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  1. #1

    Default Carb Jets 79 70 johnson

    I replaced my reeds with a set of boyesens and there saying I need to richen up the mixture if I have the one style carb there saying I need to go down 3 to 5 sizes on the idle jet and if I have the other style to increase the jet size but there not specfic on which one I have also where can I find the jets I can't seem to find them anywhere on the web thanks

  2. #2
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    Default Re: Carb Jets 79 70 johnson

    I would try it first, then go from there. Be sure to check it out on the lake and you will get a more accurate assessment. Of course you know the symptoms of a lean idle, right? If it's too rich, you will note a stumbling idle with more smoke.

  3. #3

    Default Re: Carb Jets 79 70 johnson

    Do not do that whatever you do. The reason you have to go richer on the jets is because the reeds cause a lean condition at an idle. That can cause a lean sneeze which can destroy the reeds. Boyesen reeds are more particular about that because the first stage of the reed is so thin it blows out. There are reeds out there that you do not have to re-jet. Call Boyesen and see what they say or look at the parts fiche on this site to determine which one you have.

  4. #4
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    Default Re: Carb Jets 79 70 johnson

    Thanks for the correction, sir. Looks like I need to study these Boyesen reeds better. Really not sure what the advantages of them are, but to richen the mixture might mean a faster acceleration, but by the same token, by richening the mixture with the same timing synchronization it could have limited benefits. The tech line there is 800 441-1177
    Last edited by timguy; 09-10-2019 at 01:32 PM. Reason: add info

  5. #5

    Default Re: Carb Jets 79 70 johnson

    I already have them in so I want to use the noes I have if possible but cant seem to find any jets other than the stock ones does anybody. O where I can find jets

  6. #6
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    Default Re: Carb Jets 79 70 johnson

    If Boyesen requires a jet modification, perhaps they can direct you. If a larger jet is required, they should have a table to guide you to the correct size. A complete machinist drill set can provide the needed enlargement. I have one here based on decimal sizes. Not sure what they require, but you can simply order the correct bit on line and do it yourself. Boyesen is a very reputable outfit.....I'm sure they can help.

  7. #7
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    Default Re: Carb Jets 79 70 johnson

    first i hope this is is correct, here goes, your idle jet is at the top front of carb( i think) behind washer and screw (#25&26) believe to rich'n you go up in size,because gas passes thru the jet, on later models carbs the jet is not covered, so air passes through it, like a 1987 70hp, check parts break downs for this year, to rich'n in the 87" model(i think) you restrict air flow, smaller jet, hence less air more gas,makes sense.
    one other thing is the older carbs have another jet behind a screw at the top back of carb, i'm not sure which one , the front or back is idle, i'm assuming its the front because of the 87" design. need a guru to step in here!
    i changed my 87" 48spl reeds to Chris Carson Marine reeds, no re-jet, and like the results. for those who like to tinker with these old motors, something to check out.

  8. #8

    Default Re: Carb Jets 79 70 johnson

    Do not drill out your jets you can damage them and they will not flow right. You have to richen the jets up because the boyesen reeds flow more air at an idle. The 2 stage reed has a thin light petal that opens easily and farther than a standard reed. The second part opens farther into the throttle range and is stiffer so it starts to act like a more normal reed. You get better throttle response out of them and a smoother idle. I have used them there are no issues with setting the idle. The Chris Carson reed are I believe a fiberglass copy of a standard reed. There is really no performance advantage biggest thing is if it breaks it just shoots through the motor.
    Last edited by flyingscott; 09-10-2019 at 06:15 PM.

  9. #9
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    Default Re: Carb Jets 79 70 johnson

    Parts show you have a #35 as stock.... a 32 is #320016, 31 is #318823 and 30 is # 317473.....
    Pappys Sales and Service
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    Former racer KDBA (Kentucky Drag Boat Association)

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    Default Re: Carb Jets 79 70 johnson

    Your probably right Mr. Scott. I was giving him option in case he couldn't find the correct jets, or if they are too expensive. Pappy has some additional info for you as well. If you have a jet size that is recommended for your application, then let me know. I have a box of jets from years of collecting.....and no, they are not drilled out.

  11. #11

    Default Re: Carb Jets 79 70 johnson

    So I talked to boyesen head tech and he was very helpfull he said go head and try it with the stock jets if runs lean and sneezes at idle call him and he will set me up with the right jets and if it's not. Available they can take a stock one solder it shut and use a jet bit to make me 3 but he said the 70s are usually fine with out a rejet he also said if I break one he will send me a replacement because I talked to him first probably the best customer service I ever had I would highly recommend them it's rare to get this kind of service on anything letlone a 50 dollar part sorry about the crappy grammar I'm using a small cheap phone

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    Default Re: Carb Jets 79 70 johnson

    Great, so refreshing to see service with the sale. It certainly pays to be kind and appreciative to those who can help us.

  13. #13

    Default Re: Carb Jets 79 70 johnson

    So I ran it yesterday on the Ohio River ran perfect gets up on plane like right now. Also no lean pops so I think I'm good. I damaged my prop slightly on my way back it's a 13-1/4x17 so I want to replace it and need some recommendations budget is like 200 right now I'm spinning 5200 wot doing about 26 27 mph don't no if I can do any better the boat is a winner couger18.5 foot runabout

  14. #14

    Default Re: Carb Jets 79 70 johnson

    I would run a 15" pitch prop to get closer to 5500 rpms. Those motors do not make a great deal of torque on the low end.

  15. #15
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    Default Re: Carb Jets 79 70 johnson

    Quote Originally Posted by Winner couger View Post
    I replaced my reeds with a set of boyesens and there saying I need to richen up the mixture if I have the one style carb there saying I need to go down 3 to 5 sizes on the idle jet and if I have the other style to increase the jet size but there not specfic on which one I have also where can I find the jets I can't seem to find them anywhere on the web thanks
    A short note to explain that statement: It would pertain to whether one has a carburetor incorporating "Air Bleed Idle Jets"... or... actual "Fuel Measuring Jets".

    If "Air Bleed Idle Jets"... The jet would be visible in looking down that jet location. <-- Decrease ID to richen.

    If "Fuel Measuring Idle Jets"... The jet would not be visible but would be covered and plugged with a screw and a red fiber washer. <-- Increase ID to richen.
    Last edited by joereeves; 09-15-2019 at 11:25 AM.
    We occasionally have questions. If you fail to answer, it may affect ours.

  16. #16
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    Default Re: Carb Jets 79 70 johnson

    That gives sense to the original question, thanks Joe. Now just another example of a zillion years of experience.
    Last edited by timguy; 09-15-2019 at 02:37 PM. Reason: Add info.

  17. #17

    Default Re: Carb Jets 79 70 johnson

    Thanks for that because I had that backwords whene I was talking to boyesen but it runs like a champ. Deffently bigg difference with the boyesens gets up on plane fast. I hit bottom. A little trolling in the bay getting to the main river and chewed up the prop a little so got to decided on what I want to replace it with

  18. #18
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    Default Re: Carb Jets 79 70 johnson

    Quote Originally Posted by timguy View Post
    That gives sense to the original question, thanks Joe. Now just another example of a zillion years of experience.
    I appreciate that Tim. I came down with something a couple weeks ago, couldn't shake it. Finally went to Urgent Care a couple days ago & am on Antibiotics and a few other things now. How old do I feel right now... you just about got it covered.
    We occasionally have questions. If you fail to answer, it may affect ours.

  19. #19
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    Default Re: Carb Jets 79 70 johnson

    I wondered why you were answering few posts, that explains it. Without you on this forum it's not what it should be.....,..like the wrong prop on a motor. It runs......but not efficiently.

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