February 21st, 2019, 01:58 AM | #1 |
ninjette.org member
Name: Garry
Location: Bungendore Australia
Join Date: Jan 2019 Motorcycle(s): GPX250 1989 model and 1990 model Posts: 98
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Idle problem improvement
After cleaning the carbs and setting everything up to the book my 89 GPX250 still would not idle satisfactorily when hot. When cold OK but when the engine was fully warmed up it would remain at 4000rpm after stopping for 15 seconds or so and then drop back to around 1300rpm at which point the bike would stall if I tried to increase throttle to take off again. Adjusting the idle with the thumbscrew only served to make the problem worse as small adjustments caused it to either rev too high or stall. These seem to be sysmtoms that many people with these bikes on this site and other similar sites seem to experience. Fortunately I seem to have managed to improve this problem although not to have eliminated it. My air screws are now at 4.5 turns out each and I did discover several slightly loose screws holding the caps on the diaphragm on the LHS carb. The bike will still hang up slightly on stopping but returns within a few seconds to a steady 1300RPM idle. It does not stall now when idling but some care is required when taking off again as it requires a gentle touch getting the revs above about 2000 before dialing in the throttle. As before the idle adjustment thumbscrew is pretty useless and I am wondering if this ‘fix’ has as much to do with cooler weather as much as anything else. Only real difference is the air screws out fron 2.5 to 4.4 turns and some tightening of a couple of loose diaphragm cover screws. What do others think?
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February 21st, 2019, 06:55 AM | #2 |
Guy Who Enjoys Riding
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If your carbs are similar to later ones, you don't have air screws. The idle mixture adjusting screws make the mixture richer if you turn them counterclockwise. Needing to have them 4.5 turns out would indicate the idle circuits are still not fully clean.
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February 21st, 2019, 08:06 AM | #3 |
Rev Limiter
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As TJ noted - the carbs.
Or maybe a vacuum leak...and the carbs... The tiny passages and jet openings can be stubborn to clean out, but the fact that changing the setting on the Idle Mixture screws (out is richer) doesn't change the idle significantly suggests the passages may be blocked. Sometimes the o-rings break and get lodged, which restricts the fuel flow. The hanging suggest a lean mixture or air leak. |
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February 21st, 2019, 07:28 PM | #4 |
ninjette.org member
Name: Garry
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The interesting thing to me is that there seem to be an awful lot of these bikes that suffer from this particularly as they get older. No-one really seems to ever completely solve the problem and it seems that people either learn to work around it or change settings as I have done to partly mask the problem. People clean carbs and set valves and replace rubbers, jets and inlet rubbers but still the problem persists. People say you can’t clean some of the fuel passages because they are hidden but that is not correct. Every hole was drilled from either end or both ends and a piece of wire will fit in any passage so I really don’t believe everyone is running around with dirty carbs. There must be something underlying that everyone is missing.
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February 22nd, 2019, 02:47 AM | #5 | |
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"clean carbs" has different meanings depending on who's talking. Do a search for "ducatiman clean carbs" for real meaning of cleaning carbs:
1. completely disassemble carbs down to last component, o-ring, spring 2. soak in caustic radioactive solvents in ultrasonic cleaner 3. ream all holes with matching size copper/nylon wire 4. floss hidden secret fuel passage with expando wire 5. soda-blast all fuel-circuits @ 10,000psi With the removal of chlorinated compounds, "carb" cleaners nowadays are as effective as pee. I used to clean my sprockets-guard with them back in old days and chucks of grease and oil would slide off leaving clean parts. Stuff you get now drips off clear and grease and oil stay right where they are. If anyone thinks carbs are clean after spray this stuff, they really do not have clean carbs and their problem symptoms will persist until real cleaning steps are taken (see above & below). Quote:
Take apart emulsion tube into constituent parts: main jet, holder, needle jet collar. Note how needle-jet collar is oriented so you can re-assemble later same way. Unscrew pilot jet being careful to not lose spring, washer and O-ring. Might as well replace O-ring, float-bowl seals and float-valves. Then use soft copper wire of various diameters to poke through all tiny little orifices in all parts. Some people use guitar string to floss out secret passages in carburetor body. Blow compressed air through all circuits and verify you've got air coming out other end. Here's good site for working on these carbs: http://www.vulcangadgets.com/files/keihin_carb.html These real cleaning steps restores carbs back to factory-fresh condition and bike runs exactly as it did when rolling off dealer floor with zero miles. If bike doesn't run like that, then carbs are not factory-fresh clean. Last futzed with by DannoXYZ; March 8th, 2019 at 10:47 AM. |
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February 22nd, 2019, 07:51 AM | #6 |
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b.. b.. but i keep reading on the internet "carbs are easy!"
All according to how far you want to go.....a useless "toothbrush" or "spray" clean? Right on up to full service/refurb/restoration, which takes pro equipment and great effort. Obviously, also based on starting condition. Replacing broken, missing parts, repairing inherited "mistakes". Never know what you'll find inside....precisely why carbs are NOT "easy." Yes, you can quote me on that.
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February 22nd, 2019, 03:05 PM | #7 |
ninjette.org member
Name: Garry
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Many thanks to everyone who replied to this and posted the pictures. I can see now that these are not simple carbs with only a few easy to access fuel passages as found on most bikes I have worked on but are complex pieces of equipment with a network of passages which are not in some cases obvious unless you know what you are doing. Using the advice and pictures you all have provided I will pull the carbs apart once more and attempt to clean those passages inside I was not even aware existed.
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February 22nd, 2019, 03:46 PM | #8 |
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Ducatiman specializes in professionally restoring carbs if you decide you don't want to do it yourself. I've always done my own work, but plan to send him my 250 carbs for restoration shortly.
Last futzed with by Triple Jim; February 22nd, 2019 at 05:23 PM. |
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February 22nd, 2019, 04:31 PM | #9 |
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If still available in your area, find carb-cleaner spray with carbon-tetrachloride or trichloroethane . Stuff really cuts grease and dissolves dried gas-varnish. Solvents with only non-polar compounds don't work nearly as well.
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February 22nd, 2019, 04:52 PM | #10 |
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^ @Triple Jim I am honored.
I'd like to clarify...referencing Danno's pics...notice some of the invisible, internal passageways taking abrupt, angled turns? This is where the machines are so extremely effective... while safely leaving surface structure unaffected...inside and out. Impressive brass restoration too. Provided jets have not been previously damaged or mauled, eliminating the cost of new. Yes, pic is legit before/after...not "faked".
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February 22nd, 2019, 06:01 PM | #11 |
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@59096 1989 GPX250 in your profile, if thats the carbset you are working on, WOW 30 years old...... at that age...its imperative to renew ALL the seals while apart...the tiny pilot screw orings, bowl orings, the actual float valves, and both *rail and *vent orings.
*these require "splitting" the rack to accomplish and may have never been done.
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February 22nd, 2019, 07:17 PM | #12 |
ninjette.org member
Name: Garry
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It’s actually a 1987 Gordon made for the Japanese home market. It was imported into and registered in Australia ten years later in 1997 and for some reason they called it an ‘89 model. I bought it for nearly nothing because the owner thought it had a bad bottom end - turned out to be nothing more than the usual clutch rattle that seems to effect these bikes. It is a lovely little bike and although I have only done around 800km on it has become the firm favourite. Wish I had bought one 30 years ago! It has 23,000km on the clock and is mechanically very good. The carbs are an annoyance but if that is all that annoys me I can live with it as overall performance is excellent. This is a great site and I thank everyone for their input and advice.
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February 23rd, 2019, 08:14 AM | #13 |
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an oldie, that vintage likely to employ the older 32mm, metal slide carbs
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February 23rd, 2019, 02:35 PM | #14 |
ninjette.org member
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Yes exactly. These are the 32mm carbs and apart from the idle issue seem to be in excellent overall condition. Next project is to solder some extensions onto the mixture screws to extend them down under the float bowls for easier adjustment. Carb kits, including all washers, gaskets and O rings have been ordered. Have also managed to acquire an identical second complete of carbs from eBay for a very reasonable price which seem to be in excellent condition. Parts for the GPZ250 are very cheap in Australia as they are viewed here as simply an old rather than useful bike. They are a little bit too new to be considered a classic by riders of my vintage (68 years old) and don’t have all the bells and whistles that the younger riders seem to need these days.
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March 5th, 2019, 11:26 PM | #15 |
ninjette.org member
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Thanks to all those who posted on this. Carbs were cleaned ultrasonically and all passages and jets were blown through with compressed air before reassembly. The idle problem has now completely disappeared - the engine now reliably idles at 1500rpm with no hang up or variation. Very happy with this outcome. Two minor issues still remain which is a slight flat spot at around 4500rpm and the engine performance at the top end is slightly improved if the throttle is backed of slightly from full throttle. There are no holes or tears in the diaphragms but they could be suffering from age related stretching perhaps? Is that feasible?
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March 6th, 2019, 07:43 PM | #16 |
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Let's see some photos of this bike!!
Flat-spot in mid-range is common on carbureted carbs due to helmholz-resonance effects. Air-pressure pulses move back & forth through carb, head, exhaust and frequency is determined by RPM, cam-specs, physical dimensions of carbs, intake-runners, exhaust pipe diameters & length, etc. Final effect is that in this RPM-range, you have a reversal of flow. This causes a triple-fueling effect where petrol is added to piece of air on its way in, then more petrol is added to it on way out, then yet again when it gets sucked in final time. Going to smaller carb increases air-velocity, changes resonance frequencies and reduces this triple-fueling effect. |
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March 7th, 2019, 06:24 AM | #17 |
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March 7th, 2019, 08:07 AM | #18 | |
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Quote:
Back to specific topic.... @59096 whats your intake/exhaust config?
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March 7th, 2019, 11:14 PM | #19 |
ninjette.org member
Name: Garry
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Everything is completely stock. Stock air filter, stock exhaust, stock carbs. Stock the lot!
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March 8th, 2019, 07:29 AM | #20 |
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You can still get real carb cleaner in Florida. The kind with methylene chloride.
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March 8th, 2019, 10:51 AM | #21 |
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March 8th, 2019, 01:24 PM | #22 |
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@59096 perhaps some more tuning in need. Verify valve clearances, synch with a reliable, precise manometer and finish with properly setting the pilot screws, engine hot, each side for highest RPM.
I don't believe it left the factory with, nor would I give up on solving your reported 4500RPM and full throttle anomalies until the above tasks have been completed. When carbs were apart, you verified stock pilot/main jet sizes/correct needles? No jets "hogged out" or otherwise incorrect size/type? I do diaphragm replace on metal slides (much easier than plastic 30mm slides) I believe same diaphragm as EX500, which I keep in stock, though Auz is a long ways away, unfortunately.
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March 8th, 2019, 02:14 PM | #23 |
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I forgot to mention one other tuning variable...not sure if you checked the actual working fuel levels in each carb....aka "wet testing" using clear tubes...aka "clear tube method".
Though my pic taken off the bike...this can be done on the bike**, easily substituting a gravity fed fuel source to assure both unimpeded fuel levels and integrity of the float valves ability to seal properly. ** engine NOT running, not relying on vacuum petcock, hence needing the gravity fed source
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March 8th, 2019, 02:44 PM | #24 |
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I will check on th cost per case. Shipping may be a problem because of contents.
I will check it out. |
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March 10th, 2019, 07:39 AM | #25 | |
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Quote:
apologies to 59096 for threadjack Besides the fact that @DannoXYZ was being facetious.....shipping of hazardous chemicals to ANY destination must be marked as such, different rates and regulations apply. Non-compliance may lead to legal ramifications from your chosen carrier. Shipping may also create a further problem, Danno being in Ca. Many auto clean products these days are marked "not to be sold in Ca. " , heck even Factory Pro will not sell jets kits there due to Ca law. Technically, the shipping of banned products into Ca would no doubt be breaking some Ca emissions type law. Otherwise, hey, have at it.
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March 10th, 2019, 09:21 AM | #26 |
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If you work with that stuff make sure you use an organic solvent mask and gloves that are resistant to it, and don't splash any on your skin. I can give you specific details of what it did to my blood counts if needed.
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March 10th, 2019, 02:48 PM | #27 |
ninjette.org member
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Methylene Chloride as well as the all other Halocarbons have been deemed very bad for your health. They all are suspected of causing cancers. Everyone on the world has varying levels of perflurooctanoic PFOA in their blood. One of about million chemicals that are suspected of causing cancers.
OK what is PFOA? It is a chemical in Teflon suspected of causing cancers. Hell it is even th snow in Antarctica. When I was in my teens a company sold Parker Throat Discs. They numbed you sore throat. The active ingredient was chloroform. Drink too much water all at once and you will die. Everything in moderation. |
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March 10th, 2019, 04:12 PM | #28 | |
Guy Who Enjoys Riding
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Quote:
I'm not trying to be an alarmist, but that particular solvent is something to keep out of your body. |
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March 10th, 2019, 06:46 PM | #29 |
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Weird that they used this stuff in fire-extinguishers and for dry-cleaning. They actually banned stoddard's solvent for this stuff in dry-cleaning. Authorities and regulators claimed they didn't know its side-effects or how it contaminated ground-water (well, politicians aren't exactlynthe brightest lot).
Better get out of burning buildings fast! When fire department gets there and starts spraying this stuff around, the heat will convert it to phosgene gases and kill you real quick. At least that'll be less painful death than getting burned alive. |
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March 11th, 2019, 06:32 AM | #30 | |
Guy Who Enjoys Riding
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Quote:
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March 14th, 2019, 10:18 PM | #31 |
ninjette.org member
Name: Garry
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An update,
While pulling the carbs for the umptheenth time I noticed some writing on the end of the rubber boot that connects the left side cylinder head to the carb. It said “Head”. I checked the boot on the right side and it said “Carb”. Hmm! Why are they different? Well they seem to be tapered with a bigger hole at the carb end tapering to a smaller hole at the head end. I pulled them both and re-installed both of them with the “Head” end towards the cylinder head and the “Carb” end pointed toward the carbs. Seems that all my mid range and top end problems have now disappeared! Every day I seem to learn something new? |
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March 15th, 2019, 04:52 AM | #32 |
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sweet!
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March 15th, 2019, 06:30 AM | #33 |
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Free repairs, my favorite!
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March 15th, 2019, 06:57 AM | #34 |
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As we are diagnosing via keyboard, EVERYONE must remember the cleanest carbs in the world WILL NOT mask other parts, tuning, setup errors or deficiencies...glad you nailed it!
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March 15th, 2019, 09:46 AM | #35 |
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I'm glad you figured out what was wrong!
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