RV7 To Go
Well Known Member
Needing a carb for my newly overhauled Lycoming O-360 A1A 180 hp engine for my work in progress 7, I purchased a Rotec TBI. The decision was based on the advertised more power, smoother running, better economy and cheaper price. Started flying the plane in July 2017. The unit ran lean at WOT from the start. The fuel flow would reduce from 44-46 l/hr (11.9 USGPH) max down to 40 l/hr (10.6 USGPM) at WOT. The TBI ran excellent from 500 RPM idle to 2550 RPM with slightly hot CHTs on TO(up to 430*F). CHTs in cruise were very even around 350*F leaned out to 25 l/hr (6.6 USGPH). At WOT 8000'DA I had an instant RPM reduction and cooling EGTs when trying to lean. I did my TO's at max fuel flow not WOT. After searching the forums I found that this was a common issue on the O-360 size TBI. After emailing Rotec, Paul replied back saying I needed a "richer" spray bar and he made me a deal on a new unit with this spray bar and the parts to rebuild my 2013 unit with a new spray bar. The new unit was worse than the old one running rough through all RPMs. Switched back to the old unit. I emailed Paul with the info 3 times over the next couple months requesting a spray bar drilled to the old spec so we could play around and try to resolve the issue. Still no answer to date.
Considering the lack of support from Rotec, I decided to switch to a carb in 2018 after 150 hrs on the TBI. I acquired a used MS10-3878 MA4-5 carb. After installing this I found I was no better off. Even higher CHTs at WOT on a 100-115 kt climb out (between 430-450*F) and not able to lean at 8000'DA WOT. Not happy! After searching the forums I found this to be a common issue with the 3878 in an RV (should have done the research first).
After much deliberation I decided to try the 666-660F richer carb mod. The reason for doing this, instead of just drilling the nozzle, is because the kit supplies a restrictor for the economizer circuit air bleed which enriches the mixture at WOT, along with a larger nozzle. I read that the air bleed restrictor allows the use of a smaller nozzle while still providing additional fuel at WOT where needed. Worked great! Now at WOT 8000'DA fuel flow is 59 l/hr (15.6 USGPH) full rich and 36 l/hr (9.5 USGPM) at peak. EGT rise is 2-300*F and RPM increases from 2660 FR to 2760 at peak. TAS went from 172 kts FR to 177 kts at peak. Best of all is the less than 400*F CHTs on a WOT 90-95 kt climb at 88*F OAT. CHTs are 355-365*F at 2350-2400 RPM (FP Sensi prop) in lean cruise burning 26 l/hr (6.8 USGPH). Finally something I can be happy with.
The above are the facts of my experience which is not meant to bash anyone but I hope might be helpful to someone in avoiding the time, cost and stress I went through. FWIW.
Al
Considering the lack of support from Rotec, I decided to switch to a carb in 2018 after 150 hrs on the TBI. I acquired a used MS10-3878 MA4-5 carb. After installing this I found I was no better off. Even higher CHTs at WOT on a 100-115 kt climb out (between 430-450*F) and not able to lean at 8000'DA WOT. Not happy! After searching the forums I found this to be a common issue with the 3878 in an RV (should have done the research first).
After much deliberation I decided to try the 666-660F richer carb mod. The reason for doing this, instead of just drilling the nozzle, is because the kit supplies a restrictor for the economizer circuit air bleed which enriches the mixture at WOT, along with a larger nozzle. I read that the air bleed restrictor allows the use of a smaller nozzle while still providing additional fuel at WOT where needed. Worked great! Now at WOT 8000'DA fuel flow is 59 l/hr (15.6 USGPH) full rich and 36 l/hr (9.5 USGPM) at peak. EGT rise is 2-300*F and RPM increases from 2660 FR to 2760 at peak. TAS went from 172 kts FR to 177 kts at peak. Best of all is the less than 400*F CHTs on a WOT 90-95 kt climb at 88*F OAT. CHTs are 355-365*F at 2350-2400 RPM (FP Sensi prop) in lean cruise burning 26 l/hr (6.8 USGPH). Finally something I can be happy with.
The above are the facts of my experience which is not meant to bash anyone but I hope might be helpful to someone in avoiding the time, cost and stress I went through. FWIW.
Al
