Rochester F.I. Replacement

[Jim L.]

Re: Rochester F.I. Replacement

I recall there is an old adage among experienced FI owners that goes something like "90 percent of FI problems are the ignition system".

And the other 90% of all FI problems are owner inflicted.

[G B.]

Re: Rochester F.I. Replacement

I have a dilema with my '58 fuelie car. I restored my car some 8 years ago and have enjoyed it a lot. However, in the last year or so she has left me stranded a few times. The problem seems to be warm start ups (perculation?). My first thought was to go to a carb set up and just have fun with it.
The engine is a numbers matching (but not original to the car) 283 ci with low hp F.I. Early on, I because of a smoking problem I opted for Pro Comp aluminum heads with 2.01" intake and 1.75" or so exhaust valves and 63 cc combustion chambers. I run it with non-ethenol fuel. It runs well until the temp approaches 180. As long as your moving it stays below 170.
There is a fellow that remans "clone" 245 and 270 hp 2x4 carbs for our year car. Considering the heads upgrade, does anyone have some good advice as to which setup would be best for our car? I'd hate the thought of not driving my car in the summer.

Thanks to all,
Gary Sparks

Here's what I would do in your shoes:

1. Call Ken Hansen and ask his advice. He takes a lot of pride in his FI work (even 8 years later) and will want to help. His number is (731) 783-0815.

2. Put undiluted VP 110 racing gas in your tank. Don't use any pump gas, non-ethanol marine gas, aviation gas, or home-brewed mixtures of anything else in a '57 - '62 Rochester FI except in emergencies.

3. Change your ignition coil. Old coils produce a weaker spark when hot but will start your engine cold.

4. Post on here the results of your conversation with Ken and the changes you've made.

People with '63 - '65 Rochester units will tell you their engines will idle fine in hot weather with pump gas or 100LL aviation gas. That's true except in the desert climates, but they still have percolation for the first 20 - 30 seconds after a hot restart. The same is NOT true for '57 - '62 units. They use a different spider feed system that is very prone to percolation in even moderately warm weather.

[Jack H.]

Re: Rochester F.I. Replacement

Wow, what an impressive thread this has turned out to be. A veritable "who's who" in Corvette FI world all taking the time to reply with insightful and helpful advice. I applaud you all...this is why I love the NCRS and follow/lurk this site as a habit.

[Darryl D.]

Re: Rochester F.I. Replacement

Wow, what an impressive thread this has turned out to be. A veritable "who's who" in Corvette FI world all taking the time to reply with insightful and helpful advice. I applaud you all...this is why I love the NCRS and follow/lurk this site as a habit.

Yes, I have found that the guys that do a lot of the old F.I. work are always willing to help. I have not owned an F.I. car since I sold my 58 in 1985 and have always had a soft spot for them since. However in light of the fuel available today and the cost of racing fuel purchasing one today is "off the table" for me.

[Tom P.]

Re: Rochester F.I. Replacement

I find all the comments above to be rather interesting and some are very valid.
I have been rebuilding (as well as some modifying) FI units for over 40yrs and I have 2 FI cars myself. Yes, sometimes, they can be a little cantankerous! But I put up with it and drive the heck out of them whenever I get a chance. One of the most applicable comments pertains to today's gas. I routinely use 91 octane NON-ethanol and generally ---------------- MOST OF THE TIME----------------everything is fine. Sometimes I have the same hot start issues the others experience. I live with it because I love FI cars more than most people.
In the past, I have used 100LL Avgas as well a 110 race gas and the results were not sufficient to justify the high costs of those.
The FI unit on my 23 T-bucket is a 7380 unit (1964-65) and it runs flawless--------------------but because it is out in the open full time with alum heads, it is not affected by heat. The unit on the SB400 in the 56 is a Bill Thomas (and Tom Parsons) modified unit. It frequently has the typical issues of early units (57-62), but over the years I've been able to minimize MOST issues. But for sure, in the summer time IT DOES NOT LIKE ethanol gas!!!!! I drove from Okla City to a Chevy event in Dallas this summer and filled up on some 93 octane gas in Texas (mistakenly, I thought that would be great). NEVER AGAIN WILL I DO THAT!!!!!! It really ran like crap until I ran out all the ethanol. Went back to 91 octane NON-ethanol and things went back to normal (well, as normal as possible).


With the idle set at about 1000-1100rpm, I usually don't have any problems.

https://www.youtube.com/watch?v=V1I9q3QAMac

[Darryl D.]

Re: Rochester F.I. Replacement

I find all the comments above to be rather interesting and some are very valid.
I have been rebuilding (as well as some modifying) FI units for over 40yrs and I have 2 FI cars myself. Yes, sometimes, they can be a little cantankerous! But I put up with it and drive the heck out of them whenever I get a chance. One of the most applicable comments pertains to today's gas. I routinely use 91 octane NON-ethanol and generally ---------------- MOST OF THE TIME----------------everything is fine. Sometimes I have the same hot start issues the others experience. I live with it because I love FI cars more than most people.
In the past, I have used 100LL Avgas as well a 110 race gas and the results were not sufficient to justify the high costs of those.
The FI unit on my 23 T-bucket is a 7380 unit (1964-65) and it runs flawless--------------------but because it is out in the open full time with alum heads, it is not affected by heat. The unit on the SB400 in the 56 is a Bill Thomas (and Tom Parsons) modified unit. It frequently has the typical issues of early units (57-62), but over the years I've been able to minimize MOST issues. But for sure, in the summer time IT DOES NOT LIKE ethanol gas!!!!! I drove from Okla City to a Chevy event in Dallas this summer and filled up on some 93 octane gas in Texas (mistakenly, I thought that would be great). NEVER AGAIN WILL I DO THAT!!!!!! It really ran like crap until I ran out all the ethanol. Went back to 91 octane NON-ethanol and things went back to normal (well, as normal as possible).


With the idle set at about 1000-1100rpm, I usually don't have any problems.
https://www.youtube.com/watch?v=V1I9q3QAMac

Tom,
The bolded area in your text above is the key for it working for you until it gets REALLY hot. Unfortunately for the rest of us that don't live in a gas and oil producing state like you do we don't have that option available.
On my trip on Rt. 66 when my brother and I stopped to see you with my 1965 300 h.p. car I had problems through out the trip with fuel perc except for the states where I could buy non ethanol gas. I can buy it in AZ. in select gas stations but ONLY in 87 octane. That is not good enough for an F.I. car and really not good enough for my carbed 383 stroker with aluminum heads in my 57 either, so I run 91 octane WITH ethanol and put up with it on restarts. Lucky for you to have the 91 non ethanol available otherwise you would be facing the same thing as the rest of the F.I. owners risking burning a hole in pistons.

[Jim L.]

Re: Rochester F.I. Replacement

Lucky for you to have the 91 non ethanol available otherwise you would be facing the same thing as the rest of the F.I. owners risking burning a hole in pistons.

Huh? How???

[Darryl D.]

Re: Rochester F.I. Replacement

Huh? How???

Because of the lean condition created with the perc. You can read about it in Jerry Bramlett's article I posted earlier in this thread.

[Jim L.]

Re: Rochester F.I. Replacement

Because of the lean condition created with the perc. You can read about it in Jerry Bramlett's article I posted earlier in this thread.

The only reference Jerry makes to burning a hole in a piston is this:

This also means sustained engine operation (many minutes) at very high rpm (above 5,000 rpm) with pump gas could burn a hole in a piston or a head gasket on a hot day.

And it has absolutely nothing to do with fuel perc. It relates to a different calibration curve being needed for pump gas vis a vis racing gas.

Fuel perc results in a lean condition. Fuel perc is also a transient condition which stops the moment you start driving. As such, it's unlikely to burn a piston.

[Darryl D.]

Re: Rochester F.I. Replacement

The only reference Jerry makes to burning a hole in a piston is this:



And it has absolutely nothing to do with fuel perc. It relates to a different calibration curve being needed for pump gas vis a vis racing gas.

Fuel perc results in a lean condition. Fuel perc is also a transient condition which stops the moment you start driving. As such, it's unlikely to burn a piston.

OK, but the bottom line is that with the poor pump gas we have today (other than maybe 91 non ethanol) you run that risk. Unless your going to back the timing off and who wants to do that with a performance car. We buy them to drive with the optimum tuning.

[Jim L.]

Re: Rochester F.I. Replacement

OK, but the bottom line is that with the poor pump gas we have today (other than maybe 91 non ethanol) you run that risk. Unless your going to back the timing off and who wants to do that with a performance car. .

I think you've completely mis-read and mis-understood what Jerry wrote.

As long as the FI unit is calibrated for the correct air/fuel ratio under the conditions of actual use, taking into account Jerry's observations, you won't burn a piston. Ever.

And you don't have to dink around with the timing.

[Darryl D.]

Re: Rochester F.I. Replacement

I think you've completely mis-read and mis-understood what Jerry wrote.

As long as the FI unit is calibrated for the correct air/fuel ratio under the conditions of actual use, taking into account Jerry's observations, you won't burn a piston. Ever.

And you don't have to dink around with the timing.

Below is a copy and paste for what I am referring to. If I have an F.I. car I am going to drive it above 5000 rpm often or I don't want it. I also don't want to buy racing fuel as often as I drive my cars.

"It took four hours on the chassis dyno for me to understand the Air / Fuel ratio differences between running modern pump gas and true racing gas. I was in shock by the end of that test session. I found that pump gas burns much leaner at idle (below 1,000 rpm) and high rpm (above 4,000 rpm) during hot weather than racing gas. Oddly, pump gas burns richer than racing gas at legal cruising speeds (30 to 70 mph). This means that although your car will run on pump gas, it won't run its best. In the summer your idle will be rough after the engine is fully warm, and you'll foul spark plugs more frequently while cruising. This also means sustained engine operation (many minutes) at very high rpm (above 5,000 rpm) with pump gas could burn a hole in a piston or a head gasket on a hot day."

[Ken H.]

Re: Rochester F.I. Replacement

Gary, I would be more than happy to take your call and help with any issues, coil etc. Jerry is dead on that we take pride in all our work even our restorations and stand behind them. It takes a life time to build a reputation and only 30 sec to ruin it. I just returned from Skippack, PA where I was working on a collection of FI cars. I have no problems in making a trip to Florida if that's what needs to be done. As Jerry stated and others please put VP 110 racing fuel in your car and note the difference. You are welcome to call anytime and look forward to hearing from you.


Great posts Guys, Nice group we have

Regards
KenHansen
731-783-0815

[Jim L.]

Re: Rochester F.I. Replacement

Below is a copy and paste for what I am referring to. If I have an F.I. car I am going to drive it above 5000 rpm often or I don't want it. I also don't want to buy racing fuel as often as I drive my cars.

"It took four hours on the chassis dyno for me to understand the Air / Fuel ratio differences between running modern pump gas and true racing gas. I was in shock by the end of that test session. I found that pump gas burns much leaner at idle (below 1,000 rpm) and high rpm (above 4,000 rpm) during hot weather than racing gas. Oddly, pump gas burns richer than racing gas at legal cruising speeds (30 to 70 mph). This means that although your car will run on pump gas, it won't run its best. In the summer your idle will be rough after the engine is fully warm, and you'll foul spark plugs more frequently while cruising. This also means sustained engine operation (many minutes) at very high rpm (above 5,000 rpm) with pump gas could burn a hole in a piston or a head gasket on a hot day."

You don't really drive for minutes at a time with your engine spinning north of 5000 RPM, do you?

[Paul Y.]

Re: Rochester F.I. Replacement

On pure_gas.org I counted over 350 non ethanol stations in Arizona. That web site has an app for your smart phone so you never have to gas up without pure gas.