gas engine problem, Mike this is ? 4 u

[67hat34c]

We have crusader model 350, 454 engines. for some reason we can no longer get past 3700 rpms wot. same props etc. everthing else is good. you hear secondarys open and engine groans , smooths out when you back of to 3200, I am guessing quad jets need to be rebuilt.

question is at what rpm do the secondary's open up?

also what about vacuum leak in fuel system. we installed flow scan over the weekend and it was getting odd readings. directions indicate vacuum leak prior to the flow sensor will cause this. also said small vacuum leaks will not cause engine performance problems but what about large vacuum leak? if the lids on my Racors are not sealing properly and we are sucking alot of air would this also cause the problem? the o ring on the T handle either tears up or if you grease it it rolls out.

 

[yachtsmanbill]

Is that a RACOR 1000? It should have a fiber washer under the T handle. You definitely have a vacuum leak somewhere. ws

 

[MikeP]

If they pulled proper RPM the day before the floscans were in and now they don't and there were no other changes, I'd sure look first at the floscans/related installation issues.

Onward from there -

question is at what rpm do the secondary's open up?

Quadra Jets, like virtually all oem carbs regardless of brand used on production street engines, open the secondaries based on engine load, NOT RPM. That's why you can run the engines at say, 4000 RPM with no load and the secondaries may open only slightly if at all. Therefore, there is no way to really say what RPM they should open. They should open when the engine needs the additional fuel air, not before. That can vary depending on a variety of issues.

Ideally, when a carburetor is set up and working properly, you should never "feel" the secondaries come it. The old hot rod thing of "Wow, feel those secondaries kick in!" means you have a problem with the set up and the engine is not producing the power it should be across the rev range.

The fact that the secondaries are opening indicates that sufficient vacuum is being applied by the engine across the secondary air valve to require the additional fuel/air. So the question is, why is the RPM not continuing to rise to the 4000-4400 range that it should.

What follows is based on an assumption that I gathered from the post (perhaps incorrectly?) that both engines are doing the same thing.

Yes, it may very well be fuel related (floscan installation) but if you described these symptoms without the floscan installation, the fact that the secondaries are remaining open and drawing fuel would lead me in a different direction initially.

Usually, if there is a fuel starvation problem, the eng will pull up until the carb bowls run low on fuel. Then, if the throttle is held fully open, the rpm will drop off to some stable level but seldom will their be enough fuel for the secondaries to remain open. Since that isn't happening, the first thing I'd consider, if the engines used to pull to the proper RPM is a dirty or fouled boat bottom OR a lot more weight in the boat than used to be there. If both engines are doing the same thing, it's unlikely that both carbs/fuel pumps/etc went south at the same time.

For that reason, suspecting an engine problem - both engines doing the same thing - would not be first on my list. However...

I assume there's no obvious misfiring going on, right?

Did anyone rewire the spark plugs with new wiring before this behavior started? It's easy to misswire cylinders 5 and 7 on these engines. The bad part is that they will run fairly well this way and actually sound OK. Of course they will NOT produce the proper power. 5 and 7 can also crossfire quite easily if the wires are not in top condition.

It sounds as if no one has messed with the carbs but has anyone worked on them and perhaps changed the airvalve settings?

If you brought me a car with these symptoms, the first thing I'd check wouldn't be fuel - it would be timing and then for an exhaust restriction. But the fact that BOTH engines are doing this make it hard for me to think it's engine related.

Certainly, the fuel system is common to both engines but it seems unlikely that a fuel starvation issue could still provide enough fuel to sustain operation of both engines at 3700 RPM. I have heard that floscans can cause or exacerbate small bubbles in the fuel flow which might be related but I don't have any experience with trouble shooting them. Maybe that can cut the fuel volume a bit but not all that much. There are folks here with flo-scan experience that can help more on that specific issue.

 

[Jackman]

In addition to Mike's great explanation I'd say look at the plugs. That is where everything basic in an engine is occuring (The firing part). Plug condition/color will tell you quite a bit more than you'd expect. Black, white and crusted ect all mean something...usually point to a root cause of a problem.

 

[67hat34c]

clarificaiton. they wot problem has been there for over a year now, we thought it was over propped and we put old ones back on when i bent them up in october 07. i am only thinking air in the gas since the flow scans installed over the weekend were not working right. and the meters are exactly the same. not sure i have proper setting on the meter, will rule that out on friday night.

Mike I did re wire the spark plug wires, did them about a year apart so i cant be sure if it was before or after the problem started. in know it was well over 1.5 yrs ago when i did the second motor.
I can say for sure that we did get full wot 4400 with the 3 blade props in the past. I will also say the the rpms have been dropping. we were able to get 3900 and 4000 in november now it is 3700. engines use about the same amount of gas as always, that has remained consistant over the last 4 years. spark plugs are fairly new, cap rotor, new. does not burn oil and no smoke. valve guides leak a little. normal running 2800 to 3200, only do wot once in a while and only for engough time for it to winde up all the way. then back off to normal opperation. with the exception of our last fishing trip the fuel consumption has remained about the same. last trip we used a butt load more than normal but there were other circumstances so i cant count that yet.

Flo Scan sensors installed prior to last trip and meters installed over the last weekend.

 

[Jackman]

Gradual loss sounds like a build up on the bottom to me...or as some of the northern gas boaters (I think you're in FL) a buildup on the intake from the crap in the tank that makes it to the engine. On the other hand....it could be a lot of air in the fuel system as well. Wouldn't that make you burn lean on heavy load situations and make the plugs white and the engine burn hotter?

 

[67hat34c]

bottom ruled out. props are clean, my paint job on them is holding up perfectly by the way, I spent about an hour or 2 at the sand bar cleaning the trim tabs, shafts, keel and pick ups, rest of the bottom was clean for the most part. ran it up just after we did this.

found it odd that the barnicles on the shaft were only on one part, lenght of the shaft but only about 1/4 of the diameter, strait line of them. not sure if this was the up or down position when the little turds grew there . trim tabs were completely crusted over on the bottom side only. the entire lenght of the keel but the mottom edge only not sides. all engine, ac and gen pick ups
a few rogue ones here and there on the hull, mostly near the water line but for the most part the hull was clean.

I will say that we drug this crap around on the last trip which contributed to the fuel burn.


now my paint job . I had spare props at home , they were re worked a couple of years ago and never painted so i acid washed them with ospho, cleaned with lacquer thinner then sprayed the Dupont epoxy green zinc primer on them, several coats then i sprayed non ablative anti fowling paint, several coats. installed these props in october or november, not been touched since, only some short trips, x mass parade, sand bar and 2 long fishing trips and as of 2 weeks ago there was not one thing on them. the outer edge had paint warn but that is expected. the boat was hauled when we changed, see prior thread on prop lapping etc. and by the way lapping the props and grinding the key took care of the vibration that the 3 blade set always had.

 

[MikeP]

I'm trying to look at this as far as what could be affecting both engines...

How about the air filters/flame arrestors...are they the correct ones and clean? Dirty/clogged air filters could cause this - allowing enough air for power through the upper midrange but not enough to allow the engine to achieve full RPM. Unlike a diesel, a gas engine will not produce black smoke with a partially restricted filter - it pulls fuel from the float bowls based on load/vacuum. If there isn't sufficinet flow through the filter it will only pull as much fuel as it can use based on the carb jet size. So it may have enough flow to turn 3700 but not enough to turn 4400 (under load).

Perform a WOT run with no flame arrestors/filters and, if possible have someone watching to see if the secondaries on both carbs open fully. Obviously if the engs will pull full RPM without the arrestors/filters, you've found the problem. In any case, whatever they do or don't do will help diagnose the problem. Also, be sure the chokes are fully open! Usually if they aren't you will get black smoke and stumbling once the engine is warmed up. So the black smoke, if there is any, would be a giveaway that there is an overfuel problem - usually a choke or bad carb needle/seat.

A partially restricted air filter won't usually cause black smoke. They can if the fiilter is basically plugged and now acting like a choke. But since your engines will turn 3700RPM under load the filters are not plugged though they could be restricted.

 

[Will]

Over the past few months, I've heard a number of folks complain about the loss of a few hundred RPM at WOT. The 7.5 HP outboard on my Zodiac isn't putting out like it used to either. Could this be caused by the reduced energy output of Ethanol gas?
Will

 

[Boatsb]

OK Steve here it comes from a diesel guy.

Get some gauges. First you need the fuel pressure coming out of the pump and second the draw at the filter. If there is not a good seal at the filter that could be the first problem.

Are both engines doing the same thing? What else is common to them? Its not easy for 2 engines to have the same problem at the same time without something effecting both. Maybe a fuel valve or a filter leak on the pickup side or a crossover that effects both engines. Maybe a clogged carb filter or two.

 

[MikeP]

Hmm - ethanol; now there's an interesting thought. I don't like to over-science stuff but I suppose it's a possibility depending on the amount of ethanol used in gas in that area. I have no expereince with fuel additives that are desigined to reduce power; only with those that are supposed to increase it (with the associated engine and or tuning changes). If the enthanol concentration in the fuel sold in that area is enough to reduce the power noticeably, I'd think it would be well publicized and well-known.

If it is the problem, you could change the carb jetting to compensate but at this point, barring some hard evidence re power reduction w/ the local gas, I'd still look at "traditional" causes.

Along those lines, how old is the fuel in the boat?

 

[Jackman]

I thought he was in Fla? Thought they did not have ethanol in their gas? If he is using ethanol check for the telltale signs of buildup on the intakes and carb throttle plates. This will surely slow you down...could cause a stuck float in the carb...maybe kill a fuel pump ect....but I thought he was in a non-ethanol state..

 

[67hat34c]

no ethanol,

Flame arrestors are original ones and i keep them very clean. I take very good care of these motors, change oil every 50hrs which is over kill but cheep insurance. I did a compression ck on one motor a while back, it was not that bad, one cyl was a little low.

next time i can get some help, i will go through them, timing , compression etc, guess i will have to wrangle my buddy scott to give me a hand. however home projects have now taken priority, wife has me installing wood flooring and with that i replace door case and base boards. 5" base boards and larger door case etc.

for now on the boat i will ck out the racors for vacuum leaks and attempt to get the flow scan to work properly. will ck this stuff friday night as we are going out fishing satruday am as well as the following weekend.

when i have time i plan to cut holes in the deck to access fuel senders and pull them out , get fuel guage to work and inspec pick up. will then replace the shut off valve and copper fuel line from the tank to where it connects to the aeroquip hoses.

by the way i seem to remember back in november when we tried wot that it spun up to about 4200 or so on one engine and 3900 to 4000 on the other and i believe rpms did drop.

 

[Boatsb]

The weekend of the 19th I will be down there with the wife as its her Bday party. The one after that I'm free I think.

 

[Maynard Rupp]

Here comes thoughts from a guy that used to build 454s and has a pair in our 36 Hat. Check carefully that you do not have any plug wiring issues. 5 and 7 are the most common ones to cross. If you do it on 1 engine you probably will do it on both, I have. Go to the top of your tank and remove that group of fittings and the shuttoff valve. Take them apart and find the one with the spring loaded check ball. Make sure you dont have crap blocking these little balls. I have had that problem and it took 2 months and Pascal's suggesrtion before I found that problem. Why do you have Racors on gas engines. I am not sure those seals are compatable with gas. We use a spin on Merccruiser filter system. I have never heard of gas engined boats with Racor fuel filters/ water seperators. We have Navman flow sensors and they require that you install them vertically as they can trap air if installed any other way. Go to any Auto Zone and buy a can of "Sea Foam". This stuff is poured into the carburator slowly until 1/3 of the can is gone. You shut the engine off for 10 minutes, then start again. We were amased what that did for our 454s. We were turning 4050 max. and running 24 mph. After that treartment they turn 4250 and the boat is doing 27.8 mph. I think the stuff cleans the crap buildup from the valve stems. I am not sure. We have digital tachs and no syncronizer. The engines always floated plus or minus 20 rpm. Now they don't change ever. Set them together at any decent rpm and they hold like glue. Try the stuff, you will like it, but don't ask me why.

 

[67hat34c]

Racors have been in there since 1988. I changed the plastic bowls with petcocks to metal bowls without petcocks to bring them up to date for gas engines. They are Racor 500 series.

I will also try C - Foam or Sea Foam . Onan sells stuff called C-4 that i used in the gen about a year ago. most likely the same stuff.