Holley Carb Float Bowl Idle Vent

[Joe L.]

Some Holley carbs are equipped with a primary float bowl idle vent. Some are not. The idle vent is actuated by mechanical linkage from the throttle lever. Has anyone out there ever had problems with a Holley carburetor equipped with an idle vent as a result of it being so-equipped OR has anyone ever had problems with a Holley carb not so-equipped as a result of there being no idle vent?

[Stuart F.]

Re: Holley Carb Float Bowl Idle Vent

Joe;

I recently had to rework a vent on a brand new Holley tri-power center carb. It was not lifting at all as the mechanical linkage was not installed/designed properly. I suspect it was assembled new by someone in Ethiopia who had no idea what it was there for. I recall, I had to remove, bend and reinstall the linkage at least a dozen times until I finally got it working right. The reworking kind of went in a direction that didn't make common sense, but it worked. The vent was not working well on the original carb either, but I never got a chance to spend much time adjusting it. Whether or not it was one of the problems with it I'll never know except we could not get that carb to idle properly. In fact, the engine would die and no usual adjustment would solve the problem. It was on my son's 69 L-89, and he never gave me enough time to sort it out. However, once he got the new carbs I had his blessing to spend the time and I finally got it running well.

Oh yes, did I mention that I hate Holley carbs?

Stu Fox

[Timothy B.]

Re: Holley Carb Float Bowl Idle Vent

Some Holley carbs are equipped with a primary float bowl idle vent. Some are not. The idle vent is actuated by mechanical linkage from the throttle lever. Has anyone out there ever had problems with a Holley carburetor equipped with an idle vent as a result of it being so-equipped OR has anyone ever had problems with a Holley carb not so-equipped as a result of there being no idle vent?

Joe,

My 3810 has the bowl vent and I have never had any problems associated with it. I believe it's purpose is to vent vapor to atmosphere whereas the Holley without the bowl vent will vent vapor out of the stack vent and into the air horn.

[Stuart F.]

Re: Holley Carb Float Bowl Idle Vent

Thereby assisting on hot restarts? That was the principle used with the vapor vent holes on some older Rochester 2GC's and 62/63 Carter AFB's. Many people aren't aware of the latter because they are just small drilled holes above the primary and secondary throttle plates from the outside of the body clear through into the throttle bores.

Stu Fox

[Mark E.]

Re: Holley Carb Float Bowl Idle Vent

Joe, Why are you asking? Are you thinking of swapping a carb with a different bowl vent config?

It's not a Holley, but...

My '70 Corvette Q-Jet (7040205) has a similar type fuel bowl vent which is opened by the linkage at idle. I replaced the carb with the NA9 version (7040505) which does not have a vent there at all. It works fine even though the car doesn't have the matching NA9 vapor canister system. (Don't worry, I still have the 7040205 )

[Gerard F.]

Re: Holley Carb Float Bowl Idle Vent

Joe,

Haven't had any problems with my 3810 (with the front bowl vent) until today.

After doing about 2800 miles to the Denver Convention back and forth to Sonora, then a trip to Tahoe, I started to notice problems with idle on a cold start, and then hard to start when hot (like a hot soak and flooding condition). The carb is a 3810 Holley (dated 751) which I restored about 10 years ago, and have had it on my 67/327/300 for about that time and about 12,000 miles.

For the past couple of weeks, I have noticed this rough idle on a cold start which smooths out when warm and with a little idle adjustment. But today after warming up, she started to stall at hot idle. Pulled into a shopping center about a half mile from my house to check it out, and adjust the idle again. After pulling the air filter and enclosure, I was horrified. Gas was just pouring into the carburetor at low idle and coming out of the front bowl vent and all over the intake manifold. It was apparent that the front float had hung up, and tried rapping on the front bowl to try to free the front float, but to no avail.

So rather than risk a fire on the way home, I had it towed home. With the vented bowl and with a float failure, gas will go over the intake manifold. Without the vent, gas would just go into the intake.

So, tomorrow I am finally going to use my coffee table 3810 dated 763, the one I restored about 5 years ago and did a Restorer story on. It does have a front bowl vent but this time I'll make sure it is adjusted correctly and keep tabs on the front bowl float. Maybe, I'll get a 5 year warranty out of it, like the original. Here's 3810 dated 763, a week before my assembly date.

Photo45 CarbFinished (Medium).jpg

[Timothy B.]

Re: Holley Carb Float Bowl Idle Vent

Hi Jerry,

I am curious what you find when opening the bowl, have you ever replaced the filter in the gas tank. If these float N/S's are the black rubber tips are you using e-10 fuel.

[Gerard F.]

Re: Holley Carb Float Bowl Idle Vent

Tim,

I'll let you know when I take it off and get the other one on. Funny thing, I had just replaced the filter yesterday morning. Thought that was the problem, it was a little dirty. Using 91 octane California gas.

[Joe L.]

Re: Holley Carb Float Bowl Idle Vent

Hi Jerry,

I am curious what you find when opening the bowl, have you ever replaced the filter in the gas tank. If these float N/S's are the black rubber tips are you using e-10 fuel.

Tim-------


EVERYONE in California uses E-10 fuel. Non-ethanol fuel is just about impossible to find at any gas station.

[Joe L.]

Re: Holley Carb Float Bowl Idle Vent

Joe,

Haven't had any problems with my 3810 (with the front bowl vent) until today.

After doing about 2800 miles to the Denver Convention back and forth to Sonora, then a trip to Tahoe, I started to notice problems with idle on a cold start, and then hard to start when hot (like a hot soak and flooding condition). The carb is a 3810 Holley (dated 751) which I restored about 10 years ago, and have had it on my 67/327/300 for about that time and about 12,000 miles.

For the past couple of weeks, I have noticed this rough idle on a cold start which smooths out when warm and with a little idle adjustment. But today after warming up, she started to stall at hot idle. Pulled into a shopping center about a half mile from my house to check it out, and adjust the idle again. After pulling the air filter and enclosure, I was horrified. Gas was just pouring into the carburetor at low idle and coming out of the front bowl vent and all over the intake manifold. It was apparent that the front float had hung up, and tried rapping on the front bowl to try to free the front float, but to no avail.

So rather than risk a fire on the way home, I had it towed home. With the vented bowl and with a float failure, gas will go over the intake manifold. Without the vent, gas would just go into the intake.

So, tomorrow I am finally going to use my coffee table 3810 dated 763, the one I restored about 5 years ago and did a Restorer story on. It does have a front bowl vent but this time I'll make sure it is adjusted correctly and keep tabs on the front bowl float. Maybe, I'll get a 5 year warranty out of it, like the original. Here's 3810 dated 763, a week before my assembly date.

[ATTACH=CONFIG]64717[/ATTACH]

Jerry--------


The problem you describe is EXACTLY the concern I had about using a carb with the primary float bowl vent.

[Gerard F.]

Re: Holley Carb Float Bowl Idle Vent

Joe,

What would be the consequences of just plugging the vent in the front bowl? Holley 3810

[Joe L.]

Re: Holley Carb Float Bowl Idle Vent

Joe,

What would be the consequences of just plugging the vent in the front bowl? Holley 3810

Jerry------

That's a question I REALLY wish I knew the answer to. 1968 model year Holley 4150 carbs did not have the primary bowl vent. 1971 model year 4150 carbs didn't have the vent, either. 1969-70 Holley 4150 carbs did have the vent. Presumably, the 1968 and 1971 carbs had some means of venting other than the primary bowl vent. The question is did Holley carbs with the primary bowl vent also have the means of venting used in the 1968 and 1971 carbs?

[Steven B.]

Re: Holley Carb Float Bowl Idle Vent

When I bought my 67 a little over three years ago, it had a 743 dated 3810. It was obvious that there had been some issues with the carburetor, because it was a mess. The rear bowl was off off something else and had a sight plug. The front bowl vent had been plugged with a cup plug, and was inoperative. It looked OK, and did not give me any problems. It also had some JB weld or other cement applied to the factory soft plugs that had been leaking. With the vent plugged, it functioned OK but I was interested in getting it back to stock. After replacing both bowls, and numerous other problems I finally got it on the car and tuned. I had a 4777 on the car as a temporary carburetor while I sorted out the 3810. I'll have to say it seemed to me that the 3810 out performed the 4777. I believe it to be a lot more responsive because of the vacuum operated secondaries (they know better than my foot did with the mechanicals on the 4777). I have not experienced any problems with the 3810 even in warmer weather (I've been using straight 91 octane gas). I'm just South of Seattle, so warmer (80-90 here) is going to mean something different in other areas. The vent is covered at off idle, so I don't know that plugging it would cause a problem. Someone else may have a different take on this.
Steve

[Gerard F.]

Re: Holley Carb Float Bowl Idle Vent

[QUOTE=Joe Lucia (12484);756417]Jerry------

That's a question I REALLY wish I knew the answer to. 1968 model year Holley 4150 carbs did not have the primary bowl vent. 1971 model year 4150 carbs didn't have the vent, either. 1969-70 Holley 4150 carbs did have the vent. Presumably, the 1968 and 1971 carbs had some means of venting other than the primary bowl vent. The question is did Holley carbs with the primary bowl vent also have the means of venting used in the 1968 and 1971 carbs?[/QUOTE]

Joe,

I think the removal of the bowl vent became mandatory with the Evaporative Emission Control (EEC) system in 1970 (CA) and 1971 nationwide. There were some internal and bowl modifications which eliminated the venting of fuel vapors from the carburetor, and to a canister. Attached is an excerpt from my Chiltons 63-83 Corvette manual in regard to EEC systems. I notice that all the new generic replacement 4160's and 4150's have this port on the passenger side of the primary metering block which would overflow, if the fuel level was too high in the bowl.

Not sure what they did in 68 with no bowl vent, but didn't the small block Corvettes go to the Rochester carbs in 68. Also, when did the unvented gas cap come in.

For 69-70 Holley 4150's, I guess the EEC system was not mandatory, and some applications still had the bowl vents.

Just guessing,

[Joe L.]

Re: Holley Carb Float Bowl Idle Vent

[QUOTE=Joe Lucia (12484);756417]Jerry------

That's a question I REALLY wish I knew the answer to. 1968 model year Holley 4150 carbs did not have the primary bowl vent. 1971 model year 4150 carbs didn't have the vent, either. 1969-70 Holley 4150 carbs did have the vent. Presumably, the 1968 and 1971 carbs had some means of venting other than the primary bowl vent. The question is did Holley carbs with the primary bowl vent also have the means of venting used in the 1968 and 1971 carbs?

Joe,

I think the removal of the bowl vent became mandatory with the Evaporative Emission Control (EEC) system in 1970 (CA) and 1971 nationwide. There were some internal and bowl modifications which eliminated the venting of fuel vapors from the carburetor, and to a canister. Attached is an excerpt from my Chiltons 63-83 Corvette manual in regard to EEC systems. I notice that all the new generic replacement 4160's and 4150's have this port on the passenger side of the primary metering block which would overflow, if the fuel level was too high in the bowl.

Not sure what they did in 68 with no bowl vent, but didn't the small block Corvettes go to the Rochester carbs in 68. Also, when did the unvented gas cap come in.

For 69-70 Holley 4150's, I guess the EEC system was not mandatory, and some applications still had the bowl vents.

Just guessing,[/QUOTE]


Jerry------

Actually, for 1970 even Holley 4150's for EEC applications had the primary fuel bowl vent. However, it was a special and somewhat weird configuration. So, GM apparently thought it was important enough to go through all this effort to maintain the vent for even EEC applications. Of course, they abandoned that after 1970. The 1970 EEC Holley carb, R-4489A, is extremely rare and difficult to find.

Small block Corvettes all went to Rochester Q-Jets for 1968. However, the 4150 Holleys were still used on many other 1968 Chevrolet applications such as Z-28 Camaro, L-78 Chevelle, and L-72 full size passenger cars. None of these had primary bowl idle vents.