I have a newer 500 cfm model 2300 2 barrel Holly on my 1973 351 Cleveland. There are two sets of numbers on it: 5925-3 on the body and 4412-3 1335 on the air horn. The choke and fast idle do not release the way they should and, at start-up, the engine speed is way to fast and can't be kicked down. I've monkeyed with the choke linkage a little and it seems too stiff at the various warm-up settings. I've adjusted the electric choke and it seems to function properly but the fast idle needs help. Where can I find some technical info on what the problem is? The last carburetor I worked on is a Mercury 4 barrel teapot so this new fanglled stuff has me stumped.
I used this sites info , i hope it helps https://www.marineengine.com/parts/technical_information/sierra_18-7081.pdf
The high speed idle screw is behind the choke housing with the head of it pointing down at an awkward angle. With the engine OFF, open the throttle by hand and you can reach the screw much easier, usually with a 1/4" wrench. Give it one turn out and check the results at the next cold start.
andrewok1 and pmrphil, I peered down into the space between the choke housing and main body and was unable to locate the screw. The choke rod comes up to the butterfly from a red plastic body attached to the back side of the choke assembly. The red body is somewhat round, but irregular, and rotates with click stops to step the idle speed from low to high. The rotation seems stiff between clicks and I cannot find a way to adjust it. Possibly this is a newer carb/choke assembly than the one posted in the above reply?
The end of that screw is in contact with the stepped surface on that red plastic cam. If you look straight-on at the choke assembly, at ey, the screw would be in about the 7 to 8:00 position, behind the choke thermostat housing. It is hard to get to, so short screwdrivers, really short ones, will help you access it.
Yay, I stretched and leaned waaay over the fender, poked my face in the hole, rotated the throttle, and found that little rascal. But, I have another question now. On the front edge of the carb just elbow the choke housing there is a small brass screw, see the attached pic with red highlight. What is the function of the screw? I screwed it in a few turns and the backed it out. There is no spring tension against it as there is on a jet. What setting (# of turns) should I use? Or is it to all the way down or up?
If you're referring to the screw in the metering block (between the float bowl and airhorn), that's the right side idle mixture screw. There should also be one on the opposite side, but I can't recall if they have a tensioning spring or not. I don't think these do.
I think that is what they used to plug where they drilled a vacume passage in the choke housing. Some have a tiny steel bb peened in place in that same spot.
Many thanks to all of you for the help! The screw I asked about is not the idle mixture but apparently the one for the vacuum. I'll head down to the shop later today to make the various choke adjustments and go for a test drive.
Oh. Then I must not be seeing the one you're talking about. I've looked the pic over again, I still don't see it.
Andy, remember the choke housings on most older Fords ? Remember that little piston on the linkage behind the bi-metal coil ? There is a drilled passage at the bottom of the barrel the piston moves in. Vacume pulls the heated air past the piston on into the carb base and also pulls that piston in the direction that opens the choke. Holley didn't go to the lengths Ford did to hide the plug in the drilled passage. On many Ford carbs you'd be hard pressed to find that plug, but it is there. Now look at the pic again and you can find what we are talking about.
Easy cold start this morning, high idle dropped like it should after warming a little and the test drive was smooooth. With your help I am good to go. Many thanks !
