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Rebuilt IDFs and my engines idle is all over the place.
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Agent47
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PostPosted: Sun Aug 14, 2016 11:52 am    Post subject: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

I just rebuilt a set of early 40 IDFs and installed them on my car (73 Std Beetle). Now I am having troubles Sad

The car will start and idle very slowly, as it should; you give the carbs a little gas to prevent it from dying, the idle jump up to 2k-3k and stays their for about a minute then creeps back down. The linkage is disconnected, fyi. The engine is backfiring out of the exhaust and the carbs, all 4 cylinders.

They have CB performance rebuild kits in both, CB performance offset manifolds.

My engine is a 1641 with a stock cam.

I have adjusted to the valves to ensure they are correct (.006) I took starting fluid and sprayed the intakes to see if I had a leak and there was no noticeable difference. Timing is around 7 degrees btdc at 1k rpms(German 009) ran fine with my 34 Pict 3. I tried advancing and retarding the timing; advancing increased the idle; retarding stalled the engine .

I replaced my old Kadron glasspack with a Hot dog muffler, the Kadron I suspected was leaking. I am running the factory heat exchangers as well.

Any advice on what to try to check? I am running out of ideas.
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mark tucker
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PostPosted: Sun Aug 14, 2016 1:26 pm    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

sync the carbs & linkage, and go from there. sync idle then sync opening times.
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PostPosted: Sun Aug 14, 2016 1:33 pm    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

Idle probably lean, or has vac leaks
Hows it drive?
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PostPosted: Sun Aug 14, 2016 1:56 pm    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

I haven't driven it yet. I am having trouble trying to sync the carbs, with the constant fluctuations in idle. I have been able to get them all close, about an 8 on the ste snail gauge.
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PostPosted: Sun Aug 14, 2016 2:02 pm    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

Once you get the linkage on you can do a slow "idle up" to see if the idle jets are close, but really you have to drive it to know. If you have to change idle jets then it will throw everything off so don't tire yourself out fine tuning the idle just yet.
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PostPosted: Sun Aug 14, 2016 2:20 pm    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

What Mark said. Get them synched first. Then bring them down in small steps until you reach the desired idle RPM, and they are synched at that RPM.

But first get your linkage synched the same. The engine doesn't even have to be running. Bring both carbs down to not pushing the linkage at all, but making contact. Then add one turn to each, then two. Then try starting it, and if it runs, then synch. TAKE YOUR TIME!
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PostPosted: Sun Aug 14, 2016 3:34 pm    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

So I took it out for a drive up the block. If you press the gas pedal more than 1/4 of the way I get hesitation the back firing all but stops after 3500 rpms. Deceleration increases the backfiring. With the linkage installed I readjusted the timing, 30 degrees btdc at 3000 rpms.

The car had great power (compared to stock at least) after the lurching and hesitation stopped. It had no problem accelerating up 4500 rpms, I have a stock crank so I let of then.

After I put the filters on the backfiring lessened.

If I am interpreting everything I have read correctly, I would think the carbs are running lean.
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PostPosted: Sun Aug 14, 2016 6:36 pm    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

Think you need to take them off and start over...... something is definite wrong with rebuild....

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PostPosted: Sun Aug 14, 2016 6:52 pm    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

Dale, what would you be looking for if you were to pull the carbs?

Here is what the rebuild consisted of:

I soda blasted the bodies, used as least one can of carb cleaner on each and brushed the ever living shit out of them to get all the crap out, and put about 50 gallons of air through each carb making sure each jet passages were clear. Then replaced all the seals and gaskets. Replaced the seat and needle valve and mixture screws and springs; as well adjusted the float to the specs from CB performances kit. I also regressed the bearing once I was done cleaning the carbs.

There was a lot involved with rebuilding the carb but I took my time to try and prevent mistakes, which doesn't mean I didn't make any though.

But if you have a starting point for me with I would be appreciative of it.
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PostPosted: Mon Aug 15, 2016 8:42 am    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

You have a vacuum leak. Use the snail gauge on all 4 bbls, the one that reads low is the one where the leak is.
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PostPosted: Mon Aug 15, 2016 9:14 am    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

When using the snail gauge is the number supposed to be steady? When I am using it the number bounces and I am going off the highest number. I assume that's the correct way, since it is reading the intake cycle.

But I have all the cylinders reading 8. These carbs do not have the vacuum port nipple. I will make a video of it running after I get off work, so you all can see what's it's doing and are not relying on my descriptive skills.
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PostPosted: Mon Aug 15, 2016 9:29 am    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

you are omitting details.

What idle speed?

Normally at ~800 idle the snail will read 5.5-7 range. If you are at 8 that's already a red flag to me.
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PostPosted: Mon Aug 15, 2016 9:52 am    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

It is idling at 1100 at 1.5 turns in on the idle adjuster screws. I have been able to get the idle down to about to around 700; however it wont stay that low. it wants to die. If you give it gas to stop it from dying the idle goes up to 1500 and stays; eventualy after a few backfires it stumbles, the rpms drop and it dies unless you feather the throttle.
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PostPosted: Mon Aug 15, 2016 10:02 am    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

Also according to the fuel pressure gauge it is just above 3 psi (VDO mini gauge). I know the carbs are sensitive to fuel pressure.
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PostPosted: Mon Aug 15, 2016 10:30 am    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

According to the PO the jets sizes are

28 vent (confirmed)
F11 Emulsion tubes
115 mains
50 idle

I dont recall seeing any numbers on the jets while i had them out, except the venturis.
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PostPosted: Mon Aug 15, 2016 10:59 am    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

You have a vacuum leak, and/or a bent throttle shaft.

Also, there are no idle adjuster screws. There are idle speed screws, and idle mixture screws.

Agent47 wrote:
It is idling at 1100 at 1.5 turns in on the idle adjuster screws. I have been able to get the idle down to about to around 700; however it wont stay that low. it wants to die. If you give it gas to stop it from dying the idle goes up to 1500 and stays; eventualy after a few backfires it stumbles, the rpms drop and it dies unless you feather the throttle.

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PostPosted: Mon Aug 15, 2016 11:07 am    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

Thanks for the advice John! It definetly narrows down what I need to look for.


I will do like you said and see if i can find one of the cylinders reading off from the others, I will post up what i figure out.

Will spraying starting fluid around the vacuum ports show if they are leaking? How do you determine if the throttle shaft is bent?
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PostPosted: Mon Aug 15, 2016 11:08 am    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

The idle speed screws is what I meant Embarassed.
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PostPosted: Mon Aug 15, 2016 11:15 am    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

When the carbs were out of the car I had set the idle speed screws based off of the amount of the lowest progression hole exposed (exposing only half of it). But both looked equal to me (on both carbs), but i am not sure how much difference would be visible if the shaft was bent.
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PostPosted: Mon Aug 15, 2016 11:51 am    Post subject: Re: Rebuilt IDFs and my engines idle is all over the place. Reply with quote

Look around the I-net and find "lean best idle document" for adjusting Webers....

1.5 turns out for idle mixture screws is only generic setting to start, final setting is what your engine tells you, but if your idle jets are less them one turn out you jets are to rich if more then 2 turns out your idle jets are to lean...

Might look here to tuning procedures/documents... Look in "sub categories"...

http://www.piercemanifolds.com/category_s/308.htm

Dale
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Last edited by Dale M. on Mon Aug 15, 2016 11:54 am; edited 1 time in total
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