Repropping 2005 Honda BF90

[Jprevat]

Hey guys,

I just picked up a Scout 162 with a 2005 Honda BF90 and need to find a new prop. I have that famous lean out condition right after I apply the throttle that I am trying to work around. Right now it has a stainless 3 blade 17 pitch and I would like to switch to a prop to allow the engine to spool up a little quicker to work through the lean condition in the rpm range. Would a 4 blade be worth considering? Should I drop farther down than a 15 pitch?

I know there is a prop section but I thought some of you may have found a good work around for this Honda specific problem.

Thank yall ahead of time for any help or suggestions.

 

[ahicks]

Is this an injected engine, or carbed?

If carbed, I run the idle adjustments pretty rich and have no issue with that flat spot many talk about.

Our 90 is on a pontoon boat, but I can share that a 13" prop lets the engine turn up just a hair over 6k. Low and mid range punch is incredible, but the engine is sounding pretty busy at WOT. I ran across a deal on a NOS Honda 15" prop, so I picked that up. Now, max rpm is about 5300. I still have a pretty incredible low mid range punch, the boat picked up 1mph (a big deal on a pontoon!), and the engine seems/sounds much happier at WOT. It does however, pick up the last 10-15% of it's top speed at a little (noticeably) slower pace.

Bottom line, I like the bigger prop much better than the prop that let's it turn up max rated rpm.

 

[Jprevat]

Thank you for the information. Does running it rich have any adverse effects on the idle. I read it can cause it to be choppy but that seemed vague.

 

[Sea Rider]

If you haven't tached current 3 blade 17 pitch prop won't know if performs good, bad or extremeky awful. Need to know what's the min-max wot rpm range factory stated for that engine. From there need to tach current prop as usually loaded on calm. flat water cond and report max achieved wot rpm numbers.

Can go from there maximizing a less pitch prop to pull wot revs up to suit best for your application. No prop will cure the lean out cond, need to fine tune the carb to cure that issue.

Happy Boating

 

[ahicks]

No not the way they're set. I have them set about 1/2 turn richer than the suggested. My thought is the "suggested" is the reason for the stumble.....

Been a while. Not sure if they are at 1.5 turns or 2.5 turns....

 

[Jprevat]

Thank you for the input guys. The one article I read by a certified Honda mechanic said to reprop first because the carbs weren't supposed to be messed with. It was even said that I needed a 1000 degree soldering iron to pop the covers off the mixture screws. So that had me spooked.

how did you adjust yours?

 

[ahicks]

Though these 90's are nearly all identical, the older engine weren't equipped with those covers. I haven't had to remove a set of them-yet-so I can't be of any help there.

 

[Jprevat]

I was looking at mine yesterday and didnt see any caps on the starboard side of the carbs maybe I got lucky and they aren't there.

 

[Sea Rider]

Any carb setting factory adjusted to when engine was delivered new will need to be re adjusted afterwords as needles will eventually get loose over time due to engine's usual unavoidable vibration, such issues happens with carbs in which you can mess with exposed idle screws. Assume applies same with carbs having hidden idle screws ?

Ideal would be to idle adjust any 2-3 or higher carbed engine with a analog or electronic vacuum gauge, only possible to install in carbs which count with a protruding neck to attach vacuum's rubber hoses to re adjust each carb to work with spot on idle rpm.

Happy Boating

 

[ahicks]

The 90 is set up with a set of 3 screws in the intake manifold that are replaced with nipples allowing you to run a vacuum gauge (or better yet, 3 of them fastened to a board or something hung on the side of the engine!) to balance the carbs. If you're familiar with doing this on a motorcycle (or other multi carb setup), it's the same process

I'm not real sure carb balance might be causing a flat spot on acceleration though. Generally, that's a good place to go if you can't get the nice even idle the 4 strokes are known for, and you know for absolute sure the carb internals are spotless!

 

[Jprevat]

I'll have to take a look into all of this and see what I can find out. It idle beautifully right now but as I lean into it at about 2200 rpms I get a half second pause and momentum stalls. It picks back up quickly and continues to plane.