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Thread: no idle left side

  1. #16
    beemerfield
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    I will look closely at the points cavity, but I imagine that spring has been missing for years. I have a little magnet that I will sweep around with. I didn't see anything lying at the bottom or in the cover.

    Can't wait to see if this makes it run right!
    beemerfield

  2. #17
    Registered User lmo1131's Avatar
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    Also- just curious- the cover says "Hilderbrand" on the front and inside has a BMW logo, below which is a little "clock face" with 70 in it ad 11 to the rigt of that. It has a part # 1.255.0059 which does not match the parts list. Does anyone know anything about this cover?
    70 is the year the cover was die cast; 11 is the month.

    1.255.0059 is not a BMW part number... or I should say, it does not conform to BMW's 11 digit part numbering system. Weather Protector (front cover) p/n is: 11 14 1 259 469

    "Hilderbrand" on the front? Where? Is it cast in, or stamped? Typically there is nothing on the front of the cover.

    Got a pic?
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  3. #18
    beemerfield
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    The name is probably stamped in. I'll have to learn how to upload a photo to this site, but basically it is just what it says- "Hilderbrand" across the front -exterior. There is a definite BMW logo inside with the numbers.
    beemerfield

  4. #19
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    Wouldn't the dipping of the carbs eat up the butterfly seals?

  5. #20
    beemerfield
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    I have had otehr cabs dipped before and had to remove all the orings,etc. The post mentioning this seems to indicate a type of solvent that would not damage the rubber bits, however.
    beemerfield

  6. #21
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    To clarify dipping rubber bits in Chem-dip: I have only left o-rings to soak for ~6 hours. Longer times may soften the rubber, but Buna-N o-rings have held up OK after 4-6 hours. That is for o-rings in good condition also. Generally, replacing all the o-rings after dipping a carburetor is needed.
    Stan

    AH# 13238

  7. #22
    Registered User lmo1131's Avatar
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    And then there is the throttle shaft o-ring that requires the butterfly to be removed to get to it...

    I suspect that it is over looked, or ignored, more often than not.

    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  8. #23
    Registered User ebeeby's Avatar
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    I don't think the missing advance spring has anything to do with that cylinder not idling. A severe vacuum leak that side, a tight valve or a blocked muffler would explain it. How old are the mufflers? If they are original, a constricted muffler would kill the idle while letting the cylinder fire at higher RPMs. You know you have fuel and spark. I think it is compression related to the 3 things listed above.
    It would be simple enough to loosen the muffler clamp and bracket and run it on the header.

  9. #24
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    Yes, a blocked muffler would cause similar symptoms. When diagnosing a non-firing cylinder situation back in June of this year, I found you can feel with your hand if there is flow out of the muffler from a non-firing cylinder with the engine idling. The tell-tell sign is that one muffler's exhaust is hotter than the other. The cooler side exhaust is not firing during idle. That is a very good simple check. You can also tell a difference in the exhaust tone from one side to the other when one side is not firing, but that is more subtle and requires experience with the correct sound.


    Edit: the exhaust flow check can also - roughly- show if the cylinder which is not firing is also not pumping air. If the flow from both sides of the exhaust is noticeably different, then valve problems are likely.
    Last edited by Stan_R80/7; 08-30-2012 at 03:14 PM. Reason: added a comment
    Stan

    AH# 13238

  10. #25
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    Unlikely muffler causes fail to idle - remember there is a crossover forward of the mufflers and at idle speeds probably only one muffler clear would be enough - single clogged muffler would probably seriously cut power at higher speeds

    I didn't see you post yet whether switching carbs from side to side changed anything

    You switched the spark wire ends from one side to the other without disconnecting from coils
    and no change but how about the carbs

    You might as well switch the plugs from side to side also - just because they are new or new looking does not mean they have not developed a high voltage track to ground other than across the electrodes - just because they appear to fire outside the cylinder does not always mean they will fire under compression in the cylinder.

    This project needs to proceed in a logical sequence to zero in on the problem - as I read it to date there are still too many variables - switching the carbs will conclusively prove if the problem is within the carburetors and their adjustment or not

    If the same pair of carbs cause the engine to fail idle on same side when they are switched then the carbs cannot be the problem - if the idle problem changes sides with the carbs then there is your problem

    You can test the flyweight issue at idle and slower speeds by just wrapping the weights inward with tape - see if this has anything at all to do with idle problem - probably does not but easy test

    Also look for air leak other than rubbers joining carbs to head
    The flange the rubbers ride on is threaded into head - is it loose or cracked?
    Did some fool drill a hole through the flange or casting to use a manometer and the plug fell out?

  11. #26
    beemerfield
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    I did not switch carbs sides yet, only coil/plug wires. I have tried several new plugs and switched plugs side to side. Last time, both plugs fouled, but I had idled longer and did not take it out on the highway.

    The left side muffler is not blocked. The baffles were rusted and I pulled them out. The right side is not much better. I actually do not like the noise and I'm sure my neighbors are tired of me revving in the driveway.

    The boots between carbs and cylinders are brand new with new clamps. I replaced them early on in this process.

    Tonight I am driving to pick up new advance springs and I am also going to replace the left side air filter to carb tube.

    As it is supposed to rain all weekend, I will not be going to Davenport and will likely have lots of time to mess with this.
    beemerfield

  12. #27
    Stage Crew beemerPhil's Avatar
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    Not mufflers- he says it cleans up at anything but idle. This points towards poor valve seal or bad idle circuit in the carb. Whatever you're looking for appears to go away at speed-

    Unlikely to be ignition timing/camshaft wobble- doesn't sound ignition related at all. The missing advance spring is a good thing to find & fix, but isn't the culprit. Be sure to use the newer springs- they're slightly heavier, and delay the advance curve somewhat for modern fuel. Obviously, replace the pair, not just one!

    Compression tests are way too easy to do wrong; too many variables left open, and if you crank long enough, even an engine with serious issues will come up near spec. A combustion chamber leak test is much more revealing. Leakage higher than 15-20% is not good, and any leakage back through the intake valve will cause trouble at idle.
    If you don't have access to a leak tester, a compression test will help IF- done with a warm engine, fully charged battery, carbs off of the intakes(remember, cv carbs are NOT open just because you opened the throttle!) and with both plugs out and grounded. Turn the engine no more than 4 times, and compare pressures side to side. Don't worry too much about numbers, unless they're really low- it's more important that they're comparable within 10-15%.

    You mentioned swapping a new idle mix screw from one carb to another- are you certain they were the same? It's much harder to track down 2 problems at once..

    I'd get back to base- step one with the rebuilt carbs. Try swapping them side to side and see where the idle problem follows. If it follows the carb, I'd go through the idle circuit a step at a time with solvent & compressed air; a blockage in the air or fuel path here will do just what you describe. Next step, I'd be looking for an air leak, at the carb(o-rings, shafts, cold-start valve, etc) or intake tube. A small leak, (false air), significant at idle, effectively disappears at higher flow volume.

    I'll re-read this thread and see if anything else pops up-
    Phil Keppelman #20331
    MOA Rally Stage Manager
    The shortest distance between two points.............
    ain't how I got here......

  13. #28
    Stage Crew beemerPhil's Avatar
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    Did you mention mileage on this engine?

    You could probably never see camshaft wobble from a bent shaft- too small. you need a dial indicator. A timing light is the easiest way to check this.
    What you might see is wobble from a shot front camshaft bearing; valve opens on the right cylinder and pushes the shaft to the left, valve opens on the left cylinder and pushes the shaft to the right. This can be pretty pronounced on a high-miler, but if it's really bad you'll have oil in the points cavity; the seal won't tolerate this for long.

    You've already replaced the intake tubes. Were the spigots tight in the heads?

    Swap the carbs- it's a nuisance, the cables may not cooperate, but it'll tell you for sure if that's your problem.
    Phil Keppelman #20331
    MOA Rally Stage Manager
    The shortest distance between two points.............
    ain't how I got here......

  14. #29
    beemerfield
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    The bike is a rescue. It was in a fire and I felt sorry for it. Big mistake. The odo says 27K and i could see most of the damage was to paint/plastic. I just wanted to make an inexpensive rider out of it.

    Final drive and rear wheel splines look worn, however. Maybe replaced earlier, maybe not maintained, maybe it has 127K, but I think that is highly unlikely. Anyway milage is unknown.

    A friend who knows cars helped me check compression with a tester he said "is a nice one". It was cold, but carbs were left on. Right side said 155 and left was 145. Another experienced BMW club member who tried to tune it said he thought it had "good compression".

    Going to pick up the new parts tonight and try them hopefully by the end of the weekend.

    Looks like maybe rain will not be so bad at Davenport, so may try and ride there on my good bike instead of sitting here in the rain messing with this old thing! I'll make a "game time decision" tomorrow night.
    beemerfield

  15. #30
    beemerfield
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    Oh- I will check the spigots too. I want to try the advance springs before swapping carb sides because that will be easy.

    Note when I used timing light the markings on the flywheel jump around. This makes me think it is not carb related.
    beemerfield

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