Just finished a 276C.I. ab flathead w/offenhauser dual manifold ,two Stromberg 97's idles great, starts and runs great except, just above idle, low speed its hesitant, bogs before it goes like a raped ape, above 2,000 rpm with the five speed its just a pleasure, but off traffic lights its disappointing and a little doggy. feels too lean and idle screws don't matter where they are. Does anybody know how I can open up the low speed carb circuit , maybe a little richer? until the mains get enough vacuum to pull thru? the cam is not wild its a .375" lift with 280 deg. duration. any advise welcome to make this a better driver
There are two settings for the rod that goes to the accelerator pump. One is marked S and the other is marked W. Disconnect the rod at the bottom and attach it to the W location. This will give you a larger squirt upon accelerating from a dead stop. If that doesn't help check with the guys on the fordbarn.com web site.
What is the deal with the carbs? New or rebuilt? If rebuilt who did it and how thoroughly did they clean them? If the idle mixture screws are not working then there is something wrong with the carb or you have a vac leak.
Attempt the move of Tue accelerator rod...if that doesn't effect anything u have a leak somewhere...very possibly throught the rod the butterflies attach to... Those holes often get opened up from use if your bases are the cast original... Sent from my DROID device using the TJJ mobile app
Before you think about anything else...put a timing light on it. Flathead want advance to start going up rapidly right off idle...like immediately. If this isn't happening it is not going to go right no matter what else you mess with. To crudely check carbs on this, though, hook up your chokes and run it through the weak spot over and over, closing the chokes more each time...eventually you will find it going better IF too lean is your prob. If it just gets smokier and slower, look elsewhere. Off-idle circuit is important, as car runs entirely on that at low revs, then it tapers off slowly as mains begin to function...but I doubt it is too lean. Parts to check first are idle jets, then passages leading down to and through base, then outlet holes.
Everything that has been said is good information. The acclerator pump gets you off the line. W setting squirts more gas. Verify the acclerator pump is squirting gas, the valve can be leather and shrunk up and you aren't getting the volume you need. 97's stock main jets are 45's and the power valves are #65's at sea level. You need a Stromberg jet wrench to remove and check the main jets. It is a combination of the idle discharge circuit and then the main jets that give you gas until the throttle is about 75% open (depending on if you are on S or W setting. The acclerator pump pushes the power valve open at that point. So if your engine does not respond to the adjustment of the idle circuit screws that might be a problem. Verify to make sure that you don't have a vacuum leak or crud in the fuel bowl stopping passages. Another problem is that the idle screws need to be a Stromberg style, other brands can screw in but the needle is the wrong profile. Insted of me trying to explain the different profiles, pull what you have and compare it to a photo of a genuine Stromberg replacement that you find a photo of on line. Basically what you should see is that the taper on a Stromberg screw goes right up to the threads but a Holly (that will screw into a Stromberg) the taper stops short of the threads. They are sensitive to float level and fuel pressure also. They like 2.5 psig and the float level is set dry at 5/16" + or - 1/32" Then it needs to be set running with the top of the carb off to a fuel level of 15/32" + or - 1/32" from the top of the fuel bowl with out the gasket. All of the disclaimer and safety stuff about working with gasoline around hot surfaces, ignition sources and rotating assemblies. Have a fire puter outer handy. Good luck LJ
Bear in mind that in a clean, properly functioning 97 with a new accelerator pump, the powervalve starts to come to the party the moment you stab the gas, due to the 'hydraulic' action of the accelerator pump and becomes fully open at the bottom of the stroke. When the pedal is depressed less violently, the checkvalve stays open and does it's job. It's important that the main jets and powervalves are sized and matched properly, especially with multiple carbs.
hey guys! thanks for all the info, they are brand new chrome carbs from Speedway, not rebuilts. the fuel pressure is regulated to 3.0 psi and the accel pumps have been on W since new. I need to look at the ignition timing, I set max advance to 22 degrees @3,000 rpm but have not checked to see where it is at idle and in between, so that's a good tip as well. I have a choke in one carb so I will also try to leave it on partial to see if any difference. it idles smooth and does not have any vacuum leaks. I will check the ignition and report back, I still think I have a power valve or transition leanness, but need to check the basics first, again thanks to all who replied.
Advance should be finished well before 3,000...also curve should start moving immediately off idle. So these are not actual Strombergs, but the Speedway 9 super 7 or whatever they call it?? If bog is right off idle, there probably isn't any real flow at mains or power enrichment yet. With slow acceleration you are probably still running on off idle, if you pork it you are then getting a lot from accel pump to cover things until engine starts to get up some air flow.
All bets are off the table since you mentioned Speedway carbs. The last one I looked at - out of the box - had the pin of the powervalve broken off and laying sideways in the pump well. Did I mention the leather pumps are similar to rhino hide.
Funny! (for us, not the OP) Wouldn't the hot rod world be a lot easier if everybody did a search on the HAMB before they bought a new part? We'd avoid countless crap products and sleazy vendors.
I have super 9 7's from Speedway on my car ( 4 cylinder model A banger) and they run great. I run the acc pumps on the "W" setting and have a pretty quick mechanical advance . See if you can "dial out" the hesitation with the mixture screws by making them a little richer also I found that the adjustable main jets sold by Speedway help to get the jetting squared away. Car runs good and doesn't stink when you stand behind it.
The Acc linkage doesn't nessassery mean 'richer' it maybe a case of you Acc pump needing to kick in 'earlier' to stop the hesitation.
I did have a problem with new stromberg 97s , well the primary of three anyway , basically would not run worth a darn as they forgot to install the main jets!!!!!!?? Bit once I fitted them it ran like a dream on triples. So please stromberg check you have installed main jets for new in the box carbs. Super 97 whatever's , definitely not. No Chinese here.
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