Engine won't slow down to tickover.....
01-14-2007, 10:29 AM
#1
Drifting
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Engine won't slow down to tickover.....
OK engine and carb experts - please ponder this.....
engine rebuilt with headers, ( open at the moment - kinda noisy ) comp cam, performer and q -jet
I have checked the carb out this morning - its running 72 primary jets.
In order for it to run without dying the idle screws are turned out 7 complete turns. Its still a little lean and will pick up some more if I place my hand over the choke plate area to richen it up a bit.
However, the big problem is that although running really sweet and very even, it will not drop below about 1500 revs ( a guess not the tach reading ) Idle speed screw is backed off all the way and choke stuff also.........are the internals of the q-jet such that it can achieve this sort of rpm with the throttle plates closed ??
Please do not refer me to Lars tuning paper. Have got the Rochester tuning book on my lap already.
Next, loom wire for tach - where does it exit the loom and what colour is it - because I have misplaced mine - loom has been played with by previous owner when removing CCC.
engine rebuilt with headers, ( open at the moment - kinda noisy ) comp cam, performer and q -jet
I have checked the carb out this morning - its running 72 primary jets.
In order for it to run without dying the idle screws are turned out 7 complete turns. Its still a little lean and will pick up some more if I place my hand over the choke plate area to richen it up a bit.
However, the big problem is that although running really sweet and very even, it will not drop below about 1500 revs ( a guess not the tach reading ) Idle speed screw is backed off all the way and choke stuff also.........are the internals of the q-jet such that it can achieve this sort of rpm with the throttle plates closed ??
Please do not refer me to Lars tuning paper. Have got the Rochester tuning book on my lap already.
Next, loom wire for tach - where does it exit the loom and what colour is it - because I have misplaced mine - loom has been played with by previous owner when removing CCC.
01-14-2007, 10:34 AM
#2
Race Director
You going to have to post the carb model #, engine specs (stock or not) and any engine changes (if any) other than the headers.
No one can give you an intelligent response without that. All that cn be said now is that you are lean.
No one can give you an intelligent response without that. All that cn be said now is that you are lean.
01-14-2007, 10:50 AM
#3
Drifting
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Carb is 1975 170-45223-R7.
Cam is mild road, heads are 58cc alloy 113's, block and bottom end is stock, new rings and bearings.
Was just thinking, as I have backed out the idle jets so far to head to a richer mixture, am I inadvertantly giving the engine a lot more juice to the extent that its speeding up getting its air via various air bleeds.
Therefore - if i used richer primary jets - eg 74/ 75/ 76 whatever, the engine should be getting enough juice that the idle jets can be screwed back in to their typical 2 or 3 turns out..??
Does that sound about right or am I looking in the wrong direction ??
Cam is mild road, heads are 58cc alloy 113's, block and bottom end is stock, new rings and bearings.
Was just thinking, as I have backed out the idle jets so far to head to a richer mixture, am I inadvertantly giving the engine a lot more juice to the extent that its speeding up getting its air via various air bleeds.
Therefore - if i used richer primary jets - eg 74/ 75/ 76 whatever, the engine should be getting enough juice that the idle jets can be screwed back in to their typical 2 or 3 turns out..??
Does that sound about right or am I looking in the wrong direction ??
01-14-2007, 11:08 AM
#6
Race Director
If that's the stock sizing for that model, it's safe to say that at least 2 sizes up in jets is needed, hope you have them.
Are you sure that carb is a 170. Most of them had 1705xxxxx after it.
Plug all vacuum ports and dist if it will run without can and see what your vacuum is. Test for leaks with start fluid ot propane etc.
Are you sure that carb is a 170. Most of them had 1705xxxxx after it.
Plug all vacuum ports and dist if it will run without can and see what your vacuum is. Test for leaks with start fluid ot propane etc.
01-14-2007, 12:21 PM
#7
Drifting
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Vacuum gauge is reading 19 at the engine speed its holding.
Having done some research over the last hour, I now think my carb is non Vette.
The main jets are 72 and from what I discover they should be at least 76 and more than likely 77+ due to cam and headers etc.
Best way forwards I think is to get some exhausts on there before I go deaf and then start richening up the main mixture.
As I don't have access to a range of jets, will have to do it by drilling out what I have and pick up a mixture when I visit Florida in a couple of months time.
Having done some research over the last hour, I now think my carb is non Vette.
The main jets are 72 and from what I discover they should be at least 76 and more than likely 77+ due to cam and headers etc.
Best way forwards I think is to get some exhausts on there before I go deaf and then start richening up the main mixture.
As I don't have access to a range of jets, will have to do it by drilling out what I have and pick up a mixture when I visit Florida in a couple of months time.
01-14-2007, 01:13 PM
#8
The tach wire is white. Look for it about the middle of the car firewall.
