The awesome Rochester Monojet...

Discussion in 'Troubleshooting & Diagnosis' started by Don F, Nov 30, 2017.

  1. Don F

    Don F New Member

    Nov 30, 2017
    I guess I've been lucky after owning 27 cars or so that I've never had even a minor carb problem... but I somehow actually fell for a 1976 Camaro (stored for 30 years with much of it still looking pretty nice and original) and I now must live with the stuff that happens with a 41 year old car that has had chunky stuff in its fuel lines. And you'll probably think I'm even stranger when I say I've actually grown to like the boat anchor 250 six (less tickets than with my LT-1), so I'll just get on with it.

    When I bought the car, it started and ran reasonable well, with just a hint of hesitation when you hit the gas from the one-barrel Monojet. Unfortunately it had a nasty flooding problem after being driven more than 5 minutes. So last week I removed and rebuilt the carb (my first time), and I cleaned it thoroughly and was pretty proud until I found I did solve the float bowl flooding -------- but now there is a huge hesitation problem and the fast idle has also stopped engaging.

    Can someone tell me some of the fundamentals of carburetor function? If I am screwing in the adjustment screw, am I reducing air or fuel? Could the adjustment of the needle valve that goes into the jet in the float bowl cause a lack of fuel if its mounted too tight (too low)? The stats say to adjust needle 5/64 above the top of the mid-carb body, but it was previously adjusted 5/32 (and ran fine), so i compromised between the two. Could that be the problem?

    And is there any way to tell if this hesitation and lack of power is for sure fuel rather than air problem?

    I'll add that their are two filters (the fuel inlet one new... I'm trying to replace the other but there's only three inches of flexible fuel line). But I don't think dirt or inlet restriction is the problem.

    Thanks in advance for any help you can give!
  2. budro6968

    budro6968 Veteran Member

    Apr 2, 2016
    Jax Florida
    Try find some pic's of an assembled Carb. You probably have the linkage upside down or backward. I remember doing one many moons ago I think it was my 1st too. I got the linkage on wrong and it would start and scream on high RPM. The hesitation might be the Accelerator pump is bad or got damaged in the rebuild. A buddy of mine put a Mono-Jet on a VW rabbit. That was cool. That thing could burn tire in 3 gears.
  3. Gary S

    Gary S Administrator Lifetime Gold Member

    Apr 14, 1999
    Bismarck, North Dakota
    Years ago I had a Chevy pickup with a 292 6 cylinder and a monojet. When I got it, mine had a hesitation off idle too, and sometimes would even backfire when it hesitated. It would also occasionally overflow with gas. I took it apart and found that the previous owner had removed the fuel filter and allowed crud into the carb. I cleaned the bowl and float and that solved the fuel overflow problem. I also noticed that when I opened the throttle, the gas stream from the accelerator pump looked weak. Tearing it down farther, I found a tiny piece of that unfiltered crud had lodged in the passage for the accelerator pump. After cleaning that out and putting it back together, that old monojet ran like a dream for as long as I owned the truck.
    In my experience with carbs for the last 50 years, almost all carb problems are caused by the owner of the car who doesn't know what he is doing and messes with or "tunes" the carb. On mine, the carb would never have had problems if the fuel filter had not been removed.
  4. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

    Nov 4, 2004
    Ringgold, GA
    First off, welcome to NastyZ. :)

    It's been years since I've touched the mighty one barrel on a I-6. Unless that's an inverse circuit (don't think so), idle screw controls fuel, so in is less/lean, out is more/rich. The best way to adjust idle mixture is with a vacuum gauge. Float level can cause tip in stumble and affect idle, usually to a lesser degree. You need to replace the filter to ensure you have a good flow of fuel coming into the carb. One of the major causes of carburetor problems is vacuum leads. Check all your hoses and fittings for leaks.

    There are a lot of resources available on the web related to adjusting idle. You're probably not going to find much on that specific carb, but the principle will be the same.

    As for the linkage, find a picture or diagram and make sure you have it set up correctly. Good luck with your new project.
  5. Don F

    Don F New Member

    Nov 30, 2017
    Thank you all for your suggestions, and for the welcome. Love that yellow '70 SS, Gary ! (couldn't see it on my phone). Going to pull the carb off this weekend, replace the old second (add on) filter, pull the accelerator pump, clean the passage again, and possibly replace it. Mike at Mike's Carb, where I bought the kit and brass float, agrees the accelerator pump shaft should be stiff, not loose between the rod and plastic bottom.

    I will also check the vacuum hoses, since it has as many as a mid-'80s car, what with the CA smog pump. And there is no vacuum line diagram... yikes.

    Here is the car so far, amazingly like new below the mid-line, few spots of surface rest above, especially the hood, which I will likely replace but I will do my darnedest to save most of the original paint. Documented 85,000 mile and the long storage IMG_0839.JPG
    IMG_2842SMALL.jpg IMG_1169.JPG IMG_1180.JPG

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