67 L71 Carburetor temperature

[Duke W.]

Re: 67 L71 Carburetor temparture

Assuming it has an OE equivalent cam, converting from ported to full time vacuum advance requires replacing the 15" OE 201 15 VAC with a 12" B26. The easiest way to implement is to buy a couple of feet of 1/8" vacuum tubing and a Tee. Remove the existing hose from the choke vacuum break and make a new harness with the tubing and tee to route vacuum to both the choke vacuum break and VAC.

The above can be easily "undone" for judging. Full time vacuum advance can also be implemented by plugging a hole in the carb base plate and drilling another hole to get manifold vacuum directly at the carb vacuum advance port. This mod is invisible other than the non-OE VAC.

Normal L-71 idle behavior with an OE equivalent cam is 900 @ 14". Once implemented you will also need to adjust idle speed/mixture and reset fast idle speed as the additional idle advance from full time vacuum advance will increase both. Low speed driving in hot weather will reduce engine temperatures and the tendency to diesel will go away because the additional idle advance cools down the combustion chamber surfaces and EGT and eliminates the pre-ignition that caused the dieseling.

Duke

[Kerry A.]

Re: 67 L71 Carburetor temparture

Chris, I finally had the chance to address the problem by making the vacuum and timing changes as outlined in the Duke Williams article for which you provided a link. I have to say the car ran better than it ever has but there's still an issue. I have a route I use regularly for test drives and it's about a 35 minute round trip. As I mentioned the car ran great except after I parked. It sat 20 minutes and when I tried to start it so I could park it in the garage, it wouldn't start. It tried at times but wouldn't stay running longer than two seconds. It did finally start and I was able to move 80 feet and it died again. It eventually started again but I had to stay on the gas until I could limp it into the garage where it immediately died. If this was a modern day car I'd say I have a lemon or demon as this car has been problematic since the day I purchased it. I'm at my wits end. Do you have any other suggestions? Possibly you made adjustments in addition to the Duke Williams article? Please let me know. Thank you.

[Guest]

Re: 67 L71 Carburetor temparture

Chris, I finally had the chance to address the problem by making the vacuum and timing changes as outlined in the Duke Williams article for which you provided a link. I have to say the car ran better than it ever has but there's still an issue. I have a route I use regularly for test drives and it's about a 35 minute round trip. As I mentioned the car ran great except after I parked. It sat 20 minutes and when I tried to start it so I could park it in the garage, it wouldn't start. It tried at times but wouldn't stay running longer than two seconds. It did finally start and I was able to move 80 feet and it died again. It eventually started again but I had to stay on the gas until I could limp it into the garage where it immediately died. If this was a modern day car I'd say I have a lemon or demon as this car has been problematic since the day I purchased it. I'm at my wits end. Do you have any other suggestions? Possibly you made adjustments in addition to the Duke Williams article? Please let me know. Thank you.

Check your float levels and needle and seat for dirt on Center Carburetor it flooding , i would also check end Carburetors also for the same.

[Frank D.]

Re: 67 L71 Carburetor temparture

Chris, I finally had the chance to address the problem by making the vacuum and timing changes as outlined in the Duke Williams article for which you provided a link. I have to say the car ran better than it ever has but there's still an issue. I have a route I use regularly for test drives and it's about a 35 minute round trip. As I mentioned the car ran great except after I parked. It sat 20 minutes and when I tried to start it so I could park it in the garage, it wouldn't start. It tried at times but wouldn't stay running longer than two seconds. It did finally start and I was able to move 80 feet and it died again. It eventually started again but I had to stay on the gas until I could limp it into the garage where it immediately died. If this was a modern day car I'd say I have a lemon or demon as this car has been problematic since the day I purchased it. I'm at my wits end. Do you have any other suggestions? Possibly you made adjustments in addition to the Duke Williams article? Please let me know. Thank you.

If your car starts normally an hour or so after this issue, then I'd say you're exhibiting classic heat soak. Heat soak has all the symptoms of a flooded car as the hot engine percolates gas out of the carb to sit on the intake runners in raw form, until that evaporates you're starting a flooded car. You can confirm with an I/R temp gun aimed at the fuel bowls after a hot run; any temps north of about 140* are a problem with modern gas...

[Chris H.]

Re: 67 L71 Carburetor temparture

Kerry, as they say it "could be anything"...Fuel related, ignition related, etc. Based on the systems you describe, my initial thought is fuel system related. Do you have access to ethanol free gas? (race or aviation fuel). If so I would try some to see if it reduced the symptoms you describe. Another low-hanging fruit thing to look is the fuel filter. And check to see if accel pump squirters are squirting.

[Duke W.]

Re: 67 L71 Carburetor temparture

If you haven't already done so wire open the heat riser valve with some stainless steel safety wire. After installing a B26 VAC and converting to full time vacuum advance the normal hot idle and hot fast idle speed will increase significantly, and I assume you noticed that, readjusted as required and performed the idle mixture-speed adjustment procedure shooting for about 900 and vacuum should be about 14".

The OE distributor centrifugal is 30 @ 3800, but the initial is only 5. With the VAC disconnected and plugged and engine revs at about 750 (centrifugal stats at 900) increase initial to as high in the 6-10 range as the engine will tolerate without detonation.

Duke

[Kerry A.]

Re: 67 L71 Carburetor temparture

Float levels are set about .125" to .25" below sight hole. Not that it means there isn't an issue, but the carbs were recently rebuilt and refurbished by Chicago Carb. The carbs were also inspected prior to being installed. No flooding noted. Fuel pump pressure seems to be fine. I have also installed phenolic spacers to eliminate as much heat as possible. But the car sure behaves as if it's flooded. I'd like to add that I'm running racing fuel. I don't always run it but I am for testing purposes. I assumed that if the car ran properly on racing fuel but not on premium non-ethanol gas, then the gas itself may be part of the problem. Again, I'm at my wits end.

[Larry M.]

Re: 67 L71 Carburetor temparture

I am guess here, but if OP has done all the things listed and still has issues, I would start looking at the TI system and the coil.

FWIW.

Larry

[Chris H.]

Re: 67 L71 Carburetor temperature

Kerry, the float level is too low, should be right at bottom edge of site plug.

[Chris H.]

Re: 67 L71 Carburetor temperature

Kerry, I recommend purchase of the CSM. It contains the entire tune up process and troubleshooting sections. Available through the NCRS bookstore. I use it all the time. For these motors to run right, everything needs to be perfect. (Fuel/ignition). Be patient, go through the procedures in the CSM and chances are pretty good you’ll fix it.

[Kerry A.]

Re: 67 L71 Carburetor temperature

Chris, thank you for your reply. I have a copy of the CSM and to my knowledge we have done everything possible. Not that it matters but the shop I use builds carbureted race engines and is quite good at it. After going through all of the basics I don't know what else to do. The float level has been set according to specs, set high and low and it doesn't make a difference. Also, the shop does restorations and build rods or restomods from the ground up. Again it doesn't make the owner of the shop, which I'm good friends with and I get extra attention, an expert on the L71. I'm mentioning this just so you know I'm not working on it myself.

[Duke W.]

Re: 67 L71 Carburetor temperature

Not that it matters but the shop I use builds carbureted race engines...




.

Yes it does. As I've said time and time again racing engines and road engines are completely different animals, yet there are countless times when guys claim their mechanic or "engine builder" builds great race engines, but can't solve the problem or botches a rebuild.

I made some suggestions in this thread that was endorsed by at least one other contributor, but you never said anything about implementing it. It may not solve the problem completely, but should definitely help.

I understand you don't do your own work, which is too bad because owning a vintage car and not being able to do simple maintenance tasks and repairs puts you at a great disadvantage. You might try to explain my recommended spark advance map changes to your mechanic, but I'll make an even odds bet he will say I don't know what I'm talking about... no problem, I just smile and try to help someone else.

Duke

[Kerry A.]

Re: 67 L71 Carburetor temperature

Duke, I agree that just because a person can build a race engine doesn't mean they can handle vintage engines but I have no question about him. You bet wrong He agrees with you and we used your article to make the most recent adjustments. I may not have made it clear in an earlier post that I have tried everything suggested in the thread. My original post was about heat soak which is what I thought the problem was. I addressed that with phonelic spacers. It did bring my carb temps down to an acceptable temp but it didn't solve the problem of not starting when hot. I replaced the module guts with a modern board. Installed three coils. Ran an aftermarket regulator and replaced the magnetic pickup. The carbs have been completely restored and inspected prior to installation. Float levels. Jetting. CSM adjustments. Fuel pump pressure on and on only to have the same problem. Because of the plethora of issues that were discovered during a routine valve adjustment the engine was completely rebuilt stock from the bottom up sparing no money on parts. The engine was blueprinted and dialed in on a dyno. When it's running it gives you that hold onto my seat feeling. I feel confident in the engine itself. I found out the previous owner had cobbled the engine together to pass Top Flight and he failed to inform me of this. The first time I drove the car for an extended period the problems started and haven't stopped. I've owned the car for nearly seven years and I may have 150 miles behind the wheel and probably 90 percent of them were test drives. There's approximately 700 miles on the rebuild and almost everyone of them were on the dyno for both testing and trying to replicate issues. When it comes to tri powers and engine rebuilds, I don't touch. Minor repairs? Yes. Major? No. I do maintain my 63 327/300 but it's a piece of cake. So please understand I've bent over backwards trying to get the car to run right. My wife reminds me almost daily that she told me not to buy the car. Oh well. I didn't listen and maybe I should've listened. I hope this additional information helped. Kerry.

[Kerry A.]

Re: 67 L71 Carburetor temparture

Frank, When you say you blocked off the intake heat risers with fuel injection gaskets, do you mean the base gaskets? Also, are you referring to a tri-power? Thank you.

[Frank D.]

Re: 67 L71 Carburetor temparture

Frank, When you say you blocked off the intake heat risers with fuel injection gaskets, do you mean the base gaskets? Also, are you referring to a tri-power? Thank you.

No tri-power, but I've blocked off the heat risers on my '61 with aluminum dual quad manifold (first picture, yellow circles) and my 63 with base motor (single carb) cast iron manifold (second picture)...if you think those risers don't get hot just look at any of those intakes that have been run for a while and the scorched paint.