Choke stays on too long
09-13-2012, 12:51 PM
#3
Burning Brakes
The rod can be bent but it is all orignal I have to wonder if the spring is not heating up, which in turn opens the choke. Have you changed your thermostat, eliminated the crossover in the manifold, removed your heat riser, etc. While I dont know the configuration of your vehicle I would first look at the components that heat the spring before bending rods or making other adjustment.
09-13-2012, 01:03 PM
#4
Drifting
Thread Starter
I haven't made any adjustments to those functions myself, but the car does have a non-stock riser between the carb and the intake, I'm guessing likely to help with hot start characteristics...it's maybe 1/2" at most, though this also means that the choke rod is longer than normal. The riser is in place and I believe functional.
I recently had the carb rebuilt. Before this, the choke wouldn't close completely. Now it does close fully...just takes a long time to get it off...I'd say I need to drive for close to 5 minutes before it will come off totally, sometimes longer...and if I want it to come off at idle parked? Forget it.
I recently had the carb rebuilt. Before this, the choke wouldn't close completely. Now it does close fully...just takes a long time to get it off...I'd say I need to drive for close to 5 minutes before it will come off totally, sometimes longer...and if I want it to come off at idle parked? Forget it.
Last edited by Brcmpbl; 09-13-2012 at 03:09 PM.
09-13-2012, 01:08 PM
#5
Drifting
Thread Starter
Sorry, trying to do this via blackberry is a challenge!
I meant to say that it won't come off high idle when parked on the first start of the day, cold. No choke problems with the engine warm...just takes forever to get there compared to my 76...which is bone stock.
I meant to say that it won't come off high idle when parked on the first start of the day, cold. No choke problems with the engine warm...just takes forever to get there compared to my 76...which is bone stock.
09-13-2012, 01:45 PM
#6
When cold and the engine off remove the choke rod from the choke linkage hole on the carburetor. The rod should not be any higher/lower than 1 diameter of the hole with the choke fully closed. If it is higher/lower the rod has to be bent. The reason I say higher/lower is I'm not sure whether your setup pulls down on the linkage or pushes up on the linkage.
Last edited by MelWff; 09-13-2012 at 01:48 PM.
09-13-2012, 02:13 PM
#7
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Hi B,
Is there a chance that the choke wants to close sooner, but the throttle linkage is preventing it?
The little cam that catches and holds/releases the choke should flip out of the way very easily.
I've observed while helping with Operations checks that 70-72 sb block engines often take what seems like 4 minutes to warm-up even in summer weather.
Also, do you have the TCS system hooked up? Is there any chance that's what's holding the engine at the higher rpm? That system receives a temperature signal from a sender in the right side head.
Just trying here!
Regards,
Alan
Is there a chance that the choke wants to close sooner, but the throttle linkage is preventing it?
The little cam that catches and holds/releases the choke should flip out of the way very easily.
I've observed while helping with Operations checks that 70-72 sb block engines often take what seems like 4 minutes to warm-up even in summer weather.
Also, do you have the TCS system hooked up? Is there any chance that's what's holding the engine at the higher rpm? That system receives a temperature signal from a sender in the right side head.
Just trying here!
Regards,
Alan
Last edited by Alan 71; 09-13-2012 at 06:19 PM.
09-13-2012, 03:14 PM
#8
Drifting
Thread Starter
Thanks for the replies. I'll check the rod height today after work. Alan, I have an AIM coming in the snail mail that I'm hoping will allow me to determine if things like my TCS are in a stock state or if they are not operating. I'm a study bug that's learning to diagnose and work on my cars slowly (very slowly, ha) through this forum and manuals. It's fun...but the 70 loves to stump me and everyone else on the regular...the 76 seems easy, even with all that emissions equipment!
09-13-2012, 03:30 PM
#9
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Hi B,
The AIM will be a help in learning what's still on your car and what isn't compared to when it left St.Louis.
BUT, for the operation of various systems the GM 1970 Chassis Service Manual will be a help too, maybe/probably a bigger help.
Perhaps your budget will allow for the purchase of a copy of that too.
I use both of them constantly.
Good Luck!
Regards,
Alan
The AIM will be a help in learning what's still on your car and what isn't compared to when it left St.Louis.
BUT, for the operation of various systems the GM 1970 Chassis Service Manual will be a help too, maybe/probably a bigger help.
Perhaps your budget will allow for the purchase of a copy of that too.
I use both of them constantly.
Good Luck!
Regards,
Alan
09-13-2012, 03:39 PM
#10
Drifting
Thread Starter
Thanks Alan. I actually just got that manual recently, along with the 1970 supplement that is Corvette specific. They have been a massive help, no question.
09-13-2012, 03:47 PM
#11
Melting Slicks
The 'riser' 75 was talking about is the heat riser. It goes in between the passenger side exhaust manifold and the exhaust pipe.
With everything cold, reach down where the exhaust manifold connects to the exhaust pipe, and you should feel something like a lever on a spring. It should move freely, and go back to position with the spring. That's the heat riser. It's job is to help heat up the carb on a cold start by restricting exhaust. After it's heated up, the bimetalic spring will open it up. If it's missing, or stuck open, you could experience problems like you are having.
With everything cold, reach down where the exhaust manifold connects to the exhaust pipe, and you should feel something like a lever on a spring. It should move freely, and go back to position with the spring. That's the heat riser. It's job is to help heat up the carb on a cold start by restricting exhaust. After it's heated up, the bimetalic spring will open it up. If it's missing, or stuck open, you could experience problems like you are having.
09-13-2012, 03:59 PM
#12
He described the "riser" as being between the intake and carburetor so the correct term was a "spacer". The spacer requires a properly adjusted choke rod capable of compensating for the additional 1/2" in height.
09-13-2012, 04:02 PM
#13
Drifting
Thread Starter
Also the actual heat riser valve on the exhaust manifold I believe to be operational, it appears intact...unless maybe the butterfly is missing inside. I don't believe this to be the case.
09-13-2012, 04:30 PM
#14
Drifting
Thread Starter
When cold and the engine off remove the choke rod from the choke linkage hole on the carburetor. The rod should not be any higher/lower than 1 diameter of the hole with the choke fully closed. If it is higher/lower the rod has to be bent. The reason I say higher/lower is I'm not sure whether your setup pulls down on the linkage or pushes up on the linkage.
http://s1078.photobucket.com/albums/...0715-00414.jpg
09-13-2012, 06:23 PM
#16
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Hi B,
I wondered about what s69 suggested.
Wondered enough to check $, looks like around a $25 possibility.
Maybe?
Regards,
Alan
Have you stood there and looked at what happens (or doesn't) when the choke is released by blipping the throttle?
I wondered about what s69 suggested.
Wondered enough to check $, looks like around a $25 possibility.
Maybe?
Regards,
Alan
Have you stood there and looked at what happens (or doesn't) when the choke is released by blipping the throttle?
09-13-2012, 09:31 PM
#17
Drifting
Thread Starter
I checked choke rod with the choke engaged and the car cold. The rod pulls down to close the choke. The rod does seem to go down a little far unhooked from the linkage, probably a bit more than the diameter of the hole it fits into. The fast idle cams seem to operate freely.
I've got a stock carb base gasket and choke rod coming in the mail as part of an order from Corvette Central because I've wanted to get rid of the stack / spacer for a while now. This might help me. The elongated rod that is on the choke now cannot be lengthened, I think it was a fab job by the previous owner.
The hear riser is something else though: I tried to move this by hand (the weight looking part, or lever maybe) and it would not budge at all. I think it might be in fact stuck open.
I've got a stock carb base gasket and choke rod coming in the mail as part of an order from Corvette Central because I've wanted to get rid of the stack / spacer for a while now. This might help me. The elongated rod that is on the choke now cannot be lengthened, I think it was a fab job by the previous owner.
The hear riser is something else though: I tried to move this by hand (the weight looking part, or lever maybe) and it would not budge at all. I think it might be in fact stuck open.
09-14-2012, 07:43 AM
#18
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Hi B,
If riser is stuck open... up position on the weighted arm... you MAY be able to free it with some penetrating oil.
Have the heat riser working will certainly help your choke situation.
Regards,
Alan
If riser is stuck open... up position on the weighted arm... you MAY be able to free it with some penetrating oil.
Have the heat riser working will certainly help your choke situation.
Regards,
Alan
09-14-2012, 08:05 AM
#19
Burning Brakes
FWIW, I to had this problem earlier this season. Shortened the choke rod approx 1/16" and problem was solved. Used the Chassis Service Manual for my guide.
Last edited by redrdstr72; 09-15-2012 at 07:56 AM.
09-14-2012, 08:59 AM
#20
Team Owner
To properly assess your choke situation, you need to follow the set-up procedure in the Chevrolet Chassis Service Manual for your model year. In the "Fuel System" section, it details all of the carb adjustments required, including how to make choke set-up.
But, your photo shows other concerns:
1) You have a rubber fuel line and plastic filter between the fuel pump and carb. This is potentially a dangerous condition. If either the filter housing or the rubber hose fail, you get pressurized spray of fuel into the engine compartment and onto exhaust manifolds. Your car...and it's passenger(s)...could go up in flames. Please install a solid line and a filter with metal housing.
2) Your choke appears to be fully ON in that photo; but the secondary lockout lever (little silver 'doohickey' at the base of the carb between primary & secondary bores) is NOT engaged with the rod at the end of the secondary throttle shaft. This leads me to believe that the choke linkage bolted to the right side of the carb is not operating freely. You need to understand what all that linkage does and clean/polish any pieces that prevent free movement so that it works properly.
3) The carb "spacer" you mentioned is just the 'thick' gasket that comes in the rebuild kits. And, that can be a good thing, if it is the right configuration for you carb. Those kits are generic and they can be used for rebuilding many carb P/N's. There are multiple gaskets/spacer for you to select; and the intent is that you replace the identical parts that are discarded during the rebuild. Since you indicated that this larger spacer is different than what came on the car, it may not be correct: both because of the added length required for the choke rod, and (possibly) because the passages in that spacer might not allow the carb to function properly [blockage of manifold vacuum from reaching necessary ports in your carb]. I'm not saying it shouldn't be used...just that the use of that thicker spacer should be assessed on its ability to allow the carb to function correctly.
4) If that spacer is OK to use with the carb, and if the choke rod needs to be lengthened, you will have to fabricate another rod, as yours is completely straight and has no more ability to be lengthened.
But, your photo shows other concerns:
1) You have a rubber fuel line and plastic filter between the fuel pump and carb. This is potentially a dangerous condition. If either the filter housing or the rubber hose fail, you get pressurized spray of fuel into the engine compartment and onto exhaust manifolds. Your car...and it's passenger(s)...could go up in flames. Please install a solid line and a filter with metal housing.
2) Your choke appears to be fully ON in that photo; but the secondary lockout lever (little silver 'doohickey' at the base of the carb between primary & secondary bores) is NOT engaged with the rod at the end of the secondary throttle shaft. This leads me to believe that the choke linkage bolted to the right side of the carb is not operating freely. You need to understand what all that linkage does and clean/polish any pieces that prevent free movement so that it works properly.
3) The carb "spacer" you mentioned is just the 'thick' gasket that comes in the rebuild kits. And, that can be a good thing, if it is the right configuration for you carb. Those kits are generic and they can be used for rebuilding many carb P/N's. There are multiple gaskets/spacer for you to select; and the intent is that you replace the identical parts that are discarded during the rebuild. Since you indicated that this larger spacer is different than what came on the car, it may not be correct: both because of the added length required for the choke rod, and (possibly) because the passages in that spacer might not allow the carb to function properly [blockage of manifold vacuum from reaching necessary ports in your carb]. I'm not saying it shouldn't be used...just that the use of that thicker spacer should be assessed on its ability to allow the carb to function correctly.
4) If that spacer is OK to use with the carb, and if the choke rod needs to be lengthened, you will have to fabricate another rod, as yours is completely straight and has no more ability to be lengthened.
Last edited by 7T1vette; 09-14-2012 at 09:02 AM.