Loads up at idle
 

This has been bothering me all summer..Hopefully someone has a suggestion.. With my silent choice in the quiet mode, I can idle all day at 850 rpm with no loading up. If I open the exhaust pipes to loud mode the engines start to slowly load up where i have to rev them and clear them out.. and if i close them again they idle fine.. Seems like they like the back pressure from the quiet mode
509's dual plane intake Nickerson carbs 850 DP ( 78 pri--86 sec-- pv 6.5 ) cam specs 559 lift 236 duration @ 050 lba 114..msd base timing 16 and full advance 34 light springs
one turn out on each idle adjustment screw 4 corner and an extra 1/2 turn on anyone .. as per Nickerson Instructions. Emi thunder exhaust

Any suggestions would be appreciated

you would think that you are lean at idle as the back pressure richens it up....try adjusting the carbs running hot with exhaust open, also throw timing light on and watch the timing...make sure its not falling off at idle and causing this...seen that many times

Put a vacuum gage on it and see how close you are to 6.5" at idle opened and closed. Maybe something changes when you open up the exhaust and power valves are opening, if you find you are at lets say 7" with closed and 6" open then you need power valves with lower# like a 4.5", Smitty

How could the timing fall off? They are msd distributors with
the light springs and the black 18 degree advance stop bushing..I set the base at 16 and with the 18 bushing = 34 degrees. Total Timing comes in about 1200-1500 rpm
I'll check the timing today. I thought the opening of the exhaust was making it richer. I'll try and adjust the carbs also
Thanks

The last time i checked with a vacuum gauge it was 14 exhaust closed..I'll check again with them open

Did you try to clean out the idle air bleeds.

Fixx
 

check to see if the engines run hotter with the QQ closed opposed to open..holleys are cold harted and will load up when cold..also try adjusting the air fuel mixture screws on the carbs,,1/8'' turn in may cure it..

Update Vacuum with exhaust open or closed 16". With exhaust closed it idles perfectly and vacuum stays steady within 1/2 a mark. I opened the exhaust and within 3-5 minutes the vacuum started to drop and the needle started to vary 2" slowly back and fourth. If i rev'd it up cleared it out the vacuum went back up to 16" and in 3-5 minutes same thing again. I then closed the exhaust and it stayed at
16" give or take a 1/2 notch maybe because of the cam profile.
I also checked the timing.. dead on 16 idle. I then tried adjusting the 4 corner idle screws out a 1/4 turn each and the problem got even worse with exhaust in the open mode.
then i tried to close each idle screw 1/4 turn and it seemed to start to die too lean
I'm giving up

Fixx
 

when adjusting the 4 corner air fuel screws adjust a tiny bit at a time..even if you just adjust the 2 front ones and not touching the rear ones may cure it..It only takes a little bit of adjustment then wait to see it it clears..most people will go 1/4 turn and then the motor dies then gives up...their real touchy..adjust then wait a few minutes for idle to clear then rev it to see if the engine stumbles then readjust..could take up to a 1/2 hour of messing with them to get it rite..

Well, you are nowhere near the power valve opening point so you can rule that out, do both motors do the same exact thing?

+1000 very small tweaks and be patient :drink:

yes both do the same

One thing i did mess with is the secondary idle adjustment. I changed the adjuster to the new quick fuel type with the screw and spring on top for easy access. I know there is an adjustment for that something like .020-0.60 of throttle blade before the transfer slot shows. I could never figure out how to set them with a feeler gauge.. They are in the closed position now. Besides this adjustment there are 4 holes drilled in the throttle blades for additional air flow. Nickerson carbs originally set them up like this.

still sounds like carb issue, but you asked how timing get can do that...with very light springs they can start moving around at idle, causing timing to bounce around...then starts idling a bit slower, that retards timing slowing idle even more, timing then falls off as idle falls..a circle until stalls...