Carb question

[intofx]

what are your engine temps? What intake manifold are you using?


vince

The gauge reads fine but the mechanic said the carb was hot when they pointed the temp gun at it. How hot I'm not sure. I should know more details tomorrow. The intake is a CERAMCOATED EDELBROCK RPM.

[Pro Stock]

If you suspect that a fuel line is to close to a source of heat (header ect.) fix that first, put an insualator between the block and fuel pump and make sure that the fuel line from the pump to the carb is isolated from heat with proper routing and an insualting sleeve over it, also run an insualating gasket under the carb this way you will have addressed all of the heat issues at once. Check your float levels while the engine is running, your Demon carbs floats should be set so that the fuel level is halfway up the sight glass, are you running a regulator ?, if not you should be, set he regulator to about 6 1/2 psi, I would also run a BG regulator with a small guage attached to it so that you will always be able to see what your fuel pressure is if your having a problem. When you said that your fuel pump was to big, were you talking about an electrical pump or mechanical ?, if it is electrical and big enough you can take the mechanical pump out of the system and eliminate that source of heat. As stated above correct timing is critical and incorrect timing can show up as a carb problem,retarded timing will also cause the engine to run hot, unless your running a compression ratio above 10.5:1 and less than 92 octane fuel you should be able to run 36* total timing.

Dale

[intofx]

If you suspect that a fuel line is to close to a source of heat (header ect.) fix that first, put an insualator between the block and fuel pump and make sure that the fuel line from the pump to the carb is isolated from heat with proper routing and an insualting sleeve over it, also run an insualating gasket under the carb this way you will have addressed all of the heat issues at once. Check your float levels while the engine is running, your Demon carbs floats should be set so that the fuel level is halfway up the sight glass, are you running a regulator ?, if not you should be, set he regulator to about 6 1/2 psi, I would also run a BG regulator with a small guage attached to it so that you will always be able to see what your fuel pressure is if your having a problem. When you said that your fuel pump was to big, were you talking about an electrical pump or mechanical ?, if it is electrical and big enough you can take the mechanical pump out of the system and eliminate that source of heat. As stated above correct timing is critical and incorrect timing can show up as a carb problem,retarded timing will also cause the engine to run hot, unless your running a compression ratio above 10.5:1 and less than 92 octane fuel you should be able to run 36* total timing.

Dale

The old pump was mechanical an the smaller replacement one is as well. They added fuel filter near the tank and a regulator between the pump and carb. They say they solved the percolating issue. I have not had much time to drive around yet to test the car,tho... They said they set the fuel pressure to 5 lbs per the gauge. Should I run more (6.5 as you suggested)? Octane here in Kalifornia is 91 unless I go to race gas which is 101 (and $10 a gallon). Thanks for the help!

[Pro Stock]

The old pump was mechanical an the smaller replacement one is as well. They added fuel filter near the tank and a regulator between the pump and carb. They say they solved the percolating issue. I have not had much time to drive around yet to test the car,tho... They said they set the fuel pressure to 5 lbs per the gauge. Should I run more (6.5 as you suggested)? Octane here in Kalifornia is 91 unless I go to race gas which is 101 (and $10 a gallon). Thanks for the help!

Was the regulator on before the fuel pump change? if not the bigger pumps pressure could have been too high, the bigger pump was the better choice of pumps as long as the fuel pressure was set correctly, 6.5 psi is a good number, that way when the pressure fluctuates it will be neither to high or to low. also the filter should be placed between the pump and the carb because pumps are more efficient on the pressure side than they are on the inlet side. You didn't say whether you have addressed all of the possible heat issues that I talked about in a previous post so don't forget to do that, that is probably where your problem is. Lastly, you can greatly improve the gas by using an octane booster or mixing 2 or 3gallons of race gas with it, just experiment with it a little for the right mix, it's not much of an issue here in North Carolina because we still have 93 octane gas available.

ps, I can help you with that Demon if the problem persists after all of your fixes, I do R&D for BG
Dale

[intofx]

Was the regulator on before the fuel pump change? if not the bigger pumps pressure could have been too high, the bigger pump was the better choice of pumps as long as the fuel pressure was set correctly, 6.5 psi is a good number, that way when the pressure fluctuates it will be neither to high or to low. also the filter should be placed between the pump and the carb because pumps are more efficient on the pressure side than they are on the inlet side. You didn't say whether you have addressed all of the possible heat issues that I talked about in a previous post so don't forget to do that, that is probably where your problem is. Lastly, you can greatly improve the gas by using an octane booster or mixing 2 or 3gallons of race gas with it, just experiment with it a little for the right mix, it's not much of an issue here in North Carolina because we still have 93 octane gas available.

ps, I can help you with that Demon if the problem persists after all of your fixes, I do R&D for BG
Dale

Thanks for the help, Dale. I'm from High Point, NC originally so I miss the days of 93 octane.

The regulator was put on after the big pump was replaced. The shop said it was faulty and I needed a new one... I still have the part. Is there any way to tell if the pump is working correctly?

I mentioned the filter being after the pump as that is what I was always told and the tech said he wanted to filter before the pump so it would protect the pump.

I took the car out for a spin tonight and I am still getting a hesitation when I put my foot into it from a stop but overall the car runs much better.

Matt

[Pro Stock]

Thanks for the help, Dale. I'm from High Point, NC originally so I miss the days of 93 octane.

The regulator was put on after the big pump was replaced. The shop said it was faulty and I needed a new one... I still have the part. Is there any way to tell if the pump is working correctly?

I mentioned the filter being after the pump as that is what I was always told and the tech said he wanted to filter before the pump so it would protect the pump.

I took the car out for a spin tonight and I am still getting a hesitation when I put my foot into it from a stop but overall the car runs much better.

Matt

Mechanical pumps aren't near as sensitive as electric pumps are to debris, and the filter will only hinder flow to the pump unless it is a high flow racing filter, so if your guy won't remove it do it yourself, just make sure you have the filter after the pump. the only way for you to check the other pump is to bolt it on the car. set the fuel pressure, and drive it. The hesitation sounds like a carb tuning issue independent of your other problems, don't know where you live in CA but I know a really good carb guy in Ontario. I hear ya on the octane thing, it's funny, I used to live in Southern CA and now I'm living in Davidson, NC.

Dale

[intofx]

Mechanical pumps aren't near as sensitive as electric pumps are to debris, and the filter will only hinder flow to the pump unless it is a high flow racing filter, so if your guy won't remove it do it yourself, just make sure you have the filter after the pump. the only way for you to check the other pump is to bolt it on the car. set the fuel pressure, and drive it. The hesitation sounds like a carb tuning issue independent of your other problems, don't know where you live in CA but I know a really good carb guy in Ontario. I hear ya on the octane thing, it's funny, I used to live in Southern CA and now I'm living in Davidson, NC.

Dale

Looks like the heat issue is still a problem. I went to pick up the car yesterday and they wrapped the headers on the fuel line side but the line is still pretty close to the header in a few places. May have to re run the line. The other issue is that the fuel pressure is steady for the most part at 4.5lbs but if it sits (and gets hot I assume) it drops into the 3 lbs range. It seems that there is just a ton of heat in my engine bay. This is getting ridiculous and expensive.