bradjones

Hi I got a traxxas t maxx 4907 and have run in the engine about 9-10 tanks im running it at 4.5turns out on hsn and flush with carb slide low speed needle (factory).

Im running 20% nitro model technics, without the shell off and when I feel the head it feels very hot 2seconds and itll burn ur hand! So I shut it off!

To my understanding the hsn is set up very rich at 4.5 turns out.

And the lsn is factory which seems quite lean?, getting loads of smoke out of it and unburned fuel aswell with good take of no wheelies but top end seems poor, it judders when going up the revs like it would cut out?.

Am I doing somthing wrong here guys? Normal temperature around 15-16C

I dont want to lean in hsn and blow it up, do i need a few
More tanks through it?

Running stock gearing 22cb 58t spur
Trx 3.3 engine just broke it to traxxas specific guide
Pull start
Violator 145cc tank

Any help much appreciated

Bradlee

jkdv8

My Feedback: (1)

Probably wouldn't hurt to add a shim. You'll need to look up what thickness traxxas recommends. 10-15% you're usually good from factory. 20-25% add a shim and 30% or higher you add another. Have to retune afterwards as well. Fuel could be a problem to. Traxxas engines are picky.

Maj_Overdrive

My Feedback: (11)

You shouldn't need to add a shim under the head when running 20% on a Traxxas engine. Putting your fingers on a nitro engine is not how you check the temp either, it will always be too hot too touch. You really need a temp gun and take the temperature at the glow plug. Opinions and engines will vary but if you're 250F or lower you're ok.

I'd really recommend viewing some nitro tuning videos online if you're new to nitro. It's hard to diagnose without hearing the engine and watching videos intended to teach nitro tuning will tell you what to listen for. I will give you a tip, the hsn controls total fuel flow and does effect the LSN slightly. The LSN is only effective from 0 to about 35% throttle and limits the total availible fuel flow in that range. To make an example in numbers let say the hsn is set to 10 and the LSN limits that to 4. Set the hsn to 9 and without touching the LSN it may effectively be 3.5 now.

I will say if you're spitting lots raw fuel at idle and when you apply some throttle you're running rich. The sputtering in the higher rpms can be too rich and the engine not clearing out. Or it could be the engine starving for fuel and being too lean. Only the sound can tell you the difference.

jkdv8

My Feedback: (1)

Yeah what he said. Although, if it is indeed running that rich and still overheating, something is up. Water or spit test on the head button is an easier and more dependable way of checking it.

I know the pro.15 was completely backwards in regard to shims compared to others. I went to look at the 3.3 specs and find it hard to believe that a traxxas engine can run right with the tolerance being the same running 10% or 33% when every other engine manufacturer (usually start with one or no gasket at all and say to add one every 10% of nitro) recommends you add a shim a certain thickness every 10% of nitro. It'll run regardless when setup right but with the right setup it'll run a whole lot better. Now that I think of it I removed one from my .15 running 15% and it made a huge difference in performance and temps. Just a thought.

bradjones

What you mean shim as in a copper washer under yhe head gasket?

Ive had a few rc cars schumacher menace jato 3.3 savage hyper 8.5 and always been able to keep them running well with a cold temp.

I took it out today at the bmx track and it was running really well nearly wheeling and temperature was ok spit test was 5-6 seconds to burn up apart from when id been ragging it round the whole track the hsn is set to 5 turns out and lsn is about 2 turns out. I am getting used to the 3.3 engine now i think factory settings on model techniks 20% is lean tbh my mates revo is 6 turns out and runs great, now I have a better tune I can really tear it up but I think I need to tune hsn abit for top rpm. When wot take off is amazing then when it changes gear it sounds like it is slowing down ? And thanks for afvice everyone.

jkdv8

My Feedback: (1)

Think they are aluminum unless they changed them. Placed in between the cooling head and sleeve iirc. Don't remember which I removed cause they are different thicknesses.

bradjones

Ok so I have put my new violator tank on and got a video for you to see how its running, ive modded the tank and drilled the exhaust hole one size bigger, and its at factory settings 4turns out high speed and 1.75 lsn. Spit test will burn it up in 5seconds and pinch test it would rev up and die at 3-4seconds . I have put a longer piece of fuel tubing on between the carb and tank not sure if this will make a difference good or bad, but check out the video and let me know if you think its running good, cheers brad https://www.youtube.com/watch?v=3Dg23OcTiwM&feature=youtube_gdata_player

jkdv8

My Feedback: (1)

Sounds good man. Does that model have a slipper clutch. If it does sounds like it's slipping a bit to much. Try tightened it a bit at a time til the wheels dig in. Once you dial that it you could probably lean out the hsn a bit more. Sounds like it loading up from the excess fuel after a high rev. If the spit takes 2-3 seconds to boil off its good for it. Just don't want it to dance around on the head. Also be careful of modding the exhaust tip or it won't create enough back pressure to push the fuel through. Doesn't look or sound like it's an issue though except maybe at idle. Nice truck to by the way.

bradjones

Cool thanks ye I drilled it out one more size than normal so that will do noticed bit better top end from it.

Never thought about slipper clutch ill try tightening a touch.

Yeah its at factory needle settings so I guess it needs a bit better tune does bog a touch at top end when its changing into second, but feels quite hot maybe factory is abit lean?

Havent really had a chance to tune it since I put tank on cause its killed off a glow plug!
When I go to start it, it will starts every time but will stop running when pull start has recoiled :s

Noticed that I was getting lean throttle response juddering.

So ill try smooth it all out and get a video with my mates monsters too.

The_Shark

Thats what we call mooing, too lean.

tank leak
hose leak
line disconnected from pipe
pipe seals bad
carb leak
head leak
backplate leak


also, LSN is supposed to be level on the carb ridge (the part the LSN sits in) you may be compensating for lean LSN setting by setting the HSN rich, however on some carbs it makes the engine run lean no matter how rich the HSN is.

bradjones

Mooing I'll look into that, well the LsN isn't flush like you said it's more on the rich side or maybe too rich, when I put it to flush it seems to get really hot, but have all symptoms of richness, loads of smoke on take off unburnt fuel at exhaust hard to start always floods if I just keep on the pull start soon as I un flood will start fine again.

i broken the engine mount so can't try her out for a little while, guna get a wing mount and proline wing hopefully will make for a better basher.

bradjones

Here a pic after wing installed, was very easy and made for a great mod saves the engine being the first point of contact when the inevitable happens, with the tune am still having trouble I can get it running great but it's way past factory like 5.5turns out and can't go anywhere near flush on the LsN or it overheats, I guess that's just my engine still runs good clocked it at 39mph 45mph+ Stock is a joke never get that