Bogging/stalling when braking

[luvbowties]

Originally Posted by tenni126

Yep. The Edelbrock is maybe an apples to orange kinda thing compared to your specific carb, but that was my problem. It was after I swapped to 4 wheel power discs from manual drums, so the added vacuum load kind of exacerbated things. It used to only kind of stumble on braking, then after the brake booster it'd stall completely. IIRC it was that the fuel level was too high, and when I'd brake what was happening (I think) was that it would flood the carb temporarily. It didn't take much to correct it, and I remember being surprised at how sensitive it was to float height. That advice was from the troubleshooting chart in the carb's manual.

Hey, tenni126. Personally, I don't see apples and oranges here--I see fruit in both cases. Have had that issue w/so many carbs--Holleys included--that I see them all operating basically the same. On one Holley, I knew float height was my issue, but even so I must've opened it up and readjusted it 12-15 times. It was on a '69 Chrysler New Yorker with 20-some thousand miles, 440 engine, & 4bbl Holley. Traded to me by an elderly, wealthy farmer...car looked on outside like it had 220 K miles, where he'd bumped it numerous times, always had dent partly knocked out, & close to correct color paint put back on; on the inside looked brand new! They just couldn't find anybody who could fix the carb problem.

While I was working on it, I finally tossed the carb. specs & began my trial-and-error routine. Found a wee bit of range between its previous flooding-syndrome just prior to stalling, and leaning just prior to stalling. Within that tiny range, it became perfect. It was like you described, float too high would give it too much gas initially as fuel level sloshed over into venturi, then quick braking, and ka-plunk...stall from instantaneous overly rich condition. Then when float was too low, it'd act like bad accel. pump when you began to move off, then when you suddenly hit the brake, ka-plunk again and stall again--this time from being too lean an instant earlier.

Betcha that even a Weber carb could present similar symptoms, & I've never seen inside one of them?!?!
Sam

[cg285]

i've encountered this issue a couple times in the distant past. both times the vehicle started and ran fine but stalled upon heavy braking. this is what i found on 2 different occasions:
1.there was (for lack of a better word) "silt" in the float bowl. when braking the material moved and covered the main jet(s)
2.float level was too high

take that info at your own risk

[thelawdoc]

cg285, Well we did check the carb and it was clean as a whistle. I rebuilt it very recently. Maybe the float settings were off. I don't think so. But, like gapping plugs, I suppose it is not all that difficult to be off some few thou. I am waiting to hear back yet from the shop where they said they would swap out the carb and see what that does. I should know more in a couple hours.

[chevy_mike]

Man this reminds me of a VW I had once. Perfectly running engine. Removed engine (was building a Manx style dune buggy from it) and placed on floor in garage. Reinstalled engine with zero changes made to it but it would not run no matter what we did. Bought a different carb setup and it ran perfect. It was the weirdest and most frustrating thing and no one could explain why.

Don't give up and good luck.

[thelawdoc]

Chevy, yeah, that is why I am kicking myself for doing the tune-up. I was better off without it. I just want to know exactly what the problem is now. Or I will be too paranoid to even change oil in the future.

[TJ's Chevy]

I would also consider float level...where I work at...when I have to work on a chain saw carb...I've had the float just about a millimeter under specifications...and it wouldn't run right...fix that little millimeter gap and it runs like a gem..but that's on those little carbs these bigger carbs aren't quite that touchy, but...its a possibility as well.

[thelawdoc]

Gentlemen, Well the mechanic brought back the truck and said I should swap out the carb. He said there can be no other cause for my symptoms. (He did not have a carb on hand to test his diagnosis.) I decided that before I order a carb, I will dismantle my carb and check it out again. Today I dismantled the carb. I found the float height at 1-8/32" instead of the specified 1-9/32". I cannot know yet whether this was the cause of the symptoms I mentioned in my original post because when reassembling the carb I found that one of the bolts that holds down the air-horn suddenly will not grab the float bowl. I will have to tap it out. Maybe I will re-install the carb as it is just to check it.

As for tapping the float bowl, the bolt appears to me to be a 3/16" x 28tpi. What would be the proper next size larger to tap? (I have available what appears to me to be a 1/4" x 20tpi machine bolt.)

[thelawdoc]

Sorry: the bolt seems like a 7/32" x 28 tpi. I mic'd it.

[tenni126]

Do you have room to get a time sert or heli coil in there? With that soft-ish metal I'd try that before just tapping it out larger maybe.

[thelawdoc]

Tenni126, could you please elaborate as to what a 'time sert' and 'heli coil' are? I have to repair a bolt hole in my carburetor float bowl.

[blown240]

A heli coil is a threaded insert that lets you put the original size bolt back in. They usually only require you to tap a slightly larger than original hole. You can get them at most auto parts add hardware stores.

[thelawdoc]

Blown, well that sounds nice! I can walk over to an Advance Auto Parts near me. Hopefully they will have it. But if I have to tap the hole anyway, why do I need the coil?

[ACK]

Originally Posted by thelawdoc

Blown, well that sounds nice! I can walk over to an Advance Auto Parts near me. Hopefully they will have it. But if I have to tap the hole anyway, why do I need the coil?

Best practice calls for bolts to be the same size. My carb had 3 different size bolts, made reassembly a PITA, so I drilled them all out, tapped it, and now no assembly issues. Also, the carb body is aluminum, the wrong bolt could easily strip the threads.

I don't recall what size I used to tap it, might have been metric because it was what I had on hand or because it was a good size to make all the holes the same.

[thelawdoc]

Ack, Thank you. My carb is a zinc alloy, maybe Zamak. The airhorn fastens onto the float bowl via four 7/32 x 28 tpi bolts. One hole is stripped. I have on hand four 1/4" x 20 tpi bolts but I am not sure about the size and style of tap to use.

[blown240]

1/4-20 is probably fine if you want to do all 4 the same. But I cant say for sure because i cant actually put my hands on your carb. But that size is only 1/32 larger.

[thelawdoc]

Blown, my thinking is that since it is only 1/32" larger, I should be able to tap the holes easily. I realize that I am going from a 28 tpi to a 20 tpi, but since the hole's threads are stripped away, I do not see that as a problem. Plus, I have 20 tpi bolts on hand. The only remaining issue would be whether a 1/4" x 20 tpi bolt can satisfy the fastening specification. I am not an engineer, but I daresay it should. Alternatively, I could tap the holes for 1/4" x 28 tpi, but then I have to order those bolts from somewhere.

[blown240]

Is it was me, I would tap it 1/4-20. Just go buy a 1/4-20 tap. But that's me and I can't promise 100% success. But it should be totally fine.

Plus a 1/4-20 tap is a very useful size.

[thelawdoc]

Blown, yes, I am going to go with the bolts I have on hand. I have to get this truck on the road already! Plus, I like my 1/4" x 20 tpi bolts. They came off of a 1940's lathe that I restored.

[ACK]

Just want to start with, I don't work for Harbor Freight. In case there's one near ya', I have this tap & die set and it has served me well for light work. They also have a 25% off coupon, probably find it online, that's good through the end of today.

[thelawdoc]

Thanks, Ack. I just borrowed a 1/4" x 20 tap from a buddy. Now let's just pray I don't 'screw' things up!

[blown240]

Just remember not To turn the tap too far without backing it off and clearing the threads. The last thing you want is to break the tap off inside the hole your tapping.

[thelawdoc]

Blown, yes. Will do. Thanks.

[tenni126]

How deep are these holes? My only concern without looking at it is whether or not you have enough depth for a standard tap...if they go all the way through you'd be good to go with a tap, as long as you are careful with the torque applied on the new fastener. I like the thread inserts because you are removing (for the most part) the chance of the hole in question stripping again. It's a permanent fix. Time serts seem more better-er, lol. But heli coils work well too. Or, like you said, tap it to 1/4-20 if you have room and call it a day.

[Jimal]

This reminds me of the stalling issue I was having with a newer Dodge D-100 with a slant 6 and a one barrel carb. Ends up that there was debris in the carb at would sit in the bottom of the float bowl, but get stirred while driving, leading to flooding, which would manifest itself as a funky idle and stalling at lights (the engine could handle the extra gas while driving, but not at idle) in my case, there was a problem with tank venting and the charcoal canister on the newer truck. The charcoal from the canister was being drawn up into the carb thought the vent for some reason.

These trucks don't have charcoal canisters, but a deteriorating fuel line, vacuum line or vacuum cap could have the same effect.

[thelawdoc]

Gentlemen, the holes I am referring to are the ones that take the bolts that clamp the air horn to the float bowl on the Rochester B carb. The holes are on the outside of the carb and they are through holes. I am a novice at tapping, but I am going to jump in and tap the holes out to 1/4" x 20 tpi. Currently, they seem to be 7/32" x 28 tpi. I managed to borrow a tap which is for 1/4" x 20 tpi and that is why I did not go for tapping them to 1/4" x 28 tpi -the latter probably what a machinist would go for. Plus, I happen to have on hand four 1/4" x 20 machine bolts from a 1940's lathe restoration that I did. So wish me luck, lol.

I do not know whether the fact that I had a bad fastener for one of the four corners of the carb is the cause of the stalling I described in my original post. I am hoping that it is, because otherwise I am at the end of a check list that I have gone through a few times already. I would simply have to replace the carb -something I hope not to have to do.

My carb, which I rebuilt myself, is squeaky clean. You could eat out of it. The float was adjusted with a machinist's rule. The check balls are exactly as specified in the manual. All consumable parts have been replaced. The throttle body shaft is fine. I will reinstall the carb, re-do my timing and reduce idle rpms (right now I have idle at 900 to help reduce said stalls) and see what results.