msd backfire
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 1,028
Likes: 0
From: San Antonio Texas
msd backfire
just installed an msd digital 6 ignition on my 79. rev limiter is great BUT as the rev limit is reached i get an occasional bad backfire with the normal rev limit "roughness". is this normal? also, rev limit kicks in about 200 rpm before my tach (stock) says it should. which is the correct rpm... what my tach is reading or what the msd says is the rpm (ie 4000 rev limit set on msd, kicks in when my tach says about 3800).
Burning Brakes
Joined: Aug 2004
Posts: 971
Likes: 7
From: roanoke va
it is normal for roughness and backfire when the rev. limiter kicks in. how it works is that it cuts out dist. fire to alternate clys. as it is trying to keep revs. in control and with out the fire to the clys. the gas gets in the ex. system and accumalates and that is where the backfire comes in. it is a crude system but it will save your engine it is not wise to keep your foot in it other than getting it set where you want it and leave it. you can blow or swell your mufflers from the backfireing. also you will need to try diffrent (pills) to get it to kick in where you want it to. generaly if you have a stock engine and want to protect it put in a 6000 rpm or a 6500 and leave it for it to do it's thing.
Thread Starter
Burning Brakes
Joined: Nov 2004
Posts: 1,028
Likes: 0
From: San Antonio Texas
no "pills" with the digital 6. it has round "dip" switches. can adjust in 100 rpm limits from 2000 up to ........ 12K i think. one reason i bought it. didn't want to spend extra on more pill plugs. also, wanted the retard function when starting. that's a cool feature. i knew how the rev limiter worked just didn't know if the backfire was normal. you say it is. i guess the idea is for the idiot behind the wheel (in this case, me) to take his foot off the pedal when the rev limit is reached. set mine at 6000 for stock.
Le Mans Master
Joined: Jan 2000
Posts: 8,721
Likes: 108
From: Canada
I have found on some MSD units (ie. my 6AL) that even though I have a 6000 rpm pill installed it actually kicks in at 5700. Others have commented on the same with their units that the limiter kicks in before the dialed or pilled in limit.
Drifting
Joined: May 2003
Posts: 1,414
Likes: 2
From: Barrie
Originally Posted by gdh
I have found on some MSD units (ie. my 6AL) that even though I have a 6000 rpm pill installed it actually kicks in at 5700. Others have commented on the same with their units that the limiter kicks in before the dialed or pilled in limit.
Testing with a 3000 pill I noticed that at full throttle I get the backfiring, but at part throttle it is smooth and barely noticeable. Takes about a second to realize you're not going any faster.
Instructor
Joined: Apr 2004
Posts: 235
Likes: 0
From: Mansfield Ohio
I think the factory tachs don't read very accurate. I used my new digital timing light to compare and my tach reads 200 rpm less than the light. I use the pills, but thinking about that adjustable rpm unit as an addition so I can quickly bump up the rev limit if needed.
