carb adjust

6balls

Hello all,
Ski buddy wanted to run some gas through his boat, so we put his boat on my lift for some free skiing before we get the courses up. It's an '87 MC with stock Holley carb. Runs great while skiing. At idle can smell gas and it's lumpy/surges on n off about twice per second though never dies. If we turn the idle set screw up to higher rpm it's runs smooth but too many rpm's for a nice engagement of forward/reverse from neutral.
I know zippo about carbs. Any easy adjustments for someone that knows virtually nothing?
THX

dchristman

Probably time for a rebuild. Lots of fun. Little springs and balls falling all over the place. Satisfying when the job is done though.

skihacker

I haven't dealt with a carburetor in a really long time but it sounds like it's running too rich at idle, the idle mixture screws are different from idle speed adjustment, any chance service manual available?

Orlando76

If you go to correctcraftfan.com and ask them how to adjust carb on an '87 Ski Nautique they can be helpful. Sounds like it needs a rebuild which I really recommend just buying a brand new Holley 4160 Marine from Summit. Most of the time Holley has them adjusted darn near right for the 351.

dchristman

A brand new one will cost hundreds - a rebuild kit is about $40 and an experience.

Dano

First check idle mixture screws for proper adjustment (there is one on each side of carb), then check for vacuum leaks (especially around base of carb). Then check float bowl level. If those are good, cheque if ignition is strong and timed correctly. It's likely a points ignition system and worn out points or a weak coil will cause weak spark, which causes low vacuum, which causes problems for your carburetor. holleys are pretty basic carbs. Once running decently you can cheque idle mixture screws and set them using a vacuum guage.

DUSkier

Float level set too high?? Overflow runs straight into inlet manifold if it is, which will make it run rich/lumpy/smelly
AND just remembered i had this site saved as well, a bit of reading but very helpful www.bob2000.com/carb.htm

Orlando76

If you shut it down will it crack up easily enough 3 minutes later? 20 minutes later?

Wayne

Stuck float or some dirt in one of the little orifices (Hollys have many little holes that bleed air or fuel into the metering circuits). I've had some crud sneak through a fuel filter and cause the same behavior.

@6balls I would just pull the carb and go through it. They are pretty simple animals and a rebuild is easy as long as you have the right kit and match up the right gaskets. Usually all you need is the number off the choke housing as a reference and a good parts store cans get you a kit. You will have to pull the flame arrestor to get the number, it's on the front of the choke housing above the front float bowl.

LeonL

As mentioned above, adjust the idle mixture. Slowly turn clockwise until engine speed slows, then counterclockwise until rpms increase. Keep going until it slows again, then back to the max point. If this doesn't help you most likely have a leaking power valve, especially if it was running good last Fall. Holleys as the easiest carb to work on ever created.

ALPJr

Give SkiDim a call. Discount Inboard Marine.

Wayne

I wouldn't adjust the idle screws by idle rpm alone. To do it right you need a vacuum gauge. The process @LeonL mentioned is correct except you target the highest vacuum reading. You can use rpm but it's not as accurate. I've had engines where the idle mixture screws do nothing to idle rpm so a vacuum gauge was necessary and became my standard practice.

6balls

@orlando76 yes it fires again easily after shut-down.

Thanks for all of the responses, Ballers.

Orlando76

Tyen it's not flooding out from a stuck needle.

LeonL

But, with the described condition, it can get in the ballpark if he doesn't have a vacuum gauge, and if he gets no improvement he can eliminate that and move on to other potential problems. I feel that a leaky power valve may be a possibility.

Fast351

I will second a vacuum leak. It's easy to trouble shoot. Get a can of carb cleaner. Spray around the base of the carb. If you hear the RPMs increase and the idle clean up, you have a vacuum leak. The symptoms you describe are typically associated with a vacuum leak (crappy idle but fine over about 1500 RPM).

Idle screw adjustment second. Run them all the way to seat (carefully, while counting turns) and back them out 1.5 turns. That's usually a good starting point. Remember that you want them both adjusted the same amount so if you turn them, turn them both the same.

Dano

@6balls I mentioned in an earlier post to check your ignition. The reason why is that my boat had the same symptoms as yours a couple years back. I too thought it was a carb issue. It turned out to be faulty points and condensor. Once replaced the boat ran perfect again with no changes to the carb. I ended up replacing the old points system with Ford duraspark electronic ignition. It's an easy upgrade with junkyard parts.

6balls

Thanks again. Looking to try some easy stuff we only run this boat about a month in the spring for some free-skiing. Once the courses are installed it's SN 196 time.

@fast351 could you be more specific on where you are spraying the carb cleaner (base of the carb)?

EFW

@6balls. I may not be a Master Mechanic but I'm way better than average and for the amount of time and money I've spent rebuilding carbs and the last time I spent money to have it professionally rebuilt and flow tested. They hot tanked it and replated it for I believe $125 . It looked,idled and ran like new. Plus big deal but 1 mile an hour solidly more. Be sure what you want to do.

Fast351

How to check for vacuum leaks...

Basically you have a square baseplate where the carb bolts to the intake manifold. Those gaskets dry out and crack, especially when you only run it a couple times a year.

Another one is vacuum lines, especially big ones. Not sure what that model year of boat would have on it, but cars of that vintage would have a brake booster that took a large vacuum hose. Unplugging them one at a time, and then holding your finger over it is a good way to check these.

6balls

@EFW it's not even my boat, just on my lift for a while each spring. Anything beyond turning a few screws will be my ski partners deal...not going to put a ton of time into it.

Since it ran fine in seasons past, I'm guessing vacuum leak rather than a carb that fell out of adjustment...but no reason not to try the idle mix screws can always put 'em back where they were.

boarditup

I have seen this issue with local changes in the amount of alcohol in the fuel. It causes the float to dump more gas into the intake - causing the symptoms noted. Using the blue Sta-Bil kept the issue at bay.

6balls

So far not the idle mixture screws as near as we can tell. Did not have vacuum guage but put them in full simultaneously and experimented on how far out. Tried 1.5 turns out which didn't help so tried quarter turn adjustments both inward and outward without benefit. All we had time for today other than a free ski run, more to come.

Beastmode

I have had a boat repair business for 4 yrs now and have rebuilt hundreds of Holley carbs.
All the comments about the floats are spot on. I would guess that the needle and seats for the floats need to be replaced.