351W Running Issues

[ledzilla]

I've had a variety of issues with my Bronco running solidly. I think I have it all figured out now as to why. I'm pretty sure it's all related to the fact that a prior owner installed an Edelbrock carb and manifold. Correct me if I'm mistaken, but I do not believe that a factory mechanical fuel pump designed to run a 2bbl carb can efficiently supply enough fuel for a 4bbl carb. Some of the issues really point to a problem with fuel delivery, especially given that the fuel filter is clean and the carb was professionally rebuilt, and the fuel pump is an old crusty factory-type pump. I'm planning to replace it with an Edelbrock pump that should give it that little extra that's needed. From what I found, the normal fuel pump that would supply a factory 2150 provides about 4.5psi and the Performer series carb installed likes 5.5-6 psi, which this fuel pump will provide.

The other problems seem related to warm weather driving. In the winter it behaves just fine, but in warmer weather, especially after its been driving around a bit, it just runs absolutely terribly. All of the symptoms point to heat soak, which seems likely given that there is no insulation of any kind between the carb and manifold. It's mounted directly to the manifold with only a standard gasket between them. I'm thinking I'll install an insulating gasket and a heat shield between the manifold and carb. I was also thinking that with the new pump I'll also install some new braided fuel line between the pump and carb and cover it with an insulator.

If I'm right, getting all this done should make a marked improvement in how that 351W will run all year 'round. I'm also concerned that the ignition timing could be a little off. I'm going to be installing a new harmonic balancer since the current one has the timing marks corroded and is falling apart anyway. However, it seems really difficult to reach the retainer bracket. There's a lot in the way. Is there a nice little trick for improving access? I think I have a set of offset wrenches specifically designed for the task, but I'm still concerned about actually reaching the bolt. I think it also needs a new vacuum advance, since that appears to be yet another old crusty part. Are there any recommendations for a reliable replacement?

 

[ledzilla]

Got some of the supplies to fix things up. Figure I'll split it into phases. For Phase I, I got insulator gaskets, a heat shield (that came with some spacers and gaskets), and some items to help route the fuel line away from rubbing on the edge of the heat shield.

 

[wyo58]

I've had a variety of issues with my Bronco running solidly. I think I have it all figured out now as to why. I'm pretty sure it's all related to the fact that a prior owner installed an Edelbrock carb and manifold. Correct me if I'm mistaken, but I do not believe that a factory mechanical fuel pump designed to run a 2bbl carb can efficiently supply enough fuel for a 4bbl carb. Some of the issues really point to a problem with fuel delivery, especially given that the fuel filter is clean and the carb was professionally rebuilt, and the fuel pump is an old crusty factory-type pump. I'm planning to replace it with an Edelbrock pump that should give it that little extra that's needed. From what I found, the normal fuel pump that would supply a factory 2150 provides about 4.5psi and the Performer series carb installed likes 5.5-6 psi, which this fuel pump will provide.

The other problems seem related to warm weather driving. In the winter it behaves just fine, but in warmer weather, especially after its been driving around a bit, it just runs absolutely terribly. All of the symptoms point to heat soak, which seems likely given that there is no insulation of any kind between the carb and manifold. It's mounted directly to the manifold with only a standard gasket between them. I'm thinking I'll install an insulating gasket and a heat shield between the manifold and carb. I was also thinking that with the new pump I'll also install some new braided fuel line between the pump and carb and cover it with an insulator.

If I'm right, getting all this done should make a marked improvement in how that 351W will run all year 'round. I'm also concerned that the ignition timing could be a little off. I'm going to be installing a new harmonic balancer since the current one has the timing marks corroded and is falling apart anyway. However, it seems really difficult to reach the retainer bracket. There's a lot in the way. Is there a nice little trick for improving access? I think I have a set of offset wrenches specifically designed for the task, but I'm still concerned about actually reaching the bolt. I think it also needs a new vacuum advance, since that appears to be yet another old crusty part. Are there any recommendations for a reliable replacement?

I think your on the right track in your thoughts of why it is doing what its doing. keep the fuel line as far away from the engine that you can for sure!

 

[ledzilla]

I thought that I had attached a photo I took of my Phase I supplies, but I guess I didn't. Looks like I did it correctly this time. Waiting on a test mount to finish on my 3D printer and then I'll be pulled the car so I can verify layout of the pieces and correctly measure what I need for the fuel line.

 

[ledzilla]

So, my test mount finished up, and I have a preliminary layout of the components. I had also designed a mount for the bulkhead adapter fitting I got (-6AN to 3/8" hose barb), but just laying out the Edelbrock hard line and filter makes me realize I'm going to need to completely redesign it. I have a lot to do this weekend, but I'm going to try to squeeze in pulling the carb and then I can get the fuel line arrangements better measured and designed.

 

[ledzilla]

It took a while before I was able to pull the carb. We had some tornado issue around here. Looks like I need to adjust my spacing between the carb and the spacer.

-- Edit --

Forgot to add that I ordered a spacer and some AN fittings/adapters/pre-fab fuel line. I think I can make this work and look fairly decent. I had almost enough space until I realized that I had some stacked gaskets just below the carb. There are a couple spacer plates in there that came with the shield along with insulating gaskets to help with mitigating the heat reaching the carb. I think with the thicker insulating spacers I won't need the extra think plates and gaskets. I figure I'd be better off just using on thicker spacer than more thin plates and gaskets. Less risk of developing a vacuum leak.

So, the "stack" will essentially be something like this, bottom to top:

- 1/4" insulator
- Heat shield
- 1/4" insulator
- 3/8" spacer
- Gasket
- Carburetor

That should help alleviate the heat soak issue and provide sufficient space for the new fuel inlet above the heat shield. I guess I'll know more once parts arrive.

 

[ShadetreeSeattle]

hope that ya made it thru the tornado stuff! at least in Seattle we just have to worry about the impending doom earthquake and Mt raineer blowing its lid haha.

i sort of think perhaps there might be something more to this runability issue, seldom do i see a situation where this amount of spacers is required, i also sort of worry that it may end up creating more problems than solving. its a lot of separate places for leakage, also no doubt the spacers and gaskets will shrink and create vacuum leaks if torque is not maintained on those carb bolts, which can cause a lean condition and create even more heat. are we absolutely sure that the carb is tuned correct? timing set appropriately? as for fuel delivery issues, a stock and good mechanical pump should give you very appropriate performance unless you are at WOT under load. otherwise, the stock pump psi makes no difference unless the float bowls are becoming depleted of fuel. i don't necessarily think we have ruled out fuel/carb adjustment/timing/VAC leaks. obviously without setting eyes on the thing i don't know. the carb itself may not be a great fit either. does the engine adequately keep a temperature as well, that's a whole thing too.

 

[ledzilla]

hope that ya made it thru the tornado stuff! at least in Seattle we just have to worry about the impending doom earthquake and Mt raineer blowing its lid haha.

i sort of think perhaps there might be something more to this runability issue, seldom do i see a situation where this amount of spacers is required, i also sort of worry that it may end up creating more problems than solving. its a lot of separate places for leakage, also no doubt the spacers and gaskets will shrink and create vacuum leaks if torque is not maintained on those carb bolts, which can cause a lean condition and create even more heat. are we absolutely sure that the carb is tuned correct? timing set appropriately? as for fuel delivery issues, a stock and good mechanical pump should give you very appropriate performance unless you are at WOT under load. otherwise, the stock pump psi makes no difference unless the float bowls are becoming depleted of fuel. i don't necessarily think we have ruled out fuel/carb adjustment/timing/VAC leaks. obviously without setting eyes on the thing i don't know. the carb itself may not be a great fit either. does the engine adequately keep a temperature as well, that's a whole thing too.

Well, it's not a stock carb, and the stock fuel pump doesn't deliver enough fuel. But that's a minor thing compared to the heat soak issues. I also had the carb rebuilt and retuned last fall, and it ran great all winter. Well, as good as it does with that old crusty stock fuel pump. With the current setup, I can drive around all day during the winter. But as soon as it starts getting up over 70, it'll be fine until it's been running long enough to fully warm up the engine. It's not super noticeable, though, until I need to accelerate to over 45mph, which is common for the roads around here. The local roads I use the most have 50-55 mph limits, and I can't give it sufficient throttle on one leg that goes uphill from a stop without it struggling. But take that same route at night if the temps drop into the 60's, it'll run just fine. Everything I've looked up on its behavior says heat soak/vapor lock, and it's the only vehicle I have with a carb without some kind of insulating spacer, and the only one having these issues. I'm pretty much of the mind that when some previous owner before me installed this carburetor/intake manifold setup, they only intended it to run during the winter as a plow truck, so none of what I'm trying to do now mattered to them.

I'm trying to minimize the spacers. I have one arriving today that will eliminate several of the displayed spacers. I ordered it specifically for the reason that the chance for leaks increases too much with the current stack. I actually found some insulating spacer kits that are a series of aluminum plates and thin insulation gaskets. I don't doubt that they do the job of insulating heat from the carb, but that's just too many pieces. Ultimately, this will be the heat shield, a 1/4" insulating spacer, the new aluminum spacer, a gasket, and then the carb. And yeah, like I've done in the past for carbs, I go back and check the mounting to make sure it remains torqued into place.

Anyway, once all the pieces I ordered come in and everything is looking good, I'll definitely know for sure if my assessment was right. The AN fittings I ordered to raise the height of the fuel filter didn't quite lift the filter up high enough to also give sufficient clearance to the PCV hose. I ordered a 90 degree elbow and a 45 degree elbow, and while the setup looks nice and almost lines up the Edelbrock logos on the filter and carb, the layout doesn't move the filter out of the way enough. So, I have another 90 elbow ordered, and I think that ought to make the necessary adjustments for sufficient PCV hose clearance. I'll also be replacing the stock fuel pump with an Edelbrock pump that kicks out more pressure, and puts it where that carb likes it. Figure when I get to that part I might also install an insulating sleeve around the fuel line between the pump and the carb to help keep the fuel cooler. It's amazing how hot it gets under that hood, and how fast.

As an interesting aside, speaking of the PCV hose, there wasn't even a PCV valve installed when I bought the truck, and the PCV vacuum port on the carb was connected to a weird spot under the hood, but I can't quite remember. I think maybe it was connected to the brake booster. It was very weird.

 

[L\Bronco]

Hey Led
Is there any way you could post a pict of underhood showing the setup with the air cleaner on, plus a couple picts underneath showing the fuel line from the pump back?
Ive won this battle a few times and stock pumps move enough fuel for most applications if they are good. Yours sounds like the verge of vapor lock, or your intake air is too hot. (Carbs are usually calibrated to 90-110 degree air)
Vapor lock can happen in the carb but usually its in the suction line between the tank and pump.
Hot air gives you a lack of power and rich mixture, vapor lock gives you lack of power and lean. Really hard to tell the difference.
A look underhood and underneath might help.
Cheers

 

[ledzilla]

OK, so I have the better spacer, and the alternate AN fuel line fittings. Definitely have better clearance for the PCV hose now. I redesigned the mount for the AN-to-hose barb bulkhead fitting to better accommodate the new arrangement, and printing has been kicked off. So hopefully that won't need any serious redesign again. With everything in place, it's looking like the new carb studs are long enough.

 

[ledzilla]

OK. So I'm a little behind where I wanted to be because the additional AN fittings I ordered ended up taking a detour to the wrong side of the country during the shipping process after they arrived in the area. So that was fun. I have a revised version of my bulkhead mount printed up quite nicely, and everything seems to be lining up smoothly. With any luck, weather permitting, I'll be getting it all installed this weekend. If all goes well and my assessment of the situation was correct, there should be a major improvement. Part of the improvement will be long term. The insulation and shielding should keep the carb cooler, and less fuel should evaporate, thus making startups easier on hot days. Crossing my fingers with that.

I also got the new fuel pump ordered. Given that the age of the current pump is unknown, one way or another I'm better off installing a new pump. I'm hoping the slightly increased fuel pressure makes a noticeable difference in how the carb behaves. It's a 6psi pump, the carb wants about 6psi on the fuel, so there should be some form of improvement. Doing these steps one-at-a-time should certainly help highlight whatever improvements were gained.

 

[ledzilla]

Got everything installed. Had a few issues during the process because the hardware for the new studs went missing. After a long time spent looking for it, I reused the old hardware. Then found the old hardware was missing a washer, so spent forever finding a washer. Had plenty of 5/16 washers, but they're mostly either oversized or lock washers. Then I noticed that I needed new fuel hose, so ran to the store for that. Other than those issues, installation went well.

Regrettably, I am not able to see what, if any improvement, this will have. I can't get it to start. It almost started, but just almost. Tested spark, was OK. Pulled the new fuel line apart, a couple dribbles. Pulled the new hose that connects the hard line from the pump to the new AN lines, grabbed my trusty underhood remote started, and gave it some cranks. No fuel at all except a couple small spurts. Looks like the pump is dead now. So I guess it's good that I already ordered a new pump, too bad it'll still be a while before it ships.

 

[ledzilla]

Ok, so I'm going to try an experiment. Before getting to replacement tank/pump/sender/wiring for the rear tank of my '87 F-250, when I bought it, it was using an inline pump screwed to the bed being fed from a fuel cell (the mid tank was missing, the rear tank leaked and had a bad pump). For a while I was using a modified 6gal plastic fuel can as a gas tank. The old beastie still needs a lot of work to actually get running again, but I digress. That truck has a 460 and it was the last year it came with a 4bbl. Since I still have the pump and modified gas can, figure I can use those to temporarily feed the Bronco's 351W. Not going to try to drive it around like that, though.

 

[ledzilla]

The experiment was something of a success. After it fired up fuel started pouring from the line off the mechanical pump. Got that shut down real quick. I was a little surprised given how much cranking I had done previously with hardly any fuel ever reaching the carb. Got it all hooked back up the right way, and it was doing great except for a sizable leak. I think maybe the clamp was a little too big because I couldn't get it tight enough. I was running out of light, though, so I'll get back to it later. Double check the clamps and everything in that spot.

 

[ledzilla]

OK everything is put back together, and it's running well with no fuel leaks. It seems warm enough outside to cause issues, but it behaved pretty well. Need to try again on a warmer day to verify. But it did pass the first test which was to drive it 4 miles to the next town over, then come back and try to accelerate uphill to 55-60 mph. It did so without any major struggle. Tomorrow I'm going to see how well it starts again on a cold start. If it fires up again without the usual major struggle, this will definitely be a victory.

Two issues I noticed, though...

The RPMs were stuck high. The new height of the carb was not friendly to the throttle cable. It's bending in a way that is causing it to push on the throttle linkage. At least it's not as harsh on the C6 as the high idle on my LTD wagon is on its FMX. Would anyone be able to tell me anything about the bolts that hold the throttle cable bracket in place? I figure that I should get some spacers and longer bolts to lift it up a little higher so the angle on the throttle cable is closer to normal.

It still doesn't run as smooth as it should when giving it some throttle. I increased the space between the carb and manifold more than I wanted, and I'll probably have to install new jets. I think I might also need to inspect the ignition timing and adjust it. But, like I'm doing with my LTD wagon, I think I need to replace the harmonic balancer first. The outside gets so crusty, can't read the timing marks. Probably needs a tune-up, as well. Thankfully I have the parts for that, just need to get it done.

 

[Tiha]

No idea about the bolts. Probably a standard 5/16 NC bolt, that seems to be most common.

Glad you are making progress. Fun to read through.

 

[ledzilla]

No idea about the bolts. Probably a standard 5/16 NC bolt, that seems to be most common.

Glad you are making progress. Fun to read through.

Hehe

Glad it's a good read.

 

[ledzilla]

It's running better and more consistently than it did previously in warm weather. Which is great. I did find, though, that the weird tension from the throttle cable on the linkage is causing the fast idle to engage after accelerating. Figure that will resolve itself once the bracket is repositioned.

 

[johnnyreb]

It's running better and more consistently than it did previously in warm weather. Which is great. I did find, though, that the weird tension from the throttle cable on the linkage is causing the fast idle to engage after accelerating. Figure that will resolve itself once the bracket is repositioned.

When you lean over the motor. Just think if you slipped and fell down and your face would hit the stud . Sticking up from your carb? Another thing you might think about is. Do you have a big air breather that goes on it? If so--you might want to consider a small one. That way when you raise the hood. You can see the manifold around the carb. m If you have or get a bad gas leak and it starts up--the manifold will get puddles of gas in it and can catch on fire. It happened to me and I almost lost my life fighting the fire. i ENDED UP IN THE BURN CENTERAND WAS LUCKY. Good luck.

 

[ledzilla]

OK, so my Bronco sat around for a while because the steering was feeling weird and it took some time before I could inspect the front end. So, good news is that there appears to be nothing wrong with the front end, and I believe what I felt was the fast idle getting tripped as I was maneuvering around cars parked in the street. Making sure to goose the pedal before any of that seems to do the trick for now.

Bad news is that even though it was behaving better after I got this work done, it has reverted back to being disagreeable. Looking into things a bit further, based on a number of factors I am now of the mind that the carb may be calibrated and jetted for cold weather. But as I write this, I'm thinking maybe I have forgotten to get back under the hood to re-torque the nuts on the carb.