Hi,
i have a 86 irocz manual trans with non control comp carburetor with 350. Either when I shift or press the gas for more power, the car jerks or chugs one time. Then rides fine until next shift or another gas press. I replace the mechanical pump, wires and spark plugs are good.

any recommendations to what else to look for?

thanks in advanced!

 

Not sure what a non comp carburetor is. But is the accelerator pump working?

 

Sorry about that… non computer control carb. Not sure if this info helped.

I have not check the accelerator pump. I have a holley carb 650 street avenger. I guess they way to check is to look the adjustment of the red screw?

 

Finally got around to check the accelerator pump. It seems to be working and not leaking. From what I have seen in youtube , the screw might have been preloading the lever arm a little much but i adjusted it but the bog got worst.

i just replaced the mechanical fuel pump too so I am not sure if it needs to do with that or if I need more tuning in the accelerator pump. I am thinking is not a good idea to preload the lever arm too much?

 

It's supposed to do that.

Not surprising since you adjusted it in the wrong direction.

The way that thing works is, the screw should be adjusted to the length such that it almost bottoms the pump out when the throttle is fully opened. Then when you are driving around and open the throttles normally, the fuel in the pump (which is incompressible of course) is forced out of the squirters; butt the spring on that adjustment screw allows the screw to be pushed back under spring pressure, and the spring keeps that regulated pressure on the pump arm as it delivers its shot of fuel. The spring's official name, since it regulates the pump shot duration, is "duration spring". With most of the various pump cams, that will "preload" the pump quite a bit.

Correct adjustment is .050" - .060" of gap between the pump arm and the screw head, when you hold the pump fully bottomed by mashing the arm, and hold the throttle open fully.

Yes you need at least 3 hands to do this; it's easier with about 5.

Also sounds like your power valve is a MUCH too low number. If you're using the "half of idle vacuum" stuuuuupidity to select it, that's the actual reason for the bog, which the pump is then unable to cover up because it's misadjusted. The PV number is the vacuum to which it must drop before the PV recognizes that it needs to supply extra fuel, and the usual stock 65 (6.5") means that you have to nearly floor it before the PV opens, which then requires excessive jets and a gigantic pump shot to cover up the bog. That WRONG setup will approximately HALVE your gas mileage, besides of course causing the bog you're enjoying.

A properly set up Holley carb almost doesn't even need a pump at all. If messing with it makes the carb screw up, something else is wrong.

Follow the Holley Tuning sticky on the carb board, from start to finish, each and every step in the order given, skipping none and performing all. You'll be ASTOUNDED at how much better a Holley carb works when set up that way instead of ... that other.
-

1. Fuel level
2. Idle mixture screws to ¾ turn out, pump adjustment as described
3. Ignition timing to where it just barely begins to spark knock under the heaviest possible load at the slowest possible RPM with the engine fully hot, then back off until it quits
4. Idle speed out of gear to the desired RPM (700 - 750 is usually good to start with)
5. Idle mixture screws to max vacuum; shouldn't take too much adjustment from ¾, should end up at between ½ turn and 1¼, butt probably closer to 5/8 or ¾; average their 2 settings, should already be within 1/8 turn or so of each other anyway, if they're not you have other issues that need to be sorted out before continuing
6. Turn carb upside down, set primary throttle blades to where about .050" of the primary transition slot is exposed (will look a little narrower than a square is exposed); most likely you'll find WWWWAAAAAAAAAAYYYYYY too much exposed
7. Adjust idle speed back up to desired RPM using the secondary throttle stop screw (it's a little Aleen head set screw accessible only from the bottom; might be worthwhile to get a longer one and screw it in from the top so you can get to it without having to take the carb off)
8. Lean the jets about 5 numbers from stock; test drive; adjust jet size from there until the car just barely has a flat spot when giving it a small throttle input going up a slight incline, in high gear, going about as slow as you ordinarily use high gear (probably 35 - 40 mph); ignore all other misbehavior at this time of which there is likely to be plenty, just find that little flat spot
9. Put in jets 2 sizes larger than that
10. Go back to step 4, repeat 4 - 9 until no further improvement can be made
11. Put in the PV 2" lower than cruising vacuum; most likely end up 105 or 125 (10.5" or 12.5") for a street car with a street cam

There are different pump cams available that change the rate and ratio of shot volume to throttle opening. Odds are, you won't need to worry about that, butt it's there in case it's needed.

 

Sofa,
Thank you so much for the information! I will verify as you recommended.

very dumb question but where is the power valve found? I would like to check it as well.

 

​​​​​​​Speed shops, Summit/Jeg's, maybe some of the board sponsors.

 

Hi,
i finally got around and remove my bowl. See the pictures. It is not what I expected to see. I thought I could remove the power valve with a 1 inch wrench but it seems from the picture that it is somewhere inside the body of the carb. Did I miss something or remove the wrong part?

Thanks for any information!

 

Hmm 🧐 not a carb guy but assume the pv is on the metering block.

 

The piece that the PV screws into is about 5/8" thick or so. Its official name is "metering block". It's held on by the same 4 screws that hold the fuel bowl on. Just look about that far behind the flange you can now see, and you'll see the parting line where it meets the actual carb body. Right now all that's holding it on is the stickiness of its gasket. Mind you, that gasket is an almost continuous rectangular flat piece, with only a few little holes; it often tears when removing it. Holley puts some kind of adhesive on it for some reason, although those blue gaskets don't have that, so it might cooperate. I always schmeeer a good bit of silicone dielectric grease on those so they come back apart without a fight. Also be aware, all of those parts have a REAL FINE ridge cast into them for sealing, which you can see the witness mark of, in the gasket that's now exposed; be SOOOOOOOOOOOOPER careful not to damage that ridge while scraping gasket remnants off of things.

 

Thank you! Yes you are exactly right. It came off with a little force. I was able to see the power valve and replace with a 10.5.

The bowl gasket fold a little so I will replace to be safe. More to come…

i will make sure preserve the ridge.

 

I am back…so I replaced the power valve to 10.5. I removed the secondary bowl to tune and saw this. See picture. Could some one tell me what is the crude?

 

EEEEeeeeeeeeeewwwwwwwwwwww... [/ 5th grade girl]

There's a technical term for that. Used only in the most enlightened educated erudite circles of accredited technician majesty.

It's called "crud". Maybe some other 4-letter words as well. NOT good news.

Actually, it's also known as "varnish". Happens from fuel sitting around too long mostly. If it's THERE, no telling where else it might be, upstream from there. Not a good sign AT ALL.

If we'd had any inkling you were dealing with THAT, we wouldn't even have started talking about tuning yet. NO WAY you can "tune" a carb when it's full of THAT.

First thing ya gotta do is tear down that carb to its most intimately tiny parts, and get all of that OUT OF everything. Every passage, every orifice, every EVERYTHING, likely has that ... STUFF ... (sorry, I was going for another word that starts with "s") stuck in it. No possible way for it to work right like that. Once fully torn down, soak it in lacquer thinner for acoupla days, then brush everything you can get to, and stick a SOFT wire or something into every hole a brush won't get into. Copper wire (4-pr telephone station wire), thin fishing line, stuff like that. NOT steel, like tag wire or that sort of thing; it can damage the holes. Blow it out with spray-can carb/TB cleaner (NOT brake parts cleaner) followed by compressed air. Reassemble with all new gaskets and a NEW fuel filter. Doesn't matter if you just replaced it yesterday; replace it NOW.

If the rest of your fuel system (pickup in the tank, sock filter protecting it, lines, pump, ...) looks like that, you're in for a rough ride for awhile.

 

Thanks for sofa! I will do that. Interestingly I checked the primary bowl and it is totally. So I am not sure that I don't drive my car long distances at all so the fuel sits in the secondary way too long. Either way the carb is due for your recipe of cleaning. Here is pucture of the primary.