carb issues

[rwhite65]

Ok, I posted on this last fall, and I am just now getting around to trying to fix this problem.

Long story short, when I put the new cam, heads, and 1.7 roller rockers in the car, I developed what I thought was a vibration at low rpms. It was noticeable right off of idle (leaving a stop sign, it would “stumble”) or at cruising speeds at only a slight throttle off idle (like in overdrive). As soon as I give it throttle, past that very slight point, the vibration would go away. It almost felt like a chug at cruising speeds, but it is definitely not a balancing issue.

Jester suggested a long time ago I change the accelerator pump squirter to one size bigger. I had a few respected local guys tell me to change the accelerator pump cam, one going as far as to say change it 2 sizes up.

My carb had the white cam on it, which is stock according to the Holley website. I changed it out tonight to the red, which is two up from the white, and one over the blue (next over stock).

This change definitely did not make it better, it is definitely worse. Now when cruising I can get the throttle actually caught in a sluggish bog and unless I give it more throttle, it just makes the car shake like something is out of balance.

Should I change the squirter? What else could it be? The floats should be set just fine, and the timing SHOULD be good, but I will check it when I can get a vacuum gage.

I need to just go buy a Holley book and see what I can figure out.

Ryan

[rwhite65]

I called Holley and they were confident that I have the wrong powervalve for my set-up. They told me how to check and c which one I need. More to come.
Ryan

[Dark Knight]

If the power valve is opening to soon, it will load up. Adding a big pump shot will make it worse..

[PKRWUD]

Just out of curiosity, did you readjust the accelerator pump linkage after swapping accel. pump cams?

[rwhite65]

Originally Posted by PKRWUD

Just out of curiosity, did you readjust the accelerator pump linkage after swapping accel. pump cams?

No I did not. I cant say I have ever personally done that. I have been waiting for you to drop in PKRWUD, good to see you.

Dark Night-
Are you saying you think Holley has given me bad advice?

Ryan

[PKRWUD]

Originally Posted by rwhite65

No I did not. I cant say I have ever personally done that. I have been waiting for you to drop in PKRWUD, good to see you.

Thanks! It's good to be seen! lol.

Any time you change the pump cam, or the screw hole with which you mount the cam, you must check the linkage, and make sure it's properly adjusted. You want to see fuel come out of the squirter at the slightest tap of the throttle. If someone sneezes hard enough, standing next to your engine, you want to see fuel start to spray out of the squirter. It needs to be adjusted that precisely. On the other hand, though, you don't want to bottom out the pump while there is still more lift coming, otherwise you won't get a full shot. If there is even the slightest delay between tapping the throttle, and fuel coming out of the squirter, you'll have a flat spot on acceleration. As you open the throttle, you are letting in a large amount of air, and without the added fuel the accelerator pump instantly provides, you will experience a lean bog until the fuel can catch up.

Pull the air cleaner, and look into the primaries, and tap the throttle lightly. Does fuel instantly start to come from the squirter?

[rwhite65]

Well, I have not pulled the old power valve, but using the Holley way of checking...I used a vacuum gauge with the car warmed up and in gear. I pulled only an eight on the gauge. Holley stated to cut that in half, so I bought the 3.5 power valve. I have not put it in yet, but I am thinking I have the stock 6.5 power valve.

I hope to change it out tom before work and update, I will also check the throttle linkage as you stated.

thanks,
Ryan

[PKRWUD]

You've only got 8" of vacuum at idle?!?!?

I suspect you'll discover that your engine leans out at the peak of your powerband with a 3.5 PV, but give it a shot and see.

I would install a green pump cam, screw in hole #2, adjusted like I mentioned. Your car will bark the tires every time you just look at the gas pedal.

[rwhite65]

Originally Posted by PKRWUD

You've only got 8" of vacuum at idle?!?!?

I suspect you'll discover that your engine leans out at the peak of your powerband with a 3.5 PV, but give it a shot and see.

I would install a green pump cam, screw in hole #2, adjusted like I mentioned. Your car will bark the tires every time you just look at the gas pedal.

Now that is what I like to hear! I have the entire pump cam selection, so the Green is no problem. Is the 2nd hole the top or bottom hole? Now that I think about it, I think they might be numbered? Anyway, I will do that and get back with you. Do you want me to do the power valve switch with the pump cam or try them separately?

It did only measure 8", which surprised me. I only have the stage 1 cam.
Thanks,
Ryan

[PKRWUD]

Check my reply to your last post in Brian's thread.


Also, the green cam (should have '290' stamped on it) will work as promised, but you MUST adjust the linkage correctly, as I described earlier.

[Dark Knight]

I may be wrong, but that doesnt seem like alot of vac for a stage 1 cam..

And I meant that if the PV is opening early, a bigger pump shot would make it worse off idle..

[PKRWUD]

Originally Posted by Dark Knight

I may be wrong, but that doesnt seem like alot of vac for a stage 1 cam..

You're not wrong.

[rwhite65]

The car had 11-11.5 tops Vacuum when in park and idling (warmed up). Are you suspecting a Vacuum leak? I am going to try and tackle this carb tomorrow, I have the whole day to work on it if needed.
Ryan

[PKRWUD]

Do me a favor and answer the hypothetical question I asked you yesterday.

[~The Jester~]

Originally Posted by PKRWUD

Do me a favor and answer the hypothetical question I asked you yesterday.

Do ME a favor, and put the stock cam back on it, and jump up 1 size on the squirter.

I WILL say, as stated earlier. When you change the cam you MUST readjust the linkage! "If someone sneezes next to your car" is almost correct, I use 0.010" clearance between the linkage and the actuator arm, with engine off and "zero" vacuum.

[PKRWUD]

I prefer 0.000 clearance, but I'm funny that way.

[rwhite65]

pkrwud-
Slamming on the brakes would not kill the engine, or so I believe. I have gotten on the brakes pretty hard before and it did just fine.
Ryan

[rwhite65]

Ok, here is the latest. I bought my own Vacuum gage thinking I might have a Vacuum leak. With the car in park, I had 15.5" and in drive I had 11” Now according to Holley, my 6.5 stock power valve would still be wrong, a 5.5 would be perfect. Is it worth changing?

Put the green cam on, using what I think is suppose to be the 2nd hole (see pic). Adjusted the pump linkage, to where the slightest touch would make it squirt the fuel, and then took it for a drive.

Well....Ryan has some serious traction problems now.....(insert Ryan worshiping PKRWUD) . I have no more hesitation off the idle at all.

However, I will say that I still have the shutter in overdrive...and slightly in third, but not always. It is most noticeable when just cruising, with overdrive at 45 mph or so, right at 2,000 rpms? Any suggestions on that one? I am leaning towards Jesters recommendations of slightly bigger squirters now.
Thanks,
Ryan

[rwhite65]

Here is the pic.

[82 GT]

Not taking anything away from Jester, cause he's never steered me wrong, but I don't see how changing squirters will solve your shutter problem.
The squirters only provide a shot of fuel when the throttle is pressed to prevent a lean condition when the throttle blades are initially opened. They do nothing for part throttle conditions.
If you don't have a stumble or bog off idle, then I would say your squirters are fine.
Jester, did I miss something on your line of reasoning here buddy?
I've been reading some of my HOLLEY CARBURETORS book and thought I was starting to figure out how these buggers worked.
I'm also curious who's method of figuring the correct PV is more accurate....PKRWUDS or Holley's.
Holley says to check vacuum at idle, in gear and PKRWUD says check it in Park.
I ordered an 8.5pv today so I must have decided Chris was right