PDA

View Full Version : Carb problem


alecams
09-06-2005, 08:59 AM
So my boat won't idle, carb has been cleaned, yet still only one intake is receiving enough fuel to keep things barely running. I suspect there is varnish/lime deposits clogging the other side and thus results in low fuel flow. Am told it is very hard to clean the internal channels and perhaps a new/rebuilt carb may be needed. The boat runs ok @ full and 1/2 throttle but at any slower speed (less than 15mph) it will stall or puke from not getting enough fuel.

I see skidim has the 4160 Holley's, but isn't there a size bigger carb that i can use and is it worth it. Anyone have an extra carb in a box somewhere?

Any thoughts?

Workin' 4 Toys
09-06-2005, 09:32 AM
So my boat won't idle, carb has been cleaned, yet still only one intake is receiving enough fuel to keep things barely running. I suspect there is varnish/lime deposits clogging the other side and thus results in low fuel flow. Am told it is very hard to clean the internal channels and perhaps a new/rebuilt carb may be needed. The boat runs ok @ full and 1/2 throttle but at any slower speed (less than 15mph) it will stall or puke from not getting enough fuel.

I see skidim has the 4160 Holley's, but isn't there a size bigger carb that i can use and is it worth it. Anyone have an extra carb in a box somewhere?

Any thoughts?
The mechanic we use for such projects claims and I now believe him, the carbs themselves should not have to be replaced.
They have rebuild kits for them. It is more than I would want to do myself. I don't screw with oil or fuel issues anymore. Fuel leaks and fiberglass don't go well together.
At any rate, we had issues with starting and idling and ran very rich on two boats, both 351 carbs. He took and rebuilt the carbs on both of them. After that they started, idled, and ran perfectly. Like new. One of them is sold, and the other on its 3rd year and still runs perfect.
Sitting stale fuel is a carbs enemy.

alecams
09-06-2005, 09:45 AM
I thought my mech did a rebuild, but maybe not. What is actually in a rebuild kit? I suspect their are clogged passages, so how does a rebuild kit clean the passages?

jmyers
09-06-2005, 02:50 PM
I thought my mech did a rebuild, but maybe not. What is actually in a rebuild kit? I suspect their are clogged passages, so how does a rebuild kit clean the passages?
My Nautique wasn't ideling either I found the floats were sticking and the boat was loading up with fuel, I replaced the needle and seat in it. It was the holley in the 351 ford windsor, same thing it would run when I gave it gas but not at an idle! I got a brand new Holley from ski dim and it still had a problem so I don't know which is better new or rebuilt? :rolleyes:

alecams
09-06-2005, 03:09 PM
i don't follow you, you got a new carb from skidim and still didn't work, and then replaced the needle and seat?

Hoosier Bob
09-06-2005, 03:28 PM
What do you mean "pukes?" I would think it may be getting too much fuel as it tends to clear out as you throttle up. Check the secondaries and in severe instances check for black smoke. If the primary or secondary float is stuck or mis-adjusted you will see it pumping or not as the vehicle is running. First guess would be to set your floats. Good luck! There are some good books that will give you some insight at the local autoparts store. :D So my boat won't idle, carb has been cleaned, yet still only one intake is receiving enough fuel to keep things barely running. I suspect there is varnish/lime deposits clogging the other side and thus results in low fuel flow. Am told it is very hard to clean the internal channels and perhaps a new/rebuilt carb may be needed. The boat runs ok @ full and 1/2 throttle but at any slower speed (less than 15mph) it will stall or puke from not getting enough fuel.

I see skidim has the 4160 Holley's, but isn't there a size bigger carb that i can use and is it worth it. Anyone have an extra carb in a box somewhere?

Any thoughts?

jmyers
09-06-2005, 03:33 PM
i don't follow you, you got a new carb from skidim and still didn't work, and then replaced the needle and seat?
I bought a brand new carb and it worked fine I took it in to have the carb put on correctly because I thought it was leaking! When they took it off I think they did something to it like drop it or turned it upside down which can get any sedament that was in there from running bad fuel through it that I did before I replaced everything in it! When I got it back it was loading up and doing exactly what yours is doing, so I called Ski Dim and they said sometimes even on a new one it can have a bad needle and seed and sent me a new one it stopped loading up but I then had to adjust the float levels. Mine was way beyond a rebuild so I went new that is why I said even with a new one it is not always easy. A rebuld kit has new seals and some small stuff for about $50 instead of $500 but it sounds like it could be what I had with the loading up. My next door neighbor is a ford mechanic so we started the boat with a fake a lake with the arrestor off and when it warmed up it started pouring fuel so we tapped on the round circle where the fuel line comes in with a plastic mallet and it stopped but then did it again that is how I new it was the needle sticking but it kept doing it so I replaced it.

martini
09-06-2005, 03:34 PM
The rebuild kit will not clean the passages, nor will there be instructions on how to do it. The rebuild kit contains only the replacement parts you will need once "you" disassemble and clean the carb yourself. The cleaning process is what clears passages and carb of all the gunk and old fuel that collects on the inside of it over the years. You will need to purchase a cheap Holley rebuild manual that will cover all the basic steps. Assuming you are doing this yourself. It is not hard, just a little attention to detail is needed. If you want to PM me about specific instructions, or what is actually needed send me a message.

alecams
09-07-2005, 10:59 AM
Martini, we disassembled every thing and soak it in a cleaning tank, some of those passages and very small and have right angles, can' imagine how one would clean any varnish or lime/scale build up. A rebuild kit was used so all the seals and such are new. no black smoke, the secondary's seem to work fine. My mech is going to water test it Friday he thinks when he sees it for himself he can figure out whats next. I can see the problem though and on idle or low speeds only 1 intake is getting fuel the other is dry as a bone...i think its got to be the passages.

Leroy
09-07-2005, 11:05 AM
I've used very fine stainless steel wire. Size it to fit the hole easily.

can' imagine how one would clean any varnish or lime/scale build up

Hoosier Bob
09-07-2005, 08:24 PM
When you manually operate the pump diaphram (w/o the engine running) do you see two clear streams of fuel in the primaries? If not some local carb cleaner and some gas treatment may help. You may also need to replace the pump diaphram again if already done.Martini, we disassembled every thing and soak it in a cleaning tank, some of those passages and very small and have right angles, can' imagine how one would clean any varnish or lime/scale build up. A rebuild kit was used so all the seals and such are new. no black smoke, the secondary's seem to work fine. My mech is going to water test it Friday he thinks when he sees it for himself he can figure out whats next. I can see the problem though and on idle or low speeds only 1 intake is getting fuel the other is dry as a bone...i think its got to be the passages.

ProStarMike
09-07-2005, 09:54 PM
So my boat won't idle, carb has been cleaned, yet still only one intake is receiving enough fuel to keep things barely running. I suspect there is varnish/lime deposits clogging the other side and thus results in low fuel flow. Am told it is very hard to clean the internal channels and perhaps a new/rebuilt carb may be needed. The boat runs ok @ full and 1/2 throttle but at any slower speed (less than 15mph) it will stall or puke from not getting enough fuel.

I see skidim has the 4160 Holley's, but isn't there a size bigger carb that i can use and is it worth it. Anyone have an extra carb in a box somewhere?

Any thoughts?

Sorry she's not running like she should! A few thoughts:

First off, bigger is not better when it comes to carbs. If you are keeping the same heads and intake that you have today (I assume it's factory MC), you don't want to over-carb the motor with some monster. It won't run well and you'll be unhappy with your purchase. If you are going to repower, rebuild, or change heads/cam/intake for more horsepower, then you can certainly upgrade the carb to match. Have your engine builder or the carb manufacturer recommend one that's right for your set-up if you change from factory components.

Secondly, while Holly makes a good carb, you might want to check out the marine carbs from Barry Grant (aka Speed Demon Carbs). Here is a link to their marine carb section:

http://www.barrygrant.com/demon/

The thing I like about Speed Demon carbs is that they set up the carb at the factory for your engine specifications...not one size fits all. You will get peak performance out of the box. If you do want to fine tune it down the road, it's much easier to adjust. They cost about the same as the Holly, too. And they look cool as hell! :-)

Edelbrock also has a nice marine carb product that I'd consider over Holly. Like the Speed Demon, they do some tuning at the factory for each application, so it will run great right out of the box.

The cheaper option would be to rebuild the one you have. But I have not had good luck in past projects with rebuilt carbs. YMMV. Plus carb technology has gotten a lot better (just look at the Speed Demon and Edelbrock carbs) and with fuel at $3+ a gallon, you're going to gain some efficiency with a new carb over a rebuilt one from the mid 80s.

Good luck!

-- Mike

Storm861triple
09-11-2005, 03:32 PM
There have been some decent guesses on this thread but let's cut to the chase. The first thing you need to determine is whether your engine is not idling because it's too lean, or too rich.

Get it running, then bring it down as low an idle as you possibly can w/o it stalling (it willl probably be running pretty rough) and then manually actuate the accelerator pump, on the carb itself w/you finger. If doing this brings the engine "back", then your problem is that it's too lean -not enough fuel.

If the accelerator pump exacerbates the poor running, then it's too rich.

Please perform the above test, then post back here, so we can then pursue this issue in an educated fashion.

alecams
09-12-2005, 12:43 PM
I can't image it being lean as nothing has changed, still the stock jetting in the carb. Yes the acc pump when manually activated will prevent the stall. I suspect there is a smal blockage somewhere in the left front barrel as at idle little/no gas is seen dripping in the motor while the right barrel has plenty (so yes not enough fuel but yet not necessaliy a lean condition due to jetting). When the choke comes off the idle goes to hell. Today we are pulling the front float bowl and cleaning with air & cleaner to confirm all passages are clear. I hope to water test tonight too. my feet are getting itchy.......

Storm861triple
09-12-2005, 01:26 PM
I can't image it being lean as nothing has changed, still the stock jetting in the carb.....

Yes the acc pump when manually activated will prevent the stall. When the choke comes off the idle goes to hell.

There you have it: It's lean. The accel pump and the choke prove that. It doesn't have anything to do w/"jets" or "jetting". You're right, those are fixed. But the jet's don't control the A/F ratio at idle; the idle mix screws do.

You either got a piece of crud in your idle passages, or your idles screws are turned in too far, either from your rebuild or from vibration (unlikely). I'd say there is a piece of crud in the idle circuit. Use a piece of wire or use brake cleaner and shoot it forcefully through every passage way.

-Tom

alecams
09-12-2005, 09:27 PM
Storm,
after reassembling carb bowl and assuring every passagve was free, the boat started great, and after warming up i got the base idle down to about 1k. ran great for 30 minutes or so and then suddenly wouldn't idle very well, i guess i'm back to that lean condition. especially when just clicking into fwd gear is really dies and needs some finess to keep going. i have the enricher (air screws) out 2 turns (std i am told). Again was thinking of pulling the bowl and recleaning again thinking its getting plugged somehow. the fuel filter is new so i assume we can rule that out. have not checked fuel pressure, perhaps after some time it drops but that doesn't make sense.

anything above slow idle or slow speed it runs great, 1500rpm+ to WOT.

i do have a question though and that is at idle, should i be seeing gas dripping from the carb to the bottom butterflys? as tonight after warming up and bringing the base idle down i noticed there was no noticable fuel dropping in the barrels. is the proper fuel delivery at idle via internal ports and should not be seen?

this is frustrating as i can't ski cuz no one else can keep it running.

redmike
09-12-2005, 10:56 PM
alecams, no, you should not see gas dripping into the bottom of the butterflys at an idle. When you had the bowl off of the carb, did you take the idle plate off and clean it, or did you just clean the bowl?

alecams
09-13-2005, 08:59 AM
Ok so no gas dripping is some progress, thats good.
I idle plate meaning the piece between the bowl and the carb body? Isn't that the metering block? Yes we cleaned it with cleaner & air. I should also mention that when the idle went to hell there was some surging, which i guess is expected being lean. What about the fuel accelerator, can the stroke be adjusted to help with the initial off idle response?

Below is some steps i have been told to follow, yet i don't understand the difference between #3 & #4. Is #3 the base idle?
1. Fully warm engine and ensure choke is fully open.
2. Air cleaner in place.
3. Set desired speed with the air screw.
4. Adjust the Idle Mixture Screws on ONE side to get the maximum possible RPM. Do not go rich beyond the maximum speed point.
5. If the above changed the idle speed more than 40 RPM, then readjust the speed.
6. Adjust the side OPPOSITE of that in Step 4 to get maximum RPM.
7. Reset the speed.
8. Carefully trim each Idle Mixture Screws to again get the maximum idle RPM.
9. Go leaner just enough to get a 20 RPM drop in speed.
10. Reset the speed to the desired RPM.
11. This is a Lean-Best Idle Set. Setting richer than this will not improve idle quality or performance, but could tend to foul plugs.

redmike
09-13-2005, 06:32 PM
sounds like that is what they mean, and yes I meant the metering block, just couldn't think of the "real" name at that time.

Storm861triple
09-14-2005, 01:41 PM
Storm,
the fuel filter is new so i assume we can rule that out. have not checked fuel pressure, perhaps after some time it drops but that doesn't make sense.

anything above slow idle or slow speed it runs great, 1500rpm+ to WOT.

You're right, it's not the fuel filter and deminishing fuel pressure over time is HIGHLY unlikely. Even if that were the case, power under load would suffer long before idle and your symptoms are the opposite.

#3 and #4 aren't right.
You need to set the desired idle speed w/the throttle stop adjustment. THEN adjust the idle mix screws to obtain the best/highest RPM you can muster from it, doing one side at a time. After you have maximized the idle air/fuel adjusting screws, your idle speed will most likely be too high and you'll have to back the idle speed back down some w/the throttle stop adjustment again. Doing this will make the idle circuit more sensative, and you can probably get another improvement w/the idle speed adjusting screws again, and lastly, make the final idle speed adjustment w/the throttle stop screw. Then you'll be done.

What Redmike said about seeing fuel dripping at idle. You shouldn't see that. If you do, that is caused by one of two things; either you have the throttle stop screw so far turned in (holding the throttle open) that you're pulling fuel out of the main discharge nozzle), or you're float setting is too full for a variety of reasons and it's pushing fuel through the main discharge nozzle at idle when it shoudln't be.

The fuel for idle discharges from a tiny "slit" just below the throttle plates, so you should never see any fuel flow at idle. In cleaning the carb, you need to make sure that you clean the passages in both the metering block (as you have), and ALSO, in the throttle plate. An obsruction in the tiny passages that go through the throttle plate (from the metering block to the point of fuel discharge), will give you the symptoms you are seeing now.

Also check for vacuum leaks that are intermitent. A PVC hose that is cracked and flexing, somthing that is heating and opening w/time? Check that stuff too.
A vacuum leak will give you the symptoms that you are experienceing, but they are GENERALLY consistent. Not always though. One more thing to think about.
-Tom

alecams
09-14-2005, 01:52 PM
going out again tonight to try after another clean. I was thinking of getting the base idle down to just 1k rpm rather than trying to go down the extra 200-300 rpm. Is there anything wrong with a slightly higher idle at 1000-1100 rpm for the time being?

I also noticed the gasket on the inside of the metering block appears to cover one of the holes in the lower half by 15-20%, perhaps this is blocking fuel during idle? what thinking of shaving a few hairs off to make it match the hole better... what do you think?

alecams
09-15-2005, 04:15 PM
Well, last night brought other problems. seems the right exhaust hose melted, obvioucly from not getting water through that portion of the system. so the carb issue is on hold until further notice.

Storm861triple
09-17-2005, 12:42 AM
Bummer. Let us know when you've gotten that fixed and you're back on the carb issue.

going out again tonight to try after another clean. I was thinking of getting the base idle down to just 1k rpm rather than trying to go down the extra 200-300 rpm. Is there anything wrong with a slightly higher idle at 1000-1100 rpm for the time being?

I also noticed the gasket on the inside of the metering block appears to cover one of the holes in the lower half by 15-20%, perhaps this is blocking fuel during idle? what thinking of shaving a few hairs off to make it match the hole better... what do you think?
1K is fine...for now. But it should idle fine from 600-700 RPM once it's "dialed".
I think shaving the gasket is fine as long as there is enough material to seal the bowl. Don't forget to chase teh idle passages in the throttle plate.

-Tom