CRUSTY - COUPE
Member
can someone tell me what the throttle blade to throttle body clearance is on the small 2g 1 3/32 that has the 3 off idle holes instead of the transfer slot. not sure where to set it up at. thanks
small base 2g rochester
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CRUSTY - COUPE
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has anyone got a 2g that they have taken of an engine that they can flip over and look at the throttle blade to off idle transition holes location? a pic would good. if the carb was on a running engine when it was removed the throttle blades would be in the idle position 750 rpm? which is what i need to put my carb back to the correct blade location at idle. i had to drill holes in the blades to lower them as they were above all the transition holes at idle and had no response on the idle mixture screws and was pig rich idleing on transition fuel. thanks geof
wristpin
Well Known Member
At this point id set the butterflys in the closed position and start the car. Then reset idle speed where you prefer it to be. With the holes drilled in the butterfly's the car may idle different at selected RPM. In that case reset your idle fuel screws and idle air to balance air/fuel ratio.
CRUSTY - COUPE
Member
wristpin, thank you for the reply. i did today what you suggested and at 750 rpm that gives me 12 th blade clearance with the first off idle hole exposed to vacume. What i did before posting my question and why i asked. drilling the blades with a 1/8 hole (started smaller) had to go this far to get idle mixture screw response and no nozzle drip, as all 3 transition holes were exposed to vacume prior to drilling at 750 rpm. Now when i set the throttle blade to bore clearance to 20 th like most modern carbs my idle is now 1100 rpm in park and the first and half of the 2nd transition holes are exposed to vacume at idle. I was thinking that if i could find out where the blade sits in relation to the 3 off idle transition holes on this 1 3/32 2g from factory or on a carb that was taken off a motor that was set for about 750/850 rpm with no holes in the blades i could set my carb blades to that and then adjust the 1/8 drilled hole in the blade up or down in size to get my 750 rpm idle speed and then the off idle transition circuit would work as rochester intended. hope this explains what and why . thanks geof
CRUSTY - COUPE
Member
wristpin, thanks for the paperwork offer but i have all the factory settings except for the blade to throttle bore clearance,the dough roe book mentions it and says how important it is but does not give a measurement. someone must know what it is on a 2g. some 2g have a air bypass screw which you adjust for idle (its different from the curb idle adjustment which is fixed ie blade to bore clearance) mine is not but i want to do the same thing by making the throttle plate holes larger or smaller to bypass air to give idle mixture control and idle adjustments without nozzle drip. by the way i paid $9 a gallon of fuel here in australia today which is about $6 US, we may electric sooner than we think.
Has someone reversed blade when maybe rebuilding it or rebushing thottle shaft. If not blades should be correct and fall into place when setting idle running rich due to other problems in carb.
There was a plastic based treatment for the throttle blades to help seal the gap but it will be dissolved by some carb cleaners. Somewhere I have a TSB on how to re-treat the blades but so far I haven't been able to find it. Meanwhile here are all the other specs if it helps.
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CRUSTY - COUPE
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wristpin, the nozzle drip was when i first started the engine. i fixed this by drilling holes in the throttle blades which then gave me idle mixture screw response when the throttle blades were lowered in the bore. prior to this they were above the top transition hole in the throttle bore at idle.
CRUSTY - COUPE
Member
blkblk63ss,the throttle blades have not been reversed. running rich was cured by drilling holes in blades to get the carb out of the transition circuit at idle. this is a center carb on a tripower intake. its a smallbase 2g as that what fits the intake and a large base 2g will not fit in between the front and rear carbs. this is why i think i had to drill the blades to change their blade location, because this carb is small for a 350 cubic inch engine as a single application but i have 3 of them. end 2 carbs are just dumpers before anyone asks and are sealed off at the moment till i get the center carb sorted. so if someone has a 2g with 3 holes for a transition off idle circuit instead of a slot and can turn it over and tell me where the blade edge is in relation to off idle transition holes ie 1 or 1 1/2 holes exposed to vacume ect because it would have been set at idle from previous engine it was on. i can then set my blades to this location and then size the throttle blade holes to give me my idle speed. hope this explains things.
CRUSTY - COUPE
Member
oldskydog, some good information there my friend. i will get some dag213 for the end dumper carbs, i have spent a lot of time sanding the blades for a tighter fit. i am limited to the 1 3/32 2g as that is what fits the intake spacing. larger carbs would be good. i did not think you could get bigger than 1 3/32 in a small base?
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CRUSTY - COUPE
Member
Guys, something else i thought i should explain is, when i drill the throttle blades to correct their position, i get idle mixture screw response back with a 7/64,1/8,9/64 or a 5/32 hole size in the throttle blades. this places the throttle blades in several locations in the throttle bore at a 750 rpm idle. thats why i am after the throttle blade at idle location in a carb with 3 holes instead of a transition slot to put the blades where the factory intended them to be for the carb to operate at its best performance. thanks geof
The only reason that you're having to go thru this is there's something else wrong[as far as the factory design goes],like the wrong cam choice.As has been stated,there is no ''spec'' or what you're trying to do.This is a modified set up and to make it work will require persistance on your part to make it do what you need it to do.How much cam have you got in that thing? What is your vacuum at idle? What is your timing curve like? Are you running a vacuum advance?
CRUSTY - COUPE
Member
Don thank you for your questions, my problem comes from small 283 carb on a 350 engine as i said above but on this tripower manifold it only has room for small base 2g rochester and i have a matching set of 1 3/32, if i could fit the large base 2g on it i wood but there is just not enough room between the 2 end carbs. have not seen a bigger small base than a 1 3/32 all the larger carbs look to be the large base type ?. i am persistant because the tripower has not yet been replaced by a 4 barrel ha ha, have thought about it but that would be the easy way out. ok cam is 262 h 110 lobe seperation, 1500 to 4500/5000 rpm, 10 to 1, tube headers, idle vacume in drive at 750 rpm is 12 or 13, no vacume advance on a (joe hunt mag look hei) all in at 1900 as i cruise at 2000 rpm at 60 mph, in 4th,turbo 700. on a holley you show a small bit of the transition slot at idle about 40 th and no more than 60 th. on the 2g with the 3 holes about 25th each instead of the transition slot , i would think there would be something similar ie 1st hole exposed to vac or 1 1/2 holes at idle ect because blades do not open enough pulls to much fuel through idle mixture (rich) and open to far your past the transition and also running rich at idle due to incorrect blade location at idle . thats why i was after someone with a 2g with throttle blades that have NOT had holes drilled in them and has the 3 transition holes in the throttle bore to flip it over and tell me where the blades are in location to the 3 transition holes and yes the carb may have come off a worn motor and the idle screw opened up a bit to compensate but it would give me a ball park figure and i can allow for that. as you said rochester does not mention this clearance, because it is factory set, but once you drill the throttle blades and open up idle fuel jets because the 1 carb was intended for a 283 and it is now on a 350 with 2 other dumper carbs blade position can change causing rich running, hesitation ect. i want put the blades back to the origional location by adjusting the throttle blade hole size once i find out the origional position of the blades. rochester had a air bypass system on some carbs that you adjusted your final idle with , you did not adjust the curb idle screw setting on these carbs for your idle. hope this has explained things better. .geof
I believe that the basically the throttle blades need to be closed (no clearance) in the bore at idle with the blade above the lower (primary) idle hole but below the second and third holes in it's original configuration. The size of the holes are different and are in the specs.
Description, illustration and original specs can be found here:
http://chevy.oldcarmanualproject.com/carb/Rochester/2GCp03.htm
Description, illustration and original specs can be found here:
http://chevy.oldcarmanualproject.com/carb/Rochester/2GCp03.htm
The treatment is name DAG 213 and you can purchase it at Ladd Research.com