Idle control - Big cams and carbs
08-23-2007, 08:22 AM
#21
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Jack,
Thanks for the idea. I sent an e-mail to MSD last night and asked them to read this OSO thread. As they have a number of marine focused products, maybe an idle RPM control feature is something they might want to add to their marine product offering.
Thanks for the idea. I sent an e-mail to MSD last night and asked them to read this OSO thread. As they have a number of marine focused products, maybe an idle RPM control feature is something they might want to add to their marine product offering.
08-24-2007, 11:54 AM
#23
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Although an ignition advance would likely fix/mask my in gear idle problem, I got a great off-line lead from an OSO'er. He has the same size twin engine Vee and he can shift from 1000 RPM in neutral @ 650 RPM in gear at idle with out stalling.
During our discussion on how similar our set-ups were, including total timing, ignitions, cam profile, carbs, HP, etc. we discussed vacuum. I know my vacuum at idle in neutral, but never tested the vacuum at idle in gear. His vacuum drops from about 10" @ 1000 RPM in neutral to close to 0" @ 650 RPM in gear. He uses no PV's and more jet, and I use 3.5 PV's and less jet. If my vacuum drops low at idle in gear, I may have been trying to fine tune my idle in a flood. (A/F ratio at mid-range on the top end are dialed in)
I plan to run an in-the-water vacuum test & an A/F ratio test at all RPM's on both engines. One engine as is, and one with no PV and +6 sizes on jets. I think we may have hit on the problem and solution. After my next boating trip, I will post the results. I can at least feel good for the next two weeks!
During our discussion on how similar our set-ups were, including total timing, ignitions, cam profile, carbs, HP, etc. we discussed vacuum. I know my vacuum at idle in neutral, but never tested the vacuum at idle in gear. His vacuum drops from about 10" @ 1000 RPM in neutral to close to 0" @ 650 RPM in gear. He uses no PV's and more jet, and I use 3.5 PV's and less jet. If my vacuum drops low at idle in gear, I may have been trying to fine tune my idle in a flood. (A/F ratio at mid-range on the top end are dialed in)
I plan to run an in-the-water vacuum test & an A/F ratio test at all RPM's on both engines. One engine as is, and one with no PV and +6 sizes on jets. I think we may have hit on the problem and solution. After my next boating trip, I will post the results. I can at least feel good for the next two weeks!
08-24-2007, 06:29 PM
#24
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Thanks for posting this solution...I learned not only this, but realized my earlier post was kinda negative toward your carb setup...I apologize.
Let us know how that worked out.
Let us know how that worked out.
Last edited by Back4More; 08-24-2007 at 06:32 PM.
08-24-2007, 08:18 PM
#25
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Back,
No problems here. Maybe we can all learn something in a few weeks. If the in-gear idle vacuum is real low, this would be the best reason I have heard for no PV's. It will also be interesting to see what happens to the A/F ratio & vacuum at each RPM level from 3000-6000 with and without PV's. Do the PV's ever close at cruise above 3000 RPM? I'll let you know...
No problems here. Maybe we can all learn something in a few weeks. If the in-gear idle vacuum is real low, this would be the best reason I have heard for no PV's. It will also be interesting to see what happens to the A/F ratio & vacuum at each RPM level from 3000-6000 with and without PV's. Do the PV's ever close at cruise above 3000 RPM? I'll let you know...
08-26-2007, 06:51 PM
#26
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Ben,
I know that guy your speaking of from the P.M. you got. He's no dummy and I wish I could remember half the crap he has forgotten. He helps me out all the time when I'm in a jam, but then again that what fathers are for . He called me and told me about your set up, pretty amazing that they are so close on all aspects down to hull choice.
I know that guy your speaking of from the P.M. you got. He's no dummy and I wish I could remember half the crap he has forgotten. He helps me out all the time when I'm in a jam, but then again that what fathers are for . He called me and told me about your set up, pretty amazing that they are so close on all aspects down to hull choice.
09-13-2007, 08:43 PM
#27
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Here is am update on my carb testing last weekend. The testing got cut short because of a little water in the oil issue...
The base line set-up's on these Holley #7320 1150 CFM 2-circuit carbs were:
Base line:
87 X 87 jets, 47 X 47 idle air bleeds and 3.5 PV. The A/F ratio was 13.6 to 1 from 3000-5500 RPM and then 12.5 to 1 @ 5600+. I was good with this mid range and top end A/R ratio #'s, but the idle quality sucked.
My off line OSO tip was to try no PV's as the vacuum gets low at idle in gear and the PV's then open and ruin the idle.
1st test:
I set up one carb to the Holley factory spec of 95 X 95 jets, 53 X 53 idle air bleeds and no PV's. The vacuum dropped from 5.0-6.0 + in neutral idle to 2.0-2.5" in gear idle confirming that the 3.5 PV's had been opening at idle in gear.
With no PV's, the idle was now great (no stalling!) and we could idle @ 600-650 RPM in gear. However, the mid-range set-up was not close with the A/F ratio now at 11.9 to 1 from 3000-5500 RPM.
2nd test:
88 X 88 jets, 47 X 47 idle air bleeds and no PV's. The mid-range A/F ratio was now 13.6 to 1 from 3000-5500 RPM (measurements at every 500 RPM) but...at 6000 RPM (constant-not WOT) the A/F ratio climbed to 14.1 to 1! Too lean for me so we backed off.
As you can see, the no PV's fixed the idle quality but the trade off is no extra fuel from the PV' s at the low vacuum levels as you approach WOT.
Test #3 didn't happen due to the water issue.
The question for the 2008 is would I be able to get a good/acceptable idle with 2.5 PV's and at what RPM does the vacuum drop below 2.5 so the PV's open at high RPM? Another choice will be to live with 90-93 jets and no PV's and a constant rich fuel condition from 3000-5500 to have a safe A/F ratio at WOT.
I will report back in the spring of 2008! Maybe it is time to go EFI...
Hey Straight, tell you dad that he was "right on" with the tip on low vacuum at idle in gear and he may also be "right on" with the 93 X 93 jets.
I will have to wait to find out.
Ben
The base line set-up's on these Holley #7320 1150 CFM 2-circuit carbs were:
Base line:
87 X 87 jets, 47 X 47 idle air bleeds and 3.5 PV. The A/F ratio was 13.6 to 1 from 3000-5500 RPM and then 12.5 to 1 @ 5600+. I was good with this mid range and top end A/R ratio #'s, but the idle quality sucked.
My off line OSO tip was to try no PV's as the vacuum gets low at idle in gear and the PV's then open and ruin the idle.
1st test:
I set up one carb to the Holley factory spec of 95 X 95 jets, 53 X 53 idle air bleeds and no PV's. The vacuum dropped from 5.0-6.0 + in neutral idle to 2.0-2.5" in gear idle confirming that the 3.5 PV's had been opening at idle in gear.
With no PV's, the idle was now great (no stalling!) and we could idle @ 600-650 RPM in gear. However, the mid-range set-up was not close with the A/F ratio now at 11.9 to 1 from 3000-5500 RPM.
2nd test:
88 X 88 jets, 47 X 47 idle air bleeds and no PV's. The mid-range A/F ratio was now 13.6 to 1 from 3000-5500 RPM (measurements at every 500 RPM) but...at 6000 RPM (constant-not WOT) the A/F ratio climbed to 14.1 to 1! Too lean for me so we backed off.
As you can see, the no PV's fixed the idle quality but the trade off is no extra fuel from the PV' s at the low vacuum levels as you approach WOT.
Test #3 didn't happen due to the water issue.
The question for the 2008 is would I be able to get a good/acceptable idle with 2.5 PV's and at what RPM does the vacuum drop below 2.5 so the PV's open at high RPM? Another choice will be to live with 90-93 jets and no PV's and a constant rich fuel condition from 3000-5500 to have a safe A/F ratio at WOT.
I will report back in the spring of 2008! Maybe it is time to go EFI...
Hey Straight, tell you dad that he was "right on" with the tip on low vacuum at idle in gear and he may also be "right on" with the 93 X 93 jets.
I will have to wait to find out.
Ben
