A partially blocked main jet could cause carb to run lean on the top end. Mixture and idle screws don’t adjust anything above the midrange of the power band. A fine wire can be used to clear any debris that could block fuel flow through the jet. Also check the float level. If the float is set too low it could be starving for fuel at higher rpms with full throttle. Chuck
> On Jun 10, 2020, at 11:45 AM, David Risch via CnC-List > <cnc-list@cnc-list.com> wrote: > > > Thanks Josh > > Yamaha 4hp 2 cycle. I can get serial number if you need more info… > > David F. Risch > (401) 419-4650 > > From: CnC-List <cnc-list-boun...@cnc-list.com> On Behalf Of Josh Muckley via > CnC-List > Sent: Wednesday, June 10, 2020 10:36 AM > To: C&C List <cnc-list@cnc-list.com> > Cc: Josh Muckley <muckl...@gmail.com> > Subject: Re: Stus-List Yamaha 4hp 2 cycle > > David, > > There has to be an orifice (jet) or screw. Are you sure a screw isn't hidden > under a plastic cowl? > > Get me an exact make and model so I can do some research. > > Josh > > > > On Wed, Jun 10, 2020, 08:08 David Risch via CnC-List <cnc-list@cnc-list.com> > wrote: > Josh and Chuck, > > Mixture is new with AV gas so no issues there. Only one adjustment screw on > carb. Seems to only affect low throttle. As said all good in neutral and > good up until ¾ throttle in gear. Chuck mentioned if spark plug grey and > chalky, which it is, it is running lean at top end. How does one adjust top > end without adjustment screw. > > Thanks in advance. > > David F. Risch > (401) 419-4650 > > From: CnC-List <cnc-list-boun...@cnc-list.com> On Behalf Of Josh Muckley via > CnC-List > Sent: Sunday, June 7, 2020 10:17 AM > To: C&C List <cnc-list@cnc-list.com> > Cc: Josh Muckley <muckl...@gmail.com> > Subject: Re: Stus-List Yamaha 4hp 2 cycle > > Follow my carb tuning video. Post back with questions. > > https://youtu.be/caIdvC8WGDg > > Sounds like the idle/throttle screw (T) is keeping the butterfly open too far > with no throttle applied. It just so happens that in gear there is enough > load to slow 'er down. At full throttle is sounds like probably too much > fuel (H). I think that if it was too little it would die. Since both of > these "symptoms could be a result of too much low throttle fuel (L) you > should probably start by dialing it back a bit and see how thing go. By > doing this you will lower the fuel at idle AND lower the fuel a full > throttle. If you're lucky and my diagnosis is correct then you'll kill too > birds with one stone. > > My advice is based on having 3 adjustment screws H (high throttle), L (low > throttle), T (min throttle). If you're missing any one of these then it has > a jet which serves in its place. > > Josh Muckley > S/V Sea Hawk > 1989 C&C 37+ > Solomons, MD > > > On Sun, Jun 7, 2020, 09:29 David Risch via CnC-List <cnc-list@cnc-list.com> > wrote: > So instead of giving it away I rebuilt the carb and half dozen other fixes > this winter. > > Runs and idles great, but at full throttle she bogs down continues to run, > but sounds rougher. When out gear it goes right to full throttle. > > Perhaps overpropped? > > Sent from my Android. Please forgive typos. Thank you. > > _______________________________________________ > > Thanks everyone for supporting this list with your contributions. Each and > every one is greatly appreciated. If you want to support the list - use > PayPal to send contribution -- https://www.paypal.me/stumurray > > _______________________________________________ > > Thanks everyone for supporting this list with your contributions. Each and > every one is greatly appreciated. If you want to support the list - use > PayPal to send contribution -- https://www.paypal.me/stumurray > > _______________________________________________ > > Thanks everyone for supporting this list with your contributions. Each and > every one is greatly appreciated. If you want to support the list - use > PayPal to send contribution -- https://www.paypal.me/stumurray >
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