Hyper 21 revs then bogs for 1/2 second then revs.

[Scalded-dog]

I am learning nitro engines and steadily getting better. But i have a minor issue that i can't get my head around.

I have a hyper 21 engine that when i gun the throttle from idle it revs for about a second.. sputters or bogs for about a half second then revs up and runs full throttle. The rest of the time it runs as it should. If i open up the theottle slower it doesn't bog at all.

I somewhat suspect a lsn too rich or maybe a throttle servo or rx glitch. If the wheels are off the ground it wont bog at all.

Any suggestions to point me in the right direction?

 

[cbaker65]

I am learning nitro engines and steadily getting better. But i have a minor issue that i can't get my head around.

I have a hyper 21 engine that when i gun the throttle from idle it revs for about a second.. sputters or bogs for about a half second then revs up and runs full throttle. The rest of the time it runs as it should. If i open up the theottle slower it doesn't bog at all.

I somewhat suspect a lsn too rich or maybe a throttle servo or rx glitch. If the wheels are off the ground it wont bog at all.

Any suggestions to point me in the right direction?

Does that hyper still have the old composite type carb on it?
If it does ,then that maybe the issue ,its probably leaking like a siff sucking air!

I changed mine to the aluminum carb ,to a Ae 28 carb.!

 

[Scalded-dog]

This is the carb. I robbed it off of a used savage mill of unknown history. The o rings looked ok and I set the screws to factory as far as I could find. centered the midrange screw flush and did my best to tune it. If the carb is suspect... I can get a new one.. preferably without a midrange setting. For the average basher all the info i've seen on the mid needle is "don't touch it".

 

[cbaker65]

Lol ...We think alike ,I can't stand that mid range screw!

That is the composite carb ,an they don't seal well especially around the aluminum parts ,when the heat off the
engine ,an engine cool down ,the material flexes that causes leaks!

I use the Ae 28 or 21 first gen carb.s which are only a 2 needle carb an more stable ,
I have one left if you want it ,just pay for shipping!
The throttle throw is a little long ,so you may have to alter your throttle linkage!....

 

[Certified Mike]

The mid range needle is enough to have me looking for a new one! Everything I have ever read about 3 needle carbs is just as you said, leave the mid needle alone. IF you have access to another carb, swap it and let us know how you did. IF you DON'T have another carb, let us know. I will have to do a lil digging BUT I do have some good info about tuning those carbs somewhere.
Also, I would check to be sure you are getting a good deal at the fuel tank (make sure you aren't looking any pressure) and make sure you aren't running out of fuel in the fuel line to the carb. Make sure the fuel and air filters are nice and clean as well.

 

[Scalded-dog]

ok i will check the tank and fuel lines. I assume I can just blow in the line off the exhaust, plug the line to the carb and see if any air leaks. I don't have a spare carb to try on this outfit. Cbaker65... I would be happy to send you $ for a spare carb if you don't need it. I would pay for shipping and some for the carb itself. Let me know the easiest way to get it to you if the offer is still open. Paypal gift etc?

 

[Certified Mike]

My recommendation would be to actually remove the tank, drain it and clean it. Then, submerge it in water and block a line, blow into the other and look for bubbles. Its a lil more work but I think it cuts out any questions. Then again, if it's TOO much work, you can always just try a carb first. Its at least as likely that what @cbaker65 is recommending is the culprit. Either way, good luck and let us know.

 

[cbaker65]

This is the Ae or some call it Thee thunder Tiger carb ,It is well known ,an I run it on my 21 Hyper B-block LD3
street car ,its a bad ass!

The car ,
Ofna hyper 21 with Ae carb.

 

[cbaker65]

ok i will check the tank and fuel lines. I assume I can just blow in the line off the exhaust, plug the line to the carb and see if any air leaks. I don't have a spare carb to try on this outfit. Cbaker65... I would be happy to send you $ for a spare carb if you don't need it. I would pay for shipping and some for the carb itself. Let me know the easiest way to get it to you if the offer is still open. Paypal gift etc?

Yea ,let see if can find it ,I will see how much the actual cost is ,should only cost a few bucks in a padded envelope!
An will check back with you!
I will take the Hsn needle so it don't get broke!...

 

[Scalded-dog]

Cbaker... nice car man. I like the setup youve got there.

Pulled the tank and blew through the lines. When i plug one end and blow as hard as possible.. there is the ever so slightest air escaping from the filler lid. The spring is strong and the rubber gasket is still intact.

Would this indicate that the tank and lines are ok? Assuming if the pressure was so high to make the lid crack open it would spray fuel out too right?

P.s. nitro fuel tastes bad.

I ran the car some tonight.. and the tune acted so random. I'm going to double check linkage adjustments next. I've tuned a fair share of gasoline carbs from trucks and motorcycles to weedwackers. I even have my savage nitro tuned up pretty well. This old ofna setup is giving me fits though.

 

[cbaker65]

Cbaker... nice car man. I like the setup youve got there.

Pulled the tank and blew through the lines. When i plug one end and blow as hard as possible.. there is the ever so slightest air escaping from the filler lid. The spring is strong and the rubber gasket is still intact.

Would this indicate that the tank and lines are ok? Assuming if the pressure was so high to make the lid crack open it would spray fuel out too right?

P.s. nitro fuel tastes bad.

I ran the car some tonight.. and the tune acted so random. I'm going to double check linkage adjustments next. I've tuned a fair share of gasoline carbs from trucks and motorcycles to weedwackers. I even have my savage nitro tuned up pretty well. This old ofna setup is giving me fits though.

Thnx!...

You might have a leak at the head ,sometimes the head screws will loosen up.
Your fuel tank is good !

You can also try smearing a light coat of silicone on the carb over the mid range screw & housing ,that's
where mine leaked at ,that would tell you if it leaks there! Mine leak fuel from the screw itself though!

 

[Certified Mike]

You could also have air leaks in the engine itself. There is a post or 3 here about sealing engines. I'll see if I can find one and post it. Sealing an engine is a pretty common thing and it could account for your freakish behavior... (we've talked with your neighbors)

 

[Certified Mike]

Ok... So check out the 'sealing engines' how-to in this post. There is also carb building info you'll find helpful.
As you'll see, sealing an engine isn't THAT big of a deal to do. Its something I would do if I was in your situation as it just eliminates a lot of 'what-ifs'.

https://www.rcnitrotalk.com/forum/threads/nitro-tuning-tips-and-tuning-flow-chart.60832/#post-726317

 

[Scalded-dog]

That is some great info mike thanks. I took the carb back to stock settings... found a good article on resetting the mid screw. Sealed up the carb to engine fitting with silicone and retuned. Its running much better now.

Final thoughts.... possible air leak in carb... noob tuning incorrectly.. possible mid screw wrong. Total carb reset and retune seemed to fix it.

 

[Certified Mike]

NICE! Always good to hear another success story! Run it for a while, get some hours behind the work and let us know how it's going. Vids would be even better if you can pull it off!!! Congrats!!!