DeTomaso Mailing List: February 2001, Message #151

(Second try, since my computer ate my first e-mail and I had to retype the whole thing from scratch!!! Welcome to Monday!)

Friday I went back to the garage to install the new carb. In case anyone missed it, I pulled the factory-installed Holley on my GT5-S and was going to replace it with a 4777-C. The old Holley is still a mystery, even the Holley tech support line is still researching what it was! It had vaccuum secondaries, and should be a 650, that's all I know. I was never really happy with the performance of this engine, and the carb was probably in need of a rebuild. There was not the rush of the secondaries opening that I could feel on my (mech secondary) '72 car. And at constant throttle it ran a little rough.

The garage had fabricated a fuel line extension, since the 4777 drinks from the passenger side instead of the drivers side. They also relocated the coil for me, since the new fuel feed would interfere with this. I put jeans on and installed the new carb (gotta love a garage that will let you work on your own car in their facility!) I wired the choke open (off), since it is a mechanical choke on this carb. 

After a second, the car fired right up. With no choke, I had to keep my foot on the gas for a minute or two, keep the revs up to 2500 or so. The engine warmed up quickly enough, I set the idle at about 800rpm, but will have to reset it a little since once the car is completely warmed up it idles closer to 1100. 

I left the garage and headed home, threw my ski boots and a suitcase in the car, and headed out. My initial impression with this carb was disappointment. It felt identical in performance to the previous carb, although somewhat smoother. It accelerated briskly, but didn't feel as adrenelin-pumping as a Pantera ought to be. And I still didn't feel like the secondaries were opening, even though Iverified there was no interference and the linkage worked. My problem must not lie with the carb....

I got out on the highway and my disappointment grew. I put my foot to the floor and could only get up to 180 or so (all speeds in kilometers), the limit seemed to be about 4500rpm in top gear. With the old carb I had easily pulled to 5300, 5400, probably with more in reserve but those speeds are pretty darn illegal anyway. But not now, I could feel the gas pedal firmly against the stop, (I thought), I had my foot to the floor. 

Then, something magical happened. For whatever reason, I pushed just a little harder on the gas pedal and I felt it give some. Instantly the note of the engine changed. It went from just a loud yell to a viscious howl. The speedomoter instantly went up and up - 200km/hr, 210, 220, 230, YAHOO!!! I remembered from playing with this carb in the sink that there was a certain amount of resistance before the secondaries opened. I can bench press 300+ pounds, but I WASN'T PUSHING THE GAS PEDAL HARD ENOUGH!!! In my defense, when I felt a fairly firm resistance I didn't push harder, I don't like to force anything...

Once I made this realization, I felt like I had rediscovered the car. The highway was fairly curvy, with short stretches of straightaway between the curves. Each straightaway of course HAD to be done full-throttle, the engine sounds so very different with all 4 barrels open. I had complained to Mike Drew that my GT5-S was too quiet, despite the Euro-GTS exhaust. My '72 with the Mindtrain exhaust sounded much more like a true race car, as it had a much more aggressive tone. Under full load, with all 4 barrels pouring fuel in, the 5-S was suddenly transformed into a full-blown race machine as well. This was awesome! 

The second part of the trip was secondary roads. Traffic was moderate, but there was enough room to be able to pass periodically. Turn signal, drop a gear, push the gas, feel that resistance, push a little harder to open the secondaries, feel that car fly! Pass2 or 3 cars with a SIGNIFICANT speed differential, hop back in the right lane. Boy that was fun! Repeat. Stop for gas. I guess this kind of driving is not very good for mileage. With the old carb I had been filling up every 300kms, but now at 250 my fuel light occasionally blinked at me. Who cares when it is this much fun?

I arrive at my hotel, there is no more room in the enclosed parking so the manager pulls his car outside so that I can park in his spot! That's what I call service!! 

I spent 2 days skiing, the first day had some simply amazing conditions, the second day was cold and very windy. They closed one side of the mountain due to high winds, I had fun anyway. I took the shuttle back down the mountain to my car and headed for home.

I headed for home about the same time as 3/4 of Spain, I think, so I hit the traffic jam from Hell. This gave me time to make some more observations about the new carb. Below 2000 rpm it still runs rough under constant throttle. It bucks, lurches, and generally isn't real happy. The first-gear crawl requires some clutch-work as the car will buck a little. Under full-throttle there is no hesitation, and once it gets above about 2200 rpm it smooths out as well. I know from my '72 that it doesn't have to be so, that car pulls very smoothly from idle. But the improvement in acceleration is impressive. 

After an eternity I hit the highway part again and could stretch my legs. Back up to 180. I again made the observation that driving at night with that wing and a bunch of lunatic Spaniards isn't the easiest thing :-) I like to stay in the right hand lane because there are some big boys that run considerably above 180, and I want to be out of their way. Rear vision with that wing is a joke, and it is tough to gauge the approaching speed of a set of headlights using only your side mirror, knowing that he could be going either 230 or 130. It makes you hesitate before changing lane. And no, I don't care, I still love that wing!!! 

Another stop for gas (a fully functinal carb, like any addictive thing that you find yourself using over and over, has its price!)and I was home. I unloaded my stuff and put my car away. 

This was a fun and informative weekend. This confirmed that my previous dissatisfaction with the performance of the engine was in fact carburator related. This entire test was made possible by this Forum and the generosity of Thomas Tornblum, who sent me his carb so that I could run some tests. It doesn't make sense to go throwing money after possible fixes without knowing what the problem really is. By doing some tests, I can isolate the problem. Now that I know that the area to address is in fact the carb, I can proceed. 

A weekend of combining skiing with a Pantera road-trip. It just doesn't get much better than that!!!