annoyed with the motorcraft

[superj]

had issues initially and put a new accelerator pump and power enrichment valve. worked good for one day and then a pop through the carb and back to having the original trouble.

no idea why it back fired through the carb, never done it before or since but it did.

everyone says the motorcraft is such a good carb for the engine but i keep finding stories of people having trouble after trouble.


so what ruptures on the power valve that makes it bad when you get a back fire through the carb?

 

[rock316]

had issues initially and put a new accelerator pump and power enrichment valve. worked good for one day and then a pop through the carb and back to having the original trouble.

no idea why it back fired through the carb, never done it before or since but it did.

everyone says the motorcraft is such a good carb for the engine but i keep finding stories of people having trouble after trouble.


so what ruptures on the power valve that makes it bad when you get a back fire through the carb?

hey hoss i have 2 spare carbs wana try them out

 

[808CJ7]

Bro you may want to pm gronk and see what he says. I had that problem with my Holley, it was dumping in too much fuel causing it to backfire thru the carb.

 

[RudeDog]

Haven't worked with a motocraft carb. On Holley's the diaphram rips or tears. This allows excess fuel to trickle down in to the cylinders (run rich) if not burned up it can go past the rings and into the oil. Way back I lost an alcohol engine to bad power valves. The excess went past the rings, thinned the engine oil out and I seized a crank and 3 rods. Now with alcohol your flowing much more fuel than gasoline engines.

 

[superj]

that must be what happens then because this is a holley power valve. the motorcraft is made by holley for ford.

jake, what do you got?

 

[808CJ7]

What type and size power valve are you using? I believe a single stage 8.5 or 9.5 works best. Also the rod going to the accelerator pump should be on the second hole from the top.

 

[superj]

i have the 8.5 and i tried all the hole settings for the rod but i think its on the top right now

 

[808CJ7]

Moving the rod down slows the fuel shot. On the accelerator pump side,inner hole is more fuel, outer hole is less. Mine came from gronk on the second hole from the top and the outer hole on the pump side. Also 8.5 single stage pv. I believe you said yours has the 1.14 venturis which equal 300 cfm. The 1.08 is 287 cfm. Not that much of a difference

 

[superj]

the inner hole shoots more fuel?

i think slowing the shot down would help. you mean, though, it makes it start later or it makes it take longer to squirt completely?

 

[superj]

and mine is a 275ci engine so i figured the 1.14 would be better then the 1.08 since hte 1.08 works well on the 258ci engines

 

[808CJ7]

Oh yeah, I forgot yours was stroked. Your right, I would think the 1.14 would be perfect. If you have more mods, bigger cam and stuff you may need more on the intake.

 

[RudeDog]

PS: Standard (safe) practice is to replace power valves if you have a back fire though the carb (better safe than sorry). From what I read they can be tested, but i believe it requires a certain type vacuum tester..

 

[808CJ7]

Yep. And there's the old school method of using your lips and tongue to test the power valve. Doesn't taste very good but if it holds it's fine. Lol

 

[superj]

what, just suck on it? i think its bad so i'll get another, just in case

 

[808CJ7]

Dude, that's cutting edge technology right there haha ha

 

[69jeepcj]

In your first post you asked what would make it backfire through the carb. TIMING! Your engine is stroked, your timing will not be as others with stock 258's. Yours will be more advanced probably. Read up on dist timing recurve kits and when they are needed, not saying thats what it is but its something to look at as a posibility. Incorrect timing curve can also cause backfireing through carb. If you end up getting a recurve kit in the future for the HEI, DO NOT USE THE WEIGHTS THAT COME WITH IT< JUST THE SPRINGS. throw the weights in the garbage, use the weight that are already in it.

 

[superj]

i have found the trouble, besides the power valve being bad.

that adapter under the carb is leaking, fairly badly. so i have horrible vacuum leaks. it appears that whenever you use any adapters, you have to rtv them down. i figured since i used all new gaskets and everything, that would be sufficient because normally i rtv the crap out of everything on a jeep motor but i was wrong, should have rtv'd it this time too

 

[69jeepcj]

Cool, simple solutions are always nice!

 

[808CJ7]

Mine came with the thermo spacer that goes between the adapter and the carb. It's suppose to correct the misshaped mr. Gasket adapter I have. Glad you found the problem.

 

[gearheadmb]

Every time i have ever replaced a carb and it had a thick (roughly .25") gasket i have had to retighten the carb bolts after the first few hours of use because the gasket seems to shrink causing vacuum leaks. I wouldnt jump into rtv'ing it down. I avoid rtv whenever possible. It looks sloppy and makes for alot more work next time you have the carb off. But i guess you gotta do what you gotta do.