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Elite Veteran
 
Location: Medford, OR | So I took FMC #850 out for a family cruise last weekend over to the in-laws house for a bbq, maybe an 8 mile round trip is all, 75-80 degree Spring day. It was my girlfriend and my daughters first time riding in it (I've been working on 850 in the driveway for the last two years!) They both loved sitting in the front seat looking out at the world. It's a completely different experience driving and riding in an FMC coach then a standard class A motorhome. We stopped at the gas station and I put 25.00 of non-ethanol fuel in it for kicks. Everything was working great, the only issue I was feeling was a mild flat/dead spot on acceleration from a stop, and at times it would not build rpms real fast with the throttle hammered. Like the 440 was a little loaded up?, OR was it running too lean?? (These were thoughts that were running through my head at the time). It could be caused by multiple things, I will dive into that after I fix my vapor lock/fuel starved issue. Anyway, upon leaving the In-laws bbq, after showing off the rig, and getting ohh's and ahh's. We loaded back up. As I was getting in and about to start 850 up, I happily said to Kt, "I'm really feeling good and confident about the old FMC", (After all, I just got done with ALL the mechanical maintenance you can almost do to a motorhome's running gear!!!) So we headed out, got about two miles down the road, then bam! 850 starts obviously starving for fuel, luckily I was able to nurse the throttle through a few lonnngggg stale green stop lights that we got lucky on, and didn't have to stop before turning onto the old back streets of neighborhood that we live in. So as I still nurse the throttle, I see my house is in sight! Going to make it to the driveway! Nope! Died flat on her a$$ one block from the house. I put on the four ways, ran to the back and opened her up, first thing I did was unscrew the fuel filter canister and found only a table spoon on the bottom (should of been full of fuel), and the filter looked like new still. I put the filter back together quickly, took the air filter housing loose on top of the carb (Thermoquad) and pumped the throttle by hand to listen for fuel. I didn't hear any fuel spraying, so I pumped it maybe ten times then I heard fuel spraying!! yay! Closed the rear doors, run to the front and she fired right up! Kt looked at me and said, "Damn, you are good?" I laughed hahaha.
In my history with a manual fuel pump motor vapor locking, I've never been able to get them started back up and running "on there own" until they cool off, like 30 minutes. 850 was only shut down/out of service/capput for 1-2 minutes in the middle of the road. So by me opening the fuel filter before the manual pump release pressure? Or? Why would the carb start pumping fuel again? Where did the fuel come from? Kinda weird.
What I did different with the fuel system before this "Sunday Drive", was I installed a 3-port fuel filter "after" the manual pump, 5/16" in and out, 1/4" vapor port to return to tank (I read that this style of system prevents vapor lock) I didn't have my new vented fuel cap arrive in the mail yet, so I left the old factory gas cap loose so the tank would vent. Even with the original straight fuel line from the pump to the carb, I think it would have still vapor locked, but who knows, this was the warmest temp day I've driven it so far.
The fuel pump that is on the 440 is old, I don't know what pressure it's pushing either, I need to go pick up an inline gauge and check. But in my history trying to stop vapor lock situations, replacing the manual pump never solved it. So I need to just go electric. I want to run the best pump available, should I buy the Red Holley and regulator? Or?? We have a Red Holley on our 1986 P30 rig, it's been working well, but kinda loud, the P30 also has a built in fuel return system in the manual pump. The 440 does not, that pump will have to go, and put a fuel pump block off plate on.
Which electric fuel pumps and regulators do you run? And at what pressure is your Thermoquad happy at?
Thank you,
Dan #850
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Extreme Veteran
Location: Scottsdale, Aridzona | 3 Port filter that prevents vapor lock ? Mechanical pumps and fuel lines that run past very hot exhaust manifolds have vapor locked since Henry Ford started all this.
But a small VAPOR bleed (?) is going to stop vapor lock ? Why do you have VAPOR in the fuel line between the mechanical pump and the Carb ?
Used this pump in everything since Auto Shop in High School . . . with a regular Fram fuel filter before the pump.
http://www.summitracing.com/parts/crt-p4602rv/overview/
Gas ON ! Lou #120
Edited by hemi354az 2016-05-02 1:48 PM
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Elite Veteran
Location: Medford, OR | That is the pump that used to be in 850 Lou, the 3 stud mounting style. Thank you. That mounting bracket is already installed beside the radiator from a previous owner, someone stole it for a different project I guess......sweet.
I read that adding the 1/4" vapor port filter between the pump and carb keeps the fuel moving? I guess not! ha |
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Elite Veteran
Location: Medford, OR | Should I run a regulator with this pump? |
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Extreme Veteran
Location: Ignacio Colorado | I think you still need to fix the problem! Vapor lock is caused when the fuel boils before the pump in most cases. You only drove 8 miles, hot soaked it then started back for home. First get rid of the 3 way filter after stock pump and go back to the 2 port filter. Look at the rubber fuel line from the top of tank to the steel line going towards fuel pump and all other rubber fuel hose before the pump. If you have not replaced them it would be a good time to do so. A small crack on the very top is all it takes, plus now some of your pumped fuel is going back to the tank. Remove return line and replace the supply lines before you condemn your pump. Bill |
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Elite Veteran
Location: Medford, OR | All my rubber lines have been replaced within the last 2 years. The rubber line just before the "in" port on the pump runs within 5-6" from the rear port of the exhaust manifold, that would probably be a good spot for vapor lock issues. My steel lines running along the frame from the tank back to the filter (filter is mounted on the side of the radiator), that line runs above the duel exhaust system also. The previous owner wrapped different styles of rubber line and black tape around this steel line also? Looks like crap.
I am going to check fuel pressure in the next day or so...I will remove the 3-port filter and go back to the stock set-up. |
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Extreme Veteran
Location: Ignacio Colorado | I am amazed how fast fuel lines deteriorate with todays fuels. I replaced the line from the tank 3 years back. Tried to fire it up for spring over the weekend but it never fired. It was late and then yesterday it snowed like crazy. I'll bet my line is already cracked. Time is short as we plan to take it to the lake this weekend. Bill |
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Extreme Veteran
Location: Scottsdale, Aridzona | Regulator ? Regulators are for HOT ROD RACE CARS that have very high fuel flow at big RPM numbers. I know this is hard . . . A FMC 2900R is NOT a race car.
If you choose the Carter 4602 electric fuel pump you can run it safely without any regulator. Don't know about mounting it to the radiator, and tape and other stuff.
Mechanical fuel pumps that vapor locked got Genuine Reynolds Aluminum Foil on the metal fuel line . . . if you were a rich kid. The rest of us used wooden clothes pins.
You have the good low exhaust manifolds. Why not mount it on the firewall where the fuel hose comes out of the firewall, and run the line straight over to the engine, along the inside of the valve cover to the rear gas line hook up on the T-Quad carb. I like steel braided/rubber/teflon lined Aeroquip hose and fittings for fuel line. Gas ON ! Lou #120
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Elite Veteran
Location: Medford, OR | If I end up going with the electric pump, I was definitely planning on mounting it on the firewall etc..and loose some sweet tape. |
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Elite Veteran
Location: Medford, OR | Ok! Conclusion! So not everything you read on the web is true? Ha. The 3-port filter screwed me. I put a fuel pressure gauge on it, 0-3 pounds, crimp the 3rd port vapor line, and I have a solid 7 pounds out of the old mechanical pump. So I will be putting it back to stock, then I will carry a spare mechanical pump in the rig if ever needed...Thanks for helping me fix my dumb decisions
Dan
#850 |
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Elite Veteran
Location: Medford, OR | Well...just took 850 out for a cruise with the new meats. Handled great! Good news for that unknown. Filled the fuel tank, then hit the highway....45-50 mph she runs out of fuel! Back off the throttle and cruise on the shoulder about 40 mph and she holds strong. I'm going to call this a "volume" issue. It runs great around town stop light to stop light, and it's hot here today too. The water temp stayed between 180-190. The fuel pump is the same mechanical pump that's been on it for ump-teen years....So do I bite the bullet and buy the Carter electric pump and all the associated bs to install? Or do I buy a new quality mechanical pump and give her a shot??? What do you super FMC experienced gents think.....
Dan
#850 |
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Veteran
Location: Olympia, Washington | You might want to test the pressure, the volume and the suction of the existing fuel pump to determine if it is good or bad. Had a bad coil, wire once darned if it didn't act like it was running out of gas. |
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Elite Veteran
Location: Medford, OR | Pressure was close to 7 at idle. The only time it has issues is on a hard pull, like a freeway on ramp. Runs out of steam. I think if it were coil issue, I would have a more reacureing issue all over the board?? Idk |
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Elite Veteran
Location: Oceanside, CA | You sure you don't have a carb float level issue? Not keeping enough fuel in the bowl?
Also could be an ignition advance problem, bad/no vacuum advance while loading at speed would make it feel like it has no power.
Be sure your choke is fully opening as well. |
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Veteran
Location: Olympia, Washington | All I'm saying is in my case what seemed like a fuel problem was actually an ignition problem. Test don't guess if you suspect lack of fuel figure out a way to add more fuel. If the engine picks up with enrichment you have proven that lack of fuel is the problem. Now you must find out why the engine lacks fuel. If it does not respond to enrichment it's time to look somewhere else for the problem. |
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Elite Veteran
Location: Medford, OR | I need more fuel like you said George...I rebuilt the Thermoquad and adjusted per spec. And used a vacuum gauge to fine tune. Choke is good. Distributor advance worked fine last time I manually checked it. I'm not lacking power, just running out of fuel after an 1/8 mile hard pull then everything goes flat until I back off the pedal and cruise at a slower speed. I may look into an Edelbrock pump? Idk. Fuel line is 3/8 to the pump, 5/16 to the carb. I'm not sure how to do a volume test other than put the hose in a bucket and keep the motor running with some fuel out of a bottle? Is there a gallon per minute number or something I need to shoot for?? Thanks for the ideas guys |
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Extreme Veteran
Location: Scottsdale, Aridzona | I (and lots of my Hot Rod friends) have had good reliable service with this one - https://www.summitracing.com/parts/crt-p4594/overview/
Pump ON ! Lou #120 |
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Elite Veteran
Location: Medford, OR | Ok. I need one pint in 30 seconds or less. I'll check that first, then on to the other. |
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Elite Veteran
Location: Medford, OR | Ok, just did the volume test: 1/2 pint of fuel with engine idling for 30 seconds. I think my fuel pump loses. All hoses and the fuel filter itself before the pump are great. |
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Contributor
| #850, I have experienced this before in the past in a truck from the same era. It is possible the problem is in the fuel tank, namely the fuel sender unit getting clogged. I have not seen a picture or line art drawing of the sending units FMC used, but rust scale could be clogging the fuel sock (a fine fabric mesh screen) located on the end of the pickup tube in the sending unit assembly or clogging the pickup tube itself if a fuel sock is not used. You start and drive down the road just fine and after a few miles your engine starts starving for fuel. You stop, and after awhile the rust scale/particles settles down and falls away from the fuel sock and/or tube; You start up and everything is fine again until the agitation in the fuel tank stirs up the scale, clogs the sock filter and/or pickup tube yet again and the engine is starved of fuel once more. I would check the sending unit and inspect the interior of the fuel tank.
(Just an FYI, Duramaxer's FMCMotorcoach.com manuals page is missing a page in the fuel section, removal of the fuel sending unit - page 11-16. I checked my hard copy manual and the directions for removal and installation of the fuel tank sending unit are there on page 11-16 but no drawing of the sending unit).
Edited by TX-FMC 2016-08-06 10:23 PM
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Extreme Veteran
Location: Scottsdale, Aridzona | No socks (or shoes, or coverings of any kind) appear in the in tank fuel pickup in the FMC PARTS BOOK Group 11 . . . of that era.
Dance ON ! Lou #120
Edited by hemi354az 2016-08-06 10:58 PM
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Extreme Veteran
Location: Ignacio Colorado | Hate to say it but I have seen the seats (needle and seat) back out and starve the TQ carb for fuel. If the pump does not solve the problem this is the next place to look. BTW what did you set the floats at? TQ? Bill |
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Elite Veteran
Location: Medford, OR | I can't remember off the top of my head forsure, but I believe I set the float level just shy of 1". I do have a slight weep on the air horn gasket at one corner. I am planning on removing it sometime and sanding the body a little, but it's really nothing that dust won't just catch....So I believe if I have fuel wanting to weep out up that high in the carb, I have a full bowl. Just my own theory. I already know a new fuel pump is going on hopefully tomorrow. I will fully test the new pump before driving. Tex, as much as I have ran this engine, I've never had accumulation of any kind trapped in the fuel filter. Like I said earlier (kind of), the only time I can make/or duplicate the issue I'm having, is if you lined up #850 next to.... say a GMC Palmbeach! For a quarter mile drag race, about half way down the track that's when 850 starts to shit......lol |
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Veteran
Location: Olympia, Washington | So the existing pump passed the pressure test but failed the volume test? 9 out of 10 cars it would be fine but alas our 440's are way to thirsty for that. Drives like a sports car and passes everything except a gas station. |
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Elite Veteran
Location: Victoria, BC. Canada | This is interesting and I'm looking forward to you finding the solution, Dan.
Terry
#846 |
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To vapor lock, or not to, that is the question.
