Runs rough/intake popping when secondaries kick in.
Hey guys, just joined. I'm a boat owner with a 351W that has a Holley 600cfm on it. Posting here because I need info from guys with a lot of engine/carb experience, and I don't see much of that on boating forums.
So, I bought the boat late last season, and I only used it twice. Honestly, I'm not sure if it did this last year, as I might not have been getting into the secondary carb circuit, 'cause it goes pretty good down low, and we were only wake surfing with it (which doesn't require a fast start).
I'll give you all of the info below, but now I'm to the point that even after rebuilding the carb (it was horrid inside...very dirty...and it had this problem before I rebuilt it), when I the secondaries start to dump, the engine 'pops' and runs rough. It's like it won't take the fuel. I think the rpm's are about 4000 before I hit the secondaries, and it runs very smooth until then. It starts fine, it accelerates fine (note that I'm testing out of the water), but once those secondaries open up, the issue occurs.
That's the Reader's digest version....here are the details that've lead me to this point:
So, I put the boat in storage over the winter, but I didn't drain the fuel. When I brought it out of storage, the boat wouldn't start. There wasn't any spark coming from the coil. This is a points ignition system. I checked the points, and they were fine. I bought a coil, and the boat started. However, when I took it to the lake, it would start to stumble after running for a few minutes. It got to the point where I couldn't start the boat.
I got the boat home, found a kinked fuel line, it still ran like crap after fixing that. I checked the timing, and it was about 10 degrees ATDC. I adjusted it to the spec (I believe it's 6 degrees BTDC). It started and seemed to run fine, except at high revs it'd start exhibiting that popping situation. I assumed it just needed to get into the water and run some fuel through it. I did check the fuel filter, and it looked clean.
I took it to the lake, it ran ok, but when I tried to put it into full throttle, it'd run like crap. I cruised around a bit more, tried again, and it ran so bad that it stalled and I couldn't get it started. When I looked at the carb while trying to start, fuel was dumping into the carb at what seemed like a high rate, so I thought I had a hung fuel float. I assumed it was time to rebuild the carb...thinking that crud got into it.
So, I brought it back home and I rebuilt the carb. I pulled the fuel lines after the filter, blew them out, and I put the carb back on the engine. Although it starts and runs well, I noticed that as soon as the secondaries opened, the problem would occur. Before deciding to replace the carb, I checked to see if there was play in the timing chain (assuming it might have a slipped chain - I checked this by rocking the crank back and forth, but the rotor shaft seemed to move immediately), checked plug gap (they were in good shape but over spec...set to 0.034"), checked the points (0.016"), and I sprayed starting fluid around the base of the carb to see if there were any intake leaks. Everything seemed fine.
One weird thing I ran into was that I checked the timing, and it was ATDC. Maybe I missed something like not tightening the distributor lock bolt enough, or maybe I had a couple too many brews. I readjusted the timing, and it runs fine....until those secondaries open up. I'd pop the valve covers, but two bolts are covered by these huge cooled exhaust manifolds, and I might have to remove those to get at those bolts. I'm afraid that trying to remove those exhaust manifold bolts is going to result in a broken bolt...which is no fun to remove, as most of you already probably know.
Note that I haven't tried any changes to the carb. I'm in Denver (5280 ft. altitude).
So, before I drop $600 on a new carb, I thought I'd pass this along and see if someone here could help.
Is it still dumping fuel down the carb after the rebuild?
No. It did that during my start up attempt at the lake. Now it seems to be working fine. When the secondaries open, a healthy spray is pulled in.
If you can, use a white permanet marker to make a line from the dampner hub to its outer ring. Your timing changes could be from the outer ring slipping on the rubber. Re-set your timing and keep an eye on the line for any changes down the road.
Have you checked the timing advance to see if its sticking. It could be stuck in an advanced position when you set the timing, then broke free and returned to the no advance position when you looked later?
The popping from the carb has always been a lean condition for me. Sounds alot like the secondaries aren't flowing enough fuel, but you need to get the timing squared away first before adjusting the carb. Maybe you can borrow a carb to test with? Worth a try before you blow $600.
I'll check that ring. I didn't check the mechanical advance, but I'll take a look at that.
I've read that it could be lean. But, I'd think at this altitude, the jets would run rich. Nevertheless, I'll see if I can mess either with the secondary linkage or hand choke the secondary venturi, just to see if it makes a difference.
Do you think the valve timing is fine?
Get the ignition timing sorted out starting here....
Carter, Edelbrock and Rochester carbs will tolerate only 5 psi at the fuel inlet before the pressure unloads the needle and seat and allows the pump to blow raw fuel into the intake manifold. Holley carbs will generally tolerate up to 6 lbs before doing the same thing. Tap off at the carb inlet and monitor the fuel pressure with a 0-15 psi mechanical gauge. If fuel pressure is excessive, using a mechanical pump, replace the pump with a common, simple pump from Autozone. If using an electric pump, install a regulator and adjust fuel pressure. A regulator generally will not work on a mechanical pump due to the pulsing.
Have you added fresh fuel? Check fuel pressure and delivery volume.
I recently rebuilt a holley for a co worker. He tought to rear float level was too high. He screwed the adjuster nut so far thar the needle was jammed into the seat and was getting the same problem. I went over there to see what was going on. Put a new needle anad seat aand adjust it to the same position that I had previously done and now it's running like a top. At idle no fuel is being used from the rear float bowl, unless it has 4 corner idle. So when he turned the nut he seen neo change in fuel level so he kept on turniing it more until he jammed the needle into the seat. Check for proper float level by pulling the float bowl off and turning it upside down. Or if you want to see the fuel level in the window and not pull the float bowl loosen 1 lower float bowl screw to let out a good amount of fuel. Tighten that screw. Lower the float setting enough that you know it will be too low. Now start the engine or electric pump and raise the fuel level to the desire level.
Just had a chance to check out the mechanical advance and it appears to be functional. I also put the mark on the damper to see if it's moving. And, I ran it again, and I can pull about 4700 rpm's before the secondaries kick in, where the problem manifests itself. I tried putting my hand over the secondary venturies to choke it down a bit, but I couldn't get a good cover over them.
No, I didn't change the fuel, but I've run into bad fuel in the past, and usually the problem is the engine simply won't start if the fuel's taken on enough moisture. Not saying this couldn't be the issue. There was about a third of a tank in it, and I filled it up, so I might've diluted the problem.
It's a mechanical fuel pump, but I'm not sure of the pressure. I'll have to check that.
This carb is the type that you have to adjust float level by bending the arm on the float bowl; there is no external adjustment. I turned both bowls upside down and made sure the floats were level with the bowl when that was held level with the ground.
Thanks again for the input, guys. Any other thoughts are welcomed. Not sure if I can find a carb swap just to see if the metering is way off.
Remove the linkage that opens secondaries and wire them shut. If it repeats the problem you've eliminated the secondaries and probably the entire carb. Perhaps a broken valve spring?
tresi, thanks for suggesting that. It'll at least get rid of another possibility. I was thinking of disconnecting the vacuum actuator linkage, but sometimes when you're in the middle of the trees, you can't see the forest, yanno? Forgot about the value of just shutting down the secondaries to see if they're the problem. I'll give it a shot tonight and see what happens.
Oh, at this altitude, anyone have an idea what the idle screws adjustment should be at 5300 ft. altitude? Before I removed them (during the rebuild), I checked their setting, and they were only 1/2 turn out. I opened them up to 1 turn when I reinstalled them, but that was just a guess. It starts ok.
Thanks again, guys. Great suggestions/feedback.
Popped off the e-clip of the secondary vacuum-powered linkage. I didn't lock out the secondary butterflies (mechanically). Nevertheless, I could pull 5200 r's before the vacuum would suck the secondary butterflies open, and then it would do the same as when the vacuum secondary valve would open at 4700 r's.
Lean? At 5300' altitude? Not sure a new carb would fix it. Any secondary jets I should buy to see if I can get the mixture right? I'm thinking it's jetting....but at least the mechanicals (valve springs/timing/chain) seem to be ruled out.
What're your thoughts?
My guess is that there's NO fuel in the rear bowl.
What type of bowl? (Dual inlet or fuel transfer tube?)
Are there no sight plugs on that bowl?
Needle / seat stuck?
What is the Holly List Number stamped on the front of the choke housing?
It would be much easier if we could identify the carb and/or have some pics of it.
You mentioned doing a carb overhaul ... I'm assuming this carb to be a 4160 series with a metering PLATE, not a metering BLOCK with removable jets, right?
If so, I seem to recall that most kits include metering plate gaskets for both 4160 (square bore) and 4165 (spreadbore) carbs. Any chance that you may have installed the wrong gasket and blocked the hole in the metering plate? (Just a thought ...)
Holley #108-13-2 Fits 4160 Chrysler
Holley # 108-27-2 Fits most 4160 models
Excellent feedback. Thank you! You're correct, it has a metering plate and not a metering block with a transfer tube and only one fuel supply inlet, so the only removable jets are on the primary circuit. I didn't get a chance to look at those numbers this morning. I realize that would be valuable to this thread....my bad.
Fuel does deliver when the secondary butterflies open....it's obviously visible. Good thought on the gasket. However, this problem existed before the rebuild and is still present, so I'm suspect it's something other than my installing the wrong gasket out of the kit.
I'll post those numbers and some pics tonight when I get home. This one has me scratching my head.....maybe I need to verify the fuel pump's performance?
Oh, here's some more info:
I noticed that when the secondaries are delivering fuel, it's not a steady spray. Again, it's been since around 1980 that I was into the carb stuff, so I'm not sure what's 'right' and what's 'wrong' or even 'suspect'. So, when the secondary is delivering fuel, it's sporatic spraying.
Also, I had to adjust both fuel bowl floats; they're the type where you have to bend the linkage to adjust them. When inverted, both floats needed to be bent up to get the float level. Thinking about it, I think that would mean there would be less fuel in the bowls after my adjustment. Right? Wrong? Keep in mind that this problem seemed the same prior to rebuild, so I'm not sure if my adjustment made a difference or not.
To answer the questions 66GMC posted that I didn't in my previous post (I guess when you quote someone, you can't edit your reply):
There must be some fuel in the secondary bowl, as there is a visible spray, albeit sporatic.
It's of the transfer tube type.
No sight plugs or external adjustments on either bowl.
I installed new needles and seats that came with the kit. They seemed to move freely after I put the float/needle/needle seat in.
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