The Stovebolt Site Forums The Shop Area Engine Shop Manual Choke Time

How long should the choke be pulled out on a well tuned carburetor? I recently rebuilt my YF 2100S and also re-jetted the metering jet. It runs great and only needs the choke to be used for about 20 seconds just to start it up from a cold start. It doesn't seem like it's running rich. I've got the mixture screw turned out 1.5 turns. Just wondering what the consensus is on a well tuned carb and a manual choke.

Mark

What is the air temperature? It may be you only need it for a cold start.

The less choke you use the better it is.
Sounds like you're doing it right.

I run a Rochester B which has a step cam on the choke linkage that slightly opens the throttle plate with full to partial choke applied which slightly raises the idle rpm while it warms up.
I used this feature at 1st but soon found out I only need partial choke to warm up in winter and none during the warmer months.

If you really want to fine tune your idle mixture, get a vacuum gauge, connect it to the vacuum port on the manifold then set your idle speed to between 450-500 rpm then adjust the idle mixture in/out to get the highest and steadiest vacuum reading. A reading from 16 to 21 is acceptable.
Good luck
Dave

My 235 with a Rochester B will need the choke on the fist start of the day..why? I don't know. After that is good to go. Summer time it is on for about 15-20 seconds. Then off you go. Last winter it took a few blocks pushing it off a bit at a time until it was all the way off. Well tuned? It starts easy, runs well and gets me there. Gas milage? Maybe 15 in town, and a bit more on the road. Works for me.

I'm getting a reading between 19 and 20 on my vacuum gauge. We're about 20 ft. above sea level. I'm hoping that I did everything right on this rebuild.

All motors require choke use in every climate, for every cold start, "cold" being 12 hours off.
If it needs none or less, it's too rich and you're dirtying your plugs, adding gas to your oil, and killing your mileage.

Mark - I personally have converted ALL of my older vehicles to manual choke except for one numbers matching show vehicle that I no longer own (no fun after it was done).

How long the choke should be engaged depends on the ambient temperature, city or highway driving, and the type of transmission (auto transmissions REQUIRE longer choke times).

Take a look at the post by Panic right above mine. He is absolutely correct. MOST calibrate their carburetors TOO RICH for a variety of reasons. Lots of fuel wasted because of this.

My current shop truck from the 1960's with a large 450 HP V-8 with dual 4-barrels obtains about 22 MPG at 70 MPH. And yes, I have manual chokes on both!

It IS possible.

Jon.

I do prefer the manual choke on these older carbs. Jon - That makes sense your reference to temperature. It doesn't get very cold or hot here for that matter compared to other parts of the country. I'll check my plugs in a few weeks to see if there are any dark carbon deposits. Hopefully my jetting and mixture level is correct.