Fuel delivery and timing issues???

[Old Man Powell]

Okay guys... I'm back! Got new tires for Rooster and have been doing some test runs on the interstate. Runs good but really struggle beyond 55-60 mph. In fact, to get to 60 the gas peddal isn't to the floor but man it is real darn close. Now, I realize this beast weighs 12-13k pounds but I'm really surprised by this. My 77 Holiday Rambler (24 ft class C with the ford 460) would cruise 70 mph all day long. Also, i'm running about 3400-3500 RPM at about 60-62 MPH. Damn!

Now, the carb was in pretty bad shape and I found a remanufactured Carter Thermoquad on Summit Racing's website for a decent price. Bought it, slapped it on and that sucker fired right up. Did some minor adjusting and now it is awesome. Time for another interstate run.

I do have much more throttle response around town but again I'm in pretty much the same situation when hitting 55-60 MPH. I can get to those speeds a bit better but again my foot is awfully close to the floor.

I did adjust my tire pressure. Not sure what the guys at Big O were smoking but my tires each had different pressures... ranging from 50psi up to 92. So, got them all at 85 for right now. The max for my tires is 110.

So, last night go on another run. Maybe a slight improvement. HOWEVER, as I'm going up a hill... again, on the interstate... suddenly the engine starts hesitating. Felt like someone was hitting the gas and letting off... over and over again. Our first thought was, running out of gas. Hit the gas station and then headed back out. I was going in the opposite direction on the interstate so no hills going up. Runing great but again 60-62 is my cruising speed. Go about 15-20 miles without any issues. There are some more hills in the opposite direction so I get off and head back.

As soon as I hit another hill and have to give it some more gas... bam... i get that same hesitation issue. I get to a flat spot and everything smooths out. I hammer the gas, feel the secondaries kick in and she's doing great but then again the issue comes back.

Long story (too late for that apology) short, under heavy load and having to give it more gas, the engine does the back and forth hestitaion. My first thought... starving for gas... clogged fuel filter possibly. Now, you would think that with all the work I've done on Rooster one of the first things I would have done is replace the fuel filter. DER! I will be doing that this eveing.

Thoughts... comments... suggestions... winning lotter numbers....?

Few questions..

1) Best I can tell I have one fuel filter right at my fuel pump. On the RM400/M500 chasis is there a filter along the rail towards the back?
2) what exactly is that canister right by the fuel pump? Quick glance and it appears the fuel line runs through this canister before going to the pump.
3) What RPM's do you run in your rig at 55, 60 and 65 MPH?
4) I noticed my vacuum gage is almost at zero when I'm running about 60mph. Is that about right? I am a "tach man" and never really dealt with vacuum gages.
5) When I got home and shut Rooster off it "dieseled" briefly. Never done that before. Anoyone know what the timing spec is for the 440? Ususally on the valve cover but mine has been rubbed off over time.
6) Last but not least, how do you adjust the secondaries on that carb? They are vacuum controlled and I'm more used to "mechanical/manual" secondaries. Trust me, I don't want to use more gas but I think my secondaries should be kicking in much sooner. Right now you basically have to hammer the gas all the way before they kick in.

Any help would be greatly, greatly appreciated!!!

[legomybago]

Check a few spark plugs and see if your running rich or lean.

Hesitation can be either

From what you wrote, it sounds like fuel starvation (vapor lock) or something, but your accelerator pump may not be pumping too?? To lean of primary jet/needle size? You mainly run off your primaries, secondaries are only used under HEAVY peddle...Some ideas

[TripleJ]

From your description, it sounds like a pretty clear case of fuel supply not keeping up with demand.

Like you said, fuel filter(s), then fuel pumps. And the thing next to your pump is probably a filter. There needs to be a filter in front of the pump.

I wouldn't worry about secondaries just yet. On vacuum or venturi controlled carbs, it's not a linear thing. It needs demand AND rpm. Besides there's plenty of big blocks running just fine on 2bbl carbs.

I just ran into a similar problem on mine, and I'm actually planning on installing a fuel pressure gauge at the carburetor to help me with my diagnosis

[Old Man Powell]

Good stuff so far... thanks guys.

I was wondering if I should look at white size the needle valves are on my new carb. I'll definitely yank a plug or two also.

I know where the fuel filter is but this canister thing has got me scratching my head. Kinda reminds me of one of those charcoal type emission canisters. Obviuously I need to look at it again.

I like the idea of a fuel pressure gage. Never hurts to know exactly what you are running and/or should be running. Besides... who doesn't love having one more gage to play with!

[DaveVA78Chieftain]

My first question is going to be have you purchased the Dodge MH Service Manual yet?  It will  answer several of your questions
http://www.classicwinnebagos.com/forum/index.php?action=store;sa=view;id=209

1) Best I can tell I have one fuel filter right at my fuel pump. On the RM400/M500 chasis is there a filter along the rail towards the back?

As described in the manual, only stock one is the can style by the fuel pump.

2) what exactly is that canister right by the fuel pump? Quick glance and it appears the fuel line runs through this canister before going to the pump.

As described in the manual (Fuel and Emissions sections), Evaporation Control System

3) What RPM's do you run in your rig at 55, 60 and 65 MPH?

Depending on model variation, do to the use of 4.10 to 4.88 gear ratio's, RPM's are typically in the 2800 to 3200 range for those speeds.

4) I noticed my vacuum gage is almost at zero when I'm running about 60mph. Is that about right? I am a "tach man" and never really dealt with vacuum gages.

When tuned correctly, vacuum normally runs 8 to 10 lbs at 60.  Should increase to around 12 around 50 to 55.   Make sure your primary high speed circuit piston moves freely and the metering rods are moving smoothly.  Adjustment of the tiny screw on top of metering rod affects air/fuel ration.  Vacuum is affected by:
Carb adjustment (service manual)
Timing - As indicated in service manual, In the absence of the Emissions label, 5BTDC +/- 2.5
Distributor vacuum can broken
Distributor mechanical advance binding
Stretched timing chain

5) When I got home and shut Rooster off it "dieseled" briefly. Never done that before. Anoyone know what the timing spec is for the 440? Ususally on the valve cover but mine has been rubbed off over time.

As indicated in service manual, In the absence of the Emissions label, 5BTDC +/- 2.5

6) Last but not least, how do you adjust the secondaries on that carb? They are vacuum controlled and I'm more used to "mechanical/manual" secondaries. Trust me, I don't want to use more gas but I think my secondaries should be kicking in much sooner. Right now you basically have to hammer the gas all the way before they kick in

.

Please refer to the service manual

Dave

[Stripe]

As to the no gas / sputtering going uphill, one would suspect a problem with the pickup line, like this one:

Hey baby, is Heaven missing an angel cuz you got great gams..

Thus broken, dun work..

Or maybe in this next  example.. When going uphill maybe there is a hole in it or it's only reaching the gas when driving flat.

Pickup line:      |
                       |
Fuel level:--__  |
                     --__
                           --__

[DaveVA78Chieftain]

Oh, forgot

Dried up rubber fuel line that sucks air instead of gas.

Dave

[Old Man Powell]

I crawled all around the underneath of Rooster yesterday tracing fuel lines and looking for any signs of problems. Also was looking for any fuel filters along the rail a PO may have added. All good. So, I go to change the filter right at the fuel pump. Again, someone did a horrible job the last time that filter was chaged. The was almost a 90 degree "crimp" in the line. Hmmm... starving for fuel! I disconnected the lines and dumped the gas out of the filter just to see how it looked. My lord it's a wonder that thing ran at all. Some nasty, nasty crap came out of the intake side of the filter. I replaced it with a clear filter.

Got on the road and no more hesitation. In fact, I was actually able to go from 60 to almost 70 while going up the exact same hill that previously started all this. Vacuum is a bit low per Dave's post. Even though the new carb seems fine I really need to re-tune it. My "on the fly quick install" has been sufficient enough to at least get me going again but obviously there is some room for improvement.

No more "dieseling" but I will still check the timing.

Per a previous post I mentioned the mind boggling radiator hose/exhaust pipe fuel fill line some PO came up with for the auxillary fuel tank. Finally got a chance to drain that tank. Never seen anything like the gas and debris that came out. Again... no idea how that generator ran at all. Plumbed in a clear fuel filter for it to so I can monitor what's in the fuel system. Regardless, it's purring like never before.

Today we leave for our first official camping trip in Rooster. Nothing big... about an hour drive down the road. Can't wait.

[legomybago]

See how simple that fix was?? Good job finding the problem...

Nice detailed reply by Dave with ALL the answers to Old Mans Q's

[Stripe]

Groovy. Camping pics or it dinna happen..  N:(

[M & J]

Ya. Pictures.

Gravy.