Dead GT380

Curmudgeon wrote: The Mikunis on my XS have a lever on the left and a pull knob on the right. You push the lever down and pull the knob up to turn the choke 'on' (richen the mixture). Yeah, I know: nice and confusing. Piston port 2 strokes tend to not have much low end power, that bike doesn't have expansion chambers which doesn't help low end at all so what you are feeling may be perfectly normal. You may just have to get used to staying a gear lower and winding it higher than you'd expect. IIRC that engine did not use induction reed valves. If you can find them, reed valves are an enormous bottom and mid improvement. Reed valve: Greatly simplified reed valve operation: Animation: http://www.2strokeengine.net/2strokeenginetuning/2strokeengineanimation.php You might be able to adapt a reed cage from a 125 of some sort.

Funny you brought this up. We're having a big discussion on the Yahoo GT750 mailing list about this very issue.

In reply to Curmudgeon:

The bike has no knob, but it will only run with the lever pushed down. It does have small expansion chambers fahsioned into the pipes. All this started after I flooded it. It ran perfectly before that. Throttle response was great.

Okay 1st lets deal with the lever thingy. On the carb there should be a brass 10mm nut with a rubber nipple (get your mind out of the gutter.. ) coming out of it should be a brass post around 3mm in dia. Some post have knobs some have forks that go to levers. Anyway with the post in the risen position the enricher system is active.

Two things come to mind.
1) When you flooded it crap from the bottom of the float bowls was forced in to all the small passages in the carb and thus plugged the pilot jets running the "choke" helps so that sort of provide proof along with the fact you say once you get it on the main jet it pulls is more proof. Clean the carbs well again... 2) Your exhaust pipes are now full of "Spodge" 2 stroke oil that was not completely burned collects in the pipes and now has been thinned by the flooded gas forced down the pipe and has now plugged all the tiny passages in the pipe and so called silencers... Remove pipes remove silencers then burn out pipes or bake in old gas grill until smoke stops pouring out the end then pass an old chain through and shake the hell out of it to loosen the carbon.

In reply to 44Dwarf:

You are sooo right about my pipes.

I used to hate getting behind a loaded up 2 smoker in the woods, not only was there the smoke to deal with but there would be black spooge dots all over my bike, helmet, goggles, gloves...

I sucked out the silencers with my shop vac and now the bike will idle without the enrichment system engaged. It runs better too. It wasn't making that "bouncy" two-stroke exahust "ping" before, but it does now. I notcues that my left cylinder had a miss. I pulled the plug and it was wet. I cleaned it off and dried it until it looked like new, but I think it fouled gain. I am going to replace all three plugs, but I think my carbs are running rich or my exhaust is still not flowing correctly.

Wow, they were that goopy? Methinks they need a hi temp burnoff: several full throttle passes.

Youl need to burn out the pipe some how. old school trick was remove from bike pour 1/4 cup fresh gas down swish it around and lite it off let it burn for a few minutes then slowly add compressed air in to one end to aid in the burn.

Other ways... Camp fire toss'em on glowing embers...(Note: not for chromed pipes!!)

Gas bar-b-que grill, pull out grates let pipes stick out the end and bake untill smoke stops..let cool wrap sides with rubber mallet pour out dust.

Oxy-Ace torch heat the inside then once burn starts change mix to more oxy.

EZ-Off oven cleaner. whole can of the foamy stuff in each pipe let it sit roll pipe 180 let sit hose out....Makes a mess and lots of water that needs to be evaporitated for disposal but works good and is chrome safe.

Played with the pilot screw to get it to idle better. It works for awhile, but goes back to its old ways after a short ride. Here is what I have noticed. The bike starts better with the choke in what appears to be the off position and runs better with what appears to be the on position. After a short ride, the power is so bad (with the choke in either position), that while cruising in by development at 20 mph in second gear, I can crack the throttle wide open and the engine just takes a crap.

I can adjust the idle by turining the idle knob or the pilot valve and afer a short ride, the bike is back to its old crappy idle (it dies with the choke off with a warm engine and idles at 4,000 rpm with the choke on). When the bike is cold, it does the opposite. Once screws are adjusted, they do not move. Sometimes, the bike will idle at 2000, it will start to miss, then bing, then the idles jumps to 4,000+

Lastly, the carbs to not appear to be the VM's described in my Clymer manual. They are not BS carbs either. They have the choke mechanism like a BS carb, but the bodies resemble (somewhat) the VM carbs, but the tops and screws are different. Here are some pics:

Those our the original carbs and usually get replaced with regular mikunis with a cable setup.

There is a website that specializes in street two strokes - www.2strokeworld.com and you will

find a nice pic of a GT380 with Jemco pipes - http://www.2strokeworld.com/forum/index.php?topic=11787.0

Here's a T500 if your looking for another Suzuki - http://newjersey.craigslist.org/mcy/3029842804.html

The binging then jumping to a 4k idle by itself says it's leaning out on its own. That points to a fuel delivery problem or a vacuum leak which opens up as the engine warms up.

In reply to Curmudgeon:

Fuel delivery seems ok. Trying to find vacuum leaks by spraying carb cleaner around likely areas. So far, no luck.

Also. It starts when cold with the chocke lever level and warm when the choke is down. Seems backwards.

Yeah, the choke operation seems counter intuitive. On my XS, on the carb with the lever when you push it down it lifts the plunger which opens the air and fuel circuits for the cold start. On the other carb, you pull the knob up which does the same thing, both carbs actually have the exact same cold start device. The left carb has the lever because the knob is way under the tank where you can't reach it.

On this diagram, it looks like #4 through #10 are the choke plunger parts, #60 is the lever which moves the plunger and it appears that it's like mine: lift to enrich. If that is the case, then the choke would be 'off' in the down position.

By the way, everything in that diagram shows 'obsolete/NLA'.

Since it has a vacuum operated petcock, is it possible there's a leak somewhere in that circuit, causing it to have very low flow? XS's are known for that, that's one thing I had to do to mine: replace it with a full manual version.

In reply to Curmudgeon:

I have a clear fuel line an can see it flowing seamlessly. I am thinking that something is just screwed up in the carbs. Now I am at a crossroads. Do I simply tear these down or do I replace with something better and what would be better?

Since everything is NLA, I'd say toss 'em and get some Mikuni VM's. Sudco has about everything you'd ever need. They can put together kits for just about any bike.

http://www.sudco.com/mikuni.html

If that's on the pricey side, VM's were used on all kinds of stuff so finding some through a bike salvage yard wouldn't be hard. Just keep in mind that you will need to go through any used carbs and may possibly have to rejet them, plus you still need the cables etc. That might wipe out any cost advantage to used carbs.

Sudco told me they cannot help. Not with new carbs, alternatives or rebuild kits.

Then it's time to get inventive. Spigot mount VM's are pretty plentiful. Measure the bore of what you have then find something in the boneyard that matches, get two more, make sure all 3 have the same slide/needle/main/pilot jets, then the hardest thing is to come up with a throttle cable. Flanders http://www.flanderscompany.com/index.html has all kinds of cable parts, here's a 4-1 splitter that you can use to make a 3-1 cable.

http://www.flanderscompany.com/action.lasso?-search&-database=_Flan_Levers.fp5&-layout=Cables1&-Format=FlanCableResults.html&-Error=FlanCableError.html&-Operator=Contains&Type=Splitter&Catagory=CablePart

I took them off and have them soaking in carb cleaner. Got this advice from someone I know who plays with two-stroke triples (mostly Kawasaki's however. His advice was:

The float is stuck. I would take the carbs off and soak them up. you can buy a gallon of carb cleaner from NAPA stick them in there and let them soak for 3 days. then spray them with brake clean change the float valve and check the main jet and the idle jet. blow through all the ports so that there clear and it should be ok. I think you have something in there. Let me know how you make out. Thanks D

Somethings just not right in those carbs....

What do you want to do with this bike? Is it for around town fun or all out balls to the tank hang on grudge night drag racing?

You could call Paul Gast at Fast by gast and see about a set of Lectrons for it but starting when cool out is a pain as they have no choke (unless thats changed..) Easy to tune as theres just one "Jet" the main needle but it takes time to do it with 3 carbs but in the other hand once their done you never have to f with them.

http://www.fastbygast.com/

In reply to 44Dwarf:

I want it for a back road blaster. I live in a rural area with low traffic volume and many twisty roads and hills. I want good smooth acceleration and power application.

I opend the carbs last night and they were not gummed up at all. I did notice that my left carb was slow to drain fluid out if its float bowl. I think that is where my problem lies. Float drop was right on and the floats look relatively new.

I am not a bike guy at all. The closest Ive come to a 2 stroke bike is the craftsman weed eater in my shed. That said, I desperately want to see this bike running well...Im not sure why I am so anxious to hear the fix for the idle problem. Maybe its because theres so many folks chiming in. I love it when a forum group all pitches in and cures a sick and aging beast, getting it back on the road....makes me feel good to be a man

Picking up a 1970 CB450 today, if it checks out as advertised.

Moparman wrote: Picking up a 1970 CB450 today, if it checks out as advertised.

Got the 450. It is weather beaten as it pent the last two years in and out of doors. 9600 original miles. Needs paint, tires and rust removed from chrome (or new chrome). Engine has compression. Transmission shifts ok. Frame is clean (pint looks almost new on frame). I will post pics later. This is my son's project. Looking for ingtion cables (sparkplug wires). Can't seem to locate a pair.

OK, I started work on the CB. The battery is dead, but I can kick it to get a comrpession reading. I am getting 150 PSI on both cylinders for a cold engine, which was drained of oil before I refilled just before I kicked. I could probably get more, but I am old and get tired. DK if it runs because I have to fix a leaking fuel line near the tank.Discovered that the hard way. The electrics all work because when I put my booster pack on it, everything goes on. Booster is not strong enough for continues cranking,

As for the GT380. I have to pull the main jet. It appears to be clogged as it is the only one of the three to not let fuel drain from the bowls when inverted. Have to pick up a skinny screw driver later. Also, the bowl gaskets did not especially great so I ordered new gaskets.

There was very little varnish in the carbs when I opened them up. I think I know what happened. I flooded the carbs right after I replaced that petcock gasket (which was disintegrating). I think a piece of old gasket or some other debris made its way in there. I also orders a fuel filter. ;)