PDA

View Full Version : Engine Mag drop problem



Fortysix12
05-01-2010, 08:14 PM
Ok, I need some help. Here are the Simpsons,

First, no 50 RPM rise at cut off,screw out 3.5 turns and still nothing
Second, mag drop of over 200 both mags, vertually identical. I have checked to see if the switch is grounding out properly-Ok there.
Pers like a kitty at idle, today I got 2350 Static runup with a Stock 150 Sensenich 74M6-0-56
Gave it a shot of prime to see at the helped with the mag drop, nothing. Flooded it as expected.
O320 E2D with HC pistons. .25 SMOH


Are there different jets for these carbs? Is anybody rejetting with higher compression?

I was thinking I've got a bad plug on both mags, about all I could come up with.

NimpoCub
05-02-2010, 12:04 AM
Jeeze, so far, 78 people have no answer. I'm amazed!

You'll get a couple good suggestions by morning! :)

skywagon8a
05-02-2010, 06:35 AM
Ok, I need some help. Here are the Simpsons,

First, no 50 RPM rise at cut off,screw out 3.5 turns and still nothing
Second, mag drop of over 200 both mags, vertually identical. I have checked to see if the switch is grounding out properly-Ok there.
Pers like a kitty at idle, today I got 2350 Static runup with a Stock 150 Sensenich 74M6-0-56
Gave it a shot of prime to see at the helped with the mag drop, nothing. Flooded it as expected.
O320 E2D with HC pistons. .25 SMOH


Are there different jets for these carbs? Is anybody rejetting with higher compression?

I was thinking I've got a bad plug on both mags, about all I could come up with.

First start with Second: You have an issue with the mags. Check the timing to the engine. It sounds like they are retarded, both by the same amount. Do you have two impulse couplings? If so, both mags likely were timed without snapping the impulse first. Easy to do. Thereby both mags are firing late giving a smooth idle. If the mags are properly internally timed and properly timed to the engine your mag drop should be well under 100 rpm preferably around 25 or even less. Since the 200 rpm drop is the same on both it is unlikely that it is a spark plug.

StewartB
05-02-2010, 09:59 AM
I had a new engine act as you describe. Mine was a lean problem. The carb required work to increase fuel delivery.

SB

cubdriver2
05-02-2010, 10:19 AM
Check your wires, I somehow had 2 plug wires switched :oops: and never had a miss fire but had a large rpm drop, and would idle.

Glenn

NimpoCub
05-02-2010, 11:37 AM
There ya have it... coupl'a good suggestions.
Told ya! :)

Fortysix12
05-02-2010, 12:22 PM
I had a new engine act as you describe. Mine was a lean problem. The carb required work to increase fuel delivery.

SB

I'm starting to think this is the case. Checking mag timing in a few minutes. The idle circut is suspect ,at least for part of the problem. Then I'm going to do the chalk test on the exhaust pipe. If I only had an engine anylizer. :) With HC pistons I'm thinking it will need more fuel to maximize the engines potential.

Fortysix12
05-02-2010, 12:23 PM
Check your wires, I somehow had 2 plug wires switched :oops: and never had a miss fire but had a large rpm drop, and would idle.

Glenn

I'm going to go over this as well.

Hardtailjohn
05-02-2010, 02:35 PM
Don't just check mag to engine timing...it sounds more like someone screwed up the e-gap to me...especially if both mags were done by the same guy at engine overhaul? It can happen......been there, done that.
JH

nanook
05-02-2010, 02:49 PM
First problem, you are checking the "idle" mixture. The RPM's need to be above @1000 to pull the throttle plate off the idle jet. Check the fuel/air mixture with the throttle opened up to see how lean/rich you are, or use the EGT if you have one...

Fortysix12
05-02-2010, 08:19 PM
The mags are timed very well so not them. Wires are correct. So not mag timing.
E gap, perhaps.
I want to eliminate two bad plugs as a possibility.
From my research it still seems like I"m just too lean.
Carb should be under warranty.

What's the consensus on richer jets for higher compression engine. I"m at 9 to 1. Was a standard 150HP before the piston change.

Fortysix12
05-03-2010, 09:17 PM
Most of my problem has been solved. A eenyteeni teyney piece of carbon shorting out no. 1 top. Who'd a thunk it. Now, I'm hoping a fine tune of the carb and I'm back in business.