Hot Rods Y Block backfire!!! help!

So I have this 312 merc. Y block i'm trying to start and it keeps back fireing thru tail pipe. I took the spark plugs out to check if valves were coming down when piston traveled up, wich i belive it should be doing that to create the explosion right?? correct me if im wrong! I checket the timing chain and they are both(cam and crank gears) at 3 o clock with 12 pins beetween them. does the #1 piston have to be at TDC when installing timing chain? PLease help, thanks!

 

When I was young and did a full tune up on a perfectly good running y block it wouldnt start and did what your describing. ......I had he rotation of the wires backwards on the cap.

Check that first.

 

In answer to your question, yes #1 has to be at TDC when installing the tining gears & chain. As a teenager we about wore one out trying to start it with the marks set up like a normal V8. Instructions, we didnt need no stinking instructions !

 

Remove No1 spark plug.
Remove the opposite rocker cover.

Carefully turn the motor over and get the No1 piston to the top. Check the timing marks are aligned to TDC, and that the exhaust and inlet valves on No6 cylinder are rocking (exhaust closing and inlet opening). At this moment the points should have just opened and the rotor arm should be pointing towards the terminal carrying the No1 plug wire. Then check the plug wires follow the correct rotation.

If these things are not happening at the same time, you have the cam timing out.

I goofed when I put my T-Bird 312 together 30 years ago. Thats when I found out about the wierdo Y-block timing marks on the gears and the chain.

You could also have a bad condenser, This will not help firing up a fresh motor.

Mart.

 

alright thanks alot guys! Im driving my self crazy over hear! because I would see pistons going up and valves not closing :O in my head i was dooomed xP jeje. Im glad to hear I still have a chance before removing the timing cover. Ill do all of the above and get back on the progress! thanks again

 

How long since you witnessed it running well?

 

Switch the two front wires on driver's side and report back.

 

while you have the valve covers off check to see if all the pushrods are there.
Go thru the basics get the proper firing order traced out. Its easy to get it wrong WITH a Diagram for me anyway. Dist runs counterclockwise. Let us know

 

I never saw it run I purchased it a while back it wasn't stuck or anything but never heard it run, I just recently replaced gaskets and rebuild heads. Now I checked for rockers on #6 to be rocking when #1 is at tdc and Thrs no rocking. So now Im thinking the rockers might not be adjusted because some valves travel lower than other. So How would I adjust rockers and How tight? Never done this before

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Are you following the Ford method of cylinder numbering?

Cyls 1-4 on pass side and 5-8 on the drivers side. (LHD assumed).

Turn the motor over and see if the No6 rockers rock at a different time. It's unlikely the rockers are that badly adjusted that the valves do not open at all.. the pushrods would fall off the rocker ball.

Mart.

 

I memorized the firing order in 1967 trying to get my 421 super duty Pontiac running. I new it was a timing problem but I checked it so often that I memorized it. Yes a Pontiac turns the other way from a SBC. It would only fire on 1 and 6....1, 8, 4, 3, 6, 5, 7, 2. It would pop but not start. Rearranged the wires and it fired right up.

 

Been there on my Studebaker flat 6 motor. Check distributor rotation direction. I had mine backwards when swapping the distributor once. It ran but not well and turned the exhaust manifold red hot. Finally figured out rotation was wrong, changed it and it ran perfectly.

 

Y Block valve adjustment;
turn motor to TDC.
Do 1 I E
2 I
4 E
5 E
7 I
Turn 180*
4 I
5 I
6 E
8 E
Turn 270*, 3/4 turn
2 E
3 I E
6 I
7 E
8 I
The Ford books ask for .019. Because of wear on older engines, I like to adjust them to .017 or .016. If its a fresh engine, this will give a bit more duration and lift and is still safe. Feel free to email me for more Y block info on making the valve train last longer.
Ole Don

 

Mart: yeah im fallowing that method, the #6 rockers rock but ones the #1 piston is traveling down from tdc. push rods are loose enough that when its not traveling up or down i can wiggle up and down and rocker are about less than 1/4 loose.
Im going to be checking for dist. rotation now, id be really glad if that was the problem, itll avoid so many other things. alright thanks ole don ill be checking that ones I get home, ill let you guys know the outcome. thanks alot

 

So I did the following set the #1 piston at tdc and put all sparkplug wires in their firing order. Then I changed points to pertronix. I tried starting it and nothing, just trys to start but won't. At least it doesn't back fire anymore. The carb is now leaking might consider getting a new one, any recomendations?

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Other than try and get some people around to help, no.

Mart.

 

just my 2cents,but dont think i would have compounded your problem with changing over to petronix(although that is a good idea,)until i had it running. since you say it is trying to start, i think now it may be a timing issue,and by that i mean it may take aliittle advancing until it "bumps" and then retard alittle at a time..hard to diagnose far away. mart's counsel is a good one...

 

If the carb is leaking (from where?) it may be a sign of a stuck needle valve or the float is hung up. Pull a plug to see if its soaked with gas. That may be the not-starting cause.

If you have no history on the carb, especially if its been sitting: rebuild it, they're real easy.

Bob

 

What is your point gap (.014-.016)? Firing order for wires, 1-5-4-8-6-3-7-2. You can bottle feed the carb, if it needs rebuilding, to just do a test run.

 

Bottle feed, as in pouring gas unregulated down the carb throat? This is more likely to result in flooding than helping.

Bob

 

Yep, that's what I meant. I would think it would be better to do one thing at a time then change a bunch of parts to get it started. This would only be to get it to fire. Don't pour the whole bottle down the intake.

 

If you have 1/4 of play you may have lost the ball off push rod.Best turn motor around twice and make sure all valves are moving up and down. The dist should turn counter clockwise,best go back to points and make sure the dist isn,t binding.Take it out and adjust points.Then if the cap is marked #1 wire from there ccwise. tdc both valves closed.

 

Stop replacing parts & find out whats wrong with it. You seem to be all over the board on this. Check out one system at a time, make sure it right then move on to the next.

 

I once did the same thing on a 1932 Pontiac straight 6 !!

BTW that's not a backfire it's a misfire.

 

Get that leaking carb rebuilt! Gas leak...backfire....crispy.

 

Ugh magoo... Ya disconnect that carb.

Your first post also mentioned the timing chain, did you change that?

 

Alright so I got the timing cover off, and the #1 piston is at tdc and timing chain is on correctly( both gears at 3 o clock and 12pins between them). Now what Im thinking is that the cam isn't on correctly, since #6 rockers should be rocking when #1 is at tdc. So now How can I fix that?

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You sure 1 is at tbc? What makes you think so? The cam can be out 180. 2to1. should run just fine with the dizzy set out 180 too.

 

If the timing marks line up and you are on TDC on #1 you got that part right, now you have to set your distributor. To do that I usually pull the distrubutor, take the plugs out, turn the motor over by hand so that you are are on TDC on the compression stroke, both rockers will be slightly lose and both valves are closed on #1 and your timing marks should line up on the balancer, put the distrubutor in so that the rotor is pointing to #1, install the plugs and wires correctly and time the beast.

 

Here, read this. http://www.ford-trucks.com/forums/1119274-cam-timing-272-y-block.html

Not saying this is whats going on. Might be more simple, Good luck.