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ChrisM

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Reply with quote  #1 
Hi Patrick,
Greetings from Oz.
Carb # 27482.
Where is the correct position for the Primary and Secondary plates in relation to the Transition slot.
Long story short, carb was lent out and came back with all adjustments changed and silly me never took note.

If I put the Pri plate showing 040" of slot it idles way too high...2000rpm, even when Sec are nearly closed.
Idle, hi-air, PV and other settings are as per tech sheet.
Only changes are jets (up two on original) and Pri pump cam flipped over. 
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Reply with quote  #2 
Close both shafts, then put 3/4 of a turn on them.  Fire it up, then adjust evenly the shafts to get your desired idle rpm.
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ChrisM

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Reply with quote  #3 
Ok, I got that thanks.

The other issue is stinkin rich at idle, even the neighbor has complained lol.
Reduce IFR or increase idle bleed?
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Reply with quote  #4 

It was built about 8 years ago and I dont have any record of it being rich at idle prior... so it wouldn't be a bad idea to have it freshened and cleaned.  

 

Then if its still rich at idle, simply go larger on the idle air bleeds.  Originally they are .070, so if your idle mx are IN more than 1.5 turns come out to .080 range.


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ChrisM

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Reply with quote  #5 
Hi, carb has been cleaned out and freshened up.
.078 iab's fitted and that's when the fun began.
mx screws out to 1 7/8 to get it to idle in gear @ 1000rpm- in Park is 1600rpm?Too much drop?
Throttle plates are closed at this point, to get the idle speed as above, which is the best I can get at this stage.

Checked for vac leaks, floats at 25% and is still way rich.

Help!
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Reply with quote  #6 
Its an older carb and has no history of being rich prior, so I would assume someone has done something to it and we should probably get someone to look it over and see whats different from how it was built years ago.

Possibly someone enlarged an idle feed OR maybe it has a bad power valve or metering block gaskets OR base to body gasket.

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ChrisM

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Reply with quote  #7 
It has had rich idle since day 1, but I was not too concerned 8 years ago.

Idle feeds are still .033 which is how it came, all other passages are as you supplied, after checking this out. Only change I made was the iab's to .078.
The person that borrowed this carb has vowed that the only things he touched were idle, mx and float level external adjustments and I do tend to trust this person.

Now after a clean-out, I freshened it with the only kit I could get at the time for a 4150, it's a 3-202QFT kit. Is this not suitable?
The gaskets supplied match exactly, all orifices on the main body and metering blocks.
The base to body gaskets... there are 4 supplied in this kit and only 1 exactly matches orifice, bolt holes and bore size.
A new 6.5 power valve was also supplied and fitted.

I have rebuilt several carbs over the years and have never had a problem before.

Please don't let my frustration allow you to think this is a personal attack, as I actually am very happy with this product until recently.

It's probably something very simple and I will pull apart and recheck everything again.
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Reply with quote  #8 
If the blades are open too far, it will let transfer fuel pass that you can't control.  

ON that carb I would like for very little of the transfer slots to be showing UNDER the blades.

So set your idle and then lift it off and if the transfer slots are just barely peaking through, thats good.

If they are square OR rectangular in shape under the blade, then drill larger holes in the blades.

Be sure your timing at idle it at least 22 and you are not idling at too low of an RPM and loading up the intake with reversion from the
camshaft overlap.



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Patrick James-President
ChrisM

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Reply with quote  #9 
Hi again,
Please note post #5 : throttle blades are fully closed and mx are at 1 7/8 out, gives 1600 rpm in park and 1000 in gear.
Any less on mx will stall in gear.
600 rpm drop is unbearable.

Timing is 24 initial and 32 total.
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Reply with quote  #10 
OK, well there you go.  So now we know its probably not a carb issue.  

We have enough adjustment with the mx screws to make it leaner or richer at an idle and it doesnt solve the issue.

Right now the engine is telling you one of two things.. my converter is too tight OR I am unable to burn the fuel you are giving it at an idle.

If the converter is not too tight, now we need to burn the fuel at an idle.

The richer it is at an idle the less the rpms will drop when you pull it into gear.

So if its not burning the fuel at an idle,  a hotter plug OR more timing OR a stronger spark is the only way to burn what you are giving it.


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ChrisM

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Reply with quote  #11 
Ok, pulled the carb off and stripped it down and found no anomalies.

Put the .070 iab's back in and bingo, back to running normal again albeit the rich idle smell is back. 1500 rpm in Park - 1100 in gear.

With an 8" 5000 rpm converter, I would of thought this should be a much smaller drop, considering it's eye watering rich.

Maybe I have a brake booster problem that's undiagnosed as yet?
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Reply with quote  #12 
Plug the brake booster vac port and find out.  Obviously dont drive it... but if your engine idle rpm suddenly drops, you have a leaking booster.
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Patrick James-President
ChrisM

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Reply with quote  #13 
Ok, got back to this today and after warm up, disconnected vac booster hose and plugged the port at manifold.

Re-started the engine and straight to a rock steady 1500 rpm - no change at all!

Picked up the hose and can suck air from the booster, but not blow air in! That tells me the booster and check valve are good?

Got me beat.

ChrisM

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Reply with quote  #14 
Been thinking about your comments on not burning the fuel and that will be investigated.

I have a Bosch HEI ignition, (factory) supposedly good for 500 hp, NGK 6 heat range plugs at .030" gap and a new coil recently.

No misfiring or anything evident under hard throttle.

Starts up easy when warm but, typical cold blooded first up. 
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Reply with quote  #15 
Look and see if your ground strap is staying clean.  That will tell you if it needs a hotter plug or stronger spark.  We know we have enough adjustment in the carb with the mx screws to make it leaner or richer at an idle than it wants.  SO the carb can do its job, its now up to the rest of the parts under the carb.
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