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Thread: Chasing vacuum leak, carb cleaner kills engine?

  1. #21
    Just Some Dude in Jersey The Scifi Guy's Avatar
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    I never liked those vacuum trees on a GT. The close proximity to the heater box forces a sharp bend in the brake booster hose, which can cause it to leak. Other Opel models have way more room in that area. The last time I had a stock manifold I removed the tree, tapped the hole to the closest NPT thread, and screwed in a big T-fitting from the hardware store. Then I added various reducers and barbed hose fittings for the 3-4 things that needed vacuum(Brake booster, vacuum gauge in the dash, and auto tranny modulator. My engine didn't need vacuum advance.) Now the brake booster hose ran straight to one side of the T and the other side of the T went to the auto tranny. I spliced a smaller T fitting into the auto tranny hose to feed my in-dash vacuum gauge.

    The nice thing about the vac gauge in the dash, where the clock used to be, was that it would let me know if a vacuum leak was starting to develop, which would happen about once a year when I drove the cars every day. I had a vacuum gauge in all my GT's for 30 years, including the wiz bang GT I have now.


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  3. #22
    Just Some Dude in Jersey The Scifi Guy's Avatar
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    Quote Originally Posted by mbasura View Post
    The screwing in or letting out the idle mixture screw had no effect on the engine timing.

    Probably you misspoke, but, of course, turning the idle screw wouldn't affect engine TIMING. You probably meant to say "engine running".

    Go back to whatever the baseline idle speed and mixture screw settings are supposed to be and maybe fiddle with the dizzy to adjust the timing to work with things at those settings.


  4. #23
    Opeler
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    Chasing vacuum leak, carb cleaner kills engine?

    Question for the readers. Could the vacuum leak be tied the the A.I.R. ports?

    The vacuum gauge reading and the Weber troubleshooting guide indicate a “manifold leak.” I have tightened and re-tightened the bolts and no indication of a leak there.

    I am wondering if the remnants of the 1969 only (as far as I know) A.I.R. System could be an issue? The AIR pump was corroded solid and went straight into the trash. I cut and crimped the metal tubing but left the ports in place. I figured it didn’t matter much if they were not closed completely as it was exhaust. Is this notion correct or is there a way these exhaust ports could be part of the vacuum leak issue?

    And a clarification. SciFi guy is correct, I should have said the the mixture screw was not affecting the speed of the engine, not the timing.

    Matt

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    Last edited by mbasura; 4 Weeks Ago at 10:38 PM. Reason: Adding info

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    Senior Member The Cub's Avatar
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    Quote Originally Posted by mark1 View Post
    I've had a number of vacuum leak issues with my Mini. A couple of times I got some good information by taking it to the one shop in the area that has a smoke machine. I'm not sure how well it would work on the Opel with a carb, but if it really is a vacuum leak, running a smoke test might give you a clue. I'd also thought that there might be some way to rig a "smoke in a can" (the type used for smoke detector testing) for a crude DIY smoke test, but haven't had the need for a smoke test since the last time I had it done with the commercial rig.
    I’m a true believer that is the best way to find it or them. Absolutely no margin for error. I think because the Opel is so simple there’s not much interest. I agree wholeheartedly with you. I used an alternate method 3 psi of air pressure and soap bubbles only to find my worst offender was the throttle shaft. That’s what got me to finally spring for a new carb. Problem solved though. Your problem may be internal with the carb. Did you try taking out the idle jet and blowing compressed air through to clean out the idle circuit?
    Last edited by The Cub; 4 Weeks Ago at 09:01 PM.
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    Senior Member The Cub's Avatar
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    No mention of the smog pump on the accompanying thread I don’t think. Just be sure you have everything sealed off on the intake manifold, whatever it takes then read the attached if all else fails. If your vacuum is that low. My next step would be to check the cam timing. Some of the legitimate mechanics on here are better at explaining how to do that than myself or may have a different suggestion, it’s just what I would check next. There’s a 22mm timing chain tensioner bolt on the passenger side of the timing cover that gets backed out to adjust the chain if it’s off a tooth, the chain should be tight enough where you would have to do that if it’s not overly stretched or worn. The how to to check it is easy. I’m pretty much all stock on my GT & I’m able to get a 19mm wrench on the crank bolt to line up the timing mark on the flywheel after I get it close with the starter. Here’s a good how to link to read through on the subject if you haven’t read through it already.
    https://www.opelgtsource.com/system/...pdf?1540359732
    Last edited by The Cub; 4 Weeks Ago at 11:29 PM.

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    I'm not sure what's right for you, but at this point, if it were me, I'd pull the carb off the motor, tear it down, and give it a good cleaning & inspection. If you're not showing any leaks with the smoke, and the idle screw is doing nothing, it might be you'll see something in a tear-down & clean that's an obvious culprit. Worst case is that when you're done, you're absolutely sure of the state of the carb because you did it yourself.

    Maybe one last thing to check before that, although I'm sure you've done it, is to make sure the throttle stop screw doesn't have the throttle cracked open a bit too much for the idle mixture to do anything.

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    Opel Rallier since 1977
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    Good deal on the rigged smoke machine, OP.. I like that. Where did you introduce the smoke? If through the carb, then that misses one area of problems. BTW, the vacuum INCREASING at idle is what you should see as you eliminate leaks in the intake system so that is good.

    Do you have a stock cam or mild cam? If so, and you have gone from 2" of vacuum in the intake manifold to 6" of vacuum, you have eliminated a gawd-awful vacuum leak but still have a very bad vacuum leak, or some other non-trivial problem. No wonder the engine ran with the idle screw closed, and dieseled to boot! With everything sealed up well and tuned right, you ought to have 15" or more of vacuum on a stock engine at a low idle RPM.

    Now I am assuming that your vacuum gauge is connected to the intake manifold itself, not to ported vacuum on the carb. You say the gauge is connected to the vacuum advance on the distributor. Make sure the vacuum source you are measuring here is from under the base of the carb. Intake manifold vacuum levels are what you use to use vacuum signals to diagnose leaks, and that is what that Weber info is assuming.

    OBTW, re-check your hose connections and adapters to the gauge to make sure there are not leaks there. Get rid of any tapered push-in adapters that may leak. And it never hurts to check your gauge against another one.
    Last edited by Manta Rallier; 4 Weeks Ago at 01:57 PM.

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    Quote Originally Posted by mark1 View Post
    Maybe one last thing to check before that, although I'm sure you've done it, is to make sure the throttle stop screw doesn't have the throttle cracked open a bit too much for the idle mixture to do anything.
    Exactly! Either butterfly could be hung open a bit and it will drop the vacuum levels. Smoke testing through the carb will not show this.

    There is a secondary stop screw, and the linkage and operating parts of that portion of the carb, which could be hanging the secondary side open. And if the primary idle screw is open too far, then the idle mixture screw will become ineffective. Check your throttle linkage to be sure it is not binding the primary side throttle open, and make sure the linkage adjustments are such as to let the primary fully close.

    This is tied up with ignition timing; retarded ignition timing will force a more and more open primary idle speed screw. (But I cannot say that I have seen vacuum levels drop to anywhere like 6" with just this.)

  11. #29
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    Chasing vacuum leak, carb cleaner kills engine?

    Quote Originally Posted by Manta Rallier View Post
    Where did you introduce the smoke? If through the carb, then that misses one area of problems.

    Would it make any sense to introduce via the intake tree fitting?

    Do you have a stock cam or mild cam?

    Now I am assuming that your vacuum gauge is connected to the intake manifold itself, not to ported vacuum on the carb. You say the gauge is connected to the vacuum advance on the distributor. Make sure the vacuum source you are measuring here is from under the base of the carb.

    Thanks for the feedback.

    The smoke was introduced with a hose into the carb primary throat with the throttle plate held open.

    Would it make any sense to introduce via the intake tree fitting?

    Stock cam.

    I had the vacuum gauge attached to the carb base, where the vacuum advance hose is usually attached.

    I moved the vacuum gauge to the intake tree fitting and got a bit more vacuum, maybe up to 8 in/hg.

    I checked the throttle plates and they look like they are not hanging up. Moved the mixture screw and the idle screw a bit and still can’t get the idle up much above 700 rpm.


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    Last edited by mbasura; 4 Weeks Ago at 07:40 PM.

  12. #30
    Opel Rallier since 1977
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    How much is each throttle plate open when the engine is not running? It ought to be just a hair open on each. You might have to pull the carb off to really see this. The mixture screw not responding would be typical of too much opening of the primary throttle plate; if too open, then the carb will be working off of the transition circuit.

    Smoke down the carb will not tell if the plates are hanging open too far. But if you put it in under the carb with the plates closed, and closed off the carb throats from the top, and got a few psi pressure in the intake (like described) then you might get better results.

    Looking back through your posts and the symptoms, your first symptoms are consistent with a very bad vacuum leak. You could not get the idle above 500 RPM with the idle screw backed out at all from 'max open'.....bad leak! Now it sounds like it is better so and the increase in vacuum from 2" to 6-8" shows that. But the idle screw too far in says for sure that the primary throttle plate is too far open; that will be part of the reason for low vacuum levels. Try backing out the idle screw a bit (closes throttle and moves the carb more into the true idle circuit operation), and then turn the mixture screw in a bit (richer)to see if it helps the idle quality.

    Just to be sure: What mark are you using to check ignition timing? What year engine/car?

  13. #31
    Senior Member The Cub's Avatar
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    It looks like you have some good help with your possible vacuum leak. After you’ve exhausted everything and I would double check the calibration of your vacuum gauge the low reading would have to indicate a significant vacuum leak. Unless this smog pump plumbing goes from the intake right into the exhaust (where it might mask the visibility of the smoke) I’d think a leak that big would show up. I don’t hear Mant Rallier picking up any cam timing issues so I could be off. Here’s a suggestion someone else made to me a while ago if you don’t want to lift the valve cover off. “A simple test to check if the cam is retarded by one tooth(9°).
    Take the air cleaner off the carb..rev the engine up.
    If there is fuel vapor, mist...coming out of the carb throats backwards....the cam might
    be a tooth out”. HTH

  14. #32
    Opeler
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    Thanks Manta Rallier and Cub

    The car is a 1969 with a 1969 engine.

    I will work more with the smoke and see if I can get it to indicate any issues with the throttle plate. It looks closed, but so hard to tell fm the top.

    I set the timing using a method I saw on opelgt.com about rolling the car back and forth in fourth gear. Essentially you lock down the distributor when the rotor sparks at TDC. It seems dead on. As a check i advanced the timing a bit and the car was not happy, wouldn’t start at all.

    I have seen fuel and vapor coming back up through the carb, but it is hard to isolate the cause. Usually it is after messing with the car, revving, killing the motor, messing with the idle mixture, etc.

    Matt


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    I am not at all keen on that method of setting timing... too much possible inaccuracy in the observations. With all your troubles, you really need to get a timing light and use that. Honestly, the engine behavior sounds like the timing was retarded instead of advanced.... turn the distributor CCW to advance and CW to retard.

    The vapors out of the carb throat after stalling may be a sign of excess fuel leaking into the carb and running overly rich. (Or may not...) Are there any spitting or mild popping sounds out of the carb throats when it is running? Any drops of fuel seen dripping out of the booster venturi's in the carb throats?

    Does this carb have a choke? And what ignition system?

    What prompted the carb rebuild? With that rebuild, there could be some things amiss like the float setting not correct. That setting is VERY critical to all phases of carb operation.
    Last edited by Manta Rallier; 4 Weeks Ago at 10:42 AM.

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    Senior Member The Cub's Avatar
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    Quote Originally Posted by Manta Rallier View Post
    I am not at all keen on that method of setting timing... too much possible inaccuracy in the observations. With all your troubles, you really need to get a timing light and use that. Honestly, the engine behavior sounds like the timing was retarded instead of advanced.... turn the distributor CCW to advance and CW to retard.

    The vapors out of the carb throat after stalling may be a sign of excess fuel leaking into the carb and running overly rich. (Or may not...) Are there any spitting or mild popping sounds out of the carb throats when it is running? Any drops of fuel seen dripping out of the booster venturi's in the carb throats?

    Does this carb have a choke? And what ignition system?

    What prompted the carb rebuild? With that rebuild, there could be some things amiss like the float setting not correct. That setting is VERY critical to all phases of carb operation.
    I agree with all the above, retarded ignition timing would also cause low vacuum readings (a better problem to have) your engine would more than likely run hotter. Using the timing light with your vacuum lines plugged off is the only way to go. If you get the ball & pointer lined up at 8-900 RPMs you’re right in there, you’ll probably want to advance it a little more later. If the timing light drifts you may have spring issues inside of the distributor but let’s not go there yet I’m just pointing to a common problem at idle speed with older distributors. Most of the time engine trouble on the Opel CIH is either on the carburetor or the distributor side. Here’s couple of links to compliment what Manta Rallier said about the carburetor adjustments. I didn’t mean to interrupt here because he asks some good questions.

    Weber CARBURETOR SET UP AND LEAN BEST IDLE ADJUSTMENT
    https://www.piercemanifolds.com/category_s/317.htm

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    Thanks again Rallier and Cub, please keep the feedback flowing, my base of knowledge with carb adjustment is low, so all advice is helpful.

    Well noted about the timing light, it was starting to dawn on me too that I was relying quite a bit on the tach for info which may not accurate. A trip is in order to Harbor Freight as I think I may have blown my vac gauge messing around with the car yesterday anyway.

    It will be an easy check for me to try to retard timing a bit and see if there is any effect. The note about the engine running hot is interesting. See note about fuel boiling below.

    Here are the answers to the questions.
    The carb was retrofitted last year with an electric choke. Power comes via the horn wire.

    The ignition is a Bosch coil, running the original two wire set up (resistor wire and 12v). This was replaced last year as well as a new cap and rotor.

    The root cause of the issue that prompted the carb rebuild was heavy dieseling. This was overlaid by a serious fuel boiling issue that cropped up once I put the hood back on (the hood was off the car for months while I worked on brakes and other parts).

    Fuel boiling issue seems to be in check with re route of fuel line and insulated shroud.

    No noises that I can hear at carb other than a distinct hiss of air.

    Currently, i can coax about a 700 rpm idle out of the car with a combination of idle mix screw and idle setting screw. Car starts hard at this setting but idles steady once fired. Once on the road, it will hesitate and often die once rpms drop once you let off the gas when shifting or approaching a stop sign.

    Matt



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    One more setup question OP: Is this the stock points distributor?

    And as for the retarded timing causing hotter running: It may leave the fuel burn less complete, so a bit of unburned fuel gets in the exhaust and gets burned there. It also makes the engine efficiency lower (less torque/power to the crank) so the energy released has to go elsewhere in the form of heat.

    Retarded timing was put in these engines in this era mainly for emissions compliance and nothing else. The problems of hot running sprang partially from this, compounded by higher thermostat temps (for emissions too). The issue of dieseling is also exascerbated by retarded timing; the torque pulses at idle from the engine get lower, the engine slows down, and the idle screw is opened to get the desired idle speed despite the retarded timing; the more open throttle at idle contributes to dieseling.

    Add in the modern fuels with ethanol and the summer fuels required in some urban areas, and the extra volatility of these fuels just makes the dieseling worse. (And contributes to the separate problem of fuel boiling!) New fuels are just plain problematic for these older carb'ed engines, but the gov't has forced things to go in a certain direction for better economy and lower emissions. So we're adpating...
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  19. #37
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    Finally had a chance to redo the smoke test. I input the smoke in the intake tree below the carb. No leaks apparent in manifold, carb base or throttle linkage bushing. Lots of smoke up through the primary throttle plate.

    No matter how I messed with the plate I could not get it to close more to reduce the flow of smoke up through the throttle plate.

    Is this normal? Could this be the source of my low idle issue? He are stills in sequence fm a video.








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  20. #38
    Opel Rallier since 1977
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    Seems like good test results for the secondary, and the shaft bushings. I see the choke plate is open but is there any chance that the fast idle screw is hanging up on something? BTW, too low an idle would normally not be caused by a too far open primary..... it would idle too fast, if everything else was good.

    Can you tell us if this is a points distributor? If so, then if the points gap is too small, or other wear is a factor in the points, then it ca cause your symptoms. I want to make sure you are not missing something important there.

  21. #39
    Senior Member The Cub's Avatar
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    First of all be sure that your choke adjustment screw is backed off all the way when the engine is at running temperature, when cold it’s normal for the idle speed screw not to make contact as MR noticed. There’s always enough of a gap around the throttle plates to let smoke pass through. You can’t pressurize the intake system to 3 psi without sealing off the top of the carburetor and exhaust. When I did a similar test with the same pressure reading of nitrogen and sprayed all areas with soap bubbles. I just used duct tape to seal off the top of the carburetor I have a good exhaust so I masked off my exhaust tips as well. I think that the smoke testing is superior to the way I did my check. The bubbles oozed out the primary throttle shaft. Everything else was and should be totally sealed. I capped off the tree using the check valve on the brake booster hose and golf tees on the other smaller hose connections. An in line pressure gauge to keep it at 3 psi & you’re good to go. A little smoke out the throttle shafts would be normal. If you don’t see it anywhere else and nothing from the intake is going directly into your exhaust (it shouldn’t) your only culprits would be in pecking order from top to bottom IMHO ignition timing, carburetor replacement and or cam timing. That smoke machine is a great tool I’ve considered buying one several times. It’s a fool proof way of finding those vacuum leaks. Keep up the good work and let us know the status on your ignition timing.

  22. #40
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    Quote Originally Posted by Manta Rallier View Post
    Seems like good test results for the secondary, and the shaft bushings. I see the choke plate is open but is there any chance that the fast idle screw is hanging up on something? BTW, too low an idle would normally not be caused by a too far open primary..... it would idle too fast, if everything else was good.

    Can you tell us if this is a points distributor? If so, then if the points gap is too small, or other wear is a factor in the points, then it ca cause your symptoms. I want to make sure you are not missing something important there.
    Yes, it is a points distributor. I replaced the points, cap and rotor with parts fm OGTS last year. The distributor is old stock, but not a 1969 as best I can tell. It only has one lobe.


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