Hey everyone, I swapped out a '78 f150 body and engine onto a '79 f150 4x4 frame and tranny. Got it all finished up and now i have an issue.

First off heres what i have: stock 302, 2bbl 2150 carb, np435/205 trans and t case. I swapped out the dizzy from the old 302 and set timing, new duraspark box, I checked all wiring- correct, rebuilt the carb, new plugs, wires are new, fresh oil and antifreeze and new starter and solenoid because i over-tightened posts on the old one.

Now what its doing is, starts right up, idles ok but a little rough, if you ease on the gas, it with accelerate rough at low rmp then evens itself out, if you stomp on it from idle it backfires through the carb, once its past the first 1500-2k or so of rpm it is perfect. Going down the road it has no power through the rough low rpm either. any ideas? its got my head spinning.

 

Could be several things.

In no particular order:
Plugged idle jets or emulsion tubes.
Incorrect or misadjusted accelerator pump (probably not this).
Wrong vacuum port for vacuum advance.
Mechanical advance not returning to home due to weak springs or wear.
Vacuum leak.
Firing order, higher rpm will "hide" two wires swapped.
High float level. I had visable fuel running into carb due to a float that was over 1/2" off. Caused poor idle and stalling on low speed turns.

 

Where should vacuum advance hose be located? I've checked for vac leaks and leaks around the carb and when I rebuilt the carb I also blow out everything with a hole. I've checked firing order 5 times now and it's correct. I did check the vac advance, however, if I unplug the line it doesn't change. Never thought about the float, what is the float supposed to be set at?

 

Vacuum advance usually goes to ported vacuum. You probably have connected right since it didn't change. Manifold vacuum is under butterflies. Ported is near or just above butterflies.

Vacuum leaks can be sneaky. Spritz carb cleaner on every connection and along intake. If it smooths out even briefly, you've found a possible leak.

Sounds like you took care of any plugged jets, as long as you have a good fuel filter that is. I still haven't changed my sexy chrome and glass filter with the bug screen for an element for a cheap plastic one that actually filters stuff out. Thus the plugged idle jet once or twice a year.

Firing order is probably correct.

I'd have to google "2150 float level" to tell you what it should be. There are actually two settings. Droop sets the float level with no fuel in the bowl. I forget the official name for what you think of when you think float level. Both are important for correct operation.

 

Replaced the dizzy with an hei, and tried a different carb with no change. Did a compression check and all 8 cylinders were at or around 120. Checked the vacuum for leaks, no leaks... Very puzzling any other ideas?? I'm lost at this point

 

What's your initial timing set at?
Total timing?
All in by......?

The HEI's vacuum advance can is adjustable but not too bad from the gate.

Have you adjusted the carb with a vacuum gauge?

 

A mechanic's gauge connected to manifold would be useful here. Low power, and backfire through carb, sounds like the timing is off.

Dry float height is the carburetor bench setting during rebuild, a ballpark adjustment. It may end up being correct, but maybe not. Wet float fuel level is whatever the fuel height ends up at, and this is what is important.

On level ground let it idle for a few minutes. Shut the engine OFF. Pull the air horn and observe the fuel height in the bowl. On a 2100 (you need to look up your carb, for your application) a typical fuel height might be 29/32" from the top of the machined surface of the carb to the surface of the fuel. It's important that the fuel height at least be close to spec, at all times under all conditions. Need the Shop manual to get the correct figures. All of this info is available online if you dig around. To reiterate you can set the dry float setting and end up with a fuel height that is way off, and sometimes people also confuse _float_ height #s with _fuel_ height numbers.

 

My dad adjusted the timing and said it's exactly where it's supposed to be, he didn't give me numbers, but he's pretty particular when it comes to stuff like that. I just bought a vac gauge to see where that's at but haven't installed it yet. I'll ask him when I get back to the shop and post some numbers on what I find out

 

A timing light is used for timing the engine. A vacuum gauge is for setting the carb's mixture screws and to check for overall engine health. You wouldn't use a timing light to set the carb would you? Don't use a vacuum gauge to set the timing, although its been done. I would trust a timing light over a vacuum gauge to set the timing all day long.

 

I got the vacuum gauge to see if it was irratic, I'm currently getting a steady 16 in-hg at idle, timing is 8 deg. advanced

 

That vacuum reading is a bit low unless the engine is old and worn out. Close to 20" - 21" Hg is what you want for a good stock engine. What's your elevation?

Use the vacuum gauge connected to manifold vacuum to adjust the carb. You want the highest reading in inches Hg. Turn the mixture screws a little at a time to achieve this.

I think 8* BTDC is low for timing. Once the carb is set bump up the timing to around 12* BTDC and let us know how it turns out.

 

Not if the outer steel damper ring has slipped off its clock.

Defective dampers are a VERY common problem with Fords. Not sure if it's an issue with this particular engine, but it's something to look into. While it is true a timing light won't work for carb tuning, a vacuum gauge will indicate if engine timing is late and cut through issues like defective dampers mentioned above, maybe the wrong pointer is installed, the distributor is installed 180 degrees out etc.

Especially useful when trying to troubleshoot remotely over the internet 2nd hand. It doesn't replace the timing light, and the mechanic needs to verify total timing and vacuum advance with a light, but it is an essential tool for engine tuning and diagnostics.

In this case, if a slipped damper is a likelihood, a useful quick diagnostic would be to adjust the distributor for just short of the maximum steady vacuum achievable at normal idle RPM with vacuum advance disconnected and plugged. A stock engine at Sea level should draw 18" to 20" Hg of vacuum. Then see what the light indicates. If the damper HAS slipped, it needs to be replaced, as it no longer is absorbing the crankshaft vibrations. But it will get the engine running right for the time being.

 

Alright everyone, i got it fixed and couldnt feel more stupid. I was going by a firing order i found on the internet instead of checking the one on the manifold. I could kick myself. Thank you to everyone that gave me some insight, i feel pretty confident having done the diagnostics on this motor that itll last me a little while. I love this community and your threads have helped me a ton in the past. Keep up the good work! To anyone reading this needing help, i say make sure your firing order is correct for your engine by looking at the manifold, or searching for different 302 firing orders. They are not all the same.

 

Been there done that!


I usually, as in always, install the distributor 180° out. Unless I try to second guess myself, in which case, I install it 180° out cause I actually had it right.


I was helping the neighbor put the 302 in his boat together last summer. We went round and round with the same problem you had until we tried a different firing order. It seemed like there were at least 4 different choices and we didn't know for sure what motor he had since it was a mishmash of marine and car parts.

 

Thats crazy, yeah, the funny thing is, i had them wired the way they are now on the dizzy from the other motor which when i switched that dizzy to this motor it was backfiring and causing chaos so i looked up the firing order and said "wth im so stupid!" Changed it, and still had the issue. Thats when i went hunting for another issue, i.e. timing and the other crap i listed, and come to find out timing was my original issue and initial firing order was correct. By the way the hei i installed is pretty awesome, i wired it to the 12v side of the coil wires, diconnected the ignition control module and it runs flawlessly. Next is the one wire alternator. After i get a bit of the interior finished that is.