Eureka! But now I need help finding a part number and source for this carb part...

[NMShooter]

1988 85hp Force

Was going to take my boat out for a test run tomorrow, and tried to do a cold start here at my house. No joy.

Found out that my idle advance was too much, and the engine was not choking right (probably flooding from the primary being open).

Pulled off the cam linkage, let the carb butterfly close all the way, and it started right up. Rats.

Here was/is the problem. Remember that I mentioned in a previous post that I could not get the throttle cam mark to line up with the carb roller and touch at the same time? I pulled the oblong screw that holds the roller sleeve in place, and the screw is bent.

Because of this bend, I can do one of two things. I can lengthen the cam link long enough so that the butterfly is well open at full throttle, or I can shorten the cam link so that the butterfly is closed at idle. But not both.

So.... I am going to put this screw in a vice and see if I can gently straighten it out. However, I want to get a replacement screw for this thing.

Does anybody know the part number for this oblong screw, and a source for the part?

This bend might not look like much, but it is enough to screw up the travel of the link :

Thanks....

 

[NMShooter]

Re: Eureka! But now I need help finding a part number and source for this carb part.

I managed to straighten that screw out a bit, and reinstalled. However, another question about the synchronization sticky.

How much is "significantly open", when talking about the butterflies? Should they be perfectly horizontal or slightly closed?

Even now, in order to get to about 900 rmps idle (running off of water muffs), I notice that the cam is driving the carb roller forward a bit. The carb butterflies are not completely relaxed at the idle / start position. I am concerned again that it won't start well from dead cold.

I can adjust it one of two ways :

1) So that the carb opens fully, but does not close fully with a 900 rmp idle.
2) So that the carb closes well and idles at 900 rpm, but does not open anywhere near fully.

This really makes me wonder if my timing is screwed up.

Argggghhhhhhh.

 

[NMShooter]

Re: Eureka! But now I need help finding a part number and source for this carb part.

My engine number is : 858F8B

I believe that the number for that eccentic screw is F333316, and the roller is F92759. Any confirmation appreciated!

 

[Frank Acampora]

Re: Eureka! But now I need help finding a part number and source for this carb part.

If you look at the operation of the carb butterflies, you will see that they open about 1/4 of the way until timing is fully advanced. This is cruise position where you get almost maximum speed and best fuel mileage. The finger on the cam uses the last bit of travel on the control handle to fully open the butterflies. The engine makes a lot more noise, goes a couple of miles an hour faster, and uses way more fuel.

Now, because the butterflies are so much larger than the venturis, because there is such a large difference between cruise and full throttle positions, and such a small difference in speed, a slight deviation from horizontal will make no difference in performance. Eyeball horizontal is "good enough for government work."

Significantly was worded for those anal perfectionists who would spend multiple hours trying to get them perfect when it is not absolutely necessary and then would come back onto the forum worrying that they could not get them exact. ---Yeah, Guilty as charged: I spend a lot of time trying to get them perfect but it makes me feel better and does not help performance. Mr. Monk is my mentor. LOL

 

[jerryjerry05]

Re: Eureka! But now I need help finding a part number and source for this carb part.

That screw is supposed to be bent!!
It's called an eccentric cam screw.It's supposed to help align the lines on the cam.J

 

[NMShooter]

Re: Eureka! But now I need help finding a part number and source for this carb part.

Eccentric does not mean bent. It means deviating from circular, or being elliptical. The axis of the threaded shaft should be parallel to the axis of the roller shaft.

The threaded portion of the screw is bent such that the roller that rides on it is not perpendicular to the throttle cam. I edited the above picture to more clearly illustrate the problem.

You can see in the second picture above that the roller clearly is not perpendicular to the thrust line of the throttle cam. This is a bad thing for multiple reasons.

I'm hoping that the screw that I ordered is the eccentric one. if not, I may have a roller machined slightly oversize to see if that will correct the linkage. I don't want to overstress that screw more than it already has been.

 

[NMShooter]

Re: Eureka! But now I need help finding a part number and source for this carb part.

The "significantly open" question was because the butterfly was no where near horizontal. I would say that if you were looking at it from the side, using clock notation, instead of the leading edge pointing at 3 o'clock, it was actually closer to the 2 o'clock position.

 

[jerryjerry05]

Re: Eureka! But now I need help finding a part number and source for this carb part.



(Eccentric does not mean bent. It means deviating from circular, or being elliptical. The axis of the threaded shaft should be parallel to the axis of the roller shaft.)
Clearly made that way!!!

One more time the screw is supposed to be that way.
It helps align the roller with the mark on the throttle advance!!! SEE PICS!
How much did the new screw cost??

 

[NMShooter]

Re: Eureka! But now I need help finding a part number and source for this carb part.

$3 Hopefully here this week.