SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: SLCKREG on April 11, 2009, 01:55:02 PM
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Got the new motor out yesterday, and according to my a/f meter she seemed a little lean at cruise(15.5ish). I've bumped the jets up a couple of steps,front and back. I guess my questions at this point are, how does temp effect things? It was only about 50* yesterday. And if I idled/cruised about 8-9 lbs of vac would a 6.5 pv make me too lean, or too rich at transition. I don't really know what pv is in there, it must be marked on the opposite side that the bowl comes off of. Fwiw I have a pv only on the primary side , nothing on the secondary side. Thanks in advance, Kreg
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Got the new motor out yesterday, and according to my a/f meter she seemed a little lean at cruise(15.5ish). I've bumped the jets up a couple of steps,front and back. I guess my questions at this point are, how does temp effect things? It was only about 50* yesterday. And if I idled/cruised about 8-9 lbs of vac would a 6.5 pv make me too lean, or too rich at transition. I don't really know what pv is in there, it must be marked on the opposite side that the bowl comes off of. Fwiw I have a pv only on the primary side , nothing on the secondary side. Thanks in advance, Kreg
Hoping you meant 8-9 inches of vaccum, not pounds...The colder the air is the more dense it becomes, if you're running at 15.5 at cruise your pretty close, wouldn't mind a bit more fuel I use 14.8:1 as a good clean ratio, I would get two more steps up on the primary, leave the secondaries alone until you know what she's doing balls out. As for the power valve, I would think a 6.5 will get you close as far as a cruise, depends on what your going to do with it. Not really enough info to otherwise know if the setup is close...
GT
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Ummm I guess that gauge is inch pounds.lol It idled about 12.5-13,wot was 13ish. At times at cruise it went 16+ and even off the scale (over 17) Everything else I thought looked "close". So as whether warms up, typically you need to go richer? And what direction would I go with the pv to take a step richer?
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Ummm I guess that gauge is inch pounds.lol It idled about 12.5-13,wot was 13ish. At times at cruise it went 16+ and even off the scale (over 17) Everything else I thought looked "close". So as whether warms up, typically you need to go richer? And what direction would I go with the pv to take a step richer?
Virtually anytime you are speaking carburation, up is more, so the bigger number on the PV the more vacuum it will hold closed, I'm thinking on a boat engine properly carbed you should be in the 6.5-7.5 zone, so that being said, the PV (if it was a 6.5) would have been closed or non- richening, the jetting will effect the cruise numbers not necissarily the PV unless you pulled in a bit more throtlle which would have lowered the vacuum below that magic 6.5" (again if it were a 6.5).
When you talk about a cruise mode, I am asuming that you are only in the primaries, is this the case?, vacuum amounts are an indication of how much the carb is restricting the air intake, that's all, so it's a prety good tool to use to check engine load, the more load the less vacuum.
I would not focus on the PV unless you think the throttle response is somewhat soft or "spongey".
What jetting do you have now and do you have the AF meter set up for the fuel you are using? You can get some pretty ugly numbers if the meter is set up for gas and you're using methanol enhanced fuel, just a thought...I would not take the air temp too seriously but for the record, the more dense the air (lower temp) the more fuel you could potentially need, so if it's lean now, it may be OK on a hot day (read;less air)...
I hope I didn't confuse the issue and/or blow it out of my ass, I am speaking of the top of my head which is somewhat hungover from frosty adult beverages from last night... ;D
GT
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Thanks GT, I think the gauge is calibrated for gas, but I don't know for sure. I think it's about right, yesterday I had stock jet's and pv. 72'S up front, and 87's in the rear. I had no idea what way to go with the pv, if the jetting change didn't help. One last question(yeah right) if the ground strap(on the plug) is/was solid white, would that be a mixture issue? or a heat range /plug issue.FWIW The boat ran great, that's why I'm worried.lol
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Thanks GT, I think the gauge is calibrated for gas, but I don't know for sure. I think it's about right, yesterday I had stock jet's and pv. 72'S up front, and 87's in the rear. I had no idea what way to go with the pv, if the jetting change didn't help. One last question(yeah right) if the ground strap(on the plug) is/was solid white, would that be a mixture issue? or a heat range /plug issue.FWIW The boat ran great, that's why I'm worried.lol
What color was the insulator? Sorry to answer a question with a quesion, but that is what matters, not necissarily the tip or the electrode, you're looking for a maple syrup or tan color, but don't even try reading a plug that idled, the information will be worthless, make a run and get out of the throttle and as soon as the boat feels safe to shut down hit the key, then pull a plug and read it, mo betta info...MoFo O0 ;D
GT
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I gave up reading plugs, that's why I invested in a gauge. Fwiw the insulator is tan. You've answered a lot of questions, thanks. I think a pv change is in my near future too 8).
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Thanks GT, I think the gauge is calibrated for gas, but I don't know for sure. I think it's about right, yesterday I had stock jet's and pv. 72'S up front, and 87's in the rear. I had no idea what way to go with the pv, if the jetting change didn't help. One last question(yeah right) if the ground strap(on the plug) is/was solid white, would that be a mixture issue? or a heat range /plug issue.FWIW The boat ran great, that's why I'm worried.lol
I hope you're working on a spread bore carb....(primaries smaller than the secondaries), If not, try to stay fairly square on the jet sizes, maybe one or two jet sizes down from the secondaries on the primaries, if a square bore..
Good luck with it ;)
GT
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GT, shouldn't it be squared only on carbs that have a secondary power valve? All the carbs I've done have about 8 to 10 sizes different between the primary and secondary, except for an HP carb on my Mustang, they're only a couple apart but it has primary and secondary power valves.
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GT, shouldn't it be squared only on carbs that have a secondary power valve? All the carbs I've done have about 8 to 10 sizes different between the primary and secondary, except for an HP carb on my Mustang, they're only a couple apart but it has primary and secondary power valves.
Yeah but 15 jet sizes.. :o, IMO he should be like 80/85, he is reading fat on top, and lean in the middle, the only thing we don't know is if the secondaries were totally closed, I made an assumption based on his vacuum readings they were closed....
The secondary powervalve only comes into play in either overcarbureted or heavy accelleration situations...IMO
Also, FWIW I said "fairly" square ;)
GT
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I have no pv in the secondaries, the carb out of the box had 72's and 87's.
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I have no pv in the secondaries, the carb out of the box had 72's and 87's.
Is it a square bore, do you have a list #?
GT
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4150 series # 9022, 800 cfm marine dp.
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You are running a PCV valve aren't you? :sly:
GT
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Just 2 breathers. no pcv
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Just 2 breathers. pcv
Hmmmm, I would think it would work right out of the box, but it sounds a tad lean to me, it will get good mileage though, so you gonna go with a 7.5 PV? I think it would be a good move either way...
Looks like it did come with a 6.5 PV, (which should be really close IMO) a 7.5 will somewhat improve throttle response, but I would think that would be about it. :-\
GT
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To really adjust the mains, you need to see what MPH / RPM you get at WOT and adjust for max.
If you are trying to find a balance between milage and performance, leaning the primaries while bumping up the secondaries is acceptible (but won"t give you as much power as if a 4 bbls were ratio'ed the same).
I notice on my engine, I cruise around with 9-11 inHG , so by me having a 6.5 PVs in there, it is (intentionally) lean at mid throttle. Unless the carb is super lean, the PV should have nothing to do with throttle response, that is the job of the acc pump(s). In tuning my engine BTW - I needed the smallest pump cam on the smallest pump setting with a very large squirter (.40) to get the throttle response great without bogging.
You typically size the PV's according to engine idle vaccum. I pull 10 inHG at idle - so I need to run something about 2 inHG lower (at a minimum) to be right - the 6.5's are the most common size so that is what I used. The factory 8.5's in my 9776's were marginal and showed when I came off plane and the inHG dropped to 8 ish - the PV's opened dumping a ton of gas in like I was at full throttle (because that is what the PV's thought), and killed the engine. The 6.5's eliminated the dreaded off plane engine stopping along with a bit more fuel on the idle screws.
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All in all I was pretty happy with the throttle response, max r's was only about 5400 which was a little disapointing. I bumped up both the primarys and secondarys 2 #'s and haven't got to rerun it yet, and this weekend isn't looking real promising weather wise either. It just seemed lean enough it had/has me worried,I don't want to hurt my motor. I have to say the af gauge is one of the better purchases I've made. Not overly concerned with milage. Idle vac was 9ish if I remember right. I can't find a # anywhere on the pv(front or back) so I have no idea wtf is in there. The carb is also too small for the motor fwiw.
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Is 13.3 ish to lean for wot #'s?? I took both sides up 2 jet sizes, I think I'm going to go 2 more. Will/would I make more, or less power at 12.5 than 13.5? Is 13.3 or so a little to "on the edge"? Also it seemed to idle alot leaner than I remembered last time. Like 14 ish
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Glenn, you wanna attempt my 750's with a hangover? no digital info, just spark plugs! I may bring it up there for yah, lol
Ray