Evinrude argument

[gustafsonerik]

76 70hp rude long story short,it hestitates sometimes and bogs down unless you give it a little choke,carbs were modified,i run it without the air intake on just plain carbs,my friend says that could be part of the problem , I don't see how that makes a difference,any opinion if that really matters or not??

 

[RogersJetboat454]

Re: Evinrude argument

76 70hp rude long story short,it hestitates sometimes and bogs down unless you give it a little choke,carbs were modified,i run it without the air intake on just plain carbs,my friend says that could be part of the problem , I don't see how that makes a difference,any opinion if that really matters or not??

More air with no adjustment to raise the amount of fuel = lean mixture.
The choke is helping to balance things out (restrict air flow, and add fuel).

 

[Chinewalker]

Re: Evinrude argument

The air box also acts as a small bit of tuning as there is a standing sonic wave in front of the carbs while running. The plate actually "bounces" that wave back into the carb, giving a small charging effect. Not much, but it does make a difference.

 

[metriccrescentwrench]

Re: Evinrude argument

carbs were modified

How were the carbs modified?

i run it without the air intake on just plain carbs

That will mess up the air/fuel ratio. I don't know about the "charging effect" (not saying it ain't so, just that I don't know about it) but I do know that the factory uses the intake cover to balance airflow between carbs.


Edit to add: If it were so easy to make our engines run better by leaving off the intake cover surely OMC would have figured that out a long time ago and saved themselves the cost of designing, manufacturing, and installing all those intake covers.

 

[phillnjack2]

Re: Evinrude argument

at first it seems that no air covers gives better breathing, like a sort of raim air if plenty is circulating round the motor.

But in reality these covers are actualy tuned tto the engines,sounds daft but its a fact.

if you get totaly different set up like say with the tuned carb velocity stack trumpets then that is a different matter,but even they
have to be made just right to get the fuel/air mix perfect.

ive had it before several times on cars where you take of the air filter housing and it goes wonky.
sometimes people think the motors run better due to hearing more noise, but the proper air cover made to work with the
carbs is the best thing to put back on and set carbs up like they should be to get better all round performance.
maybe your good at WOT but it wont be good at idle or vice versa.


exactly what is the mods you have done with the carbs ? have you re-jetted to give more fuel or less fuel ?
what is the cfm of air needed for this set up, and at what pressure is it needed.
there is a lot more to getting fuel/air right than we often think.

plus there is also the dampness of the air if not on and the more chance of dirt going straight into the throats and
straight the through into reeds and then the crankcase etc etc.

just my thoughts on it


phill

 

[gustafsonerik]

Re: Evinrude argument

There was a tbs bulletin saying the jets needed to be rejetted,I did that but it would still big down without choke but today I learned that the air intake has to be on for it to run right,I never thought it made that big of a difference but it does ,

 

[fireman57]

Re: Evinrude argument

They didn't get rejetted but were drilled out to a different spec. I know that it took all the hesitation out of mine and it runs great. Easy fix too.