Idle way rich

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downsr

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Have 750 dp 4779 carb on 416 stroker.Everything is good except at idle.Gas smell is so strong
runs you out of garage.Power valve is correct size and is not blown float levels are correct. Have not cked throttle blade for correct setting yet.Are these 750 dp known for rich idle circuits.Holley tech says no.Any ideas .Thanks
 
Check transfer slots first, then crack secondary butterflies open a C hair if you can't lean it out by idle adjusting screws.
 
what I did was to drill an 1/8 th hole in each primary throttle plate to let a little more air in with out drawing more fuel - re adjust mixture and idle speed and it should lean right down
 
No need to drill holes...Holleys have a small screw near the sec. linkage that when turned, will open up the sec's slightly to allow you to close the primary blades to allow the mixture screws to work properly.
 
OUTLAW said:
what I did was to drill an 1/8 th hole in each primary throttle plate to let a little more air in with out drawing more fuel - re adjust mixture and idle speed and it should lean right down
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this is a band aid fix, do it right, do you have removable air bleeds? if not, drill and tap the high and low speed circuit's and put jets in them, I am assuming when you turn your corner idle screws in they don't do much correct? if you turn them almost all the way in can you kill the engine off?
 
downsr said:
timing is 18 initial 36 total
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Is that what the engine wants or where you are limited by what you have on hand?

Depending on camshaft, it may want more than 18 initial. Find the point it kicks back on the starter when hot.
 
crackedback said:
Is that what the engine wants or where you are limited by what you have on hand?

Depending on camshaft, it may want more than 18 initial. Find the point it kicks back on the starter when hot.
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I agree with this although I don't think it has anything to do with the rich idle, also advancing the initial timing will give it way to much total timing, I personally lock out my distributer's and just run it at total timing all the time, have done this for years, even before I had a digital ignition that retards it at idle
 
torkflight said:
I agree with this although I don't think it has anything to do with the rich idle, also advancing the initial timing will give it way to much total timing, I personally lock out my distributer's and just run it at total timing all the time, have done this for years, even before I had a digital ignition that retards it at idle
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Got to fix the idle issue before worrying about total.
 
Camshaft specs?What power valve, actually installed? Idle vacuum at idle, the way, it stands now?
Sorry,not enough information , to make any kind of call.Start by getting the car ,out of the garage...
 
crackedback said:
Got to fix the idle issue before worrying about total.
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I agree, but you are the one bringing up timing, this is not a timing issue, this is a low speed air issue which I believe is caused by to much signal at the carb caused by a carburetor that is to small for the cubic inch he is running, I know others will say the carb is just fine or that they run a carb this size on there motor and it is just fine, but a 750 is to small for this motor
 
If it want 24-26, it will clean up the idle a bunch. Allow the carb blades to close even more and stick the thing strictly on the idle circuit.

Simple test, give the distributor a slight twist CCW at idle and see if it picks up RPM. If it does, it wants the timing.

Lowering the bowl level as little as 1/8 turn can have a HUGE change in how the engine runs at idle.

Good luck with it.
 
hey, I've got an 850DP that would be perfect for this motor. I agree with bumping the initial timing up. That motor should like more than 18. Have you pulled the carb to see how much of the slots are exposed on both the pri and sec?
 
It wants the timing....there is no doubt.

Someone here has some 10* bushings... Wonder who that could be?

You then can get it at 24-26* initial , 34-36* total , then start tuning on the carb
 
Mad Dart said:
It wants the timing....there is no doubt.

Someone here has some 10* bushings... Wonder who that could be?

You then can get it at 24-26* initial , 34-36* total , then start tuning on the carb
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I don't know what distibutor he has so I didn't assume. Yes, I still have some 10 and 14 degree bushings. The18-18 numbers sure sound like an MSD billet with a black bushing.

Put more than one 4779 on a 400+ inch engines without issue.
 
torkflight said:
I agree, but you are the one bringing up timing, this is not a timing issue, this is a low speed air issue which I believe is caused by to much signal at the carb caused by a carburetor that is to small for the cubic inch he is running, I know others will say the carb is just fine or that they run a carb this size on there motor and it is just fine, but a 750 is to small for this motor
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He brings up timing, because the timing is the FIRST tuning aspect that needs to be addressed and ironed out before moving on. If it's not right, nothing else will be.
 
The engine has 570 lift 235-240 dur solid mech roller
Power valve is 65.I have msd dist and 6al box.I am
going to check the carb blades this weekend.I measured
12'' of vac at idle but i did not ck it in gear.I am going to recheck
this also may need smaller power valve
 
Yeah, timing first.
Try it the other way round, then when it just wont come to ya, go back to timing, and start all over. Why not just ballpark the timing first? Learned that decades ago.Got a real surprise when I first learned about throttle controls on 2-cycle outboard marine engines.
-The absolute fastest way to get rid of the idle-stink, is to; crank in the timing, sync up the transfer port, fine tune the idle speed with, if you really have to, the secondary cracking screw ,block the v-can and bump the fast idle up to around 2000-2200 (where ever the cam vacuum peaks), and fine tune the idle mixture screws to the rich side. Drop the idle speed back down and, maybe, readjust the mix ever so slightly.This assumes the float level is correct and that the power valve is not dribbling. Finally, reset the A-pump, and reconnect the V-can and tune that.Doing it this way has the distinct advantage of usually preventing/curing any idle tip-in issues.Theres only one caveat; It helps to correctly guess/set the initial timing reasonably close the first time. This number varies, mostly, with cam design and Dc/r,and sometimes carb selection,Oh and as crackedback is going to mention, in post#25; with starter kickback.
-Holleys arent known for their stellar low speed operation.
So, if youre a newbie, you can take most of the guesswork out of the equation, by following the advices above given by old-timers,tuners and regulars, and you will be well on your way to stink-free idling and issue-free motoring.
 
Unless your power valve is shot, or you have really low vacuum (you said you had a 6.5 pv installed so it shouldn't be a factor to your idle unless your vacuum at idle is less than 6.5) I don't see how a power valve is relevant to your too rich at idle issue.

What size are the idle feed restrictors in the carb right now??
 
rednesss said:
Unless your power valve is shot, or you have really low vacuum (you said you had a 6.5 pv installed so it shouldn't be a factor to your idle unless your vacuum at idle is less than 6.5) I don't see how a power valve is relevant to your too rich at idle issue.
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x2


I would be looking at adjusting the timing first, then looking at the primary and secondary throttle blades and adjusting the mixture screws.


What is idle vacuum at idle? In gear?
 
crackedback said:
Simple test, give the distributor a slight twist CCW at idle and see if it picks up RPM. If it does, it wants the timing.
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Is this true in all cases? I assumed it would always pick up RPM with more timing advance. I have a similar problem with a rich idle, but know it is, at least in part, because my carb is totally wrong for my engine. If I can bump up the timing even more (18 initial now), I'll try this test and see how it works.
 
On a correctly running engine the PV has no effect at idle. I have a car that pulls 8.5" of vacuum with a 10.5 PV. Runs no different at idle with a PV plug in the carb. I suggest all the time to get idle set with a PV plug in place. Completely removes the circuit and if you put a PV back in and it runs like junk, something isn't right.

Nuke, You are trying to find the point of best efficiency. If the idle speed picks up, it's more efficient at those settings. Dial the idle speed back down to where you started and give another twist. DO NOT just continue to feed timing in without resetting idle speed. You'll find a point where it doesn't pick up any more RPM.

Find the point the engine kicks back on the starter when hot. That's my preferred method. Another, hook up a vacuum gauge, advance timing and reset idle speed, did vacuum increase, if so do it again. You'll reach a point where it won't increase. Dial it back 2* and then fix mechanical advance to hit your total number.

I tend to do things where it's one method or starter kickback whichever is lower. If starter kicks at 20 and dialing in or vacuum shows 24, you can't get 24 because the starter won't let you.
 
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