Gary Lewis Posted June 23, 2018 Share Posted June 23, 2018 Do you know if your stock power valve (PV) is a single or 2 stage unit? I had seen it posted (other forum) that someone had a 2 stage in the carb but the rebuild kit came with a single stage. PV's come in different sizes of HG they work. To see what size you need you will need to hook up a vacuum gauge to the motor in a way you can see it when driving. When driving you take the average of vacuum when driving under steady speed. Once you have this reading cut it in half and that is the size PV you want as a good starting place. Say you are pulling 13 HG half of that is 6.5 and this just happens to be what comes in rebuild kits. You can go up or down to see what works best for you. I know on older Holley's if the carb sneezed (back fired thru carb) it would blow out the diaphragm of the PV. New Holley's have a check valve to prevent this. I am thinking the Motorcraft 2100 & 2150 carbs would also blow out the PV if it sneezed but not 100% sure. Dave ---- Well explained, Dave. Yes, it easily could be the power valve since the accelerator pump appears to be working. And, as Dave explained, that's the problem with earlier Holleys - a backfire usually blows the power valve. There's a fix for their poor engineering in the form of a check valve that can be installed. But a blown power valve will cause the engine to be terribly rich, and I'm not sure that fits your symptoms. However, it is certainly worth a try. Link to comment Share on other sites More sharing options...
JMUBullnose Posted June 25, 2018 Author Share Posted June 25, 2018 Well explained, Dave. Yes, it easily could be the power valve since the accelerator pump appears to be working. And, as Dave explained, that's the problem with earlier Holleys - a backfire usually blows the power valve. There's a fix for their poor engineering in the form of a check valve that can be installed. But a blown power valve will cause the engine to be terribly rich, and I'm not sure that fits your symptoms. However, it is certainly worth a try. Gary - At this point I think I'm just hunting for answers on why the truck is stumbling at certain speeds, especially when accelerating up a hill or trying to accel to highway speed. Sometimes I have to come off the gas and then gently roll back on and it'll get thru the bucking. All the while I'm gritting my teeth worrying I'm going to break something even more expensive! Now that I have the choke back to where it was previously- the truck is definitely running rich. I'm going to also use this walk thru to set the choke, idle, etc: FMC400 Writeup Dave - Not sure on the one stage v. two stage PV. I'll have to figure out how to rig up a vacuum gauge to do what you've described. That's a good methodology - I should really just get myself a gauge! Link to comment Share on other sites More sharing options...
FuzzFace2 Posted June 26, 2018 Share Posted June 26, 2018 Gary - At this point I think I'm just hunting for answers on why the truck is stumbling at certain speeds, especially when accelerating up a hill or trying to accel to highway speed. Sometimes I have to come off the gas and then gently roll back on and it'll get thru the bucking. All the while I'm gritting my teeth worrying I'm going to break something even more expensive! Now that I have the choke back to where it was previously- the truck is definitely running rich. I'm going to also use this walk thru to set the choke, idle, etc: FMC400 Writeup Dave - Not sure on the one stage v. two stage PV. I'll have to figure out how to rig up a vacuum gauge to do what you've described. That's a good methodology - I should really just get myself a gauge! You know I have never played with a 2 stage PV I just know they open a little at 1 setting and then the rest at the other setting. To tell the truth I would just go with the 1 stage PV and tune for it. Cant help on how to run the hose / gauge that's up to you LOL But you said something about "stumbling at certain speeds, especially when accelerating up a hill or trying to accel to highway speed". Do you have the vacuum advance hooked up to your dist.? As a test remove and plug the hose and take for a test drive to see if it happens. Also try with the gas cap removed. Dave ---- Link to comment Share on other sites More sharing options...
JMUBullnose Posted July 12, 2018 Author Share Posted July 12, 2018 You know I have never played with a 2 stage PV I just know they open a little at 1 setting and then the rest at the other setting. To tell the truth I would just go with the 1 stage PV and tune for it. Cant help on how to run the hose / gauge that's up to you LOL But you said something about "stumbling at certain speeds, especially when accelerating up a hill or trying to accel to highway speed". Do you have the vacuum advance hooked up to your dist.? As a test remove and plug the hose and take for a test drive to see if it happens. Also try with the gas cap removed. Dave ---- I think I may have a 2 stage PV - that sucker sticks out a fair bit on the underside. I'll go back out and plug the hose going to the vacuum advance after I get some more work done here at the house. I just got done attempting to reset the choke pull off and fast idle. How the heck do you guys actually see where the cam is hitting the set screw with the freaking Carb installed on the block? Woof! I think it's pretty close to where it's supposed to be. Overall the carb is starting to leak a bit I think (noticed some bubbles at the blue circle while truck was running). I see a rebuild coming in August (when I'll ostensibly have some time). I also found that the bottom retaining screw for the choke cap does not tighten at all. Someone must have stripped the hole (red circle). I also found that the hose going to the PV was not fully snugged up on the nipple so I pushed that on better. After starting the truck up (which it did and ran well), I drove it around a bit. I'm back to feeling like there's a misfire on the driver side as I feel it when accelerating. Talk about peeling back an onion! Everytime I think I'm a step closer...oy! Link to comment Share on other sites More sharing options...
1986F150Six Posted July 12, 2018 Share Posted July 12, 2018 Talk about peeling back an onion! Everytime I think I'm a step closer...oy! Yes, but don't the onion rings taste good! Â Link to comment Share on other sites More sharing options...
JMUBullnose Posted July 12, 2018 Author Share Posted July 12, 2018 Talk about peeling back an onion! Everytime I think I'm a step closer...oy! Yes, but don't the onion rings taste good! Lemme guess...you're here all week and don't forget to tip your waitress? And yes - they do. I just don't like how frequently I'm eating them! Link to comment Share on other sites More sharing options...
Gary Lewis Posted July 12, 2018 Share Posted July 12, 2018 Lemme guess...you're here all week and don't forget to tip your waitress? And yes - they do. I just don't like how frequently I'm eating them! You are lucky if you just get onion rings. Some trucks give you Blooming Onions, and that's way too much cholesterol. Link to comment Share on other sites More sharing options...
JMUBullnose Posted July 12, 2018 Author Share Posted July 12, 2018 You are lucky if you just get onion rings. Some trucks give you Blooming Onions, and that's way too much cholesterol. Hahahaha - thanks Gary. I appreciate it - just frustrated at moment. Link to comment Share on other sites More sharing options...
JMUBullnose Posted August 4, 2018 Author Share Posted August 4, 2018 Hahahaha - thanks Gary. I appreciate it - just frustrated at moment. Well, got the plugs and wires swapped out today. Yay! One plugs were decently fouled (Bosch Platinums). Discovered that the second plug in on driver side was was partially backed out/loose (cylinder 6?). Might've been part of issues, but I'm still going to rebuild care next month. The #4 & #8 cylinders are a bit of a pain to get out aren't they? I ended up going under the truck for #8. #4 was a pain to get out and a pain to get new one in. Finally get it threaded nicely annnnddd over tightened and cracked the ceramic! Luckily auto store 10 min away and they had the plug in stock. Sheesh! Fired up nicely and held idle quite well. Ran out of time for a test drive, tomorrow! Link to comment Share on other sites More sharing options...
JMUBullnose Posted August 4, 2018 Author Share Posted August 4, 2018 Well, got the plugs and wires swapped out today. Yay! One plugs were decently fouled (Bosch Platinums). Discovered that the second plug in on driver side was was partially backed out/loose (cylinder 6?). Might've been part of issues, but I'm still going to rebuild care next month. The #4 & #8 cylinders are a bit of a pain to get out aren't they? I ended up going under the truck for #8. #4 was a pain to get out and a pain to get new one in. Finally get it threaded nicely annnnddd over tightened and cracked the ceramic! Luckily auto store 10 min away and they had the plug in stock. Sheesh! Fired up nicely and held idle quite well. Ran out of time for a test drive, tomorrow! Forgot to ask, I've been finding water on the top of the air handler, is there a gasket along good I can replace? Link to comment Share on other sites More sharing options...
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