I give up! Help!!!

[searaymon]

Last spring I blew a head gasket in my 1984 Mercruiser 228R (Chevy 305 V-8). Water got into one of the cylinders and the piston rod bent when it tried to compress the water.
I pulled the engine, the block and head checked out. I replaced the piston and rod, all the gaskets and had the carb rebuilt.
The engine starts and idles (somewhat roughly though), but when I give it gas, the engine backfires and cuts out! It's almost like one of the spark plug wires is not connected. I have checked the following:

- The timing is correct
-The carb is supplying plenty of gas
- The firing order is correct

What am I missing?

 

[cannonford57]

Re: I give up! Help!!!

when you say the head was checked out were the valves done

 

[maxxman04]

Re: I give up! Help!!!

bad plug(s), wire(s)

 

[airmail]

Re: I give up! Help!!!

My guess is the carb. Might be to lean. You said it's not idling real good. Did you set the air fuel mixture screws. If you did how did you do it? First with the motor NOT running check and see if the accelerator pump is working. Take the air cleaner off and move the throttle and look down the carb. Do you see gas squiring into the bore? Just move the throttle slowly and look then move it fast and look. You should see fuel both ways but more when you move the throttle fast. If the answer is yes then next lets set the air fuel mixture screws. Engine running and warmed up. First I'll need to know what kind of carb do you have. Is this a Holley carb or a Rochester carb?

 

[cr2k]

Re: I give up! Help!!!

If carb was rebuilt did they reuse the old (much stiffer) spring from the accelerator pump? The new kits come with weak springs that just don't do the job very well.

I agree it sounds like a carb problem, however 90% of carb problems are electrical.

 

[searaymon]

Re: I give up! Help!!!

when you say the head was checked out were the valves done

No, the valves weren't done, but seemed to be in fine shape

 

[searaymon]

Re: I give up! Help!!!

bad plug(s), wire(s)

Plugs, rotor and dist. cap are new. The wires are not new but seem fine. I think i'll replace them though, just in case

 

[searaymon]

Re: I give up! Help!!!

My guess is the carb. Might be to lean. You said it's not idling real good. Did you set the air fuel mixture screws. If you did how did you do it? First with the motor NOT running check and see if the accelerator pump is working. Take the air cleaner off and move the throttle and look down the carb. Do you see gas squiring into the bore? Just move the throttle slowly and look then move it fast and look. You should see fuel both ways but more when you move the throttle fast. If the answer is yes then next lets set the air fuel mixture screws. Engine running and warmed up. First I'll need to know what kind of carb do you have. Is this a Holley carb or a Rochester carb?

I did check fuel flow, as you said, by moving the throttle both fast and slow. The fuel flow looks just as you say it should. As far as the air/fuel mixture screws (Rochester 4-barrel) I cranked them all the way shut, then backed them open 2 turns to start. I found that adjusting the mixture screws had little or no effect on the idle. For example, with the engine running, I can close the screws all the way and the engine continues to run. Weird

 

[coastalcruiser]

Re: I give up! Help!!!

make sure you check the firing order, and that # 1 is really at tdc and not 180 degrees from it check timing and advance

 

[searaymon]

Re: I give up! Help!!!

Have you checked for a vacumm leak? VERY easy to have one after reinstalling the carb.

There is only one hose on this carb (which runs to the fuel pump). That is on tight. While it was running, I sprayed carb cleaner around the base of the carb to check for a vacumn leak, it didn't run ant better. Is there a better way to check?

 

[searaymon]

Re: I give up! Help!!!

make sure you check the firing order, and that # 1 is really at tdc and not 180 degrees from it check timing and advance

I checked and rechecked firing order and timing. Everything is exactly right in that respect.

 

[searaymon]

Re: I give up! Help!!!

My guess is the carb. Might be to lean. You said it's not idling real good. Did you set the air fuel mixture screws. If you did how did you do it? First with the motor NOT running check and see if the accelerator pump is working. Take the air cleaner off and move the throttle and look down the carb. Do you see gas squiring into the bore? Just move the throttle slowly and look then move it fast and look. You should see fuel both ways but more when you move the throttle fast. If the answer is yes then next lets set the air fuel mixture screws. Engine running and warmed up. First I'll need to know what kind of carb do you have. Is this a Holley carb or a Rochester carb?

My next thought is that it's something I did wrong deeper in the engine (though the fact that the motor still runs when I crank shut the mixture screws still bothers me). Could I have the rockers too tight which might be holding a valve open? I did this by the book, and I could spin all the rods with my fingers before I closed it up. Your thoughts....

 

[sarantis]

Re: I give up! Help!!!

I 've an old Sea Ray and i've experienced this or similar problem.Before doing anything else check this .Put a clear hose from pump's output to carb's input and a friend to drive.If you see any bubbles through it,it's a fuel delivery issue.At my Sea Ray the tank's output had a grid to prevent the dirt to enter the line and as for many years nobody had cleared it up ,.each time the engine needed more gas all the dirt raised up and clogged the pick up.In adition the antisiphon valve is a suspect (a connector from the tank's output to the filter's input ).Finally the air relief valve of the tank is a suspect(check it by leaving the gas tap opened.

 

[gadget73]

Re: I give up! Help!!!

If the motor idles with the mix screws turned all the way in, it sounds like the carb bowl may be cracked and leaking fuel directly into the manifold. It should not run with those screws turned in.

Though if you cranked them hard, it will destroy the needle screw and the seat, and all bets are off at that point. When they get turned in, they should be lightly bottomed, not turned hard until they won't go anymore. Might want to pull those mix screws out to verify there is no groove cut into them. If they have a groove, you'll need to replace them and verify the seats themselves aren't trashed.

The spinning pushrod thing doesn't really mean anything, other than they have some oil on them. Its not really much of an indicator of zero lash. Exactly how did you set the rockers? It should be zero lash and turned past that 3/4 of a turn if memory serves, though I'll admit its been a while since I've touched one. There is a whole sequence of how to do it including what valves at what crank position, etc. Its all way more involved than I can recall. I used to have a cheat sheet whenever I had to do this, but I've since lost it.

 

[mla2ofus]

Re: I give up! Help!!!

Hook a vacuum gauge to the intake manifold. If it doesn't hold at least 15" and the needle staying steady at idle, you have a vacuum leak somewhere. If the leak is on the underside of the intake manifold starting fluid won't help you find it.
Mike

 

[searaymon]

Re: I give up! Help!!!

If the motor idles with the mix screws turned all the way in, it sounds like the carb bowl may be cracked and leaking fuel directly into the manifold. It should not run with those screws turned in.

Though if you cranked them hard, it will destroy the needle screw and the seat, and all bets are off at that point. When they get turned in, they should be lightly bottomed, not turned hard until they won't go anymore. Might want to pull those mix screws out to verify there is no groove cut into them. If they have a groove, you'll need to replace them and verify the seats themselves aren't trashed.

The spinning pushrod thing doesn't really mean anything, other than they have some oil on them. Its not really much of an indicator of zero lash. Exactly how did you set the rockers? It should be zero lash and turned past that 3/4 of a turn if memory serves, though I'll admit its been a while since I've touched one. There is a whole sequence of how to do it including what valves at what crank position, etc. Its all way more involved than I can recall. I used to have a cheat sheet whenever I had to do this, but I've since lost it.

I didn't crank the mix screws tightly, just until there was resistance. The pushrods I did as layed out in the manual. I first cranked the motor over until the # 1 piston was at the top of the cylinder, then tightened to zero lash, then back 3/4 turn, and followed that process for each piston in the firing order. I appreciate everyones help in this matter. I think that I am going to take the boat and get a pressure test. I will report back as I know more. Again, thank you all!

 

[xltier]

Re: I give up! Help!!!

I didn't crank the mix screws tightly, just until there was resistance. The pushrods I did as layed out in the manual. I first cranked the motor over until the # 1 piston was at the top of the cylinder, then tightened to zero lash, then back 3/4 turn, and followed that process for each piston in the firing order. I appreciate everyones help in this matter. I think that I am going to take the boat and get a pressure test. I will report back as I know more. Again, thank you all!

should be tightened 3/4 turn at zero lash.then turn 1/4 turn and do #8 cylinder.then 1/4 turn and do #4 cylinder and so on 1 8 4 3 6 5 7 2 .

 

[airmail]

Re: I give up! Help!!!

Man, I just wrote a long post and lost it. This has been happening lately. Sucks .

OK if you have an EGR value check that. With the motor running push up on the bottom of the value with your finger. The motor should stall or run bad. If there is no change the value is stuck. Might have some carbon on the seat or might just be bad. If no EGR and idle is under 900 I would say carb was not over hauled right. Float might be bad or set wrong or idle passages not cleaned.

A vacuum gauge is a very good tool. You are looking for a steady needle. It's checking the mechanical operation. As long as it's steady your mechanicals are good.

Also just thought of this check the hose that goes to your pcv value. Sometimes they will rot and suck in. Plus they will leak. Look underneath all along the hose.

Let us know what you find.