just one to blow the power valve?Yes it just take 1 and they are toast, Have you noticed really bad fuel consumption? It will drink up the petro pretty fast with a blown powervalve.

[Longhorn21]

When was the last time you changed your fuel filter on your fuel/water separator. I'm having the same problem with surging and called the guys at skimid and they pointed me to the fuel filter first. That's the cheapest so try that first. Locate your fuel/water separator and unscrew the bolt at the bottom (have a cup to catch the fuel) if the gas comes out milky or dirty it needs to be change, it should be changed once a year. That could be the culprit to your problem, a dirty fuel filter can cause alot of problems, if that doesn't do it, it's got to be your carb. You probably got a marine 4160, I've never rebuilt one and did it in about 4 hours but try the fuel filter first you'll be suprized at how that can affect your engine

[OUI]

The Blow Out Preventer only applies to street carbs. Marine carbs are different and the Power Valve will blow if there is a back fire.

[jdholco]

Any ideas? Does it sound like a fuel issue...maybe the pump or choke? Or does it sound more like an ignition issue. I did not change the points or condenser this year.

Dan

http://www.skidim.com/prodinfo.asp?number=RP173072

best thing i've ever done for my boat.

[Hematoma]

The Blow Out Preventer only applies to street carbs. Marine carbs are different and the Power Valve will blow if there is a back fire.
I don't think so, Marine and street use the same style power valves, the blow out kit is an add on to carb not the powervalve.. Other than the J-tubes and different fuel metering the carbs are the same.

[rludtke]

So I finally got her in the water. The rebuild is great and it looks great. Took her out on her maiden voyage and she ran great. Still have some trouble with the carb with it stalling at low rpm and when it is cold. Took her back to the dock then went out for another run and started to have a strange problem. The boat started to surge like I was pushing the throttle back and forth in a cycle at low to mid rpm. Seem to happen around 20 mph...it didnt seem to affect the performance a lot but the you could hear the engine surging in and out in a perfect cycle. It didnt do it a low rpm 5-10 mph and it didnt seem as bad or was non-existent at faster speeds. The engine wasn't hot and all the guages read where they should be. Same thing the next day. The first time out no problem, second time out when it was warmed up same problem again.

The boat is a hot rod on water and I think she is telling me she likes to go fast...but I kind of need it to run well at slower speeds.

Any ideas? Does it sound like a fuel issue...maybe the pump or choke? Or does it sound more like an ignition issue. I did not change the points or condenser this year.

Any help would be much appreciated. Its good to be back on here again!!!!!

Thank you.

Dan

Hi Dan,

The screws on the side of the carb are the idle air bleeds, and will only adjust the idle mixture. The idle circuits close around 1000 rpm, so I don't think this is your problem. Carb tuning is for the most part, changing the fuel metering jets, power valves, and the like to change the carbs performance charectoristics. Most likely your jets and power valve are the originals specified for the marine carb, and do not need to be changed or tuned to something else. I guess what I am saying is that there isn't much tuning for us "stock" engine users. I think what you need is to "restore" your carberator with an overhaul kit. The kit will come with a new power valve, new needles and seats, new accelerator pump diaghram, and new gaskets. It is easy to install, and you don't even need to remove the carb from the engine to replace the key parts.

There is a lot of technical information at www.holley.com. An exploded view for the 4160 carb can be found here: http://www.holley.com/data/TechService/Technical/4150-4160%20Exploded%20View.pdf