Wil I. Finish's Dieseling Problem
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Thread: Wil I. Finish's Dieseling Problem

  1. #1
    Just Some Dude in Jersey The Scifi Guy's Avatar
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    Wil I. Finish's Dieseling Problem

    Will I. Finish sent me this message:

    <<<Was wondering if you could answer a question. 1970 Opel GT with a camshaft of .430" lift with a SOLID
    grind camshaft, installed with 1.72/1.50 Chevy valves,
    and 2.0 (.030" OS) pistons, purchased from Opel GT Source - new/rebuilt engine only has 1400 miles. Car totally rebuilt by me, not a mechanic - had the car since 1972. But most everything is new, not the distributor or the brake booster. I have plugged the carb and continue to get just a slight variation on my tac, about the same with everything hooked up - Just a blip, which I could actually live with. Its the dieseling that is driving me crazy. I have a Weber 32 36 DGAV and recently changed the idle mixture jet from 60 to 65, Gil's recommendation, which allowed the car to idle without having the screw out more than two turns.
    My name is Carl I live in the Charleston, SC area. Have been working on the car on and off for about 25 years - I have never really been to enjoy it. If I had it to do over again I would have stayed with the solex carb and the 1.9 as I have no memory of the engine compartment getting do hot and never had gas boiling. Any ideas you could share. I have read a lot of material and tried a lot of things and am some what frustrated. Thanking you in advance for any assistance. I would start a new post but frankly can't figure out how to do that. Best Regards, Carl Wil I Finish >>>

    .....so I started a thread for him.

    I'm no engine guru, so I'll turn this over to you guys.

    My guess is ignition too far advanced or idle set too high.
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    3000 Post Club m610's Avatar
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    Vacuum leaks will do this.
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    Senior Member heliman's Avatar
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    Engine run on can't happen without an ignition source. You have excessively high combustion chamber temps which causes the detonation. The cause? It can be many things that cause high cylinder temps. Assuming you have the correct heat range. (you can run 2 or 3 heat ranges cooler, a lot of modified engines like cooler plugs) First thing to do is pull the plugs and look for overheating. I'm betting they will show excessive heat. This can be caused by to much or to little timing, but it's more then likely an excessively lean low speed mixture. the fact that it ran better with one size bigger jet would support this. To lean can be wrong jetting or more probably caused by a vacuum leak. Before the engine gets hot, get the hose out and while idling wet down everything from the base of the carb to the head, especially underneath the intake. Providing there is no leaks, timings good, plugs are ok or cooler ones installed. Then all that's left is jetting. Note, excessive carbon build up can also cause this problem, but that's highly unlikely with a new engine.
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    71 GT, Ford 2.0 Zetec, Jenvey throttle bodies, Omex engine management. Subaru 6 speed transmission , Ford 7.5 4.10 posi narrowed torque arm rear end. Coilover front end with tubular A arms. Electric power steering. Wilwood 4 wheel discs. Budnik 17" wheels. In dash Vintage Air. Dakota Digital gauges. Power windows. Keyless entry. Cruise.

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    Opeler Will I. Finish's Avatar
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    Thanks for the feed back, I really appreciate it. I will try the cooler plugs and recheck the carb and manifold for vacuum leaks. I have plugged the vacuum advance, retard, and brake booster and that changed nothing but again the small blip on the tach is something that I can live with. Regarding the carb Idle mixture setting is about 2 turns out and I do have the idle set at around 1200, I will lower the idle and see how that goes. When I set the timing by the light the engine really sounds labored and the more I read the more I wonder if I set/put everything back together correctly - I started putting it all back together around 20 odd years ago and frankly have forgotten a lot of that. So regarding the timing I have moved the distributor to a position where the car just seems to sound/run better.

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    Try closing down the secondary idle stop screw to close down the secondaries some. The re-adjust the primary idle and idle mixture.

    It is item 72 on this diagram linked below and is accessed by pulling the carb off.
    Weber 32/36 DGEV DGAV Diagram

    Also, retarded timing will cause hot running and idling, and promote dieseling. Retarded timing was common in the 70's for emissions adjustments and anti-dieseling solenoids were used on many carbed cars to get around the resulting dieseling issues.

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    Senior Member heliman's Avatar
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    Quote Originally Posted by Will I. Finish View Post
    Thanks for the feed back, I really appreciate it. I will try the cooler plugs and recheck the carb and manifold for vacuum leaks. I have plugged the vacuum advance, retard, and brake booster and that changed nothing but again the small blip on the tach is something that I can live with. Regarding the carb Idle mixture setting is about 2 turns out and I do have the idle set at around 1200, I will lower the idle and see how that goes. When I set the timing by the light the engine really sounds labored and the more I read the more I wonder if I set/put everything back together correctly - I started putting it all back together around 20 odd years ago and frankly have forgotten a lot of that. So regarding the timing I have moved the distributor to a position where the car just seems to sound/run better.
    Your Idle is definitely to high. Bring that down to the 750 - 850 range. And you shouldn't be getting the timing response you are. I would suggest you pull the cover and check the cam timing, you may be a tooth off.
    71 GT, Ford 2.0 Zetec, Jenvey throttle bodies, Omex engine management. Subaru 6 speed transmission , Ford 7.5 4.10 posi narrowed torque arm rear end. Coilover front end with tubular A arms. Electric power steering. Wilwood 4 wheel discs. Budnik 17" wheels. In dash Vintage Air. Dakota Digital gauges. Power windows. Keyless entry. Cruise.

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    It's always a vacuum leak....

    Will, you didn't by any chance have the head or block milled, did you? That could make it hard to ever time your engine right.


    Here's my little tale of Opel success:

    In the 80's I bought a rebuilt engine from one of our Opel suppliers. It was a 1.9 made into a big valve 2.0 and I put the next step up cam in it with a 32/36. I didn't know schitt about cars back then. Nothing. I lived in an apartment complex, no shop equipment like a timing light. I never jetted the carb for the GT, I just took it out of the box and put it on. Timing? I advanced until it started to stumble and then backed it off a bit, then test drives and readjustments if I heard pinging or the car became hard to start. I drove that car for 225K miles and it was running like a kitten when I sold it 18 years later. The only thing I ever had to do was chase vacuum leaks, always at the carb/manifold or the manifold/block unions. ANY problem was always because of vacuum leaks. Occasionally I'd get some dieseling, but I never did find out what caused it. I was a dumbass. But the car kept on running and I drove it to Florida and Texas a few times from Jersey.

    So, you can definitely overthink a problem and sometimes just going back to basics is the answer.

  10. #8
    Opeler Will I. Finish's Avatar
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    Quote Originally Posted by The Scifi Guy View Post
    Will, you didn't by any chance have the head or block milled, did you? That could make it hard to ever time your engine right.


    Here's my little tale of Opel success:

    In the 80's I bought a rebuilt engine from one of our Opel suppliers. It was a 1.9 made into a big valve 2.0 and I put the next step up cam in it with a 32/36. I didn't know schitt about cars back then. Nothing. I lived in an apartment complex, no shop equipment like a timing light. I never jetted the carb for the GT, I just took it out of the box and put it on. Timing? I advanced until it started to stumble and then backed it off a bit, then test drives and readjustments if I heard pinging or the car became hard to start. I drove that car for 225K miles and it was running like a kitten when I sold it 18 years later. The only thing I ever had to do was chase vacuum leaks, always at the carb/manifold or the manifold/block unions. ANY problem was always because of vacuum leaks. Occasionally I'd get some dieseling, but I never did find out what caused it. I was a dumbass. But the car kept on running and I drove it to Florida and Texas a few times from Jersey.

    So, you can definitely overthink a problem and sometimes just going back to basics is the answer.
    Great Story.......My carb was new out of the box so it only has the 1400 miles on it as well. When I received it I slapped in on and it ran great for about 5 minutes and stopped. I called the dealer, out of Gilroy, CA and they said it may be the float that needed to be adjusted - took the top of the carb off and the large brass fitting over the float was completely disconnected, brand new carb???.
    Anyway since I have capped the three holes in the carb, regarding three possible vacuum leaks that only leaves the carb to manifold and Manifold to engine, right. Regarding the secondary idle screw which is accessible by removing the carb - what are the possibilities and I have never read about that before. I hate the thought of removing that carb but I know if I have a leak around the manifold then its coming off anyway. My first Weber as a supposedly rebuilt carb from a local competitor of ogts - piece of junk - no more business with them after that. I have looked at the bottom of this carb and cannot find that other idle screw and the diagram that was provided shows that piece but not the location. So I am now going to fire the GT up and pull out the CARB spray and check that manifold. Thanks again everyone for your help. I bought this car when I was 19 and have put a lot of love and money into it - looks like a new car inside and out - I would really like to drive it again and enjoy like I did when I was a kid. Because you know as each year that goes by it gets progressively more difficult to get in and out of and to crawl under it as well.

  11. #9
    Opeler Will I. Finish's Avatar
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    And no I never had anything done to the head - these are the specs that I was supplied by OGTS - it was a rebuilt from OGTS...It specifies a camshaft of .430" lift with a SOLID
    grind camshaft, installed with 1.72/1.50 Chevy valves,
    and 2.0 (.030" OS) pistons.

  12. #10
    Opeler Will I. Finish's Avatar
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    So It appears that I have a small vacuum leak at the gasket between the carb and the manifold, specifically on the back nearest the fire wall . Since I am going to be taking this apart do you recommend the thicker gasket and a heat shield - anything thing else, while the carb is off you can recommend would be appreciated.

  13. #11
    Über Genius First opel 1981's Avatar
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    FWIW, I had a diesel ing problem for the longest time.
    Nothing I did fixed it. Hotter or cooler plugs, didn't matter.
    It was a brand new rebuild with everything fresh.

    I finally added an idle solenoid to the carb and all is well.

    I did find out MUCH later that I had a vacuum leak in my brake booster hose so the vacuum leak theory is a valid one, especially since you are running a .65 idle jet.
    Opel GTs are not GM products
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    First get your timing squared away, check the function of both the vacuum advance and the mechanical advance of both checked out okay then if you can get a timing light with a dial, set up your total timing between 34 and 37 degrees, I like to set mine at 4,000 rpms I hardly ever hear of anyone running 38 degrees total but I suppose it’s allowable, whatever the engine likes best. On your carburetor. The people at Redline Weber say the idle speed screw should be no more than 1.5 turns in from contact. The reality is that you start drawing additional fuel from the progression holes above the throttle plate when it’s adjusted in too far in causing engine to do it’s little sputter or dieseling run on thing on shut off. Weber CARBURETOR SET UP AND LEAN BEST IDLE ADJUSTMENT
    Timing can exasterbate that as previously mentioned. The idle cut off solenoid is one solution if you like to have your idle up that high. I personally have a hard time with one of my 32/36 carburetors (the new one) keeping my idle speed screw under those specs so I cheat it a little bit to about 1 3/4 turns in from contact, that gets me a 750-850 rpm idle using a 60 idle jet. Now the other 32/36 I have can easily maintain a 850 rpm idle on the same engine with 1.25 turns in after contact on the idle speed screw, the mixture screw about 1.5 to 2 turns out from bottom with a 70 idle jet I believe it’s only due to the throttle shafts being more worn on the second carburetor, that meters in a little bit more air causing the jet size increase. The other two critical components to the engine run on with the 2.0 higher compression pistons that I didn’t experience with my lower compression 1.9: #1 the engine timing this engine likes to be just a degree advanced at idle and 34 degrees of total advancement, 3 degrees of advancement and 36 degrees total was too much causing detonation. Here’s a little more information on the distributors:
    https://www.opelgt.com/forums/1b-ign...#/topics/29092
    The second critical component is the octane of the fuel I’m running, if I’m at 94 with everything else set up as described I get absolutely no engine run on and the detonation has vanished also.
    Finally today’s gasoline with the stock manifold set up is a sue-aside set up if you live in an area that gets routinely hot and also has blended ethanol fuel at the pump. If you follow this thread and many others there are several successful methods that can help with that. https://www.opelgt.com/forums/1b-ign.../108301?page=5

  15. #13
    Opeler Will I. Finish's Avatar
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    Thanks again for all of the information. Regarding the firing order based on what I have read - order is 1-3-4-2 with number 1 being closest to the fan - is that the top one closest to the fan or the bottom one closest to the fan? It appears that I have the firing order as 4 on top closest to the fan- 3 0n the bottom closest to the fan - 2 on top closest to fire wall and 1 on the bottom closest to the fire wall. The cut mark on the edge of the distributor housing is in the 5oclock position. Do I just need to set it up as described above1-3-4-2 and I just found another thread that seems to say that I have it right. Just need some clarification. Thanks, Carl

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    That is correct the way you have it 1,3,4,2 #1 in front #4 closest to the transmission. Here’s a pic of the correct position of the distributor with the cap & rotor removed.
    Attached Images Attached Images

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    1342 with one being wherever the rotor points when the #1 cylinder is TDC on the compression stroke.

    OP's often just toss the dizzy in and leave it at that. I was one of those POs
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    Humans are not an endangered species!
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  18. #16
    Just Some Dude in Jersey The Scifi Guy's Avatar
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    How old is your carb, did you say years and years, like 10 or more? There are rubber parts inside like the acceleration pump that can go bad with age and possibly dump fuel into the engine. Just a thought.....

    Knock out that vac leak and go back to basic settings and work from there.

    Too high an idle will cause the acceleration/power circuit to start dumping fuel into the engine prematurely, also.

  19. #17
    Opeler Will I. Finish's Avatar
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    Carb was purchased new but has been on the car for around 20 years mostly just sitting as it only has 1400 miles on the new engine/carb/restoration project.

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    Opeler Will I. Finish's Avatar
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    Having fun at the car show???

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    Opeler Will I. Finish's Avatar
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    So I checked timing with the car off. Rotated the distributor rotor to line up with the mark at 5:00 on the distributor housing. That puts the first piston at exactly TDC and it is. The BB on the fly wheel is about 3/4 inch below the pointer. What does that mean.

    Should there be any play in the rotor, that is should it move back and forth by hand. My moves back and forth by about 1/4 inch.

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    Über Genius First opel 1981's Avatar
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    Quote Originally Posted by Will I. Finish View Post
    So I checked timing with the car off. Rotated the distributor rotor to line up with the mark at 5:00 on the distributor housing. That puts the first piston at exactly TDC and it is. The BB on the fly wheel is about 3/4 inch below the pointer. What does that mean.h

    Should there be any play in the rotor, that is should it move back and forth by hand. My moves back and forth by about 1/4 inch.
    When you say it has play, does it turn one way and spring back? If so, that's normal.
    If it turns and stays, then you turn it back, that's not normal.

    Do you have points or a different system in the distributor? Just curious. It probably doesn't affect the dieseling..
    Opel GTs are not GM products
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    Humans are not an endangered species!
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