Carb Adjustments
11-12-2005, 05:29 PM
#101
Registered
Thread Starter
Re: Carb Adjustments
Finally a better ride. New carbs made all the difference. Good throttle response, smoother, less fuel burn for sure. Getting closer every day to finished with the basic setup I guess.
Rt engine topped at 4500 RPM, left at 4100 RPM. Still room for improvement. I thought I heard some faint pinging above 3500 so I ceased any runs above that. I did a plug check from 3500 RPM and found several white electrodes on both engines. Specifically stbd: #1, 6, 7 / port: #2, #6 lean #7 black with some carbon. (I figure it is on there from before or weak ign to that cyl. or something.) It was 50 degrees out there today which I think would lean it out a little anyway.
I have to check the jetting supplied with the new carbs. I'm thinking the guy was not sure how he jetted them but thought he rememberd what was in there. I just have to see with my own eves. If they are leaner I'll set them up as a baseline MCM 420 which someone said was 79 front and 90 rear and see what happens then. I set timing for 30 degrees total advance which is about 9 degrees on the bottom and it seems to work ok. I have to stop that pinging, and it only seems to be the left engine from what I can tell that is doing it. That engine also is running slower at WOT at only 4100 rpm. I think she is still overloaded with props since the right engine only hit about 4400 - 4500 max. After about 3000 RPM I also get a throttle handle split. They are even to that point and after it takes more throttle to get the port engine spinning. At least a click or two split on the kiekhaefer throttles at 3500 and up, and thats where the pinging started. I think it was pinging anyway, it was a faint sound that was not there at lower power that came on with power, almost sounded like the sound of a loose belt or something. Maybe after re-jetting and giving them some more fuel they will spin up faster. It seems the primarys are at work at 3300 and below and that sound starts when the secondaries start to open above 3300. (I indexed the throttle handle positions for primarys / secondaries)
I think I'm getting closer, at least it runs on plane now. 55MPH on top, still room to improve. 3000 RPM was about 35 and 3500 was about 42. Not a bad cruise for a big old heavy boat.
Rt engine topped at 4500 RPM, left at 4100 RPM. Still room for improvement. I thought I heard some faint pinging above 3500 so I ceased any runs above that. I did a plug check from 3500 RPM and found several white electrodes on both engines. Specifically stbd: #1, 6, 7 / port: #2, #6 lean #7 black with some carbon. (I figure it is on there from before or weak ign to that cyl. or something.) It was 50 degrees out there today which I think would lean it out a little anyway.
I have to check the jetting supplied with the new carbs. I'm thinking the guy was not sure how he jetted them but thought he rememberd what was in there. I just have to see with my own eves. If they are leaner I'll set them up as a baseline MCM 420 which someone said was 79 front and 90 rear and see what happens then. I set timing for 30 degrees total advance which is about 9 degrees on the bottom and it seems to work ok. I have to stop that pinging, and it only seems to be the left engine from what I can tell that is doing it. That engine also is running slower at WOT at only 4100 rpm. I think she is still overloaded with props since the right engine only hit about 4400 - 4500 max. After about 3000 RPM I also get a throttle handle split. They are even to that point and after it takes more throttle to get the port engine spinning. At least a click or two split on the kiekhaefer throttles at 3500 and up, and thats where the pinging started. I think it was pinging anyway, it was a faint sound that was not there at lower power that came on with power, almost sounded like the sound of a loose belt or something. Maybe after re-jetting and giving them some more fuel they will spin up faster. It seems the primarys are at work at 3300 and below and that sound starts when the secondaries start to open above 3300. (I indexed the throttle handle positions for primarys / secondaries)
I think I'm getting closer, at least it runs on plane now. 55MPH on top, still room to improve. 3000 RPM was about 35 and 3500 was about 42. Not a bad cruise for a big old heavy boat.
11-13-2005, 05:16 PM
#102
Registered
Thread Starter
Re: Carb Adjustments
Re-jetted today, found each carb had different jetting. 1 was 82f / 90 R and the other was 76F / 87 rear. Since both were showing white plugs yesterday I jetted both fatter than the richer carb. 83/84 front - 91/92 rear each (jet kit only had 2 of each size)
Another run and another plug check from 3500 RPM showed nice tan plugs with a little lightness on the grounding strap. I had one black plug....#7 port engine. Since all other cylinders checked fine I figure that has to be a weak ignition on that cylinder. I'll replace the cap and rotor on that side tomorrow.
No change in performance at all though....4400 Stbd / 4100 port at WOT trimmed out. 55 MPH on GPS. I'm not certain that what I heard yesterday was detonation pings since I could still hear it a little today with the jetting right on. What I hear happens as soon as the secondaries start to open on that carb. It might be due to lack of power from the weak #7 cylinder (dry,black, lightly carboned plug, also plug was new before I went out.) and overloading? I'm definitely staying away from higher RPM's though until I get rid of it, whatever it might be.
Would advancing the timing slightly to say 32 degrees from the 30 that I am at now make a jetting change required again? Might that help get the RPM's closer to where they should be? I want to stay on the conservative side, but I do want to get the power that I need to move this hefty boat, and keep trying to use the 22P Bravo 1 props without needing to change over to the 3 blade mirage 21P that I have.
I'm also wondering if that single plane intake that I have is robbing me of the torque that I need in the lower to mid RPM range to help get the RPM's up with the 22p props.
Finally I feel like I'm getting closer to the setup being finished thanks to all the help and advise everyone has provided to this point.
Another run and another plug check from 3500 RPM showed nice tan plugs with a little lightness on the grounding strap. I had one black plug....#7 port engine. Since all other cylinders checked fine I figure that has to be a weak ignition on that cylinder. I'll replace the cap and rotor on that side tomorrow.
No change in performance at all though....4400 Stbd / 4100 port at WOT trimmed out. 55 MPH on GPS. I'm not certain that what I heard yesterday was detonation pings since I could still hear it a little today with the jetting right on. What I hear happens as soon as the secondaries start to open on that carb. It might be due to lack of power from the weak #7 cylinder (dry,black, lightly carboned plug, also plug was new before I went out.) and overloading? I'm definitely staying away from higher RPM's though until I get rid of it, whatever it might be.
Would advancing the timing slightly to say 32 degrees from the 30 that I am at now make a jetting change required again? Might that help get the RPM's closer to where they should be? I want to stay on the conservative side, but I do want to get the power that I need to move this hefty boat, and keep trying to use the 22P Bravo 1 props without needing to change over to the 3 blade mirage 21P that I have.
I'm also wondering if that single plane intake that I have is robbing me of the torque that I need in the lower to mid RPM range to help get the RPM's up with the 22p props.
Finally I feel like I'm getting closer to the setup being finished thanks to all the help and advise everyone has provided to this point.
11-13-2005, 08:04 PM
#103
Registered
iTrader: (3)
Re: Carb Adjustments
I dont think the bravo 4 blades are good for your boat. I believe they were designed for boats with a higher x dimension. I think the hydromotive 4 blade works well. A bravo 22p and a hydromotive 21p should turn the same rpms. I was told bravo's are light on pitch. My boat had 22p hydromotives on it when I bought it. I defintly gained rpm by going to the 19p revolutions. I would like to try some 20 or 21 hydro's next season, I like the speed and handling of them. I believe throttle up will loan some props to try.
