Tuning problem 235 six...need help

Hi guys. Got my '37 Chevy coupe up and running. Dropped in a 235, stock configuration for now. The problem is, I can't seem to get it to idle without choking the carb. I've adjusted the rockers arms, (made sure they weren't too tight...they're good) the spark-plugs are new, points are clean and gapped, the coil and resistor are fairly new, and the timing is close. I mention these things because I'm aware that rockers tightened too much, a weak spark, or bad timing can be culprits, so I tried to eliminate these possible causes before I got into the carb...again. In my experience, even though tight rockers can keep an engine from idling well, a weak spark will not so much affect idle quality, but will show itself in the higher rpm's...and this engine is running very well off-idle...very smooth and responsive...as long as the carb is choked. I naturally figured that the carb was probably to blame, (clogged idle circuit) or that I had a vacuum leak, so after attempting to eliminate the other possibilities first, I looked for vacuum leaks. I sprayed carb-cleaner anywhere there could be a leak, but didn't really notice any change in rpm's, except maybe when I sprayed around the intake at the head. I did notice my intake/exhaust manifold bolts weren't super-tight, so I cinched 'em down. The gaskets were new when I freshened up the engine. (Honed and re-ringed, valve job, new lifters, bearings, gaskets, rebuilt carb, and tune-up parts, etc. Finally, I reluctantly removed the carb and dissasembled it again...clean as a whistle. Cleaned it anyway. I did find a split in the small gasket where the choke-housing mounts to the carb-body, so I made and installed a new one. Reinstalled the carb, condition remains. Vaccum advance works, so I assume the diaphram isn't leaking. I did remove the vac adv line from the carb, started the engine while covering the port, then uncovered it, which should have made it run like crap...but I noticed almost no difference. This leads me to believe I do have a vacuum-leak elsewhere, but because I'm compensating by choking the carb, it didn't make any difference. Sound right? What doesn't indicate a leak to me is the fact that when I've witnessed vac leaks in the past, the engine doesn't come right back to idle after being revved, kinda "hovering" at a higher rpm. This engine seems to come back to idle ok. This lean condition shows itself at all rpm's...at idle and choked, ok...open the choke and it leans out and stalls...at higher rpm's and choked, ok...open choke and it leans out and runs crappy. Of course, running it choked like that is fouling my plugs, (all black and fuzzy) and I've had to remove and clean them 3 times. I'm considering replacing the plugs with new ones...again, but be aware that this condition was present even immediately after replacing the plugs previously. Concerning spark quality...I held one of the spark-plug wires away from the plug while the engine was running, and witnessed what seemed to be a pretty good spark...though maybe not as snappy and blue as it should be...maybe a little too "pinkish orange". Maybe I need to replace my coil and/or condensor.

Well, I've tried to provide as much info as possible. I know you guys will tell me if you need more. It's a difficult thing to diagnose long distance, and as my old buddy Roy Montgomery says, "One thing I've never learned to do is see over the phone." Hahaha. But a lot of you guys are pretty darned good at it, (stroke) I've seen y'all in action, and I look forward to your input. I can usually sort this stuff out myself, but this one has me scratchin' my head. I thank all of you in advance. Rick

 

Waitin' for any help guys...thanks. Rick

 

Thanks for responing, 440roadrunner!.....No bad fuel, had crap in the tank, was getting crap in carb, replaced orig. tank with my boat tank for now and cleaned everything, condition was present before I installed engine in '37 though. Low float level maybe!...carb was rebuilt years ago and sat, not sure of the rebuilder's expertise. Float level did cross my mind, but didn't think it was a likely culprit...will check. May end up removing intake to check. I did blow through orifices with compressed air after carb clean, air seemed to flow free...not saying I'm 100% confident with carb. I may end up putting on another carb to check. Thanks man. Rick

 

One last request for additional thoughts...anybody? Thanks again. Rick

 

could be a condenser being that you did not replace it... I did a tune up once without replacing the condenser, the thing ran rough, replaced it and all was good.........

I have also found that in most cases, a carb is the last thing to look at..but I am no expert.....good luck

 

Thankyou, sun down. For as easy and cheap as it is to replace the condensor, I should've done that first. I better try it. Thanks again. Rick

 

Just if it was me...

1. Check (THOROUGHLY) for vacuum leaks. Nothing idles good with a vacuum leak
2. Open up carb and check for crap. You said there was crap in the tank, it could've made it up the needle and seat.
3. Listen to the exhaust... if it has a good rythm to the miss, it's running to rich, if it's popping when you rev it and let off, or the miss at idle is uneven and "splashy" it's too lean.

You said that the carb had sat for a while... you may want to throw another kit in it.

With a background in British cars (i know, i know), i'd agree with sundown as that's the LAST place you should look... but with you saying crap in the tank, and an old rebuild... i'd say it could very well be the culprit.

Best of luck.

-Chris

 

RU sure it's a lean condition? If so, I concur the float level may be a part of the trouble. Can you stall the engine by closing the idle mixture screws? If not, you're seeing a definite problem in the carb (although this may not the primary issue).

Have you, or can you, run a vac gauge and monitor engine vac? RU sure the vac port is clear?; the vac hose is clear and not collapsing? Can you see the timing advance? Finally, have you checked the dizzy shaft bearings?...in line chevy 6's have been known to develop a shaft wobble at the oddest times and conditions.

 

did you straight edge the manifolds??
put the o rings back in??
leaky hose or wipers?

not related but why not hei the ignition so you can run 080 gap plugs and fire that lean mixture
a 6 cyl dist and some lathe work and grind a oil pump tang would give you much more fire

 

Chris - Yes...I think I still need to check THOUOUGHLY for any vac leaks. I'll remove intake if I need to. (check for cracks) I think the carb is clean, and the pollution issue is resolved. (key words - "I think") And as far as British cars go, we're still talkin' the same language...tuning.

rodsnhawgs - I'm quite sure that with the choke off, it's runnin' lean...when I choke it, the rpm's come up some, and she smooths right out with good acceleration. Of course, then my plugs start fouling after running it for a while with the choke on. I'm gonna look real close at my float-level. The idle adjustment screw will stall the engine if adjusted to much less than 1 1/2 full turns off the seat. But it doesn't seem to richen that much if I unscrew it a lot....??? The vacuum line is steel, so it's not collapsing, and I remember seeing the dist. turn when revving, so I guess the vac adv is working...will double-check. I'll check the dist shaft bearings too.

Thanks fellas. I don't take lightly the time and effort you spend to help me ponder this, and will get back to you with results, 'cause it's good to share in small triumphs............Rick

 

440roadrunner - I actually don't believe it's ignition either, but will check anyway. It doesn't really have the ign symptoms I've seen before...it runs good with the choke on...doesn't "fall on it's face" at higher rpm's, and good acceleration. It was just that I wasn't super-impressed with the spark-quality, but seemed sufficient. It'll arc from the terminal to the plug up to a distance of about 3/8" to 1/2" or so.

eugene vik - I assembled this engine a few years ago, and I'm not sure that I straight-edged the surfaces. But I usually pay pretty close attention, and I'm aware of what can happen to those inliner manifolds, especially having had a few Buick straight-eights! So I believe that I probably held the intake up to the head to check. I'm sure I installed the rings, in-fact, I think I remember making one or two that I lost. Not ruling it out, though. The wipers aren't hooked-up yet, and the wiper-vac-port is plugged for now. Regarding adapting an HEI dist, it's a good way to go, but later maybe. Need to get'er runnin' good with stock components first.

Many thanks guys. Rick

 

One thing I may have missed; Have you ever had this running well or are you just getting it going for the first time? I think you mentioned before something about "before it was in the '37" or something.

I'm curious because I worked on a 235 once that had a leaky carb (1 BBL Carter) so I bought a rebuild kit, and put it all back together. Well, the kit came with two completely different needle/seat assemblies...at least I think it was the needle and seat but it was a few years ago so my memory about it isn't great...anyway, whatever the piece was, I replaced it with the one that was identical to the one that I had taken out. When I got it all back together it still leaked. I took it apart again and put the other needle in there and it was fine...
Long story short, maybe whoever built the carb did something like that, or used the wrong gasket and it's covering an orifice, or something.

 

Maybe the mtg gasket to the manifold...does it have notches in it for vac ports??Does the intake man. have pilot rings in the head ? Still sounds like a vacuum problem...Windshield wiper hose leaking? Good Luck...

 

I'd rebuild the carb again anyways! regardless if it has been "rebuilt" by somebody already. One of the main jets could be plugged with crud coming from the tank again. I had this same issue by having to run the choke on an international truck i had with a 6cyl and tore the carb down to find one of the jets plugged. make sure to run an in line fuel filter before the fuel pump after you rebuild the carb to make sure this does not happen again...if this is indeed the problem. Good Luck

 

Blow out the carb good - all the passages, and rebuild it good. Use a good fuel filter before the inlet. I think your carb has junk inside, or maybe just some dirt form sitting. They are sensitive to being crapped up. Clean the carb.

 

Thanks Deyomatic...Thanks RCR...Thanks belairbubble...all good thoughts. I appreciate it. I freshened-up this engine a few years ago, to put in the '53 Chevy pickup, and the carb was rebuilt for it, then it sat. I just recently decided to "steal it" for my '37. Carb base gasket does in-fact have the slots. Carb is clean as a whistle as far as I can tell. In-line filter is in-place, right before the pump, and pump has the handy-dandy sediment bowl...or as some of the old-timers say, "settlin' bowl". Today, I be-a-lookin' at all we've discussed here. Thanks, guys. Rick

 

What carb are you running? The Rochester Model B has a snatch idle circuit that feeds fuel across the top of the throttle bore and down the verticle idle passage to the idle and off idle ports. If this passage is clogged or restricted, too little fuel is delivered. The choke only speeds up the velocity of the air entering the carb. This enhances the siphon effect of the venturi. This is why plugs foul from too much fuel. When You disassemble the carb check for this passage being clogged or restricted.
I hope this helps.
Buffalotrux
Keepin em inline since '53

 

one thing you will find out about the old single barrel gm carbs is they really didn't have much of a idle circut. i have been through enough of these carbs to honestly suggest going to a newer holley 2300 that langdon offers. combined with hei ignition you will notice big difference. you can do your own hei for under $ 50 bucks. do a search as i did a tech article on it or use gmc bubba's conversion as both will work.

 

Are you sure all the intake tubes were installed in the intake?

 

yeah i had a 49 chevy with a straight six and it was giving me similar problems. Looked down the carb, wasnt squirting enought fuel, thought it was a weak fuel pump(factory mechanical) so i replaced that nothing worked. so eventually took the carb apart AGAIN and really worked the fuel inlet with some pipecleaner and an air hose and it ended up running mint. so i would double check that especially if there was crap in the fuel tank, even if u cleaned it before, there could still be something in there. the problem wouldnt be ignition. if it was. it wouldnt matter if u choked it or not


good luck post the result

 

Hey, 38Chevy454...I'll bet you did a search for '37 and/or '38 Chevy...and found me. Well, I've clean the carb good a couple of times, and all dirt is gone, but I still don't rule out the possibility that some stubborn varnish remains from sitting so long...I doubt it, but maybe. Thanks much for input........now I'm going to your profile, and see if I can take a look at that 454 '38 Chevy! Rick

 

Can't keep up with you guys...Great! Hey buffalotrux...now you're talkin'! Yes, it is the Rochester...didn't see if it's a model "B"...will look. It's got the kinda fat bowl, with an exterior hard line running from the base to the upper portion of the carb. Is this part of the "snatch idle circuit" you refer to? (that's a new term for me) It actually sounds like you are referring to an internal passage though. You were quite specific, but if you can expound further, or "draw me a picture", it would help. Regardless, I basically understand though, and when I dissasemble the carb again, I'll look for the passage and port, though I thought I cleaned her but good...(cleaned her butt good?!!?) That exterior line I spoke of seems a little loose at the base. I actually temporarily (just for a few seconds) stuck some chewing gum there, but made no diff. I know...I shouldn't use gum on my carb...'cause it makes the gum taste funny. 55 dude, I will look at upgrades after I get this thing runnin' right with the stock stuff. Thanks for all the input, gentlemen! Rick

 

Can't keep up with you guys!...Great! '38Chevy454, Thanks. Hey buffalotrux, now you're talkin'! Yes, it's the Rochester carb...didn't see if it's the model B, will look. It has a fattish bowl, with an exterior hard line running from the base to the upper portion. Is this part of the "snatch idle cirtuit" you speak of? This line seems a little loose at the base, and I actually temporarily (just for a minute) put chewing gum there...no diff. I know, I shouldn't put gum on my carb! (It makes the gum taste funny.) It actually sounds like you're referring to an interior passage though. You were quite specific, but if you can expound more or "draw me a picture" it would help. I thought I cleaned her but good, (cleaned her butt good?!!?) but when I disassemble it again, I will look for the exact thing you refer to. 55 dude, I will consider upgrades after I get'er runnin' decent with the stock stuff, though I am just about ready to get another carb to test with. Thanks gentlemen for all the input. Rick

 

Can't keep up with you guys!...cool. 38Chevy454, cleaned carb more than once, but not ruling out some deep-set old varnish. Hey buffalotrux, now you're talkin'. Yes, it's a Rochester, didn't see if it's the model B, will look. It has a somewhat fat bowl, with an exterior hard line running from the base to the very upper portion. Is this part of the "snatch idle circuit"? This line seems a little loose at the base. I actually temporarily put chewing gum there, but no diff. I know...I shouldn't put gum on my carb...'cause it makes the gum taste funny. Sounds like you're referring to an interior passage though. You were quite specific, but if you can expound further or "draw me a picture" it would help. Regardless, when I take the carb apart again, I will look to see exactly what you mean. I thought I cleaned her but good, (cleaned her butt good?!!?) but I'll look. 55 dude, I will consider upgrades after I get'er runnin' reasonably well with the stock components, though I'm just about ready to get another carb to try. Thanks gentlemen for all the input...I'll let ya know. Rick

 

Wow...those first two posts of mine didn't show up until I submitted for the third time! HA!

 

No wonder...they were on page 2! aaaaarrrrgghh! I'm learnin'.....Rick

 

Thanks oneratfink57. I'll look....................back to the garage. Rick

 

What carbs are you running? We had a similar problem with my wife's car, only it idled really fast. Eventually we figured out that this screw was actually a valve of some sort and it was loose. Once we got it adjusted, the car ran fine.

 

I feel your pain! I've got two of these carbs on my 235 with a fenton intake. Got the front carb dialed in perfect. Still fighting the back one, but getting close. The car runs ok, just an intermittant small stumble off idle. But I've only been tinkering on them a week.

I'll be watching this thread, I've already learned a lot. Good luck!

 

Hellfish - those carbs are similar in size and shape as mine, but not quite the same. I have one Rochester that looks a little older than yours...no screw on top. davidparker - So we're both messin' with our carbs...and you've been fiddlin' with it for only a week...hahahahahahha...in no more than a month, we'll have it!!!...........It sure does help having some others to help, even if only for moral support! And no matter how long we've been doing this stuff, sometimes you miss things. 100,000 heads are better than one!

OK, so I think I've narrowed it down to two problems...when spraying some starter-fluid/carb-cleaner here and there, I noticed a rise in rpms when I sprayed around the base of the carb...a leak...maybe a bad gasket. Also, in spite of the fact that I said the idle adjustment screw was working, and I could swear that it was...it was...it is not now..........I now turn the screw all the way in, and the engine doesn't stall!....I unscrew it and take it out and it continues to run!...........idle circuit clogged I guess. Time to take the carb apart again, clean it really really good, and maybe try a new base gasket. You know guys, that carb has a thick phenolic...? spacer under it in addition to the thinner gasket. Has anybody had experience with these things becoming pourus? Back to the garage. Thanks fellas. "I'll be back". Rick