I have been having a problem with fuel flooding into the manifold and I’m not sure what its root cause it. I did read Keith Kibbe’s NCRS Restorer article “Holley Internal Leaks” and it got me thinking that this may be a common problem with other Holley carbs. I figure others with the 3x2 setup may have experienced this before and may be able to share their experience.

My problem is a bit more acute. I was actually driving the car when it seemed to become overwhelmed with fuel. I managed to get it home without it stalling. When I tried to restart it for troubleshooting, it would not start – flooded! I pulled all three carbs and slowly did an open and inspect. There were no obvious signs of anything failing. But there was about 1/4 inch of fuel pooled in the manifold. I replaced the PV, needle and seat and the metering plate gaskets (in all three carbs). The floats looked good. The only gasket I did not replace was the base-to-body gasket, but did tighten the screws. Still haven’t been able to get it started – and yes, I checked the timing…

Anyway, to make a long story short, if the base to body gasket is dry or not sealing, can the bowel fuel leak into the manifold if left to sit for a while? Can the engine suck fuel past that gasket if it’s not sealing completely?

Appreciate any and all responses…

Thanks

 

Just a stab at it, but did you replace the power valve? 1 engine back fire will kill it. Make sure to use the correct gasket for the valve your using and have it the proper size for engine vacuum where you want it to enrichen.
Z QQH 6

 

yes, the power valve was replaced...

 

The only other thing I have seen is the center carb will leak down after shutdown if throttle plate is open too much from improper idle setting.
Flooding while running?? Carb works on vac. Sure you got all the right gaskets for metering plates?

 

Have you tried removing the screws on the side of each of the bowls to check the fuel level in them? The fuel should be high enough to barely dribble out. Any more is too much.

 

High fuel level, blown power valve....just because it was replaced doesn't mean it's good....had the same thing happen to me many many moons ago...new valve was worthless....take the valve out and suck on it..if the valve doesn't hold vacuum, it's worthless.

 

Hey all..

Yea, this is all to wierd.. still hunting this problem down. I did check the new and old power valve before replacement. I finished changing out the base plate to body gaskets, and three new floats today. Put all three carbs back on. I did go through an adjust the floats so just a little fuel dribbles out when the level screw is removed. Still not firing up. May be flodded becaust of the mokeying arround. Starting pulling pluges and most are dry. Found two, 3 & 5, that were soaked. So, I'm still digging.

How much fuel in the manifold is too much? Each time you pump the peddle tha accel pump puts 30cc of fuel in there. after about 5 - 10 pumps, seems its puddeling up pretty good!

Gonna start looking at ignition now... running out of ideas..

 

When there's enough fuel in the manifold that it dribbles into one of the cylinders and fills the combustion chamber to the point of hydraulically locking it, that's too much fuel.

I'd say if the walls or floor of the intake were slightly wet with fuel that's normal but if you're seeing puddles that's way too much.

Although my earlier comment may sound a bit sarcastic there's some truth to it. I've seen many engines damaged where a stuck fuel injector continued to pump fuel in before the motor was fired. Then when the customer tries to start the motor the engine gets damaged. The results are usually a spectacularly bent conn-rod, piston damage and more.
Be aware of this if you are really experiencing a LOT of fuel in the intake.

Have you checked your fuel pressure up near the fuel manifold to the carbs? I'm wondering that if fuel pressure was excessive due to a faulty fuel pump that it's overcoming the seating pressure of the float needles.
Just a thought. I know we're talking 3 Holleys here but I've heard that Rochester Q-jets were prone to this. That's why they use a fuel return line and an internal pressure regulating fuel filter. Later pumps for Q-jets regulated fuel pressure internally.

Another thought is to suggest using a shot of starting fluid into the center carb. I've found starting fluid works very well at clearing out a flooded motor. The motor will fire up just long enough allow the engine to burn up the excess gas. A big puff of black smoke later and the engine will be purring like a kitten. Make sure your choke is blocked open when you do this.

 

Well, I decided to send the carbs off for a flow test. He offerend to do it for free. I hope to be able to eliminate one problem. Good advice on the hydraulic lock. I was really tempted to pick up the starting fluid, but felt I had other options rather than a force firing!!! I'm planning on pulling all the pluges, and doing a complete purge and maybe a compression test to verify that I dont have any other problem while the carbs are gone.

The fuel pump on the 69 had no return line, so I guess it could be suspect for "over pressurizing" the system... but how likely is that?

Thanks for the feed back...

 

Cars equipped with Holleys have no return line. The '68 and '69 fuel pumps don't have a return line, the filter does if it's Q-jet equipped. I've read that the reason for this is that the Rochester carb has one small float bowl which services the primaries and secondaries while the Holley carbs have two, much larger float bowls. In the case of the tri-power, three. The Holleys are less prone to high fuel pressure overiding the regulating action of the float needle and seat....or so I've read.

One of the quick and dirty tricks I've always used to discern whether the ignition system or the fuel system is at fault for a no-start is to use the starting fluid. If the engine fires on the starting fluid, it is likely related to a fuel problem. If it doesn't, this may indicate that the problem is elsewhere. Not very sophisticated, but for lack of availability of other tools or time, surprizingly effective. A no-start with starting fluid may also indicate valves that aren't sealing etc. but even then, you'll get a backfire or stumble if the spark plug is firing.

You may also want to consult with Lars Grimsrud. He hangs out in the C3 section and is very knowledgeable on Holley and Q-jet carbs.

 

Thats a great trick to keep in mind - using the starting fluid... One of the first things I did was to use my timing light to check and see if the distrib rotated and caused all the problems. I was able to set the timing .. had spark on No 1 anyway! I will have a can ready when the carbs come back...

Thanks

 

How did you make out?? Watch that starting fluid stuff...its known to have bent a few valves when timming was off.

 

Well - I got my carbs back and put them on today. Before putting them on, I went ahead and ran a compression test on all eight cylinders - they were all about 150lbs +- 5lbs. So, I dont think I have anything major going on. Put all the plugs back in and put the carbs back on. Its seems as though they may have been leaking down with all the fuel I was finding in the manifold. They bench tested okay so I think I eliminated one problem.

So, after everything was buttoned up, I hit it with some starting fluid - and it fired... briefly.. but would not stay running. I was able to do this three times... all three times it fired up, then died out....

So, I'm thinking BAD GAS or a bad fuel pump... what are the odds? starting to run out of stuff to check...

 

The compression check results sound OK. Check.
The fact that it fired means you've got some spark. Check.

Check to make sure that all the cranking you did got fuel up into the carb float bowls. Make sure the float level is OK. Open the throttle on the center carb and see if you get a pump shot into the venturis. Some times you gotta pump the gas a few times while cranking to get it to keep running long enough that the float bowls fill up.

Look in your tank to check to make sure there's not water or substantial rust in there. Might be hard to see but you'd see bubbles of water at the bottom of the tank if so. Vettes are sooo convenient for this check. No smokin' while lookin', though!

If you can get access to a fuel line pressure gauge, check to see that your getting decent fuel pressure out of the pump to the carbs. I think about 6-8 psi is good but double check in your service manual if you've got one.

I assume you didn't mess with the distributor and that timing's ok (or close) since you drove it last. You may want to check just to make sure.

I might suggest removing the cap from the distributor without disturbing the wires if you can and check the points gap. Going from memory here but should be about 0.025" for a start. Even though it fired, the spark may be weak. In fact a new set of points, plugs, rotor and condensor wouldn't hurt if it's been a while since those were changed. Even look into a set of wires if it's been awhile since those were replaced. If you change points, you'll need to set dwell once it's running and adjust the timing.

If there's someone in the area who can check your coil or let you try a new one, I'd look in to that too.

Good Luck. Too bad I'm not closer I'd come over and lend a hand. On second thought, the weather really stinks here in MI and I've got spring fever bad. Since you're in SC, I'll be right down.

 

Thanks for the tips. Dwell, timming, points, rotor, cap, wires are all good/new. Checking the timming was the FIRST thing I did - then the points/dwell. I did change the coil with a new one.

While I was doing the comp test, I had to run a return line to a gallon jug... because the fuel pump was still pumping... I just dont know at what pressure right now. So, I ordered a new one.

I'm gonna drain the tank this week... I can belieave its bad, but all these problems appeared right after I put gas in it. The tank was out last winter... its clean... spotless actually!

The main carb primes just fine... two squirts when throtteled. When I hit it with starting fluid, it fires up briefly... I'll throttel it, then it dies out like it flooded... really weird!



The only other thing I can think of - which is really a worst case though, is that I'm getting coolant into the intake... is this possible? It should at lease start and run rough.... show me some steam or something... like I said.. no water in the oil...

Temps were in the 60's today - Great BB weather! Come on down!

 

You should have been able to see some water in the gallon jug if that's the problem unless it's all in the carbs now. Wouldn't hurt to drain the gas and try new. Sounds like you've got everything else covered.

I've heard some horror stories about old gas, and water in the gas, so it's not unheard of. I friend of mine was having trouble with his riding mower. I found water in his gas tank. We then checked his 5 gallon gas can and about half of it was water!! I imagine there were some unhappy motorists where he last filled up.

I wouldn't say it was likely that coolant was getting into your intake. There is a water crossover passage in the intake but it is separate from the intake runners. If there was a coolant leak you'd most likely find it in the oil.

If the new fuel pump doen't work, another possibility may be a BIG vacuum leak. Only thing I could suggest here is to plug all vacuum lines connected to the intake including the PCV and power brake booster. If that doesn't help there could be a leak between the intake and cylinder head joint face but the fact that the car was running before makes me think this is unlikely. Also, are the throttle plates on the outboard carbs closing completely?

I have also experienced getting a bad condensor even though it was new. Changed points and condensor to "tune" up an old Mustang. Car wouldn't start afterward. Put old condensor back in and car fired right up. Again, I doubt this is the cause but who knows at this point? There's only so much to these old cars and I'm about out of ideas for ya.

Five inches of snow this last week and five more inches last night. We're already a foot over the total yearly snowfall and have March to go yet. Not good BB weather. Time to trade the Vette for a snowmobile. C'mon global warming!!

 

Eric,

Thanks for the tips - yea, I'm scratching my head on this one. I may end up digging deeping into the distro if the fuel pump and new fuel dont fix it. It does fire up with starting fluid though. Anyway, I've been getting home to late to work on it this week... I did check out your web site - nice ride! I ended up doing mine because of a leaky break as well... funny how some small thread can lead to large project!

http://home.sc.rr.com/jandre/

 

Hey Red, Just got an idea...Since the tripower's giving you so much trouble, how about a trade for my Q-jet setup He! He!!

Awesome car! Awesome attention to detail. Too nice to have out of comission for long. Hope you get it running soon.

I will remark that when I rebuilt my distributor I noticed that the upper bushing was starting to go. There's an oil resevoir for the upper bushing that the service manual states is a "lifetime" reserve. Ha! Ha! The lube in mine was all coagulated, dry and crusty. If that bushing wears too much I could see that adding considerable slop to the timing, dwell, etc. My tach drive gear on the main shaft was stripped prompting the rebuild.

I also used an engine hoist to pull and install my body. Worked great!!

 

Blue - I'll pass on the Q-jet setup...

I got the tri-power fired up this week end. It WAS bad fuel. I dont know what exactly was in it, but I'm willing to bet that it was kerosen or deisel fuel. The station I got it from doesnt even sell those types of fuels, so I know I wasn't spaceing out and pummed the wrong stuff in. That explains the white smoke I was getting...

I drained the tank and lines, and changed the fuel pump while I was in there. Dumped a fresh 5 gal of 93oct Exon in... Once I got the carbs primed, hit it with starting fluid and it fired up. Took a few min for the residual crap-fuel to clear but then it setted down. Took her out for a spin late yesterday ... va-room! Running like a champ! I'll be headed back to that station tonight to try to get some restitution! Thanks for the help!

 

Glad to hear you got it running. Don't feel bad, I just caught myself attempting to pump diesel fuel in my rental car this past week. I was wondering why the nozzle wouldn't go into the opening on this dern car, then saw what I was doing. Duuhh! Since the early Vettes don't have the obstruction in the nozzle, switching fuels would be really easy to do with brain switched to auto-pilot like mine often is.

Did you know that weed whackers WILL run on kerosene (albeit very badly). Don't ask me how I know!

If you got bad gas, there's probably a bunch of people in the same situation. Hopefully you'll get restitution.