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Pertronix & MSD Timing Question  Rating:  Rating
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 Posted: 07-07-2007 08:01 pm
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John Finch
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I've completed the installation of a Pertronix and MSD on 18309. Plugs are gapped at .35. Dellorto 45's spec 5. Starts and idles fine. I am getting minor backfire during over run. This is new. Per previous posts I see a timing recommendation of 12^.  Is that at 1000rpm? The illustration in the manual shows the front oil seal timing mark at TDC is 0^  and moving to the left or CC from the front of the engine, in 5^ increments to 20^. I am at approx 10^ at 1000rpm using the svc manual info. I'll adjust to 12^ and see if that helps. Fuel pressure is at 2.5psi at the rear Dellorto at 3000 rpm. Am I on the right track with adjusting the timing to 12^.  Any info will be appreciated.

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 Posted: 07-07-2007 08:20 pm
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John Kimbrough
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John, I would say your idle circuit is running a little lean.  Mine did this same thing until I got the idle mixture right.

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 Posted: 07-07-2007 08:25 pm
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John Kimbrough
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In addition, you cannot usually correct the problem by adjusting the idle screws.  The idle circuit also feeds the progression holes and needs to be richer there.  Only way to correct for me was to change the idle jet and holder.

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 Posted: 07-07-2007 10:45 pm
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John Finch
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John Thanks. I balanced the carbs with my Carbtune after installing the Pertronix and all was ok actually. I am currently running 55 idle jets. Thats what I had in with the points and MSD prior to installing the Pertronix and really didn't have any backfiring to speak of with that combination. Would the Pertronix require additional fuel vs points? If so then I've got a set of 58 idle jets I can install that are in a set of 45E's I have on the shelf for a future 2.2 upgrade. The 45E holders are 7850.9 which is weaker than the 7850.7's that are in there now, so I'll keep the 7850.7 holders and install the 58's for the first try. However my plugs have historically been sooty with the 55's. What holder and jet did you end up using? ALso will changing the timing to 12^ from 10^ help with this or is that a seperate issue? Thanks again for your advice.

Last edited on 07-07-2007 10:45 pm by John Finch

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 Posted: 07-08-2007 11:19 am
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John Kimbrough
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John, my dell 45s came with 7850.9 idle jet holders and 55 idle jets.  I left the holders and put in the 58 idle jets to get rid of the stumble.  I still set the timing at 10 btdc.  All I can say is that every car is different.  My engine has never been rebuilt so the right setup for it may be different than one newly rebuilt. 

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 Posted: 07-08-2007 02:32 pm
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Judson Manning
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John,

I don't think your specific new problem is in the carbs.  When I rebuilt Ron Earp's engine last year we found a similar timing problem.  It turned out that when the distributor was tested it was firing all over the place. 

MSD is known for their "Multiple-Spark-Discharge".  Translation:  A single spark doesn't fire at a 10^BTDC, rather the first one fires at 10^ then several more over something like the next 30^ of rotation. 

A really cool thing to watch is uncap the distributor and rotate the engine by hand.  If you watch the underside of the cap where the terminals are you will see a brilliant lightning show of dancing 2"-3" sparks.

The point is:  I think your distributor has a minor wobble due to a worn bushing or slightly out of aligned reluctor.  This minor alignment problem is multiplied 100x by the multiple 40,000 Volt sparks resulting in a stray misfire.

Richening the carbs to clean-up a firing problem is a very common trick but IMHO not the best solution.  In my experience Spec5-9 is ridiculously too rich and I've had much better luck with Spec10.  Of course I'm also running a brand new Lucas 45DM distributor.

Judson

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 Posted: 07-08-2007 03:51 pm
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John Finch
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Great insight. Thanks to both! John

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 Posted: 07-08-2007 08:54 pm
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Ron Earp
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Judson Manning wrote: John,

I don't think your specific new problem is in the carbs.  When I rebuilt Ron Earp's engine last year we found a similar timing problem.  It turned out that when the distributor was tested it was firing all over the place. 

MSD is known for their "Multiple-Spark-Discharge".  Translation:  A single spark doesn't fire at a 10^BTDC, rather the first one fires at 10^ then several more over something like the next 30^ of rotation. 

Judson is right on here. I had my dizzy rebuilt by a fellow who does MG dizzys and the spark scatter went away. My timing would jump around a fair amount that of course got worse as the RPMS increased.

After rebuild you could hold it at 6k and put the light on it and get a steady, rock steady, timing mark. That wasn't the case before the rebuild by any stretch.  This is with an MSD on the system.

The MSD is fine to use, but your dizzy has to be in good shape as well as the dizzy cap and rotor.

Ron

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 Posted: 07-08-2007 11:23 pm
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John Finch
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Looks like I am in the market for a 25D4. Thanks again for all the excellent knowledge and advice.

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 Posted: 07-08-2007 11:55 pm
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Ron Earp
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Get Jeff to rebuild it for you, he can do it and does a good job, fast and cheap.

His email is:

jschlemmer1@mn.rr.com

Jeff Schlemmer, in MN. Roughly about $75 and includes all new bushings, recurve, etc. I thought it well worth it.

Ron

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 Posted: 07-09-2007 02:58 am
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John Finch
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Great lead! Thanks Ron!

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 Posted: 07-09-2007 04:01 pm
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Joel
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How about just buying the drop in Pertronix distributor?  I know Delta has them.  Next time something goes awry with my dist - that's what I plan to use. 

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 Posted: 07-09-2007 08:03 pm
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Ron Earp
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There is an entire dizzy made by Pertronix for the JH? Sounds expensive! I knew about the points replacement and everyone runs those, but I didn't know about the entire dizzy.

R

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 Posted: 07-09-2007 08:06 pm
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Joel
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http://pertronix.com/

This is the way I'm going next time.  I think they're under 200 bucks.  If I remember right the original special was something like 150 or something. 


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 Posted: 07-09-2007 09:05 pm
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Ron Earp
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Dang, that is a good deal. If I ever get back to racing the JH I'll get one of those as a spare. Judson, I need to send you your dizzy spare I borrowed, shoot me an address. R

R

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 Posted: 07-10-2007 12:37 am
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Jensen Healey
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I think it's curved for the MBA and MGB so you would still have to re-curve the thing.

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 Posted: 07-10-2007 01:37 am
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Joel
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Call Delta or Bean and ask them.   No more futzing around w/ rebuilds etc. 

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 Posted: 07-21-2007 01:09 pm
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John Finch
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Got the dizzy rebuilt and recurved by Jeff Schlemmer at Advanced Distributors jschlemmer1@comcast.net, 612-804-5543. He also repaired the clamp collar I damaged and fine tuned the Pertronix installation I had done. Bead blasted and cleaned entire unit and installed new cap hold down springs, eliminated end play in the shaft,  installed new ground wire, etc etc. Works great! Completed the job in 3 days $120.00. I suggest calling or emailing for his opinion on the construction of the Pertronix dizzy compared to his rebuild. Highly recommended. Ron thanks for the tip, Jeff did an excellent job!

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