97 carburetor

flatjack9

flatjack9

Well-known member
Building an engine for a customer and he bought 2 new chrome 97 carbs, the good ones. They look pretty but when tested on my test mule engine, I turn the left screw all the way in and the engine still runs. In fact, it runs quite well. Idles at around 20" Hg. Both carbs act the same. Any insights? Thanks, Jack
 
flatjack9 said:
Building an engine for a customer and he bought 2 new chrome 97 carbs, the good ones. They look pretty but when tested on my test mule engine, I turn the left screw all the way in and the engine still runs. In fact, it runs quite well. Idles at around 20" Hg. Both carbs act the same. Any insights? Thanks, Jack
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I bought my pretty chrome 97's from Speedway. One had to be returned for a cast passage that was not open. Both float levels were way off. The nitirle float in one sank, probably because I was not careful enough in bending the tab to make float adjustments. The needle valves seemed to attract gum and started sticking if left to sit too long. Replaced with Grosse ball type valves and put some Seafoam in the gas a couple times a year.

After all that they run as good as they look.
 
Do you see any fuel being pulling from the dump tubes up above? If you have enough air/vacuum being pulled, then the main jet dump tubes will begin to flow fuel - which will keep the engine running even though the idle circuit is closed.
 
drolston said:
I bought my pretty chrome 97's from Speedway. One had to be returned for a cast passage that was not open. Both float levels were way off. The nitirle float in one sank, probably because I was not careful enough in bending the tab to make float adjustments. The needle valves seemed to attract gum and started sticking if left to sit too long. Replaced with Grosse ball type valves and put some Seafoam in the gas a couple times a year.

After all that they run as good as they look.
Click to expand...

To be clear; were these carburetors the "Strombergs" made in England or the infamous "9Super7"'s?
 
England. I did find a little fuel flowing on the left side. Will check float levels tomorrow. What threw me is how nice they ran and both acted exactly the same. I mostly run 94's and if I have leakage down the throat, I can usually hear it and the idle is not smooth. First rule of troubleshooting, check the obvious first.
 
Jack, your experience with the English Stromberg's is a bit disappointing to me. However, I was actually asking "drolston" about the carburetors he got from Speedway. Sorry I wasn't clearer.
 
Got the carbs running much better.The floats were a little high, so set them to spec. Idling at around 21" hg at 12.5 - 13 A/F ratio. Runs best with the left idle screw out about 1/4 turn, but it does control some now. Will try lowering a little more. Goes to show something i knew, but overlooked. Never trust anything out of the box. I do think these are excellent carbs. Just need a little TLC. I hate to mess with the throttle plates, but it could be the left has a slightly larger opening than the right.
 
flatjack9 said:
Got the carbs running much better.The floats were a little high, so set them to spec. Idling at around 21" hg at 12.5 - 13 A/F ratio. Runs best with the left idle screw out about 1/4 turn, but it does control some now. Will try lowering a little more. Goes to show something i knew, but overlooked. Never trust anything out of the box. I do think these are excellent carbs. Just need a little TLC. I hate to mess with the throttle plates, but it could be the left has a slightly larger opening than the right.
Click to expand...

As you suggest, you could have one of the two throttle plates in one or both carbs not perfectly centered, leaving the other with a slight gap when closed. Unless the mismatch is pretty bad it probably would not cause a problem. Try this: Disconnect the linkage between the two carbs. Completely back off of the idle adjust screws so that the throttle plates go full closed. Now peer down into the carbs with a flash light to see if it looks like the throttle plates on both sides are equally tight in the bore. If you can visually detect that one side is not fully closed, the problem is bad enough that it should be corrected. That is a tricky thing, but you can do it on your work bench (not on the engine).
 
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