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Fuel tank/motor issues.... Again...

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Fuel tank/motor issues.... Again...

Old 07-04-2006, 01:12 PM
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ThermalRD
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Default Fuel tank/motor issues.... Again...

Well i had gone over this last summer when i bought this truck, and its apparent again this year. This truck needs constant tuning. Seems every 3 minutes the tune changes. Does anyone have a newer genesis, or Nemesis, that DOESNT do this. If i tune this to run cool all the time, it will run horribly slow for the first half tank of fuel. Then get slightly better near the end. I just wonder if a newer .46 would help, or if this is just common with this truck. Right now its just not fun. I had told myself i was done selling trucks from my collection, but this ones about to go...
Old 07-04-2006, 01:54 PM
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blackrain
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Default RE: Fuel tank/motor issues.... Again...

i wasnt to crazy about the stock engine my self thermal it gave me some issues on my nemesis. but since i changed to a .28 i couldnt be happier. other people seemed to have better luck with the stock engine. i wouldnt sell it i would mod the engine mount and go with a .28 or .32 or wait till the new CEN GST come out with its new upgraded 46. i sold my engine on ebay with pipe and made 135 dollars on it
Old 07-04-2006, 04:04 PM
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Default RE: Fuel tank/motor issues.... Again...

This is a common issue with all the trucks with fuel tanks like this. HotBodies, Savage, Gen's, and Nem's. The only way to omit the whole problem is to nip it early, as early as when you first break in the engine. If you tune the engine with only a half tank of fuel and get the temps to run fine there with a good smoke trail at around 260-280F then you should do fine even with a full tank. Only thing is you may need to go with a hotter plug to keep it running at the full tank. But give that a try. Tune your LSN and HSN with only a half tank in those temps. At a half with temps in 260 you will end up empty at 280. With a full tank it will seem a bit slugish but will get going after it warms up and should temp at about 220-230 full. I hope this works for you, the only other option is to go with the HB's style tank for the savage and mod it into your CEN to work like a buggy.
Old 07-04-2006, 07:02 PM
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ThermalRD
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Default RE: Fuel tank/motor issues.... Again...

Bash-m-up, that is exactly what Andrew Smolnick had me do last year, and i've done this year. To me, its un-acceptable. The performance at a full tank, when tuned that way, is horrible. Theres no point in having a huge motor, if it doesnt give huge performance. I mean what is CEN doing wrong here? I've had several savages, and never experienced the half tank lean issue to this degree. Further more, i can run the 220cc tank on my LST without any issues at all. I sent an e-mail over to the guys at CEN one last time. Im hoping theres a carb fix, or motor update, or some solid fix for this. I like the truck, but this issue just kills the fun. I can only imagine how bad im gonna lose my butt, when i sell this truck.
Old 07-04-2006, 08:43 PM
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Default RE: Fuel tank/motor issues.... Again...

Hey boys, I noticed this problem when I first tuned my Genesis @ full tank. Once I tuned it with half tank it was alot better, but here in the desert were it gets up to 105 degrees in the summer, the problem would re-appear were no tuning would help as well as the hot ambient air was a fight to tune without overheating anyway. So I got to thinking "why". I had a thought,, so after checking a few things on the trucks fuel delivery system, this is what I came up with:

First thing we need be sure I understand how the fuel delivery system works. The Exhaust provides pressure to the fuel tank via a pressure nipple and fuel tubing. The pressurized fuel tank pushes fuel thru the [restrictive]filter in to the waiting carb which via the venturi effect and High Speed Needle actually draws a measured amount of fuel to help delivery, Thus the more pressure in the tank the easier it is to get a good volumn of fuel in the carb. And the most important thing to remember is, Air Pressure=Compressed Air=Increased Air Volumn In A Given Space. Ok, thats it in a nut shell.

Now the problem with this simple system is the pressurized fuel tank cannot hold a constant pressure to feed the fuel line and carb due to the changing volumn of air inside the tank. To be more clear, when the tank is full there is a small amount of pressurized air volumn in the tank, quicker to build pressure. As the fuel gets used up, there is more air volumn in the tank to be pressurized, thus more volumn that can be compressed , takes longer to be compressed and build pressure.Theoretically you will need more Pressurized volumn to keep a constant fuel flow to the carb, however the exhuast pressure nipple will provide more pressurized volumn as the engine is revved higher but when the engine suddenly slows the lower pressurized volumn at exhaust nipple cannot compensate the gain of air volumn in a half full tank quickly enough to maintain the same pressure thru the filter and tube, as well as possible release of pressure exiting back out the exhuast nipple from the tank, thus a flame out due to the sudden loss of pressure at the carb.

When you tune the carb you are actually controlling how much fuel(volumn) is allowed into the venturi, so when you tune with a full tank it is easier to build pressure in a small volumn of space and you dont need to let as much fuel into the venturi. When you tune at lower level of fuel in the tank(preferrably half full) you will need to allow more fuel in to compensate for the lower pressure or lower volumn at the venturi, to minimize flame-outs When there is a sudden drop in RPM's(exhuast pressure). But if you allow too much fuel in you will be running very rich, so a fine line must be maintained to run at optimal performance. This all is highly affected by atmospheric condintions as well, but that is whole new topic.

This is all made more difficult by the somewhat restrictive brass filter in the tank, which I will be removing to see if it helps.

holy*****!!!I hope that was clear.

Now, if we were to solve this problem what would we need to do?? HHMM...Maybe a check valve between the Exhaust Pressure Nipple and Fuel Tank might help with sudden back feed from the tank to exhaust nipple..but what about maintaining pressure in a higher air volumn condition??have to think about that one some more.....
Old 07-05-2006, 06:51 AM
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Default RE: Fuel tank/motor issues.... Again...

It sounds like a one way valve would be the solution as you suggest.

But why has CEN not come up with this fix?????
Old 07-05-2006, 07:46 AM
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ThermalRD
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Default RE: Fuel tank/motor issues.... Again...

I thought that last year. I put one on the pressure line at the time, and it continually flooded the engine.


ORIGINAL: Scott_GTR

It sounds like a one way valve would be the solution as you suggest.

But why has CEN not come up with this fix?????
Old 07-05-2006, 08:03 AM
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Default RE: Fuel tank/motor issues.... Again...

Thermal, did you retune after installing the check valve and running it for a bit??
Old 07-05-2006, 11:27 AM
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Default RE: Fuel tank/motor issues.... Again...

quote: This is all made more difficult by the somewhat restrictive brass filter in the tank, which I will be removing to see if it helps.

holy*****!!!I hope that was clear.

Now, if we were to solve this problem what would we need to do?? HHMM...Maybe a check valve between the Exhaust Pressure Nipple and Fuel Tank might help with sudden back feed from the tank to exhaust nipple..but what about maintaining pressure in a higher air volumn condition??have to think about that one some more.....


i removed mine a while ago but havent tried it yet because of the move. i just installed an inline fuel filter from a plane i had and hopfully it will help.
here is my other post that i got no responce to either by cen
http://www.rcuniverse.com/forum/m_43...tm.htm#4364205

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Old 07-05-2006, 02:27 PM
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Default RE: Fuel tank/motor issues.... Again...


ORIGINAL: ThermalRD

I thought that last year. I put one on the pressure line at the time, and it continually flooded the engine.


ORIGINAL: Scott_GTR

It sounds like a one way valve would be the solution as you suggest.

But why has CEN not come up with this fix?????
how about a check valve and a regulator?

an inline regulator would make the tank pressure up till the lid popped open, but if you were to screw a regulator into the tank, so that the tank stays at a constant pressure....

Would that work?

Where do you even get valves that small?
Old 07-05-2006, 08:47 PM
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Default RE: Fuel tank/motor issues.... Again...

Check this site out and their cheap!!

http://www.usplastic.com/catalog/pro...ookie%5Ftest=1



here is another one but I'm noty sure if we need it yet.

http://www.globalspec.com/FeaturedPr...ULATOR/21641/0
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Old 07-05-2006, 09:36 PM
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Default RE: Fuel tank/motor issues.... Again...

i had thought about this as i was having issues with my Maxx, and i thought about the check valve, but you would also need to put in a pop valve as to allow any pressure over 11lbs i think it is allowed to be released. can find the check valve via any rc plane place, but the pop valve was an issue i couldnt find.
Timmahh
Old 07-05-2006, 09:55 PM
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Default RE: Fuel tank/motor issues.... Again...

I have not checked but I would be suprised if that kinda of pressure is coming thru the pressure tube. But you never know..
Old 07-06-2006, 12:49 AM
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Default RE: Fuel tank/motor issues.... Again...

A regulator like that one in the pic would function like a pop valve, but smoother. Just drilla little hole in your tank and thread that in and set it for whatever pressure you want the tank to stay at, and pua check valve in the line form the exhaust to the tank, and you should have a constant pressure from full to empty....

Anyone know where to get a price on that little regulator??

And does anyone have a pressure tester taht would be suitable for less than 20 PSIg?
We would need to know what the tank pressure is while the truck is running good, and set the regulator at that.


Good find on that reg, dogman. Never seen one that small.
Old 07-06-2006, 02:48 PM
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ThermalRD
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Default RE: Fuel tank/motor issues.... Again...

I spent a long time trying to retune it to run right. With no luck. I'd like to see CEN step up and fix this issue. Apparently many people have this problem.


ORIGINAL: [email protected]

Thermal, did you retune after installing the check valve and running it for a bit??
Old 07-06-2006, 11:04 PM
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rolland
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Default RE: Fuel tank/motor issues.... Again...

How about using a fuel pump and doing away with the pressure line all together, something similar to one of these.
http://www.perrypumps.com/prod02.htm

They are primarily used on airplanes so they should be reliable.



rolland
Old 07-08-2006, 08:13 AM
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Default RE: Fuel tank/motor issues.... Again...

I swapped e-mails with Gary at Perry pumps. He stated that it would cure the probs. It is drivin by engine pulse. You have to drill and tap a fitting in the backplate. Lol .. not sure how you'd do that with a pull or roto start.
ORIGINAL: rolland

How about using a fuel pump and doing away with the pressure line all together, something similar to one of these.
http://www.perrypumps.com/prod02.htm

They are primarily used on airplanes so they should be reliable.



rolland
Old 07-08-2006, 09:04 AM
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Default RE: Fuel tank/motor issues.... Again...

Nomobux-You couldn't without some fancy drilling angles. I am off to work so when I get home I will look into it. But I had figured this would be the solution. I am looking at how to package it on the truck so the install would be clean..
Old 07-08-2006, 09:36 AM
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Default RE: Fuel tank/motor issues.... Again...


ORIGINAL: [email protected]

Nomobux-You couldn't without some fancy drilling angles. I am off to work so when I get home I will look into it. But I had figured this would be the solution. I am looking at how to package it on the truck so the install would be clean..
They have a pretty trick bypass system also. Go to their site and download the info
Old 07-08-2006, 09:50 AM
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Default RE: Fuel tank/motor issues.... Again...

Nomobux-I have their site saved on my desktop. In fact I think I am going to order a kit to see if it works. I just wonder if it is legal for racing?
Old 07-08-2006, 12:03 PM
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Default RE: Fuel tank/motor issues.... Again...


ORIGINAL: [email protected]

Nomobux-I have their site saved on my desktop. In fact I think I am going to order a kit to see if it works. I just wonder if it is legal for racing?
I see no reason why it would be illegal. Not changing carb size etc. I used to race 1/8 pan cars years ago and they would ck the carb, etc. Thermal would be the man to ask. He's doin alot of racing. I'd be interested to know where you tap in at on the motor. Don't wanna pull mine back out to lookyloo if you are. We'd have to pull the starter, etc to see if there was clearance on the side somewhere.
Old 07-08-2006, 10:16 PM
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Default RE: Fuel tank/motor issues.... Again...

I had the same problem and was getting quite frustrated and I read here that someone recommended an O.S.8 glow plug and it was like night and day.I very seldom have to tune it from one time to the next and it performs flawlessly.Because of the hotter plug I can run it on the richer side and the temp runs between 240-270.I found that if the truck stalls at less than half a tank it will loose prime at the carb and you will have to hold your finger over the pipe as to put fuel back to the carb.But you better be wearing gloves or use a rag as the pipe gets very hot.If it does stall and your close to the truck you can see the fuel drain back.Someone here said they went to a smaller engine to get away from tuning issues.I can't imagine having anything else in this truck for power.I say if lots is enough than to much is just right. Hope this helps someone else, like it helped me.Thank you.
Old 07-08-2006, 11:34 PM
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Default RE: Fuel tank/motor issues.... Again...

you dont need a pump. at all. at best you should be at max getting about 12lbs of tank pressure, anything more is too much and overkill. the lid should, if spring tension is correct, pop at about 14-15lbs. a releif valve set to go at 11-12 lbs would keep a consistant pressure to the tank while the motor is running, just drop the one way valve between the pipe and the pressure inlet on the tank. this will do 2 things. number one, it will stop the fuel from flowing into the pressure line causing the dreded left turn bog some experience. 2nd it will keep constant pressure to the tank from the regular souce. no modding needed. the motor and muffler pressure will be more than enough to keep a steady amount of pressure in the tank pushing the fuel to the carb at ALL times. unless you roll over with low fuel ofcourse. so with a releif valve installed in the tank set to 11 or 12 lbs. then you should be all set with consistant pressure to the carb. so you only need to 2 parts, a releive vavle installed into the tank, adn a oneway valve in the pressure line.
Timmahh
Old 07-09-2006, 12:02 PM
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ThermalRD
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Default RE: Fuel tank/motor issues.... Again...

I already use OS #8 plugs, and it helped considerably. Just not good enough. Truck still requires tuning during each tank, and im not happy about that. I wish I knew how to be happy and have fun, but I dont.
Old 07-09-2006, 12:45 PM
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Default RE: Fuel tank/motor issues.... Again...

Thermal--Here,Here. I also am using the O.S.8 plug and it did help alot, but.....
now I want to run thru a complete tank with out flame-outs or bogging.

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