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-   -   Target Air Fuel ration N/A engines.? (https://www.offshoreonly.com/forums/general-q/339679-target-air-fuel-ration-n-engines.html)

Eliminated572 08-12-2016 09:25 AM

Baja - In theory either way would smooth the transition, and the larger the plenum volume along with single hole spacer use would encourage even higher blend rates. This is assuming a square jetted/channeled carb. Conventional thought on progressive linkage would tell you the opposite actually. Let the primary come in before the secondary (6.5 P - 4.5 S). Overall its splitting hairs but you are staging delivery, hence smoothing the curve

Baja Rooster 08-12-2016 09:31 AM


Originally Posted by MILD THUNDER (Post 4470192)

They mentioned less reversion with the 4/7 swap in that article. I wonder if it's enough to be significant in marine use.

Baja Rooster 08-12-2016 09:36 AM


Originally Posted by Eliminated572 (Post 4470200)
Baja - In theory either way would smooth the transition and the larger the plenum volume and single hole spacer would encourage even higher blend rates. This is assuming a square jetted/channeled carb. Conventional thought on progressive linkage would tell you the opposite actually. Let the primary come in before the secondary (6.5 P - 4.5 S). Overall its splitting hairs but you are staging delivery, hence smoothing the curve

Since I'm super fat at 1k - 3k with 11.2 but smooths out in the upper into 12.5 at wot that was telling me that my primary jets are too big as its so rich at cracked throttle before the 6.5 PVs open up. I was thinking of going to 4.5 and down a jet size on the primaries.

Does that seem reasonable or am I screwing things up?

bck 08-12-2016 09:38 AM


Originally Posted by SB (Post 4470173)
Sound sells many things. Think Harley Davidson and think "I want a heavy thump at idle." :smile:

I actually have a lot of info on the firing order swaps but I need some time to put it into better english than my attempt about an hr ago that I never posted because of brutal english flow. I'll work on it in a bit.

Harley spent years in court trying to get patent/ trademark protection for that sound. I believe they gave up before a decision was made due to the huge legal expenses from other manufacturers challenging it.

MILD THUNDER 08-12-2016 09:43 AM


Originally Posted by Baja Rooster (Post 4470202)
Since I'm super fat at 1k - 3k with 11.2 but smooths out in the upper into 12.5 at wot that was telling me that my primary jets are too big as its so rich at cracked throttle before the 6.5 PVs open up. I was thinking of going to 4.5 and down a jet size on the primaries.

Does that seem reasonable or am I screwing things up?

Keep in mind , going down jet in primary, is also gonna lean wot unless you add fuel somewhere else.

MILD THUNDER 08-12-2016 09:47 AM

All this fuel tuning talk. And some guys still think they can call a carb shop, give them cubic inch, cam specs, and get a carb that will have perfect afrs out of the box??

Eliminated572 08-12-2016 09:48 AM

[QUOTE=Baja Rooster;4470202]Since I'm super fat at 1k

Well, is the super fat condition at cruise due to the PV's opening? Or simply over jetted? Could be both. Have you checked vacuum under these conditions to know what is happening? Note: blown PV's would do this as well. Verify leakage before proceeding with changes..

F-2 Speedy 08-12-2016 09:51 AM


Originally Posted by SB (Post 4470173)
Sound sells many things. Think Harley Davidson and think "I want a heavy thump at idle." :smile:

I actually have a lot of info on the firing order swaps but I need some time to put it into better english than my attempt about an hr ago that I never posted because of brutal english flow. I'll work on it in a bit.

My double swap thump at idle, its difficult to explain how an LS fo sounds, it radical then mellow, then it repeats, then it syncs. I like em...........getting a little off track sorry

Hope you get the boat sorted Tim,

Full Force 08-12-2016 10:06 AM

Ask my buddy Tommy how that worked out!!!

Originally Posted by MILD THUNDER (Post 4470209)
All this fuel tuning talk. And some guys still think they can call a carb shop, give them cubic inch, cam specs, and get a carb that will have perfect afrs out of the box??


MILD THUNDER 08-12-2016 10:24 AM

Ive heard a bunch of firing order swap cams. Never heard a cam with identical specs , in an identical engine, with identical tune, back to back with just a different firing order.

Carb idle tuning, and timing can also have a dramatic effect on the idlle sound


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