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305 bored .60 over

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305 bored .60 over

cajunpaul cajunpaul
New User | Posts: 3 | Joined: 06/12
Posted: 06/23/12
08:00 PM

New member here hoping for some input.  Long story short - my daughter and I rebuilt a 305 (I know shoulda bought a 350) for a school project.  The donor truck was a 1989 so the 305 is that year model.  We swapped it into a 91 chevy 1500 that had the 4.3l.  The block had to be bored over .60.  Since this was going to be a street motor only werent looking for high performance.  all machine work was professionally done - block, crank polish and rework heads.  We went back with stock cam and stock tbi.  I have 2 cylinders that arent firing correctly.  Good compression in those cylinders (#7 and #8), getting fire to the plugs but those two cylinders are still dead.  Have a tech friend helping and he is stumped

Our best guess is that my problem is with the stock cam and injectors.  Tech thinks maybe we are not getting enough fuel to those cylinders to compensate for the .60 over bore. So I thought I would ask people who do this all the time!  I'm sure I'm not giving enough information here so please ask.  Would really appreciate some input so I dont just throw money at it.  Should I have gone with a different cam with more lift and different injectors?  Of any other suggestions?  Thanks  

waynep71222 waynep71222
Enthusiast | Posts: 448 | Joined: 03/12
Posted: 06/23/12
08:41 PM

did you swap in a V8 distributer with 8 tips on the pick up coil and 8 tips of the reluctor mounted to the shaft...

V6 distributer...


a V8 Distributer..

these may not look exactly like yours... as these are aftermarket replacements for the stock ones with the sheet metal relutor with magnets that crack causing ignition issues..


waynep71222 waynep71222
Enthusiast | Posts: 448 | Joined: 03/12
Posted: 06/23/12
08:46 PM

please.. also be sure that the #5 and #7 wires on the drivers side are separated by more than an inch.. if they are too close.. you will have misfiring issues..

you also had to put on new spark plug wires...    please check at the cap end. that they are actually SNAPPED on.. pull them straight off..  look inside... see if you can see the inner terminal..

i have run into a few that the cap terminal was not fully aligned with the boot opening..  

cajunpaul cajunpaul
New User | Posts: 3 | Joined: 06/12
Posted: 06/23/12
09:03 PM

Wayne - thanks for the replies, yes new 8cyl distributor.  new plug wires but i didnt buy the real expensive ones.  My tech and i actually discussed this, asked if i should try premium wires, he seemed to think since we were getting fire at the plug it probably wasnt an issue.  When you say separate buy an inch at what point?  the entire length of the wire?  I do have them zip tied together above the valve cover because the wire guides broke during disassembly.  

waynep71222 waynep71222
Enthusiast | Posts: 448 | Joined: 03/12
Posted: 06/23/12
10:19 PM

ooh.. bad idea...   the magnetic field created by the HIGH voltage spark going through the wire will INDUCE a spark in the wires next to it...  this normally effects the last 2 cylinders on the drivers side of the car as the the #5 fires a 90 degrees before the #7 fires..   this is when the piston has a full charge of fuel and air but is only half way compressed...  the spark is enough to burn off some of the fuel and air charge.. leaning the cylinder out and usually melting the piston and damaging the cylinder wall...   sometimes  will cause a misfire... this is not just a chevy issue.. its a ford issue..   look at how ford produced a TSB on the issue..


as for wires...   wires are wires until you wear them out or run a serious after market ignition system..

see if you can find this in delco someplace.. it should be the proper wire separator set..

ac delco Part Number:  8073
Product Notes:
Spark Plug Wire Retainer
Per Vehicle: 1; Years: 1989-1992

8073 Primary

this looks like its missing a bottom piece... so it might not be what you want.. just separate the wires.. like ford did it...   5, 1, 3, 7 ..

there are probably other issues...  but these are the easy ones.. that have to be fixed first..  

waynep71222 waynep71222
Enthusiast | Posts: 448 | Joined: 03/12
Posted: 06/23/12
10:38 PM

right side of cap



left side of cap

separator over the valve cover, instead of    1,3,5__7
____________5, 1, 3, 7

spark plugs in LEFT/Drivers side head


waynep71222 waynep71222
Enthusiast | Posts: 448 | Joined: 03/12
Posted: 06/23/12
10:50 PM

now...  a few more questions.. but the spark plug wires are probably one of the problems..

did you swap in a 305 computer or chip...

did you use a 305 throttle body and injectors.???

the 4.3 sized injectors are TOO small and will create a FLAT spot on acceleration..  a hesitation just off idle...  but they will work.. please don't do any full throttle testing..

there are several options..  depending on your answer..  

pepsi1 pepsi1
Guru | Posts: 1718 | Joined: 09/11
Posted: 06/24/12
01:05 AM

Cajunpaul: Welcome aboard.

I'm sure you have checked all the obvious, and have gone over the firing order and make sure the plug gap didn't close up on you.

How does it idle? If it idles rough then I would follow my suggestion below.

Make sure you don't have any tight rocker arms. (If you do your compression will be weaker in those cylinders). It's easy enough to check. All You need to do is a compression check on those 2 cylinders.If the compression is lower then the other cylinders thats your problem. Readjust the valves for those 2 cylinders...
Thanks Bob  

cajunpaul cajunpaul
New User | Posts: 3 | Joined: 06/12
Posted: 06/24/12
08:27 AM

Wow guys!  Thanks.  Wayne, I did swap the computer and put in a new hot chip from Harris Performance for the 305.  I used the 305 TBI.  Most everything I used for the engine was from the 305 or I purchased it new.  All the electronics are new since I didnt know what condition they were in from the donor truck.

@pepsi - yes, all the obvious has been checked and triple checked.  I did incorrectly lash the valves and had the rocker arms too tight initially, but we corrected that.  We also checked the valves to make sure I didnt bend or burn anything as a result of that mistake - tech said everything there is good.  compression is the same for all cylinders after the proper adjustments

I'm going to get the wire guides and see what that does.  this actually makes sense and wires was a problem my tech considered but he was thinking a broken wire and didnt consider the wires being bunched like this.  I bet he will kick himself in the butt when I tell him this.

I really appreciate everyone's help.  I will report back on the results  

skyeking skyeking
Addict | Posts: 2738 | Joined: 08/09
Posted: 06/24/12
05:34 PM

Hi there,
Have you tried aa different dizzy cap?.
A part being new guarantees ZERO these days.
 Good luck with which??? Hunt...Skyeking...