Do I Really Have a Blown Power Valve??

[gregintexas]

Recently installed a reman Ford 351W. First time out, I primed the throttle a couple-three times and hit the key. It was flooded! We did get it running, and it ran well, but when I hit it, the engine started popping loudly, then backfiring and died.
My shop guy says the carb needs to be rebuilt, that it blew the power valve when I nailed it. Does this sound reasonable to you guys?
The engine started and ran fine at lower speeds after that, but no high speed runs now or it starts to backfire.
Does this sound like a simple carb rebuild thing?? Any help is really appreciated!

 

[calwldlif]

Re: Do I Really Have a Blown Power Valve??

Is it a holley carb?

 

[gregintexas]

Re: Do I Really Have a Blown Power Valve??

Sorry, yes. A 4 bbl.

 

[calwldlif]

Re: Do I Really Have a Blown Power Valve??

It is the common belief that
1 backfire will blow the valve.
Symtoms suggest it.
it is not a hard change, can do it with carb mounted.
Remove front bowl, metering block, Violin..............

 

[salty87]

Re: Do I Really Have a Blown Power Valve??

a backfire could blow the valve but i don't believe a blown valve will cause a backfire. i'm thinking timing but i'd check/change the power valve first. it's quick and cheap.

 

[bjcsc]

Re: Do I Really Have a Blown Power Valve??

Sounds like your timing is not advancing to me. I would check that timing was set correctly and then check to make sure it is advancing to spec.. I'd do that before doing anything with the carb.. While it is possible for backfires to blow powervalves, it doesn't happen very often and like salty87 said, the backfire happened first. What ignition system do you have? What's the history on the carb.? New?, rebuilt?, not used in 2 years?, etc...

edit: come to think of it, if your powervalve was blown you'd be rich throughout, not just at high rpm's...

 

[gregintexas]

Re: Do I Really Have a Blown Power Valve??

Full Gallop:
The ig. system and carb were stock, as far as I know, on this 1989 Bayliner Capri 2150. The enfine is a reman from Thunderbolt Engines in Houston. The mechanic who installed was to have fully checked it out, so I'd initially assume timing was set properly. Of course, that assumption could be a mistake.
Boat was run each summer before I got it. Where would I get details on changing the valve. salty87 and calwldlif both seem to think its a quick and simple fix, though life tells me that is usually an overstatement! Where might I get the part?
Thanks for all the input!!

 

[calwldlif]

Re: Do I Really Have a Blown Power Valve??

Greg
If you feel your power valve is bad
then change it.
A auto parts store that deals in some
"Hi Performance" should carry it.
To remove
Disconnect battery
Disconnect fuel line in.
Front of carb there is 4 bolts/screws remove
Gas will leak (I use paint can cap under 1 lower
screw and remove it first)
gently pull "bowel" forward /note gasket
after bowel there is a "metering block" / pull forward
gently to perserve gasket / note gasket orientation
in the back of the MB is the power valve.
(@1 in in dia bottom center of block
Unscrew/note number stamped on valve ex. 6.5
this is the vacuum that it opens/take with you to
store.
Reinstall reverse order.

Before you do this you should verify:
Wires are not crossing or grounding
Cap/rotor distributor correct
Timing set/dwell correct

Check carb float level/existance of gas
ther are 2 sight gauges/ 1 on back bowel
1 on front/ on the side of bowel 3/4 up
from bottom. adjust with top screw that has a
locking nut. CAREFULL the engine must be running
and some gas will spill.
Verify fuel flow from tank through filter

It is hard to know what your problem is from here
I cannot see it/touch it.
We/I am dependant on your discriptions/experiences

Good luck

 

[calwldlif]

Re: Do I Really Have a Blown Power Valve??

Note I forgot
The only pain in the arse is the feeder tube
from front bowel to back.
This tube has O rings.
They can/will leak if not gently placed
during reassembly.
A little lub can help

 

[bjcsc]

Re: Do I Really Have a Blown Power Valve??

The mechanic who installed was to have fully checked it out, so I'd initially assume timing was set properly. Of course, that assumption could be a mistake.
Boat was run each summer before I got it. Where would I get details on changing the valve. salty87 and calwldlif both seem to think its a quick and simple fix, though life tells me that is usually an overstatement! Where might I get the part?
Thanks for all the input!!

I'd check the timing and the advance anyway. Even the most competent techs can make mistakes (we're all still people you know) . I had my timing checked and supposedly set at the VP service dealer here and it wasn't even close once I learned how to do it myself and checked it during my month-o-boatfun. The powervalve is easy to replace, it just unscrews. It does have a gasket and the valve is specific to the application, i.e. it will have a number stamped on the housing from 2.5 to 10.5. This is the manifold vacuum level at which it opens. You probably have a 2.5 as it is the most commonly used one in marine engines, but check to make sure you replace it with the correct one. You're in luck as I scanned and posted the carb rebuild procedures from my Volvo manual and they are still on the free server I put them on. They are for a 2bbl, but they show the powervalve on page 4 of the PDF, page 2-14 of the document. It is "D" in number 2. You'll only need to take down the primary bowl. As already mentioned, there are seals on the crosstube that runs to the secondary bowl. Mine are not o-rings, but rubber cups. Whatever you have you'll want to replace. I would take the carb down first, then take every gasket, o-ring, seal that came out and the old powervalve with you to get your new parts and make sure you get them all (which you can get at any auto store that distributes Holley) . That way you won't be tempted to reuse something old if you didn't think of it in advance

http://www.freefilehosting.org/public/13113/VP 2V Carb.pdf