No Acceleration Above 45mph or 1/2 Throttle

Hey guys!

I recently picked up my first bike and am becoming familiarized with the general mechanics of carburetors and motorcycles. I have a Clymer's arriving in the mail this week and also have a digital FSM.

1982 KZ 440 LTD "D" with 3,100 original miles completely stock that has been garaged so no rust. PO said that the carbs had been rebuilt.

The bike starts great, able to disengage the choke within 30 seconds, idles well and opening the throttle in first or second produces fairly good pull. Once she gets up to around 40 or 45 however, opening the throttle causes the acceleration to suddenly slow down for a bit jolting me forward, then just as quick I can feel the acceleration begin again. She reallllly doesn't want to run faster than 6 or 7k RPM and am unable to achieve 65mph going downhill in 6th for a quarter mile! She accelerates up to 50mph at about the same rate as a honda accord which doesn't feel right, even for a 440. I feel like I have to shift at a lower RPM than she really needs, but my RPMS get stuck right around 6000 with WOT.

I have checked both plugs and they are tan, both pipes sizzle and vaporize.

A few things could cause this condition, and I have narrowed it to a few. If I am missing something please feel free to constructively criticize me

1) Damaged diaphragms - Worn or split diaphragms could cause too much air to enter / not enough fuel and it isn't noticed until the diaphragms are being moved fully up and down (at speed)

2) Clogged main/afterburn jet - The jet responsible for 1/2 or 3/4 to WOT is not allowing enough fuel to let the engine increase in RPM

3) Leaks - Air may be getting in to the system from somewhere other than the airbox. I did notice the rubber tube connecting the top of the engine to the airbox is split with age at the ends and may not be completely air tight, but it is a tight fit and feels snug.

If there are other possibilities besides these please let me know it would be very much appreciated and I look forward to spending a good amount of time on this girl and these forums :laugh:

Pictures can be had if needed...let me know

Cheers

Firdt of all, pctures are always welcome. More pictures please, just for us.

Secondly, It sounds like your having a top end problem. This could be many things. But first some questions. What kind of exhaust, air filter, carb, jets, are you running?? what do your plugs look like?? Any modifications to the bike??

The first rule with a used bike is that the PO always lies!

The 3 items you mention are relatively easy to check but first would suggest checking the timing if you have points and particularly the timing advancer. It may just need a lube.

Next try running with the fuel cap open. You may just have a blockage at the vent in the cap causing fuel starvation.

That hose from head to airbox could be the problem and should be eask to replace.

Taking the carbs apart is easy. Good call on the diaphragm. Worth checking. And if you get that far you might as well go the extra and spray carb cleaner throught the jets and all passagways. Make sure you have the diaphragms out when you do this .... and wear safety glasses

Hopefull your problem is something simple to fix.
Good luck

Your symptoms are exactly like the problem I had with my 79 kz400. Ended up being a torn diaphram.

sounds definitly like a carb problem if it was advancer related it would be show up earlier in the rpm range like say between 15-2500 rpm.

JR wrote:

The first rule with a used bike is that the PO always lies!

Absolutely - RULE #1 !!!


Use that clymer/fsm to perform every operation/check in the maintenence chapter.

As said, it deffinately sounds like a carb issue, not ignition, but as regular maintenence suggests... check timing/points/condensors anyways.

All the other advise hear is a good start, and will probly have you going along fine soon enough.

It would generally take a huge air leak to cause what your saying, but who knows... maybe the PO forgot to put the main jets back in, or thier way too small for some reason... meh!

Just remember, (try) to be patient with these old girls. :laugh: They need it like the rest of em'

Good Luck.

Becker wrote:

Firdt of all, pctures are always welcome. More pictures please, just for us.

Secondly, It sounds like your having a top end problem. This could be many things. But first some questions. What kind of exhaust, air filter, carb, jets, are you running?? what do your plugs look like?? Any modifications to the bike??

I am glad to oblige...








The exhaust, air filter, carb, and I would imagine that the jets too are factory original. The plugs are..

Left Plug


Right Plug


The right plug looks a little sooty, overall the cylinders don't appear to be running lean or overly rich, do they? This is where having pictures helps!

The bike has no modifications.

Thanks for your response Becker! Hopefully this info proves useful to us.

JR wrote:

The first rule with a used bike is that the PO always lies!

The 3 items you mention are relatively easy to check but first would suggest checking the timing if you have points and particularly the timing advancer. It may just need a lube.

Next try running with the fuel cap open. You may just have a blockage at the vent in the cap causing fuel starvation.

That hose from head to airbox could be the problem and should be eask to replace.

Taking the carbs apart is easy. Good call on the diaphragm. Worth checking. And if you get that far you might as well go the extra and spray carb cleaner throught the jets and all passagways. Make sure you have the diaphragms out when you do this .... and wear safety glasses

Hopefull your problem is something simple to fix.
Good luck

Good suggestions JR! I don't have the Clymer's yet but will look into checking the timing. Just not sure how to do it yet. I will try running it with the fuel cap open, although gas dribbles out of the overflow tubes when I open the drain screws with the tank closed and the petcock set to PRI. I am meaning to replace the spark plugs and so while I am at Kraegan I will look and see if there is a hose. I will also look for a stock replacement hose from one of the diagrams on kz400.com

Taking the carbs apart implies removing them from the engine and the bike, and working with them on a bench right? I feel like the rubber mounts or gaskets on the engine are sealed now, but don't look like they could hold up to unmounting and remounting. Especially with my big doofus hands doing it for the first time. I have heard of k1enterprises and would imagine they would sell replacement rubber in a carb rebuild kit?

Thanks

Link14 wrote:

Your symptoms are exactly like the problem I had with my 79 kz400. Ended up being a torn diaphram.

That would be ideal. After removing the gas tank inspection of the diaphragms is possible without removing the carbs from the engine correct?

timebomb33 wrote:

sounds definitly like a carb problem if it was advancer related it would be show up earlier in the rpm range like say between 15-2500 rpm.

That is good to know, thanks!

TeK9iNe wrote:

JR wrote:

The first rule with a used bike is that the PO always lies!

Absolutely - RULE #1 !!!


Use that clymer/fsm to perform every operation/check in the maintenence chapter.

As said, it deffinately sounds like a carb issue, not ignition, but as regular maintenence suggests... check timing/points/condensors anyways.

All the other advise hear is a good start, and will probly have you going along fine soon enough.

It would generally take a huge air leak to cause what your saying, but who knows... maybe the PO forgot to put the main jets back in, or thier way too small for some reason... meh!

Just remember, (try) to be patient with these old girls. :laugh: They need it like the rest of em'

Good Luck.

Tech9ine thanks for the heads up about the PO's! I wanted him to ride the bike home behind me but he insisted on his pickup. I guess maybe he knew it wouldn't keep up with grandma on the freeway haha. Then again maybe he didn't. Either way I have a great excuse to spend time in the AC'd garage where my house isn't lol. I agree with being patient, but in third fourth or fifth the ONLY way to accelerate past 1/2 throttle is to shift up...but I want to hear her scream a little bit first! Not shift her at 5k RPM. Too bad that's what I have to deal with, but sure as hell beats not moving at all.

I have a new rear tire coming in the mail, along with a static balancer and some tire irons. The rear I have now was made in 2001 if what I am reading is correct...and the slight cracking around 3/4 of the circumference made me order the new tire right away.

So, before I can start commuting her 180 miles a week on the highway I will inspect / clean / rebuild the carbs and diaphragms as well as replace the rear tire. The trip odometer doesn't work correctly, looks like the assembly was heated with a magnifying glass or something...doesn't look like fire damage. So after that, she will be able to cruise at 75mph, right? I don't care how long it takes to get going, but I need to have that HUGE top speed haha

Today I got my M1, hurray!

Thanks for all of your responses I feel much more confident about owning and maintaining my KZ for a long time to come

Cheers

Plugs look very rich but hard to tell from a picture.

When I had slits in the diaphragms, I had a nasty throttle hesitation coming off idle because the slides didn't lift when they should. The good news is I have seem new diaphragm sets on ebay for this bike if that's the problem.

I would check the main and pilot jets and make sure some dumbo didn't sttick in some ridiculous size. Also check the needle positions in case PO screwed that up.

Yes those plugs look very rich like bountyhunter said. Your problem may be to much gas !

Check this out
www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

Very nice bike

Carb Cleaning 101

By M. Shively

The elements of internal combustion engines are: correct fuel/air ratio, spark at right time, and adequate cylinder compression.

There are many passageways and openings to check and clean. All are important in function and when obstructed or not working properly, have subtle to radical effects on engine performance. Vacuum leaks and carburetor synchronization also effect performance and should be inspected and adjusted following the below procedures.


Warning: Remove all rubber parts before you begin. These parts usually include vacuum diaphragms, needle valves, o'rings, hoses, and other parts. Spray cleaners will damage these parts. Do not disassemble individual carbs from the carb bracket.

Air & Fuel Passageways: Trace and learn individual fuel and air circuits from beginning to end. Machines can only drill straight through the cast passageways. To change direction, another angled passageway must be drilled. The union is plugged with a brass or bronze bead. Inspect and clean each passageway with spray cleaner, brushes/pipe cleaners/etc, and compressed air. Remove any discoloration and debris. Look for spray cleaner to exit from one or more passageways.

Jet Cleaning: Inspect jets by holding to light and look through them. You should see an unobstructed round hole. Clean the jets with one or more of the following: jet cleaning wires, soak solutions, carb spray cleaners and compressed air. Re-inspect jets after cleaning and install when clear of obstructions. Some main jets have paper-like gaskets. Most have metal spacers between the jet and the emulsion tube. Some screw directly into a brass emulsion tube which is machined for a 7mm wrench at its float chamber exposed base.

Inlet Fuel Valve: Inspect the needle valve & spring. Press down the tiny metal rod that protrudes from the butt or float end of the needle valve. The spring should move freely and return the rod to its location. Check the needle valve's seat area for a groove or other wear. It should appear highly polished. Some needle valve seats are rubber and wear may not be visible. Inspect the needle valve jet seat. You can clean the jet seat with Q-tips and semi-chrome polish if necessary.

Carb Body Castings: Blow air through the atmospheric vent holes located on the dome of each float bowl chamber. Air should exit via hoses or brass nipples. Inspect the emulsion tubes and passageways (cast towers that jets thread into) for discoloration and debris. Clean interior emulsion towers with a soft bristle gun cleaning brush. Clean each Venturi (main carb bore).


Needle Jets & Jet Needles: Clean the needle jets, jet needles, and passageway or tower that needle jet screws into. Clean the emulsion tube (pipe between needle jet and main jet) (Main Jet may screw into emulsion tube). Jet needles are part of the throttle slides. See below…

Throttle Slides: There are several types of throttle slides: Mechanical linkage, vacuum, diaphragm, and cable. Disassembling the jet needle from the slide is not always required for cleaning. If you have vacuum piston type throttle slides (large diameter solid metal slide), avoid cleaning the lubrication from sides and caps. If piston type check cap vents and passageways with air. Clean if necessary and re-lube. If you have rubber vacuum throttle diaphragms, inspect for dry-rot, defects, and tears by gently stretching rubber away from center. Do this until all areas around diaphragm have been inspected. Replace any defective part as described above. Clean carb body areas around diaphragm including air passageways and air jets. Diaphragms have a locator loop or tab fabricated into their sealing edge. Observe this locator upon reassembly. Avoid pinching the diaphragm when reinstalling caps.

Fuel Screws: Fuel screws have sharp tapered ends. Carefully turn one fuel screw in while counting the turns until it seats lightly. Warning: These screws are very easily damaged if over tightened into their seats. Record amount of "turns-in" and remove the fuel screw, spring, washer, and o'ring. The fuel screw is part of the enrichment (choke) circuit...clean passageways as described above. When carbs are assembled, spray low PSI compressed air into diaphragm air vents located at intake side of carbs. Throttle slides should rise, then fall when air is removed. Lightly lube external moving linkages. Reinstall carbs and follow through with carburetor synchronization.

Throttle Cables: Lubricate cables periodically. If cables are disconnected from carbs or removed for replacement, etc . . . remember cable routing and ensure proper reinstallation routing. Avoid bread-tying, sharp bends, and pinching cables. Adjust cables so throttle grip has about 5mm of play or throttle slides or butterfly valves may not open completely (full throttle)(wide full open).

Float Bowls: Inspect float bowls for sediment, gum or varnish, crystallization, and defects. Clean all pipes, tubes, passageways, and embedded jets with cleaners and compressed air. Remove and clean the drain screw and area. Inspect bowl gasket and replace if necessary. Clean and inspect overflow pipes and tubes, look for vertical cracks.

Floats: There are several types of float materials: plastic, brass, black composite, tin, and others. Handle floats carefully. Avoid bending, twisting, denting, or other means of mishandling. Most floats are adjustable by bending a small metal tab near the float axle end. Do not change the float adjuster tab unless tuning fuel service levels. Clean metal floats by soaking or by spraying cleaner and wiping clean. Other material type floats may require replacement if cleaning is necessary. Inspect the needle valve (float valve) and seat. Check needle valve's spring loaded pin. It should depress and return smoothly and without resistance. Check the needle valve's tip for a worn groove. Replace needle valve and seat if either symptom exists. These parts wear together and must be replaced as a set.

Synchronization: This is a fine adjustment performed usually and preferably with the carbs installed and the engine running. The unusual part is performed with gauged wire with the carbs on the work bench. Carburetor synchronizing balances Venturi vacuum at the exhaust side of each carburetor, resulting with smooth idling and optimized performance at all throttle openings. Synchronization is checked using a set of gauges which are either air vacuum type or liquid mercury type. The gauges are connected to vacuum ports on the intake manifolds via nipple tubes or if sealed with screws, sync gauge adapters will be needed. With the engine running at temperature, and with a fan or means of forced convection aimed onto the engine, the carbs fuel screws and idle are adjusted, then the synchronization is adjusted via adjustment screws on the carbs. A reserve fuel tank is recommended for convenience of accessing carbs during this procedure. See gauge instructions and repair manuals for detailed use of synchronization gauges.

Notes: While carbs are apart, record the jet sizes. Look for a very small number imprinted on the body of the jets. Verify that numbers are the same for all jets on models with in-line cylinders. A few transverse-4 models and V-engines, the inner and outer carbs use some different size jets and it's important to not mix them up. If you have dial or veneer calipers, measure and record float heights. Perform measurements with floats just touching needle valves, though not depressing the needle valve rods. Replace fuel and vacuum hoses. Be sure to use fuel rated hose for fuel. Install or replace in-line fuel filters. It's a good time to remove and clean interior petcock fuel filters. Inspect carb manifolds for dry-rotting, inspect all clamps and air ducts. Inspect, clean, lube, and/or replace air filter(s).

hey is your throttle cable opening the butterfly enough, could be a misadjusted cable. check and make sure when you twist it full, the throttle lever on the carb is opening as far as it can go.

could have been mentioned above, but i didnt read em. im drunk. Although this would be the first thing i would check out if it were my bike. :dry:

-luke :huh:

Thanks for the advice everyone! Very much appreciated!

I removed the carbs from the engine and am now in the process of blowing out the passageways with carb cleaner. When I removed the top end cover and lifted it off, the diaphragm was stuck to the cover and so the diaphragm, piston, and needle assembly lifted out all at once. Unfortunately, before I could free my other hand to secure the assembly it dropped four feet straight to the concrete, landing needle first and bending it a good 30 degrees from straight. Doh! I tried to straighten it, got the tip to be where it was, but there is still a slight bend. That is what I get! I'm assuming z1 enterprises will have a replacement needle, but haven't ordered it yet as I am not sure if I need anything else.

I checked the jet sizes, and the only two I could find were the main primary and main secondary jets. Comparing to the FSM, the main primary jet should be 62, but mine is numbered 65? Not sure if the difference would cause but just thinking about it, bigger hole means more gas which could cause the rich plugs? The primary main jet was also fairly clogged up with debris, was probably about 50% smaller in diameter than it is now when it is nice and clean. The main secondary jet is numbered 88, which matches the FSM.

From what I could tell when I disassembled, the throttle cable was installed correctly. It was kindof a bitch to disconnect the throttle cable from the pulley, although after I figured out the angle for my fingers to reach around the bottom of the pulley it came right off. Now with the carbs removed, the butterfly valves appear to open fully but I will verify when I reinstall the cable.

So, as of now, the carbs are removed and I am going through the FSM in the maintenance section cleaning out everything but focused on the primary main and primary secondary air jets and passageways. I did get some gunk out of an air jet when I sprayed carb cleaner backwards up through the bottom end. In general, it is pretty clean in the carbs except for small deposits in the bottom of the float bowl which I think contributed to gunking the main jet and main air jet.

I am wondering what is/was the bigger problem..."Rust dust" in the bottom of the float bowls which partially obstructed the primary main jet as well as the primary secondary air jet...or the incorrectly sized 65 instead of 62 size primary main jet?


The PO put this red sticky goopy shit all over the old float bowl o rings instead of replacing them. I should just junk the old o ring, clean the goopy shit, and wait for the replacement o rings to come in right? I don't need to apply that stuff if the o ring is new, right? Or is it some sort of "wet gasket" that needs to be added in addition to o rings?

Thanks for ALL of your input and responses guys...I am getting close to really making this girl shine (as long as I don't keep dropping vacuum piston assemblies on the floor! lol) I can feel it!