Technical Carb Spacer Question on my 53' Chevy SBC350

Hi All,
I've read several threads but haven't gotten the info I need. I have a SBC350 in my 53 Chevy (I believe its from a 73 Chevelle) which I use to just cruise around. It's harder to start up after driving it for a while and letting it sit for a few minutes. I suspect I need the right spacer or gasket combo. I have an Edelbrock 1406 carburetor and what appears to be a 0.5" (or maybe thicker) aluminum spacer.

I thought about getting the Edelbrock 9266 insulating gasket and keeping the aluminum spacer and getting a new thin gasket for the aluminum spacer to intake side. Does anyone think that will work fine?

While we are at it, should I be getting gaskets with an open center or divided center?
Edelbrock has the 9265 which is an open insulating gasket and I don't know if I should use the 3899 open gasket for the spacer to intake mating.

I could also dump the aluminum spacer and get a phenolic and two gaskets.

I checked and have a 5psi rated fuel pump but haven't observed the actual fuel pressure. Here is a photo I had from a while ago, (not at home right now to take a new photo, note I also added a second return spring).



Thanks.

9266 insulating gasket


9265 insulating gasket

 

I used a insulating gasket and that took care of that problem for me.

 

The gasket to use should match the intake plenum.

 

the "spacer" on that is most likely an adapter to fit the square bore Edelbrock carb, onto the stock Quadrajet intake. Not really the best setup.

My old Suburban has a quadrajet on a similar intake, and doesn't have any heat soak issues at all. But it also has a return line and 3 port mechanical fuel pump.

 

Is that a spacer or is it a spread bore adapter? Can't tell from the picture.

 

Thanks I'm not sure but will need to look at some old photos from when I took a cylinder head out or take the carb out when I have time.

I wonder if I just need the insulating gasket regardless.

 

The electric choke operates off of the amount of time it receives power. It's calculated off of generic cold engine requirements and then designed into the internal spring's movement based off of a timed heating cycle. It is not a heat sensing device. The electric choke will open at a predetermined rate once the choke receives power regardless of the engines temp or if the engine is running or not. It will also begin to close once the power is stopped regardless if the engine cools enough to need the choke again or not.

Swapping gaskets won't hurt but don't be baffled if it doesn't cure the issue.

 

Thanks and I see your point. I definitely notice I have to crank longer on a hot start than cold start. I want to get the gasket/spacer combo set up right so I can rule that out but realize it may not cure the issue.

Speaking of electric choke, I would like to get mine dialed in but am not sure if mine is bad. Is there an easy way to tell? I have mine set up so a 1/4 of the way press of the pedal closes the choke butterfly fully before starting. Sometimes I don't press the pedal at all and the butterfly plate is at 1/8th inch gap opening. I remember taking the electric choke apart and cleaning it and it taking 2-3 min to open all the way fully. I've thought about getting a brand new electric choke and trying to adjust it to also rule out any issues with it idling rough for 2-3 min and almost dying when I don't feather the pedal on a cold start.

 

I don't know about that...I think it's more of an assist; the choke will open partly from engine heat

Try adjusting the choke a bit and see if that helps. If it has a blurbling sound and puts out black smoke, turn it lean a bit. If it's more of a sneezing and hesitation, and no black smoke, turn it rich a bit

 

Edelbrock carbs are crap. I have three of them, & there won't be a fourth!
The guys at Edelbrock told me to install an insulating spacer/gasket & lower the float level. Even they know there is a problem.

 

If you do have a quadrajet intake, I'd go with a good quadrajet carb. Try Mountain Man in Arkansas for a core and a build to match your needs. PM me for his contact info, if you can't find it on the internet. Phil

Sent from my Nexus 7 using The H.A.M.B. mobile app

 

Thanks, I want to make my carb and intake work without changing them for now. In the future I would consider it for sure but was just trying to spend a small amount of money to change/add a spacer and gasket.

 

Can anyone tell from the photos below whether I have a spacer or an adaptor?

These are old from when I took out the driver side cylinder head early 2015. I supposed I could also take the carb and that adaptor or spacer out and look at the intake to see what looks like under the spacer/adaptor. I can't remember.

I was thinking of getting the Edelbrock 9266 heat isolator gasket that has the center divided and placing it between the carb and that spacer, and then replacing the gasket on the plenum to spacer/adaptor with a regular open non divided one.

Sadly, when I took out the head/intake out and put it all back together, I reused the carb gaskets. I imagine that was a bad thing to do reflecting back now and perhaps could be the cause of a vac leak that may have to do with the mysterious beep noise I've reported before, although I could swear the noise is coming from the trans.

 

That is an adapter.

It facilitates mounting a square-bore carburetor on a Quadrajet manifold.

 

Thanks it looks like it might be a 2697 adaptor. Do some people use a 1" phenolic spacer on top of an adaptor like the one I have?

My preference is to get the Edelbrock 9266 divided center metal insulator gasket which is 0.3" thick and use it between the carb and that adaptor, and use a thinner gasket for the adaptor to manifold side with the four round holes (whatever gasket the 2697 needs). Any thoughts?

 

If you keep stacking, your throttle linkage and transmission cable are not going to work anymore.

I am pretty sure that you can get that adapter in phenolic resin, but you need to weight that cost against getting a decent used aluminum manifold.

 

True, but the insulating gasket is only $18 and may cure heat soak issues (assuming I have that).

 

Worth a try.

 

idling rough for 2-3 min and almost dying when I don't feather the pedal on a cold start.

there is an adjustment for the "high idle". i can't remember where it is on that carb, but it may be on the choke side of the carb. it should increase the rpm's when the motor is cold and the choke is on.
is the choke opening up completely when it is warm?
after it warms up, shut the motor off and look down the carb and see if it is dripping/seeping. extra fuel in intake will cause a hard hot start condition.

 

I'll say that a 1/2" phenolic spacer on top of the adapter may do the trick. I'm using a 1" thick Moroso spacer under my Holley 700 CFM and it works fine, always starts when hot. I find that the starter on a SBC has got to be working right for hot-starts to be successful. I had my truck starter converted to a high torque since I'm close to a 10:1 CR.

 

Cannot tell for certain from the pictures, but appears to be a square->spread adapter. Before spending more money on band-aids to fix a poor installation, try this fix THAT COSTS NOTHING for hard starting when hot:

http://www.thecarburetorshop.com/Troubleshooting.htm#Hardstarthot

Save your funds to fix it right in the future. If you really want to use the clone then purchase a square-bore intake to install; or, as previously mentioned, find a Q-Jet core or TQ core, rebuild it, and install it. If you watch NASCAR racing, think of the adapter as a poorly designed restrictor plate. You can easily lose 40 percent of the carburetor's capability using the adapter!

Jon.

 

Thanks I will check that and yes the choke butterfly opens up fully when warm. I will spend some more time to get an accurate measurement of how long it runs rough on a cold start and how the choke butterfly behaves.

 

Thanks, I can try that next time on the hot start. I typically don't touch the pedal at all on a hot start, only one pump on a cold start.

I think it won't hurt anything to buy the $18 heat isolator gasket Edelbrock makes.

That is really interesting regarding how that adaptor can act like a restrictor plate. I never thought about that. I understand it would be better to switch to a different carburetor or swap the intake with a square bore but I'm hoping not to spend much money or change too much for the time being. I'll consider it early next year though. I was just looking for suggestions on the spacer or heat isolation gasket. It seems either solution would be fine on top of that quadrajet to square bore adaptor. It may not cure the heat soak issue but I just want to rule out the gasket/spacer.

 

I dont even have my choke hooked up and im running the same carb i do have a slight hard start after sitting but not realy. Mechanical fuel pump runing 3psi vaccume is 18psi. Mayby you should change your intake to an aluminum kind later. Also timing could play a roll in you hard start. But i could be wrong.

 

A little bit more on the restrictor plate (adapter).

Since the clones are permanently banned from our shop, I have no idea what CFM yours is, but for the sake of arguement, we will consider it to be a 750.

Chevrolet 350 Q-Jets up to about 1977 were also 750.

The Q-jet is 150 primary 600 secondary
The square bore is 375 primary, 375 secondary.

So using the adapter you restrict the 375 primary down to 150. So your total CFM would be 150 plus 375 or 525. Your 750 carburetor is now a 525.

As to the spacer, try it if you wish. The only possible negatives I can think of would be: (A) hood to aircleaner clearance, (B) possible misalignment of throttle/transmission attachments, and (C) a slight degradation of idle quality. It may, depending on your maximum RPM, add 1 or so percent power improvement at wide open throttle. However, I have two (2) genuine Carter 625 CFM AFB's on my shop truck with 390 CID. My guess would be that the Ford 390 gets hotter than the Chevy 350, but I can't prove that. I use NO spacers, and have no starting issues.

Jon.

 

Sorry to ask the same questions.

I'm going to use a 1/16" thick Mr Gasket 56C for the intake to adaptor side.


I will use a heat isolation gasket for the adaptor to carb side but should I go with an open, a split or 4 hole? The open and split are 0.3 thick and the 4 hole comes with two gaskets that are 0.125" (not sure why that one has two)

9265



9266




9267

 

In keeping with the idea that this adapter is likely restricting your airflow, if it were mine, I would remove material to effectively this a two-hole adapter, with the two holes comprised of a combined primary and secondary hole. So a left hole, and a right hole.

Or wide open:


This would allow primaries to feed the former secondary bores in the manifold, instead of being necked down to the itty bitty Q-Jet ones alone.

Not ultimately ideal, but practically free.

If the manifold were off, I'd butcher that, too, opening the adapter and the manifold all of the way.

 

notice the gaskets that have a grommet at the bolt holes...that will help keep the carb from warping, as it limits how much the gasket can compress.

I would not worry too much about the flow restrictions, I get the feeling this car is not used for racing very often.

 

Thanks! In fact I barely step hard on the pedal ever, occasionally when I feel a little frisky I will to feel the acceleration but mostly I accelerate very easy and slow like a grandma with the 53'