valk

1941 Roadmaster coupe

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Thank you Peter. I hope to visit you sometime to see it in person.

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Congratulations on the successful delivery!  She looks stunning -- the red wheels are the icing on the cake for that color scheme. 

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15 hours ago, valk said:

She arrived yesterday on Good Friday, which, henceforth, shall be called Very Good Friday.  I absolutely love it  and spend all day yesterday and some today going over her. I will post more pics for sure, but these starters are for the scrap book. 

Peter

 

Beautiful Buick.  Love the color combination.  I also live in MD.  Maybe I can see the beauty one day at a show!  Enjoy!!!  

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So I've had a chance to go over it a bit and I want to sort out the engine as it runs a little rough I believe due to going from 7,000 feet above sea level to about 500. I tried backing the idle mix screws out 1/4 turns but no improvement.  I now have all 4 idle mixture screws out 1 and 1/4 turns and it still a bit rough.  Plan is to adjust them in and out to get the fastest idle.  Another option would be to hook up a vacuum gauge but I'm not sure if this works on a straight eight?? 

Next step is to adjust the valves as I think they could be a bit quieter and I've read it is imperative to have the engine warmed up completely.  I don't think all need adjusting so I may use a stethoscope to find the worst offenders. Any thoughts or suggestions? 

Peter

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Runs a little rough at idle only or all speeds?    Vacuum does work on the straight eight. There may even be a vacuum leak.  On the valves, warm it up by driving. 10 -15 miles.  Then use feeler gauge.  14 go,  16 no go.   Pull the plugs and inspect.

 

  Ben

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Thanks for all the kind comments.  

 

To answer your question Ben, she stumbles a little upon take off but then smooths out nicely.  

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 Peter, it depends on how the ports on the intake are. Mine had a mod long before I had it that allows me to put a vacuum gauge on it. On my engine is there a fitting on the area in between the two carbs that goes to the fuel pump (I think), which is where I'm able to get a gauge on. The other possibility, and one has to be careful, is to get a line on the end that goes into the fuel pump vacuum assist, and see how the manifold vacuum reads.

 Valve adjustment is tricky, I've found as it has to be at full operating temp, and with the cover off, and the engine off, the rockers cool very quickly, which tightens the clearances, due to the aluminum stands. I've done it with the engine running, which is messy, of course, and more hazardous to you.

 I'll tell you that it is tricky to get these engines set up so that you have a nice smooth idle. I've always been a pretty good setup guy, but this always challenges me. A air flow meter will help. I did it by feel for ages, and when I got the flow meter, it was much easier to get both carbs drawing close to the same. Sometimes tough to get them exact to each other, but close is usually good.

 The other thing that I've had issues with is the butterfly which is positioned under the rear carb. This makes the rear work like the vacuum secondary on a four barrel carb. When air flow is high enough, it opens the allow for greater airflow through the rear carb, but on mine, at least, it tends to stick in one position or the other. Also, unlike the heat riser valves, this won't mess you up, it just affects performance. If it is stuck open, you will have rough idle, if the carbs have been balanced with it closed. One and quarter to one and a half turns out on the mixture screws is a good starting point.

 Also, what about the heat riser, is it stuck?

 Also, as Ben said, how does it drive?

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All good advice. I use 0.017 go, 0.018 no go on the valves, this is what the Shop Manual suggests when doing the old run-it-and-then-pull-off-the-valve-cover-real-quick-before-it-cools routine. On the vac gauge, the manifold connection should be tapped for 1/8 MIP unless someone has messed with it. It will probably have an elbow which goes to the vacuum steel line. If you run into problems PM me, I think you are only a few miles away.

 

Cheers, Dave

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Thanks for the comments. Having trouble locating a good (or any) vacuum port. Would hooking up a tach essentially do the same thing? I could monitor RPMs while making adjustments. 

And is this thread getting too long?? Maybe I should start another one now that the subject has changed. 

Oh, and while I don't name my cars,  folks are pressuring me to name it Jessica Rabbit. Must be the wide whites..

Peter

41buick5.jpg

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8 hours ago, valk said:

And is this thread getting too long?? Maybe I should start another one now that the subject has changed. 

 

I don't think any thread on here gets "too long."  We're all interested in whatever you want to post.  But you might consider starting a thread in the "Me and My Buick" forum.  That way you can have a place to post any and all developments about your Buick going forward.

 

https://forums.aaca.org/forum/58-me-and-my-buick/

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I am committed to getting this car running as well as it looks. Been fiddling with the idle mix screws and I am in need of some detective work.  

After cleaning the plugs, I adjusted all 4 idle mix screws (2 carbs) 1 and 1/8 turns out. Ran it a few minutes, gunned it a little (not hard),  and idle was a little rough, some body shake, and so was coming off idle. Ran better at higher RPM. Pulled the plugs and found a wide spectrum of differences. The 4 plugs nearest the rear were really wet, almost as if the cylinders were not firing. Of course they were because I would have noticed if half the engine wasn't firing. Of the remaining 4 plugs, the 2 nearest the rear were sooty and the 2 most toward the front were actually good. So I'm figuring the rear carb is way too rich and is messing up not only the 4 rear cylinders, but also the 2 nearest them, and the main carb is set pretty good. Does the rear carb have a choke that could be stuck closed? I haven't checked that yet. Lucky for me I have fellow member Dave Stovall coming over tomorrow to take a look. 

Am I on the right track?

Peter

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Posted (edited)

You are definitely on the right track to have Dave coming over! 😄  As far as your questions, I'm not super knowledgeable about this topic, but unless you mean that you REALLY gunned it and actually drove it at high RPM, I don't think the rear carb would have had any effect on what you observed.  My understanding is that the rear carb is mechanically linked to only kick in at around 75% throttle or above.  You can observe this by just tweaking the throttle linkage when you are under the hood.  The rear carb doesn't begin to open until you've moved the linkage quite a bit.  Also, the manifold is set up so the both carbs supply fuel to all eight cylinders.

Edited by neil morse (see edit history)
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Another thought, Peter.  Do you have the shop manual?  If so, take a look at pages 6-38 and 6-39.

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Thanks Neil. I've learned both carbs work at idle but the rear doesn't do anything else until you jump on it. The rear carb also has no choke (I looked) so I think I just have the rear carb set too rich. I'll make a correction and check the plugs again. Regrettably, I don't have a shop manual yet but I do have portions of it. 

Peter

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From shop manual, p. 6-38: The outside barrels of both carbs feed cylinder Nos. 1, 2, 7, and 8.  The inside barrels of both carbs feed cylinder Nos. 3, 4, 5, and 6.

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Well that does muddy the waters...I'm going to give it try and see what happens. Hopefuly Dave will know what's happening. 

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Actually, I just plotted that out and that's a fancy way of saying the front carb feeds the front 4 cylinders and the rear carb feeds the rear 4 so I should be good. I'm just a bit puzzled why there was so much difference between the 2 carbs when they have identical settings. 

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I have a shop manual, and could scan a few pages for you, if it would help. Also, I have a Stromberg carb manual, if they are Stromberg's. Carter's were used as well, but most I've seen are have Strombergs.

 There is that butterfly under rear carb, you can see the counter weight on the side. That might need freeing up.

 But Dave might have all of this info.

 Let me know if there is anything that I do to help with.

 Keith

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Thanks you guys - much appreciated. Dave will be over in a couple hours and I'll chime in after his visit. 

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Dave and I gave it the once over and we were able to determine a few things.  The compression, timing, spark strength and firing order were all good but we could not eliminate all the fluctuation on the vacuum gauge by tweeking the idle speed and idle mix screws. The front 4 cylinders appear to be firing correctly but the rear 4 are still running very rich, even when the mix screws are leaned out.  We concluded that the rear carb may be the cause but noted a bad carb usually results in a lean condition as opposed to a rich one(?)  So the jury is still out...any ideas? 

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...and a hearty thanks to Dave for taking the time to come over to my house and check all this out.  Great guy and knows his stuff....

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You are welcome! One thing I noticed was the lack of the counterweight on the rear carb damper and according to the '42 shop manual it should be there. So that may be part of the problem.

 

Cheers, Dave

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