Re: Carb Adjustments
 

Increasing the timing should make the engines run better, but shouldn't solve this problem. The simplest thing to do at this point would be to swap the metering blocks from one carburetor to the other. You should be able to do this in five or ten minutes. The problem will either stay with the port engine, or travel back to the starbord engine. Without knowing what has been done to these carburetors in their past it's impossibly to say specifically what is causing this problem.

850 Demons are going to be extremely big for this type of combination, which will lead to rich idle, and part throttle drivability, and potentially lean at wide open throttle. Also, there are other changes besides just installing or making "J" tubes. The jetting, and air bleeds are different as well as the baseplate on the carburetor. Just installing "J" vent tubes would not be recommended.

Re: Carb Adjustments
 

If you're going to take the carb apart, I would check for damaged parts, warped body components, drilled out passages etc. Back in the "old days", guys used to buy a hot rod magazine, and think they could modify their Holley, or Quadrajet. After drilling everything out, and screwing everything up, they would end up at a swap meet for some other sucker to get stuck with. You should see some of the mutilated abortions I've seen. Honestly though, it seems like you've done almost as much as you can do with this carb. I think time and money would be better spent on a set of more appropriately sized, and known good carbs.

Re: Carb Adjustments
 

Theres more to marine carbs than just j tubes. Those are easy to make. Sealing the throttle shafts is another story. Not to mention calibrations to handle the sustained loads at all speeds.

But, I am not familiar with the BG's either. Well, at least not the carbs. :D

Re: Carb Adjustments
 

She finally woke up!!!!!!!

The problem motor loves the 800 CFM Holley I tried today. It is a blue mercruiser 13549T21 carb tuned for the HP 500, which means it is most likely a little fat for my engines but she finally turned over 4000 RPM's with nice response. I did notice some things today I did not like now that I had her running better.

After about 3700 - 3900 RPM on the left motor (the one with the test carb) I would notice a little like a ping when I tried to go higher on the power and pulled back right away. As soon as I pulled back it went away. The right engine would do this only at nearly max power, since it is an 850 it is most likely running richer and I really did not notice that sound as much. I'm thinking the timing is too far advanced for 89 octane at around 34 degrees total. I figure backing that off may solve that problem. Perhaps that test carb is too lean. (I did wire tie the choke plate wide open since I did not have electric choke wireing in place to set it up.) I don't know what is in that carb, but most likely stock jetting for the HP 500 Mercruiser. I could reach a top RPM of about 4100 - 4300 or so on the left side (test carb), A little more on the right engine with the 850 carb at around 4500 - 4600 RPM +/- . Seemingly a little low. I did not think I was over propped but perhaps I am. I am turning 22P Bravo 1 - 4 blades. Perhaps these engines are making less HP than I thought and 22P is too big. I guess I have to finish fine tuning everything and figure out how it runs when everything is dialed in.

The 850 carb (right side) gives a bad stumble out of 1000 RPM through about 1400 - 1500 or so. Almost like the engine is chugging to life. It almost sounds like it is not fireing on all cylinders. If the throttle is opened just a little too much is starts sounding like that until I get it above 1400 or so where it abruptly clears out, or if I pull it back even just a little below where it starts, it clears out and idles perfectly. When this happens, even though the RPM's do increase the Tach falls off to 800 - 900 RPM or so while it is chugging along, like I am drowning the ignition or something, and reads normal when the engine gets cleared out. It also did this with the other 850 carb when I had the sides switched. I was figuring that it is a big carb on that single plane intake with a low / mid range cam causing that. It also seems to happen on a lesser scale when in neutral and reving up slowly. It has done this since day one but I have had other concerns with this thing. I mentioned it to the mechanic the day we had our oil pressure problem (day 2) and he did not seem worried about it.

At least I am making steps in the right direction now. No more fuel in the water behind the boat and the transom is cleaner, less smoke etc. And finally goes fast (er)! I saw only about 55 or so for the second or two I had the handles that far forward. If I can get these RPM's up I think she might do 65 - 70, which is where is was from the factory with 400 cyclones in 1985.

MT what does your Eagle do with your 420's? What props?

Re: Carb Adjustments
 

Yeah, glad to hear the progress!! Persistance wear resistance my Mom always used to say.

Make sure your floats are now set at the bottom of the site glass. Maybe the bowls are running dry? It is imperative that if you are hearing pinging you fix that post haste or pop the engine. Definatley get base timing in line at around 8* before going out again. Also do plug readings to check for lean.

BT :cool:

Re: Carb Adjustments
 

What eagle? I have a Excalibur hawk!

Its actually identical to the stinger 390 hull. My port engine was down on Rpm this summer some. But I was turning 19p Revoltion 4 blades. Starboard spinning 5200, port 4600, at 50-53mph. I plan on tearing into the port engine soon to find the problem. I also have the crappy 3" log manifolds and dual plane intakes :mad: I think with some 450Hp 454's, running right, should be able to turn 22p 4 blades and the boat should be doing around 60-65.

Im glad to hear you got it running better. I still suggest getting your hands on some 9022 holley 800 double pumpers, get your timing dead on, fresh plugs, wires and cap, and I think your problems should be solved.

What intakes are you running? I think the weiand team G manifolds were stock on the 420/425 models.

Re: Carb Adjustments
 

sorry...sorry....Hawk / Eagle (both winged, sleek, powerful critters though, and both Excaliburs right? ). :D

The carbs I have available to me are from the HP 500 Mercruiser. They are 800 CFM with automatic electric chokes and mech. secondaries. They are rebuilt be a Mercruiser dealer and performance boat specialist here in CT.

I think I definitely need to look into intakes in the future and get some good Edelbrock air gaps or something. These Aluminum single planes are just a mismatch to these engines.

Hopefully I'll get everything dialed in on the engines and get the power to spin up the 22P props and not have to get new ones.

Now the right engine seems to be spitting oil around the base of the distributor, running down the back of the block, and is making a mess in the bilge. One more thing to take care of!

Re: Carb Adjustments
 

Probably just the o-ring under the distributor flange. if you can get a good deal, I say go for those carbs. Those are what they put on the 420's. Just get them jetted correctly and you should be fine. Then buy a full rebuild kit, go thru the 850's thoroughly, and put them on ebay. I hear the air gaps are good, Im not sure about what intake would be ideal for you.

Re: Carb Adjustments
 

Make sure the carb builder gives you some type of warranty with the carbs, and make sure he tells you exactly how he sets them up (jets, power valves, etc).

Re: Carb Adjustments
 

Wieand X-celerators were used on the 420's but the Air Gap may be even better. Just because I don't know anything about your intakes,I would be inclined to change them. You couldn't go wrong imitating the old 420. They were strong, smooth running engines. With a little more compression ( stock advertised 8.8 to 1) and better exhaust they were an easy 450 hp.

Re: Carb Adjustments
 

New carbs are bolted on but I have not had a chance to take it out since it started raining on me. Carbs are 9022 Holley's, 800 CFM, they are jetted 82 front / 90 rear,1 power valve, electric automatic chokes. I think stock from Holley is 72f / 87 rear jets so these might be a little rich, but I will soon find out. Richer is better at first anyway right? They do start and run fine. One choke is not wanting to open fully, but I figure that is just a quick adjustment somewhere.

Even at the dock I can tell a definite difference in throttle response, even in neutral. I can't wait to get it out and see what it is like under way.

Where is the best place to wire the choke power? The Holley manual says not to wire it to the coil due to a reduction in voltage to the ignition system. The place that sold them to me said to wire it to the coil! Every diagram I can find in the Mercruiser manual shows the choke power going to the coil. Holley's reasoning makes sense but there really arent that many more ignition switched 12 volt sources right at the engine to wire to are there? Any ideas? I have it wired to the coil right now and it seems to work but if there is a better way, I'm all ears.

Re: Carb Adjustments
 

I find it is best to maintain the out of the box split in jetting front to back. Stock is 72/87. That is a split of 15 jet sizes and volumetrically represents the amount of enrichment that can be expected from the power valve channels. For instance, my 800 holleys are jetted at 77, 92 a 15 size split. You are plenty good with what you have 82/92, but may want to work back to the 15 size split.

BT :cool:

Re: Carb Adjustments
 

I think your ok to wire it to the coil. They probably dont want you to hook it to the coil if you had a ballast resistor, like in a points distributor, but you have the Thunderbolt IV, so your coil should get a full 12v.

Re: Carb Adjustments
 

New carbs are set up and ignition timed at the dock and ready for a ride to see what will happen. They seem to be singing at the dock. Hopefully it will stay that way.

The right engine still gives a bad stumble for the first few hundred RPM. Almost sounds like 2 or 3 cylinders are dropping off line. Sounds like a nasty chugging until 1500 RPM or so where it clears out and runs smooth. It does not sound like the engine wants to die, just a real struggle to accelerate.

Could that be a symptom of bad valve timing? Intake leak? Bad plug wires? Bad ignition module? (advance works fine and advances 20 degrees perfectly like it is supposed to (V8-HP module)) Total advance is set at 30 degrees as recommended by the local performance shop with the fuel and setup I am running. (89) Different base timing also seemed to make no difference. Runs great at idle, and after 1500 RPM or so. Everything in between sucks.

When this problem starts the tach drops a few hunderd RPM, but it does not sound like the engine is slowing down. Really hard to describe accurately but sounds like a constant chug...chug...chug, until I advance the power more or bring it back to idle. Carb change made no difference to this problem. Right engine only, and really wierd. Replaced coil with no difference either.

Re: Carb Adjustments
 

I would pull the cap, and check for moisture or carbon tracks. When it gets dark out, start the engine and spray all the plugs with a windex bottle full of water. See if you see any sparks jumping around. How old are the wires?

Re: Carb Adjustments
 

I'm really thinking about the props now. I am starting to think that the power I have will never spin up 15 1/4" X 22P 4 blades on this boat. I don't think it is making the power I thought it was. I'm still setting up the engines and will take it out tomorrow for a try with the new carbs, but after reading Mild Thunders reply a few back about a nearly identical boat with about the same power turning 4 blade 19P revolutions, I think I'm way off the mark on props.

I bought a used set of 14 3/4" X 21P Mirage 3 blades to try from ebay for a song. I figured even if they don't work I can always sell them again. The $265.00 I paid with shipping seems like a no brainer.

I read a 1983 and 1984 test report on this boat last night, and it seems the 390 Stinger came from the factory set up with 15 X 19P cleavers with 400 cyclones and would do 62 mph at 5100 RPM. I figure with difference in power that I have, and MT running 19P 4 blades successfully, that 21P 3 blades with a slightly smaller diameter than what I have now may make the engines wake up all the way, not work as hard, and be easier on the drives. I'll see what happens I guess.

Re: Carb Adjustments
 

Do some plug checks. After going up 10 jet sizes, you are probably quite rich on the primaries.

Re: Carb Adjustments
 

I ran some numbers on the Bam website prop slip calculator. www.go-fast.com A 19 pitch prop with 12% slip at 5200 rpm equals 55 mph. A 22 pitch prop with 14% slip at 5200rpm equals 62 mph. The numbers in that report may have come from a speedo. GPS wasn't in use then. My old 40 Scarab with 400's would go 60 at 5000 rpms with 23 pitch 4 blades. It will be interesting to try the 21 Mirages, but my experience is that they slip a lot when used on big,heavy boats. All around I think you will be happier with the 22 4 blades. If your compression is 9 to 1 or less, run 34 to 36 degrees total advance with the 89 octane gas. Then work on getting the jetting right. Running rich kills power.

Re: Carb Adjustments
 

I think you should be able to turn the 22's. My ran 5200 on the starboard, 4600 on the port with the 19p revs. I think with both motors turning 5200 I should be able to step up to a 21-22 rev. I actually like the hydromotives on our hulls, it seems as if they need stern lift, not bow lift. Heres a running shot of my boat with 22p bravo props

Re: Carb Adjustments
 

you said those carbs are auto carbs? and auto fuel pumps?? thats a fire waiting to happen and your insurance will not cover it. safety should be your first concern.

I see you went with the 800 marine carbs , did you change to a marine fuel pump?
and the edelbrock rpm intakes youll be in your power band more toque where you need it . you may have a intake leak try some carb cleaner around the intake and see if the rpm changes personaly Id just change the intakes a single plane is not good till over 5000 rpms

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.

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.

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.