I hope someone can guide me. I have twin 327Q's both were re-built approximately 150-200 hrs ago. The starboard engine had the carb re-built twice by the previous owner due to stalling.
My problem seems to be one that is common. I run the boat for a day on the river and both engines perform perfectly. The next time I use the boat my starboard engine stalls as I idle out of the slip. It seems to happen when I reverse the engine to turn the boat. After the stall it takes a few minutes before it will start again.
Now I've read many entries on the web page and I believed it was a fuel flow problem. I changed the seperator and the stone filter in the carb and this will seem to fix the problem for a short while but the problem returns. Recently I switched the starboard engine over to the port fuel tank running both off of one tank and had a great day on the water. I figured I cured the problem and I would empty the starboard tank and get it cleaned out. But guess what happened the next day. Stalled out again when leaving the slip and my wife and I had a hell of time keeping the boat off of my neighbors anchors due to the breeze.
I'm out of answers and don't know what to look for next. Before I rip off the carb I turn to the knowledge of those who came before. Any guidance would be greatly appreciated.
First I'd swap carbs between engines and make sure it is the carburetor causing the problem. If you swap them and the problem persists on the original engine, it obviously isn't the carb. Confirm it is the carb. Second, idle mixture adjustment and idle speed must be set with the engines in gear. Is the choke opening properly?
Ascertain it is indeed the carburetor first by swapping between engines.
The problem with clean carbs, is they can get dirty in a heartbeat once you hook it up to a dirty line. You can get debris off the fuel pump, and if you have one of those cast aluminum filters like the 327F has bolted to the front of the 327F motor, it may be literally full of junk. I put a RACOR fuel water seperator on a recent project boat as protection, and also a final filter right before the carb, to protect the fact that it was a new carb and didn't have any dirt in it. I used a fuel injection filter, and fuel injection clamps (again, as I always say, this is not a "recommendation", it is what I did on my motor, rightly or wrongly).
In the end, if you have a clean carb and good fire from the cap, wires, plugs, and if you time that motor to the dimple on the flywheel, it should idle down very reliably.
There is a remote chance you have blockage at your fuel tank, and sometimes you can test this by drawing down some fuel from the fuel line and looking at what you get, if you have a manual suction gun, you can hook it to a container and pull some out rather than letting it flow, which would draw any debris with it. As ethanol becomes a fact of life on the East Coast, Great Lakes, and elsewhere, this sort of thing will become more of a routine diagnostic for we old boat boaters because ethanol is a solvent for the stuff that forms on the inside of the old tanks.
Normally what I do is to start a process of elimination. Bill is right on target with swapping the carb, that is an excellent place to start.
Well I swapped the carbs and both engines performed beutifully. I had to adjust the idle a bit but we took her for a cruise and no stalling. Next week when I get back to her will be the real test. Whenever I change a filter or just swith tanks she runs fine until the next time. I'll see what happens next.
Well thank you gentlemen. I was sure I could get some guidance and I did. I now have a new project for the weekend and surelly I'll get some answers. We're expecting the remnants of Hanna to hammer the North East on Saturday so I wont be leaving the slip. I'll let you know how I make out and thanks again.
The same thing happened to me.Mostly its the SPARK Plugs,You need Champion J12Y's,they are a HOT Plug and it stopped My Stalling,Now another thing is MOISTURE gets in the DISTRIBUTOR CAPS,Keep the Blower On and see if that Helps,Also Im taking my Q Motors out of my 31 Commander and will be selling the Vital Parts and Trasnmissions if you know anyone,I will be a while before i get them Out,I have to go DIESEL..Dennis Sacco
make sure they aren't stalling due to the carb flooding. The engine will be running rough and uneven. When the engine dies immediately put the trans into nuetral and hold the throttle wide open (keep your hand on the throttle because if it starts it will go wide open, so you have to pull it back quick). Try to start the engine, and if it starts get the engine speed back down. This will tell you have a rich condition,i.e. flooding. You have to turn the starter long enough to clear the excess fuel out of the intake before it will start. Be careful with backfires, keep the flame arrestor on. You will see the black exhaust smoke if it was rich.
Bill and Paul are right as usual, some other things to check.
When the carb is running on the idle circuit you shouldn't really see fuel dripping out of the venturies. Make sure the choke plate is wide open when the engine reaches running temp (if it isn't adjust it), and look down the throat of the carb(flame arrestor removed) and idle speed at around 750 RPM or less (varies a little with engine and carb type). You should not see any fuel dripping, as the idle circuit fuel is coming in below the throttle plate. Always make sure the ignition system is up to par before trying to diagnois carb problems. The carb has to have the correct intake vacum and air velocity through the venturies before they can work right. You have to have 8 good cylinders, proper cam timing and a good ignition system. What causes the carb to flood?
Idle fuel mixture not adjusted properly
High float level
Dirt in need and seat
Dirt in internal air passages
Warped mating surfaces allowing vacuum leaks, etc
After switchimng the carbs I'm stalling on the port engine now so I believe it to be a carb issue. I pulled both carbs off , took them apart and cleaned them both. Floats appear to be good. I want to get rebuild kits but seem to have a problem finding the right kit. The carbs are Carter AVS number 6117, however when I look up the carbs they look like Carter AFB's. Not sure which kit to use and I cannot find a supplier of kits in NY or NJ metro area.
Ray
Ray, send in a photo or two of the carb, it won't take long for the group here to give it the proper ID. Assuming they are stock carbs, which is a risky assumption, they would most likely be the AVS. Carter AFBs will bolt right on, so they could be either.
It will take Mark Weller 2.5 seconds (or less)......
September 28 2008, 12:07 PM
.....to identify that carb. You can post directly with an uploaded direct photo link or email directly to me at chriscraftcommander@hotmail.com and I'll upload it for ya.
Most stalling at idle is caused by a lean condition. A new kit won't help if there is a plugged idle jet or an air leak. If the plugs are sooty, then it's rich from slobbering fuel. Are the secondaries closing completely? Do the idle mixture needles have much affect? If it's been rebuilt a couple times already, something else is going on.
Thats the same carb I have use NAPA carb kit #2-5300 or there are many places on line to get them. almost forgot Car Quest #441 can also be used any more questions?
Thank you,I found the kits through my NAPA dealer and you are right they are 6117 AVS. I'm going to clean them up and rebuild them while I have them off. I hope to have them done for the weekend so I can run up river to Kingston. With all the direction I'm getting from you guys I'm confident my problems will be corrected. I'll let you know how I make out.
If your carbs are especially dirty, you know the dirt got in through your fuel system, and you know your filters were not doing their job. When you rebuild, you might take the opportunity to install new filers too.
My feeling is..the "settings are relatively unimportant.
Float level..because the cabureretor sits at a steep angle and changes with the angle of the boat, this must be adjusted to compensate for your specific mounting conditions.
Choke stuff..again, affected by individual application.
Accelerator pump..I always go for maximum, especially with alcohol laced fuel.
Enrichment circuits..most open at 6-9" of vacuum. This means the typical marine carb is usually running kinda rich, which protects the engine and hurts the wallet. Only Holleys are easy to correct.
Secondary opening..usually too early for marine engines. The secondaries should NOT be open at cruise.
Bill, you have a good point about the specific mounting conditions. The marine settig for CC would encompass the entire range of applications from small runabouts to the larger boats up to 35'. The mounting angles in these boats does vary quite a bit, especially during running conditions such as a nose up running condition in a runabout. This is magnified with a runabout due to the fact that if the motor is an inboard, the installation angle is pretty steep to begin with.
This because quite interesting with my Edelbrock swap on the 327F, the carb fit nice, worked pretty well, but I discovered some conditions when the gravity controlled parts were starting to bind. I had the choice of using a wedge or grinding on the parts. Since I had the wedge on another boat, I made the swap to see how it worked and it worked just fine. Without the wedge the carb would not work properly out of the box, therefore it had to be adapted to the specific running condition as you noted. Float settings, etc., are all undoubtedly a compromise within the range of expectations, across the board. One only wonders what the ideal setting would be for each individual boat.
"My feeling is..the settings are relatively unimportant." Well I tend to disagree you need a starting point for any carb and considering the AVS is a rather rare carb for Chris Craft you don't want to just start picking stuff out of thin air.
"Float level..because the cabureretor sits at a steep angle and changes with the angle of the boat, this must be adjusted to compensate for your specific mounting conditions."
This Carb was only used on the Q motor as far as I know and it has a wedge built into the intake manifold to compensate for the angle. So the stock float setting works just fine.
"Choke stuff..again, affected by individual application."
Tim Toth would argue this one he is meticulous about setting his chokes to the exact specifications down to it being the right temperature when he does it and his motors start better than any others I have seen or heard. (ask Paul)
"Enrichment circuits..most open at 6-9" of vacuum. This means the typical marine carb is usually running kinda rich, which protects the engine and hurts the wallet. Only Holleys are easy to correct."
The metering rods used on the Carters I agree are absolutely useless on a marine motor you are always running under load. That's why I dont have them Carter got rid of them on some versions of the marine AVS.
"Accelerator pump..I always go for maximum, especially with alcohol laced fuel."
Don't like that idea at all too much fuel on the acelerator pump washes the oil off the rings and pistons meaining premature wear of moving parts and increased fuel consumption.
"Secondary opening..usually too early for marine engines. The secondaries should NOT be open at cruise."
Thats the best thing about the AVS carb extremely easy to control the openning of the secondaries a simple screw and spring system I can go to 3500 rpm and not get into the secondaries
and mine are set to the settings on the sheet.
Float levels: Float levels basically affect the point at which the crossover from idle to main metering occurs. It has essentially no affect on overall fuel metering. Way too high, and fuel will slobber into the venturis. Way too low, won't meter properly. Actual metering is controlled by the main jet, metering rods on some carbs, air correction jets, and emulsion tube calibrations. Only the mains are usually available replaceable. Engines that stumble at about 1500 rpms are usually victims of low float levels, as the crossover is too lean. The idle circuit only meters when the throttle plate is adjacent to the idle port/slot. Good ol' Bernoulli at work.
I rebuild and dial in carbs as a sideline. I've got vacuum gauges on my twin 302's w/Holleys to observe actual conditions. After decades of dialing carbs in, I've learned marine applications have so many variables it is dangerous to say one setting fits all. The printed settings are a great starting point, but don't assume they are perfect or even adequate.
Choke settings: Those bimetallic thermostats are notoriously inaccurate, whether electric or heat well heated. Be aware that many times there is a fast idle cam attached to the choke..the more closed the choke is, the higher the idle is. A COLD engine won't idle slowly..not enough velocity in the intake to keep the fuel vaporized.
Accelerator pump: Marine engines run relatively cold. As such, fuel vaporizes poorly in the intake system. The only way to get a decent shot is to make the pump fat. This is very important on carbs with secondaries, as they tend to bog. The amount of fuel momentarily injected is insignificant in the big picture on marine engines, as the throttle is not moved very often.
Frankly, I have little experience with AVS's. Like quadrajets, the secondaries are easily adjustable for opening point. I think quadrajets are great carbs, but limited by unavailability of tweaking parts. The tiny primaries are great for street applications, but are marginal for marine applications without opening the secondaries. I evaluate each carb and application on its' own merits or disadvantages, and proceed accordingly.
Enrichment circuits: I've yet to plug my Holleys power valve, but it doesn't open until 3" of vacuum. A holley power valve is good for 4-8 jet increments of enrichment. We agree these are relatively useless on marine applications.
Secondary opening: if your secondaries are open at cruise, it may be caused by other factors such as overpropped, restricted flame arrestor, lazy timing. If the secondaries open prematurely, a fringe detriment is as the manifold vacuum drops, the power valve/enrichment circuit opens. This causes a richer mixture than needed, which removes money from your wallet rapidly.
So, has anyone reading these threads learned anything? There's a test at the end of the week.................
Bill being an old MOPAR guy from my teens I am familiar with the Carter carbs and mopar used the avs a lot. At one time there were tons of tweaking parts for the Carters unfortunately with Carters demise a lot of those parts are gone now. The new Thunder series of Edelbrock carbs are based on the AVS design. But having never seen one I have no idea how close they are. Unfortunately they do not make marine versions of those carbs just the performance series are marinized. I agree with most everything you said. And I can see your point about marine motors being cold blooded on the accelerator pump deal but how often do you slam the throttles down? As far as chokes yes the spring controlled chokes are not real good but with some work mine are fine. How Tim Toth gets his so perfect is amazing but he is a fanatic about them. On eother thing about the Carter is the check valve they need to be replaced every so often to keep the carb from bleeding down and draining the bowl dry makes a big difference in cold starts. I like your methods vacum gauges on the motors in real time is very nice to have and they will tell you a lot.
OK everbody like Bill said paying attention? Test later this week!
From what I've read, the AVS is an air valve similar to the quadrajet set-up. This set-up provides a much smoother transition when opening, and is much more accurate, being controlled by airflow. AFB's used a counterweighted air valve, as I remember wasn't as easy to adjust. Holley uses a vacuum secondary on some carbs..this vacuum is flow generated at a venturi, not manifold vacuum.
On my 302's w/450 cfm Holleys, I get 4200 rpms wide open. At 3000 rpm cruise, vacuum is about 6". This drops rapidly as the props get dirty. If the secondaries open, it really drops. I suspect a quadrajet with the small primaries may get slightly higher cruise vacuum. Quadrajets use a power piston system with metering rods, which is held closed by vacuum against a spring. I think AFB's use a similar set-up. They're also useful for idle set-up, but I always fall back on the "lean 'em until the engine stumbles, then fatten a 1/2 turn. This is substantiated by the vacuum readings. Interestingly, my 2 engines have about 3" different vacuum at idle, probably due to differences in cam timing and connecting rod offset.
Quadrajets have a similar leaky well plug that causes dry starts. There's enough fuel in the accelerator pump to light off....once, briefly.
Because of the cold nature of marine engines, and the fact that often the throttle is "firewalled" rather than opened gradually, I still prefer a maximum accelerator pump shot.
We haven't even discussed inlet air temperature or the effect of flame arrestors on breathing. Or timing.
