Port engine lean. Why?
 

Back in September, we took the 311 out and it ran great. Solidly into the upper 70s. Strong acceleration. Scared the Mrs. Perfect (not the part about scaring her).

Two weekends later, the boat was uncooperative and the port engine started sporting some strange AFR readings. AFRs in the upper 13s and getting into the 14s. Put her on the trailer and went after the carbs.

To note I’m running O2s on the even bank (I will pop the tail pipes off this winter and add bungs so that I can swap sides).

Carbs are Demon 850s (1000+ cfm) and now use aftermarket custom metering blocks. Current jetting is 84/90. Pv circuit is .063 (up .006 from .057). Stock jetting was 86/93 but we lowered based on changes we made to emulsion.

Today we ran the boat. We never took it beyond 3500 because we were worried about burning it down. Port side even bank was going into the 15s for AFR. Was hoping the original metering blocks had shaving issues. Guess not.

84/90 with 8.5 pv

Here’s what we gathered for data:

Starboard DLG-1 A

RPM / Vac / A/F-R

1000 11 12.6

1500 10 11.5 - Power valve beginning to open

2000 8 11.5 - Power valve should be wide open.

2500 7 12.2

3000 7 12.9

3500 5 13.5 (lean secondaries)



Port DLG-1 B



RPM Vac A/F-R

1000 11 12.1

1500 10 12.7 (where’s the power valve?)

2000 9.5 13 (no power valve?)

2500 7 14 (really no power valve)

3000 7 14.8 (umm)

3500 4.5 15.7 (ouch)


We didn’t run her harder. Interesting finding was that the port engine was running twenty degrees warmer (190 vs 170) so it seems that running leaner is affecting temperature by a good amount.

Based on the starboard numbers and speaking with my carb expert here in VB, we’re going to run jets two numbers higher and change high speed air bleeds to tone down the emulsion speed some.

Pulled plugs on 6 and 8 looking for a misfire (burnt plug wire grounding out) and they looked great. I didn’t pull the other side.

Intake leak with smaller jets making worse? Anything stand out? The engines were running pretty close numbers before it skewed.

Any thoughts on troubleshooting on the trailer? We won’t be back on the water until later March or April depending on weather.

If it was okay before and new issue, clean out every passage both directions with carb clean then same with compressed air.

Exhaust leak ? Ck and fix.

Swap 02’s see if condition follows 02 ?

Anithervthing, Misfires will typically make 02’s read lean.

You may have volume issue too, so change your needle and seats , check your fuel psi, and since your float bowls have glass windows for fuel level, put a go pro or telephone pointed at it to video your fuel level while your running into this issue. If volume still issue, ck fuel pump and fuel pick up area.

would have to agree with SB. if it ran fine one week and not the next the jetting didnt change itself so it is somewhere else. what ignition is on it? possible that the timing is not advancing for some reason which will make it run hotter. or one of the air bleeds has something in it. or as said fuel pressure is dropping off. bad hose or pump or even filter.

Yep, ran it Labor Day weekend and it was perfect. And then took it out for the Blue Angels the 17th and it was jacked.

I did a jet change on the primaries prior to going out on the 17th and ended up with this (on the old BG metering blocks - one jet size, 86 down to 85 just to lean it a tiny bit). The starboard side was okay (still rich) but the port was way off.

It’s going to be a bit before I can mess with it again. I’ll winterize the plumbing and change the oil and oil/fuel filters this week, fog it. I’ll yank the carb and go through it again and hope to be back at it in late March or so.

Side note… I swapped the O2s from one to the other and recalibrated. There was no change. Swapping carbs would have been a good test, too, but I didn’t want to get into that yesterday - was getting late and we were three miles offshore. As it was we had to putt-putt back in (load on plane was making her heat up pretty good).

Could be as simple as a piece of trash in one of the needle valves. I had it happen to me when I made a new fuel line.

I know at idle it’s showing good fuel pressure and the float levels are all good. Doesn’t mean squat though if it’s not filling fast enough. I’ll go out tomorrow and yank off to see if anything is in it. I’ve got a bunch of new needle and seat assemblies. Easy swap.

Coming back around to this now that spring isn’t too far away. I had surgery not a week after I posted this so carbs remained where they were. I did get to winterize (and when I did, both engines started like they were efi).

Plan is to yank the port carb and go through the whole thing to make sure there’s nothing causing an issue. I’m going to change the fuel filters.

Hoping to get here straight early so that spring is an easy transition to summer. It’s time to enjoy this thing!

Hope everyone is being successful with getting winter projects done.

Do you have fuel press gauges at the carbs?

I ran into low fuel press issues with my current boat when I purchased it. Found tiny shards of teflon tape inside the mechanical fuel pump check valves preventing them from sealing on both engs. Had to go thru the entire fuel delivery sys removing all remnants of teflon tape. Went back with liquid thread sealer.

I do have fuel pressure gauges at the carbs - trouble is that I can’t see them while running. With that said, everything was great until I screwed around with them so I’m thinking that something became dislodged somewhere and there’s now a blockage that I haven’t discovered.

No teflon tape anywhere - I don’t use it. Instead use
liquid Teflon where needed and those connections are few and far between.

Possible too that there’s a blockage at the tank or something similar. It is 34 years old after-all. Disconnect everything from the tank to the engine and purge/flush.

Had a well respected marine mech tell me at the time, never use teflon tape on fuel or hyd sys (P/S, trim, etc). Some get away with it if applied right but some don't..

Maybe a Go-Pro mounted in bilge to watch the fuel press gauges once you're back on the water? My old Go-Pro has a wifi broadcast function so phone can be used to monitor Go-Pro in almost real time (abt 1-2 sec delay).

Yep, I have some old iphones as well as go-pros that I can put in there to see what's going on. I didn't the last time it was out, but I'm thinking of going out without the engine hatch on so we can see what's up a little more easily.

Any thoughts about the vacuum readings? They look okay to me - nothing too far off from one another.

Tom,
I found your problem. You can thank me later...

Hahaha… Thanks!

Not really. So many little things that can make manifold vacuum slightly different.

Did have a random thought abt the power valve... AFAIK, most carbs have a check-valve to protect the power valve diaphragm form excessive pos press spike during a back-fire event. My old carbs don't have the check valve and if I get backfire during start-up, it blows at least one of the power valves out. So if yours have a check valve, make sure it's not stuck closed blocking the vac signal.

Thought about that one… the trouble is that if vacuum is closed off, the pv will hang open and allow more fuel.

Doh!! You are correct. It was past my bedtime last night.

Haha! I had a similar response in the original thread I posted about the carb being off. Glad I’m not the only one!

Alright. Both carbs are back on the bench. I took everything apart and have somewhat of any idea of why these things have been problematic.

The vacuum source for the PV’s on both carburetors were never drilled. The PV’s were never working to begin with. I’m not sure how I missed it - I guess I just assumed they were drilled in a different manner (connected to another vacuum channel perhaps). Nope - I fished through every hole to make sure there was no trash anywhere.

What a waste of time.

For now I’ll baseline the carbs back to 86 and 93 and see what it does (it has 84 and 90 jets now). PVCR is opened up to .063 from .059. We’ll see where we end up. The original combination seemed close with the 86s and 93s at wot.

Is this the vac passage in the main body or the fuel passage within the metering block from PV to booster circuit that wasn't drilled?
If it's the vac passage in main body, wouldn't the PV be ON all the time??

Here's a pretty good video on Holley power valves. It's geared more towards cars but he explains the operation pretty well.

It was the vacuum orifice in the baseplate. There was nothing making it to the PV.

I dropped a lot of main jet and that messed the whole thing up.

Honestly, feel like an idiot having missed this. Oh well, live and learn.

When the boat ran great on the top end back in September, it was still running really rich at cruise so I took jet out of it. Then changed some of the metering, and took more jet out of it because of those changes and really screwed it up.

I think starboard was more tolerant because idle transition was richer - the idle on that engine was richer compared to port. It too started to go lean with RPM.

Will be interesting to see what happens next time out.

I got ya and feel your pain. I once burned 100+ tunes on my Camaro trying to get the WB02 happy before I realized I had a vac leak.

Is drilling out the vac passage a possibility?

Yes and it’s already done. The opening for the vacuum source in the baseplate was there, but it wasn’t drilled through to the underside of the base plate. Pic for reference:

https://cimg5.ibsrv.net/gimg/www.off...66e4d5eaf.jpeg


I checked it with air before making any changes - completely blocked. I drilled through it and now the well for the PV diaphragm is connected to vacuum.

These carburetors were used on a blown setup that the previous owner had lots of trouble with. These were not blower carburetors - just standard issue Demon 850s. The baseplate is factory Demon. My thinking is that it was a quality control problem - I found similar quality issues with the metering blocks (mentioned in another thread) so this isn’t all that surprising.

I know how to setup a carburetor but this situation had me doubting myself. Nothing that I was doing seemed to work. This was a big “ah ha!” moment - should work as intended now. The fuel curve might need some attention, but now that the PV will work as intended, I’ll be able to get better data if a change is needed.

I also ordered a set of PV blowout protection kits to make sure the PVs don't get damaged from backfires. My carburetors were made circa 2009-2010 (during Holley's purchase/selling of BG's assets) and should have had the check valves on the primaries - another clue that I missed.

Are you SURE this is the carb? Would you gain anything from swapping carbs. Maybe it’s an issue with vacuum serving the carb, fuel, timing, etc.

You could very very quickly minimize your list of potential issues by seeing if this follows the carb.

Good catch !
Thinking out loud round table talk…..if there is no vacuum to pv, then it’s open right ? If it’s open it adds much more fuel so should be rich when the pv is supposed to be closed.
Your thoughts ?

From my experience aftermarket carb components are a PIA and just complicate things. A boat basically idles, runs part throttle at cruise and WOT.

I took out the fuel dump PV`s and just used larger jets. The fuel curve was much happier.
You say it starts to open at 1500rpm , so basically its open most of the time running , why not just jet up 5-8 sizes and meter the fuel better, eliminate a potential issues.

I fell down that rabbit hole myself. Apparently the PV was stuck ON and he leaned the jets to compensate for the over-rich condition at cruise. Now that vacuum passages are open, I believe he's putting the jets back to orig and starting over.

Okay. Cool.
Well, then sounds like he’s probably good to go. :thumbs

Pretty sure the carb has the majority of the fault. Vacuum wasn’t being served - the base plate wasn’t drilled through.

These are great carbs when they work. Trouble is that they’re from a time where BG went way down on the quality control side of things.

Ignore the opening comment - the PV was always on and I was just interpreting the data thinking the circuit was working.

I’m not against trying it with jets only, but with this being NA, I think the PV is needed for a cleaner cruise. Right?

Back to the way it came with exception of the fuel curve change in the metering blocks. Should be minor and only help.


We shall see!

I’m going to replace the base plates - only thing original will be the main body and bowls. The PV kits that I installed left too little of a margin between the throttle bore and the casting. The main body orifices line up perfectly with a Quick Fuel/Holley base plate and gasket so should be fine (maybe an upgrade even).

Getting closer to water testing.

I replaced the base plates with parts from Quick Fuel. They were comparable to the Demon parts but with exception of visible quality control improvements over those from BG/Demon. I added alignment pins to the base plates - made a big difference in the alignment of the throttle bores and venturii.

Initial startup last weekend was good but eye-bleeding rich. That was quickly fixed and and I got both engines to run well on the hose. Wednesday, I dragged the boat to the ramp and started working on in-gear idle on the trailer. Out of gear both are running about 12.6 with vacuum at 18 inches, but as soon as she's in gear she drops to about 8-9 but a/f climbs 13.3-13.5. Blipping the throttle in-gear (from 700 to 2000 rpm), a/f rises but quickly recovers - very crisp. Idle is about 850 out of gear, 650-700 in gear. Trying to raise the in-gear idle makes for excessive out of gear idle so it appears that this is where both engines want to be.

I was thinking more idle would be good to combat reversion, but with the long tail pipes of the TRS set-up and squat of the 311, I don't think there's much of a concern. These were Rookie's old 454 cams and he didn't have reversion issues with his TRS set-up so I think I'm good.

Time to yank the engine hatch off and get some seat time to work on the jetting. I'm pretty sure they're going to be pretty rich. I did a whole lot of math to get the primary and secondary sides close to one another so I'm sure both will need to come down. Have to start somewhere though.

Thanks Dan. Based on the what I found with the orifices not being drilled, anything that I mentioned about PVs opening at a given RPM aren't accurate - they were always open and I guess I may have been seeing the handover of the idle circuit to the mains. It'll be interesting to see with the reconfigure.

I have thought about going that route, but with an NA set-up, I felt the cruise economy would really suffer. That's the whole point of the power enrichment routine - allow the engine to cruise on the mains, and then use the PVCRs to add another 25-40 percent more fuel when giving it the beans.

Maybe the boat is less affected with it's constant load - possibly. Did you (or anyone reading) run a similar set-up without blowers?

Tom,

I'll never understand carbs. Little vacuum "computers" doing shizzit because voodoo. They amaze me.

I fought and fought and fought and fought and fought the carb on the 454 in our Rinker. For the life of me, I could not get it to run between 3600 and 4200 RPM. As soon as the secondaries would want to open, they'd open. as soon as they want to close, they'd close. And that was it. It was either under or over or transitioning between the two. Never just.... running. It would hum along at 3100 all day long, purring like a kitten, and it would just sing at 5100 WOT until it ran out of fuel. But 4K? Not a shot. I took it to a local carb shop numerous times and he would "fix" it on his shop engine (He refused to work on it in the boat. Probably a liability thing), it would do the same thing, and I'd farq it up again trying to make it work right. Never did figure it out. Sold the boat to a buddy. Still does it. He doesn't care.

Glad SoMeBoDy understands how they work. :cool:

Thanks. Brad.

Took her out yesterday and did a lot of stepped rpm testing. It was a cold but fun day messing them. We were out there for a good four hours running back and forth.

At the end of the day, both carburetors are pretty consistent to one another (within a couple tenths) but they’re both still running lean.

A/f ratio getting above 4500 is in the upper fourteens with the following setup:

Primaries: 88
Secondaries: 98
pvcr: .063
pv: 8.5 - primary only

We tested with the secondaries disconnected and held closed was able to run up to about 4500 rpm but a/f was high 14s wide open. Hooked the secondaries back up and a/f didn’t change. The flame arrestors were off and I could see that the secondaries weren’t starting to draw fuel until around 4300. Decided to bump jetting on primaries and secondaries from 86/95 to the 88/98 listed above. Ran to about 70-71 and a/f was mid 14s on both.

Trying now to figure out what the next step should be. Seems that the idle circuit is running until about 2k rpm than the mains starting coming along with the power valve. Thinking that maybe we need to go up to 92 on the primary and maybe increase the pvcr to .067-.070. From there test and see if I can safely get to wot.

Also, the distributors were a little loose and had backed down to the indentations on the body resulting in 30 degrees. I bumped them back to 35 and the engines seemed to really love that.

Any thoughts?