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21BB flameout and hot start ??s

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ronvdp

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I have a relatively new HPI 21 BB engine that i have some trouble with. It starts easily when it is cold and runs perfectly at about 250 for about 10 minutes then dies. When I try to restart it it seems that the fuel is not able to get to the carb, it is in the line but pushing the prime doesn't get it into the hsn, as if it is being pushed back into the tank. This continues until the engine cools way down.

The engine was broken in according to the manual and has had an additional 5 tanks run through it. At one point it would not start at all and hpi found the backplate had loosened off of the engine. Other than that it has had no unusual problems beside what I described.

Any help would be greatly appreciated!!!

Thanks.
 
Sounds to me like the engine is overheating. Do you know what your needle settings are? If so, post them. That will give us a place to start.

Otherwise, my first recommendation is to richen up the HSN, and give it a go.
 
Thanks SkyyMaxx, I tried to delete the other post-sorry about that.

I checked the settings and the hsn is 3 1/4 turns out and the lsn is 4 turns out. These are the settings the guy at hpi put it at.

I initially had concerns from the backplate being loose. I spent 3 days trying to start it but never could, that's when I took it to hpi and they fixed that as well as put on another carb. seems the original was a little tight. I was only at three tanks at that point. I checked the compression by hand and it is just slightly difficult to turn the piston past tdc when the engine is at room temp.

It does seem to run at 230 or so until about 7-8 minutes of good hard running and then it seems to jump up past 270. Just before it dies. I've read a few posts about the tank problem. Is this a standard problem with all Savages? What is the best solution? I am sure I could get another tank from hpi if I find a leak but I don't want to have to go through it again.
 
What fuel are you using? Answer this question and then read on...

Hmmm...after reviewing the manual on the needle settings for the NitroStar .21BB ( http://www.hpiracing.com/graphics/instr/21bbmanual/6.jpg ), it would seem that you are running on the rich side of things after all.

That leads me to believe you have an air leak somewhere you shouldn't. The first thing I would do would be to defuel the tank (empty it into a container or your fuel bottle...your choice...or just chuck the fuel from the tank). Then disconnect the tank and fuel line (fuel filter and all) from the truck by disconnecting the fuel tubing at the carb and pipe. Kink one side of the fuel tubing. Submerge the tank in water. Then blow in the un-kinked fuel tubing side. Watch the tank and fuel lines for air bubbles escaping. If none show up, then you are probably good to go there.

Check the carb housing for damage. Make sure all o-rings and seals are in tact. A little carb sealant couldn't hurt even if there is no visible damage.

Check to make sure the header is making a good seal at the exhaust port of the engine.

Finally, make sure that the cooling head is securely fastened to the engine. You should also check the backplate to make sure it is in place and snug.

Once you have ruled out the air leak issue, I recommend going back to the factory pre-sets mentioned in the link I posted above. Fill the fuel tank half-way. Start the engine. Run it until you empty the tank. The re-fill the tank half-way and start the tuning process. As mentioned in the link I posted, you should be able to get the needle settings down to about 2 and 1/2 turns out on HSN and LSN. Running on the rich side of things helps with engine life, but tune for performance and a lean condition will come about.

Finally, if none of this helps and based on how you answer the fuel question...your solution may be as simple as getting a better fuel.
 
Thanks for taking the time to go through that Skymaxx.

I went to HPI and they gave me a new one. Incredible customer service!! I had a loose backplate the first time and now the difficult starting. They rebuilt it and decided to just give me a new one and use my rebuilt one for testing.

I did however check my tank by blowing into the exhaust end of the tubing and found that unless my cap was manually pressed into the fill hole, it would leak badly. I haven't gone through and checked it underwater yet. I did go through the other suggestions to make sure everything is good to go.

I started the breakin process today using O'Donnel 20%. The first tank went easy and the temp was only 160. My feeling was that it should be hotter but I didn't want to stray from the recommendations. I ran the second tank while moving in a figure 8 and increasing then decreasing the throttle between off and 1/2. The temp was even cooler-140 or so. I haven't gone past this point yet. I want to call and make sure that temp range is ok for breakin. It seems the sleeve would be tighter and increase the amount of wear such that at normal running temps of 250 there will be too much clearance and blowby will occur. All the settings were per the instructions.

Any thoughts Skymaxx? Also, what fuel do you recommend and why?

Thanks.
 
No change to the fuel necessary. O'Donnel is one of the better/more popular fuels.

As for the break in temps, you do need to get the temps up or that engine will never quite break in. Where are you checking the temps and with what are you checking them (gun or onboard sensor)?
 
I am using a infrared temp gun that I've checked for calibration on boiling water. It seems to be very accurate. I put it right on top of the head, pointed at the glow plug.

Do you think I should lean it out some? During the second tank I couldn't get the rpm's much over a very high idle and it really spit out the unburned fuel.

Also, what do you recommend for the next few tanks?

I have heard that running 30% actually helps to keep an engine better lubricated and extends the life of it as you can run it richer to get the same power. It was something I read from someone who should know.
 
Actually 30% you can run leaner and get the same power. It has more nitro content. Thus it tends to run cooler at the same needle settings for 20% nitro.

As for the next couple of tanks, I'd suggest goosing the throttle a bunch to get the temps up. If the engine does not get into its normal operating range, the internals will never get properly set. The end result will be poor performance until the engine breaks in on its own (usually takes about a half a gallon of fuel to go that route). So don't go WOT, but do add some gas on the next tank and see if you can get those temps up into the 220-250 range.

As for the spitting of unspent fuel from the exhaust, that is normal during break in. The break in settings tend to be ultra-rich.
 
Thanks Skymaxx! You've been extremely helpful, I'll let you know how it goes.
 
No problem. Looking forward to hearing some positive reports on the new engine. Have fun with it.
 
Well I finally got the temp over 200, I had to lean it out to about 3 turns out and it really picked up. I ran another three tanks through it conservatively allowing it to cool every few minutes. Then I headed to my local homebuilt track which is actually pretty awesome-tabletop, berms, double jumps, ripple section, the works! Trying to hold back a little and keep it running slightly rich wasn't too hard with all the power I was getting! It was much quicker than the last "new" engine I had which obviously had issues. It stayed between 220 and 240 the whole time and I was really tearing it up. What a blast!! Never stalled once!!

Thanks for the help Skymaxx.


BTW, the whole leaning out after half a tank thing was pretty obvious, is there any way to get around this problem?
 
No problem. Glad to hear things are going much better.

On the self leaning nature of the fuel tank. Tune the engine with the tank half full. The end result will be an engine that is a little rich at a full tank, just right at the midway mark, and a smidge lean at the near empty point. That is what I do to get around it.

The other option is doing a dual fuel tank mod. There is a fellow on here who swears by it, but I think that my method works just fine.
 

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