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Performance Issues on my '41


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Hey guys,

So, I've been trying to solve a long standing performance issue on my '41. As many of you may know, she's an SSE with the stock 248 and dual carbs. She sat off and on from 10-12 as I rebuilt the brakes and chased an annoying electrical problem that ended in the starter solenoid relay being bad. Up to the summer of '11 during test drives, I had no performance problems from her.

Last summer, I had the starter completely gone through and a new solenoid relay put on her. I started trying to drive her again and at certain angles of throttle, she would stall out. The stalls take place around the threshold where you need to shift into 2nd and third (around 10-15 mph/30-35 mph respectively.

First step was to check and correct the timing. I used a vaccuum gague and a battery powered induction timing light. I had another gentleman "check my homework" we found TDC and set the time from there. Supposedly he's a more experienced mechanic than I and he used the timing light and mark on the flywheel after I had set it with a vacuum gague. I don't completely trust his judgement as he works primarily on imports and newer cars. I am going to go back and recheck the timing regardless.

After this last summer, I replaced: Coil, points (set points correctly,) plugs, condensor, dizzy cap, and plug wires. Both carbs are now rebuilt and she's sporting a brand new fuel pump. From her backfiring slightly at idle, I'm willing to bet I've fixed a lot of stuff without actually solving my problem which leaves: 1. The timing is still not correct, 2. the vacuum advance is not working or there is a problem with the dizzy (although I checked the plates for movement by hand last summer and they seemed ok,) or 3. I have a stuck/worn/burnt valve or pushrod. Have I missed anything else?

I'm kind of eager to rule out the fact that I have valve troubles before I go about fixing more stuff, like the dizzy or vac advance that may not need it. So, do I just pull the valve cover/side cover and let it run for a little bit while obersving for anything irregular. Mike in CO, I read your recent post on the pushrods and pulling the side cover and it really got me thinking. Anyway, how would you reccomend going about checking the valves. I'd like to get some closure as to whether or not a valve job is in my future. Thanks for allowing me to write books on my automotive problems on here and for your help guys!

(If it wins me any brownie points, I just renewed my BCA membership :)

Cheers!

Tim

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Hi Tim,

I am no expert, but I have done a lot of fixing over the years on the farm. The first thing I would do is check and record the compression of each cylinder. Do this both dry, and with oil added to seal the rings. Record both readings for future reference. If you have a stuck/burned valve the compression on that cylinder will be low and the oil will not help much. If all cylinders are relatively even then valves are not your problem. It is also nice to have the compression readings for reference in future years when things age more and you want a number to compare to. If the compression check is good then I would move on to the timing and possibly carburation. I am no expert here so I will simply say to check the shop manual and follow the instructions as to setting the timing etc... Hopefully someone with more experience in this area will chime in and offer you some ideas on the best way to proceed to find your problem. Personaly, I think the timing and carburation are most likely the problem as you stated that the car did not have the problem prior to working on the distributor and the timing. I have also heard that the dual carb setup can be a bit finickey, but I know nothing about that first hand... others will chime in to help.

Good luck,

Robin

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Tim,

I would have thought that a valve problem would have shown up when you had the vacuum gauge on.

Vacuum gauges can tell you a lot about how your engine is running by the amount of vacuum and how the needle is reacting and moving.

No harm in putting it back on and having another look see.

If you don't already know how, you can Google how to read a vacuum gage and what signs to look for.

I also would suggest doing a good compression check as well as taking off the rocker cover and checking the gaps on all the rockers.

When you changed the points etc, did you check that little lead that runs down to the points ?? Those little buggers tend to fray and break inside the sheath.

Danny

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Compression check will find a burnt valve. Do that first as it seems to be your primary concern.

Check for vacuum leaks before setting your timing with a vacuum gauge. I spray WD-40 around manifold gaskets etc. Engine will speed up when you hit a leak.

Just my $0.02

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I'm betting your problem is fuel related. You say she backfires through the carb at idle? And the car falls on it's face as the rpm peak before gear changes? Seems to point to a lean condition. Have you looked at float height, mixture settings, and as Mark suggested, vacuum leaks? With the choke on, and your hand partially blocking the other carb, try reving her to see if the condition is still there.

Cheers

Grant

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All right,

I've added a compression test kit to my shopping list. I may try to play around with the vacuum gauge this weekend. For reference, where do you all typically hook the gauge up? Not many options for hook up on the intake manifold. I think I used the vacuum line to the wiper motor last time. When I tried setting the timing I did disconnect the vac advance and plugged the end leading to the advance by wrapping electrical tape around it. I don't think the other gentleman did though. He used the timing light and mark on the flywheel. Although he mentioned that the timing seemed right to him I'm not all that convinced now. Again, not his fault as he was trying to help, but he was more versed in newer cars.

She backfires through the exhaust at idle making intermittent little "pop..pop" noises every few minutes. If you stand on the gas, you'll get an even bigger backfire, but yes Grant she falls on her face at peak RPM right before the gear change. I'll try the WD-40 check around the manifolds as well.

Danny, I'll check the dizzy again, I'm not sure where the lead is at this moment, but I'll pop the cap off and have a good look. Maybe I'll even video/photograph some of the stuff and put it on here so you all can help direct me at what I'm looking for. I'll probably ask for some guidance on how to do the "dry" and "wet" compression checks. Never done one of those :)

Thanks again guys for responding and being engaged.

Tim

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Do the easy stuff first Tim. Danny is right about that wire in the distributor. We had the same issue, only the car wouldn't start at all. Do check the carbs by choking them. Doesn't take much to pop the air cleaner(s)? and partially block the carb without the choke. Be nice to eliminate that! But they do say that 90% of carb issues are electrical!

Cheers

Grant

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Raining cats and dogs here in the D.C. area. Started her in the garage tonight and sprayed WD-40 around the manifold gaskets and base of the carbs. Didn't seem to affect anything I tried covering half of the rear carb with the choke on the front while revving her up and she just flat out died. Did that a couple of times with the same result.

Couple of other things to note. In addition to the intermittent backfire "pops" through the exhaust, I noticed if you just let her idle for a bit without revving her her and there and then get on the gas hard, she tries to stall and then I get a BIG backfire through the carb :eek:

Anyway, I'll get her out in the daylight tomorrow weather permitting and check that dizzy..

Tim

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Tim:

Torrential rains tmw I am afraid. If you are in a big hurry to get this sorted I may be able to come over on Sunday for a bit if you don't want to wait 'til the 16th. I can show you how to static time - I used to do it this way in the '70s when I had no money for a timing lite. It is very accurate if you are careful. Of course I will bring all of my usual diagnostic stuff as well.

Cheers, Dave

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Hmmm. The trick is to hold your hand just over the carb enough to hear the engine change in pitch, but it sounds like you did that. When you look down the carbs, do you see a good shot of gas when you move the throttle?

Cheers

Grant

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Update Report:

In spite of him saying not to do so, I want to say it was awesome of Dave to show up and help out today. I am glad to know you now Dave and I appreciated your time and learning from you as well as chatting about car stuff. We spent about 4-5 hours out in the driveway and the weather wasn't too bad so it was a good day to work on the car. We checked and reset the dwell of the points, the gap of the points, the timing, the dizzy itself, the vacuum advance, the plugs, and Dave did a compression test. All cylinders checked out at 100 lbs compression with one cylinder checking in at 105 and another at 110. Pretty healthy Straight 8. Vacuum on the vacuum gauge was between 15-17 pounds.

We popped the valve cover off to visually inspect the valves. Everything was moving, clean, and oiling itself. Very healthy on inspect there as well.

We listened to the exhaust and Dave could hear multiple misses. The 3 rear cylinders were not firing. Dave checked the spark and each of the 3 plugs individually and clean bill of health there so it's not an electrical issue. Based on all that we deduced that she's starving for fuel. We hooked up some tubing to the fuel line and in a 30 solid seconds of cranking, we barely got 1/4 cup of fuel in a coffee can. We checked the fuel pump pressure and it put out 3 1/2 pounds and the specs call for 5 pounds.

In the next couple of weeks, we're going to check the fuel pump, the lines, and the gas tank to further isolate the problem. This of course is with two shiny new rebuilt carbs and a shiny new fuel pump from Bob's. Did I cover everything Dave (we covered a lot of ground today didn't we :D

Any further thoughts on this? I know it's inevitable that someone will chime in with an electric fuel pump suggestion.

Thanks again Dave and I hope I can help you with your '40 in the near future and thanks again guys for all your advice.

Cheers!

Tim

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  • 3 weeks later...

post-76431-143141972106_thumb.jpg

Update to the update:

Dave and I had another great day of troubleshooting and root beer chugging last weekend! Anyway, we did a few more diagnostics using a fuel pump emulator and the bottom line was that the mixture screws on both carbs were not adjusted properly. With some tuning, the miss at idle disappeared. (Thanks again Dave!)

So, we went for a test drive and still having the performance issue under load. She runs great until that angle of throttle where you shift into the next gear and she still stumbles and falls on her face. (at the 10 mph mark, 20 mph mark, and she won't go over 30 mph.) At least she didn't backfire with the 2-3 test rides we took, properly adjusted timing and carbs seems to have eliminated that.

So I got to thinking, back in the summer before last (when she still ran good) I took her down to fix an issue with the starter and while she was down, I replaced the side cover gasket. Well, I remembered the other day that I had bent the vacuum line between the carb and the vacuum advance, but bent it back. I'm wondering if it may be permanently crimped (see photo with the white circle.) If that line were crimped or in any way cracked, or had a hole in it, might that cause the kind of performance issue I'm having? I would imagine that if it were kinked or had a hole in it, it would indeed inhibit the advance from pulling the plates on the distributor at higher angles of throttle due to lack of vacuum. I'm seriously thinking about replacing the line. If I do, I was wondering of all those other bends and kinks are normal and should I recreate them in the new line?

Might give that a shot (still haven't ruled out the possibility of a vacuum leak or problems with the fuel lines or gas tank)

Thanks again guys for all your help and advice!

Tim

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Tim,

My '40 LTD (320) stumbled at the "shift point" last summer also. After a lot of carb / timing / plug work, I finally determined she was not getting any spark advance, and just would not pull like I thought she should. Here's what I did to solve the problem.

Pull the vacuum line at the carb fitting, and apply some vacuum there. Have a friend look at the points plate in the dist. Does it move with vacuum ? Mine did not and I determined that the vacuum advance diaphram was all crumbly and laying at the bottom of the can.

They are available on evil bay as NOS but you have to get the right part #. Also watch out for the fittings at each end of the vacuum tube. They are "self swaging" nuts, and NOT the brass nut and ferrell you would expect. A little oil and gentle persuasion goes a long way here, and you can free them up.

Mike in Colorado

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I've read this thread with interest, as I have a '41 Roadmaster that I just got on the road last year and I have what sounds like the same idle issue, though I don't have any issues accelerating. An irregular pop-pop through the exhaust, just like Tim describes. My engine is completely rebuilt, but a bad valve would cause a regular miss.

Perhaps my issue is just due to tuning?

Thanks for sharing.

Keith

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The vacuum advance can be a real pain. One of the problem with NOS stuff is the "O" - OLD. You could end up with a part as old as your car and just as crumbly. I know the advances can be rebuilt and you might be better off getting a rebuilt one that doesnt have the "O".

The same holds true of any elastomeric NOS stuff.

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Stumped, stumped, stumped is the word of the day.

I pulled the vacuum line between the carb and the advance today. I ran water through it and used the air compressor to blow air through it. There were no leaks or real restrictions that I could observe, but I realize this probably is not as good as testing it with a vacuum pump through the line. We also tested the advance unit with the line off last week and it held vacuum very well and pulled the plates.

I went through the pile of receipts I got with the car. Turns out the dude that had it swapped out the distributor and advance for fresh ones from Bob's back in 2007. The guy also had the manifold gaskets replaced the same year. Not real sure if the centrifugal advance could be shot with 5 years and 1000 miles on the rebuild.

So aggravating. Trying to think of other things to look at...

Tim

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Hi,

"Baby" (1940 LaSalle, but still a GM distributor) was having similar issues recently, and most notably persistent mondo-pinging. A lot of investigation (and several long-necks) revealed that the distributor plate, onto which the points et al are attached, was frozen solid. Ergo, no motion for vacuum advance.

I sent the 73-year-old vacuum advance to Terrill Machine for rebuilding just because I don't want to crawl into the hood of this beast again, and after disassembling the distributor I cleaned up all the should-be-moving parts and reassembled it all. Hardest part was re-assembling the plate-to-distributor with the three loose ball bearings. After half an afternoon doing that I discovered that you line up two balls, set the third one on the springy-like keeper, and bonk it with the handle of the nearest bonker--in this case the handle of a scrub brush. Works great.

When the vacuum advance comes back from Terrill this week, I expect to find much better operation.

For those who have tried this and lost one of the balls (as I did), I have 99 ball bearing balls (7/32") sitting here looking at me. Be sure to mike yours before asking for new ones: another post states that on a Buick the distributor balls might be 1/4". Let me know if you need any of either size.

--Tom

Edited by trp3141592
Corrected spelling (see edit history)
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Aww, thanks Tim!! :) It was really a pleasure and you have one heckuva cool machine there! Very nice paint, really a 3 footer. Yepper, I agree we are down to a fuel starvation issue. Now to find out why...

Cheers, Dave

David ... it is folks like you that keep me interested (and impressed) in the old car hobby !!!! You are the best !!

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Thanks for the kind words Bob! Well, I am a just retired engineer and we are always trying to solve "the problem," whatever it may be, cars or something else. Drives my wife crazy! But I do love working on these old machines, I am also a history buff and it makes me feel more connected to the past. In fact, I often play late 30s - early 40s jazz when working on my Buick, puts me in the proper mood...

Cheers, Dave

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Thanks Mark, according to the receipts, the previous owner took her in and had a new muffler installed in February 2007. He later took her back to the same place in April 2007 and had "2 flat high heat gaskets" installed, new gaskets replaced at the manifolds, and was charged labor to repair & replace "3-piece exhaust pipe."

That said, I am hearing a noise, kind of like an imperfect seal noise (like you would hear if you placed a drivers license over 3/4 of a shop-vac nozzle) from the vicinity of the exhaust region where it bolts together underneath the manifold. I sprayed it with WD-40 and while the engine did not speed up, the noise temporarily went away????

Dave and I also had a look last week at the heat damper control valves and like most folks I guess, mine are frozen, the front at the 1:00 position and the rear at the 2:00 position.

Cheers!

Tim

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