Txt300 Pinking Under Load!

[brooksie]

Hey folks,

Sorry in advance if there's a post covering this. i just spent the past hour trying to find it! Great site though.

Anyway, just bought a very lightly used Gas Gas 300 TXT 07', less than twenty hours use. Not had a trials bike for a few years but absoultely loving it!

I've noticed though, when climbing steep hills the engine will start to "pink" as the load increases. I'm using premium fuel mixed at 70:1 with a touch of octane booster, and also tried a harder plug. But it didn't make the slightest bit of difference. I've read a few posts regarding "pinking", but it seems to be more of a problem on the over run, which is not my problem. I guess it's time to order some bigger main jets, but would appreciate members advice/experience of the same.

Cheers

[jse]

Hey folks,

Sorry in advance if there's a post covering this. i just spent the past hour trying to find it! Great site though.

Anyway, just bought a very lightly used Gas Gas 300 TXT 07', less than twenty hours use. Not had a trials bike for a few years but absoultely loving it!

I've noticed though, when climbing steep hills the engine will start to "pink" as the load increases. I'm using premium fuel mixed at 70:1 with a touch of octane booster, and also tried a harder plug. But it didn't make the slightest bit of difference. I've read a few posts regarding "pinking", but it seems to be more of a problem on the over run, which is not my problem. I guess it's time to order some bigger main jets, but would appreciate members advice/experience of the same.

Cheers

What is your current jetting map? (main, pilot, needle, slide etc.) Maybe we can figure out if that's the problem as I don't think Preminum at 70:1 should require adjusting under most circumstances.

Jon

[brooksie]

Dellorto PHBL26

Main Jet #118

Pilot Jet #42

Inter #60

Slide #60

Needle set on highest position (lowest clip)

The carb was as clean as could be when I stripped it to findout what size the jets were. Usually operating at 600ft ASL.

Cheers

[jse]

Dellorto PHBL26

Main Jet #118

Pilot Jet #42

Inter #60

Slide #60

Needle set on highest position (lowest clip)

The carb was as clean as could be when I stripped it to findout what size the jets were. Usually operating at 600ft ASL.

Cheers

Interesting. The pilot and needle setting are on the rich side, indicating that the previous owner probably had the same problem (and was trying to compensate for it). The main is good, #118 works well in most cases and pilots are usually #36-38 and needle is generally #2-3 groove. You'll want to make sure your floats are correctly set and say, not binding.

I would guess that the jetting is not the problem but you may have a buildup of carbon in the combustion chamber that would raise the CR to the point that a load would cause the pinking. If the previous owner ran an older type premix oil (a good oil, just not suited to the low RPM, on/off throttle settings in Trials) that promoted carbon buildup. If it were my bike, I'd pull the head off and clean the chamber throughly as a first step in diagnosing the cause.

Since you don't know what oil was used previously this is only a guess. Most of us run a full-synthetic but you would be surprized at what some riders run in their engines (usually because it always worked great in their old 1974 Bazooki MX'er).. A restriction in the exhaust system will also cause this symptom (maybe even oil-related carbon buildup in the head pipe just where it attaches to the cylinder).

A 5-range plug works well in Trials bikes, such as an NGK BPR5ES or better, NGK BPR5EIX-11 set to .024".

Jon

[brooksie]

Thanks for the reply. I know the previous owner. He's a pretty good trials rider and very fastidious regarding the maintenance of his bikes. As mentioned, the bike is practically new having had very little use. It hadn't even been truely dirty until I got it!

He used Motul 900 full synthetic mixed at 80:1, changed the trans fluid after every ride.

I'm doubtful regarding the build up of carbon because of the low running hours, and cleanliness of modern oils. The spark plug for example is the original one, and it's like new. There's not a trace of carbon on it.

The bike has plenty of grunt off the bottom end and it doesn't fade even when it starts to pink. But I'll take your advice and remove the exhaust to have a look. Perhaps I got a really crappy gallon of fuel from the gas station? Not many people use premium, so it could have been sitting in the pipes for a while. Just wondering if it might need the timing retarding a bit?

Cheers

[jse]

Thanks for the reply. I know the previous owner. He's a pretty good trials rider and very fastidious regarding the maintenance of his bikes. As mentioned, the bike is practically new having had very little use. It hadn't even been truely dirty until I got it!

He used Motul 900 full synthetic mixed at 80:1, changed the trans fluid after every ride.

I'm doubtful regarding the build up of carbon because of the low running hours, and cleanliness of modern oils. The spark plug for example is the original one, and it's like new. There's not a trace of carbon on it.

The bike has plenty of grunt off the bottom end and it doesn't fade even when it starts to pink. But I'll take your advice and remove the exhaust to have a look. Perhaps I got a really crappy gallon of fuel from the gas station? Not many people use premium, so it could have been sitting in the pipes for a while. Just wondering if it might need the timing retarding a bit?

Cheers

Well, sounds like carbon is not the problem and the pipe should be clean also. I've used Motul with good results.

Since you know the previous owner, you might ask him if he had the problem prior. It may be poor/old fuel, which can give the same symptoms and would also make the bike a little more hard to start due to the loss of high-end aromatics. A complete drain and fresh premix would eliminate that as a cause. It also may be a fuel flow restriction, which would show up on longer hills quickly (low speed unaffected but the increased fuel demand/carb angle would lower fuel in the bowl), so you may want to check the float level, petcock filters and flow and carb filter.

Obviously it could be electrical, so a throughly cleaning/inspection of connections and grounds may help (always do the cheap/easy fixes first so fresh fuel is next).

One time at a World Round I had a minder's bike do the same thing and finally found that the core in the muffler had broken and shifted, which restricted the exhaust internally (you couldn't really tell by listening to it however) but that was a weird thing I'd never seen before and I doubt that's your issue.

Jon

[brooksie]

Well I drained the fuel tank and carb and refilled with fresh fuel from the nearest Shell Station, which isn't that near really. Added the recommended amount of Amsoil Octane Booster and went out for a play. Much, much better! Guess I'll just have to be more fussy where I get my fuel from. Thanks very much for yout time Jon. Much appreciated.

On another note,I have had to bleed the clutch every two or three rides. Once it's bled, it's fine again. I had a good look at the clutch pipe, but there's no obvious signs of a leak. But the lower part is rather dirty, so it's difficult to tell. Is there any seals inside the clutch cover that could be leaking perhaps? The bike had been stood for quite some time until I bought it. Thought if I was going to order a new pipe, might as well get seals and a gasket and do the whole thing all at the same time.

Cheers

[thats_a_five]

There are seals and o-rings in the clutch master and slave cylinders. Both are relatively easy to rebuild. If the hose is leaking you would see the fluid on the outside because there is quite a bit of pressure when you squeeze the lever and the fluid would be forced out through any hole.