Hey All,

First off, Happy New Year! I have a big problem with my new-ish to me 1998 320 Gas Gas. I've had the bike 3 months or so. She was pretty hammered when I got her so I tore her completely apart, fixed broken welds, replaced nearly everything, bearings etc. The motor was left as is. Carb cleaned, but left as is. Reeds have NOT been inspected.

After the tear down I've ridden it a ton. Maybe 40 sessions. 1-3 hours per session. It's my first trials bike and also first two stroke, so I really have no point to compare the bike. It seems to run like a champ. I have 20+++ acres of California Coastal Redwoods in my yard and a typical ride is a bunch of short loops linked into a trail ride, cruising trails then blasting sections. The longest climb is probably 500-700 vertical feet with interruptions.

So everything is going great in my trials life until I do a 2500ft descent and high speed climb. Pretty much flat out trail ride on groomed single track and tarmac, maybe 12 miles non stop. Midway through the climb out the bike is down on power a bit and detonating at mid to high RPM. Just a bit, not extreme. It never pings normally except just the slightest hint right off the bottom when you rev it NOT under load. So I stop mid-ride and smoke is pouring out of the pipe at idle and the whole pipe and cast "expansion chamber" are stinking hot. Just thick nasty smoke. We can't stop where we are so I blast off another six miles of tarmac climb and park the bike. The exhaust smokes for 20 minutes and remains very hot after the rest of the motor is cool.

Ride my normal loops next morning. No problem, bike is normal.

The Fire: New Year's Day. Redding Dirt Riders annual Poker Run at Shasta. 40 miles or so. Sustained 5-6th gear pinned. Stop about 15 miles in because my leg is so hot I can't continue. Total plastic meltdown on fender/seat and plastic heat shield anything plastic near the exhaust. About a pound of molten plastic on my boot. Everything smoking. At speed the whole thing was staying cool enough to not go alight, but after a minute sitting someone kindly pointed out that flames were breaking out. Not big flames, more like multiple candles and fiery drips. Put the bike out with Camelback. DNF. Rode the return trip at a moderate pace and the bike was fine. Starts normal, runs normal.

It seems obvious that I'm over-taxing the bike in its current state of tune, but I know this bike is capable of doing these types of rides. She just wants to haul ass on occasion, I know it. I'm running 100 octane at 80:1 Redline. Fresh coolant made of Redline Water Wetter. I'm 230 lbs plus gear. Muffler clogged with goo? Jetting funky? Motor tired?

Thanks in advance.

Matt

mattpetty said:

its just you

I was looking at a Montesa 315 that was doing the exact same a few weeks back. Fathers back up bike, lent to son to rag around for the day. As you can imagine, son was blasting around everywhere pinned and sure enough after a while all sorts of smoke pouring out of the thing.

General consensus was blocked pipe. Normal pootling around doesn't put the heat into the pipe, only a sustained blast will.

Your mid box and silencer need to be cleaned out. Possibly need to de-coke your head. (may as well do the whole job IMHO).

If you are going to do long road sections like you mention, you need to richen the jetting as compared to straight section work (a couple sizes on the main jet), along with dropping to a 65:1 oil ratio. Then when riding fast, you need to continuously alternate the throttle position instead of keeping it pinned. I also suggest putting a zip tie on your choke lever (or fab a handlebar mount) and turning the choke on when flat out. I would also change to a cooler plug and check out the difference. (1 heat range)

Also make sure you dont leave the slide closed on long downhills. The engine can starve for lube. Pull in the clutch and blip it every 20 seconds or so. (2-ply can tell you alot more about this)

I think you covered it pretty well Laser... To produce the super low end torque we need for Trials Competition, the exhaust is designed to maintain more back pressure than other bikes. That holds in a lot of heat. And odds are the last person to own the bike didn't open it up for long periods so there is probably YEARS of oil and gunk in that exhaust.

I have an Enduro friend that just bought a 99 Gas Gas 321 and had the same melt-down of all the plastics but minus the fire.. He's used to long distance rides at speed without rest breaks. Once I get around to teaching him how to jump logs, maybe he'll slow down and discover the fun in the slowwww attack. And then maybe I can convince him NOT to cut EVERY log when clearing the Winter blow-down.. Mother Nature's gift to us Trials People... just gotta trim some limbs and stuff.

Back to subject... The pinging and loss of power after a high speed, high power ride can also be a plugged spark arrestor if you or other people reading this have one installed. I've seen THIS one many times.

Oh yes, one more thing.. at 100 octane, the fuel burns slower. This is especially true of Avgas. At high power high revs, the fuel is still burning as it leaves the ports. In 4-strokes, this can burn the valves.

I use Avgas 100 octane but mixed 3 gallons to 2 gallons of premium unleaded auto fuel and then I'm careful NOT to run at extended periods of high RPMs

Avgas is designed to be used in engines that never see over 3,000 RPM. Maybe high octane race fuel is different, but the octane rating is the fuel's resistance to igniting BEFORE the spark sets it off so that you can run higher compression ratios. That usually translates to a slower burn too. As in POOF instead of BANG

As Laser said, long downhills under engine compression braking only can starve your 2-stroke of lubrication.. The cylinder can handle it better than the main bearings. In the newer Gas Gas Trials Bikes, the "Pro" engine uses a pressure lube system to the main bearings using the oil in the transmission. Your older Gas Gas depends on the oil in the gas for the lower end bearings.

REALLY GUYS ???

I suppose you could force this 13 yr old "TRIALS BIKE" into a life of blasting trails. but it is not designed to do what you are asking it to do...maybe just my opinion... but you are riding the wrong bike ...do what you will ..it is yours
but you will never be happy with it as a trail/enduro bike ..because its not..
just my opinion..have fun... Chad

As far as being the wrong machine that's debatable. My buddy has an '01 280 and rode all the same rides no issues. Rode them harder too...My 30lbs of beef being the only diff. Obviously the bike isn't strictly intended for this, but my gut feel is the plugged exhaust and maybe some jetting changes will make this kind of riding possible on occasion.

How does one go about cleaning out the mid-box and silencer? Both are mostly sealed with their inlet/outlet being the only way in/out. Burn them clean? Cut them apart and re-weld?

Also thanks for the tips on oil starvation on extended decel and the varied throttle opening on heavy workouts. Also, I'm off to India for a month, so I'm banking on amoebic dysentery to lose the 30lbs. See you on the trails n trials.

MP

I ride my Mont 315 like this from time to time up in the French Alps. Much more trail than trial. I do mix a little more oil in the fuel and I kill the engine on the long descents and coast down out of gear. Actually, I play a little game of brake chicken with myself and see how far down the mountain I can get before I have to hit the anchors....

Depending on who you speak to, people will tell you it's fine to burn them out. I've heard people plug the ends and fill em with petrol or similar, leave overnight drain, then burn. I've heard people use diesel too, but I wouldn't want to myself.

Personally, I'll be cutting windows in my mid box and pulling all the old material out, fully clean and repack & close it up with ally patches & rivets. I've bought another mid box from Ebay in case I screw it up. If you are, or know a good ally welder, then you can split them in half along the seams and reweld after the work.

polarity3232 said:

You know, that's the first thing I thought. A POKER RUN, on your trials bike? Buy an enduro for those.

mattpetty said:

Yeah, it can be done just not ideal. What are you going to India for? Boy good luck!

Thanks for the suggestions on cleaning out the pipes. I'll likely try the soak and burn method.

I also understand the trials bike was designed for trials and this is pushing it a bit. But pushing it is what motorcycles are about. I've owned my share of big bikes but the Gas Gas is so damn fun I just want to ride it everywhere.

Question: Theoretically, if I told you I'd found the best trials spot imaginable but it was 15 miles of trail riding to get there, are you no-trails-on-trials crowd coming along? You wouldn't strap on that auxiliary tank you've never used and go on an adventure?

I'm going to India to do some camera work on a film project for a week or two, then another 3-4 weeks solo just checking the place out. No itinerary beyond the shoot in Kolkata except I fly out of Chennai at the end. Leave in like 8-hours!

Ride safe.

Matt

mattpetty said:

Matt, there are a number of us that use our Trials Bikes for non-competition cross-country fun. I ride maybe one or two events per year and all of the other riding is in the mountains on trails or routes that most people have forgotten about or are too difficult for them. However, I'm careful to keep within what is considered normal power and endurance limits for my bike. No extended full power climbs or top speed for any distance more than a quarter mile or so at a time. 3 to 15 miles of trail to get to a rock garden is what I do..

The bikes are tuned on the lean side and to produce the low end torque, the exhaust system retains a fair amount of back pressure that can build up a lot of cylinder heat quickly. Varying the throttle with off and on bursts of power gives just enough break in the heat to give the engine a rest. And of course, the cooling system is sized on the small side to handle the typical range of power expected in Trials Competition without adding any excess weight.

A few months ago, there was a check list of things to do for the Scottish Six Day Trial where the bikes are ridden HARD for long distances between sections. The jetting and other tips would be good to know for your type of riding. Maybe Laser can remember where that list was. I think if you can follow some of the tips in that list, you can extend the life of your bike while using the upper limits of it's performance capabilities.

When choosing places to ride for myself, I figure I'm not really having fun until the route requires me to shift down below 5th gear. Any trail where I'm in 5th or 6th is a transportation route for me.. still fun, but meant to get me to where I will be using my first three gears.

2PLY said:

This may be that post back from 5-5-11

SSDT set up tips

Some good set-up/prep tips for the SSDT for Beta & GG- probably good general information for all.



http://www.motomerli....uk/blog/?p=797

Gandalf_WR450 said:

Yes, that's it..

Cleaning 2T exhaust is one of the downside to 2T ownership. Many different ways but I pull the exhaust system and use a propane torch to blow superheated air into the pipe and expansion chamber (it doesn't look like a MX expansion chamber but that is what it is called), after a bit flame from burning oil will come out the other end. Using oil with a low flash point will help reduce build up in the exhaust.

Also repack the muffler.

Rejetting and richer oil mixture will help engine life on "long rides".

Hey there,

Thanks to everyone for the great tips and good laughs at the expense of my poor bike. Get ready for more. Bike sat for a month while I was out in India. Came back, ran it a few times. More prone to detonate and would overheat on any riding beyond putt-putting my log pile. When I got my hands on it last year it would have no problems going for hours over the same terrain, hill climbs etc. So inspected everything I could short of tearing apart the motor. Reeds look good. Carb is all clean and set-up exactly as it was when the bike was new-to-me and running fine. No leaks on the intake boots. Torched out the mid-box/expansion chamber. Cut open the silencer with built in sparky. Not meant to be packed according to two shops I went to. Sealed up design with screens and baffles and the turbine-looking spark arrestor. Welded back shut. New oil. New coolant. No signs of cross-contamination in coolant/fuel. New fuel. New plug. Old one was yellow and burnt and bad looking. Fan runs near-always.

Take bike back out and under moderate load it is puking coolant. Is there any tricky bleeding procedure to burp the cooling system?? The first go around when I bought the bike it was pour and go. Starting to think I've roasted her. Lots of detonation under load when hot and coolant is puking. What haven't I thought of in the "easy-fix" department? If I have gassed the Gas Gas, what is likely to need rebuilding engine-wise and at what cost (if performed largely by me and farming out anything I don't have the machinery for)? Any advice or I told-you-so's welcome. My next trials bike will get the SSDT treatment recommended above. Thanks. Matt.

No tricky bleeding procedure that I know of. But it sure points to a lack of water flow or air flow. I would start testing for an obstruction of some kind. You might dump the coolant and then do some flow tests with plain water, like disconnect the return hose to the radiator and run water through the radiator cap and see if it flows freely under gravity. Then step up to a garden hose held into the radiator cap but don't try to seal it tight.. City water full pressure might blow out the radiator.

Set the bike on a stand with spark plug out and return hose disconnected but held high, then in 1st or second gear, turn the rear tire by hand and see if the water pump moves any water up the hose.

You could run some garden hose water and/or compressed air backwards through the system using that return hose at the top of the head and see what blows out.

And be aware that it's not uncommon for a fan to turn but be too weak to amount to much.


The only other thing I can think of would be a head gasket installed incorrectly but if you tore it down completely, that's not likely. So, the check list is verify a good flowing radiator, A good or new water pump, Clear hoses with no kinks, a strong fan that works and a flow test of water into and out of the hoses that go to the cylinder. Disconnect them from the water pump and the radiator bottom and then test with the garden hose. If water flows and the fan move a strong flow of air, there should be no boil over except only on the most extreme, extended runs on a hot day.

Come to think of it, it's possible to change the ignition timing on the older bikes including the 98s.

So the question to others in this forum, would a severely advanced timing cause the over-heating even with a good cooling system? I know a very retarded one can make a lot of heat but would it still ping?

Hey all. Problems solved and bike given a clean bill of health by Adrian over at Lewisport. Here's what I think happened. The bike initially started getting hot on longer rides because the midbox (expansion chamber) and silencer were all gummed up. Keep both clean on some regular interval. Another contributing factor might have been using both Mercedes factory coolant and Redline Water Wetter around the time I started boiling the bike. Adrian mentioned that lots of coolant reacts badly with the Gas Gas engines and recommends straight water if your climate allows. I think that some of the SSDT tips above the bike would have had no problems. Adrian also confirmed that there should be no issues doing extended climbs, long rides etc.

The reason I couldn't stop "boiling" the coolant is that I was over-filling it. My procedure was to fill, fill and over-fill the radiator and with the expectation that the excess water would blow off. If you do this however you get a funny siphon effect where water just keeps puking out initially. This water loss then leads to a true overheating a bit later once the bike warms up. If you don't realize the coolant was siphoning when the bike was cold, you'll likely think the bike is boiling right from the start with a nearly cold engine. So, fill the radiator until you can just see water at the bottom of the neck. Shake the bike a bit, squeeze the hoses etc to burp air. Then top back off until you can just just see water at the top of the rad. If you overfill just wick some water out with a rag.

I went to Lewisport expecting for Adrian to tell me the bike was a basket case and I might as well just buy a 2012 TXT. I was pretty ready to be sold on that idea too! Just the opposite though, Adrian down-sold me all day! After I got the coolant situation sorted he took a listen to the bike, cracked the throttle a couple of times, tweaked the air-screw/idle a bit and proclaimed the bike strong. Then he proceeded to tell me I didn't need all the bits I'd been dreaming of wasting my money on. So I left with new levers and tires and many thousands of dollars in my pocket. The point is that Lewisport WONT hustle you at all, they shoot straight and just want to get you out riding with a minimum of drama and dollars.

Thanks for all the help guys!

Matt