914 carb balance
in 912 / 914 Technical Questions
10 years ago
Hi all, I have a 914 in a ch7 kompress helicopter, I have only recently purchased machine, engine has about 120hrs. The problem I have is trying to sync carbs. Since the purchase I have known that the carbs were out of sync because of a slight pop/miss at idle. So I have finally tried to balance carbs only to find that to get carbs in balance without excesive idle speed I need the 1-3 carb butterfly completely shut and the 2-4 carb needs the idle stop screw turned in about 2-3 turns this balances carbs (via carb mate) but idles about 3000rpm.This engine being in a helicopter has very little load until the clutch is ingaged which means that it will idle with both butterfly's completely shut (idle stops backed right off) in this condition idle speed is about right but I can't understand how the carb vacuum could be so different. If I do the mechanical sync from here ie back off idle stop screw .04" and then screw in about 1 turn besides the idle being to high the balance is still a few turns out. Starting to wonder if something is mechanicaly wrong with engine. Was thinking also about a vacuum leak but so far have not found one.
-this is far from the first try to sync carbs ( thousands of hrs with multiple 912uls on gyro's)
-possibly over looking something simple
-maybe things are done differently on a 914?
-engine seems to run fine above idle and will come together in sync by about 3-3500 rpm
-could throttle position sensor have an ill effect
-could valve timing be out (bent push rods maybe had an overspeed)
- so far I haven't found any other posts that could help
Any and all opinions would be great.
Thanks in advance Jim
-this is far from the first try to sync carbs ( thousands of hrs with multiple 912uls on gyro's)
-possibly over looking something simple
-maybe things are done differently on a 914?
-engine seems to run fine above idle and will come together in sync by about 3-3500 rpm
-could throttle position sensor have an ill effect
-could valve timing be out (bent push rods maybe had an overspeed)
- so far I haven't found any other posts that could help
Any and all opinions would be great.
Thanks in advance Jim
