1971 CB350 - Engine gets "bogged down" at higher throttle - Page 4
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Thread: 1971 CB350 - Engine gets "bogged down" at higher throttle

  1. #31
    Junior Member dslenz's Avatar
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    Here's what I know now that I did not know yesterday: First, I checked the flow again and can now confirm that there's flow from the petcock. So far, so good.

    Second, since the old plugs were out anyway, I put in new B8ES plugs.

    Third, I started (kick) up and revved a few times. Both exhausts felt warm to the touch. I tried pulling the right hand wire first, while wearing my bigboy pants, and it died. I popped the wire back on, started back up (kick) and tried pulling the left-hand wire. Died again. This morning, after being on a tender all night, the bike still wouldn't start without a kick. All the lights come on. Both cylinders were firing - I saw exhaust from both pipes. I rode to work - about 2.5 miles, the last half mile of which involves near-highway speed. Same problem - I struggled to get above 40 mph.

    So it seems like there must either be a timing issue or another electrical problem, right?
    chaindrivecharlie likes this.
    '71 CB350 (Stock)

  2. #32
    Senior Member chaindrivecharlie's Avatar
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    Sounds like it could be a combination of electrical and carbs. ie. weak spark poor gas mixture, Did you give 66sprint a call yet?

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    Charlie

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  3. #33
    Senior Member mike in idaho's Avatar
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    Did you check the new spark plugs for color yet? When it runs out of power,on the road, is there black smoke coming out of the pipes? When it's struggling, does closing the throttle a little bit help? Did you ever put a strobe light on it, to see if the ignition advance is actually working?
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  5. #34
    Junior Member dslenz's Avatar
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    Quote Originally Posted by mike in idaho View Post
    Did you check the new spark plugs for color yet? When it runs out of power,on the road, is there black smoke coming out of the pipes? When it's struggling, does closing the throttle a little bit help? Did you ever put a strobe light on it, to see if the ignition advance is actually working?

    I haven't checked the new plugs for color yet - this was the first time they ran for more than 30 seconds (also I don't really know what I'm looking for). I have not seen any black smoke, but will look more carefully later today. And yes, when it's struggling, closing the throttle seems to help - there's a "sweet spot" where there seems to be maximum power, beyond which it bogs down again. Haven't received a strobe yet to check timing, but that's my next move.

    Related - is there a good tutorial on using a strobe with these engines? I read through a manual online, but it was pretty sparse. The youtube tutorials all seem to be on how to adjust your timing with a simple indicator light. I haven't found anything in the FSM, but I may just be looking in the wrong place. Thanks all.
    Last edited by dslenz; 05-22-2019 at 11:21 AM.
    '71 CB350 (Stock)

  6. #35
    Junior Member dslenz's Avatar
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    A brief update: I pulled the air filters per a suggestion on this thread. Here are some pictures of the RH filter. 1971 CB350 - Engine gets "bogged down" at higher throttle-image1-3-.jpg1971 CB350 - Engine gets "bogged down" at higher throttle-image2-3-.jpg

    Are these past recovery? I tried blowing them out with some compressed air without very much success.
    fxray likes this.
    '71 CB350 (Stock)

  7. #36
    Member bexbarr's Avatar
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    Quote Originally Posted by dslenz View Post
    A brief update: I pulled the air filters per a suggestion on this thread. Here are some pictures of the RH filter. Click image for larger version. 

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    Are these past recovery? I tried blowing them out with some compressed air without very much success.
    Quote Originally Posted by dslenz View Post
    A brief update: I pulled the air filters per a suggestion on this thread. Here are some pictures of the RH filter. Click image for larger version. 

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    Are these past recovery? I tried blowing them out with some compressed air without very much success.
    First of all, I don't have much experience with motorcycle mechanics, so take my advice lightly. My filters looked like this when I first pulled them. In my opinion, you have nothing to loose trying to clean them out before you replace them (which are quite expensive). I soaked and washed mine with a mixture of warm water and a soap of some kind and used a soft bristle toothbrush to gently unclog some of the debris. I ran water from the inside out and let it seep through the filter. I remember that it took for ever to rinse all the soap residue out. They came out alright, mostly white with a few minor stains here and there. I chose to reuse them but if I had the money, I would have replaced them. Obviously, let them dry completely before you reinstall them.
    chaindrivecharlie likes this.

  8. #37
    Supporting Member crazypj's Avatar
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    Those filters can't be cleaned. The paper in them is supposed to develop an electrostatic charge due to airflow but water vapor over the years clogs them. No amount of drying or blowing out can restore them (Trust me, in view of the price of new ones, I've tried) You can however cut all the filter paper off and replace with either filter foam or cut up a 1970's Chevy filter. You'll get 3 or 4 pieces from a large single round filter (unfortunately I forget which Chevy) Glue it to sides of Honda filter housing with some silicon. You can also swap out for filter foam but it's a bit more difficult to 'glue' in place. What rpm does it pull in 2nd or 3rd gear? should hit red-line very easy. You need to hit red-line sometimes just to clean valves and exhaust soot. Motor is safe to at least 11,000 rpm in my experience, factory handbook says red zone is 'advisory' (or maybe that was 350? I forget stuff). Whatever, it ain't a 2 liter Harley, rev it like you stole it and bike will be a lot happier. Trying to 'baby it' because it's old will just cause problems. Except for idling at red light or junction it should never be below 4k when riding (even then you will need at least 2 maybe 3 downshifts if you need to accelerate)1971 CB350 - Engine gets "bogged down" at higher throttle-plug-colours.jpg
    Last edited by crazypj; 06-01-2019 at 08:00 PM. Reason: Add Spark plug picture
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  9. #38
    Junior Member dslenz's Avatar
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    Quote Originally Posted by crazypj View Post
    Those filters can't be cleaned. The paper in them is supposed to develop an electrostatic charge due to airflow but water vapor over the years clogs them. No amount of drying or blowing out can restore them (Trust me, in view of the price of new ones, I've tried) You can however cut all the filter paper off and replace with either filter foam or cut up a 1970's Chevy filter. You'll get 3 or 4 pieces from a large single round filter (unfortunately I forget which Chevy) Glue it to sides of Honda filter housing with some silicon. You can also swap out for filter foam but it's a bit more difficult to 'glue' in place. What rpm does it pull in 2nd or 3rd gear? should hit red-line very easy. You need to hit red-line sometimes just to clean valves and exhaust soot. Motor is safe to at least 11,000 rpm in my experience, factory handbook says red zone is 'advisory' (or maybe that was 350? I forget stuff). Whatever, it ain't a 2 liter Harley, rev it like you stole it and bike will be a lot happier. Trying to 'baby it' because it's old will just cause problems. Except for idling at red light or junction it should never be below 4k when riding (even then you will need at least 2 maybe 3 downshifts if you need to accelerate)Click image for larger version. 

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    I top out att 42 mph in third gear at around 7200 RPM. Bike won't rev or accelerate beyond that.
    '71 CB350 (Stock)

  10. #39
    Supporting Member Yendor's Avatar
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    Here is a Link to a USA Source for Airfilters.
    There are palces that have them for $90.00+ Each
    David Silver Spares has warehouses in both US and UK.

    https://www.davidsilverspares.com/CB...73/part_53640/
    $45.00 Each

    Have you verfied your timing with a Strobe Light yet?
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  11. #40
    Junior Member dslenz's Avatar
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    Quote Originally Posted by Yendor View Post
    Here is a Link to a USA Source for Airfilters.
    There are palces that have them for $90.00+ Each
    David Silver Spares has warehouses in both US and UK.

    https://www.davidsilverspares.com/CB...73/part_53640/
    $45.00 Each

    Have you verfied your timing with a Strobe Light yet?
    Thanks Yendor. Those who have more experience - do these filters look shot?

    Timing light is en route and I should be able to check this week sometime.
    '71 CB350 (Stock)

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