Nitro fuel tank placement and flooded engines (question)

[Doug Brumfield]

I have a vegas deuce boat, all stock save removal of the tigre drive and the addition of a proper backplate.

I have had problems from day one with the engine flooding badly (you can watch the fuel siphon from the tank into the engine and ultimately into the hull)

I have in the past raced gas trucks and touring cars, and I know how to tune well enough that my stuff always started right up, ran good and maintained good temps..

The tank in this boat, if you arent familiar with it, resembles an 1/8th scale buggy tank, and is of questionable quality.

The carb is composite, the engine is a supertigre .18

I have elavated the rear of the boat a foot (tanks in the front) and only filled the tank halfway after running it all the way out of fuel, and it still floods when I try to start it, to the point that the cyl is full of fuel.

Once running it runs alright, though it seems to be just a hair ragged at idle, and economy seems off a bit (my buddies proboats with smaller tanks run longer)

I am planning on replacing the fuel tank (I actually tried a sullivan at one point but it didnt fix the problem) and the engine (or at least the carb)

My question is, how critical is tank level in regard to engine? If the top of the tank is higher than the carb, but the pickup is below it, shouldn't I be good? Is this more likely a carb issue? any ideas whats going on? I know of other people that have this boat without these issues, so I tend to believe something somewhere has to be amiss.

Thanks for looking, sorry so wordy.

 

[Robert Elder]

That's interesting. I have one and have replaced the tank with a Sulivan slant but don't have that issue. Maybe the fuel filter that I have mounted inline is having an effect?

Have you checked your fuel/pressure lines for a leak?

I fill from the fuel line but don't disconnect the pressure line since I can see the tank level and stop the filling process before it overfills. My new tank is held in place with rubber bands going to tea cup hooks. I also have my tank angled down at the back so the pickup is probably lower than the carb inlet. When I fill it, I move the tank to be level then move it back down to be angled when it is full.

 

[Doug Brumfield]

Thanks for the responses, maybe Im not describing this well enough.. if I use hemos to clamp the line, when I release the clamp, it is not humanly possible to get the starter belt on the starter fast enough for the engine to not be flooded.. it can't be normal operation.. no one would run these boats if it were..

After I asked this question I was noticing alot of older / bigger nitro engines have the carb where the backing plate would be, and pictures of the tank clearly higher than the carb (by a lot) and also read about hopper tanks where they say to have them roughly even with the carb needle (metering needle I imagine)

I would gather from that having the fuel tank higher or as high as the carb shouldn't be a big deal, and that although they will siphon, I have a somewhat extreme case of it.. its a good thing I always take on a little water to wash that fuel outta my hull lol.. (seriously, Im glad I epoxied it before ever fueling it)

I also run a fuel filter, so I dont think thats it either.. I am leaning towards a flaw in the carb body, and I wish I had another carb to try.. I have a brand new old OS .21 I may try, and put the sullivan tank back in, and see how that goes.

 

[Charles Perdue]

This is a very common. Start spinning the engine and THEN release the hemostat......

Charles

 

[Doug Brumfield]

OK, Ill adjust my method a bit and see how it goes, may be a few weeks before I get it on the water but I'll update here if thats all it takes or what.

 

[Jeff Barnhart]

I'd lose the tank and replace it with a sullivan 6 oz. regardless of whether or not thats part of the problem here. Those tanks don't seal very well to begin with and they get worse over time.

 

[Doug Brumfield]

I think before this boat sees water this year it will get an OS CVR marine .18 and a sullivan tank, and possibly a fuel regulator if Im still having problems at that point. I've read up on the super tigre engine and my guess is its hosed as well.. On the boats maiden run, its exhaust coupler came loose, and with no pressure in the tank it leaned out a little too much, and from what I read they don't like the heat early in life.. not that any motor does..

I just want it to be as pain free as possible.. easy to start, not puking fuel all the time, no leaky tanks.. thought about going to a .21 but I hate the idea of putting in an engine that costs more than the boat did.. I do have a new old stock .21 OS engine from 1985, if I could find a good manifold I'd probably pop that engine in...

 

[Robert Elder]

Before giving up on the SuperTigre, pull the head off and check the top of the piston and inside of the head for visable damage. Being able to use the already installed engine is the least expensive option.

 

[mark voorhies]

Thanks for the responses, maybe Im not describing this well enough.. if I use hemos to clamp the line, when I release the clamp, it is not humanly possible to get the starter belt on the starter fast enough for the engine to not be flooded.. it can't be normal operation.. no one would run these boats if it were..

After I asked this question I was noticing alot of older / bigger nitro engines have the carb where the backing plate would be, and pictures of the tank clearly higher than the carb (by a lot) and also read about hopper tanks where they say to have them roughly even with the carb needle (metering needle I imagine)

I would gather from that having the fuel tank higher or as high as the carb shouldn't be a big deal, and that although they will siphon, I have a somewhat extreme case of it.. its a good thing I always take on a little water to wash that fuel outta my hull lol.. (seriously, Im glad I epoxied it before ever fueling it)

I also run a fuel filter, so I dont think thats it either.. I am leaning towards a flaw in the carb body, and I wish I had another carb to try.. I have a brand new old OS .21 I may try, and put the sullivan tank back in, and see how that goes.

Sounds like you may have a little pressure build up when you fill the tank? Check vent to top of tank and pressure line also?

 

[Doug Brumfield]

I pulled the head and the button and piston look fine.. I really think that it is going to boil down to a crap composite carb, a porous spot or something..

I would almost bet money on the tank being garbage, it has visible air bubbles in the plastic, and is really chintzy.. but I tried a sullivan tank already with identical results..

I ordered a new sullivan tank, the sullivan pressure nipple, and the HD aluminum stopper kit, I have hemos, I'll JB weld the nipple in the pipe as its constantly coming loose, and we'll have another go with the ST engine.. I do think that I'll end up ordering the OS CVR .18 marine engine and at that point I'll have a fun boat, but I think I can make it through one more frustrating day at the pond if I can potentially save spending 165.00 bucks or so..

I also ordered up speedmaster strut and rudder, and the CNC grim turn fin, hoping to get this all sorted and get some serious time logged on the water this summer.. I know sooner or later I'll get it all sorted out..

 

[Charles Perdue]

Doug, let us talk this through a little more. You said that you thought that the carb was bad because it flooded before you could get the engine started, right. Our toy boat carbs are different than say a car carb, lawnmower carb and such. There is nothing in the carb, no check valve, no float and needle, nothing to keep the fuel from running straight thru when the fuel line clamp is released. This is not a problem with the carb, lines and tank. This happens on every fuel setup of ours where the tank is higher than the spraybar except for some of the boats that are ran overseas that use a seperate float chamber. It gravity feeds the fuel to and through the carb into the engine.I hate to see you spend money on amother carb or engine just to have the same problem.

I am sending you a PM with my contact info.

Charles

 

[Doug Brumfield]

Problem most likely solved, but we may never know..

I found the low speed needle looks like its missing a portion of its tip, and it doesnt appear that it ever meters fuel, except possibly at idle.. I can watch it as the venturi closes up and its definitely not metering at the last point I can see it.. for comparison my big block slide carb motors low speed needles meter till half throttle.. I dont have another small block here but if memory serves they've always done about the same..

This explains crappy economy, and horrible flooding.. the needle doesnt stop flow at idle, but its seriously restricted.. mine wasn't at all.. It still ran right once it was opened up, but Im a little amazed it ever started at all..

I was going to order a new carb or parts, but the carb is on back order and and im not able to be certain which parts I need, or if the needle comes in the barrel assy or not.. I ordered the OS 18 CVR-mx today, should have it wed.. I'll sell off the ST engine (its good, its always been run real rich lol) and be a much happier boater this summer..

 

[Kez]

Problem most likely solved, but we may never know..

I found the low speed needle looks like its missing a portion of its tip, and it doesnt appear that it ever meters fuel, except possibly at idle.. I

The low speed needle is designed to meter fuel at idle. I do not have a lot of experience with the smaller engines but in general if you have a low speed needle, it is adjustable. Maybe it just needs some adjustments?

Back to the original post on the engine getting flooded...This is what I do. If the fuel tank is positioned in front of the engine, I position the fuel tank so that the spray bar is at 75% of a full tank, The fuel would still siphon into the engine so I pinch the fuel line with a pair of hemostat. When I am ready to start the engine, I elevate the rear of the starting stand so that the boat is sitting nose down. This does two things..First, the fuel will be at roughly the same level as the spray bar. Secondly, even if the fuel level is still higher, the fuel will drip out of the carb instead of into the crank case (I am talking about a rear induction engine).

 

[Doug Brumfield]

Hi Kez!

Its broken off, no amount of screwing would make the needle enter the orifice. With the new OS it meters almost the full range and is only out 100% from maybe 80% throttle.. really this is good news, bolt on a good carb and I have an extra engine that is broken in, but appears to be in good shape, visually, and has good compression.. probably end up building a .12 rigger for it..

Thats about where I ended up with my new fuel tank, and I anticipate a huge improvement, if for no other reason than the needle issue.. a little siphoning during starting past a nearly closed needle is nothing, I was getting WOT fuel flow with the throttle closed.. Id crack the plug to clear fuel and it would never stop.. I'm just glad I found something I could point my finger at.. was tired of trying to find it.. knew something was messed up.. I assume it was a production flaw, it acted the same way from day one.. didnt see bits of the needles tip in the crankcase either.

This is front carb, and I'll be using hemos too.. but I'm confident the 'driveability' concern is caused by a broken / malformed lo speed needle...

This boat is pretty much rebuilt at this point, putting in a stuffing tube this evening and getting the drive cable cut to length, and mid week I should see the parts from camaroboy to finish the exhaust up.. then its time to hit the water I'll post a report at that point, hopefully about how I had a great time and it started easily for me.

 

[jaxracer]

Hopefully the needle in the carb fixes your issue. If not, let me ask are you running straight fuel lines or do you have a one way valve or a fuel filter somewhere in the system? My brother had a very similar issue on an outboard not too long ago. At idle you couldn't keep it running because it would flood the carb. Removed both the one way valve and the fuel filter and the problem was solved. Most of our boat engines do not use low speed needles and we've never had a problem with flooding issues.

Hope this helps,

-Mitch

 

[Doug Brumfield]

I think it will almost certainly be an improvement, hopefully from a stream of fuel siphoning to just a dribble.. not sure what engines dont use low speed needles, I havent used any of the bigger nitro stuff yet, but Id have to imagine if there isnt a low speed needle, they are built to work that way. These little small blocks, and the .21s in cars all need em...

My fuel system originally had a filter only, and then during troubleshooting I removed it, and ran straight tube. Currently I have a filter, and a dubro fuel valve in line, I am going to try to use the filler but will still be using stats to ensure I dont flood while filling or resting.. if I have any problems I will remove the filler and go to plan B for fueling.. I used the sullivan pressure tap in the top of the tank so can use the original pressure tap in the cap as a fuel point..

I'd be afraid of a one way valve on this setup, unless I was using a regulator.. I did look into that, there are two available, but decided after finding the needle issue that they are probably unnecessary.

I appreciate everyones input

 

[RodneyPierce]

Doug, .21's dont need a LSN. I dont have a low speed needle in any of my motors, except my 2 tunnel hulls. Everything else gets removed/modified and I get rid of the low speed circuit all together.

Now, a LSN is essential in your off roar/on road cars, but not to much in boats.

 

[Doug Brumfield]

What is the reasoning for removing it? I understand once its spooled up, the low circuit does nothing, but what is the benefit, just removing it from the venturi to clean up the air?

The engine that was the original subject for this thread ran fine once it was on the water and going, but was a major pita to start.. ofc had I known what was happening I would have clamped the line and had one of my buddies unclamp it once I had the engine spinning... would probably have started ok that way.. I also have the tank a bit lower now, which should also help.

We'll see, I'm looking forward to getting it on the water and finding out how she does.

 

[RodneyPierce]

One benefit would be to just clean up the air's path through the carb throat, yes.

It also allows a large charge of fuel to enter the combustion chamber when you open the throttle quickly.

 

[jaxracer]

What is the reasoning for removing it? I understand once its spooled up, the low circuit does nothing, but what is the benefit, just removing it from the venturi to clean up the air?

You'd be surprised how much area that low speed needle takes up. Removing it makes the carb's ACTUAL bore area larger. More fuel+More air=More power. Many guys don't realize that yeah, while you may have say a .350 bore carb, that huge spray bar or low speed needle could take up enough room that it's actually like have a .290 bore carb, which in these little engines makes a HUGE difference.