gas engine trouble update

[67hat34c]

Ok I went over last night and found the problem with the flow scan. vacuum leak at the Racor filters. We have the diesel filters, 500 Series. leaking at T handle as suspected. got the flow scans dialed in.

dumped 2 quarts of MMO in each 115 gal tank and pured a half can of Sea Foam down the carburators on each motor. smoked every one out fairly well.

We ran it today and cruised at 2500 then 2800 hit it and nothing, went up to 3000 then down to 2700. this is 1000 rpms worse than last week. opened deck and pulled off the flame arrestor on the port motor, had my brother hit it again and observed the secondary not opening. pushed it in with my finger, was hard to push and it took off. did not mess with the other one. appears we need carb job as suspected.

so we found 2 problems thus far. bad carbs and vacuum leak in the fuel system.


We did not go fishing today and may have to cancel next week unless I can get the carbs off and change them out.

 

[yachtsmanbill]

Quadra jets secondaries will get stuck from non use. I need to dowse mine periodically with HOG WASH. Open the RACORs and add a couple of ounces of GUMOUT to clean internal varnish. Did you replace the RACOR O rings with fiber washers?? I just changed my filters so I KNOW they are supposed to be fiber. Dont forget to drain them periodically also.
DO NOT LET GASOLINE LEAK INTO THE BILGE!! Capture it.
I need to open the drain and loosen the cover to break the vacuum. Snug it about an eighth of a turn with a 9/16 box wrench. When I change the filters, I try to re-use the old gaskets and save the new ones for spares for emergency use. Ya never know. ws

 

[MikeP]

Has anyone worked on the carbs? A common prob with Qjets is improper tightening tourque and tightening sequence on the carb body. There is a specific sequence recommended that most folks totally ignore and it results in distorted throttle bores and jamming butterflies. In some cases of improper tightening, enough metal is squeezed out (these things are made of genuine POT Metal) that you have to file the displaced metal out of the bores. Also, if the airvalve secondary spring is too tight, the secondary airvalve will not open when it should.

The Q jet was GMs answer to emisions requirements and it is the most complex carb imaginable for no good reason. It CAN be made to run well but it's much harder to achieve and harder to keep running properly than an aftermarket Holley of the same CFM.

If you are going to rebuild or have them rebuilt, you should also address the typical casting boss leaks that they all have or will have. We never rebuilt a Qjet without doing this. It doesn't take a lot of time and only requires some epoxy - we always used JB Weld. It used to be a "trade secret" in the high performance tuning world but now it's common knowledge.

If you do a search using "quadrajet" and "epoxy" you should get a bunch of hits that will describe the process. If you take it to a carb shop (do they even exist anymore?) and tell them you want that done in addition to the rebuild and they say, "huh?" They don't know enough about Q jets to work on them - find somebody else.

Floats are also a weak point - they would tend to waterlog ( I guess that should be "gas log") and quit floating properly. Put a new float in anytime you rebuild a Qjet.

If you buy a new Qjet the same problem will exist with the castings so even a new one should be disassembled and epoxied. What you really have to watch with them if other folks owned them/worked on them before you is the tendency to change or remove certain parts in order to make them "work better." It doesn't work but a lot of backyard tuners did (do?) it. So you could have a Qjet missing some parts or with incorrect parts. That being the case, it's important to refer to a diagram of all the parts when you rebuild one - most tune up kits come with a diagram but some of them are a bit small or not very clear.

All the specs for adjusting everything will be in the tune up kit. Floats are NOT included in the kit so buy those as well.

 

[Boss Lady]

The Q-jets are great carbs if you happen to be an expert on them. There once were quite a few people who could make them sing. Holleys are great carbs for wide open throttle applications. They do make one model that is very good with vacumm secondaries, I ran one on a 455 Trans Am and it was a great carb. The only problem with holleys is the fuel enrichment valve is a very delicate part, one backfire and it is toast, then it starts dumping fuel and your engine will eat gas. I have had better success with the Edelbrock Performer carburetors, these were based upon the old Carter designs. You can get them at Advance or Autozone, the electric choke versions are under $300. Everyone who I know that has the Eldelbrock has been happy with the performance. I we use them on our 4wd trucks and trail buggies in the mountains for hill climbing and they have given realiable performance at all angles that our vehicles operate on. This is the same tilt angle challenge that a boat has, so I would recommend you give up the Stink Jets, forget the Holley, and just go with the Edelbrock. They have all the vacumm fittings needed built in and they have different sizes CFM for different applications, and they so cheap, we don't even bother rebuilding them, after 4 or 5 years, we just get another one, with a warranty.

P.S. I use these guys when I can't get parts local, and they have a nice description of the edelbrock. http://www.jegs.com/webapp/wcs/stores/servlet/product_10001_10002_743603_-1_10271

 

[MikeP]

Yep - whatever happend to the old Carter AFB? Emissions, THat's what!

Re Holleys - I sort of agree and I sort of don't agree... Actually, I think I do agree re the Air Valve secondary carbs...

THe beauty of Holleys is that they are totally and easily adjustable with tons of different selections of jets, power valves, metering blocks, acel pump cams, etc. No carb is as easy to dial in - AND externally adjustable float levels, etc. Their old 780 would work magnificently on any big block engine. Since it was an air valve secondary, not a double pumper, it was a great street carb and sort of an "automatic" for a high performance street big block. In current language, the 780 was "plug and play."

I do agree with you completely re Holleys as WOT carbs if we talk about the double pumpers. They are essentially a race carb although lot's of "look at me, I'm a racer" guys use them on the street, they basically suck at that use unless VEEEERY carefully set up. And even then they would suck (no pun intended) at the slightest opportunity or if the weather changed. But I found their air valve secondary models, especially the 780, to be totally a "fire and forget" operation. As you can no-doubt tell, the 780 was my favorite big block street carb by far and I put a lot of them on cars that went faster with the 780 than with all kinds of "higher perfromance" carburetors.

My favorite story re that was a guy in Memphis who was running a pair of Holley 650 DPs on a Pro/ET 440 Barracuda, "The Warp Factor." At the time I was sorting out my soon-to-be SS/F 440 Challenger and had smoked him pretty good although on paper I shouldn't have. We got to talking later and I bet him 25 bucks (Hey, this was the 70's, that was a lot of money for me to waste!) I could improve his 1/4 mile time by at least .2 sec by removing the aluminum manifold and two DPs and putting on an 780 with a bone stock cast iron intake mainifold. He figured he had made an easy 25 bucks but an hour later, in his first run after I put in that carb/manifold, he turned .3 quicker than he ever had!

In this case I have to admit that I knew the 780 would outperform his DPs because you could hear on the starting line that they weren't set up right for the car. He was getting really bad (relatively speaking) launches and the tunnel-ram manifold was the absolute wrong choice as well. So the bet wasn't really fair. Later, I suggested we could set up the DPs to run really well and we did. But the neat thing about the 780 is it would run great on anything just by bolting it on!

But as far as actually changing a boat carb to a different carb - Heck, I've always hated Qjets on principle but I didn't change 'em on any previous boat and they all had Crusaders w/Qjets. The Qjets were fine after a proper rebuild and I really didnt' want to mess with cobbling different linkages/choke setups/fuel line re routes, whatever.

That Holley 780 though...

 

[Boss Lady]

The biggest problem with a Q-jet that no rebuild kit will take care of no matter how careful you are in doing it, is the butterfly shafts wear out and suck air. You have to replace the base plate or you will be chasing demons. By the time you straighten out even one Quadrajet, you can buy two new Edelbrocks. The Edeldbrocks were designed and sold as quadrajet replacements. The Q-jet offered much more accurate metering and atomization of fuel than anything Holley made. The holley was very quick and easy to rejet and that is why it dominated drag racing and is still used in many performance applications today. The complexity of the Quadrajet was beyond the understanding of the average "joe six pack" to make changes so they almost always dumped them in favor of the Holley. Holley did make a highly efficient street carb, but it still has the same power valve that is easily damaged. GM continued to use the Q-jet because it allowed them to meet air quality standards and they sealed up the air idle mixture screws with metal caps. If the dealer had to make an adjustment they drilled these out and then used an epoxy to reseal them. I have a 1979 Ford truck 460 v8, that came with an OEM Holley 780. The truck has 88,000 original miles on it and it now has an Edelbrock on it. Lot better fuel mileage and none of the problems. I had 660 and 550 center squirt holleys, a Dominator, and several 850 double pumpers during my racing and hot rod days and I liked them. But I have no tolerance for problems anymore, and if I have to use a carburetor it gets an Edelbrock. LOL

 

[Genesis]

I've always liked the Edelbrocks - they're not the fastest carb out there but they ARE "bolt it on and turn it over" simple.

QJets aren't THAT tough to get right, but they're ALWAYS a pain in the butt - no way around it. Its a matter of what your time is worth - when mine was worth nothing (much younger!) I'd fix 'em up and they ran great but that was when the few hundred bucks meant more than a day or two screwing with the QJ.

Nowdays the first time I had trouble with a QJ on a marine motor it would go straight in the trash.

 

[MikeP]

Funny - we all agree (I think) on one point: "easier is better." In my younger days I would work on engines/related systems anytime - not just when I was making money at it - because I actually liked fiddling with engines. Back then it was fun, to use a previous example, to sort out a pair of Holley 650 DPs on a Weiand tunnel ram manifold and make it run well for some guy who should never have selected that combination in the first place.

Now, when I would hear engine-related conversations at the marina, most of the time I just walked on or left the conversation. Frankly, I don't want to get involved although I do on very rare occasion.

So do we all just become curmurgeons (sp?) as we get older or is it just me? No need to answer that.

 

[Trojan]

I ran the new Edelbrocks on my last boat. They ran great. But you must purchase the jet, needle and spring kit. Once set up. They run GREAT and they are easy to dial in. A real nice carb. Do not get there split high torque manifold. They don't work on boats. I have 2 to sell for a 318 chry.


BILL

 

[67hat34c]

I am going with some re-man Qjets, there are a couple of places here in FL to get them without core exchange they are 220 each. We are going to fish on saturday weather permitting so i need them done sooner than later.

No one has worked on the carbs, at least the one that the secondaries would not open. the other one i had off in november or december due to base plate gasket leak. I knew nothing of torque sequence, simply tightened them diagonaly and tried to do it evenly. Anyhow i do not believe the carbs have ever been off. Engines were in stalled in December 1988

 

[67hat34c]

I called a company in Fl regarding their rebuilds. they do epoxy the plugs, also install bronz sleevs etc. sound like quality rebuilds.

the guy there also asked me why we think we need to replace them. discussed the problems. he told me that the vacuum pot is to release the secondaries when vacuum is at certain level and if it is not releasing then we have another problem such as timing etc.

I guess i will have to go through the motors, timing, compression and also may change out the pertronix ignitors, have spares. cant imagine anything else could be the problem.

Motors sound fine, no oil use etc. But i will say that it seemed to be shaking a bit when the throttle was being pushed. i however was only looking at the port engine and did not open up the other side. 2 weeks ago we got 3700 rpms which is way low, however this week we got only 2800 the only thing i changed was the vacuum leak repaired in both racor filters and that is it.

also both engines seem to be putting out alot of steam but no smoke, also seemed to be more than usual for a hot day but dont hold me to that, both ran evenly, same fuel burn per flow scan and same when we re filled it upon returning. temp was about 170-175 each which is where is usually runs, oil pressue at usual number.

 

[MikeP]

Sound reasonable to me - like I said in my response to your first post on this, the symptoms would not have led me first to the carbs but to several other things first such as timing.

But what I'm not understanding is how both engines went from running ok to going bad together while no work, as I understand it, was done on the engines. I'd go back to the initial thoughts of timing, ign wiring, etc. But again - if no one did anything between the time the engs were running fine and now, what the heck happened?

Since you have electronic ignition, the timing/dwell shouldn't change with use. There have been cases of electronic ign modules failing - I have a friend who put them in his crusaders and one was bad out of the box. But two failing in the same way seems unlikely but I guess it's possible.

It'll be interesting to hear the final solution!

 

[Maynard Rupp]

I would also be interested in knowing the outcaom. Nothing ever, ever happens to both engines at the same time. If they share a common fuel tank, as our 36C does, I would sure start there. Timing can't change on 2 engines, neither can carbs. or anything else. If you have a carb problem on both engines, you have a fuel problem. These things are common sense.

 

[67hat34c]

separate fuel tanks. the only thing they share is age and anything upgraded or repaired on one has been done to the other at the same time.

I did compression ck on the starboard motor late last year, did not open throttle however so numbers are not right. however i seem to remember 140 to 150 area anyhow i will go through the whole thing this weekend.

 

[67hat34c]

I am trying to gather all my tests and equipment before this weekend.
Few questions:

1 out of gear Rev engines up does the secondary open and if so how much

2 Racor 500 series filters. check valve. there is a ball and a rubber seal, does the seal go on top or under the ball, cant remember how i installed them last time i took them apart. also what is the ball made of, can it absorb gasoline?

still bugs me that rpms dropped significantly after i fixed the vacuum leak on the Rocors, both were leaking from T handle.

Wonder what the possibilty is that i have clogged fuel pick ups, assuming they are orignina, 1967, what is on the end of the tube?

 

[Jackman]

Out of gear...no...you need a load on the engines to make the secondaries open.


Can't you disconnect the fuel from the engine and then cap it...then disconnect the line connected to the tank and slightly pressurize it with air and see if the guage drops? That will tell you if you have leaks. Check the pickups because they can get dirt in them. Mine actually sit in a holder that is attached to the bottom of the tank. I would guess it could get clogged at that point as well. Brings up another idea...once you've done the leak test and have no leaks then hook the pickup back up and push air into the tank upstream of the pickups to blow any dirt out of them.

Another thing, make sure your racors are full of fuel, if not fill them manually and then tighten them. I think if the fuel filters are not bled of air you could have fuel starvation which would lead to low rpms at increased demands of speed. Make sure you have no pinched hoses. If carbs had work done on them recently make suer the floats are set correctly and if the floats aer old make sure you don't have the old non-brass style...they can take on fuel and become to heavy...heck, check your carb bowl to make sure there is no crap in it making the float stick.

 

[garyd]

The best thing to do is take an O/B fuel tank use squeeze ball cut off end attach directly to carb intake. Make sure tank is above carb. Squeeze ball to hard and run engine it should run up to WOT. If it does then you know it was a fuel pickup problem.

This eliminates most of the fuel system, fuel lines, fuel pumps etc etc.

You can then back track and add the tank into system all the way along. So if the engine goes to WOT with fuel tank attached after racor and does not attached to before racor then the racor install is the problem.

At the marina once I showed the mechs this little trick we used it every time a new boat came in. Then once everything ran great we hooked back up the system to the boats fuel lines and tank. I would say at least 25% of the time there was junk in the fuel system somewhere. We would quickly find it and eliminate it.

As far as the electrical part goes buy a oscilliscope and hook it up. It will show you what ya need to know.

garyd

 

[67hat34c]

i was going to use a fuel hose and hook to the engine secondary filter housing and bypass fuel system to that point. simply stick the hose in a 5g gas can in the cockpit.

will ck the Racors again. however they are higher than the tank so when you open the top the fuel should drain down to the inlet. will try the tank shut off if it even works. never tried it.

 

[67hat34c]

regarding timing. how many degrees should it advance when accelerated.

 

[Jackman]

It shouldn't drain too much out if you have the antisiphons in line. You should be (if you're using 89 octane) 30degrees at about 3000rpms. Thats where you should have all the advance in, at 3000rpms. It changes with octane.