Tuning problem 235 six...need help

Hmmm... my old 235 started having idle problems. I detected a VERY slight chnge in RPMs when I squirted fluid at the carb base. I sealed the base with RTV and the car idled fine. Yeah, kinda hillbilly, but I was selling the car and was done messing with it.

 

Not sure that those spacers are Phenolic. They appear to be a composition of asphalt and probably asbestos . Therefore, wouln't suggest that you "fix" it by sanding it back flush...which could be your problem. They take a lot of heat off of that exhaust heated manifold and could warp. More likely they are chipped and or cracked. Time to try some new supple gaskets maybe?

I have rebuilt quite a few Rochester Model B's. I use old GM literature to do this. The NAPA kits contain parts for a wide range of applications. There are usually multiple gaskets provided for the air horn to bowl. Wrong gasket will affect operation. These are also NOTORIUS for warping at the air horn. This may be the cause of one of your vacuum leaks and result in pretty crappy performance. You can check with a straight edge. I have a jig to fix this warp. Requires baking in the oven (not microwave!). Better make sure that one's spouse in not around when you do this! Welcome to borrow it if you need it.

Tom

 

Everybody...Halt! I believe you can all stop spending time on little ole me! Who all said it was a vacuum leak?...........a vac leak it is!....at least in part, and I think it's the entire problem. By spraying around with the carb-clean, I did notice a rise in rpm's as I sprayed at the base of the carb. Then carefully, with little shots here and there, I was able to pin-point the exact location of the leak. Double...triple-checked...yup, right there. Set the can down, put my finger there, and heard a little air "whoosh". Pressed hard with my finger to basically seal it, opened the choke, and what do you know...it idled. Pulled my finger off, with choke still open, and it stalled as it had been doing. Pulled the carb off, all the while thinking that ok, I've found a leak, but the idle-screw is not working, so buffalotrux is probably right that my idle circuit is still clogged. So I'm looking closely at the location of the leak, and I can see that it's right at the slot in the gasket that lines up with the little vac port in the base that apparently feeds the vac signal to the idle circuit! I think this explains why this particular vac leak had me confused...it's small, which made it hard to find, and didn't make the engine slow to come back to idle after being revved up as most other vac leaks have done that I've been witness to. But...being right at the idle-circuit-hole, it of course had a very negative affect on the idle quality...the port was not getting its full vac signal. I'm hoping that this is also why adjusting the idle-mixture-screw didn't do much. Also, the thick spacer I was using is pretty old, and I found a crack in it right through the mounting hole. It took very little pressure to break the tip off...another leak. So, tomorrow I will buy a new spacer and gasket...mount the carb, and see what happens. It cracks me up that after I found the leak, I come back to the house to tell you guys, so that you don't keep having to brainstorm for me, and there's a post from you, 1931av8...and you hit the nail on the head. Your statement that these are "notorius" for leaking at the base shows that you've got experience. Nothin' like experience. The problem is, some of us older guys start forgetting some little things we've learned, and it's been quite a while since I've messed with a Chevy and those darned two-bolt carb bases! What I should never forget though, is to never mess with old gaskets. They are too inexpensive not to replace...comes from me being too cheap and maybe lazy. Hey buffalotrux....you really gave me a big hint when you schooled me about the config. of the idle circuit. As soon as I determined that the leak was at that hole, I realized that's what you were talking about. I took the spray-straw from the carb-cleaner, and put it in the hole...yup, it goes waaaay up there. You helped me realize what was going on. Thankyou. And thankyou to all the rest of you who posted. Every single one was a help. I love it. Now normally, I would wait till I got it runnin' good before I came to you guys and said "Yaaaaaayyy!!!...Yahooooo!!!...but I can't finish it tonight cause the auto-parts-store is closed now, and I wanted to let you all know that I think we can stop straining our brain-cells. I'm pretty confident that we've got it licked. I would show pics, but haven't learned to do that yet...I'm a gonna though. Thankyou, thankyou, thankyou, all of you. I'm going to PM every one of you who took time to post your thoughts for me, and let you know the final result. Jeez guys, I can't say enough about the HAMB and how it brings us all together. Nothin' like people helping people...makes me a little misty even. Oh...I think maybe it's just the carb-cleaner...............Rick

 

Well alright! BTW..a little clarification on the dizzy deal - As the shaft wobbles, it causes the point dwell angle to change which results in the timing dancing around when reading it on the balancer. It'll sure mess with the performance esp at low and off-idle rpms.

 

Thanks rodsnhawgs...I did understand what you were saying. I can see it. By the way, obviously you came back to check my progress. You're a good man. Rick

 

Rick:

Glad that you found the problem and that "all is well that ends well"

Tom