Help-carb back fireing
 

Hello:

I have a 350 V8.
I just replaced the hi proformance intake with a stock intake.
The hi profo n carb caught fire is the reason that I replaced the intake.
Burnt n meltted the vac lines,dist n wires.
I have replaced the intake carb Dist wires plugs n vac lines.
When I try to start the engine it spits the fuel back thur the carb.
With no responce.
No timing advance when moving dist,no idle responce either.
Have 110 to 120 comp per cyl.
Pulled carb down ck the float n clean inside.
Have ck the #1 to TDC n installed dis.
FO 1-8-4-3-6-5-7-2
Have not had this problem ever before.
It has me stumped ! ! !

All Help Appreciated

T-P Auto
Tim

Re: Help-carb back fireing
 

your 180 out if gas out the carb your not tdc on compression stroke your tdc on exhaust stroke

Re: Help-carb back fireing
 

69chevytrucker;

I will ck that on Wed.
I have a dr(eyes)appt tomorrow.
I'm going to start over from the start.
Ck the TDC first
Then ck the dist pointer
Reset dist so that #1 will point to #2 cyl .
That give the vac adv room to set the advance.
This eng come out of a corvette that caught fire.
I don't know what caused the fire under the hood.
So this as been a very big headache so far.
Been on it for a couple of days.
Going to take a brake tomorrow.

Thanks
T-P Auto
Tim

Re: Help-carb back fireing
 

Even if you pull #1 plug, turn it over till it blows your finger off which is compression stroke then pull cap and see where the rotor points, plus don't set timing to TDC, set #1 to approx 10atdc which is where the engine would approx fire and run, in other words set the rotor to match #1 plug on cap at factory rated timing, prob 10 or 12 degrees. if that doesn't solve the problem pull both valve covers and check all the pushrods, may have one bent or broken rocker arm which would cause a backfire also. Still sounds more like distrib is 180 or 1/2 turn out and trying to fire on #6 cyl instead of #1 as already mentioned. Good luck keep us posted.

Re: Help-carb back fireing
 

This may help. On every Chevy V8, the crankshaft pulley key lines up with the #1 crank throw. That is, TDC is when the key is aligned with the #1 cylinder, 45* CW from straight up (as seen from the front). Ignition stroke is when no valves are open, so the cylinder will hold air; exhaust stroke both valves will be open a bit (exhaust is still closing, intake is already opening), so the cylinder won't hold air.

Re: Help-carb back fireing
 

The rotor should point almost straight ahead as it blows your finger off the plug hole.

Re: Help-carb back fireing
 

If the distributor was dropped correctly as taken out, the problem was prior to intake installation. Is the timing chain stock? What year? If the nylon gears are breaking, it's only a matter of time before the chain strips the sprockets.

Re: Help-carb back fireing
 

Mud,man,rick, koolit;

Thanks:

I'll give it all atry later today.(6am) here.
Have to drive 90 miles to the eye dr today(one way)
I'm a vet so go to the VA dr's in Alb,NM
Again thanks for the info,will try it later today or first thing tomorrow.

T-P Auto
Tim

Re: Help-carb back fireing
 

Here's a nice wiki on finding tdc #1.
Shows pics of what Rich Weyand is describing.
http://www.crankshaftcoalition.com/w...op_dead_center

Re: Help-carb back fireing
 

Hello again;

Got back on ter 350v8 carb back firing.
Reset the TDC
Reset wires 1-8-4-3-6-5-7-2
First spin runs for about 30sec
Then starts pushing fuel back thur carb.
Pulled the front off the eng, cked the timming marks.
Set cam dot to crank dot
try to start
now belching flame out of carb not just fuel spray.
going to pull v/c off and ck the rocker arm n push rod tomorrow.
going to back off the valve adjer nuts also.
going to try to run with out the cover on the can n crank.
still can not get any info from the person who burnt up the corvette engine.
did find out that several people saw him rodding the vette on the back streets before it caught fire under the hood.
that as one thing about a small town,someone will notice things.

Till tomorrow;

T-P Auto
Tim

Re: Help-carb back fireing
 

Hi all;

Question?

What is floating the valves?
I have heard this term;
Just do not know what it means?
What are the reffect of this?
I have never had this much trouble with a small block 350 v8.

All Help Is Appreciated

T-P Auto
Tim

Re: Help-carb back fireing
 

Any chance the distributor cap is cracked or carbon streaked?

Re: Help-carb back fireing
 

Have changed out Dist cap n wires n plugs n intake.
took off the EGR intake,replaced w nonEGR intake.
have try 2 different carbs.
still same problem as stated in the first post.

T-P Auto
Tim

Re: Help-carb back fireing
 

Ok, setting cam dot to crank dot is distrib firing 1/2 turn out, that is "not" tdc, 100%. that is how to install a timing chain set but then turn engine over 1 full turn "then" drop in distrib on timing mark of approx 1.degrees and distrib and #1 plug term lined up and "done my friend. I have made that mistake many times when I first started out. Go get it done right now. So line distrib up on #6 firing now, pull distrib and drop in to #1 as mentioned. Will be right, good luck.
Mudman.

Re: Help-carb back fireing
 

mud man;

Thanks;

Will try this out tomorrow n let you know what happens

T-P Auto
Tim

Re: Help-carb back fireing
 

No problem, it will work for sure, it happens a lot, makes no sense the way Gm set the timing marks, a lot of engine guys laugh about it.

Re: Help-carb back fireing
 

mud man;

I pulled the ft of the 350v8 motor down to the timming chain.
I brought #1 up on comp stroke with the vc off.
When I did this the timing marks were at 12;00 on crank n also 12;00 on the cam.valves closed
This was with #1 all the way up in cyl hole.
With cam seting on the mark at 6;00 and crank at 12;00 , the intake was closed but the exhaust was just opening.
NO nutral lash on valves as there should be,per all information on 350v8 sbc.
So what I did was take the dist at TDC n turn it 180.
With this set up it would fire n run for a short time with no foot feed. try to acc n it would pop /denonat. move the dist n would have a hard start.(kick back)
Replaced the Q-jet with a 2bld n adptor plate,replaced dist with a known good dist.
the carb n dist come out of my 79 chevy 350v8, been running for last 10 yr with out any trouble.
would not let the 350v8 in the vette run.
So going to go into the top end of motor the next few days.
!st - check the lifters n push rods
2nd - pull the cam n ck the lobes
3rd - pull the heads if no problem found on cam n push rods.

T-P Auto
Tim

Re: Help-carb back fireing
 

So just to make it easy, pull #1 spark plug, have someone bump engine w power wire off distrib, keep bumping it till it comes up on compression and starts to blow your finger off, that is compression stroke so look at timing marks, may be slightly past tdc, turn the balancer to 10 atdc. Then pull distrib cap and make sure #1 plug wire/term lines up perfectly with rotor, that is it. If it doesn't run correct pull both v covers and turn engine over slowly w a bar on crank bolt (usually I hv s plugs out for easy turn over) and watch each valve, how much it lifts and drops and make sure "all" are the same. I have seen on Gm only the rocker stud pull out part way, since they are cheap press in and the valve won't open enough so will get a backfire. Good luck and let us know what you figure out.

Re: Help-carb back fireing
 

mud man;

That is what I did several times yesterday.
Once we change out the carb n dist, it try to run, we had to hold the gas open about a 1/4 to keep it running. Even with that going on it still had no responce to gass.
Then when you went to start again ,you had to play with the dist.
I think we run the batt down n cooked the starter try to get this eng running..
So today I think I'll remove the intake, ck out the push rods(take them out) pull the lifters out n ck them, might even pull the cam out n ck it.
With useing known good parts(carb n Dist)that were in the old 78 chevy PU. This has both of us stumped.

With today the 4th I not sure just how much I will get done.
I just might take the day off from this problem, n just work on the rat rod truck that is in other shop.
Need to plum in the fuel line n remove the fuel pump from the tank(45 psi pump).
Then refresh the Q-jet that I have for the rat rod.
Sometimes it is just better to walk away from a problem for a few days.(let the brain rest) ha ha.

Thank for the info.

Have a great 4th of July

T-P Auto
Tim

Re: Help-carb back fireing
 

Well good luck Tim, hope you figure it out soon, me I would prob camp in my garage, but your right sometimes better to take a break, let us know how it turns out. Maybe the bottom crank gear is one of the type with advance and retard keys and not in the right one. Wish I was there to help you, got me scratching my head too.

Re: Help-carb back fireing
 

mud man;

Did not work on the 350v8 problem.
I was going to try to work the rat rod.
Instead I cleaned up the shop.
I put up peg board n shelfs.
Got the shelfs full.
Hung a lot of tools up on peg board.

Tomorrow I'll get on the rat rod.
Plum in the fuel pump n lines,
Drop in the Dist
Refresh the Q-jet carb
Plum in the heater hose n rad
Trans lines
Install oil press gauage (manuel) Temp gauge (manuel)
Then try to get the valves adj
Going to leave the trans un hooked till I get the engine running.

Hope I can get most of the above done tomorrow.

Still have to wire in the elect system to steering colume.
Just going to use jumper n starter buttom to set the valves.

T-P Auto
Tim

Re: Help-carb back fireing
 

So ..what do you have for a Ratrod Tim, car, truck, sounds interesting.

Re: Help-carb back fireing
 

mud man;

I have a 52 chevy pu cab
with a 51 bed
setting on a 86 s-10 frame
305v8 just what I had laying around
86 pontiac 200r4
sets n steering wheel out of 1992 conversion van
15" smoothies on rear
14" cragers on front
92 olds 4x4 rear end
1.5" drop in rear end
I have a post on this sitein the 47 to59 chevy
I call it the "Frankenstine"
due to all the different parts (All GM)

Not working on the 350v8 till tuesday.
Have another dr appt in Alb ( leg replaced)

T-P Auto
Tim

Re: Help-carb back fireing
 

I kind of like frankenstine, cool project. Must be hard to find the time, especially if you have other stuff like Dr. appointments going on too. Still want to hear about the back fire engine.

Re: Help-carb back fireing
 

Mud man;
Got the heads pulled on the 350v8
Pulled the cam out n found 8 out of 16 lobes wore down.
Also cked the exhaust valves, looks like new valves.
cked the intake valves also
looks like the exhaust valves were never setted in.
could not find a wear ring on the valve thats looks like it was setted
The intake valves show the wear ring
Was told that the engine was a fresh rebuilt ! ! ! ! !
I just had to pull it down to see what was going on.
I also think that who ever built the engine had the valves turned down to tight.

Thats it for how.

So did you ck out the build project I"m working on?

I have a lower left artifical leg, a couple of month ago the leg fell apart. I was just lucky that I have an extra leg here. It has my tennies in it but it has gotten me thur.
I had to have the VA order me a new set up with a liter spring setting.
I get to see if it will be the right one on Monday.
If it is then I will get them to order me another set up for the other leg.
I have a work boot leg
A dress boot leg
n a tennie leg
It was the work boot leg that broke.
The dress boot spring is to hard to walk on, that is why I have not used it before.



T-P Auto
Tim