Engine cutting out when it gets up to temp

[Rick]

Whilst running the truggy this weekend we had problems completing a heat.

The engine starts OK and ticks over, there is blue smoke from the exhaust and it accelerates OK.

The problem is about 3 mins into the race it cuts out, we retrieve it and it restarts OK and then lasts till the end of the 5 min heat. During the 10 min final however it cut out again after about another 3 minutes.

At the end of the heat we check the temp at around 120 degC.

Engine - Novarossi N21B
Plug - Novarossi C6S
Fuel - Byrons Gen2 25%

NB
It ran Ok last time out, the only change being fuel. We ran Byrons 25% before (just changed to Gen2).

Any ideas?

[bigred5765]

sounds like piston and liner needs a change, when it gets hot it expands and losses compresion it then stops, classic piston and liner change time.

[Rick]

Surely not, its only a few months old and was run in as per instructons. We have only just started to lean it out.

[bigred5765]

get someone that realy knows how to tune your engine to have a look first

[Rick]

Had a look at the instructions that came with it, thought I would put it back to factory settings and try again.

BUT

It says:

High flow rate - screw fully in and then out 3.5 turns
Low flow rate - screw fully in and then out 5 turns

Now this may seem like a stupid question, what do they mean by a turn?

Is it a full 360, or just 180?

The reason I ask is that if I turn the low end screw out by 5 * 360 turns it seems too far, its well out of the casing. The top end is not as bad, whereas if I use 180 as a turn they look better.

[James]

Turn = 360


I think its going to be pretty hard to tune your engine via a forum, they're temperemental even when face to face with one , I would try to find someone who knows what they are doing at a race meeting and ask them to have a look, sorry to be of no use but i really think you need the engine infront of you to tune and diagnose...

[Rick]

Cheers James, I appreciate that but I was just after some ideas as to why it might cut out after around 3 mins. As I said in the first post it seems to starts OK and runs well until then, and restarts again without problem.

Carl has given me a suggestion but I am hoping there is another reason. Could it be down to bad tuning?

[racingdwarf]

If the engine has run to lean or by some means sucked some dirt in the P&L can be dammaged very easly in minutes, also how much use has the truck had in three months? Stan crompton once told me how long a race tuned P&L would last in 1/8th buggy........I can't remember now but it was not very long. You can get them pinched now.

But as sombody has said, if you can get someone who knows what they are doing to have a look...Engine tuning is a dark art that takes years to get right

[Rick]

Originally Posted by racingdwarf

how much use has the truck had in three months? Stan crompton once told me how long a race tuned P&L would last in 1/8th buggy........I can't remember now but it was not very long.

Only done 2 meetings

[Southwell]

Not knowing a whole lot about engines i thought they get too hot if their too lean?

I will echo others comments though. I took my car to a meeting and a regular got it running insanely well.

[bigred5765]

don't want to disappoint you but one wrong tuned run can kill a engine get someone that knows how to do it correctly to tune it while its hot.

[Rick]

No luck, second meeting in a row where we havent completed a race

A very amiable man even had a look and checked the tuning on the engine for us, but even that did not work.

So we put the spare engine in - same again

The very amiable man had a look at the plugs and said that they had blown/broken. That meant we used a new plug for every run, each lasted about 4 mins and then went pop.

May be its a coincidence, but neither engine has run since we changed to the Gen2 fuel

[bigred5765]

try going back to your old fuel or try a different brand, and make sure plugs are right temp/ number for the engine, try to find someone with same engine and see if they can look at it for you.

[bert digler]

Originally Posted by Rick

No luck, second meeting in a row where we havent completed a race

A very amiable man even had a look and checked the tuning on the engine for us, but even that did not work.

So we put the spare engine in - same again

The very amiable man had a look at the plugs and said that they had blown/broken. That meant we used a new plug for every run, each lasted about 4 mins and then went pop.

May be its a coincidence, but neither engine has run since we changed to the Gen2 fuel

is your filter shagged or blocked even air leaks in fuel line

[tjpMT2]

Few people have had a problem with the change from Gen1 to Gen2, it normally will just need a re-tune. It was recommended to richen both High and Low speed by 1/2 a turn when you 1st change over.

[Rick]

Had mixed messages about the change from Gen1 to Gen2, some said lean the engine, some said richen.

After the first miserable outing I reset the engine to factory and started again, nice trail of blue smoke and then used the pinch method for bottom end.

As I say, all is OK, engine runs sweet, ticks over well. the nice man checked and tweaked it also.

Alas, 4 mins in it stops, take plug out and its broken

I am at a loss

Reading what Bert says, I have noticed a few air bubbles in the fuel line just before the carb, but checked the line and there is no leaks. Could it be a problem with the fuel tank? Although the truggi is only a few months old, and this is only its 4th meeting, it ran sweet for the first two (on Gen1)

[Dreadstar]

If I were you I'd change back to your old fuel,I have noticed quite a few engines of various makes reacting like this to Gen2.No amount of tuning or tweeking will help,you just have to face it ,that your particular engine just doesn't like Gen 2.

[dave g]

what does the coil of the plug look like?..im guessing it looks like its been pulled out and stuffed back in again?

try adding another copper washer to the plug,so 2 in total and i think your plug problems will go away.

generally if your switching from gen 1 to gen 2 then you would lean both needles.

dave

[Rick]

Originally Posted by dave g

what does the coil of the plug look like?..im guessing it looks like its been pulled out and stuffed back in again?

try adding another copper washer to the plug,so 2 in total and i think your plug problems will go away.

generally if your switching from gen 1 to gen 2 then you would lean both needles.

dave

Cheers Dave.

Could you possibly explain the theory behind adding a second washer?

[RLGfx]

adding the second washer will lower compression slightly. Personally I wouldn't bother.

Is the engine cutting at high revs? or is it as if it is bogging down? If it's bogging it's too rich, but it sounds from your description as if it's leaning out.

My solution (presuming it's lean) would be a cooler plug, and richen the mixture a little. Are you doing a full warm up before the race start? if not then at 3 minutes your engine is probably only about 1 minute in to running at race temp.