I have an 87 Z28 with a 305 and a holley 4 barrel and i was just wondering about how many turns of the idle fuel mixture screws i should be at? Also I just cant seem to get the car to idle slower than 1000RPMS. I turn the screw but it just loosens...it stops slowing the idle when it gets to 1000...also when ive ran the car it will idle at 1500 when its in neutral.

So, any input would be helpful.

 

More info would be helpful???

Have you adjusted the throttle stop screw?

Is it a manual or automatic?

Holley makes a lot of different 4 barrel carbs, which one do you have?

What distributor are you using?

What is all done to the 305?

Martin

 

I am not a carb person. As far as Holley is concerned I really don't know a whole lot about them, However I know that Holley has a place on there website for questions concerning tuning their carbs (or they did last time I checked.) If you can't get a clear answer here you might try there.

 

Hmmmm......Sounds strange to me. I have an 86 Z/28 with a holley 4150 on a 305 and I have to constantly adjust it. Everytime I race it needs to be adjusted (not worth it). I cant figure out why your car wont idle lower than 1000. It could be a few things (power valve, throttle spring etc..) but heres' what might help. Have a tech. re-adjust your carb completely from air/fuel mixture to new intake/carb gaskets. Holleys are'nt meant to be dependable, they're meant to race, which means adjustment is always needed. plus I find that after heavy racing my plugs get gassed up alot and need cleaning. This means too much fuel is being dumped and not burning properly. Turning up your idle usually fixes the problem but it wastes alot of gas. Basically check everything!!! Also check your vacuum hoses and make sure none are disconnected from the carb.

Not alot of info but it's a start. hope it helps, I plan to go with a 750cc demon (street) in the spring.

 

A good starting point for Holley idles mixture screws is one and a half turns out. Then fine tune from there...It sounds to me like you may have a powervalve or a jetting problem. Holley carbs are dependable, and are meant to run for a long time, as long as the person who sets it knows what they are doing....I tune all my own carbs and rebuild them when they need it, and I have a Holley 650 DP that is on an everyday driver 87 Formula with 435HP, and I drive it every day with no problems, even in the winter. Do not turn up your idle to fix a problem, all it does is hide the problem. Make sure that it is jetted correctly, and that your floats are adjusted properly, and that you have the correct powervalve for your cam (engine vaccum)(6.5 powervalve is a good one for a regular street car with normal engine vaccum, but it all depends on your engine vaccum) and that it is not ruptured. Stangkilla1, it sounds to me like you have to big of jets in your Holley. Your plugs should not be like that after racing. Holleys are good for racing because they are easy to tune and easy to rebuild, not becuase they are not meant to be dependable. Let me know any info on your car so we can find the problem with your carb. Also check for any vaccum leaks. Good luck man

 

Its a 700R4. Ive never owned a car with a holley so im not sure, how do I tell? It has an accel distributor. Besides that, the engine has headers and as far as i know everything else is stock. It also has a holley mechanical fuel pump.

 

With the engine running at an idle gently tighten both screws until they bottom out. The engine should stall/die. If it does not stall you have some problem other then the idle mixture. Vacuum leaks are common.

 

I'm thinking you have a big vacuum leak somewhere causing high idle. Or the choke mechanism is kicking in the fast idle stop. Does it have manual choke? If so, the lever should be all the way forward. They can move back. You can prevent this by making a short rod to keep it pushed forward. There is a small bracket on the passenger side of carb that is used to clamp the cable used to work the mechanical choke. You can use this clamp to hold the rod. Nothing fancy needed, a piece of coathanger will work.

Holleys are good carbs when set up properly.

You can tell which model you have by looking at the air horn. It will have the List# on there on drivers side, front. #1850 is a 600 vacuum secondary, #3310 is 780 vacuum secondary. These are the 2 most common aftermarket Holleys.

Warning: my nephew swapped the qjet on his 87 Z28 for a Holley and mickey moused the TV cable bracket to hook it up. Tranny burnt up. THEN he obtained the proper TV bracket for a Holley.

 

its has an electric choke. im sure its a vacuum leak now since it seems to have gotten way worse the last few days and its pretty loud :/

 

Thanks for the info "formula2fast"!! I like my holley because I can tell the power difference from my old Q-jet, but just did'nt like having to re-set it all the time. I'll try smaller jets, Summit has the whole kit for a good price so it's worth a try. I noticed Holley has a million jetting/race kits while Edelbrock/Carter/ and Demon have none. this leads me to believe holleys' are tempermental lol.

Yea, the vacuum line might be the main problem, thats the only reason I can come up with why your idling high.

Oh yea, "formula" what kit do you recommend for my 4150 Holley to keep it dependable but able to race at a split moment (I race anywhere at any time)? Plus have you seen that power kit thats supposed to add 50 horses to any holley in 20 minutes (summit)? Does this work and how hard is it to install?