Starting problem - carb? 4.3OMC/Holley 2bbl

[whitney]

Hi everyone, just spent the lat few hours reading posts about carb issues, but I'm still stumped by what my new-to-me boat has been doing.

Last few times out I have had WOT issues, so today armed with a fuel pressure tester I hit the lake. First I went out with low fuel and a clear line on the pump output to check for bubbles due to pickup problems ... in the process I ran out of gas. Added my 1 gallon onboard and it wasn't enough. Got a tow to the pumps, filled up, and spent the rest of the day trying to get it started again ... never did. Tried pumping accelerator pump, tried full throttle starting, 1/2 throttle, everything. Even tried starting fluid, which I got a few "catches" out of but not enough to start the motor.

So it just flat won't start today. It has been starting OK the last few times out but occasionally (warm or cold) giving me problems. So it may be a new issue (aside from WOT) which is getting worse.

Here's what I know:
It's a 96 4.3 block with electric fuel pump and 2bbl Holley
When it does start it idles and cruises fine, no hesitation or flat spots
It looks to run a bit rich from the black streaks on the transom, but I hear that's normal. Every once in a while when backing off the throttle (I think) I get a backfire/pop.
Compression is great (block was rebuilt by a PO about 100 hours ago)
New cap/rotor/plugs/wires, Good spark observed during cranking
Timing is spot on at idle (6 DBTDC)
Fuel pressure is 7psi, no bubbles in line
Fuel coming out of the tank is clean, and I see no debris or junk in the tank via the fuel level sender hole. Pumping rate in the driveway is great, prob 1 gal/minute.
Choke may be a bit flaky but not bad -- 1/2 open when cold, 3/4 open when hot. Sitting at the dock for 3 hours today in 90 degree weather it stayed open to 3/4?
Carb was recently rebuilt. I took the float and metering block off and it looks great inside, no residue, very clean. Float chamber was full of fuel when I removed it, float itself looks new.
Accelerator pump does seem to be operational, pushing it causes a squirt of fuel (although only into one side ??)
Plugs are brownish and not wet with fuel.

So any ideas? I am assuming based on the clean plugs that I'm not getting any/enough fuel into the intake during cranking. Anyone know what circuits/passages actually are supposed to be providing fuel during cranking? Could I have a plugged/blocked idle mixture line? Anyone know where those are? If I ran the carb dry, and now it won't start, could that have anything to do with it?

After thinking through all this while typing I am thinking I need to try manually closing the choke and crank it a few times, see if that can force the carb to inject fuel in through the "dry" idle mixture passages... hmmm

Any advice or ideas are welcome! Thanks!

 

[whitney]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Hmm odd to see a post go without being answered overnight, I guess I was too thorough in my explanation and stumped everyone else

Let's start with the basics ... one question that is not in the Adult Ony post, nor is it in my OMC service manual is:

What causes hard-start or no-start?

 

[gbeltran]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Well, the fuel should be squirting in both sides. I know you're chasing a fuel problem, but you have checked that it is still getting a good spark, yes? What year OMC?

 

[whitney]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Well, the fuel should be squirting in both sides. I know you're chasing a fuel problem, but you have checked that it is still getting a good spark, yes? What year OMC?

Hey, thanks for the reply! Yes I am pretty sure the accel nozzle (attached with a big screw right under the choke plates) is turned 90 degrees and I will be fixing that today. Since it's only operational during throttle-ups I don't think it's solely responsible for the starting issues. If the dumb-***** mechanic who rebuilt the carb screwed THAT up I'm really beginning to suspect other carb problems too. And again I am reminded why I do all my own mechanical work

I have checked for spark while cranking twice by pulling a plug and observing sparks while grounding the plug to the engine. So ignition does look good. One thing I was thinking is if the advance springs are sticking it may be firing at the wrong time, but that's a longshot. Also it's hard to tell in daylight but the spark "looks" weak in direct sun. Again hard to tell...

It's a 1992 Sunbird Corsair 185, OMC Cobra 4.3, with a remanufactured 1996 longblock. So technically I belive by 1996 the block would be considered a Volvo LX?

I suspect the carb and most accessories are 1992 vintage and were used on the 1996 block, but it's not clear what 1992 parts mated correctly to the 1996 block. For example, my OMC service manual shows a totally different carb float than I actually have. One thing to do today is to get the Holley # off the carb.

Back to one of my main questions -- anyone have a description/diagram of the Holley fuel metering plate which can tell me where fuel is supposed to be coming from during starting?

Or any other crazy ideas for me to add to my long and growing troubleshooting list?

Thanks!

 

[whitney]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Well to make matters worse, it just fired up easily in the driveway on muffs. Didn't touch the boat since pulling it onto the trailer by hand yesterday after 4 hours on the water trying to get it running.

Ideas? I'm stumped. And unfortunately with a not-repeatable problem in the driveway I have no idea how to resolve it. Maybe it was actually flooded and needed all night to air out? Hard to believe since the plugs I pulled were dry...

 

[whitney]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Well hey, since 36 people have read this with one reply, I might as well keep documenting what I find. Think of it as my journal through this experience

So I found idiot marine mechanic error #2 ... the linkage on the choke was installed incorrectly. There is a little plastic tab which rotates on the choke shaft, with a little brass insert in the end to keep it down. This is supposed to be the weight which keeps the choke open to the coil-set limit (instead of a spring). The choke lever is supposed to be under this (weight pushing down), but it was on top so the weight was actually limiting how far the choke could open. So it was maybe going to 2/3 or 3/4 open.

I put the coil in the freezer for 5 minutes and confirmed that when cold it is almost fully closed, then hooked up 12v and saw that it took about 1 minute to open to 100%. With the alternator AC-fed 7V that this boat is wired for, it would take about 2 minutes -- sounds about right.

So this is one piece explaining the rich-running issue, but doesn't help with my at-the-lake hard starting. Might also help with WOT? Maybe.

Next for me is to pull the carb and check power valve size, check for idle circuit restrictions, and jet sizes. I want to at least make sure the "rebuild" parts are close to stock.

Comments welcome, especially encouragement, since I was tempted yesterday to literally "pull the plug"

 

[whitney]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Well another update! Wow I have made a lot of progress in 20 hrs.

Found mistake #3 and #4 of idiot boat mechanic who did the carb rebuild. Hope I'm not offending any idiot mechanics on the board

#3. Carb had the wrong power valve -- 4.5 instead of factory 2.5. Probably doesn't matter for the starting issue since it's only supposed to open in the absence of vacuum at WOT. So the 2.5 won't open until closer to full throttle ... which could help explain the WOT issues I have been having. Luckily the previous owner gave me the old valve, which looks like it's working fine (not blown or leaking) so I put it back in.

One question on the power valve -- when you shut off the engine, won't the power valve just dump the remaining fuel above the valve in the float straight into the intake? Seems odd, could be a couple of ounces. I don't see any way that would prevent it, and explains where my fuel pressure bleeds off to after shutting down. Still doesn't seem like a good idea and probably contributes to hard warm starting...

#4. The power valve had *two* gaskets under it and one of them was torn. I figured out that the engine was getting flooded whenever the pump was on because I took the carb off, attached the fuel line, jumpered the fuel pump on, and held the carb horizontal over my head. Fuel started dripping out of the power valve port between the barrels on the bottom of the carb.

So I'm nearly convinced now that my hard starting, excessive fuel consumption, and rich running must have been due to this basically partially-open power valve at all rpms due to the tear. Probably worst at idle and startup when vacuum is high. I also think that my temporary plumbing of a fuel gauge and soft lines are exacerbating the starting since it's a big "reservoir" of pressurized fuel to feed the open power valve after the motor shuts off.

It runs *so* much better on the muffs after fixing these 4 problems -- choke open, correctly positioned accelerator outlet, no leaking power valve gasket, and the correct power valve. I can't wait to get it out and see if I possibly fixed the WOT problems too...

 

[NHGuy]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Well I learned that doing stuff myself is probably the best approach. I'm sorry you had to diagnose some fool's work. Anyone that bad should not do that kind of repairs...you'd think maybe 1 mistake, but 4! GEEZ. Did the guy even run the engine?

 

[Silvertip]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Unless you fixed it, a stone cold engine should not leave the choke 1/2 open -- or any open for that matter. Note that I said stone cold. Obviously if it is 90 degrees the choke may not pop fully closed but it will more than 1/2 closed. It should be adjusted on a stone cold engine only. Hold the throttle slightly open while adjusting the choke so it just barely closes. After it starts the pull-off should open the choke slightly after which the heat system will open it fully. Fully warmed up the choke should stand perfectly vertical.

 

[whitney]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Unless you fixed it, a stone cold engine should not leave the choke 1/2 open -- or any open for that matter. Note that I said stone cold. Obviously if it is 90 degrees the choke may not pop fully closed but it will more than 1/2 closed. It should be adjusted on a stone cold engine only. Hold the throttle slightly open while adjusting the choke so it just barely closes. After it starts the pull-off should open the choke slightly after which the heat system will open it fully. Fully warmed up the choke should stand perfectly vertical.

Good point. Here in NC it's always 90+ degrees in the summer But it still at about 1/2 open. Went to full closed after a few minutes in the freezer though, so I am happy. Choke now opens to full vertical after a minute of running since I fixed the linkage problem left by the mechanic!

OMC manual calls for the electric choke to be adjusted to "5 clicks" lean, which is at the fully-lean end of the adjustment. It would be much further closed even in high ambient temps if it was in the middle range.

OMC's tuning of this motor is starting to make some sense to me:

1. Specify really rich jets to keep novice boaters from blowing up motors during fuel starvation (#70)
2. Since the jets are stupid rich, don't need to worry about the power valve opening much. Spec the lowest possible power valve, 2.5, which will open really late in the throttle swing. Why didn't they just put in a plug?
3. Since the jets are stupid rich, we don't need much of a choke. So let's just spec it for as wide open as the adjustment allows.
4. Since the jets are stupid rich, we can lean out the idle mixture. Base setting per the manual is only 5/8 of a turn, not Holley's recommended 1.5 turns.

I wish there was a way to plumb an 02 sensor in and see what my cruising mixture is like. I'd love to get to stoichiometric or so, and correspondingly enrichen the choke, idle needles, and put in an earlier power valve.

 

[gbeltran]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Well, the jets aren't stupid rich for that reason. They have a big jet in it because that is a fairly large carb to be on a 4.3, and thus the "signal" to the jets isn't as strong as it would be if that carb was on, say a 350 cubic inch engine, so the jets are larger to compensate. You could take the jets out and it wouldn't affect that 5/8 turn out, neither would a smaller jet since the amount of fuel passing thru that circuit at idle is very small. The power valve, if removed, would require an increase in jet size to about 80, which kind of ruins any part throttle economy (not that boats are economical in the grand scheme of things). Also, it won't dump any fuel when the engine is shut down, even when the valve opens, the metering block passages prevent that (fuel goes up, above the float level, and then down to the carb passages in the metering block). You're right, it is a pretty low number valve, but it's sized for use with that large carb on that relatively small 4.3.

 

[whitney]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Thanks for the explanation, that makes a lot of sense -- big carb means slower airflow so a bigger jet. Seems counterintuitive at first

Also, it won't dump any fuel when the engine is shut down, even when the valve opens, the metering block passages prevent that (fuel goes up, above the float level, and then down to the carb passages in the metering block).

Duh, silly me, of course it has to run up. Interesting that this looks like it becomes a "fuel source" for warm starting since the power valve port is open. I bet it becomes a big initial fuel spray when cranking. Interesting.

 

[gbeltran]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

No spray from that system of the carb when cranking, it's tied to the main metering circuit so the added fuel goes to the booster venturi, which doesn't supply any fuel with the throttle closed and no airflow, and just cranking the engine doesn't supply the necessary airflow to activate that circuit.

 

[gbeltran]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

The whole bowl full of fuel becomes a fuel source when warm, modern fuels seem to percolate more than stuff of yore when really warm, I know on a couple of my cars it vents out the venturis into the manifold when you shut them down. Never looked at my boat when I turn it off though.

 

[whitney]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

No spray from that system of the carb when cranking, it's tied to the main metering circuit so the added fuel goes to the booster venturi, which doesn't supply any fuel with the throttle closed and no airflow, and just cranking the engine doesn't supply the necessary airflow to activate that circuit.

Good info. So are the idle circuit ports are _below_ the throttle valves then to experience full manifold vacuum? Is that how a cranking engine gets enough fuel to start? Next time I have the carb off (on Wed when my rebuild kit comes) I'm going to spend some more time tracing the fuel circuits until I have a good understanding.

Do you have any suggestions about how to learn more about Holleys? I have rebuilt plenty of MG and motorcycle carbs but never gained a good operational understanding of the various bells and whistles. I just ordered a Holley carb book from Amazon, hopefully that will be some good lunch reading for a few weeks.

 

[EddiePetty]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

........
#3. Carb had the wrong power valve -- 4.5 instead of factory 2.5. So the 2.5 won't open until closer to full throttle ............

Whoops!!!! Wrong answer!...The number on the Holley power valves indicate the vacuum point at which the valve opens, thus, a 4.5 will open sooner than a 2.5.

........One question on the power valve -- when you shut off the engine, won't the power valve just dump the remaining fuel above the valve in the float straight into the intake? ...

Nope....that's why there is a spring on the power valve.

........#4. The power valve had *two* gaskets under it and one of them was torn. I figured out that the engine was getting flooded whenever the pump was on because I took the carb off, attached the fuel line, jumpered the fuel pump on, and held the carb horizontal over my head. Fuel started dripping out of the power valve port between the barrels on the bottom of the carb....

......and right there is probably your hard start problem. Holley's do not take kindly to back fires....they blow power valves and/or power valve gaskets.

And now, a question for you. Which Holley do you have, a two barrel fixed shaft or a two barrel progressive?

 

[EddiePetty]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Hey Whitney!!!!

Thought you might find these interesting....food for your thoughts.

http://www.holley.com/TechService/Library.asp

http://www.holley.com/data/TechService/Technical/power_valves.pdf
​

 

[gbeltran]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Whoops!!!! Wrong answer!...The number on the Holley power valves indicate the vacuum point at which the valve opens, thus, a 4.5 will open sooner than a 2.5.



Nope....that's why there is a spring on the power valve.




......and right there is probably your hard start problem. Holley's do not take kindly to back fires....they blow power valves and/or power valve gaskets.

And now, a question for you. Which Holley do you have, a two barrel fixed shaft or a two barrel progressive?

He had the first one right, the 2.5 wont open until closer to full throttle. Definitely later than a 4.5 would (so you are correct, but so was whitneys statemet). The spring just determines the vacuum setting, it wont keep the valve closed when you shut the engine off, in fact the spring will cause the valve to open when the engine is shut down. I know holleys get a bad rap for the "blowout" that everyone just assumes happens to a power valve with a backfire, but I have NEVER had a backfire take one out, and I've run Holleys on my cars/boats since I started wrenching in the early 80's. I have found that they tend to stiffen up so they don't move at all if you let them sit for an extended period of time. He has a standard holley, the only progressive 2 barrel holleys I've seen came on 4 cylinder car engines, the pinto being one of them.

 

[gbeltran]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

Whitney, the idle circuit ports are below the butterflies. Should see a small hole in the baseplate below the butterfly. Then you have the slot, usually right above that, that's the transition circuit that supplies fuel as you open the throttle as it changes from the idle circuit to the main circuit. So yes, they do get full vacuum at idle. Just about any of the Holley books should serve you well. Some of them were written quite a while ago, but that carbs basic design hasn't changed much since it came out.

 

[whitney]

Re: Starting problem - carb? 4.3OMC/Holley 2bbl

......and right there is probably your hard start problem. Holley's do not take kindly to back fires....they blow power valves and/or power valve gaskets.

And now, a question for you. Which Holley do you have, a two barrel fixed shaft or a two barrel progressive?

The valve definitely wasn't blown. The torn gasket appeared to have happened when Idiot Mechanic tightened the power valve down with both gaskets to 1000 ft-lb (my crude estimation ). It split during over-tightening and opened a direct passage from the float chamber to the power valve vacuum chamber.

As mentioned earlier I have a plain-old fixed shaft I believe ... it's a 80312.