1963 Corvette FI - Fuel Meter Ratio Lever Settings

[Lawrence S.]

Ok...finally got my 63 back on the road after a long period setting idle and did a test drive and it seems to be ok but know the fuel meter Stop Screw Calibration is off. I pulled one of my old "The NCRS Restoration and Maintenance Encyclopedia" 1963-67 Mechanical Vol 1 out and looked up the area pertaining to Troubleshooting Rochester FI for a writeup by Brian Futo.

Using a Vacuuum Gage and a Mitvac...I hooked the gage and vac up to bottom outlet of the Enrichment diaphragm and plugged the Outlet of the CVS....as noted in the manual for a quick and dirty setup.

The manual says to draw a vacuum so that the ratio level"Power" stop screw just moves off the end of the set screw at 3" of vacuum. That worked out just fine.

Then increase the vacuum to 9" at which time the ratio level must contact the "Economy" stop screw....this is where I am having issues...I am hitting the stop screw only pulling 6" of vacuum. I have adjusted the screw and the enrichment diaphragm rod and cannot get it adjusted.

Anyone out here still using this approach or any recommendations. Appreciate any assist.

Larry

[John S.]

Re: 1963 Corvette FI - Fuel Meter Ratio Lever Settings

Larry,
Your numbers are spot on from info I have. Many people with far more knowledge than me are not fans of doing it this way. My thoughts are that it is a good place to start. I have set up three units this way in the last year with good initial results. I believe that if you are having a problem here there is an issue with something internal such as the diaphragm. I think John D. Can answer these types of questions far better than I. Let's hear it from some others.

[Don H.]

Re: 1963 Corvette FI - Fuel Meter Ratio Lever Settings

Larry,
You didn't say what was done to the unit - what changed from before. Are you sure it is the right spring in the enrichment diaphragm? I know there are different ones. I set the enrichment diaphragm rod length to 2 1/32" - from the center of the 90 degree bend to the end of the threaded rod. I am certainly not an expert but have been keeping my units running for over 35 years so I have a little experience. I recently adjusted my 375 unit using an exhaust analyzer for the first time. I was very impressed and now feel that is the best way to adjust a fuel unit. Or if that is not an option, the old adjust and drive method is probably your best bet. I have had no luck with the vacuum method but that could just be me. Good luck, Don H.

[Lawrence S.]

Re: 1963 Corvette FI - Fuel Meter Ratio Lever Settings

Thanks John....I am going to go back out in the garage and tinker it for a while....I know John D is very knowledgable and assisted me with info when I rebuilt the unit about 20 years ago...where does the time go. Anyway...letting it set idle for a couple years plays havoc on it...will let everyone know if I get it adjusted.

I did find a small vacuum leak on the diaphragm and using the NCRS book under the same section I found it....so the info in the book does work.

Larry

[Lawrence S.]

Re: 1963 Corvette FI - Fuel Meter Ratio Lever Settings

Don...thanks for the info on the rod length, will use that when I go back out to the garage after I send this.....the unit set for over two years and I had to send the wobble pump out to be rebuild because the fuel setup in it....after that just replaced all the seals and gaskets with the new victron ones and after getting all the vacuum leaks fixed it fired up just fine but the high end was not what I remember from previously. So started to adjust and couldnt get the 9" of vac as before. Now I used this approach 20 years ago and it worked fine so at a loss now.....

Larry

[Joe R.]

Re: 1963 Corvette FI - Fuel Meter Ratio Lever Settings

Anyone here ever heard of a Mercury Manometer????

Made for FI and works like a champ.

JR

[Jim L.]

Re: 1963 Corvette FI - Fuel Meter Ratio Lever Settings

It is a serious mistake to adjust the Ratio Lever transition threshold before the positions of the the two stop screws are properly adjusted.

The correct sequence and process for calibrating an FI unit goes like this:

1. Adjust the Economy Stop screw for proper air/fuel ratio at hiway cruise. Anything in the 15.0:1 to 15.5:1 range will work well. The engine must be under a road load to set this correctly. You can NOT just spin the engine up to 3000-ish RPM in your driveway and get accurate results.

2. Adjust the Power Stop screw for proper air/fuel ratio during wide open throttle. An air/fuel ratio in the range of 12.7:1 to 13.1:1 should be your target.

3. **Finally** adjust the length of the Enrichment Diaphragm rod such that the Ratio Lever starts to leave the Economy Stop at a vacuum level of 9" Hg if using the 097 cam or 7" Hg if using the 30-30 cam. Don't obsess over the vacuum level at which the Ratio Lever reaches the Power Stop.

If you don't have an air/fuel ratio gauge but you do have an old mercury manometer, substitute the shop manual procedure for setting the Economy Stop and Power stop for what I described for steps 1 & 2.

Jim

[Lawrence S.]

Re: 1963 Corvette FI - Fuel Meter Ratio Lever Settings

Donald....took your suggestion and adjusted the rod length to 2 1/32"...spot on...the stop screws adjusted out perfectly per the old NCRS guildlines and it started right up on the initial start. I would like to use Jims suggestions on using the air/fuel ratio analyzer but I do not have one available but will check into it....it would be nice to get it properly fined tuned.

That being said took Red up for a front-in alignment after replacing the tires and rebuilding the brake system over the winter and it just roared to life heading down the road...just a sweet sound. Anyway...thank you everyone for the assist and appreciate the feedback.

Larry Stewart

[Paul Y.]

Re: 1963 Corvette FI - Fuel Meter Ratio Lever Settings

Anyone here ever heard of a Mercury Manometer????

Made for FI and works like a champ.

JR

.That has been my choice for 39 years. 22 MPG at 80 MPH