FI Experts Chime In

[Larry B.]

I had a siphoning problem with my '61 283/315. I got a lot of great help here and put in a siphon valve that seemed to cure that problem. Now the car runs ok until it comes off choke and gets to normal operating tempurature 180*, In cool weather here. Other than replacing the siphon and going to a one piece plenum gasket, no other changes were made.

Please watch the tach in the video to see the wide swings in RPM'S. Anywhere from 600-800 RPM swings.

http://s325.photobucket.com/albums/k367/jtranger/?action=view&current=FiVid2.mp4

[Dan H.]

Re: FI Experts Chime In

Hi Larry, sounds like you're losing your vacuum signal due to a leak in the line/fittings to the main diaphram. Check the connections, try to temporarily seal them with grease or whatever, see if that helps. Car will be very sickly if not a smooth full signal to main diaphram. Happy hunting!
Dan

[Larry B.]

Re: FI Experts Chime In

Hi Dan, I do not see any apparent vacuum leaks there.

[Dan H.]

Re: FI Experts Chime In

Larry, sounds like it's leaning out, try turning your 'cruise mixture set screw' in one turn towards the rich stop, see if that affects the 'surging'. The allen screw towards the front of the FI unit.
Dan

[Larry B.]

Re: FI Experts Chime In

Dan, I turned it in one turn, then two with no significant results.

[Dan H.]

Re: FI Experts Chime In

OK, next, what's the vacuum while running? If you changed intake base gasket, maybe it didn't seal? Still sounds like a weak signal to the fuel meter.
Dan

[Bruce B.]

Re: FI Experts Chime In

Larry,
I am by no means an expert but here I go:
First I tend to agree with Dan, vacuum is usually the culprit in Rochester FI problems.
Try starting the car cold and watching the ratio lever to see if it comes off the rich side when the choke opens.
If it does not go from rich to lean or switches back and forth it might be the vacuum signal from the cold enrichment (choke) mechanism.
If so you can disconnect the positive wire from the cold enrichment, start the car (cold engine) and see if it runs ok when warm it warms up.
If it runs ok then it might be in the choke system.
Bruce B

[Don H.]

Re: FI Experts Chime In

Also check the cranking signal valve. Don H.

[Larry B.]

Re: FI Experts Chime In

No cranking signal. The unit was modified with an electric primer.

[Larry B.]

Re: FI Experts Chime In

OK, next, what's the vacuum while running? If you changed intake base gasket, maybe it didn't seal? Still sounds like a weak signal to the fuel meter.
Dan

Dan, What should I be looking for at the fuel meter as far as a weak signal?

[Jim L.]

Re: FI Experts Chime In

Dan, What should I be looking for at the fuel meter as far as a weak signal?

Larry,

You'd need a sensitive water manometer to measure the signal at the main diaphragm. At idle, you'd expect to see a steady reading in the range of 0.1" H2O to, oh, maybe as much as 0.15" H2O.

If you don't have anything that can resolve such a weak vacuum signal, then there isn't anything you can really check.

Jim

[Duke W.]

Re: FI Experts Chime In

What idle speed are you targeting. The lower the idle speed the poorer the idle quality. Suggest you set it at 900, and with the Duntov cam it should be pulling about 12" manifold vacuum.

Also, make sure your centrifugal advance is not starting below idle speed. Constant idle advance is necessary for good idle stability.

I am assuming you have the original dual-point non-vacuum advance distributor, but if you have converted to a single point with a VAC it needs to comply with the Two-Inch Rule. If not, idle stability will be a problem.

Duke

[Bruce B.]

Re: FI Experts Chime In

Larry,
Can you post a few pictures of the FI unit?
Bruce B

[Larry B.]

Re: FI Experts Chime In

Had the car running today and the lever stayed on the econo stop screw the whole time and never moved even after the engine warmed up. I also pinched the small vacuum hose at the fuel meter to plenum and the engine speed did not change. Is this a choke/vacuum issue?

[Bruce B.]

Re: FI Experts Chime In

Larry,

First, what is the model number of your unit?

There is some sort of problem, I believe related to vacuum since the ratio lever is not moving properly.

If you have an ST-12 look on page 6M-7 where it shows the cold enrichment functions.
At cold start the ratio lever should be at the power side (rich stop, back torward the rear of the car).
When the enrichment coil heats up the vacuum is switched and the ratio lever should go to the economy stop (lean side).
After that when you pull the throttle back the ratio lever should go to the rich side like .

Check the ST-12 as it has some good info.

Bruce B