Page 16 - Spring 2018 GMC Vintage RVing

Technical Corner MAINTENANCE, PARTS, TIPS, INNOVATIONS AND MORECarburetor Replacement – FiTechRandy Van Winkle | 1977 Eleganza II | Battlefield, MissouriAre you having carburetor problems? Are you frustrated with vapor lock? Are you having trouble getting the choke to work properly for cold starting and warm up? Looking for a solution?There have been many GMC owners that are looking for remedies for the above issues. Several options exist. You can keep working to get the carburetor to work properly. A good, well tuned carburetor performs really well and can deliver years of reliable service. However, with today’s fuels, it seems many are having a hard time getting good reliable long term service from a carburetor. If you are looking for another approach, here are some options.Currently, there are several “self learning” carburetor replacement fuel injection systems on the market. These include MSD Atomic1, Holley Sniper2, and FiTech3. This article will focus on FiTech because it has set a new aggressive price point for these systems causing other Elecronic Fuel Injection (EFI) aftermarket providers to either lower their price points or introduce new competitively priced systems. These systems primarily provide fuel management although theyalso provide limited spark control ability that mimics the mechanical weights and vacuum timing curve. The Holley Sniper, a relatively new entry, promises to have a more robust timing control capability. I’m waiting for user experiences utilizing the Sniper – anybody? Then, finally, for a more robust fuel management and timing control, the Howell/EBL kit4provides excellentcapabilities.But this article isfocused on the FiTechsystem. There are twomodels of FiTech5that are available forour application. Thefirst is the 400 hpsystem without sparkcontrol capability andthe second is the 600 hp system that can support basic spark control (does not support the HEI distributor). I have nowinstalled three of these systems for other owners and have a few observations that I hope may be of help if you are considering a carburetor replacement.First, I suggest to do your own research. After all, the decisions you make for your coach will either cause you to smile (or even giggle) every time you go for a drive. Manufacturers’ sites provide a lot of information about their systems but remember, this information contains a certain amount of marketing hype. Google is your friend. There are many forums6 that discuss issues with these systems, so this is where you can learn about things to consider in your decision making process.Although this discussion covers install and usability considerations for the FiTech system, they also apply to other self-learning systems. In fact, if you look at the systems I mentioned above, you can hardly tell one from the other.Fuel delivery.FiTech encourages the use of their Fuel Command Center (FCC).I have installed systems with this setup and originally was very much in favor of this approach. One big advantage was that it continued to use the mechanical fuel pump to supply fuel to the FCC which made it very easy to revert back to a carburetor if that was ever needed.As I have worked with this system and continued to do more research, I now DO NOT recommend this approach. There are too many cases where the FCC has experienced fuel heating causing idle problems, starting issues, and poor performance under load – basically vapor lock symptoms. Additionally, instances of the float shut-off either sticking closed or open have been reported. So what approach works the best? Instead of the FCC, I recommend installing two fuel pumps either in the tanks7 (more difficult) or as close as possible to the tanks (easier). Call FiTech for approval of the pumps you select in order not to void your warranty. In both cases, replace the sometimes troublesome fuel selector valve. Now, you have a built-in backup for the fuel pump. This approach requires a fuel return from the FiTech throttle body to the tank(s). The easiest is to plumb into the fill tube which is accessible from the hatch. Many have designed more elaborate solutions for fuel delivery and return with a lot of information available on the GMC forums. More elaborate usually means more complex and harder to implement, but you decide.Throttle linkage modifications.With the FiTech, I have found it difficult to get wide open throttle and the linkage spring mechanism seems to be a bit stiff for comfortable driving. Attaching the cable lower on the throttle body linkage will provide greater range but also makes it even harder to press the accelerator pedal. FiTech has suggested that you can unseat the return spring reducing the tension on the spring. This then creates the problem that the linkage may not return back to idle so an additional carburetor like spring may be needed. Also, the bracket that holds the accelerator cable and sometimes aftermarket cruise control systemswill need to be re-worked. If you are not comfortable doing your own fabrication, there are kits that provide flexibility in this area, e.g. Fast EZ-EFI Throttle Cable Mount Kits 3041478. I have done my own fabrication so have no experience with these kits but it looks like they could save some headaches.Air cleaner clearance can be an issue.To mount the FiTech, an adapter plate is required. Most vendors are selling the Holley Adapter Plate which is fairly thick and may cause the hatch not to come down far enough without hitting the air cleaner. Options are to put on a different type of air delivery using a remote16 GMC VINTAGE RVING MAGAZINE | GMCMI.COM