simple carb q's

DjEep · Post by **DjEep** » Mon Mar 23, 2009 3:42 pm

I tried an old 34pict3 on my bus a week or two ago, trying to solve my dizzy adv and/or mixture issues.

I think the 30/31 is running too rich. Changed the oil today and it smelled pretty gassy. Could be another reason why I got that oil-light flicker the other day after running it hard and fully loaded with about 1500lbs of people.

Anyhoooo, when I tried the 34pict3, it did ok, until it just quit on me after about 30 minutes and 15 miles. After lots of cranking and pedal finesse, it started again enough to get it through an intersection and off the main drag, where I swapped back on the 30/31.

Before putting on the 34, I put in a new "top" gasket, as the old one had been removed when we were diddling with it when it was first removed. Still have the rest of the rebuild kit.

Question: I noticed in hambone's rebuild thread something about needing to re-set the float after a gasket change. Is this the likely culprit? How do I do it? I still have never done much to a carb other than turn screws and swap jets. What are other possible culprits? Simple crud in the jets maybe?

spiffy · Post by **spiffy** » Mon Mar 23, 2009 3:48 pm

If any of the passageways have gunk in them these cabs get really crabby. A bad float will really piss you off too. Carb cleaner with an air compressor hooked onto a football/b-ball etc air re-filler cleans them pretty well.

hambone · Post by **hambone** » Tue Mar 24, 2009 9:49 am

Could be the float. Or mixture settings. Or a dirty carb. Or even a worn out carb. All those variables need to be ruled out.

Post by **Amskeptic** » Wed Mar 25, 2009 7:18 am

DjEep wrote:I tried an old 34pict3 on my bus a week or two ago, trying to solve my dizzy adv and/or mixture issues.

What current distributor do you have? The 34Pict3 wants centrifugal with vacuum advance (some require retard as well for correct idle air flow).

A vacuum only distributor goes best with the earlier carb.
Colin

DjEep · Post by **DjEep** » Thu Mar 26, 2009 5:49 pm

Have an Aircooled.net SVDA w/compufire.

I was under the impression that the 30/31 was basically a smaller 34, with the same separate idle circuit as opposed to the earlier 30pict which I thought idled via a sightly open throttle plate. And that the vac signal on the "advance" port on a 30/31 and 34 was off @ idle, and off again @ half throttle and onwards, whereas the old carbs made to pair with the vac only dizzy were off @ idle, then just pulled vac until the can ran out of advance.

Post by **Amskeptic** » Thu Mar 26, 2009 8:04 pm

DjEep wrote:Have an Aircooled.net SVDA w/compufire.

I was under the impression that the 30/31 was basically a smaller 34, with the same separate idle circuit as opposed to the earlier 30pict which I thought idled via a sightly open throttle plate. And that the vac signal on the "advance" port on a 30/31 and 34 was off @ idle, and off again @ half throttle and onwards, whereas the old carbs made to pair with the vac only dizzy were off @ idle, then just pulled vac until the can ran out of advance.

The Pict # is the one that tells you about throttle-plate idle set, versus idle air circuit with big brass screw. Pict 2 is earlier, Pict 3 is the later. The 30/31/34 is the venturi diameter.
What is the Pict # on the 30/31?

For the record, the 1970 bus should have an airflow controlled (big brass idle screw) carb Pict3 with all the vacuum signal requirements for a vacuum-only distributor. I better be correct here or I have to go back to school.
Colin

DjEep · Post by **DjEep** » Thu Mar 26, 2009 8:26 pm

Amskeptic wrote:
DjEep wrote:Have an Aircooled.net SVDA w/compufire.

I was under the impression that the 30/31 was basically a smaller 34, with the same separate idle circuit as opposed to the earlier 30pict which I thought idled via a sightly open throttle plate. And that the vac signal on the "advance" port on a 30/31 and 34 was off @ idle, and off again @ half throttle and onwards, whereas the old carbs made to pair with the vac only dizzy were off @ idle, then just pulled vac until the can ran out of advance.
The Pict # is the one that tells you about throttle-plate idle set, versus idle air circuit with big brass screw. Pict 2 is earlier, Pict 3 is the later. The 30/31/34 is the venturi diameter.
What is the Pict # on the 30/31?

For the record, the 1970 bus should have an airflow controlled (big brass idle screw) carb Pict3 with all the vacuum signal requirements for a vacuum-only distributor. I better be correct here or I have to go back to school.
Colin

yup, looks like '70 had the 30 pict-3 designation and the bypass. Thought they didn't start that until the 34, and the 30/31 was a bypass idle replacement meant for singleports. From what I've been googlin', looks like the 30/31 is a replacement piece of junk.

I'll try to clean up and rebuild that 34pict3 right now, while the bus isn't going anywhere until I can get a new cv anyway. Maybe that'll be the best bet.

spiffy · Post by **spiffy** » Thu Mar 26, 2009 8:42 pm

Hey DJ....wanna try an experiment? If so I'll send you a nice German 30 and I want you to try it with either your SVDA or a 009. Trick is I want the carb back as it came from keifernet. Would be fun to see what you think of the combo LOTS of split bus and early bay folks running the 28 or 30 pict paired with a 009 with zero complaints....I am not condoning it but I HAVE experienced the combo and I really can't say anyhting bad about it....after all besides the drivability aspect of vacuum paired with mech advance paired to the appropriate carb you really will not notice a noticable "performance" improvement on a single carbed low power engine.

So I say slap whatever feels good on that center mount carbed engine and see what happens. If ya want more pep get some ratio rockers and some dual carbs. It seems like a lot of folks are pissing away time and money trying to compensate the carb/dizzy combo based on their butt dyno. Give up the 2 HP gain and just go for what werks.

Anywho,

DjEep · Post by **DjEep** » Thu Mar 26, 2009 9:57 pm

I don't care about pep, just trying to get the thing to have some semblance of low end torque. My last two single carb buses performed just dandy with a 34pict3 and SVDA and a 34pict3 and DVDA w/o retard connected.

This bus is currently more like Geri Lou when she had a 009. Chugga, chugga, lugga, chugga, vrooooomm. A little better since the last carb tune I think, but not enough. Tore down, cleaned and reassembled the 34 just now. New float valve, new gaskets, new mixture screw, etc. Wanted to slap it on, but my "landlord" wasn't to keen on carb tuning at 9:30pm in front of his house. Spoil sport...

That and I can't drive it 'til I get a new CV tomorrow.

DjEep · Post by **DjEep** » Mon Mar 30, 2009 7:08 pm

So, anyone have any ideas on getting this 34pict3 to work?

It will start and run fine with the choke closed, then lean out and die as soon as it opens. Bypass and Volume screw adjustments seem futile.

Post by **Amskeptic** » Mon Mar 30, 2009 7:27 pm

DjEep wrote:So, anyone have any ideas on getting this 34pict3 to work?

It will start and run fine with the choke closed, then lean out and die as soon as it opens. Bypass and Volume screw adjustments seem futile.

Check to see that the cutoff plunger actually retracts when supplied with 12 volts. You may have to give the cut-off plunger a little nudge. It is designed to have a slight pre-load when installed. Some instances of the cutoff not working because of poor ground have been reported because of the rubber o-ring. Removing it and using a smaller diameter o-ring has sometimes restored function. If the cut-off is working properly, check float level and clean all orifices you can reach with GumOut spray and the red nozzle that comes with it.
Colin

spiffy · Post by **spiffy** » Mon Mar 30, 2009 7:28 pm

With the choke on or see if you can put your hand over the top of the carb, I am thinking you might be able to test to see if the throttle shaft is introducing a leak. Never tried this but it might work.

Post by **Amskeptic** » Mon Mar 30, 2009 7:43 pm

spiffy wrote:With the choke on or see if you can put your hand over the top of the carb, I am thinking you might be able to test to see if the throttle shaft is introducing a leak. Never tried this but it might work.

Throttle shaft bushings are not a problem with air bypass carbs. They merely point out that there is a problem when gas drips out. Air bypass carbs can easily overcome worn bushings.
Colin

DjEep · Post by **DjEep** » Mon Mar 30, 2009 8:47 pm

You may be on to something there, Colin. When I reassembled the carb, I used a rubbery o ring on the solenoid. And when I gave it the "click"-test, I couldn't really hear it "click on" (open), but I did hear it click "off". Probably just barely opening.

I'll tinker first thing tomorrow.

DjEep · Post by **DjEep** » Tue Mar 31, 2009 1:53 pm

Bingo. Took the rubber gasket out of the equation and she runs! Still trying to tune out a bog on accel in the lower rpms. Turning the volume screw out seems to help. Maybe an accel pump adjustment ('tis a new diaphragm)? Is that just a matter of moving the the little bolt on the linkage?

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simple carb q's

simple carb q's

Re: simple carb q's