So the 97's on the Tardel/Cochran coupe have been leaking like Strombergs for over a year now. I finally got the gumption up to spend some dough and order some of those new GENUINE (not the cheap ass fake crap that Speedway sells... ahem...) Stromberg-97s. I bolted em right on and the car fired right up and idled smoothly. Throttle response was much improved and the car ran great... That said, the exhaust is popping when I get off of it at high RPM and when I come to a stop after getting on it, the car dies. Oddly though, it idles fine and smooth on start up. Plugs are black. I set the idle mixture as instructed in the manual. I started with each two turns out, turned them in until the motor stumbled and then out until it galloped, then in slightly. This worked fine on the back carb (intake is a PM7), but no matter where I turned the idle screws on the front carb there was no difference in the running characteristics. This leads me to believe the motor is drawing off the rear carb. I didn't have a fitting to hook up the vacuum gauge, but all things pointed to a rich state. Stock Strombergs come with .045 jets so I ordered various smaller sizes so I could fiddle a bit. As an after thought, I went to my old leaky carbs and pulled the jets. Guess what size they were? .048. What the shit, man? Could it be that my old carbs were just that inefficient?
I'm in Hutto and can run you a carb synch tool get your carbs working together if you need it. It works like a champ on my British multi-carbed sports cars. My MGBGT was popping like mad when i'd come off it at high RPM, turned out to be a lean pop. I pulled the choke out a hair and it went away. It's strange that your plugs are that black and it's still popping. I guess too rich could do the same thing if it's burning raw fuel in the exhaust though. Let me know if you need the tool. It looks like this:
Running rich-Thats the exhaust pop. Since the front carb wont adjust out right you may want to take a look at the float leavel first-May want to get a can of carb cleaner and spray around the base to see if possibly it has a vacuum leak-good for starters any way
The carb synch tool pictured above will let you set the carbs so that they are both drawing an equal amount of air at idle. Most likely one of the carbs throttle plates is open a bit more than the other, so more idle air is running through that carb. Get the thing idling properly and then you can shoot jet sizes.
I've got one of those tricky little devices coming (thanks for offering though CJ!). Hopefully, that will help my dumb ass out a little.
read the tech thread tommy did sometime ago on setting up multiple carbs with the uni syn. It is very simple and very affective..
I am running two 97's on a PM-7 as well and I am using .043 jets........runs very nicely...........good power and acceleration....... Might want to try a set..... CB
Here's the tech thread that Tommy wrote. It's about as basic as a process can get: http://www.jalopyjournal.com/forum/showthread.php?t=124624&highlight=unisyn&showall=1 Something i've been doing for years when i'm out of town with one of the Brit's and don't have my Unisyn tool with me... You can tap on the carbs with the palm of your hand and if you're pretty good can feel the difference in suction. Tap on one and remember what it feels like. Blip the throttle and let it settle back to idle. Tap the other one and see if it pulls harder or weaker, and adjust that carb. Pretty much do what Tommy said, just using your hand instead of the tool. Another thing you can do on sidedraft carbs is "listen to the hiss". This takes even more skill than the hand tapping method. I'm not sure if 97's will hiss like a side draft SU or British variant Stromberg will though. You can put your ear up to it and listen to it though. Adjust accordingly. Just make sure you don't get your ear drum sucked out.
hiss technique seems just as accurate as a unisyn to me.. tried doing it both ways and came up the same adjustments. I use a 2 foot length of hose to avoid slicing my face open on an engine fan..
Yup, and a good reminder to use the hose. Especially if it's a crazy, open header, satan on wheels. You'll actually be able to HEAR the hiss. haha...
One little thing I should mention: When people buy the New English carbs from me, I jet and powervalve them for their needs, so they run - out of the box - at no extra charge.
After reading Tommy's tech article, I know of at least one thing I'm doing wrong. Boy, I'm a dumb shit. I'll admit to it all after I take a crack at it with the sync-a-majig.
Don't tell me you forgot to tighten one of the carb linkages down, so one was running at idle the whole time... with the loose bellcrank spinning on the shaft... That would be classic. hahaha... don't ask me how I know... -Chris
Ryan, you have to post some of your findings. My flatty has been having the same synmtoms ( well with a new HISSING sound, but that is a different problem) only mine has the cheaper brother to the 97. Jeff
No... My linkage is tight and all is good there. Only thing is, I didn't think about the relationship with the idle screws. I just bolted the carbs on and hooked up the linkage...
Good luck with that Ryan. I just finally threw my hands and gave up on my 4 carb setup. I have missed the entire season. It's back to 2 carbs as it was before.
Ryan, didn't read all the posts... but I agree with others, must set the two togeteher. I too have run 97's on all my cars. The old ones to me seem to respond differently then the new ones. I agree, the new cabs do seem to run good, but run rich. I diald all my carbs down with smaller jets...works great. I think the new carbs like smaller jets. If you need some, let me know... A very kind old dragster builder new I messed with old flatties and Strombergs, he gave me a small box with lots of jets. Let me know what you need... got em all.
Mess with idle with the linkage loose...rubber hose good! Get both crbs fully closed, then give them a couple of turns on idle speed screw so you can tune downward. If suspicious of front carb, try it with rear carb all the way closed, speed screw off seat, and front open a bit--see if it runs then add other carb back in. Do not tighten linkage until idling with two similar hisses!
Ryan, I had similar issues with my two strombergs. I ended up jetting down to 42's with a 67 PV and 2.5#'s of fuel pressure. I am running 24 degrees advance and my plugs cleaned up to a nice coffee w/ cream color. I am running one rebuilt and one new 97.
I've never had much luck with those Uni-Synch tools on 97's...adjusting the center of the tool to get a good reading on the "ball" ends up choking out the engine. And all the tool does is verify each carb is pulling even vaccuum/throttle blade position.
Some of the most enjoyable content on the HAMB and the JJ is when Ryan sets out to stretch his mechanic wings. Good stuff! I'd chime in jus to hear myself talk, but I don't know shit about strombergs. Dang! did it anyway...
wooooooooooooooow... i have never seen you ask a question before, i thought you were the all knowing wizard of oz i do not know the answer to the question, but this does answer some for my self.
Heh... check my post history... I'm a complete hack/screw up in the shop. II just screw shit up until I learn!
Traditional hotrodding at it's best. We just paid our dues years ago. T think you should be commended for using the forum instead of your many PM contacts that would not expose your difficulties to the masses.....but then you would be the only one to benefit.
yup same here. one side always turns out better than the other, for example i am building lake headers for my model a(ill post pics when i am done), i know one side is going to be better than the other, and with the help of this site ive learned alot. thaks boss
if the unisyn tool doesnt work get a piece of pipe, maybe 3/4" in diameter and put it to your ear and hold it over the neck of the carbs and you should hear the difference in the draw of air or the hiss - i prefer to use a piece of pipe instead of putting your ear to the carb because if theres a backfire you will keep all your hair works like a dream. i always think 2 full turns out is too much for the idle screws, only ever end up with them a full turn out at most.
Here is a set of instructions without pictures: http://www.thecarburetorshop.com/Dual1barrelcarbs.htm Yes, I know it says one barrel carbs, but the procedure is exactly the same except there are two idle mixture control screws on each carb rather than one. Jon.
Ryan, not sure if this will help but I've been trying to get my new 97's settled properly for 18 months now. Here's what I have. French flathead with Edelbrock heads and Offy inlet, twin 97's and now has a Isky Max 1 cam. Always had problems with it running very rich on idle, to the point of it smoking real bad. If I turned the idle screws in it would stumble when giving it gas. Mostly it ran well with plenty of torque and was very nice to drive, but I knew it wasn't right. I tried changing the timing, float levels, different plugs and down jetting. Nothing seemed to make it work. So running out of ideas I changed the jets to .048" and turned the idle screws in to 1-1/8 turns out and it great. It's the best I've had the car run. No smoke at idle, no stumbling from idle either when giving gas slow or hard, accelerates hard and cruises smooth with no poping on the over run. I couldn't want for a better running car. Not saying this would work on your engine but the .048" worked for mine. Cheers.....Pete
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