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  #136 (permalink)  
Old 04-23-2013, 11:26 AM
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thanks metal storm , its been a long journey and a bit of bad luck recently. what with the fuel tank and I now also have to make a stabilizer bar to fix the mount on which the crank sensor sits. it tends to vibrate under load and the ecu read crank trigger errors. luckily it corrects its self some 10,000 times a second but still need to minimise it to a acceptable level.

I have re-read a lot of the posts as I haven't been on it for 4 months. will change the ign to be more in line with firebird and cobalts info. just struggling with this rich idle ??

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  #137 (permalink)  
Old 04-23-2013, 12:31 PM
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A friend of mine has an LS engine that had cam sensor issues bouncing so we ground down the cam gear where it reads from to close the duration,start of the reading,something to keep in mind if you can apply that to your situation.
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  #138 (permalink)  
Old 04-23-2013, 03:13 PM
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Start by giving it all the idle timing it wants and needs. Lock out the timing curve.
Full timing at idle. 30-32 BTDC. The more timing at idle the better it will idle.
Keep the rpm up while it is warming up.

Blower motors want lots of timng at idle.
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  #139 (permalink)  
Old 04-27-2013, 02:13 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
Start by giving it all the idle timing it wants and needs. Lock out the timing curve.
Full timing at idle. 30-32 BTDC. The more timing at idle the better it will idle.
Keep the rpm up while it is warming up.

Blower motors want lots of timng at idle.

thanks f bird. got my new fuel tank now. so fitting it tomorrow. going to go back to the start with it. so check for air leaks. ruptured pvs , then get the vacuum as good as I can overall between the 2 carbs. will change the timing and also double check the plug gaps .

I have checked all leads and plugs and all is ok there. its got to be the transition slots being too exposed , going to back the primary's off and give a little to the secondary's to allow a bit more air then try, I don't have any engine pitch or vacuum change when altering the air bleed screws so clearly too much fuel I think ?. I use around 4 litres last Sunday just running it and idling. ( didn't drive it ) its well rich on idle.

have 70s on the primary and 78 on the sec side. will also cut off the chokes and carb horns tomorrow. seems my crank sensor is fine, however I will get the stabilizer bar made next week and fit.

any more advise on tuning the idle side would be great.

cheers Shaun
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  #140 (permalink)  
Old 04-27-2013, 02:25 PM
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hi all .

as im supercharged where to I get the correct vacuum reading from to measure the highest vacuum when adjusting the air mix screws ?

I have a take off under the primary bowl at the base of the carb

I have a take off on the plate under both carbs that mount the carbs to the blower.

then finally I have a available vacuum take of in the inlet manifold.

which one ?

cheers
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  #141 (permalink)  
Old 04-27-2013, 06:28 PM
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Any of those port will do but I use the intake.You will get about 12* of vacuum at around 1,000 rpm depending on your cam and I adjust mine so it stop surging rpm so it will be rich enough to start cold and just start to surge at idle when fully warmed up but my advance is locked at 30* so that may not be best for you.
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Old 04-28-2013, 11:09 AM
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hi all . had a great day . also going to take tomrrow off work to try to finish and get it mot'ed to show its road worthiness !!

ok so I changed the timing for staring to 26d, and its pretty much flat up until about 3000rpm then it creaps up to 30d then @4000 rpm it goes up to 32d, I know they will be changed once it is @ the dyno.

I stripped the carbs down AGAIN , getting fed up with it, can do it with my eyes closed. I took f birds advise and chopped off the chokes and horns. at some point when it running I will take them off and spend time smoothing it all off. but all the burs are going. I closed the primary throttle blades to show 0.020 of the transition slots and just opened the secs a tiny amount.

runs so much better, also doesn't seem rich and I took it for a little drive around the close I live in.

so moving on - I noticed when I was driving along I put my foot down for a split second to see if it would pick up , I didn't. the shooters are functional and accelerator pump works ,I have the orange / brown cam but is more orange than brown in colour.

70 primary jets
78 sec jets

6.5 pv which needs to change . it that the problem ?

now im on to my primary tuning I think ??

getting there.

thanks for the advise. much appreciated
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  #143 (permalink)  
Old 04-29-2013, 02:16 PM
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took the day off today and got it ready for the mot tomorrow. seems the same. doesn't want to pick up , seems to stay at the same rpm when under load but when in neutral I can rev fine. seems it doesn't want to pick up ? any ideas ?
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  #144 (permalink)  
Old 04-29-2013, 02:46 PM
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You have a simple ignition system problem.
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  #145 (permalink)  
Old 04-30-2013, 12:15 PM
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hi f bird . went for the mot test today and got a few things to replace on the front steering but apart from that it was ok -BUT it is a pig to re-start when hot. also it spat back out of the carbs a couple of times when hot. I have ordered some lower jets as it is still too rich. I am wanting to get it to at least run on the primary side for now. think I have cracked the idle circuit. but I did open up the secounday throttle blades slightly and closed the primarys off just to show 0.030 of the transition slot. all plugs and leads are good and plugs fire. any other tips to settle it down ? have chopped off the chokes and horns. running 70 on primarys.

got the timing at 26d start up as it trys to push back on the starter every now and then. but mainly when the battery starts to fade.

very strange as this morning first thing I pumped once and it started straight up.
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Old 04-30-2013, 02:28 PM
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Hard hot engine restart:

Install and use the simple ignition power interupt switch.

Verify the quality of the battry cables and clean connections at the battery/starter solenoid and starter motor
AND THE ENGINE grounds.


Install the ignition interupt switch and lock out the timing. full timing at idle. No advance curve.
Fixed timing 28-32deg for now..

May have to play with the exact primary and secondary throttles idle position bias (T slot exposure) a bit to get it exactly right.

Last edited by F-BIRD'88; 04-30-2013 at 02:33 PM.
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  #147 (permalink)  
Old 04-30-2013, 02:37 PM
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but I did open up the secounday throttle blades slightly and closed the primarys off just to show 0.030 of the transition slot.

ya it only took me 10 pages of posting to get you to do this....

now you may need to adjust the exact setting and bias of the pri and sec throttles idle position.
THIS IS CRITICAL to get them all correct.
Good throttle response and low speed driving starts with correct throttle position at idle.
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  #148 (permalink)  
Old 05-02-2013, 03:03 PM
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hi f bird .

I have just received a load of jets. I got what they had ( in 2x sets)to get me going over the weekend. so I got 4x 62 4x 65 and 4x 68 . at the moment I do not have any response on the air mix screws on the side of the primary metering blocks. so seems good practice to drop to the 68's first to see if the air mix screw start to function ? with that said do I need the throttle blades showing some of the transition slots or can I get away with them closed as currently with the 70s in there is no change when adjusting the screws

I closed off the primary throttle blades and slightly opened the sec's
I also have a pair of 10.5 pvs as there is 6.5s pvs in , don't think they will be opening at the moment anyway as im not at that stage. they are not ruptured, will fix the timing on a separate ign chart at 28 d to see if its happy.

one of the problems I have is the battery is mounted in the boot as I have no room in the engine bay. so cable is big and fat and has good connection but is around 3m long which isn't ideal when starting and stopping constantly. never gets time to have a good charge ,

I will speak with the ecu guys to see about logging in a interpreter system when hot on a toggle switch to by pass the coil packs , may just be a simple isolator switch ? so how does this work and how will it help when hot ?

cheers shaun
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Old 05-02-2013, 03:15 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
Just don't get too carried away on trying to get it tuned too sharpe. ( best power) You need some in cylinder cooling (extra fuel) to keep it alive under boost. You don;t want to be on the edge. A bit rich er Under boost/throttle is fine. You can drill/hone the jet hole in the sec metering plates to fatten that side up if needed.

I'd use a minimum of a holley #21 sec metering plate in the 600VS carbs. These are found in the 3310 VS 750 holley carb.

Was it pig rich with #72 pri jets in it.? ( I assume that you had the power valve in.) Starting rich is the safe way to tune it in.

If its tuned on the edge with a #65 you may want to bump up to a #67ish pri jet. A bit rich is best.
The secondary metering plate matters. Its not that hard to modify/convert to replaceable holley jets.

How much vacuum did the wide open throttle carbs pull at WOT? max rpm. What is the blower drive ratio?
Indicated boost @WOT.

10 -11 psi can be achieved but will not be revving that hard for a good while or stepping on the gas.

I did a reading a while ago from under the carb base plate and it was around 15 hg vacuum

am running 70s in the primary's not 72s but still pig rich

I presume once I change down a jet I will know if its better as the air mix screw will start to operate ?? or with the sec throttle blades open will that also not allow the air mix screw to not function ?
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  #150 (permalink)  
Old 05-02-2013, 09:55 PM
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Quote:
Originally Posted by mustang 671 View Post

am running 70s in the primary's not 72s but still pig rich

I presume once I change down a jet I will know if its better as the air mix screw will start to operate ?? or with the sec throttle blades open will that also not allow the air mix screw to not function ?
This is not a jet issue.. Non responsive idle mix screws is caused by the throttle being too far open or too far closed at idle.
And or the primary and sec throttles are uneven or out of place at idle.

Throttle open position at idle
BOTH primary and sec is critical. Get it right and the idle screws will miraculously work.

THIS IS NOT A MAIN JET ISSUE.

Lock out the spark advance so it is fixed and does not move with rpm. Set it at about 30-32deg ( casue you got no boost retard. Now remove and flip over both carbs and reset the PRIMARY an SECONDARY throttle T slot exposure at idle.
Set the al the same as a start point. aprox .020" T slot exposure.. reinstall the carbs.
Fire it up and let it warm up and reset the idle mix screws on both carbs for best idle.
If the idle speed is just too fast then close the secondaries on both carbs the same, BY A TINY AMOUNT.
IF THe IDLE SCREWS ARE NOT WORKIN have no effect THE THROTTLES (either the primary or the secondary or BOTH) are out of position.

Last edited by F-BIRD'88; 05-02-2013 at 10:02 PM.
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