Gas Boiling in Quadrajet
Thread Starter
Drifting
Joined: Nov 2013
Posts: 1,806
Likes: 258
From: Dublin Ohio
Instead of starting a new thread, I'll just revitalize this one ---
Today after taking it out for a drive I could actually watch the gas drip onto the manifold on the driver side.
I've read that rebuilding the carb would not help because it's the gas and the fact that it was winter storage gas only makes it worse.
I've got the spacer and a GM issued heat shield under the carb.
So I want to know for those of you that have a stock L48 or similar, and you do not have issues, what's your secret?
Today after taking it out for a drive I could actually watch the gas drip onto the manifold on the driver side.
I've read that rebuilding the carb would not help because it's the gas and the fact that it was winter storage gas only makes it worse.
I've got the spacer and a GM issued heat shield under the carb.
So I want to know for those of you that have a stock L48 or similar, and you do not have issues, what's your secret?
Drifting
Joined: Dec 2004
Posts: 1,714
Likes: 42
From: Austin Texas
I have had this problem before too and agree there are two things at play, heat and possible remnants of winter blend gas.
For heat, I have done the following.
1. Check float level and lower if needed.
2. Install intake gaskets that block off the cross over.
3. Install the .25 thermo gasket mentioned.
4. Enrich the idle mix to a 12.5:1. Thinking richer is a bit cooler
5. Advance the timing at idle , vacuum advance on manifold source (per Lars papers)
6. I have electric fans and in the summer I install a mechanical flex fan for plenty of airflow while sitting still.
7. 180* thermostat
8. Buy the highest octane gas.
This may help depending on the outside temps.
Good luck,
John
For heat, I have done the following.
1. Check float level and lower if needed.
2. Install intake gaskets that block off the cross over.
3. Install the .25 thermo gasket mentioned.
4. Enrich the idle mix to a 12.5:1. Thinking richer is a bit cooler
5. Advance the timing at idle , vacuum advance on manifold source (per Lars papers)
6. I have electric fans and in the summer I install a mechanical flex fan for plenty of airflow while sitting still.
7. 180* thermostat
8. Buy the highest octane gas.
This may help depending on the outside temps.
Good luck,
John
Pro
Joined: Oct 2009
Posts: 664
Likes: 89
From: Marysville Ohio
I think it's usually a combination of factors you end up have to address with these issues. With that in mind, there may be one other thing to consider: As stated above, modern fuels have a lower boiling point that shows up in carbureted applications. In my experience, fuel was getting hot in the line leading to the fuel bowl. I fought this with both a Q-Jet and a Holley DP (it was more evident with the Holley).
Building a return line from the carb (vs the pump) allowed hot fuel to recirculate back to the tank to cool off. While it doesn't necessarily prevent the boiling, it can mitigate the issue by allowing it to vent back to the tank. For what it's worth, I did this following Lars' advice (along with a heat shield). No more hot start issues.
Building a return line from the carb (vs the pump) allowed hot fuel to recirculate back to the tank to cool off. While it doesn't necessarily prevent the boiling, it can mitigate the issue by allowing it to vent back to the tank. For what it's worth, I did this following Lars' advice (along with a heat shield). No more hot start issues.
Drifting
Joined: Jul 2008
Posts: 1,873
Likes: 27
From: Sonora CA
I think it's usually a combination of factors you end up have to address with these issues. With that in mind, there may be one other thing to consider: As stated above, modern fuels have a lower boiling point that shows up in carbureted applications. In my experience, fuel was getting hot in the line leading to the fuel bowl. I fought this with both a Q-Jet and a Holley DP (it was more evident with the Holley).
Building a return line from the carb (vs the pump) allowed hot fuel to recirculate back to the tank to cool off. While it doesn't necessarily prevent the boiling, it can mitigate the issue by allowing it to vent back to the tank. For what it's worth, I did this following Lars' advice (along with a heat shield). No more hot start issues.
Building a return line from the carb (vs the pump) allowed hot fuel to recirculate back to the tank to cool off. While it doesn't necessarily prevent the boiling, it can mitigate the issue by allowing it to vent back to the tank. For what it's worth, I did this following Lars' advice (along with a heat shield). No more hot start issues.
Sorry, not trying to hi-jack this thread . . . .
Last edited by imariver; Apr 1, 2018 at 11:04 AM.
Pro
Joined: Oct 2009
Posts: 664
Likes: 89
From: Marysville Ohio
There is a restrictor on the retuen side - it's where the short rubber section is. I used a carb jet inside a rubber fuel line for this. There are more elegant ways of doing this, but it was cheap (using things I had on hand) and looks decent (to me, anyway).
