Slow Speed Surge

[wdetzi]

70 Bronco - Stock 302 - Newly rebuilt (<2000 miles)

Driving at a slow constant speed (25-40 mph) the Bronco surges or jerks, will accelerate fine without any hesitation - is this a timing problem or a carburetion/fuel problem?

Thanks for your help.

PS. The carb is an autolite 2-barrel (original equipment) with all new gaskets and seals. (Standard gasket kit from Auto Zone) also has a manual fuel pump.

 

[CarolinaMudder]

mine does the same on my 96' at a slow crawl (about 2mph), and i can't figure it out at all.

 

[Bully Bob]

Auto, or stick shift..?

Wild guess would be;

Ignition issues

Vac. leak

-or-

float set to high

 

[wdetzi]

Auto, or stick shift..?

Wild guess would be;

Ignition issues

Vac. leak

-or-

float set to high

Thanks for your reply

It's a stick shift (3 speed Hurst)

I think I throughly checked the ignition-don't know what else to look at, the timing is around 7-8 degrees BTDC, It has a new coil & new distributor (with new points, condensor, etc., also has new high voltage cables).

I haven't located any vacuum leaks yet, but I will recheck again.

Never thought of the float being set too high, so I'll re-set that to a lower level and see what happens.

Thanks again.

PS. The carburetor is original - has around 148K miles on it, however all internal parts have been replaced with the standard rebuild kit. Could be that the bushings, etc are worn enough to cause this type of problem, is that possible?

 

[Bully Bob]

"-----Could be that the bushings, etc are worn enough to cause this type of problem, is that possible?------"

I doubt it,....that's a good carb. The throttle shaft bushings (I think is what you're refering to) can ware in & leak air but that usually causes irratic idle problems.

Otherwise sounds like you did it right....!

Try removing the vac adv. hose....or installing one....just to see if there's any diff.

I disabled the vac adv. on one of my rigs....it smoothed out, even at top end. It might have been that the dist. was getting old in my case.

Let us know what works/doesn't work

 

[Big Country]

damnit bully...you did again. I knew this one. and he's right on the money. I just changed mine about 4 months ago. That should fix 'er up just fine.

 

[Bully Bob]

Ha..! B)

I'm leave'n town again for a while......so you can field all these.. :lol:

"-------I just changed mine about 4 months ago-----"

What was it you changed....??

 

[wdetzi]

"-----Could be that the bushings, etc are worn enough to cause this type of problem, is that possible?------"

I doubt it,....that's a good carb. The throttle shaft bushings (I think is what you're refering to) can ware in & leak air but that usually causes irratic idle problems.

Otherwise sounds like you did it right....!

Try removing the vac adv. hose....or installing one....just to see if there's any diff.

I disabled the vac adv. on one of my rigs....it smoothed out, even at top end. It might have been that the dist. was getting old in my case.

Let us know what works/doesn't work

You said something there Bully Bob that may point the finger at the carb with worn shaft bushings because the idle is a bit irratic, especially right after a cold start. But I will try the other suggestions you made first. I'm still supect a vacuum problem somewhere, sure can't find it so far.

 

[Bully Bob]

Maybe you've already tried the "spray carb. cleaner at suspect areas" to check for vac. leaks. (RPM's will change if there's a leak)

Another thought....I had, what I thought, was a good PCV valve on my Land Cruiser.....got a new one & things smoothed out.

 

[wdetzi]

Maybe you've already tried the "spray carb. cleaner at suspect areas" to check for vac. leaks. (RPM's will change if there's a leak)

Another thought....I had, what I thought, was a good PCV valve on my Land Cruiser.....got a new one & things smoothed out.

Thanks for jogging my old memory cells Bully!! I did try the "spray" trick after I first fired the old girl up after the rebuild - however there were so many other issues in getting it to run consistantly - plus the excitment of seeing it run after 2 years of sitting idle - that I completely forgot about using the carb cleaner spray - Thanks - I'll be spraying tomorrow!!!

The PCV valve is new, but of course that doens't mean much - I'll try by-passing it to see what happens - Thanks