1971 ford inboard starting and backfiring problem

[rosgood14]

I am having a problem with my motor backfiring and i have yet to get it started.
The motor is getting fuel and it is getting spark to the plugs. it is not a blue spark but there is plenty of orange spark. it has a points system and they are clean and it has a new distributor cap. The timing is not perfect but we have got it close enough to where it should start. The motor tries every so often to fire but just not getting enough to crank. It is also backfiring to through the carb while trying to start it. We have played with the timing and it still backfires. Also the motor is turning over and every rotation or every other rotation it sounds like the motor boggs down for just a sec. i took fuel pump and the alternator and disconnected the belts to see if it was one of them crapping out but that was not the case it is something with the motor itself. I know the motor is a 1971 ford industrial motor and from what i have been able to gather it is a windor and i was told by the previous owner that it is a 351. how would i be able to determine for sure if it is a 351 windsor or not. thanks

 

[Aloysius]

Re: 1971 ford inboard starting and backfiring problem

The 351 is wider than a 302.

The FIRING order is also different. Sounds like you've got a firing order problem. There's no way to tell externally.

 

[rosgood14]

Re: 1971 ford inboard starting and backfiring problem

ok but how much wider or what would i measure to find out which one it is.

 

[Aloysius]

Re: 1971 ford inboard starting and backfiring problem

I'll measure my 302's tomorrow. The 351 is taller, so the width at the intake manifold is wider. Very easy to confuse 'em until you see 'em side by side.

However, the cams are interchangeable. THAT is the firing order difference. The only way to tell is to pull a valve cover or do a progressive compression check.

 

[Aloysius]

Re: 1971 ford inboard starting and backfiring problem

Just remembered..you could be one crankshaft revolution off. Remember the crank turns twice for every revolution of the distributor!

 

[rosgood14]

Re: 1971 ford inboard starting and backfiring problem

yes we almost made the mistake of getting it line up wrong at first but then we realized that it made 2 revolutions so we got it at tdc then lined up the wires according to the firing order i found on the internet.

 

[Aloysius]

Re: 1971 ford inboard starting and backfiring problem

The #1piston is at TDC twice! Gotta look at the valves, or make sure #1 is on the compression stroke.

 

[rosgood14]

Re: 1971 ford inboard starting and backfiring problem

yes i know what you mean and we made sure it was on the compression stroke. also i just found out that it is not a 351 but rather a 302 Marine 4V. thanks

 

[haulnazz15]

Re: 1971 ford inboard starting and backfiring problem

The easiest way to tell a 351 from a 302 is to look at the casted-in boss around the distributor. That boss (the half ring cast into the block where the distributor goes into the block) will be pretty much level with the deck where the intake manifold bolts to on a 302; on a 351, the deck is clearly much higher than the boss. Yes, the 351 is wider as well (due to the increased deck height), but it's harder to judge by looking at it than simply looking at the boss.

Since you think you have the 302, make sure you have the correct firing order. the 1-3-7-etc firing order is for the late model 302's and all 351w's. The other firing order is for the standard 302.

 

[rosgood14]

Re: 1971 ford inboard starting and backfiring problem

ok so i feel like a dummy because i dont quite understand what you mean about it is raised from the deck or not so i just got some pics to help you and I out. thanks

http://sphotos.ak.fbcdn.net/hphotos..._562576196362_73104065_32668800_1211490_n.jpg

http://sphotos.ak.fbcdn.net/hphotos..._576193537102_73104065_33110048_6286108_n.jpg

 

[rosgood14]

Re: 1971 ford inboard starting and backfiring problem

ok so i have another problem. i pulled the plugs to blow any thing that might be in there out and to gap the plugs and when i turned the engine over without the plugs in it my #4 cylinder went to shooting fuel out. it was not just a little mist it was a good amount. any idea whats wrong now. oh i just rebuilt the carb someone told me that it might be the carb sending to much fuel but i thought that would affect all cylinders not just one.

 

[Bondo]

Re: 1971 ford inboard starting and backfiring problem

and when i turned the engine over without the plugs in it my #4 cylinder went to shooting fuel out.

Ayuh,... Are ya Sure it wasn't Water,..??

 

[rosgood14]

Re: 1971 ford inboard starting and backfiring problem

nope just went and double checked and it is most definately gas.

 

[haulnazz15]

Re: 1971 ford inboard starting and backfiring problem

Okay here's a pic of the two engines. Pay attention to the location where the distributor goes into the block and the lip where the intake manifold sets right behind the distributor. Notice how on the 302 the distributor base and the intake deck are almost even. On the 351w, the intake sits 3/4" above the distributor base. As best as I can tell from the picture angle, you do have a 302.

On a side note, it looks like you have an automotive distributor there since it has a vacuum advance line attached. I would really question the fuel lines you have going there. Clamping rubber hose to the fittings looks like a leak/explosion waiting to happen. What size carb is on there? You fuel problem may be partly related to an oversized carb. Even a 600cfm is slightly overkill on a 302.

351w
http://image.musclemustangfastfords.com/f/14268989/mmfp_0902_06_z+pro_comp_head_test+351w_block.jpg

302 *ignore the red circles*
http://www.mackrafab.com/vmf/images/mexican_block/pix/Mexican302block.jpg

 

[rosgood14]

Re: 1971 ford inboard starting and backfiring problem

it is a 4 barrell holley and it is a 600 at least thats the rebuild kit that i just put in it. also mine is designed differently from these 2 motors, but where the distributor goes into the block where the bolt that tightens it in place up to the top on the manifold is about an inch. so that being said wouldnt that be a 351w. thanks

 

[haulnazz15]

Re: 1971 ford inboard starting and backfiring problem

Ahh, good eye. Since everything is kind of dirty/black, it was hard to see the seam where the intake stops and the deck begins. It does appear to be the 351w then, so make sure you have the correct firing order. Also, remeber that the distributor spins CCW, so arrange spark plug wires CCW. Make sure you are at TDC on the compression stroke as well to eliminate any timing issues causing the back firing.

 

[Aloysius]

Re: 1971 ford inboard starting and backfiring problem

Most 302's came with a 450 holley, but they're virtually identical to a 600.

Looks like a Prestolite distributor with screw down cap..marine stuff.

You've gotta major leak in the carb..needle and seat or float level issue. Gas runs straight into the intake manifold.

 

[rosgood14]

Re: 1971 ford inboard starting and backfiring problem

so with #4 cylinder getting way to much fuel for some reason we decided to leave the plug out all together because it was causing the motor to bog every time it had a stroke on that cylinder. we were turning it over without the plug in and it backfired with flames through the #4 cylinder hole. how is it going to fire in that cylinder with no plug to give it spark.

 

[haulnazz15]

Re: 1971 ford inboard starting and backfiring problem

I would urge you to verify that your plugs are in the correct firing order. 1-3-7-2-6-5-4-8. It was too difficult to tell from your picture, but it would eliminate a possible cause for the back firing. The fuel could be igniting because you have the improper timing/firing order which is allowing another cylinder to spark while the intake valve is still open. That causes the backfire through the carb, and that flame will reach any other open cylinder as well and ignite the fuel inside.

 

[rosgood14]

Re: 1971 ford inboard starting and backfiring problem

ok so the motor is at tdc on #1 cylinder. we have the correct firing order and they are on the distributor ccw. i just rebuilt the carb and im pretty sure that i put everything back in exactly how i took it out. i have a question though i was told that it did not matter where the rotor was pointing on a ford as long as you started with #1 wire where it was pointing. is this info correct. any other ideas as to why even if the carb is giving it way to much gas why it would only come out of #4 when all the plugs are out.