Acceleration issue on Hobao Hyper .21 turbo

[jamie2727]

Hi all, I am currently having an acceleration issue with my Hobao Hyper .21 turbo. The engine starts fine and seems to idle ok, when I accelerate however it will rev up to the max.

The carb gap isn’t moving at all whilst it’s accelerating as I’ve removed the filter and had a look it returns to 1mm when I stop applying acceleration so I’m confused as to what is causing it. The car was stored for around 2 years so could an air leak have formed around one of the o rings within the engine that have possibly deteriorated? The fuel is also around 5 years old so this might be causing something however it has been sorted correctly.

Any suggestions or ideas would be helpful

Many thanks

 

[watertrucker]

Welcome to RCT. I don’t have that particular engine but I have had a similar issue a couple times with 2 of my trucks. They would idle for a bit and then start revving up. It was because the low speed needle was set too lean. Richen up your low speed needle and see what happens. If it still wants to rev up richen the high speed needle as well. I’ve used fuel that was 4 years old without an issue so you should be ok there. Hang in there, you’ll figure it out. Nitro is awesome once you learn it.

 

[jamie2727]

Hello mate thanks for the welcome and reply. This is happening whilst the needles are set to factory settings which is a bit strange. I did try lean out the needles last time I had it running and it seemed to help slightly but they had to be so lean that acceleration was really poor. I’ll need to give it another shot this weekend. Do you think it could be worth replacing the fuel lines if I have no luck with adjusting the needles? Thanks again

 

[TeknoJ]

Hello mate thanks for the welcome and reply. This is happening whilst the needles are set to factory settings which is a bit strange. I did try lean out the needles last time I had it running and it seemed to help slightly but they had to be so lean that acceleration was really poor. I’ll need to give it another shot this weekend. Do you think it could be worth replacing the fuel lines if I have no luck with adjusting the needles? Thanks again

You may need to seal it up properly before tuning. Try richening both high and low circuits like stated above and see if it helps.
I am not really understanding what you have said here:

The carb gap isn’t moving at all whilst it’s accelerating as I’ve removed the filter and had a look it returns to 1mm when I stop applying acceleration so I’m confused as to what is causing it.

The carb gap is not moving while you accelerate yet it returns to the set idle gap. Is the servo opening the carb up or not???

 

[jamie2727]

Hi there, sorry I’ve not made it very clear. What I meant to say is when I accelerate the carb opens up and returns to its set idle gap as it should when I’ve let off the acceleration. But the engine continues to rev up despite the carb gap having returned to set idle.

Hope that clears it up, cheers

 

[TeknoJ]

Hi there, sorry I’ve not made it very clear. What I meant to say is when I accelerate the carb opens up and returns to its set idle gap as it should when I’ve let off the acceleration. But the engine continues to rev up despite the carb gap having returned to set idle.

Hope that clears it up, cheers

Ohhh way lean on the hi speed needle, and you probably have a major leak since it has been sitting. back out the HSN like a 1/8-1/4 turn

 

[jamie2727]

I think I'm going to replace all the o rings and seal it up with RTV and hopefully that will sort it. I assume it’ll be a major leak like you’ve said as factory needle settings should be running without any major issues

 

[watertrucker]

Yeah, if it’s doing that with the carb at factory settings you probably do have an air leak somewhere. I think you’re on the right track getting it sealed up. Let us know how it works out

 

[alfredwong2003]

If an engine has been sitting around for some time, it is always a good idea to take the carb apart and clean it, make sure no blockage inside. Try a different fuel tank may be next if problem persists.

 

[TeknoJ]

If an engine has been sitting around for some time, it is always a good idea to take the carb apart and clean it, make sure no blockage inside. Try a different fuel tank may be next if problem persists.

Also a good idea.
You should go ahead and clean out the tank too. I just get some denatured alcohol or old nitro fuel and swish it around then dump it. Do it a few times.
Definatley rebuild the carb at this point. Silicone isnt necessary and will probably just deteriorate but thats just what I speculate.

 

[jamie2727]

Thank you everyone for your input. Sounds like I’ve got a carb rebuild to do and I’ll go from there. Cheers