Carbureted ford 351 idling when warm

pcm2a · Soul Rider Joined: 14 Jun 2004 Posts: 318 City: LaVergne

I have owned a 1991 American Skier for a few years. It has a direct drive carbureted ford 351 in it. The problems started at the end of last season and are still present on my first trip out today.

- When the boat is cold it fires right up, idles great, runs great.
- Sit out on the lake for 20 minutes and the boat is still idling good but will randomly die.

- Try to start the boat up (after it's warm) and it dies immediately
- Start the boat up and fire on the throttle and it will run as long as your giving it some gas.
- Even when warm it will drive around the lake just fine but as soon as you slow down or put it in idle then it will die.

I already tried firing some carb cleaner down in there but that didn't resolve anything. It seems to be a problem when the boat is warm. Oil level is fine, oil temperature and pressure is in the normal.

Are there any easy things that I can do to resolve this issue or is my best option to take it over to the boat shop?

Thanks!

Suprahunter · Soul Rider Joined: 28 Apr 2008 Posts: 486 City: Lowell

Sounds like you need a carb overhaul. You could try a power valve but I would just rebuild it.

ryan351w · Addict Joined: 26 Jan 2009 Posts: 532

Is the carb a Holley List number 9392? Number will be on the choke horn.
When its running cold, take the flame arrestor off the top of the carb and look down in the barrels. At idle. See if the rear boosters are dripping fuel. Mine used to do this as well, the problem is sometimes the rear needle and seat gets stuck open usually because a little piece of stuff is stuck in it. If its not leaking fuel get the engine warm and to the point that its acting up and look again.
Thats step one and the easiest to look for.

Other thing it might be is the idle circuit is clogged. When the throttle blades are completely closed the fuel enters the intake underneath the throttle blades via the idle circuit. This carb has two idle circuit screws on the sides of the metering block. They should be between 1 to 1 3/4 turns from full seated. If adjusting these to a way outta wack position like full closed, and it still runs Suprahunter could be right with the PV thought. Because when the PV blows it allows fuel to pass though the main circuit unrestricted. So thats another simple check.

Start there.
Step one-check for fuel dripping from the rear boosters and front boosters for that matter at idle. It shouldn't be.
Step two-Count how many turns from seated your idle mixture screws are. If you can close both of them and the motor still runs you have an issue with the main circuit. Just make sure that you count how many turns so if the motor does die, you can set them back right where they were. FYI-both idle screws need to be adjusted the same amount of turns.

kartman · Posted: Jun 03, 2011 6:59 am Post subject:

what are the rpm's when it gets warm? you could turn up the idle to 8-900. if it wont run in this range, follow ryan351ws advice.

pcm2a · Soul Rider Joined: 14 Jun 2004 Posts: 318 City: LaVergne

Thanks for these great suggestions, I'll be checking for the fuel drip and adjusting those screws tomorrow hopefully.

ryan351w · Addict Joined: 26 Jan 2009 Posts: 532

here is a link to what the idle mixture screws and the curb idle screws. the curb idle is what will adjust your rpms. However the adjust is somewhat limited because boats have a hard pushrod directly linked to the throttle control unlike a car which has a pedal that moves freely.

http://www.jetsrus.com/FAQs/FAQ_rejetting_holley_carb.html

ryan351w · Addict Joined: 26 Jan 2009 Posts: 532

oh by the way on that link, don't worry that your float level isn't like that pic. Those are center hung floats and you most likely have side hung floats, they can only be adjusted by removing the bowl.

kartman · Posted: Jun 03, 2011 8:50 pm Post subject:

ryan351w, great link

ryan351w · Addict Joined: 26 Jan 2009 Posts: 532

thanks man, happened to stumble upon it looking for a pic of the two screw location we were talking about! Laughing

pcm2a · Soul Rider Joined: 14 Jun 2004 Posts: 318 City: LaVergne

I'm not sure what the model number is. Here is a picture of the side and the top. I'm waiting on an autozone battery charge and will be firing it up tomorrow.

In the second picture, where exactly will I be looking for the drip?

ryan351w · Addict Joined: 26 Jan 2009 Posts: 532

this....it looks like a list 9392 no big deal though......

pcm2a · Soul Rider Joined: 14 Jun 2004 Posts: 318 City: LaVergne

Thanks for the updated picture!

1. I ran the boat at idle in the driveway and there was no drip from the rear boosters.
2. After 15 minutes in the driveway there was still no drip from the rear.
3. The idle mixture screw on one side was 1.5 turns from seated and 2 on the other side. I changed the other side to also be 1.5. The motor sounded a little smoother after this or I may be crazy.
4. I was able to turn the idle speed screw to where the engine sounded like it was running crazy fast, maybe 2000 rpms. I put it back where it started.

Tomorrow I will take her out on the lake and run it real good. Once it starts stalling I will check the drip again and I will try adjusting the idle speed.

Could the idle mixture screws not being the same cause my problem?

ryan351w · Addict Joined: 26 Jan 2009 Posts: 532

Ok, sometimes it will drip AFTER opening up the thottle, UNDER LOAD. For example in the water at full tilt. Thats because at idle the rear bowl doesn't get used. After the engine is run at WOT in the water then brought back down the rear needle and seat have "cycled" a few times. Just a check but defiantly doesn't have to be the problem. The rear will not open without a load that is because they open with vacuum, and the motor won't pull enough vacuum without a heavy load.

Yes a mis-adjusted idle mixture screws can indeed effect the idle no question. But typically a half turn off, won't hurt it that much.

The curb or idle speed should NOT be much over 800 rpms. 1000 is ok, but no more. If it needs more rpm than that there could be a vacuum leak.
Also if the rpm is higher than 1000 it beats the crap out of the damper plate in the trans every time you put it into gear.

check this pic....that piece the guy is touching is the accelerator pump arm. AFTER you have the curb idle set, let the motor idle. Push on the top of that nut spring assembly, not very hard, (if no fuel comes out, push a little harder Laughing

) look in the carb and you will see a bit of fuel shoot into the barrel from the booster, (see previous pic with red circles) but it will be from the ones that has the choke on it, the front or primary barrels.
If the motor RPM increases then open, or "loosen" the idle mixture screws a 1/4 turn each, and repeat until the motor stays at the same rpm when you do this little shot of fuel. If the motor bogs down, close or "tighten" the screws 1/4 turn each. Now as I said before if you get to the point where the idle mixture screws are more than 3/4 turns from closed then the carb is leaking fuel from the intermediate or main circuit.
But we will burn that bridge when we get there.

ryan351w · Addict Joined: 26 Jan 2009 Posts: 532

oh btw- non of these could be the problem. But a tuned carb is easier to diagnose!

pcm2a · Soul Rider Joined: 14 Jun 2004 Posts: 318 City: LaVergne

Ok so everything has been tested and I will try to accurately describe the whole mess.

- You already knew in the driveway the boat ran fine for 20+ minutes.

- Yesterday I took it to the lake and started it up on the trailer. The boat was cold previously. It would not idle at all. I checked and there was no drip from the rear boosters.

- Got out on the lake and drove it around for 15 minutes.
- Next I adjusted the idle speed to WAY to fast. The boat would start and idle, except real fast.
- Next I set the idle mixture to 1 turn from seated and then slowly turned the idle speed back down to normal.
- I also did the accelerator pump test to get the idle mixture screws set right.
- Now the idle speed was good and everything sounded great. We put the boat in gear, did a quick lap, put it in idle and it was dead again.

- During all of these tests there was never a drip from the rear boosters
- The front boosters sometimes had the same drip on either side and sometimes it was not even close to the same.

I plan on taking the carb off and soaking it for a few days and doing all of this again.

ryan351w · Addict Joined: 26 Jan 2009 Posts: 532

Don't rip into the carb just yet....let me think a few.

vette74 · Posted: Jun 09, 2011 8:45 am Post subject:

The front booster should not drip at all. The idle circuit lets fuel in below the butterflys. To tune the idle mixture screws. Turn the idle way down until the boat barely runs. Hook up a vacuum gauge to the engine slowly turn one screw in any direction and watch for the needle to go up if it goes down turn the other direction. repeat the other side. Set idle back to normal then you are done.

You can take the carb off and squirting carb cleaner through the idle passages to help blow out any junk. If it doesn't work rebuild it.

pcm2a · Soul Rider Joined: 14 Jun 2004 Posts: 318 City: LaVergne

If there should be no drip from the front boosters at idle (the front with the choke) then maybe that is the problem. When my boat is at idle on the lake or in the driveway drips are coming out of the front boosters. It is a different amount on each side and varies depending on when I look at it.

It is a drip or mega fast drip and not a "spray" like if I primed it with the throttle and it sprayed gas out. The higher I would turn the idle speed up the faster the drip would be.

vette74 · Posted: Jun 09, 2011 2:42 pm Post subject:

pcm2a, Your idle circuit is clogged. Look at the pic at the bottom of this page. This is where your fuel for your idle comes out

http://67-72chevytrucks.com/vboard/showthread.php?t=305824

If it is coming out of the boosters it is trying to compensate. I would rebuild the carb. It only takes an 2 hrs or so do do it.

cadunkle · Criminal Joined: 16 Jul 2009 Posts: 60 City: NJ

Check your float level. Also take your can of carb cleaner with the little hose on the nozzle. Push the hose firmy in the air bleeds and give it a good spray in each (engine off). Air bleeds are the little brass jet looking plugs next to the accelerator pump discharge nozzle when you look down the carb. There are 4 on primary side and 4 on secondary side. If you get lucky it'll be fine after doing this, setting your float level, and resetting your idle mixture and throttle opening. If this doesn't fix it, rebuild the carb.

pcm2a · Soul Rider Joined: 14 Jun 2004 Posts: 318 City: LaVergne

This is just in the driveway but I fired the carb cleaner in the 8 jets, doubly so in the front ones. I also gave everything a good spray for good measure.
Fired up the boat and revved it up for 30 seconds or so. Afterwards I checked the front boosters and NO drip! Turned the boat off and now I can fire it right up without having to prime it (haven't been able to do that for years)!!!

I reset the idle mixture screws to 1.5 turns (for now) and I was able to set the idle speed screw way down and the engine still sounds great. I let it run for 20 minutes and then start and stopped it a few times. I'm super pumped to test it out on the lake tomorrow afternoon and see if things are resolved.

ryan351w · Addict Joined: 26 Jan 2009 Posts: 532

cadunkle, you beat me to it! Laughing

after he said he saw fuel from the front boosters i was about to write that exact thing!
pcm2a, good job man, just one thing, make sure the boat is warmed up and the choke is opened before setting the idle mixture screws, so after a few trips around the pond.

pcm2a · Soul Rider Joined: 14 Jun 2004 Posts: 318 City: LaVergne

I did attempt to set the idle mixture screws in the driveway after running the boat for a while. I will give it another shot out on the lake after a few laps. When I tried it in the driveway I did the following:
- Push down on the accelerator arm, bogged down
- Tighten 1/4 turn
- Push down, bogged
- Tighten 1/4 turn
- Push down, engine died
- Set to 1.5 turns for now

When it is set correctly what would the engine do?

cadunkle · Criminal Joined: 16 Jul 2009 Posts: 60 City: NJ

To set your idle mixture you adjust for highest vacuum or highest RPM at a given throttle opening. Basically start at about 2 turns out. With engine warm and idling adjust the throttle stop screw to get your desired idle RPM, generally 650-750 in neutral.

Then screw one of the idle mixture screws in until RPM drops or you notice a slight stumble or misfire... Back that screw out 1/4 turn so it smooths out. Repeat on the other side. Then repeat again for both. Now you're in the ballpark. Adjust the idle stop screw again to achieve desired idle RPM if it has changed. Then do the mixture screws again. Repeat as necessary until you get your nice idle where you want it.

Really once you've done that you should check you timing and correct that if it has moved any. If you have to adjust the timing at all, repeat the idle speed/mixture adjustment. keep doing it until you're dead on where you want it.

pcm2a · Soul Rider Joined: 14 Jun 2004 Posts: 318 City: LaVergne

I think we almost have it! The boat fires right up now, even after driving around the lake or idling for a while. I can set the idle anywhere between 700-1000 and it seems great. I can now idle forever and the motor/rpms sound great.

The only problem left is when I put it in gear, but have the throttle handle as slow as it can possibly go. The rpms will drop from say 750 down to 400-500 and if you leave it there too long it will stall out. If I push it past the slowest speed then the rpms jump back up to > 750 and things seem perfect.

What can I adjust to increase the rpms of the slowest speed in gear?
- I have tried adjusting the idle/mix screws to where I think they should be.
- Tried setting the idle mix screws open to 2 turns and to almost closed, just to see if there was any difference once I was in gear. There was not.
- Tried turning the idle speed screw up to 1200 rpms, but when I put it in gear it still drops down to 500 or lower.

Could this be a timing issue? I do have a nice timing light.

Update:
I started reading some sites on tuning a Holly carb and I see my mistake now. I should be adjusting that curb idle screw while the boat is in gear to 650-750. I'll do that this afternoon at the lake.

cadunkle · Criminal Joined: 16 Jul 2009 Posts: 60 City: NJ

Normally 650-750 in neutral will get you around 600 in gear. You're right, since you're having trouble getting it right when it's in gear just have someone else steer while at idle in gear and do your idle throttle opening and mixture while in gear at idle. Shoot for 600-650 RPM in gear, or if it doesn't like that low just go as low as it'll go and still be smooth without surging or stumbling.

pcm2a · Soul Rider Joined: 14 Jun 2004 Posts: 318 City: LaVergne

I took the boat out yesterday and set the curb idle to be around 700-750. When I take it out of gear it pops up to around 900-1000.

The funny part is now things seem to be running great when the boat is warmed up but not as great when the boat has been off for a while. We drove around the lake and then adjusted the idle. Things were running amazing. Sat on the water for about 3 hours then fired it up...and it died. It did this about 5 times before I revved on it real good and then put it in gear and gave it some gas. Drove about 5 minutes back to the dock and pulling up to the dock and trailering was perfect.

So it looks like I still got some kinks to work out but we have made tremendous progress. I may work it over again with the carb cleaner for good measure before my next trip out this week.

duckseatfree · Newbie Joined: 26 Jul 2010 Posts: 28 City: Charlotte

PCM...what's the update on this...i'm just a little curious

johnathon_03 · Newbie Joined: 04 Jul 2009 Posts: 35 City: Puyallup

I had this very same problem with my Holley carb after I had it re-built. Start perfect run perfect until it warmed up. Tried idle screws... Fried everything. Then my neighbor who works on cars looked at it for about 2 mins and figured out that the 3 and 4 barrels were not opening up. When it was re-built the shop that did it made a washer for the vacuum and it was a POS. It was easy for him to check. Right behind the electric idle there is a round object on the side. Has a control arm coming out of it. Push that arm up and down and you can feel if there is a vacuum. It will be smooth and kinda tough to push up. Once the washer was replaced it ran like new! All the great gear heads on here chime in please.