Carb question- Signs of blown power valve?

[stashtrey]

I'm thinking my carb has a blown power valve.
After going through my head of the last couple weeks and dealing with my engine here is what has happened.
Majore difficulty getting engine started.
Took to mechanic... reset timing at 35 btdc (460 Engine). Installed Pertronix electronic conversion. Got engine started but said I had gas built up in my cylinders. Cleared out cylinders and did compression check..... said I lost some compression from the gas messing with the rings????
Mechanic said I needed to get out and run the boat for a good while to build up the compression. Suggested that my carb might be leaking and I should consider replacing it as it's rusted and old. It's a Holley 4 barrel 750 ( I think ).
Replaced plugs and took boat to the river.... took nearly an hour to finally get the thing started. It would gasp and cough and just turn over and over. Backfired through the carb several times. I pulled the plugs, turned the motor over a few times to clear it out.... cleaned the plugs and finally got it started.
The idle sounded good... a bit softer and more quiet than I remember it from last year. Let the boat get up to temperature.... had good oil pressure and started to ease into the throttle.... sounded good and then when I got up int he rpm's it just gasped and bogged out.
Could that be the power valve not letting enough fuel out to support the high rpm's? OR... could that be the power valve letting too much fuel out and and drowning the plugs and causing it to not ignite all the fuel?
As you can tell by my many posts.... I'm a novice and just trying to diagnose this thing. I just ordered a 750 Edelbrock Marine carb from Summit and plan to just replace my old Holley all together. I really just want something reliable and economical as my wife is ready to kill me.
Does that sequence of events/symptoms sound like a fuel/carb issue?
Also... after it bogged out several times I thought I possibly sucked something in my jet.... I put the boat on the trailer and checked and I had nothing. Tried to start it up again and I got nothing. No cough, no hiccup.... nothing but the motor turning over.
Could I have flooded the thing?
Any thoughts?
I've had tons of great info from all of you on this board. So many nice people offering their time. I really appreciate it.

[1978 Rogers]

When mine was blown it ran rough from about 2k to 3k rpm, above 3500 it seemed OK. It ran kinda bogging down. Hard to describe. If you were here I could duplicate the sound. :)

[FASTRAT]

i personally think u need to find another mechanic!!...if he's so good...he should have found the problem rite off!...anyways...the replacement of the carb with the Edelbrock 750cfm should solve ur probs & Ford's run good on that carb...just my .02 cents
fastrat

[DelawareDave]

A blown power valve would cause it to run rich. I also think fastrat may be on to something, as far as your mechanic is concerned. Cure the original problem first, then update stuff.

[1975sleekcraft]

i've had a problem like this with my holley 750 double pumper.
mine ended up to be a float was cracked and full of gas. my secondaries were flowing gas through the breather and flooding my eingine! replaced the float--ran like a champ!!

[Oldsquirt]

Stashtrey, even with a blown power valve the engine should have started pretty easily. At idle, some fuel will be sucked past the diaphragm and the power valve will be in the "ON" position all the time, meaning the main fuel circuit will be in the richer mode all the time. This is because the PV is spring loaded into the "ON" position and requires manifold vacuum to pull it "OFF".
I personally doubt that the power valve is your problem. A stuck needle and seat or a sunk float is far more likely to give the symptoms you describe. A quick check for this is to crank the engine with the ignition disabled(disconnect plug for the Pertronix or remove coil wire from cap and ground it). Watch for any fuel coming from the bowl vents or excessive fuel coming from the venturi boosters. You really shouldn't see any from these areas while cranking.
Any time you fuel foul your plugs you should clean them with a plug blaster or, better yet, REPLACE them.
Send me that old worn out Holley when you put the new carb on and I'll tell you what is wrong with it. You probably wont want to know how much it would cost to repair, though.:)

[502 JET]

With the power valve blown the gas from the fuel bowl could leak into the motor when not running and flood it out.This may be why you were having starting troubles.Power valves are designed to open and enrich the fuel curve at a specific number of inches of vaccume (number is on the powervalve).A power valve will open when the vaccume drops below that number and enrich the motor like having larger jets.With a blown powervalve the motor will run rich unless at WOT because excessive fuel is being pulled by vaccume through the blown powervalves diaphafram instead of holding the valve shut.I dont care for the Edelbrock carbs.The Holleys are easy to rebuild.The rebuild kit cost around $40. and two cans of carb cleaner and the carb will perform like new again.

[Duane HTP]

It might be wise to check your plug wire resistance and your coil. If you don't have enough ignition fire power getting to the plugs, it will act similar to what you've described.

[502 JET]

If you have been flooding your engine you should change your oil its probably full of gas.

[1968Droptop]

I dont care for the Edelbrock carbs.
I'll echo that. I've never had any luck with those carbs personally. I think the Holley is a way better carb, and easy to tune once you learn how.
Are you sure the engine was flooded ? Did you have it to the floor when trying to re-start it ? That usually gets enough air in to get it re-fired.
Any chance your losing a fuel pump ? Just an odd thought......

[Turboelimtim]

Did you experience a backfire? Typically something has to rupture the PV diaphram, unless of course it is just really old.
My engine had a pretty big backfire last time I was out. Then it would not hold an idle. I really had to nurse the throttle to keep it running. It seemed to run a little better above 2000 - 2500 RPM. I was to nervous running it any higher since I didn't really know what was wrong. I nursed back to the ramp and got it home. After pulling the carb apart, I found the power valve was ruptured. It was leaking alot of fuel back into the manifold at idle choking out the engine. I just put another one in and it solved the problem. If your symptoms are similar to what I described, you may want to try a new PV. Even if you buy another carb, it would be good to know if a blown PV really was the problem.
Tim

[watergun4u]

i agree with all above ,but you said that your timing was at 35 degreese, is that base timing or is that at full advance, if it is set at 35 base thats way to much, should be between 8 and 12 degrees at base and around 35 at full advance, so you might want to change that first, if at 35 base, that will cause motor not to start well at all!!!!!!

[stashtrey]

Thanks for all the feedback here.
I had the timing set at 35 at 3,000 rpm's as far as I know. I did not do it myself. When the engine was running it sounded pretty good....
I'm thinking that as Old Squirt said... the float/needle causing the problems. The reason I think that is because the mechanic said it had a lot of gas in the cylinders when I brought the boat to them. They got the gas out, set the timing and got the thing started. At that point they said it was good enough to run but suggested that my carb could be leaking and I should think about a replacement.
Mind you.... I was pressuring the guy to just get it running as I was in a hurry and had a trip planned..... they definitely told me that the carb seemed to be leaking and that might have been the cause of all the fuel in the cylinders.
They called me and said it was running and I went to pick it up... they took me to the boat and attempted to start it again and got the same thing. Several attempts went by and they pulled the plugs and they were black and you could smell the fuel pretty easily. The blew the plugs dry with an air hose and then we turned the motor over to get any fuel out. They then were able to get it going but it wasn't exactly easy. So.... I take it home with the suggestion that my carb has some issues.
I replace the plugs and then go to the river to run it and I get the same thing.... coughing a little but no start. Backfire out the carb several times. REmove plugs and they are black and covered in gas. Try to dry the plugs as best I could and turned motor over again to get gas out of cylinders. After several more attempts the engine finally coughs to life.... I let it get up to temp and go to give it some throttle and it starts going just fine..... then when I really get into it it just coughs and bogs out.... I couldn't get it to go high in the rpm's without it bogging and stopping.
I put it back on the trailer.... attempted to start it one more time and I got absolutely nothing. Not even a cough or a sputter.
That's the last that I messed with it.
What could cause the engine to bog out like that when it is idling just fine? I could gas it hard and it sounded strong but once I got high in the rpms it would just bog out.
I don't think it's my spark.... that seemed to be fine once I got the motor running....
Does everything lead to my carb?
The Edelbrock came in the mail today. I guess I'll have to wait and see if that was the problem.
Another strange thing I noticed was that when I installed the Pertronix I noticed that the mechanism in the distributor below the points/Pertronix device had a small spring that was disconnected. Could this be a big problem as well? I'm not sure what to think as once the motor was running it idled just fine and seemed to be firing okay.
Jeez... sorry for this novel. This crap is driving me crazy.

[spectras only]

Thanks for all the feedback here.
The Edelbrock came in the mail today. I guess I'll have to wait and see if that was the problem.
Another strange thing I noticed was that when I installed the Pertronix I noticed that the mechanism in the distributor below the points/Pertronix device had a small spring that was disconnected. Could this be a big problem as well? I'm not sure what to think as once the motor was running it idled just fine and seemed to be firing okay.
Jeez... sorry for this novel. This crap is driving me crazy.
The Edelbrock [ weber carb ] will work just fine . You should have a light primary and a heavy secondary spring under the breaker plate .The secondary [ heavy ] spring should have an alongated eye on one end to allow the advance to come on quick .