Still get pop pop pop upon deceleration???

[fabme123]

OK I rebuilt and cleaned the carb. I checked all connection points between the air filter box, rubber connecters to the carb in take to carb output connecting to the engine intake leading to the exhaust output.

I removed the old exhaust and put on mack duels from Jackes with new crush gaskets and resized split rings. The split rings are cut to proper size. New plugs properly gapped and a new air filter. It still goes pop pop pop on deceleration.

Where do I look next? I know the carb is tuned properly via the colortune setting. I dont think the valves are bent because I never had the pop pop pop before the exhaust were replaced or the carb was rebuilt. All I can think of is that air is entering the system from some place and I dont know where.

All advice is welcomed...

Thanks

[GearJammer]

Someone will please correct me on this if I'm wrong, but with both the Mac's & the Jardine aftermarket pipes, is re-jetting unnecessary with all year 250 Rebels ? (I realize no re-jet is necessary with the '85, '86 & '87 250's after pipe alterations).

fabme, There's a possibility that the header pipe to exhaust port connection isn't yet fully sealed. You definitely want to tighten those exhaust flange stud nuts c-a-r-e-f-u-l-l-y, only snugging 'em up hand tight a bit at a time, checking again while the motor is cold before each ride until they settle in.

One way to check for air leaks in that area is immediately after fire-up, you can, again, c-a-r-e-f-u-l-ly cup your hands around the area of each pipe WITHOUT touching the pipes or fins & getting an unexpected & undesired rush from extreme heat in that area. :shock:

If there's any leaks, you should be able to feel a slight puff of air buffetting against your hands.

[cTc]

I put MAC pipes on the wifes 2001 and I also shimmed the needle in the carb to accomodate them. Under decel they would spit back, pop and sometimes backfire. Its normal for aftermarket pipes to make such noises.

[fabme123]

OK CTC please educate me. You shimmed the needle down a bit and your mac duels also went pop a pop pop a pop pop. Please explain to me how you shimmed the needle, how you knew to shim the needle, how you checked to make sure you did it correctly, how you checked the carb settings after you adjustment and the final results: IE how she sounds now?

All this info would really be worth alot to me.

Thanks

[cTc]

Here is a thread about shimming the needle.

http://www.hondarebelforum.com/phpBB2/viewtopic.php?t=116

Let me know if that helps.

[GearJammer]

fabme.......Saw that your Reb is a 450 & not a 250.

With the lean condition you described, I'd start with those air mixture screws. Being turned out as much as they are is allowing considerably more air in & that can lead to disaster.

Colortune might say one thing, but the plug reads would be speaking louder to me at this point. "Meltdown Is Not Our Friend"......

[fabme123]

The new plug tips thats the part that bends down when being gapped after 20 mins of use is a greyish silverish ash looking color.

PS I thought that when you back out the air mixture screws, your letting in more fuel.

Should I look at the last shim idea then since its a 450cc?

[GearJammer]

An ideal plug read would be light tan - light grey. Not sure if the silverish color you're seeing is grey turning to silver or grey leaning towards white. White is the dangerous one. Running too long in the white zone can toast the top-end. Even tho' grey is absolutely acceptable, I'd feel more comfortable aiming towards light tan.

I haven't done any dialing in of these 450 carbs other than messing with the idle setting screw. I may be wrong, but every air mixture screw I've encountered meters the flow of air into the carb. By turning the air mixture screw in, the flow of air is lessened/restricted, turning the air mixture screw out allows more air flow to enter the carb. (IMPORTANT NOTE: If I'm wrong on this in regards to the Rebel air mixture screws, someone PLEASE correct me, as I don't want to unknowingly mislead "fabme" towards potential disaster).

Wouldn't see any harm in using the shims on the carbs since it would act like "clips" on other carb needles, which allows more fuel supply into the mixture & it sounds like this is what you're trying to achieve to avoid a too lean or overheating condition.

[wheezeburnt]

Gearjammer:
You've touched on one of the more confusing aspects of modern carburetors. You are right, in the case of an idle AIR screw, turning them IN causes richer running. Unfortunately, the idle mixture screw on the Keihin carb is not an idle air mixture scrrew, but an idle fuel mixture screw.

The idle mixture screws can be located UPSTREAM of the carb, in which case they are IDLE AIR ADJUSTMENT screws, and if you turn them out, you allow more air in, giving a more lean condition. Turn them in, and things get rich.

Or, they can be located DOWNSTREAM of the carb (as is the case on most Keihin CV carbs as on the rebel), in which case they are IDLE FUEL ADJUSTING screws, and meter fuel flow. So, in that case, if you turn in the screw, you are restricting fuel flow, and giving a more lean condition. Turn them OUT, and you get a RICH condition (more fuel, less air)

Fabme: this is what you have.

BUT: if you turn the idle mixture screw out too far, you can reach the point where air is being drawn in through the threads of the screw, and end up causing LEAN conditions, again...

I'm with gearjammer: if you are convinced that there are no air leaks in the intake manifold, then try shimming the needles.

Brent

[GearJammer]

.....*whew*......Thanx for catching & clarifying the mixture screw adjustments in time, Brent! I'm used to the old British Amals.....as modern as a T. Rex :shock:

Along with the shims, would "fabme" be better off adjusting the idle fuel adjusting screws back in somewhere between where they are now & the baseline setting of 2 1/4 turns out ?

[fabme123]

BUT: if you turn the idle mixture screw out too far, you can reach the point where air is being drawn in through the threads of the screw, and end up causing LEAN conditions, again...

I'm with gearjammer: if you are convinced that there are no air leaks in the intake manifold, then try shimming the needles.

Brent

OK whats the best way to check for leaks? Ive asked several times but the chat always seems to lead somewhere else

Along with the shims, would "fabme" be better off adjusting the idle fuel adjusting screws back in somewhere between where they are now & the baseline setting of 2 1/4 turns out ?

How do you all set up your carbs' settings? And if I do shim, how do I go about finding the proper size shimes. I may think its the right size and find out Im wrong. How do the shops set carbs up? Man this is driving me nuts.

Thanks again for bearing with me so far

[ddouble]

I've used carb cleaner to check for leaks. Use the little red hose that comes with the can. With the bike running shoot a short blast at the suspected leak. If the idle changes you have found the culprit.

Dan

[fabme123]

I for got to mention what else happened yesterday that may shed some light onto the problem. After fitzing around with just one rubber connection yesterday from the carb to the vacume on the intake side of the engine, I noticed a bit better performance of the motor.

I also noticed at first that when you gave the bike a hard fast throttle, it would boggle down and sound like she was about to die/ stall. Let off the throttle and she would purr like a babby?

[wheezeburnt]

Testing for air leaks: yes, carbcleaner will work, but I'm very nervous about spraying it on anything rubber. In any case,the drill is this: get the bike running, then spray around the rubber intake manifolds on the 'upstream' side of the carbs (I like WD-40 for this purpose). Listen for a change in engine speed. Then do the same on the 'downstream' side (between carb and engine). Same drill.

RE: shimming: I think I'd leave the idle mixture screw where it is, then shim, and retest the colortune. The thing is, the idle mixture screw controls mixture at idle (and contributes moderately all the way to 1/2 throttle). The main jet needle controls mixture when you twist the throttle open. So, shim, then check your mixture with the colortune again.

Best source of shims is Radio Shack (or whatever they are called now) There are about 5 sizes of shims in a little bag for not much money. Honda/Keihin generally uses the second smallest size (#4?). ;you want something that will fit over the needle, but just right; not too snug,not real loose. (boy, THAT was helpful, wasn't it?)

And get ALL those vacuum lines nice and tight (replace if you need to; rubber lines are NOT expensive). There is NO way you can get the carbs tuned properly with air or vacuum leaks.

Amals? yikes. There's a nightmare, eh? Tighten up the manifold bolts too much, and you deform the barrels. And slides and barrels made of the same material, so they'll wear each other out. THEN you've got a tuning nightmare. Never much cared for the way the throttle cables just kinda sat in the top of the carbs, either.

I recall some old car carburetors that had both air and fuel mixture screws. Old datsuns, I think.

Hey, keep asking questions. No one here will mind, and among the bunch, someone will have your answer. Carb theory is a rather complex business,and there's no such thing as a typical carb. If you want to read more, get a copy of the Haynes Motorcycle Fuel Systems Techbook by John Robinson. Might be in a library near you (do they still have libraries?)

Brent

[fabme123]

You mention idle mixture screw. Im referring to the two air mixture screws on the duel carb 450 cc rebel. Sorry if I misled you on make/ model

Thank you

[GearJammer]

Brent, You're right on about the Amals....too tight to the manifold can cause distortion, slides & barrels of the same metal causing wear....but aside from that, the tuning is a relative breeze, especially with a single carb. Proper main jet, clip in right position, one air mixture screw, one throttle slide stop screw & it's easy to get in the ballpark & ballpark/tolerances on the old Brit stuff is very forgiving....thank God! LMAO!

"fabme", Not to add to the confusion, but something to keep on the back burner. You're concentrating on the carbs right now & that's cool. You actually may be closer than you think.

For the back burner: Fuel & electrical probs oftentimes mask themselves one for the other. You're dealing with obvious fuel system dial-ins right now & please keep on that track until you get it nailed down.

But you also mentioned "overheating & shut down". Please keep in mind that once you've gotten the fuel system sorted out, you may or may not have to deal with some ignition system issues. A malfunctioning CDI can cause a whole list of problems: Unexpected shut down, intermittent power loss, hard starting, no starting (no spark), and another one I recently learned about, no ignition timing advance function, meaning that after a certain rpm, the timing advance won't kick in the needed rpms & the performance will level off & run "flat" (running, but no increase in rpms)

One step at a time, you'll get there!

[wheezeburnt]

Fabme:
No misleading... I'm talking about the 450 twin carb model, as well. I have one in the garage (my wife's) and did a carb rebuild on it last winter. Not sure what the manual calls that little brass screw underneath the carb on the downstream side, but that is definitely the one I'm talking about. Screw it in, and it leans out the mixture.

GJ makes a good point. At the very least, make sure your plugs are fresh and properly gapped. If they're already carboned up, its hard to tune the carbs because you are getting a weak spark. Also, give the plug caps a turn clockwise on their wires to make sure you have a good contact with the plug wires. You can check for high voltage leakage on the caps/wires by running the bike in a dark room and misting them with a spray bottle of water. you'll see a mini-lightning storm if there's leakage. (DONT use wd-40 for THIS purpose.)

And also, even a very weak battery can cause poor idle, so make sure you have a good charge on that battery.

Brent

[fabme123]

OK its like 200 degrees here and I pulled off the carbs again. Im going to dismantle tonight and post pics. I also pulled one of the new plugs used for say about 1/2 hour of ridding and want your opinion of color even though the air mixtures are 4-5 turns out. Look lean as heck to me.

[fabme123]

OK carbs off and dismantled. Here are the pics, questions and the need for your feedback

The spark plugs. The one on the left is the new plug used only 1/2 hour. I recounted the turns the air mixture screws were actually backed out. It was actually 3 turns each side. The plug looks lean to me. The plug on the right was the old one.

http://i45.photobucket.com/albums/f98/whatyamacallit/101_0989.jpg


Now here is a picture of the right side butterfly. Notice the tan staining on the bottome. Both the left and right side carb butterfly exhibit this? What could it be a result of?

http://i45.photobucket.com/albums/f98/whatyamacallit/101_0978.jpg

Now upon dismanteling, I noticed a slick on the right side rubber mount from the air box to the carb: oil? fuel? oi and fuel? I also noticed two other probs with the right side carb. First there was a red chalk on the bottom of the float bowl. I noticed this when trying to remove the screw on the bottom of the float bowl. I guess the float bowl my have leaked in the passed and someone filled it. The screw wont come out

http://i45.photobucket.com/albums/f98/whatyamacallit/101_0973.jpg

Heres a closer pic, but a little blurry

http://i45.photobucket.com/albums/f98/whatyamacallit/101_0974.jpg

I also noticed that the vacuume piston was bent in on the side a bit maby causing my leak from earlier??? Then again it just may have come up from its mounting points when I took the cover off. Anyway heres their shape now

http://i45.photobucket.com/albums/f98/whatyamacallit/101_0968.jpg

Next Clymers tells me to make sure the slow air jets in the air horn are clear. To use compressed air if necessary. How do you verify that these holes are clear? I tried to blow compressed air through and it only comes back at me. Does this mean the holes are clogged?

http://i45.photobucket.com/albums/f98/whatyamacallit/101_0977.jpg

and again

http://i45.photobucket.com/albums/f98/whatyamacallit/101_0972.jpg

Finally Clymers says that when removong the air mixture screws there is supposed to be a spring, rubber gasket and a washer. NO washer either side L/R? I used a flashlight to look down the holes where the air mixture screws came out of and again NO washer.

OK all your feedback is needed. What is the best way to clean the carbs themselves. The jets are cyrstal clear. Its the internals of the carbs them selves Im worried about. The slow jet is #35 and the main jet #112

When looking at the air box today, I was looking for the entry point of the air into the air bow. Someone, mucosi I think, said that the air is filtered from the engine to the air box to the carbs to burn off by products of combustion. EPA stuff. The only hose I saw down there was the crankcase breather tube which I removed the plug from along time ago??? What am I not seeing? What is the actual cycling of air through the motorcycle system?

OK enough from me for now. Next, if this dont work will be the electrical system

Thanks

[GearJammer]

fabme........I'm not as familiar with the Keihins & hopefully Brent & others will weigh in on this (Phil, are you following this ? :wink: )

Are you using the same type plugs as the old ones were ? The old plug looks fine. It's hard to tell if the new plug is blurred. Is that just blurred or this that powdery build-up on the tang ? Usually, I like to see most of the "color" on the opposing electrodes (either side of the spark plug gap), but not as prominent all along the tang. I'm voting lean.

The tan staining by the butterflies could be by-products of re-circulated fumes, gas (dang EPA!)

The slick on the right side rubber mount from airbox to carb could be a combination of oil/fuel from gunked up cannister/seperator entering in thru the airbox (once again, thank you, EPA!)

The red "chalk" & the immovable screw in the float bowl. Is it possible that somone used friggin' Red Loctite to permanently install that screw ? Dried Red Loctite can look slightly chalkish once dried.

I'll have to bring the Honda Service Manual over here instead of guessing any further on the EPA routing, but I've also removed the plug from the crankcase breather hose, left it out & will continue to leave it out.

[fabme123]

Yea Jack comes back in the a m