What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

No start on 400 SBC after a tune up?! HELP

D

DizturbedOne

1/2 ton status
Joined
May 11, 2007
Posts
157
Reaction score
0
Location
Sacramento, CA
I searched, but found nothing with results. I'll try to give a few details... The truck ran decently fine before I put new plugs, wires, and cap on it.

It stumbled when I first gave it gas sometimes, more so when cold, and sometimes it would diesel for 1 to 2 seconds on shutdown. That's why I decided to do a little tune-up before maybe taking a stab at some Q-Jet tuning. It has H.E.I. also. I've never owned a carb'ed vehicle before this one.

The old cap looked new from the P.O., but the plugs and wires were old. I gapped the plugs to .050 not knowing but have since found the sticker on the air cleaner touting the 400sbc gap to be .045 so I don't see that being a problem. There were two plugs listed for my truck, one being 13/16th head and the other being a 5/8th's with a tapered seat. I ended up picking up the 5/8ths without knowing which they were, but the old ended up being the 13/16th. Think I should try those? They threaded just fine, but the plugs are shorter than the old plugs. I see fuel/air mixture out of the carb when I turn it over, and I can smell gas after trying to start it for awhile. The choke has always worked ok and seems to be working fine now.

I thought it was just flooded since the pump arm was pumped a couple times while working on it, but even after overnight it still isn't starting.

Also

New starter from the P.O. is shimmed wrong so I can't even turn it over enough to be 100% sure it isn't just flooded or something. It was a non issue before because the truck just fired up instantly everytime. I'm going to shim it correctly in the morning and see if I can get it started with some more turning over (which it didn't need before), any suggestions on what could have gone wrong with just a tune up?
 
The plugs are too short not gettng into the combustion chamber not going to fire
 
First get the right plugs, your local parts shop kinda sucks if they cant get you the right part :doah:

second thing id look at, is if you have slack on the timing chain, these do wear out, i replaced my IROC's timing chain at 150,000 miles, there was 25* of slack.

next thing..... ignition timing. You didnt mention if you set that or not. Setting the truck to TDC on spark plug number 1 (make sure its the compression stroke, and not the exhaust stroke), and then aligning the dizzy to the number 1 post. Then, with someone else cranking the engine, and the dizzy just loose enough to turn by hand, but stay put when you let go, rotate the dizzy till the engine fires and keeps running. turn the dizzy till the engine runs best. then check your timing. if its WAYYYY off, we got some work to do, if its spot on, you dun found your problem.
 
I'll lay odds that you have the wires on wrong. Put the engine on TDC of the #1 cylinder then pull the cap and see where the rotor is pointing and make sure that is where the #1 wire is and then run the firing order...1-8-4-3-6-5-7-2 in a clockwise rotation and i'll bet it fires right up if you haven't moved the distributor at all.

The wrong plugs won't stop the engine from firing but at some point you need to put the correct plugs in.
 
I might add that the cylinder arrangement as viewed from the back of the engine is as follows.

Front
1 2
3 4
5 6
7 8
Rear
 
Last edited:
I knew the firing order of an SBC and went through it several times. It's an HEI so I just automatically clocked #1 plug at 5:30 on the cap like most all HEI SBC's that are setup right. That could be wrong, maybe it's at 6:30 like an old points type dizzy??? Tommorow I'll put it at TDC and see if it's pointing to my "#1". I haven't moved the distributor at all, and it feels solid in there, not moving or anything so I don't think timing changed at all.

I doubt it's the timing belt since all internals of the engine were rebuilt approx. 20,000K ago, that's why I was looking at the top end and ignition so suspiciously, but I still wouldn't rule it out... I'm just going to bump it down on the list.

I'm going to try out some suggestions from here tommorow and report back on what I find, thanks for the help you guys.
 
fmstruck said:
I might add that the cylinder arrangement as viewed from the back of the engine is as follows.

1 2
3 4
5 6
7 8
Click to expand...

Yeah no no its not. Cylinders on a SBC go:

Back
Pass Drivers
8 7
6 5
4 3
2 1
Front

Wait now that I typed that out I think the way you said it just confuzzled me....
​

​
 
Actually in any service manuals I have ever read, right, left, front and rear have always been as viewed as if you are seated in the vehicle.

Whatever, though. It's Saturday and it's early.
 
fmstruck said:
Actually in any service manuals I have ever read, right, left, front and rear have always been as viewed as if you are seated in the vehicle.

Whatever, though. It's Saturday and it's early.
Click to expand...
Yep got up for work at 8 and my partner doesnt show up. ****ing children.
 
Well, I'm out to check if #1 is at TDC when it's pointing at #1 in the cap... It should be though, I never moved the dizzy and I started at #1 (at 5:30 on the cap) and went around clockwise to the correct pistons in firing order for an SBC. Could it have been running one off before? Either way, then I'm off to shim the starter whether that's it or not so I can troubleshoot a little better... I HOPE it's this simple, cause I was starting to think it was fuel or something at this point. BBL with updates.
 
GOT IT SOLVED

Thanks for keeping me on the ignition track you guys, I was ready to move on but after going back out this morning with encouragement to go through that ignition some more I found that the P.O. had stabbed the dizzy wrong! I was pointing at #5 at TDC so instead of finding his crazy wiring scheme which he lucked out and got to work... I just re-stabbed the dizzy (a P.I.T.A.) and set it all up how it was supposed to be with #1 at 5:30.

Thanks again for trying to help me guys!
 
DizturbedOne said:
GOT IT SOLVED

Thanks for keeping me on the ignition track you guys, I was ready to move on but after going back out this morning with encouragement to go through that ignition some more I found that the P.O. had stabbed the dizzy wrong! I was pointing at #5 at TDC so instead of finding his crazy wiring scheme which he lucked out and got to work... I just re-stabbed the dizzy (a P.I.T.A.) and set it all up how it was supposed to be with #1 at 5:30.

Thanks again for trying to help me guys!
Click to expand...

Glad my suggestion worked for you. I've seen too many people drop a distributor in however it falls and then run the firing order and i keep telling them they should drop it in as the book says it should be to save any confusion down the road should a shop or anyone else need to work on it.
 
glad to be of assistance. Youd be surprised how often the simple things are the cause. Ive spent days helping someone diagnose an engine they SWORE had the right firing order on the plugs. When i finally gave up and drove out to help em..... the firing order was off. had the truck running in 10 minutes.
 
You must log in or register to reply here.

Latest Posts

Top Bottom