Finally got it fired up but am having a problem with it breaking up when I rev it a bit.. Can't figure it out..

355, AFR 195cc, hyd roller, 10:1, MSD 6AL and GM HEI..

It idles semi ok around 1100.. When I try to lower the idle a bit it wants to stall.. But if I give it a little gas quick it was race up to about 1500 for a good 15 seconds or so..

I've tried the timing every which way, adjusted the roller rockers and sprayed carb cleaner around looking for vacuum leaks..

Another thing I noticed is my number 7 cyl header tube is quite a bit cooler to the touch than the rest.. Checked spark and is firing..

A random thought that just went through my head.. Am I supposed to have a ground strap on the motor??

Really need some thoughts here guys.. Thanks!

Check all the grounds to the MSD and make sure the battery terminals are tight. One more thing the wires coming from the MSD box to the distributor should not have any contact with other wires... Check to see if the #7 has spark.

Carb settings sound lean on the mixture screws....

is the intake valve sticking on the #7 and make sure your plug wires have good conection and even swap the 7 wire just to make sure. also run you a ground wire to your head or block where ever you can find a free spot.

and did you mic the cam befor installation and is it a 4 7 swap cam have ran into that befor

Do a compression check on #7, that will tell you if it is mechanical or something else. What cam is it? not a 4 7 swap is it?

4 7 swap cam? I don't know.. Its Comp Cams 282HR

With the idle hanging up there when you rev it, kind of sounds super lean. Are you sure you don't have a vacuum leak? If you are worried about #7 and don't have a compression tester, unhook the ignition system and crank the motor over...Does it sound uniform when cranking or does it spin faster at any point when cranking? If you have a cylinder with very low compression, you will hear it when cranking the motor over. It will crank a little faster when #7 comes up while cranking the motor over.

oh make sure #7 spark plug is tight if it is pull it and look for aluminum on it and pull your plugs if they are still white and not a light to med brown color you need to richen up the air fuel mixture befor you run it anymore i would start with 3/4 to a full turn out with the air fule mixture screw we built a crate motor for a guy who ran it way to lean and burnt 3 pistons in 45 min to an hr run time

Check all the grounds to the MSD and make sure the battery terminals are tight. One more thing the wires coming from the MSD box to the distributor should not have any contact with other wires... Check to see if the #7 has spark.

Carb settings sound lean on the mixture screws....

#7 is getting spark. What do you mean by "should not have any contact with other wires"? You mean obviously copper to copper? Or not even in the same loom? I got my box used and these wires were cut. I have them connected with butt connectors and within the loom with other wires... but no copper to copper...

With the idle hanging up there when you rev it, kind of sounds super lean. Are you sure you don't have a vacuum leak? If you are worried about #7 and don't have a compression tester, unhook the ignition system and crank the motor over...Does it sound uniform when cranking or does it spin faster at any point when cranking? If you have a cylinder with very low compression, you will hear it when cranking the motor over. It will crank a little faster when #7 comes up while cranking the motor over.


oh make sure #7 spark plug is tight if it is pull it and look for aluminum on it and pull your plugs if they are still white and not a light to med brown color you need to richen up the air fuel mixture befor you run it anymore i would start with 3/4 to a full turn out with the air fule mixture screw we built a crate motor for a guy who ran it way to lean and burnt 3 pistons in 45 min to an hr run time

I pulled all the plugs... They are all VERY inconsistent.. Pretty weird actually.. Some lean, some rich, some perfect.. I do not have a compression tester, but it cranks fine. Right now I have the mixture screws about 1 full turn out. Initial timing is around 16 or so.. not exactly sure as im using a tab that only goes to 12...

Wires, cap, rotor are all new. Carb is a Proform 750 cfm body and baseplate, the rest is holly bowls and blocks.

I would bet it is the distributor. You have a some what large cam and low compression on top of some what big runner heads. You don't have much velocity or vacuum and the distributor vacuum advance has no idea what to do. try running a ported source or lock the timing out unless you already run mech advance. i didn't read the whole thread, my car had a similar problem.
Don't read plugs at idle, they will all be rich. give it a GOOD run, don't let it idle and pull all of the plugs. Header tubes can vary temps for numerous reasons, I would bet you don't have a valve adjusted right causing the temps to be off, this is common with new motors.

Double post, windows vista sucks.

Maybe your valves are too tight,...at least on number 7...If you dont have a compression tester handy,put your thumb over the number 7 plug hole and have someone crank it over ...a lot of people adj- hydraulics too tight on new assemblys...


http://s452.photobucket.com/albums/qq247/vette468guy/:hurray:

Should I be running a different distributer? Im at the point im ready to go buy a new carb and dist....... makin me nuts.

Well I don't know if this helps but when we were firing up my brothers 383 for the first time and had everything double checked, it behaved like you described your 355 is behaving. #7 was not firing and really erratic idle / off idle RPMs.

Turned out we had a 3/8 hole unplugged at the rear of the intake manifold that really was not visible when the carb was on the intake (Performer RPM air-gap)

I'd triple check all the vacuum fittings and possible leaks at the back of the intake if you have #7 not firing. Hope this helps!

check your MSD rev limiter pill
try a differnt one too.
I had a bad rev limit pill and engine was breaking up at higher RPMs.
higher i went a cylinder would drop.

[quote=Miikeremains;1192029]#7 is getting spark. What do you mean by "should not have any contact with other wires"? You mean obviously copper to copper? Or not even in the same loom? I got my box used and these wires were cut. I have them connected with butt connectors and within the loom with other wires... but no copper to copper...

Not in the same loom . change the plug to another cylinder. cover the iab with your fingers that will tell you if it is lean. Never herd of Comp making a 7/4 swap cam in a H/R. good luck you will get it.:beers:

check your MSD rev limiter pill
try a differnt one too.
I had a bad rev limit pill and engine was breaking up at higher RPMs.
higher i went a cylinder would drop.

Bingo... Bad limiter chip. 7000 pill breaking up at 3k....

Running great now. Thanks guys for all your help

Very cool! I have yet to see a bad limiter chip. Atleast it was an easy fix. :beers:

yeah it was easy, but had be running in circles for 2 days...lol

glad you figuted it out i tslked to my moter head buddy during golf today he thought the plug may have been bad glad it was an easy fix for ya

:thumbsup:Real glad you got it ! Thanks for the update i always like it when somebody lets us know what the fix was .:thumbsup: