sublimemike
Well-known user
Couple of shots
Before and after
Before and after
Carb idle circuit issues
- Thread starter sublimemike
- Start date
sublimemike
Well-known user
It's about a square. Some you tube vid said if you have a big cam to open another half turn of the Allen key. I can wind them further in. Thought it was worth posting the pic. Reduce a further 25 per cent of what is visible?
sublimemike
Well-known user
Thank you for that, I will wind the other way and post a pic. Good to have your attention.
sublimemike
Well-known user
How's this. Tricky to photo
Roscobbc
Moderator
Wonder if these images might help. Carb is 950 cfm DP - you'll notice that throttle blades are probably open less than a millimeter with perhaps secondaries open fractionally more than primaries. Also see on primary throttle plate how close the plate is to the 'transfer slot' - this is supposed to aid the carb feeding fuel over the transition period.......from coming off it running on idle jets.........over to main jets. I suspect if the throttle plate is cranked too far open on idle it will adversely effect the transfer slot operation.
As far as I recall all throttle blades were as per 'out of the box' when I installed the carb.. In fairness this carb has '4 corner' idle mixture and replaceable idle air bleed jets. I never had an issue with mine relating to idle adjustment - my issues initially were 'stumbling' off-throttle which neccesitated largest primary 'squirter' nozzles and a 'dead spot' about 1100 rpm.
As far as I recall all throttle blades were as per 'out of the box' when I installed the carb.. In fairness this carb has '4 corner' idle mixture and replaceable idle air bleed jets. I never had an issue with mine relating to idle adjustment - my issues initially were 'stumbling' off-throttle which neccesitated largest primary 'squirter' nozzles and a 'dead spot' about 1100 rpm.
Last edited:
sublimemike
Well-known user
Thanks Ross. Rather than try and guess the adjustment for the "square" underneath - (thanks Tim) I've spun the carb off and adjusted it. So over to you guys -bigger or smaller or about right. Throats are a bit grubby as I had a kick back on shut down . Need to find some cotton buds.
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sublimemike
Well-known user
Am I to expect a lean bog if too small? Once it's warmed up I'll try and nudge the timing forward. Few things to do before while carb is off..check dizzy springs, fix annoying minor fuel leaks on O ring seals
teamzr1
Supporting vendor
I cannot see trying to do apples to apples compare with 2 different engine designs and carbs
I suspect Mike maybe trying to dial in a workaround to either an existing problem or is not seeing that his CAM design along
with engine compression etc., just will require more or less air and/or more timing to makeup for any vacuum loss due to the CAM grind or
there is some leak
Doing a workaround and if there is a problem, and it gets worse than he is back to ground one in retuning after the problem is solved
Should be very easy to rig up a tee to put a vacuum gauge in series with the engine and the distributor
and see how his engine compares with GMs spec for that stock engine
These tests should be easy to do and benchmark than to GM specs below
Starting with cold and hot idle values
The table below lists vacuum ranges for most engines:
I suspect Mike maybe trying to dial in a workaround to either an existing problem or is not seeing that his CAM design along
with engine compression etc., just will require more or less air and/or more timing to makeup for any vacuum loss due to the CAM grind or
there is some leak
Doing a workaround and if there is a problem, and it gets worse than he is back to ground one in retuning after the problem is solved
Should be very easy to rig up a tee to put a vacuum gauge in series with the engine and the distributor
and see how his engine compares with GMs spec for that stock engine
These tests should be easy to do and benchmark than to GM specs below
Starting with cold and hot idle values
The table below lists vacuum ranges for most engines:
| Engine Function | Vacuum Range |
| Cranking | 3-5 in. Hg |
| Idle | 14-20 in. Hg |
| Cruising | 10-15 in. Hg |
| Deceleration | 21-25 in. Hg |
sublimemike
Well-known user
sublimemike
Well-known user
Been a while since I've been on here. So anyway so I didn't leave this thread dead I got over it a while ago. Advanced timing a smidge brought revs up. Played around with the screw under the carbs for the setting the throttle blades - close it too much and nasty stumble between gear shifts. Played around with idle screw and setting for idle stop solenoid, no dieseling for a long time. It's 98 percent there. probably the idle circuit set screws need a bit more work - I've left them 1 and half turns out but I have an idle circuit when the carb is heat saturated and it doesn't die on idle.