Worn 34 pict 3 Throttle shaft question with video

[rippofunk]

Background:
Newly rebuilt motor, turn key from a local builder. I picked it up, put it in and drove it. installed it about a month ago. 1776, cb cheater cam, stock 34pict 3 carb with a stock exhaust with a zoom tube, it replaces the pea shooters with a straight pipe basically. The exhaust is not ideal and on my list to replace.
The idle has been not awesome since i got it. all the signs of a vacuum leak. I checked the plugs for color about 2 weeks ago to make sure i am not running lean and everything looked pretty good. In essence i think he tuned it around the vacuum leak, but it has been getting worse.
Hopefully a dumb question, is it possible the shaft is so worn when i spray the carb cleaner on the inside of the levers, it slows the motor? or is that expected behavior? i really doubt its expected, like i said dumb question, but i have never run into this. this is also my first Brosol Carb.
Thanks in advanced for your input.

Link

[torsionbar]

now you know why i hucked my leaky too-complicated 34 pict-3 into the trash, and replaced it with an easy and simple 30 pict-1.
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[Gary Massin-Ball]

Throttle shaft bushings will always have a certain amount of leakage at idle as there is nor real positive seal just bushings.

Once you crack the throttle any leak at the throttle bushings will be void anyway.

You are correct and the carb may have been tuned to run with the minor throttle bushing leaks. The carb should have bigger idle jets just due to the larger displacement anyway.

I have torn a new engine down before that had idle plroblems (weak idle, stalling, etc) that no amount of tuning would repair. We found the deck hieght was too much for the cam (.100" on a 110 cam 284 dur) and made the compression ratio around mid 6s so in combination with a bigger duration cam resulted in a motor that ran like it was worn out with really low compression.

I would do a compression test and make sure all are at least over 100lbs and go from there.

Gary.
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Equalizer 5lb pulley
Stock lifters
Stock aluminum pushrods
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[rippofunk]

it has an erratic idle. its pretty steady but it drifts. takes a lot of pedal to cruise on the highway.the idle adjustment screw is screwed in all the way. to me those seem like vacuum leak issues versus engine issues. its strong, i can accelerate up a good hill on the highway. i can take hills in higher gear then with a 1600, so i think the engine is all there and ok. I thought the extra pedal was just a misadjusted cable but now i think its part of the vacuum leak.

when i fog the carb cleaner from a distance, directed at the nuts on the shaft it speeds up. my initial thought was the gasket was leaking, but when i go closer to the gasket with the carb cleaner, it does not speed up.

I went out and idled it up, guessing between 2 and 3K and did the same spray as the video and got a lesser decrease on the cable side and no real decrease on accel pump side.

[clonebug]

A cheater way of fixing that would be to pull the throttle plate and shaft.
Get some Viton o-rings and carefully drill the ends of the carb to make room for the o-rings.

It won't fix the slop all the way but it will fix the leaks.

I have done it to two of my carbs now. I leave a little resistance in the shaft to the o-rings but the spring has lots of power and will pull it back to idle.

You can get 50 o-rings for just a couple bucks online and it only takes a couple hours to do.
I built a simple jig.

this is the second carb I did for my turbo project. That was the reason I needed to seal the shaft. You can see the 3 inch high angle iron I used as a jig and the drill press.

Here is the clearance I made for the o-ring.

Here is the Bocar I did mounted on the angle iron jig. I used a smaller bit to check to make sure the carb was square to the drill bit by pushing it through both bushing areas but NOT drilling.

Here is a pic of the o-ring sitting in the clearanced area from the drill bit. You have to do a little at a time and just take enough out to allow the shaft to turn without too much resistance.

It is easier than it looks. Just go slow.

My build on STF has the o-ring sizes or else just PM me if you need more info.

Clonebug

[rippofunk]

sweet, i have read a couple 'how to rebush' but never saw (or looked) for adding an o-ring! I was thinking about shoving one in there and seeing what happens without drilling for clearance but that makes sense.

i dont actually feel any slop with the carb installed, but maybe there will be some once i take it out.

Thanks for all your input.

[clonebug]

You have to drill for clearance since the arm is tight to the body or it will bind the shaft.
The o-ring size you need is an 011 Viton o-ring which is resistant to fuels.

If you are serious drop me a pm and I can throw 4 o-rings in an envelope for you. I have about 45 of them left....

Clonebug

[Micropassatman]

Great idea!

[clonebug]

Just remember....

What is done can not be undone......

Go slow and don't take too much out. Drill a tiny bit and then reassemble and test....repeat......repeat.

Clonebug

[Micropassatman]

Another option would be to 'groove' the throttle shaft to accept an o-ring just like the mixture and bypass screws have.

[clonebug]

The stock bushing in my Pict 34 was a plastic style split bushing. It would not take to an o-ring trying to seal against the inside of it. All that would do would be to make the bushing spin in the bore with the throttle shaft.
It would probably seal though.

Clonebug

[Micropassatman]

[clonebug]

Pict-3

Clonebug

[Altema]

[rippofunk]

Found some viton o-rings at a local auto parts store. Thanks for the offer Clonebug!

Unfortunately, mine did not come out exactly like yours.

I got a 7/16" drill which seem to be the size of shaft and the o-ring. i figured if i drilled the carb about half the depth of the o-rings width the other half would get consumed with squish and not be to much friction. when i assembled it i greased the shaft. In my hands it seemed like not much friction. but the bus thought other wise.

tried adding spring tension, discovered the hard way my pedal was missing parts. missing the spring that holds the shaft, of the lever in place under the front. part 8 that holds part 9 in place.

and my shaft seemed tired, the groove is not as deep as it probably once was. I know i need to add that kit to my list, but that wont help me today. So i drove over to Tractor Supply and bought a shaft collar that fit perfect. and wow it works great. it was a 1/4 X 1/2 X 9/32 shaft collar.

So my pedal now feels awesome, but the friction problem was still there. what i did was add thread lock (green) to the shaft and loosened the shaft bolts to decrease the friction / squish. the thread lock was probably more for comfort versus actually needed.

Seems pretty awesome as it sits now. i might go to a nylock nut at some point just to make me feel better. I am glad i did drill the carb to get the o-rings in there. I obviously wish i had drilled more, but i am overall happy with the results assuming they last.

Sprayed the carb cleaner in there and no vacuum leak. I did not power it into the shaft as the fog did not show any leak.

Thanks for the help and the awesome o-ring idea!

[brc0703]

i replaced my idle screw o-ring and noticed that its a perfect match to go on the throttle shaft too so gave me the same idea to dill out the carb for the o-rings but was wondering how long they will last? also you say Viton o-rings.. is that just a brand or is it a certain material?

[66brm]

Its a material, there are 4 different types of Viton, one in particular is very good with fuels, you want type F for fuels (easy way to merember)
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[connor2010]

my carb has brass bushings in it do you drill carb with the bushings in or out of the carb??

[Juanito84]

[Alstrup]