Running too rich

Will N

Will N

Well-known member
I have a Holley NH on my car. It was running ok, but there was no gasket around the float bowl and nut that holds the bowl to the body, so there was some seepage. Bought a gasket set and took the carb off to install the gaskets. While I was at it, I shot it with carb cleaner, and reset the float height to 1/4 inch (measured from the rim of the body to the top of the float when inverted). It was between 1/8 and 3/16 before I changed it. The float is not leaking- tested it in hot water. I put it all back together and installed it and cranked her up, and it's now running so rich that I fouled the plugs in 15 minutes of running. Turning the adjustment nob seems to have little or no effect. The float is not stuck open, as no gas seepage from the carb when it's shut down (so I cured that problem at least!)

By changing the float height from 1/8 to 1/4 inch, I lowered the level of gas in the carb. So why is it running so rich now?
 
Will,

Try this, turn the adjustment all the way down gently. Then open it up a full turn to a turn and half and see if she is still running rich. There is no hard or fast rules with NH's some times the settings are very different from carb to carb. By raising the fuel level in the bowl you have increased the amount of fuel at the spray nozzle. Turning down the adjustment should do it.

Good luck.

Larry
 
Possible the amount of fuel metered was increased by cleaning crud that was partially blocking a passage.
 
I actually lowered the fuel level in the bowl by the change in float setting that I made. I did try turning the adjustment all the way in, and it made no difference- still running rich. I would have expected the car to stall by closing off the needle like that, but it kept running. This tells me that the needle is letting too much gas in. But I took the carb apart again, and removed the needle and the jet/seat to check if it was pitted or scored. The needle and seat looked perfect- no line or dent from being seated too hard, no scratches or pits. I'm at a loss to figure out what could have changed to make it run so rich with a lower gas level in the carb.
 
Is the vent hole plugged? Now that you have sealed the float chamber there is a slim possibility that vacuum is affecting the fuel level in the carb.
 
Thats strange, when I saw the title "running too rich" I thought it mean't another politician was trying to get out of washington with more of the taxpayers money !
 
When they made these carbs they drilled the passages and then pluged the ends to allow only the needle valve to pass fuel make sure you didn't loose the plug . It happened to me once, you can't lean it out.
 
Very weird problem. Can't see how it would keep running if the needle was actually closed. If all blocking plugs (as mentioned) are in place I can only think that the needle isn't closing off the flow. Are the needle threads OK? Damaged they might give you a false "closed " by not letting the needle all the way down. Really doubt the slight change in the float level is the problem especially since the addition of a bowl gasket (lowering the bowl slightly) probably has the fuel level about where it was before the float adjustment.
 
Choke is working, and the threads on the needle are good. I'll pull the carb out tonight and open it up to see if the low speed/idle passage plugs are all still in place.
 
Well, the mystery is solved, and I feel like an a##! CharlieB and ljbohlen, you hit it on the head, the needle was in fact not closed at all. I guess I tightened down on the clamp nut too much, and it caused the needle to bind. What felt like a seated needle when I adjusted the dash knob was still many turns short of being fully seated. I generally don't force the knob for fear of scoring the needle, so when the knob stopped turning under normal force, I assumed it was seated. Wrong! It's amazing that it ran at all with that much raw gas pouring through there!

Bobtheman, all the drilled passage plugs are still in place, thanks for the suggestion.
 
Will,

Don't beat yourself up. Glad you found it.
Henry's creation can bring a grown man to tears and tear your hair.

Larry
 
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