All Small Six 68 Bronco 170 tuning

[Bronco68]

I have a 68 bronco with a 170 that has been sitting for several years. It wasn't running at first so I just did so basic cleaning up of the plugs/points. It fired right up but was occasionally missing and dumping black smoke. So I decided to replace all the plugs, wires, distributor( original was a dual vacuum advance that was plugged off I replaced it with a single vacuum distributor hooked up to ported vac), and sonic cleaned/rebuilt the carter yf carburetor. All the smoking and missing issues are resolved and it fires up idles like a champ but as soon as I start to give it gas it stumbles and almost dies. Is this a timing issue with the vaccum advance(Initial timing set at 6 degrees) or a gas pump problem (inline filter only getting about a 1/4 of the way full)? I threw a picture of the carb and distributor to see if anyone can confirm that they are compatible I've read that some carb distributor combos will not work if mismatched.

 

[bubba22349]

Yes your Carter YF carb is compatible with the 1968 distributor it is the duel advance point unit, ie has both mechanical and vacuum advance. You have one those glass type see through fuel filters they are not going to be all the way full of fuel. You won’t be able to tell if the fuel pump condition is good without doing a fuel pressure test and a fuel volume test. The base timing isn’t likely the problem either though you could advance the timing a few more degrees if you wanted to 10 degrees. Sounds more like your accelerator pump needs some adjustment. Best of luck

 

[Bronco68]

Yes your Carter YF carb is compatible with the 1968 distributor it is the duel advance point unit, ie has both mechanical and vacuum advance. You have one those glass type see through fuel filters they are not going to be all the way full of fuel. You won’t be able to tell if the fuel pump condition is good without doing a fuel pressure test and a fuel volume test. The base timing isn’t likely the problem either though you could advance the timing a few more degrees if you wanted to 10 degrees. Sounds more like your accelerator pump needs some adjustment. Best of luck

Ok so I just popped the carb back off and I think you may be right about the accelerator pump. When I pump it manually everything works fine and I get a steady stream of gas into the carb. When I use the throttle linkage it doesn't get any gas into the carb till wot and it's just a little squirt. I'm not very experienced with carbs so I have no idea what to adjust here. Any help would be greatly appreciated!

 

[bubba22349]

Ok would be gald to try and help you. Would you take some pictures of the carb showing the accelerator pump linkage and post them so can see were you are starting from?

 

[Bronco68]

Ok would be gald to try and help you. Would you take some pictures of the carb showing the accelerator pump linkage and post them so can see were you are starting from?

 

[B RON CO]

Hi, I would get rid of the extra glass fuel filter. The metal filter is enough. The accelerator pump squirt should come on as soon as the throttle starts to open. When the fuel line is disconnected from the carb the pump should fill a coffee can with gas in about 20 seconds of cranking. Good luck

 

[Bronco68]

Hi, I would get rid of the extra glass fuel filter. The metal filter is enough. The accelerator pump squirt should come on as soon as the throttle starts to open. When the fuel line is disconnected from the carb the pump should fill a coffee can with gas in about 20 seconds of cranking. Good luck

I threw the extra one on until I could get a tank or 2 of new ethanol free gas ran through the engine. It has been sitting for awhile so my thought was to show extra precaution to avoid getting contaminates in the rebuilt carb. There already seems to be quite a bit of crap making its way into the glass filter. The fuel pump has a vaccum pump on top of it to run the vaccum wipers that I currently have disconnected. Does having this disconnected affect the fuel pressure or is it purely mechanical?

 

[bubba22349]

Hi Bronco68, for your Carter YF accelerator pump adjustment settings & Instructions they are in the below link. Best of luck

Carter YF Accelerator Pump Ajustment Settings

Carter YF Accelerator Pump - Mikes Carburetor Parts

Carter YF accelerator pump circuit. Illustrated pictures of how the pump works and how to test the accelerator pump circuit on the bench.

www.carburetor-blog.com

 

[Bronco68]

Hi Bronco68, for your Carter YF accelerator pump adjustment settings & Instructions they are in the below link. Best of luck.

Carter YF Accelerator Pump Ajustment Settings

Carter YF Accelerator Pump - Mikes Carburetor Parts

Carter YF accelerator pump circuit. Illustrated pictures of how the pump works and how to test the accelerator pump circuit on the bench.

www.carburetor-blog.com

So I have the carter yf not the autolite. I did notice that my metering rod was slightly bent so I slowly worked it straight and re adjusted everything to the specs from mikes carburetors. I set the mixture 2 full turns out, checked to makes sure TDC was correct on the harmonic balancer, and adjusted base timing to 10 degrees. Now without the ported vac hooked up I can Rev it up with only a slight initial stumble. When I hook up the vacuum advance it just about kills it when giving it gas. I also noticed I have quite a bit of carbon already building up on the new plugs. Could this carbon build up be from the points and plugs not being gapped appropriately or would this be indicative of bad gas or running too rich? Currently I've got the plugs gapped to .034 and points at .027.

 

[B RON CO]

Hi, did you check to see if the vacuum advance is working? If you have a hand vacuum pump you can check the can. If you don't have a vacuum pump you can suck on the vacuum hose and watch the breaker plate move. When you block the hose with your tongue the breaker plate should hold still.
Good luck

 

[bubba22349]

Sorry about that and I even should have remembered that you had a Carter YF from your above first pictures. I edited and corrected the setting info to a Carter YF Carb in above post. That's likely to far out for the mixture screw to be optimal might be to Rich causeing your carbon build up. Do you have a Tach / Dwell meter or a Vacuum gauge you can use to set it? If not I would try 3/4 turn out to 1 turn out. X2 test that the vacuum advance can is still in good condistion and holds a vacuum. A bad vacuum advance canister will also cause the stumble you having. The Rapid carbon build up isn't a good sign have you done a compression test yet? Does the engine use oil?

1. .034 is perfect for the spark plug gap.
2. .027 is perfect for the basic point setting.
3. The point dwell angle gets set to 37 degrees
4. Base timing is set to 6 Degrees BTDC
4. The mixture screw is set with engine warmed up to operating temp, to the lean best idle i.e. The highest idle RPM then turn the mixture screw in a 1/4 to lean it out.
5. The curb idle RPM is set to 700 RPM.

Best of luck

 

[Bronco68]

Sorry about that and I even should have remembered that you had a Carter YF from your above first pictures. I edited and corrected the setting info to a Carter YF in the above post. That's likely to far out for the mixture screw to be optimal might be to Rich causeing your carbon build up. Do you have a Tach / Dwell meter or a Vacuum gauge you can use to set it? If not I would try 3/4 turn out to 1 turn out. X2 test that the vacuum advance can is still in good condistion and holds a vacuum. A bad vacuum advance canister will also cause the stumble you having. The Rapid carbon build up isn't a good sign have you done a compression test yet? Does the engine use oil?

1. .034 is perfect for the spark plug gap.
2. .027 is perfect for the basic point setting.
3. The point dwell angle gets set to 37 degrees
4. Base timing is set to 6 Degrees BTDC
4. The mixture screw is set with engine warmed up to operating temp, to the lean best idle i.e. The highest idle RPM then turn the mixture screw in a 1/4 to lean it out.
5. The curb idle RPM is set to 700 RPM.

Best of luck

 

[Bronco68]

I have a tach hooked up to it and a vacuum Guage ordered should have it by the end of the week. I have not done a compression test yet but im hopeful the carbon build up was from before I rebuilt the carburetor as it was dumping black smoke prior to cleaning it. Doesn't seem to be burning oil that I can tell yet. I am a little concerned that the oil pressure Guage is only reading 10psi but it's a original Guage so it might just be a bad reading. I'm going to check it with a mechanical Guage tomorrow. The distributer vaccum canister is working and holding vacuum. I just finished reading about how to adjust the canister so I may try to see if that helps any as well. If I can't get it figured out tomorrow I'll order a compression tester Guage. I do not have a dwell meter either so I'll look into that aswell. Thanks for all the insights so far!

 

[Bronco68]

I went ahead and got a compression tester today and here's what I saw.
1-180
2-180
3-181
4-177
5-189
6-176
These are the averages from repeating it three times turning the engine over 5 revolutions. Any reason for concern with these numbers? My Chiltons manual specs say 175psi.

 

[bubba22349]

When doing the compression test for accuracy and to be able to get the highest test numbers for best results the engine should be warmed up to operating temp. Next all the Spark Plugs are removed, and the carb also needs to have the tthrodle held or tied so it's wide open, for safety remove the coil wire. Then crank the engine over until the highest gauge pressure is reached this can't be as little as three revolutions but it might also take more in any case when the needle stops moving higher up thats it. I don't know what you mean by averages of repeating three times, the numbers all need to come from the same test or you wont be able to tell what the percentage are from one cylinder the next. I think your engine is likely in reasonably good condition though.

On your tach being hookup that's good though when your working under the hood it's not a very convenient to location to be able to see. If you can get ahold of a tach / dwell meter to use it will be far more accurate as well as easier to use. Good used tach & dwell meters of many good brand names can be picked up really cheap sometimes, I like those with a larger scale, there are also still new units available too. Best of luck

 

[Bronco68]

I just repeated the compression test on each cylinder 3 times. Sorry I come from a science background and repeatability is king . I actually just bought a aftermarket tach and have it hooked up under the hood so I can see it so I've got that going for me. Tried three autoparts stores today for a dwell meter with no success I'll look online tonight but right I'm starting to heavily consider upgrading to a duraspark 2 or dui. Today I cleaned all the carbon off the spark plugs, rechecked everything was gapped properly, and hooked up a vac line from the manifold instead of the ported vac on the carb. It made a big improvement and had no stumbles with acceleration but it seems to have a occasional miss. Probably going to hold off on anymore adjustments until my vac and oil gauges arrive. Once again thanks for all the guidance so far!

 

[bubba22349]

I appreciate that you came from a science background. I also like being scientific as far as my knowledge in some areas goes like setting up a car for drag racing yet I am limited for sure in that field. Have studied areas of passive and active solar heating and cooling that i wanted to understand and figure out problems to use in housing construction i also try to be as precise as possible. I am thinking that under the conditions we have to do these compression tests under we can have several changes from one test to next just from external sources, such as the weather conditions, engine heat loss etc. unless you could duplicate all those things exactly each time then we probably wont get a repeated result. Not to worry we are just doing the compression test will give you a good idea of the engines operating condition and if you record those results in a note book or a computer log along with any other details about your car, like tune up settings front end alaigment settings, parts numbers, ect. Over time you can tell if there are any problems starting that need to be taken care of, as well as gaving a portable record to take with you to an auto parts store saving you time too.

On the black deposits that sounds like it’s running very rich. Check the throttle shaft for looseness, also check for other vacuum leaks.

Tach and Dwell meters can be found used many place’s such as ebay yard sales, swap meets, pawn shops etc. below is one there are dozens of others also listed. https://www.ebay.com/itm/1543425099...1291&msclkid=cb32d1e1b0271c156f9eb11903ea19f1

New ones are are on Amazon, Harbor Freight, NAPA auto parts and others since there isn't as big a demand for the new ones they likely need to be ordered. Best of luck

 

[Just_Fare]

I threw the extra one on until I could get a tank or 2 of new ethanol free gas ran through the engine. It has been sitting for awhile so my thought was to show extra precaution to avoid getting contaminates in the rebuilt carb. There already seems to be quite a bit of crap making its way into the glass filter. The fuel pump has a vaccum pump on top of it to run the vaccum wipers that I currently have disconnected. Does having this disconnected affect the fuel pressure or is it purely mechanical?

Perhaps disconnecting the vacuum wiper pump would introduce a vacuum leak?

 

[Bronco68]

Perhaps disconnecting the vacuum wiper pump would introduce

It definitely could here's a picture of it. I think the vac side is independent of the fuel pump and it's only using the engine vac to boost the wipers at low rpm so I can't see any reason it needs to be hooked up. I've been trying to find a rebuild kit so a can clean it up with no success. Don't want to mess with it until I do as it seems to be working fine.

 

[chad]

"...Any reason for concern with these numbers?..."
"No"
as the other parameter: "all w/in 10% of each other" is met. These ol rigs can run well on very low compression & U R not even close yet.
I'd skip the DUI & go w/the DSII. Poor reports on it & even the racers use the DS (some w/the hei 4 pin steada da 'blue strain relief' ford box).