T

Terke

I'm New Here
Hello All;

I have searched but thus far not found these issues addressed specifically.

The airplane in question is a RV7A with a carburetted O-360-A1A and a Lycoming mechanical fuel pump.

First issue:
Flying at 1500-3000 ASL, the fuel pressure indicates 7-8psi. The indication has been tested with a mechanical gauge and is accurate. At 65% power the engine is difficult to lean and runs rough very quickly after the start of leaning.

At 9,500 ASL the fuel pressure indicates 4.5-5 psi and the engine is easy to lean at 65% and runs smooth.

Second issue:
The engine has two mags, the timing of which has been checked and double checked. Starting the engine cold results in some hard kicking (rotating) of the engine. Starting the engine when hot the kicking (rotating) is frequently much harder still. So hard infact that the baffles have hit the cowling on the inside and caused cracks in the cowling.

Thoughts and suggestions are much appreciated!

Terke
 
When starting do you man "kick-BACK". If so. it sounds like your timing is fast.
You say the timing has been checked and rechecked. Do you have 2 impulse mags? If not, possibly your ignition switch is not grounding the non-impulse mag during start.
When checking the timing, are you sure the impulse coupling has "tripped" before checking?
 
Last edited:
Mel said:
When starting do you man "kick-BACK". If so. it sounds like your timing is fast.
You say the timing has been checked and rechecked. Do you have 2 impulse mags? If not, possibly your ignition switch is not grounding the non-impulse mag during start.
When checking the timing, are you sure the impulse coupling has "tripped" before checking?
Click to expand...

No it doesn't kickback. All engines rock when they start. This engine really rocks very hard and far. It has one impulse mag on the left. The wiring has been checked and it starts on the impulse mag. The right mag is not used during the start. The timing has been checked and the impulse fires at TDC.
Good point about making sure the impulse has tripped before setting the points, and yes this was done.

Thank you for the input.
 
Sounds like your carb is very lean to me. What P/N is it? There are richer ones and some mods you can have done to others to make them richer, depending on P/N's.
Is the vent for your fuel pump and engine breather open and clear? one of them being blocked or restricted is about all I can think of that would make the fuel pressure go down with altitude. Other then possible issues with your tank vents that make it harder to pull the fuel from the tank with higher altitudes and speeds.
I don't think the leanness issue is fuel pressure related.
as far as the rocking on start goes..they all rock pretty good naturally. Are the mount bolt nuts tight against the shank on the bolts and not squeezing the mount properly? Are the inside mount spacers installed? Are the mounts too soft and the incorrect ones?
Good Luck,
Mahlon
 
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