Weber 32/36 Low RPM Even-Throttle Hesitation

[thehackmechanic]

Hey, folks, I've had my head in tiis for so long that I've forgotten all the Weber stuff :^)

 

I'm sorting out Hampton, the 48,000-mile '73 2002 I bought from its original owner last fall. It's a very stock survivor other than the Weber 32/36. It still even has the EGR plumbing and the solenoid on the firewall controlling its vacuum actuation. It sat in a barn for about a decade before I bought it, but it resurrected pretty easily; the float bowl in the carb just had a little sediment in it, no gummy horror in it or the gas tank.

 

The car starts instantly and basically runs well, except that it's got this obvious low RPM even-throttle hesitation that's fairly pronounced between about 2000 and about 3000 RPM. It smooths out a bit above that, but on the highway you can still feel it hesitating a bit. Put your foot into it (cause the accelerator pump to squirt down the primary barrel) and the hesitation goes away, then returns when the acceleration stops.

 

I don't have an AFM on it or anything, but I've always associated this even-throttle hesitation with lean running. The plugs are pretty grey. 

 

I don't think it's an ignition or a timing issue. Timing is set to about 35 degrees of total advance. I've advanced and retarded it, vacuum line connected and plugged, no difference. I've swapped everything in the ignition but the distributor itself, no difference.

 

So, vacuum leaks or Weber jetting, right? If it's a vacuum leak, I haven't found it. I pulled off every vacuum line, including the hose to the brake booster and capped the carb and intake ports with rubber caps; no difference. I sprayed around with carb cleaner while the engine was running and didn't detect anything.

 

I AM, though, inherently suspicious of the EGR. I'd like to leave it in place as it helps reinforce the provenance of the car as a 48k survivor, but it strikes me as a huge potential vacuum leak. I've ordered the intake block-off plate and the Subaru oil drain plug for the exhaust manifold, but once I start to take it off, I'll probably ruin it, and there's no going back, so that's a last resort.

 

The jets aren't anything strange. I have another old Weber, more for parts than anything else, and it has nearly identical jetting in it:

 

                   primary   secondary

idle              60          60

main            140        140

corrector      170        160

 

I enriched the idle mixture a full turn, but it didn't seem to make a difference.

What do you think? Try fatter idle jets?

 

Thanks.

 

--Rob

 

Edited June 22, 2020 by thehackmechanic

[TobyB]

Sure, fatter idle jets- maybe just on the primary first, and see what that does.

 

First, check float level though, if you haven't already.

 

t

 

[mike472]

60 seems a little rich. Maybe that’s why the adjustment has little or no effect. Try 50 or 55. This might be a stupid question but did  you take it off and give it a good blowout with compressed air and plenty of gum out?

if all else fails do yourself and Hampton a favor and ditch that thing for a 38/38 DGAS.  Really makes a big difference over that 32/36

[thehackmechanic]

Yes, sorry, I didn't say that. I pulled the top off the carb, pulled out all the jets and tubes, and blew it out with compressed air.

['76mintgrün'02]

The jetting that c.d. used to recommend works very well for me, along with F50 emulsion tubes.

 

PRIMARY

idle 60  60

main 140  140

air correction 145  170  160

 

SECONDARY

idle 55  60

main 170  160

air correction 175

 

(c.d. numbers in black, your jets are in green, my change in red)

 

I finally installed the AFR gauge and it was running a tad rich, so I bumped the primary air corrector up to a 160.

 

You  could swap your primary and secondary air correctors and you'll be close to my jetting, aside from the larger secondary idle.

 

Try that!   

 

Tom

 

Edited June 23, 2020 by '76mintgrün'02

[Senna27]

I don't know about others, but I could never get my stock Weber 32/36 to work to the point where I was satisfied. It always had a flat spot to some extent. I spent hours playing around with jetting and adjustments, to no avail. I've since learned others have experienced the same thing. That's not to say you can't get one to work properly. Solving the mystery may in fact come down to jetting, tuning and other factors. 

 

Then one day my buddy and I decided to put the trick Weber 32/36 from the engine on the Formula Ford I used to race on my car. The carb was modified by our engine builder, Quicksilver RacEngines. They remove the power valve and install brass tubing to the primary, secondary and idle circuits. They also block off some passages and solder some holes in the emulsion tubes. See photos attached.

 

This immediately solved my flat spot and made the car so much more drivable. So my buddy and I bought some brass tubing and proceeded to copy the race carb. It's served me well for the last 34 years but is being retired as we speak, in favour of 45 DCOEs. 

 

[man_mark_7]

On 6/23/2020 at 7:12 PM, '76mintgrün'02 said:

The jetting that c.d. used to recommend works very well for me, along with F50 emulsion tubes.

 

PRIMARY

idle 60  60

main 140  140

air correction 145  170  160

 

SECONDARY

idle 55  60

main 170  160

air correction 175

 

(c.d. numbers in black, your jets are in green, my change in red)

 

I finally installed the AFR gauge and it was running a tad rich, so I bumped the primary air corrector up to a 160.

 

You  could swap your primary and secondary air correctors and you'll be close to my jetting, aside from the larger secondary idle.

 

Try that!   

 

Tom

 

 

Is it correct that decreasing the air correction jet size decreases air getting mixed in emulsion tubes and therefore makes the mixture richer? 

[kbmb02]

16 minutes ago, man_mark_7 said:

 

Is it correct that decreasing the air correction jet size decreases air getting mixed in emulsion tubes and therefore makes the mixture richer? 

 

Yes, correct. And, primarily in the mid- to upper RPM range.

[Arizona02]

Car sat for tens years is the reason. Remove the carb and all the removable jets tubes valves etc. Soak the carb body & top plate to clean out the internal passages, you can't see what in there.

[jmiller]

I had a bucking problem at light throttle when I first got my 32/36 many years ago.  Raised the float level from from prescribed 41 to 39mm and solved the problem.  Maybe this will help.

[thehackmechanic]

Just to update this, the float level was already higher than spec--it was about 31mm--and the fuel in the float bowl was more than covering the passages after I ran the engine, shut it off, and removed the top. I left it where it was.

 

Removed the size 60 primary idle jet, tried the size 65 idle jet, and it made very little difference.

 

Tried the size 70 idle jet, and it made a pretty substantial difference. Driving it now, I'm not sure I'd notice any hesitation had I not spent days chasing the problem.

 

I freely admit that the bigger idle jet may be hiding some other problem, like a vacuum leak through the EGR plumbing, but I think I'll drive it this way for a bit and see if the hesitation mole pokes its head back up and I need to whack it again.

 

--Rob

[Dudeland]

Whenever I hear of flat spots, I always think flat timing, or something is sticking then opening up.  Do you have another dizzy you can try, perhaps a strait mechanical one?