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I'd adjust the floats first. Reversion off idle doesn't seem possible. But I'm no expert. However I am a person who has had some problems with it!
My understanding is you want somewhere around 12.4 AFR during acceleration and under load. Which in boats is most of the time. The wedge idea came from some early straight drive engines i have seen. And I agree, it can't tilt you any more than running level or you will get a different problem. Question, are these carbs normally used in a boat? |
Originally Posted by Ballistic Beak
(Post 4692242)
I’m looking for some guidance on getting my carb to function correctly.
Background: 27’ Fountain Fever, 509CI BBS, FAST dual wide band, Pro Systems Venom II carb, HP500 intake, AFR heads etc. Bravo 1 with 27pitch 5 blade. Currently when I try to get on plane the boat coughs and stumbles. The problem occurs around 2800-3000 PRM when the boat is at maximum bow angle. The AFRs are reading ~10.7 (I’ll verify the number, going from memory here). I can push the throttle more with no increase in engine power. Once I finally get the boat to plane out, no further problems with power. I can run to 5000 rpm, AFRs look safe. It’s only getting on plane that is a problem. I swapped on a Holley 800 set up for an HP500 clone engine and the problem completely went away. No issues getting on plane, able to increase throttle with the bow in the air without any stumbling. Where should I start looking in the carb? My thought is too much fuel combined with a severe angle the carb is sitting when the bow is in the air is contributing to the problem? |
Originally Posted by NHGuy
(Post 4692562)
I'd adjust the floats first. Reversion off idle doesn't seem possible. But I'm no expert. However I am a person who has had some problems with it!
My understanding is you want somewhere around 12.4 AFR during acceleration and under load. Which in boats is most of the time. The wedge idea came from some early straight drive engines i have seen. And I agree, it can't tilt you any more than running level or you will get a different problem. Question, are these carbs normally used in a boat?
Originally Posted by GPM
(Post 4692567)
Buy the 800, or maybe match everything to it.
I'll be attending the Sacandaga Fun Run this weekend, I'm sure there will be enough time to swap back to the pro systems carb and do some troubleshooting. Ryan |
Is it coughing back thru the carb? Sounds like it might be lean. Try richening up the primary idle screws. It might be having trouble getting good fuel flow from the boosters at such a high load / low speed situation
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next time try pumping the throttle fast while planing accelerator pumps will help if lean. |
if the AFR is 10:1 then its running way rich....sounds to me like the fuel is sloshing through the metering block vent and enriching the engine...maybe a vent extension would help in blocking the sloshing fuel from getting in when in the bow up position.......
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Afr meters work great when the engine is running in a good state. Once they start coughing, sputtering, backfiring, i wouldnt even bother turning the wideband on
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During alot of trials and tabulations doing on the water carb tuning with widebands, ive had a few engines where ive seen afrs in the 10s. While yes , its rich, it has never made the engines sputter, lose tons of power, fall on their face, etc. Heck, some hot oem engines are actually tuned so they are in the 10s at wide open throttle..
i see the lean idle circuit thing alot. The carb people tell you to adjust screws for highest vacuum reading, or basically leanest setting you can get. Works great on cars, where you have an accelerator pump, or two in holleys case, to help give that burst of gasoline to get the engine revving to a speed where the airflow makes gas able to be drawn from the boosters. In a boat, the accelerator pumps become nonexistent in a getting on plane scenerio. The engine either needs gas from the boosters, or idle circuit. He may need to adjust the high speed air bleeds if in fact its a lean condition and richening the screws dont help. #32 is kinda big for a high speed air bleed. Id prob step down to a 28 to start |
10.7 is flat out rich for a N/A application and not helping the situation. Get it closer to 11.8 at that same break point and see how it runs.
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Originally Posted by Trash
(Post 4692748)
10.7 is flat out rich for a N/A application and not helping the situation. Get it closer to 11.8 at that same break point and see how it runs.
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