Hey yall, I have yet another in my endless series of questions for yall(I'm really trying to quit). My 86 F-250 with 460 with 4barrel stock Motocraft/Holly carb, has a bit of a hesitating problem when you apply a lot of throttle from a low RPM too quickly. If you gradually push the throttle up, it never hesitates. When you stomp on it from a low RPM(both in drive and park) most of the time(but not always), the engine will almost die and come back to life when you release the throttle within one and a half seconds or so. It seems to be temperature related, to a certain extent, as it always seems to be worse before it has been driven to warm up. The truck only has 26,000 miles on it and sat up a fair portion of it's life, but is in great condition overall and does not smoke at all. I have recently checked the timing with a light and it is fireing 4deg. before TDC.

I have been told that this is simply a flat spot in my quirky Holley carb. My friend didn't really seem to know much more than that. If so, how can this be corrected? It is not a big problem, but it is very anoying to try to move about in town with this litttle problem.
Thanks in advance.

 

Have you pulled the codes yet? That'd be a good place to find a starting point.

TM

 

If you feel the engine hesitate a bit when the throttle is opened, it is likely an accelerator pump problem.

If this is a new problem (it worked OK before with the same carb) the accelerator pump plunger might need replacing. My '87 had this problem and it was relatively easy to fix.

Lou Braun

 

OK, would replacing that accelerator pump plunger be something that average me could do easy enough or would it be best to get it to a pro? I'm assuming that is part of the carb you are talking about. Thank you.

 

It might be prudent to have someone who has worked with carbs do this and you watch the first time... although if you get the instructions and this is one of the carbs which allow you to do this without taking the carb off the engine you may can do it yourself with no help... but keep stuff in order that you take them apart... and take digital pictures of each move you make...

 

It is most likely the accelorator pump as Lou said. I'd actually get a reman unit and swap it out. If you've never done one (changing the pump), it'll be a pain, and you might as well rebuild it [the whole carb], because it'll probably need it eventually anyways.

 

Motorcraft carbs are junk, my truck does (did, timing gears broke and you can rotate the crank 20 degrees before the rotor even wiggles) this and its because the carb is junk (le3aks and its to small to). If i were you i would spring for an Edlebrock or Carter

 

OK yall, thanks. I am also gathering the impression that these Motocraft/Holley carbs are a real pain in the *** and are pretty high maintenance. Is this a pretty typical problem I am experiencing? I have seen on other threads where a couple of folks have replaced the stock Holley on their 460 with a 600 CFM Edelbrock. I gather that these Edelbrock carbs are much lower maintenance and using a 600cfm (As opposed to the stock 750cfm Holley) will help the fuel economy and won't be much of a power reduction unless you run the engine at it's red line.

As far a replacing the accelerator pump goes, what would the aprox cost of this part be and is this a time consuming piece to replace? The reason I am wondering is if it is worth it to fool with this carb, or if I would be better off just getting it replaced. Thank you all for your input.

 

I have a 82 302 w/ rebulit carb. Had the same problem for a long
time! Drove me nuts. Checked everything 50 times, looked foe
vac leaks, checked timing, set the carb idel adjustments, everything.
I never thought about the inernals of the carb because it
was rebilt and said to be calibrated and tested.
2150 OEM type. 2 bbl.
Over the weekend I pulled the top of and raised the float and it now finally runs like a dream.
It was the hardest thing to find, yet the easiest thing to fix.

 

I recommended a reman cause I forget you don't have emissions. A 600CFM Edelbrock will be a sure thing to install, and requires about 5 minutes to tune the idle and it will be driveable.