Marvel Carb Experience
Posted: Mon Mar 22, 2021 7:48 am
Hi Guys. First post but I have been lurking for a while sucking up all the great info on this site. Thought I should finally contribute.
I have a C140 with C-85, fresh overhaul. With the overhaul the carb was "upgraded" to the modern Marvel. The engine made good power, but really never passed a mag check. On one mag, either one, it would cut out almost immediately and start losing rpms, 200,300, 400, etc. If you ran it up to 2100+ and were really quick on the mag check you could trick yourself it was ok, and the story was "just needs to break in", "just loading up", etc. I flew it for 25 hours till broken in. It didn't improve and as the weather got colder (in Mass) it got worse, occasionally running rough in the pattern.
Check for induction leaks, checked, cleaned, gapped plugs, changed idle mix--no change. Called Marvel and sent it back. They claimed it checked out but admitted "sometimes they just do this". When I asked to see the flow data they claimed its proprietary. They said they would change the nozzle (in some undefined way) and that sometimes this helps. Got it back and it was worse, couldn't even get to 2000 rpm.
Pulled the old Stromberg out of the trash and engine ran great, other than the stumble on acceleration. So the Stromberg is on the plane, the Marvel is in a box somewhere at Aircraft Spruce and they still have my money. When these problems started I started searching the interwebs and this sort of issue is widely reported on C-85s with Marvels after the venturi AD in the 1990s. They essentially never bothered to really fix the problem. Some work, some don't. My advice with all the normal disclaimers--If you are thinking of uprading keep that in mind. If you have one that works don't send it in as a core on a rebuild.
I have a C140 with C-85, fresh overhaul. With the overhaul the carb was "upgraded" to the modern Marvel. The engine made good power, but really never passed a mag check. On one mag, either one, it would cut out almost immediately and start losing rpms, 200,300, 400, etc. If you ran it up to 2100+ and were really quick on the mag check you could trick yourself it was ok, and the story was "just needs to break in", "just loading up", etc. I flew it for 25 hours till broken in. It didn't improve and as the weather got colder (in Mass) it got worse, occasionally running rough in the pattern.
Check for induction leaks, checked, cleaned, gapped plugs, changed idle mix--no change. Called Marvel and sent it back. They claimed it checked out but admitted "sometimes they just do this". When I asked to see the flow data they claimed its proprietary. They said they would change the nozzle (in some undefined way) and that sometimes this helps. Got it back and it was worse, couldn't even get to 2000 rpm.
Pulled the old Stromberg out of the trash and engine ran great, other than the stumble on acceleration. So the Stromberg is on the plane, the Marvel is in a box somewhere at Aircraft Spruce and they still have my money. When these problems started I started searching the interwebs and this sort of issue is widely reported on C-85s with Marvels after the venturi AD in the 1990s. They essentially never bothered to really fix the problem. Some work, some don't. My advice with all the normal disclaimers--If you are thinking of uprading keep that in mind. If you have one that works don't send it in as a core on a rebuild.
) are minor inconveniences compared to the costs & potential and serious issues with the "modern Marvel". Mac
. 
(I'm reminded of David Lowe's comment to Sara Parmenter a few years back RE her fuel caps with "vent tubes". David said "I didn't say it wouldn't work, just that it isn't necessary".) Seriously, if it functions well and you need/want true mixture control and an accelerator pump, the modern Marvel just may be the ticket...different strokes. (I just prefer to "Make things simple..."