Engine and Transmission Tech

I touched briefly on this sometime ago with the hope that it might be a carb setup problem. I have abut 6000 miles on the Buick V6 now and it really runs good. Idles at about 1000 RPM and pulls strong right up to 5000 RPM which is about my redline although it will rev higher. Plugs read light brown. The carbs are 40mm IDA 3c and have 36mm chokes. Main jets are 155 and idle jets are at 65. The problem starts when the engine is shut off. Fuel drips out the main jets, not always the same choke. To put a bandaid on the problem I went to a electric fuel pump (4psi) and wired it to a switch on the dash. I shut the fuel pump off 15 seconds before the ignition and the problem is no problem. I have fabed a plate made of plastic laminate for a heat barrier between the intake manifold and carbs and punched a lot of louvers in the hood. It got to 90 plus here in Nebraska this week and I didn't follow procedure for shutdown. One carb really flooded and backfired and things really got interesting. Never thought I could get the hood and trunk open that fast to get a blanket out to smother the flames. After that I decided that I really need to get to the root of this problem. The only solution so far is the fuel pump switch. The choke that drips will siphon all the gas out of that bowl. I know that the level is correct and has been cross checked with a sight gage on the carb bowl and a scale on the float. The ball valves have been changed out several times and rotated to check if I could get it to consistently leak on one choke. Next step might be a reminder note on the tach face to shut the pump off dummy.
This warm weather is great isn't it. Hope all of you are enjoying it as much as I have been

Greg

Do you need 4psi?
If not, perhaps a Filter King with gauge, and lower the pressure.

Ivor

Greg, The Webers only need 3-4 lb fuel pressure.

haven't looked here in a while. The pump has a regulator on it and I have varied the pressure from 1 to 4 psi so it isn't pressure. Have been getting a lot of above 90* days here lately and the problem gets worse with heat. There aren't any heat risers on the manifold so I didn't make any attempt to keep the exhaust heat from that area. I have also thought of putting a ceramic blanket between the intake gasket that forms a splash shield over the lifters and pushrods and the manifold bottom to shut off all the engine heat. With the pump shut off and the engine running out of fuel I discovered that the idle jets on all 3 chokes seem to draw off the same float bowl as only one is empty. That is just a observation on my part that I found interesting. Perhaps the manifold wasn't designed for getting groceries but I do enjoy going to Sonic and shaking up the locals from time to time With only 20 units make I doubt that there was much development time done as compared with the SBF and SBC units out there. I've talked with Jim Inglese and he doesn't have too much to say about it other than the number built and that Buick wanted the 48mm IDAs because of racing which explains why the runners are much larger than the 40mm carb bores. He wasn't too impressed with the fact that I was running the 40mm carbs on the manifold either. Oh well.
Thanks for the suggestions.

Greg, If heat is the issue, How about an aluminum plate under the carbs. Ceramic coat or wrap headers. Louvers in hood and fenderwells?

Jim, I have done all the above. The plate between the carbs and manifold seemed to help the most as without it the problem is common. I haven't wrapped the headers or vented the fender wells as the engine runs cool (195*) at all air temps from sitting and idling to high speed (interstate) operation.

Yeah, but when you shut the engine off you get heat soak. That's why some fans stay running a few minutes after the engine is shut off.

Jim, thanks, I'll try that and get back to you.

Jim, running the fan does reduce the temp in the radiator and under the hood. It does have a small effect on what is in the water jacket of the engine. What are your thoughts of a pump that will circulate water after the engine is shut off and where would the most effective location of such a pump be. My concern is that it will short circuit and draw coolant back through the pump instead of pushing the coolant through the water jacket and the radiator where the fan could cool it. Summit sells a 1-2 gpm pump that could be used wired in with the fan.

Hey Greg,

You have all the classic signs of a heat soak problem. Just as Jim said.
Try running different brands of fuels as some have a higher vapor pressure than others.
Running the fans and a circulation pump after shut down are also an excellent idea. Check the wreckers for a pump from an Audi, BMW or Mercedes as they all use them. I would plumb it into your heater hoses and circulate it that way.
Make your heat shield as large as possible and stack a few gaskets under it to insulate it from the manifold. Or better still use the rubber isolators from a sidedraft. Use silicone (sparingly) or gasket sealer between the carbs and the plate so that the plate effectively becomes a heat sink for the carbs. Drill out the carb mount holes and install some nylon "tophat" bushings to insulate the carbs from the manifold studs. You will be shocked at how much heat comes up through the carb to manifold interface.
Some or all of these fixes should be enough to get your problem licked.

Live like you mean it
Fred

Hey guys, thanks for your suggestions. I think I have taken the gasket and heat shield about as far as I can without scooping the hood, which I won't do. I will try the nylon bushings Fred. There just isn't too many fuel options around here. I probably ought to be using no lead regular instead of e10 not sure if the ethanol is helping or hurting. It is amazing how low octane fuel will run in this engine without knock. There doesn't seem to be too much info on vapor pressures of different fuels but will keep looking.

Well the corn is tall enough to cut off any view of the country side now. It may be my imagination but I believe it makes the pipes sound better especially after midnight when its a little cooler.

Greg

I hate it when people keep you hanging. Bring this up to date, I have added a 16" 2000cfm fan with a over ride thermostatic controller. Air flow seems to be a large contributor to the flooding problem. I had two 12" fans, one pushing and one pulling, and even though the temp gage read 195* it still seemed hot. The reason for the change was cosmetic as the pusher was making it difficult to clean the bugs off the radiator screen. I had a controller on it before but the override feature really works well in stop and go driving. I am back ordered on the coolant pump but still plan to implement that feature come this winter. I also changed timing to 15* @ 1100rpm and 35* total @ 3500rpm. Engine revs to 6000 with no problems although I believe that the adjustable pushrods might be getting close to problems at that speed. Anyway life is good. The car won a trophy at the local show and shine, orphan class (it can't be a sports car as Corvettes are sports cars and that is not a Corvette) We've all been there done that. Hope everyone else has been supporting the petroleum business as well as I have been. It won't be long till the corn comes down.

Greg

It was well into the 90s yesterday here in flyover land so I thought it would be a great day to see if any progress had been made in the flooding area. Previous to this I was under the 3 checking for oil leaks and happened to look at the exhaust where it makes its way through the X member. The fuel line was very close (less than 1") in this area for about a foot. As a quick fix I packed the area with ceramic insulation and decided to take a wait and see attitude about it. In the past the Webers would pop every once in a while, which I presumed was a lean condition caused by a small amount of rust passing through the jets (the fuel line is the original). Its been about a month since the fix and the pop has gone away. I retuned the carbs (they were rich to compensate for the pop) and everything is behaving even in the high heat. I am hopeful that I can remove the heat shield between the carbs and manifold which will make tuning easier and clean up the look of the engine too. Yet another small portion of my stupidity has been diluted by a simple solution. Once again I want to thank all of you for your suggestion with this problem. They have all led to a better understanding of Weber carbs on my part. I'm looking forward to the body work this winter at which time I'll run an new fuel line away from any of the exhaust system.

Greg