Stalling under Breaking

[jschwartz]

Try adjusting the float levels. I've found stalling under braking is usually too high, causing momentary flooding of the engine.
jeff

[GTRCLIVE]

Sorry to hear about that, only real solution to this problem seems to be fitt FI.

[adequatespeed]

I have set the float levels about 1/16 below the sight hole.

Should I go lower?

Another posibility I thought of was wither increasing the idle speed (will get hot in traffic).

Alternativly what does the air screw adjuster do on the side of the holly? I think it adjusts the air bleed at idle. This could be set incorectly, haking it easier to stall the engine when a bit of extra fuel gets in there

[GTRCLIVE]

The screws in the side of the metering plates (between the bowl and the main body of the carb)are for tickover mixture adjustment, normaly open about 3/4 to 1 1/2 turns depending on your engine. Wouldn't want to lower the float bowl hieght any lower than what you have it for normal running. But may be a good Idea for a test, just to see if it works.

PS. does it only happen when you are coming to a near stop, ie. with your foot is on the clutch and the engine revs lower than 2,000.???

>> Edited by GTRCLIVE on Tuesday 25th March 09:56

[Steve_D]

Have you tried posting this problem on the Chevy Talk forum?
Go to the 'Performance Related' forum. They are very helpfull and treat strangers well.
Steve

[Steve_D]

Just found this thread running on Chevy talk.
It's quite new so may run for a while. Just join in and see if it helps.

www.chevytalk.org/threads/showflat.php?Cat=&Board=UBB64&Number=378651&page=0&view=collapsed&sb=5&o=31&fpart=1

Steve

[srreck]

I surfed to Holley webpage and found this:
www.holley.com/Hioctn/prodline/carb/carbPA/26-40.html

Apparently you can test this with your problem by hooking a piece of clear fuel hose to the front and rear bowl vents. Hook the two vents together with the hose, then mahe a slit at the top. The hose should look like an arch between the two vents (air cleaner removed, of course). Drive up to speed with a passenger looking back at the hose. If you stomp on the brakes (don´t forget to warn the passenger first !!), and when you do, instead of flooding out, the motor continues to run okay, while in the meantime fuel flows up the hose from the back side to the front, you´ve confirmed the diagnosis.

[adequatespeed]

Clive,

Yes it does do it <2000 rpm when coming to a stop with my foot on the clutch.


Had a look on Chevy Talk - They seem to offer the same advice.

Float levels are too high - Fit whistle vents - try jet extensions. (all of which I have addressed)

I will try the idle mixture screw to see if I can lean off the idle a little to of extra fuel. When I had the engine set up the mechanic said he could not get the idle emissions anything like due to the cam and rough idle. So I have no idea where it is set to.

Is it an air bleed screw where out make is weaker or is it a fuel needle where in makes it leaner?

I am asuming going too weak is a bad idea but given the fact that the exhaust funmes sting your eyes at idle i suspect it is a little rich.

[Steve_D]

It's keyholes you put your eye too, not exhaust pipes.
Steve

[Vez]

Your eyes do this when you walk near the back of it.

Well AS, you could just throw away the old carbs, and have eight beautiful throttle bodies sat up top with a custom Carbon Airbox and a nice Motec controlling the whole shooting match if nothing else works

Hold on I know you detest the smiley faces that follow the stig around so

(cant find any gay clapping hand ones sorry).

>> Edited by Vez on Tuesday 1st April 15:13

[adequatespeed]

Further News.

In an effort to try and diagnose the problems I am having with stalling under breaking, I had a vacuum gauge connected last night. The cam I have (comp cams 292H) has what is described as a "radical idle" this results in only about 7" Hg at an idle of 900rpm. Which means the power valve is opening and causing a very rich mixture - probably not helping the flooding and causing the burning eyes with the fumes

This seems a very low vacuum to me and leads me to suspect there my be a leak somewhere. Has anyone else measured the vac at idle for comparison ? (some detail on the cam would help as a more normal cam will give a much better vacuum).

[Steve_D]

If you think you have an air leak and want to go looking for it, try this.
Take a propane blow torch (used for plumbing), turn it on medium but don't light it. With the engine on tickover move the torch around the suspect areas of the inlet. If the revs rise you have found the leak.
Steve

[ultimaandy]

Steve_D said: If you think you have an air leak and want to go looking for it, try this.
Take a propane blow torch (used for plumbing), turn it on medium but don't light it. With the engine on tickover move the torch around the suspect areas of the inlet. If the revs rise you have found the leak.
Steve

[Vez]

Seems like a fair suggestion! If you can hold off till friday (finish for week thursday) Ill give you a hand AS and then I can buy you a curry!

>> Edited by Vez on Wednesday 2nd April 14:41

[GTRCLIVE]

My Lambda sensor reads close to 1 when on tick over, perhaps if there is no leak, you could change the power valve for a lower one. There are lots of different vacumn spec's.

Will try and find a Vac gauge and find out what my vac is on tickover.

[Vez]

Clive, where on the exhaust is your lambda sensor plumbed in? is it after the collector on one back? or are both monitored?

Ta.

[adequatespeed]

Got a bit of info on a similar cam. 8" Hg is normal at 1000 rpm. With a slower idle it gives about 6".

I had a 5.5" power valve which you can hear opening changing the engine note and causing a rich mixture.

I have swapped for a 3.5" Valve (posibly a bit low) but will give it a go and see if it improves things.

With this, whistle vents, jet extensions I have run out of ideas.