1967 170 inline six hesitation and shake???

[iSense67]

Hopefully someone can help me figure out what is causing my 1967 170 inline six from shaking, and hesitating. The engine starts easy and idles perfectly. Then when I am driving for initial 15 minutes or so it runs smooth. Out of no where it will start to hesitate and shakes especially in third gear. Initially it will be a minor hesitation and then it becomes much harsher like a skip and shudder and it then does it at all gears (3 speed manual). I replaced the ignition coil and cleaned the carburetor and it still has the issue. My next step is to replace the fuel filter. It’s really odd as the engine operates perfectly and is smooth until it warms up then it’s constant. At one point it actually lost power and yet it restarted after immediately and then drove perfect. All said does anyone have any ideas or recommendations? Appreciate any wisdom you might have…

 

[67sport]

What ignition are you running? Stock (points) or something else?
Is the carb original and un-modified?
When was the last tune up? If it is a points ignition system and you don't know the history, that may be the place to start.

 

[DirtDonk]

Definitely.
If you haven’t already, pull the spark plugs and inspect them. Perhaps clean or even replace them.

Could be other things too of course, such as vacuum leaks etc. The likely reason it’s running better with the choke partially on when it’s cold is that it’s getting more fuel and the spark has an easier time igniting the mixture.
Once the choke goes off after warmup and the mixture is more lean oriented, you could either be getting an ignition misfire from a weak spark or perhaps it truly too lean on fuel due to a problem with your carburetor or the aforementioned vacuum leak(s).

 

[DirtDonk]

I can’t see how long ago you joined from my phone, but if you’re brand-new, welcome!
We just went through some of the basics that can cause what you described. But let us know more about your bronco. For example do you have bigger tires and maybe taller caring and the engine is just logging and doesn’t like it.

How long have you owned it? Is it new to you, or have you owned it for a long time?

 

[iSense67]

What ignition are you running? Stock (points) or something else?
Is the carb original and un-modified?
When was the last tune up? If it is a points ignition system and you don't know the history, that may be the place to start.

I believe it’s stock points but not sure. Everything in the engine seems mostly original.

 

[iSense67]

I can’t see how long ago you joined from my phone, but if you’re brand-new, welcome!
We just went through some of the basics that can cause what you described. But let us know more about your bronco. For example do you have bigger tires and maybe taller caring and the engine is just logging and doesn’t like it.

How long have you owned it? Is it new to you, or have you owned it for a long time?

 

[iSense67]

Yes i am new as a month ago. Been looking for a classic bronco for six years and finally found one in great shape. It’s pretty stock overall and isn’t lifted and does not have Overstock wheels. I tried pulling the plugs but all are tight. I am traveling this week so next weekend I am going to try to pull the plugs and change the fuel filter. If you have any advice on losing the plugs would be helpful. I was surprised how tight the former owner has them. I just bought this a month ago so I am slowing learning this bronco. My plan is to change the engine to a 302 blueprint but for now I want to simply enjoy it and this issue has made it in predictable. It drives perfect then it will start jerking and hesitating on acceleration. At first it’s mild then it progressively gets worse. I was thinking maybe they used ethanol as the former barely drove it on siesta key beach area.

 

[iSense67]

Definitely.
If you haven’t already, pull the spark plugs and inspect them. Perhaps clean or even replace them.

Could be other things too of course, such as vacuum leaks etc. The likely reason it’s running better with the choke partially on when it’s cold is that it’s getting more fuel and the spark has an easier time igniting the mixture.
Once the choke goes off after warmup and the mixture is more lean oriented, you could either be getting an ignition misfire from a weak spark or perhaps it truly too lean on fuel due to a problem with your carburetor or the aforementioned vacuum leak(s).

Great advice i tried last night pulling the plugs but the former owner had them really tight and I couldn’t get them off. Any advice on loosening them? Also how would I check for vacuum leaks? I’m mechanically inclined but it’s been over 30 years since I’ve worked on cars so I’m relearning but having fun doing so lol

 

[iSense67]

I can’t see how long ago you joined from my phone, but if you’re brand-new, welcome!
We just went through some of the basics that can cause what you described. But let us know more about your bronco. For example do you have bigger tires and maybe taller caring and the engine is just logging and doesn’t like it.

How long have you owned it? Is it new to you, or have you owned it for a long time?

Thank you for considerations. Yes I’m new I just bought the bronco in the last month so my fun of just beginning. It’s stock size wheels.

 

[iSense67]

Thank you for considerations. Yes I’m new I just bought the bronco in the last month so my fun of just beginning. It’s stock size wheels. I have a photo of the engine but can’t figure out how to add a picture to these posts?

 

[iSense67]

What ignition are you running? Stock (points) or something else?
Is the carb original and un-modified?
When was the last tune up? If it is a points ignition system and you don't know the history, that may be the place to start.

Was able to just post photos in my gallery of the carb and distributor to give reference…

 

[Pharless]

I had the same issue with my 170 last year. It ran fine for the first 5 miles or so and then would just miss and boog down. I replaced the coil with a generic coil from Advance Auto and it ran ok one or two trips, but the symptoms came right back. I ended up buying a Pertronix Flamethrower coil and I have had no problems since then. I'm convinced that even the replacement Advance Auto coil was a cheap Chinese coil.

 

[DirtDonk]

The reasons for the plugs being tight could be multiple. They could’ve been over tightened by the previous owner, or they could be so old they’re rusted in place.

You might try spraying the area with some penetrating oil or something similar, to both seep in and possibly loosen things but also to flush away any debris that might otherwise get into the engine when you remove the plugs.
Or does everything look really clean around there?

Other than that, as always, a bigger hammer!
Just kidding. No hammer involved if you can get a longer handled ratchet on the plug. Otherwise yes, I actually have used hammer to lightly tap the end of the ratchet to help break tight plugs loose.
And hopefully we don’t break the plug. Which does happen every once in a while.

 

[iSense67]

Definitely.
If you haven’t already, pull the spark plugs and inspect them. Perhaps clean or even replace them.

Could be other things too of course, such as vacuum leaks etc. The likely reason it’s running better with the choke partially on when it’s cold is that it’s getting more fuel and the spark has an easier time igniting the mixture.
Once the choke goes off after warmup and the mixture is more lean oriented, you could either be getting an ignition misfire from a weak spark or perhaps it truly too lean on fuel due to a problem with your carburetor or the aforementioned vacuum leak(s).

Ok since my last post I did the following and and was driving great.
- Changed all the plugs and the inspected the old ones which actually they didn’t show much except a little dirty. That said I replaced them with new.
-Checked all the vacuume areas and could find anything not connected or cracked.
-Replaced the ignition coil and it seemed to clear up the problem but as stated that lasted a couple days.
-Replaced the fuel filter and that seemed to give it a little more power but not sure if I was imaging the difference lol
-Cleaned the carburetor
-Checked the plug wires and all are relatively new.

Then this weekend the problems all came back with the hesitation and it even died twice. In both cases I drifted to the side of the road and it started up and drive fine then after about 30 minutes it started to kick again. My thought after all this is I was thinking maybe the fuel pump is the issue. I say that because when I the bronco died while driving it ford right up again. Seemed like it lost fuel and then pumped a little to get me going. Then after awhile the issues again but that is a theory and would love to know anymore thoughts and or if you agree is the fuel pump? All said when the issues are not happening it drives and runs perfectly. The idle is smooth and it always starts with the first turn off the switch. It’s a maddening problem so any more wisdom world be helpful.

 

[BOBS 2 68S]

May be off the wall.
Do you have a vented gas cap or some kind of tank vent? Your fuel pump might not be able to over come the negitve pressure inside the fuel tank as fuel is being pulled out.

 

[TNcowboy]

Good point about the vented gas cap. Have you tried removing the cap when this happens just to see if the tank is under a vacuum?

I had this issue on my 67, same as yours, 1100 carb and Load-o-matic distributor. I had rebuilt and soaked the carb 3 times in chemdip and it still shuddered on acceleration. Two things resolved the issue : first I cleaned the carb with a ultrasonic cleaner using diluted simple green. You wouldn't believe the crud I got out of a 3x cleaned carb. Second I made sure the power valve was freed up. Unlike a holley carb the power valve is not removable, you can see the bottom of it inside the bowl but if you remove the aluminum cap from the top of the carb you can lubricate it to be sure it's free. Mike's carburetor sells the expansion plugs https://www.carburetor-parts.com/plug-85-58.html

Another thing to check is the fuel pump as you questioned. Check it for volume and pressure. Too much pressure will overwhelm the float and cause a rich condition.

Keep us posted on what you find

 

[iSense67]

May be off the wall.
Do you have a vented gas cap or some kind of tank vent? Your fuel pump might not be able to over come the negitve pressure inside the fuel tank as fuel is being pulled out.

Interesting you say this as I noticed the other day the gas cap rubber seal was broken and missing a third of it. With that the case would it cause the lack of pressure you are suggesting? I just bought this bronco in the last month and I am simply trying to make it reliable until I pick a good restoration place. My plan is to put in a 306 bronco blueprint, auto, etc but for the next few months I just want to enjoy the inline and this issue makes it unreliable. One other thing I noticed a ground wire (5th photo you can see the wire next to master cylinder) that is connected to the firewall that is just hanging and not connected to anything. I can figure out what that is for as it’s cut. Any idea if that could be the issue and what its for?

 

[iSense67]

Interesting you say this as I noticed the other day the gas cap rubber seal was broken and missing a third of it. With that the case would it cause the lack of pressure you are suggesting? I just bought this bronco in the last month and I am simply trying to make it reliable until I pick a good restoration place. My plan is to put in a 306 bronco blueprint, auto, etc but for the next few months I just want to enjoy the inline and this issue makes it unreliable. One other thing I noticed a ground wire (5th photo you can see the wire next to master cylinder) that is connected to the firewall that is just hanging and not connected to anything. I can figure out what that is for as it’s cut. Any idea if that could be the issue and what its for? View attachment 879247 View attachment 879248 View attachment 879249 View attachment 879251 View attachment 879252 View attachment 879253

 

[iSense67]

Better shot of the mysterious ground wire…

 

[iSense67]

What ignition are you running? Stock (points) or something else?
Is the carb original and un-modified?
When was the last tune up? If it is a points ignition system and you don't know the history, that may be the place to start.

May be off the wall.
Do you have a vented gas cap or some kind of tank vent? Your fuel pump might not be able to over come the negitve pressure inside the fuel tank as fuel is being pulled out.