Trouble Reving
 

Well I cant really think of a way to sum up my bikes problems. Yesterday I tried to start it, and got nothing at all ,almost ran the battery down trying everything I could. Today I removed the carb and cleaned all the jets and holes and anything I could think of, I also checked the float hight. I reassembled it and put it back on the bike a little while ago. Now the bike sometimes has real trouble starting, but on occasions it'll start right away. The biggest problem I have is that it will not rev past id say about 2000rpm when the choke is off. Somehow it runs with the choke on, i don't really understand why. Third when try and test ride it I hear a lot of popping sound from the muffler. Does anyone out there get any of these kind of problems?? Please help.

Re: Trouble Reving
 

It would help with the continuity of the suggestions if you would NOT start a new message thread every time the symptoms change a little bit. :cuss:

It would be better if you continue with the thread you already started !! :oops:

IIRC, you've had two tries at cleaning the carb, right? It still sounds like a carb problem.
In an earlier message, you said something about buying a new carb. I suggest you DO THAT.........or take it to a shop for proper carb repair.
Somehow I feel that you taking a THIRD try at it wouldn't accomplish much.

Lean mixture sympthoms. If the carburetor is in good condition, check for any false air entrance to the cylinder or before the carb.
When I modified the air filter, the bike wasn't reving over 1/3 throttle and I had to richen the mixture.

Well excuse me, I thought it was about the choke, hmmm. This carburetor isnt as complicated than the ones Ive had on my 302 Tiger, and ive repaired them many times. I guess ill remove the exhaust, check for blocks, and try the needle shim mod. If anyone actually knows where you can buy a mikuni BSR32SS carb, itd help. I cant really spend 350 dollars for one, I only spent around 500 for the entire bike. I guess ill try dealerships, but they allways want a lot. There may be other carbs I can use too. thanks Jaime.

You should do a major overhaul of the carb if you haven't completed it already: Check the throttle valve membrane, possibly blocked air jets or fuel valve filter -outside of the carb-, or maybe broken old rubber joints. Also, verify that the intake pike isn't slashed and that there are no air entrances between the carb and the air filter (properly connected oil sump gas tubes). Run the motorcycle with the fuel valve on PRI (or constant fuel supply), to check if the vacuum membrane is damaged and the fuel isn't filling the float chamber. Once corrected the problem, you can "shim" the jet needle, not before.

Remember that when you use the choke, you're closing some air entrance and richening the mixture, so the condition improves somewhat. That doesn't mean that you've got a choke problem.

Some sympthoms of a lean mixture are: Popping exhaust when retaining the engine (mid revs and no throttle), engine overheat, loss of power, acceleration unstable, irregular reving and not going down to idle inmediatly after realeasing the throttle, etc...


(Sorry, it's hard for me to explain in English all those things)

You seem to be explaining it fine to me. Better than I could.

I have a good deal of respect for Jaime's knowledge of carbs. He's the one that carried on the re-jetting thread that I so hastily started.

If you look in the "how-to" section, there is a lot of good carb talk. (It may actually be in the "mods" section, I can't remember.) This might lead to some insight into your problem or you may be able to see other symptons previously unspoken of.
There are also some helpful photos in that section.

Jaime said, "Once corrected the problem, you can "shim" the jet needle, not before" He is right. If you start adjusting things in the dark, you'll never know what ONE thing was needed to correct the problem.

Get the carb back to all of it's default settings (this includes making sure that all of the parts are still good, as mentioned by other members) and then adjust one thing at a time. It sounds redundant, but if you made 5 changes and the carb started working properly, you would never know what it was that was actually the problem, or what it was that you "corrected".

Have you tried www.ronayers.com

I use them for all of my factory part needs. They are fairly reasonably priced.

Well I got the carb taken apart, I think the main prob with it was the main jet, in the main throttle body on the engine side. I got a stiff piece of wire to clean it out, and also did the needle shim. Its running pretty strong, despite it being cold outside. I'm gonna ride it a day and see how it does. I still have a slight popping from the exhaust, ill remove it to see what there is to see. I may bring out the welder for another exhaust, don't know yet. Ive taken this carb off enough times to know now the easiest way it to loosen the air box. Two bolts, one visible on the left side, one hidden under the battery holder. Thanks everyone for the advice. Ill try to help people in the future.

Popping like afterfire?

Or are you getting the low gear gargle?

If it's the gargle, which I get while just rolling in second gear, you are pretty close to factory.
Afterfire, of course, would mean you are running a little rich and the unburned gas fumes are exploding in the muffler.

Actually, this occurs because there's gas and too much O2 in the muffler. There's always a small amount of gas going out unburned, and it fires in the muffler because of high temperatures and enough O2.
Some causes are a lean mixture or air entering a damaged muffler because of the vacuum created. If it afterfires with 0% throttle and there are no air leaks anywhere, you can reduce it by richening the pilot screw (counterclockwise).

Also, cold weather is the best for performance, as long as the mixture is rich enough to carry the O2 increase (cold air has more density than when it's hot = more air in each engine intake).
By the way, cleaning the jets with a wire it's not recommended, as you could enlarge its size...

Sounds to me that Jaime has a great deal of knowledge to share. A big bonus for us. :2tup:

cold weather riding
 

does anyone notice a significant decrease in power when riding in coild windy conditions?/ On New Years Day i was riding home from work it had to be at least 20 degrees ..i noticed my engine seemed to be struggling to hold 55 mph its an 07 with very recent oil change ...I let it warm up about 10 mins before i took off i noticed ...the speed kept decreasing on the freeway till i decided to get off and take streets.. i was wondering do ineed to turn that lil idling screw or what

Turning up the idle will not affect the engine speed except at idle. Just a wild a$$ guess here but here goes. Was it real humid weather ?? High humidity and those temps might have caused carb icing.

Hey cleansmoke I just got back from a weekend riding a 200cc 3 wheeler through deep snow -5 C It would not idle without some choke and ran best at 1/2 choke. Try some choke next time maybe 1/8 .

I agree that Jaime is a great asset to the site, but his explanations of backfire and afterfire are incorrect. Just look it up.

The post about cold air density is right on.

Are backfire and afterfire different things? Also, which claim do you think is wrong? Just to know, I'm not angry. :)
In my experience recarbureting the GZ250, a lean mixture causes popping in the muffler, but sure that some gasoline must reach there. That happens when you give no throttle but fuel is still sucked in, for example, going down a hill using the engine brake. The thing is that fuel and fresh air would only need high temperatures to explode.
When the mixture is rich, there's a little or no fresh air remaining in the exhaust fumes (enough fuel to burn everything), so there's not enough O2 for the combustion to take place in the pipes/muffler.

Sorry, I can't explain this better, in English.

Anyway, there are many wrong thoughts about backfire, so maybe I missed something.

Regards.

+1 on the carb. icing.
Also, which direction was the wind blowing, relative to your direction of travel? A head wind (even a slight one) will have a pronounced effect to the GZ.

RE Choke: I think you will find that the carb. on the GZ doesn't have a "real" classic choke but an "enricher circuit" which has NO effect once the throttle is off idle more than a tiny bit.

Jaime,

Your english is fine and I'm really glad you are a part of this forum. You took over carb tuning where I gave up. Also, I wouldn't fare so well en espanol. That's why I don't hang out much on marauderos.org.

Backfire is an explosion that occurs in the reverse direction from the carb back into the air filter housing. It's completely different from afterfire in that it occurs in a very lean carb mixture, in my experience and research. This is the rarest type of "funny" explosion that people deal with.

Afterfire, as I said earlier, is caused by a rich fuel/air mixture and occurs in the muffler. It is also the most common hiccup commonly mistaken as "BACKFIRING". You were right when you said that there is always a trace amount of fuel vapor in the exhaust. The problem, however, in an afterfire situation, is that the amount of unburned fuel is more than trace. When the rich mixture allows enough fuel to enter the exhaust system, the ambient air, which is always in the muffler since it is not a closed system, combined with the heat of the muffler, causes a secondary explosion which may even result in flames coming out of the exhuast. This is called an afterfire.

Looking up the two words in google may give a better explanation than I did.

Sinceremente,
Jonathan

OK, now I see the difference. I thought that backfire and afterfire were the same, sorry.

Well, I've never heard about backfire, but I think it should also had something to do with a too tight intake valves clearance, maybe...

Now that you talk about it, I'm not really sure about which is the real cause for afterfire, as I've seen 2 opposite situations:

1. My GZ250 did some big exhaust popping when it was running too lean, and it didn't when the mixture was too rich.[/*:m:12tnw839]
2. I've seen motorbikes tuned too rich (visible heavy exhaust fumes) to give off flames, exploding with the ambient air just in the muffler exit (as it's supposed to have positive pressure in it (isn't it), the fuel vapor shouldn't explode right inside of the muffler; could ambient air get in at any time?).[/*:m:12tnw839]

So, considering those premises, is it possible that afterfire occurs with a too lean mixture and also with a TOO rich mixture? :??:

Well, exhaust systems aren't closed systems. There is always ambient flowing around air inside the muffler. For example, if you look at the bottom of the muffler, you can see little holes which allow trapped moisture to escape and which also let outside air in.

As far as what you were describing, slight popping and gurgling sounds aren't considered afterfire. And I have experienced then also when in a lean mixture.
Afterfire is the serious bang that everyone has heard at some point in their lives, but it comes out of the exhaust.

Like I said, it is mistakenly referred to as backfire.

I'm not a chemist or physics expert, so it's possible that afterfiring can occur in a lean mixture, I just don't see how it could happen. When there is too much air in cylinder, an engine doesn't experience a proper explosion. It would make sense to me that a lean mixture which carries over into a muffler would then encounter even more air, which would essentially kill the flame.

I may be wrong, but I'm pretty sure that's how it works.

choke
 

Hey Easy thanks for the correction I went on-line and read about cv carbs . The word " choke " is a legacy term as you pointed out the " enricher " circuit provides a richer mixture. I did some testing in late Oct and early Nov . In cold weather ( 40 F ) I applied a little " choke " when the top speed maxed @ 65 approx 6500 rpm and top went to 70 and 7000 rpm. It dropped back to 6500 rpm after opening " choke " again.

This is just an observation .

I have a tach .

Re: choke
 

Gotta give that a try.
I've always heard that the "enricher" was out of the picture at high load/rpm.
Since it doesn't restrict the input air flow like a real choke, I can imagine that it might still make the mixture a tiny bit richer without "choking" it.