• Welcome to ClassicBroncos! - You are currently viewing the forums as a GUEST. To take advantage of all the site features, please take a moment to register. It's fast, simple and absolutely free. So please join our community today!
    If you have problems registering or can't log into your account, please contact Admin.

Need help troubleshooting

lodgeskins

Jr. Member
Joined
Aug 18, 2010
Messages
62
Loc.
CT
I've got a 170 six cylinder that sounds like it misses at idle and I have some black exhaust (worse at start up than at higher rpms). It is an original Autolite carb. I changed the plugs, wires, and coil. It runs the same. It is also hard to start; I have to step on the gas petal quite a few times before cranking to get it started (7-10 good pumps is average). I have checked for a vacuum leak using carb cleaner, but realized that if I had an air leak I'd be running lean not rich...
The plugs I pulled were the blackest, crudded up plugs I've seen. I adjusted the air/fuel mixture screw and it helped a tiny bit, but not enough to really make much improvement. Previously, I removed the top of the carb and the float seemed to be functioning as it should. Playing with the choke doesn't change much. Fully open it helps a little, but again, not too much. What should I try next? I'm leaning towards taking more of the carb apart and making sure the jets are screwed in properly because I can't think of what else would be causing excess fuel to get through. However, that wouldn't really explain the missing at idle. Could it be a timing issue? Thanks for any ideas.
 

jckkys

Bronco Guru
Joined
Mar 15, 2012
Messages
5,196
Sounds like the choke is stuck. Check the choke plate when the engine is wormed up or has been running for 6 to 7 min. It should be fully open. If not see if it moves freely. If it does turn the auto choke cap until the plate is fully open. The screws around the cap usually need to be loosened to do this. If the plate doesn't move freely the choke housing needs to be taken apart and cleaned out. A better choice at this point would to rebuild the carb. The rebuilding kit has complete instructions for choke adjustment.
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
Rebuild the carb sounds to me like the needle seats are dirty or leaking and causing a flooding issue. Hard starting could be a misadjusted choke
 
OP
OP
lodgeskins

lodgeskins

Jr. Member
Joined
Aug 18, 2010
Messages
62
Loc.
CT
Video of it running/what I did today

Thanks for the responses. The choke moves freely and opens up as it should. I also replaced the distributor rotor and cap today, with no change in how it runs. Here is a video of it running after a cold start:

http://www.youtube.com/watch?v=T1PHzLrbAa8

I haven't checked the timing because I don't have experience doing so, and after reading about how I think it might be above my capability. I may have to bring it to a shop for that.

If the video doesn't give anyone more insight I will attempt a carb rebuild.
Thanks again.
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
Setting the timing is not that hard but you should have a timing light to do it. If you cant fget a timing light try this loosen the dist bolt a little then start engine rev the engine to about 3000 RPM and hold it there then turn the dizzy both ways until you find the smoothest running spot then tighten the bolt down. Take it for a drive and see if that helped any.
I would also suggest pulling off the air cleaner and look down the throat of the carb while the engine is running if you see fuel leaking into the carb well there's your issue its flooding. carb rebuild is in order.
 
OP
OP
lodgeskins

lodgeskins

Jr. Member
Joined
Aug 18, 2010
Messages
62
Loc.
CT
Some progress I think...

Thank you, I actually tried to adjust the timing once on an old VW without marking it, and learned to mark things the hard way. I just removed the air filter and looked down the carb at idle; no visible gas leaking down. Opening the choke faster than it does on its own makes it keep running, whereas if I don't force the choke open it is likely to stall if I'm not pressing on the gas pedal. So, I adjusted it forward a few degrees so that it is fully open after 7 minutes as someone above suggested. When the choke is all the way open it didn't seem like it would stall, but it still had the surge as can be seen in the video. While I had the air cleaner off and the engine was warm, I put my hand over the inlet for the valve cover and the engine evens out and actually sounds good at idle for a change. I don't understand why this would help, because opening the choke provides more air, which helps, and closing the hole to the valve cover helps, which provides less air. Does this make sense to anyone?
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
Hmm maybe the engine is just worn out. putting you hand over the valve cover hole and getting a idle increase would tell me that maybe the rings and or valves are worn a little back pressure from your hand is creating kind of a seal. Of course another possibility is that the PCV valve is not functioning correctly and putting your hand over the valve cover hole kinda stops the vacuum leak. although you really shouldnt be blowing black smoke with a large vacuum leak as it would lean the engine out. of course it could be to lean and not burning all the fuel. Might want to install a new PCV valve see if that helps.

now you may just need to adjust your idle mixture and idle speed on the carb to get it running better and not stall.
 

TDubya

Sr. Member
Joined
Aug 3, 2009
Messages
381
Loc.
Fortuna, CA
I had similar issues with my 170. Thought is was fuel related, kept fouling plugs. I ended up doing a valve job and that cured it.
 
OP
OP
lodgeskins

lodgeskins

Jr. Member
Joined
Aug 18, 2010
Messages
62
Loc.
CT
Good call Broncnaz! I had no idea about the PCV valve, and changing it did the trick and now it idles much better. I'm still blowing smoke so I think I had a few separate problems, and I think a carb rebuild is in order now as others have suggested. It starts up much better now that I adjusted the choke. Thanks a lot guys!
 

shamu

Lucky as the day is long.
Joined
Jun 18, 2009
Messages
5,290
Loc.
Sachse,Tx
Have you adjusted your lifters? It is a challenge and you will need a old Motors Manuel.
 
OP
OP
lodgeskins

lodgeskins

Jr. Member
Joined
Aug 18, 2010
Messages
62
Loc.
CT
Can anyone point me towards a good supplier of carb rebuilt kits? I've searched a little on line, and I'm having a hard time finding the right one. It's got so many #s on it that I don't really know how to search, so I think I need an outfit with good customer service. In the off chance that someone here could direct me to the correct one, the info I have is Autolite DOBF-A 4 9 k 24 off of a metal tag attached to the carb, a long list of patent #s that ends with 2658733 on the lower passenger side, 6-1962 on the front, 2038 and the driver's side, as well as Carter YF YF4778?? on the lower drivers side.
 
OP
OP
lodgeskins

lodgeskins

Jr. Member
Joined
Aug 18, 2010
Messages
62
Loc.
CT
Thanks a lot, I was thrown off by the metal tag. I played with the timing today and I think was set just right. So I'm ordering a carb rebuild kit this evening. Think I'm going with Mike's Carburetor parts b.c. They're made in the US, and you can buy other little parts to go with the kit that I don't see available from the big chains, like extra float bowl gaskets... Thanks again for the help!
 

Bronco Junkie

So Cal Broncos
Joined
Feb 29, 2012
Messages
3,232
Not sure where you are located....but I just recently bought a carb rebuild kit from a local auto parts store. And when I say auto parts store I don't mean Kragen or Auto Zone. I went to a REAL auto parts store and they got it no problem.
 
OP
OP
lodgeskins

lodgeskins

Jr. Member
Joined
Aug 18, 2010
Messages
62
Loc.
CT
Hey guys, just wanted to give an update. I ended up getting a kit from Mike's, and am really happy with the product and the service. I just finished rebuilding the carb and replacing the mixture screw. Below is a video of the truck running well now! No more smoke or surging. Starts up great, too. Thanks for the help!

http://www.youtube.com/watch?v=L1ZlzfUGPD8
 
Top