Yammie compression & rpms?

[pat246]

More findings from sick yamaha 40 all the numbers I could find are 1984 Yamaha 40 HEO 6H4 Model#101071 Rebuilt the carbs set the jets to spec. as stated in the manual. Readings from compression test are 92 lbs. for each cylinder. The moter idels great runs good untill about 3/4 speed on water. But falls on its face at WOT. If manual choke is pulled out 1/2 motor runs much better but does not reach optium performance. Does anyone have any suggestion an where to go from here.

 

[kk4df]

Re: Yammie compression & rpms?

Sounds very similar to the problem with my Yamaha 8HP, except mine was solved when I rebuilt the carburetor, removing all the old varnish and deposits. It still sounds like it is starving for fuel. I'd look at things like the fuel pump, fuel filter pluggage, cracked fuel line, or even fuel tank vent. Question: Does it get any better when running WOT if you pump the bulb on the fuel line??

 

[pat246]

Re: Yammie compression & rpms?

No even if you pump the bulb it still goes down on rpms at WOT. I have replaced the fuel lines and the filter.

 

[bubbakat]

Re: Yammie compression & rpms?

If the high speed jets were or are pluged sometimes pumping the bulb will not even effect it.

 

[rodbolt]

Re: Yammie compression & rpms?

by pulling out the choke you force the fuel to go rich. you bypassed all the circuts in the carbs and are drawing fuel striaght up the emulsion tubes. in other words do your carbs again and make sure all varnish dirt and trash is removed. this will also be a good time to rebuild or replace the fuel pump as well.<br /> good luck and keep posting

 

[pat246]

Re: Yammie compression & rpms?

First of all I have to say this is a great site lots of value in the info posted. I Finally found the prolbem or what I think could have been the problem the bolts on the reid valves were not torqued to the correct value to loose probaly by previous owner retightened also new gasket between reid valves and carbs was defective replaced and cleaned carbs again. Motor runs great now plenty of getty up and go. could have been the compination that was causing my prolbems. Thanks for all the great advise.