Pry

I have an unsteady idle on my 1959 250 hp fuel injected C1 (7017200 injection unit). Sometimes it idles a little better, sometimes it idles very unsteady and sometimes it doesn't idle at all.

Things I've already checked:
- plugs & wires
- centrifugal advance springs
- didn't find any vacuum leaks with a starter spray

Interestingly the engine doesn't stall even when I close the idle air screw and throttle butterfly completely. It seems to get all the idle air through the nozzle air duct. When I cover the nozzle air duct the engine stalls.
Is this normal and what could cause this?

jtranger

Bumped it for you

jerrybramlett

1. Boiling gasoline in spider. I suggest using undiluted racing gas with a high distillation (boil-off) curve. If you're actually located in Finland as your profile states, this may not be available to you.

2. Improper unit calibration. I suggest using accurate exhaust analysis instrumentation to set the air/fuel ratios during full acceleration and cruising under load before setting the proper tension on the enrichment diaphragm spring.

3. Original (piston-style) spill valve sticking. I suggest installing a later nail/thumbtack spill valve. This assumes you have a die-cast (rather than sand-cast) fuel bowl.

4. Sticking needle valve in spider hub. I suggest installing a new spider made with hard (not soft) copper tubing.

5. Stiff or shrunken main diaphragm. I suggest a new diaphragm with a noticeable raised "hump" around the magnesium wafer.

6. Intermittent vacuum leak between plenum and adapter manifold. I suggest using the '57 - '58 style one-piece gasket that is very thick.


There's a throttle butterfly stop stud located at the bottom of the pivot shaft. It prevents the butterfly from closing completely against the air meter bore. In other words, there's still air flowing past the throttle butterfly even when it appears to be shut.

Pry

Thanks Jerry, I'll have to look into those. Do you happen to carry some kind of database of the injection units you've restored over time?
The unit had been restored by some fuel injection specialist in the states before I bought the car. It's a 7017200 series unit and the serial no. is 1009.

jerrybramlett

All the FI repairmen I know keep a record of the units they've restored. I'll ask around for you.

You can speed up the process by posting or e-mailing me photos of your FI unit. Sometimes I can recognize a particular person's work. My direct e-mail address is jerrybramlett@comcast.net.

Pry

Ok, thank you!

Here are some photos of the unit:
https://www.dropbox.com/sh/5iijld4ao...FNTLDedia?dl=0

I actually bought the car from Canada so I'm not 100% sure if the unit was restored in Canada or US.
The wires aren't the ones the car came with.

It would be really helpful to know which ones of the parts have already been replaced with the better ones.

jerrybramlett

Your unit appears to be very nicely done. It has several features that make me think the repairman knew a lot about fuel injection. Your plenum data plate is a repainted Rochester original.

While I'm checking with some other repairmen, please clarify your fuel situation for me. What kind of gasoline are you using, and do you have racing gas available?

Pry

That's nice!

We don't have racing gas easily available in Finland. It might be available to order.
The best fuel availabe at pump and which I'm using is around 93 octane (AKI) and it has maximum of 5% ethanol content.
Here's an example:
http://www.st1.fi/files/12703/St1+be...5_01012011.pdf

jerrybramlett

If your engine idles reliably at ~800 rpm immediately after it comes off the fast idle cam (usually 2 - 3 minutes after a cold start-up), but it won't idle correctly when the engine is hot, then the problem is fuel boiling in your spider. Is that an accurate description of what is happening in your case?

Pry

Thanks for the help Jerry. I believe that's what's happening. I'm gonna have to come up with some solution as the race gas over here is around $1500 for a 54 gal barrel.

Another problem is that it doesn't run right on higher rev's. Where would you recommend to set the ignition advance on idle?
I set the advance to around 0 degrees on idle with the vacuum advance disconnected as the manual suggests. The vacuum advance doesn't seem to have any effect on the timing on idle though. Is this like it should be or do I have a problem with the vacuum advance system?

jerrybramlett

If you have a vacuum advance canister, then I'm guessing you have a "915" FI distributor. In the photos I see you have the canister connected to a "ported" vacuum source on the air meter. That means the throttle butterfly shuts off most vacuum through that port (to the distributor) at idle.

I suggest you use a dial-back light to set the distributor total timing at 4,000 rpm to be 36 degrees. Have the vacuum advance disconnected while you do this. Then let the initial timing be whatever it turns out to be with the 36 total setting. I'm guessing the resulting initial timing will be around 8 degrees if the advance limit bushing (on the underside of the mainshaft advance cam) is still in place. If you have a later vacuum advance FI distributor such as an 022, 063, or 070, the resulting initial timing should be higher.

You might benefit from reading the tuning tips on the website "Ramjets that Run".

Pry

Thanks a lot again Jerry! You are correct it's the 915 distributor. I'll try that tomorrow and see what'll happen.
Your website has been really helpful as it's pretty much the only modern source to get info about the FI units.

There's small engine fuel available at some stations in Finland so maybe I'll try that first. It's not as high octane as racing gas but it doesn't have any of the additives (like ethanol) modern pump gas has.

jerrybramlett

To me, your unit doesn't look like the work of Jack Podell, Doug Prince, John Marquardt, Gail Parsons, or Chuck Smith.

Jim Lockwood, Tom Parsons, John DeGregory, Gary Summerville, Gary Hodges, Ken Hansen, and I have checked our records and found no mention of your unit.

I haven't heard anything back from George Schreffler, Todd Schultz, or Brian Futo. They may have been kidnapped, hospitalized, or gone on vacation... or maybe they're just too busy to respond. You'll have to track them down yourself to get an answer.

It might even be an old restoration done by Frank Antonicelli or Chris Wickersham, but they no longer take on "regular" FI work for others.

The quickest way to the truth is contacting previous owners of your car. Ask them who did your unit. Good FI repair work is expensive. It's likely they'd remember who they paid.

Good luck!

Pry

Thanks I'll definitely buy you a beer next time I visit Mobile, Alabama!

Adjusted the timing to 36 degrees at 3500 rpm and on idle the timing dropped to around 4-6 degrees. The problem is I can't adjust it at 4000 rpm because the engine just bangs and pops and simply won't rev that high. To me it sounds ignition related but I'm a little lost here. I have new plugs, wires and ignition coil.
Could a wrong dwell angle cause it to run like that?
It worked just fine on higher revs a couple of months ago but then suddenly it stopped working.

jerrybramlett

http://www.jerrybramlett.net/tips.ht...ition_problems

Pry

Thanks I'll check those first. It has been a little confusing as I obviously thought these two problems were somehow related.

jerrybramlett

I admire those in foreign countries who are trying to repair Rochester FI systems. They face a lot of challenges: no local parts sources, no local experience, no foreign language manuals, and English-only help on the internet.

The good news is that now you can make your system run better than it did during the fifties and sixties. It's not easy or cheap, but it absolutely can be done.

By the way, your English is perfect. Are you an American or did you grow up in America?

Pry

Thanks for taking the time to help! It’s great to have guys like you who really know these things and are willing to share their knowledge.

I’m actually a Finnish 27 year old automotive engineer-to-be and lived in Finland for whole my life. But like you said everything tends to be in English so you’ll have to get used to the language to get along.

Sure I know much more about new school ignition and FI systems but I also find these old systems very interesting. You really have to do and learn everything by yourself because nobody knows these units in Finland.

jerrybramlett

You are probably the youngest Rochester FI owner on earth. By a bunch.

Please don't install modern platinum-tipped spark plugs. The pre-HEI GM ignition systems can't fire them at high rpm. But maybe you already knew that.

Pry

Haha that's probably true. I'm still learning so any kind of advice is more than welcome.

I'm kind of trying to avoid anything that is modern with the car as long as the old stuff is fine. The plugs and wires were just something I could find fast locally. If I remember correctly the plugs were NGK BR6S as they didn't have the ones without the resistor. I think I'm gonna order the plugs and wires you recommend at your website.