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Engine not running happy upon first start up

12K views 73 replies 15 participants last post by  evilbeef54 
#1 ·
I have a small block 350 4 bolt main, that we changed all the seals on and put a new Comp Cams cam and lifters. It also got a new cap, rotor, and wires. the old edelbrock preformer intake, Edelbrock 1406 600 4 barrel Carb went back on. The truck also is getting a whole new painless wiring harness

On first attempt to start up it didnt want to fire i removed the distributor and made sure it was inserted correctly with the #1 cylinder at TDC rotor pointing at the #1 cylinder, #1 wire on that post and double checked the wires were on in the right order. After that it fired right up, tried bringing up the rpm to 2k for the break in and i am getting some LOUD backfiring through the carb at about 2K rpm. I shut it down and reset the idle mixture screws to 1.5 turns out each and made sure the air filter was on tight. It started happier but still backfires through the carb at 2k rpm. Also after turning off the key one time it kept running, for a few seconds.

I would like to get some suggestions from you guys on what else to check/inspect/additional info you need. This is my first cam swap and want to get this thing broken in correctly. I'm not trying to tune for performance or anything right now, just want to be able to have it running at 2k rpm so i can break in the new cam
 
#2 ·
your timing has to be out . have you got the vacum hose onto the dizzy. have you timed it up with a light ? plugs ok ? no air leaks ? cheque with some carb cleaner when running. the engine will pick up quickly if there is a air gap and it will get sucked in and you will hear a different engine pitch sound for a secound or to.

bet its timed up wrong , all plug leads corrcetly fitted and to correct numbered plugs ?

i would start again with the timing light and double check everything before you start it again
 
#4 ·
#6 ·
ok, i used this method when i first set the valves

How to adjust valves on a chevy small block engine

i will try the other method, seems like the other method techinspector1 listed would have them set quite a bit looser which hopefully will help, i just brought the engine back around to line up with the timing mark on 10* before TDC and made sure the rotor is pointing at the #1 cylinder and the #1 plug wire on the cap and the wire order is correct on the cap... That should be a good starting point right?

with having to break in the new cam i dont want to sit at idle too long trying to set timing and adjust valves, is that correct, i pretty much need to fire it and get it up to 2000-2500 rpm right away?
 
#8 ·
ok

I will be checking the valves in the AM


If the ignition is ok, and it turns out that the valves are alright the other thought i had was i moved the gas tank to the bed of the truck and the old hardline was pretty nasty i ran rubber line all the way forward temporarily, maybe it is not flowing enough at 2k and that is causing the backfires through the carb? I dunno I am just trying to figure out everything i need to double check before i start it up again
 
#10 ·
If the mechanical advance springs are (God forbid) stock, or still aftermarket ones, 10 degrees initial is not going to be anywhere near enough timing.

If you don't have a dial back timing light, make a http://www.crankshaftcoalition.com/wiki/How_to_make_a_timing_tapetiming tape and use a timing light to see what the timing is at 2000 rpm. If it's not high enough, give it some more timing. I'd use at least 36 degrees w/the engine running at 2000 rpm.

Once the cam is broken in, set up the advance curve.
 
#12 ·
ok so I checked all the valves, they were all pretty close, maybe 1/4 turn looser now, hopefully that will be the difference, still planning on getting the fuel pressure gauge before start up tomorrow so i can rule out the fuel line, also i have seen that i may need a seal plate for this carb with this intake and they are cheap so i may pick that up too... hopefully start up goes well in the morning I will report back in the afternoon, thanks for everyone's help and if anyone has any other thoughts i would love to hear it
 
#13 ·
Just one or two.

If this is a flat-tappet cam, make sure that your engine is well-primed (i.e. oil coming from all rocker arms), and that you have added some ZDDP additive.
If you're running dual springs on your valves, you should remove the inner springs to reduce the spring seat pressure. (You won't need them at this comparatively low RPM range.)
 
#22 ·
ok, but since i have done the finger over the #1 spark plug hole to make sure it is on the compression stroke, lined up the timing mark at TDC, lifted the distributor and re-inserted it making sure that the rotor is pointing at the #1 cylinder and then installed the cap with the #1 wire on the post that the rotor is pointing toward, that should mean the distributor is in correct not 180* off right. If it was 180* off when the #1 is at TDC on the compression stroke the rotor would be pointing toward #6 not #1 right?

It didnt really go any better today i tried briefly to start it up and get it up to speed but it really ran like crap, would barely get up to 2k and then started the backfiring through the carb crap again so i shut it back down right away. now is where i feel stupid... I went to check the rotor again and when i lifted the cap i found out that one of the contacts had slipped off the wire in the cap end of the plug wire, so then i started taking a real close look at all the plug wires and saw that the wire seperators i used had actually cut the outer sleeve of some of the wires, so i am hoping that is the issue, that some wires were loose and had some cuts in them so they were arcing
 
#24 ·
By what you've described I do not believe you are 180 out. Cut insulators, etc. as you describe sure could do it.

Important! Be sure that #5 and #7 wires are correct at the cap and down at the head. The two are next to each other on the distributor cap and at the plugs so swapping them is easy to do- I have done it myself. The engine WILL run this way- but it'll be running like crap.
 
#23 ·
With your #1 cyl at TDC, & the distributor rotor is pointing correctly at the lug in the cap for the #1 spark plug, make sure both the intake & exh rocker arms are level.

If one rocker is lifting, you are 180 degress off on your distributor installation

Also, make sure the wires on the cap run clockwise looking down 1-8-4-3-6-5-7-2
 
#30 ·
i want to cry right now...

i am so frusterated that i feel like i am going to lose my effing mind...

i pulled the valve cover and watched the #1 exhaust valve open then close, then the intake open and then start to close while i had my thumb over the plug hole and felt air coming out while the wife turned it over untill it lined up with ... so i am pretty darn sure that i am on TDC for #1 on compression stroke, when i lift the cap the rotor is pointing toward #1 (looking at the top of the rotor the metal tab goes from the center to the out side, the out side with the metal is pointing toward #1)

new cap, new rotor, new plug wires (made sure to start with #1 at the post near where the rotor was pointing and set the plug wires acording to the firing order and double checked with the picture in the old camaro chilton manual, new coil, new carb gaskets new carb seal plate, both mixture screws set to 2 turns out

upon start up it had trouble starting, it started ran for a second and then died, it did this a few times then managed to start and idle but it did not want to come up above 1500-2000 and when it did get up to near 2k it started backfiring through the carb, while it was ideling for a second i checked the timing with a light, it was at like 15* before tdc i tried about 10* before TDC and same results with a barely running idle, i moved it the other way to like 30* btdc and it picked up rpm at idle but still didnt want to come up above 2k and backfired through the carb when it did and felt like it was missing bad below 2k. It also does not want to stop when the key is turned off...

It really feels like the timing is off or fueling is jacked but i dont know what else to do... It is the same distributor and carb that was on it when it was running a few months ago. maybe the carb got jacked up and it is just running really lean for some reason, or the diszy is jacked, or i am jacked...

I am lost and frusterated...

dont suppose anyone that knows what they are doing and is in the NorCal East bay area and would want to come drink some beers and bbq and check this thing out :mwink:
 
#33 · (Edited)
healthy & repeated backfiring thru the carb is one of 2 things:

1. A spark plug firing way too soon (like when the intake valve is open) - wires not routed properly.

2. A intake valve not closing, or open at the wrong time.

At this point, you need to make sure you are getting good even compression on all 8 cylinders. This will also tell you if the cam is lined up properly.

Do a compression test at this point.


.
 
#35 ·
got a guy from work who is pretty good with all this stuff swinging by tomorrow afternoon to help check it out, we will be doing a compression check and checking out the distributor so make sure everything is okay with that, damn this is frusterating, everything i have read says everything i did was done right so far as i can see, hopefully a fresh set of eyes will help, time to forget about this motor for 24 hours and play the new call of duty, lol
 
#43 ·
compression test tomorrow he forgot to bring the tester today, lol, will post up results, however he did stop by and checked out the dizzy and thinks it is pretty jacked, the vac advance can is stuck and doesnt want to move, it looks like it is pretty far out of adjustment and pretty dirty, i am sure i can just replace the can and clean it up, hopefully this is what is leading up to all the issues, gonna try a different distributer tomorrow and see if all is solved.
 
#48 ·
just read the whole topic again , dude i know how it feels . my bloody engine frustrates the hell out of me. but i am gettiing there,

ok i reckon from what you have said you would be better trying to get a working ( friends ? ) dizzy to douple check . you need a vacum line and it defo needs to adj the timing within the dizzy,

also get that comp test done. are you getting excess oil pressure or blow out from the oil dipstick or cam covers ? i had a problem years ago and it was blowing through the rings and pressuring the enigne oil ways . so hopefully a comp test will be ok , my money is on a dodgy timing as i said at the begining. so either wiring of the dizzy . dodgy dizzy. a plug faulty ? anything to do with the ign circuit my money is on.

if i was near you i would be there for the beers and bbq.

chin up son !!:D
 
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