Is re-jet required for .40 over bore? 1964 28hp Speeditwin

[kdiddle]

I have a 1964 Evinrude Speeditwin 28hp that I've gone through and replaced nearly everything on/in it. One of the things that entailed was to bore out block .40 over and replacing pistons/rings. My question is whether or not re-jetting is required due to the increase in displacement from the additional bore? I've read somewhere that larger jets are required, yet others say that simply increasing the richness of the mixture(s) is acceptable. Can anyone clarify?

 

[racerone]

Your carburetor is shown with an adjustable high and low speed mixture needle.-----Where have you " read " this information about changing the jets.------Your carburetor as it is , gives you infinite range of adjustment.----There is no need to change any parts.------But YOU NOW NEED TO KNOW how to adjust your setting so that it is correct.

 

[Sea Rider]

If motor runs perfect and strong at wot with previous carb settings no need to adjust anything. High speed Jets are fixed and non adjustable. Probably will need to adjust the fue/air mixture screw a bit if motor does not idle smoothly ?

Happy Boating

 

[racerone]

?????---SEARIDER----The high seed jet on the motor in question is adjustable !!------It is NOT a calibrated orifice.----Perhaps I should post a you tube video and show you this motor !

 

[kdiddle]

ok, thanks for the responses guys. I am in the process of rebuilding my carb as I can't seem to get rid of the low speed cough/sneeze, no matter how much I tinker with the low speed needle (I've already cleaned/rebuilt it once before). I wanted to check while having my carb apart, in case I needed to swap something out...

I don't have the thread where I saw the re-jet requirement mentioned, but maybe a thorough carb cleaning and readjusting the needles will straighten it out...

 

[F_R]

If you have the motor you say you have, and if it has the correct carburetor, then it has an adjustable jet---nothing to replace..If adjusting the slow speed needle won't stop the low speed sneeze, there probably is something else wrong. Take a look at the throttle linkage. Half the motors I've seen are screwed up in that area by somebody that didn't know what they were doing.

 

[racerone]

Throttle plate MUST BE CLOSED for proper idle.-----There is an adjustment that looks wrong to a novice.----When in fact it is correct.------Many folks adjust the STOP on the throttle rod when they should not touch it.

 

[kdiddle]

Thanks for the input F_R. I'll go through the carb just to make sure all is well there, and I'll make sure and read up on the linkage adjustment to make sure its set correctly. I don't 'think' I've moved it, but who knows if its been right at all. Thanks again!

 

[racerone]

Some 50 years ago a fellow brought a 28 HP motor into the authorized service shop.------" won't idle "-----I did the service work and had it running like new !--------Happened to be at the launch ramp for free entertainment on Saturday afternoon.----Spotted a motor being worked on and went over to possibly assist.------Sure , I recognized the same motor and owner.----" "Won't idle " he said.------After checking a few thing he admitted that he had adjusted the stop on the throttle advance rod.------Get this ----He said he brought it in for service and I moved the stop.-----He moved it back to where he thought it should be before he went boating !-----I set it back to where my training said it should be.-----Motor idled perfect again.-------I forget my exact words to him.----He was a paramedic he said and not a mechanic.

 

[kdiddle]

Wow - that's crazy he moved it after it had been serviced...my sneezing is more when I start advancing throttle and not so much at idle, but I suppose the linkage settings might still be to blame. I'll need to read up on how it should be adjusted...the service manual I bought doesn't detail anything around that...Off to Google I go...