Idle adjustment on triple carbs

[ianyoung77]

I have a 1990 50Hp Yammy 50DETO.<br /><br />According to the manual and other posts it appears that at idle the top and bottom carbs should be closed and the middle carb will be slightly open to set the idle speed.<br /><br />Is this correct? Isn't it normal to have all carbs synchronised?

 

[JB]

Re: Idle adjustment on triple carbs

Good question, Ian. <br /><br />I don't know why they did it that way, but I make it a practice not to second-guess the book.<br /><br />Good luck.

 

[rodbolt]

Re: Idle adjustment on triple carbs

hello<br /> never heard of a yam setting that way. post us the passage that says with the middle carb open ant the other two fully closed. I dont have my manual in front of me but ill wager it does not say that. it should say using the idle screw on the middle carb turn it CCW until the stopper no longer contacts the screw and loosen the top and bottom sync screws. or words to that effect. but post what manual and the paragraph.

 

[Ray Neudecker]

Re: Idle adjustment on triple carbs

Like Rodbolt, I suspect you need to review your manual again. Doesn't seem your interpatation could be right.

 

[ianyoung77]

Re: Idle adjustment on triple carbs

Thanks to you both for the help. I agree I am probably misinterpretting, hopefully this post will give me clarification.<br /><br />In answer to rodbolts queries<br />Clymer Manual<br />1. Install test propeller<br />2. Put motor in test tank<br />3. Remove engine cover<br />4. Fit tacho<br />5. Loosen the idle adjust screw and fully close the throttle valve<br />6. Loosen the throttle securing screws for the upper and middle carburetors<br />7. Set pilot screws<br />8. Warm engine in forward<br />9. Check speed<br />10. Adjust idle screw<br />11. Lightly push down on the throttle lever on the lower carburetor to the full-closed position. Tighten the throttle lever securing screw counterclockwise on the upper and middle carburetors<br /><br />Capt Ken said<br />Back off the idle screw to where its not touching anymore. Loosen the follower cam screw and the adjustment screw on the upper carb. Both screws turn right to loosen, not left like standard. You'll see the arrows. Make sure both carbs are fully closed and tighten the top screw, then readjust idle. Last readjust follower cam<br /><br />I tried to adjust as per the manual and the motor seemed to run rough but I think this was because the top and bottom carbs weren't in sync. I took off the air cleaner and got all three in sync and then adjusted idle and it runs ok, however, this does not appear to be by the book.

 

[Ray Neudecker]

Re: Idle adjustment on triple carbs

What you did was correct. The idle now being right is the proof. Sometimes the factory manual has errors, often the Clymer ones do.

 

[bigbrownbuku]

Re: Idle adjustment on triple carbs

<br /><br />I tried to adjust as per the manual and the motor seemed to run rough but I think this was because the top and bottom carbs weren't in sync. I took off the air cleaner and got all three in sync and then adjusted idle and it runs ok, however, this does not appear to be by the book. [/QB]

point number 10 is in the wrong location.<br />i have never run an engine until warm to adjust throttle plates, i honestly cant see how that makes a difference.<br />it takes some practice to get the "feel" for tightening a left handed threaded screw and holding the throttle plate closed lightly.<br />the important things to remember are<br />back off the throttle stop screw and the cam follower. if your engine is oil injected disconnect the link rod. this way you are only working with the throttle plates. adjust the throttle plates to all closed then reconnect everything else. <br />tech tip, pay close attention to the cam follower adjustment, its at this point you will get a "bog down " condition on acceleration if its not right. right is whatever makes the engine work, older engines that are "worn in" a lot of times require adjusting outside workshop manual specifications. i find this a lot with pilot screw adjustments.

 

[ianyoung77]

Re: Idle adjustment on triple carbs

Thanks for your replies everyone.<br /><br />A couple of points I am still unclear on if anyone can help<br /><br />I guess the cam follower is on the bottom carby linking the accel cam to the throttle control. Is this correct? If so how do you set it? My manual makes no mention of this adjustment. I adjusted so that full cam made the throttle valve hit the stop.<br /><br />The other adjustment not covered by the manual is the pilot screw. The manual says 1.75 turns without any further comments. Should I be adjusting this to minimise "bog down"

 

[bigbrownbuku]

Re: Idle adjustment on triple carbs

1 3/4 turns out is where to start and a safe place to be if you dont know how to adjust air/fuel mixture. tip, only use light pressure when turning in the mixture screw, the carb is aluminium and the screw is brass, easy to mess things up in this area with a heavy hand.<br /><br />you have picked the cam follower. adjust your throttle cable for light pressure holding closed. then adjust your cam follwer to almost touch ( a few thousandths) the throttle cam. my personal preference is very close/ touching. the pickup timing spec is usually only 1 or 2 degrees from idle timing. search for the "pickup timing" in your book if it isnt there burn it.<br />i would already have nailed it to a post covered in cheezewhiz after reading there link/sync explanation above.

 

[rodbolt]

Re: Idle adjustment on triple carbs

wow<br /> I dug out a clymers and sure enough the 3 cyl link and syc procedures are rather wrong. I have never tried to link and synch with the engine running. the throttle shutters are set engine off. while doing the shutters its a good time to check the oil pump adjustments as well. however use the factory yamaha manual not the clymers.<br /> like BenC says sometimes the manual is plain wrong, thats where experience,training and common sense comes into play. if ya know how it works you can spot errors in the manual. I even spotted a few in the diagrams on the CIWS mod 15 block 1 while going to school in damneck. so learn how it works and you can spot mistakes.<br /> yamaha sent out a TECH bulliten several years ago on adjusting the TPS on an HPDI motor. said to verify 12v on the orange wire. I called them back after I got the fax and told them if ya have 12 volts on the orange wire you have more than a TPS problem. it only took 20 min of argueing before they admitted the "new" procedure they sent was wrong.

 

[ianyoung77]

Re: Idle adjustment on triple carbs

Thanks for the comments guys,<br /><br />Since the general catchcry is RTFM I didn't think I should post without having a manual. Before buying this one I tried to get the original Yamaha and was told it was no longer available. I have been really dissapointed with the manual since it covers so many models it is a jack of all trades master of none. I have so far done the common stuff - impeller, carbys, gear oil - in every case I felt the manual short of my expectation<br /><br />The complete specs on the carby in my manual are:<br /><br />Spark plug type, gap and tourque<br />Idle timing<br />Maximum timing<br />Full throttle rpm<br />Idle timing in neutral and gear<br />Carburetor pilot screw turns out<br />Carburetor stamp mark<br />Main jet, air jet and nozzle<br />Pilot jet & air jet<br />Float level<br /><br />That's it - so I guess I should reach for the petrol and cheezewhiz!<br /><br />So I guess the pickup timing is the timing point where the throttle just starts to move. Does anyone know this setting? I would guess somewhere around TDC. There are 3 marks around TDC so one may be for pickup timing - again just guessing.

 

[bigbrownbuku]

Re: Idle adjustment on triple carbs

an engine that old falls into the "what works" category. you cant really hurt your engine with this adjustment. timing under load will be slightly different so setting it on a flusher isnt going to work. set it close then try it if you have little or no bog be happy with that. if you have noticeable bog set it a little closer and try again etc. its important your throttle lever returns to a full stop everytime before you start with this setting.<br />another important point, if your cam follower has a flat spot on it at all, replace it. they pry of fairly easily with pliers, make sure there is no material left in the groove from the old follower before installing the new one.