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TOPIC: 1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE!

1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215584

  • MentalMike
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Ok, I just got this bike recently with only 4k on it and in super condition, but it has sat for at least the last five years. So in earnest I have begun to get her back in shape and ready for the road.

At first she would crank over, but never fired up. So...here's what I've done so far...

1. Completely disassembled , cleaned, soaked, and blew out with compressed air all carburettors. Then rebuilt with new rebuild kits to stock specs, and set air screws to two turns out.
2. Check for voltage to the coils and spark to all four plugs - all good.

Bike then fired up without much problem, with the choke on, but would start to die once I eased off on the choke. Once it warmed up a bit it ran better with less choke, but still would die if I let off the choke completely. I would have to keep the choke out some just to keep it idleing (rough) at 1200 RPM. I figured the air screws needed further adjustment.

Now she won't fire at all and just cranks. I thought it was flooded, but it's not. It starts with a shot of starting fluid, but then dies once the fluid is burnt off. I thought it wasn't getting fuel, but I checked this and the fuel seemed to flow just fine.

Now I'm perplexed as to my next step. I would think if she starts with the starting fluid, then all the electrics are working fine. The carb is clean, and there is spark at the plugs.

Anyone experience this problem and what was your solution?

Thanks for any help.

Mike
I swear to God, it's like I live in a trailer of common sense, and stare out the window at a tornado of stupidity.

1982 Kawasaki KZ1000J ELR
1984 Kawasaki ZX750A2 GPz
1978 Kawasaki KZ650 Custom
1986 Kawasaki ZX900A3 GPz
1985 Kawasaki ZX900A2 GPz (Project Bike)
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215608

Sounds like your pilot circuite is still plugged up.
1980 CSR 1000. New dyna Coils, Vacumn Less Petcock, Various Handle bars depending on the day, (Drag and Clubman.)
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215633

  • sully73
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go back to your first step, and clean. then..clean..then clean.
anything i have learned while working on these bikes, is that no matter how clean you think you have your carbs, theres still shit in there. more so if it sat for awhile. two years ago, i think i did my cb750 carbs 6 times before i finally got them clean.
81 kz1000 ltd
72 cb750 chop
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215650

  • Patton
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Hello, Mike, and Welcome to KZRider! We're glad you're here! :cheer:

As known, the enrichener circuit (choke) has its own separate independent circuit inside the carb which is designed to function with the throttle left alone in the completely closed position. It's surprising how many times folks are seen frantically twisting the throttle back and forth (or holding it cracked open a tad) when first engaged in cranking a cold engine -- just doesn't work that way, and isn't supposed to.

Regarding the pilot circuit, Here's some info about restoring it to as-new condition on a manual slide Mikuni carb with side located pilot air adjustment screw. (Should also be helpful when dealing with the similar carbs equipped with bottom located pilot mixture adjusting screw -- see note included later about the difference between the passages in these two different types of pilot circuits.)

Pilot Circuit Overview

Freshly filtered air goes into a small entrance hole on the airbox side of the carb. Sometimes there's an air jet, but oftentimes not. Thinking no air jet on carbs with side located pilot air screw -- just the simple entrance hole. Anyhow, air enters the small entrance hole and continues along a passageway until reaching the pointed tip of the pilot air adjusting screw which regulates amount of air allowed to continue thereafter on to the pilot jet.

Meanwhile the pilot jet has picked up raw fuel from the float bowl. The air reaches the end of the air passage at the pilot jet where the air joins the fuel creating an air/fuel mixture which mixture then travels from the top of the pilot jet on through the pilot passage and out the pilot outlet (a tiny orifice in bottom of carb bore), from where the mixture is sucked through the intake valve into the combustion chamber.

All this is accomplished while the throttle slides are positioned completely down with no additional mixture contributed from the needle jet. And the pilot circuit continues this function of providing fuel mixture until about 1/8th to 1/4th throttle opening position. As the throttle is opened, the slides are raised, which allows increasingly more mixture from the needle jet and lessening effect of mixture from the pilot circuit.

Now, toward achieving a perfect (as new) carb pilot circuit --- And there are undoubtedly other and perhaps better methods, maybe even far superior methods (the local dentist likely won't be too keen on the idea of loaning out his ultrasonic cleaner for this purpose -- probably wouldn't be big enough anyway), but here's how I do it, until learning a better way.


Pilot Air Passage

The pilot air passage throughout its entire length from entrance hole at airbox side of carb throat to the pilot jet should be clear and ultra-clean.



Pilot Passage

The pilot passage from top of pilot jet to and through the pilot outlet should be clear and ultra-clean.



Pilot Jet

The pilot jet central hole and lateral holes should be clear and ultra-clean. The pilot jet itself should be in pristine condition and the proper size. Remember, possible damage from previous cleaning efforts (with wire or otherwise) may be visually imperceptible. Holes appearing perfectly round and clean may be faulty enough to disallow the absolute precision needed to properly meter fuel intake from float bowl and infusion of air from the air passage. Because new pilot jets are relatively inexpensive, I prefer to replace them. Opinions may differ, but new pilot jets worked for me. And I have yet to see any visual defect in the old original pilot jets (even with some slight magnification).


Cleaning The Passages

With carb on the bench, remove float bowl, float and pilot jet. Wear protective goggles. Plug threaded area where pilot jet was removed so as to block access into float bowl (using finger is okay). If pilot air screw has been removed, block its hole with finger. Direct carb cleaner spray into air passage entrance and blast away until spray freely exits from pilot outlet.


Pilot Air Screw

Remove pilot air screw and examine pointed tip to assure it isn't damaged. Carb cleaner spray directed into the (1) pilot air screw hole has three places where it may exit, (2) Air passage entrance, (3) into float bowl through pilot jet location, (4) pilot outlet. Any two of these may be purposefully blocked so the spray flows between the other two. Spray every combination until assured all the passages are clear and clean as new.

Here's a diagram for reference (with side located pilot air screw).
(Note -- In carb with bottom located pilot mixture screw, the pilot circuit is different -- having metered air from a jet at the entrance hole, and part of the mixture from the pilot jet going to a bypass outlet orifice in bottom of carb throat and remaining part of the mixture from the pilot jet going out a second separate pilot outlet orifice in bottom of carb throat governed by the bottom located pilot mixture screw.)

In any event, all the pilot circuit passages (air passage, fuel passage, and mixture passage) should be returned to as-new condition.

Good Luck! :)

[click on image to enlarge]

Last Edit: 6 years 3 months ago by Patton.
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215665

  • MentalMike
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Wow, great stuff, thank you.

I'm going to pull the carbs again today and recheck and clean those pilot circuits. I know fuel is getting to the carbs and I know there's fuel in the bowls, so it has to be the problem.

I'll let you know how I make out and thanks again for the responses.
I swear to God, it's like I live in a trailer of common sense, and stare out the window at a tornado of stupidity.

1982 Kawasaki KZ1000J ELR
1984 Kawasaki ZX750A2 GPz
1978 Kawasaki KZ650 Custom
1986 Kawasaki ZX900A3 GPz
1985 Kawasaki ZX900A2 GPz (Project Bike)
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215746

  • MentalMike
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Ok, she still won't start.

I pulled the carbs today and went through each one. The float bowls were full of fuel, and the floats were still set to spec. I removed the pilot jets and the air screw and shot carb cleaner through these alternately back and forth while I took turns plugging the holes with my finger and made sure cleaner shot through all the passages and the outlet on the engine side. I did this with each carb.

I put carbs back on and once again checked for spark at the plugs - all good.

But still she doesn't fire up, just cranks.

I set the air screws back to two turns out.Is this enough or too much?

Any other suggestions? Thanks.
I swear to God, it's like I live in a trailer of common sense, and stare out the window at a tornado of stupidity.

1982 Kawasaki KZ1000J ELR
1984 Kawasaki ZX750A2 GPz
1978 Kawasaki KZ650 Custom
1986 Kawasaki ZX900A3 GPz
1985 Kawasaki ZX900A2 GPz (Project Bike)
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215765

  • Patton
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MentalMike wrote:
Ok, she still won't start.

I pulled the carbs today and went through each one. The float bowls were full of fuel, and the floats were still set to spec. I removed the pilot jets and the air screw and shot carb cleaner through these alternately back and forth while I took turns plugging the holes with my finger and made sure cleaner shot through all the passages and the outlet on the engine side. I did this with each carb.

I put carbs back on and once again checked for spark at the plugs - all good.

But still she doesn't fire up, just cranks.

I set the air screws back to two turns out.Is this enough or too much?

Any other suggestions? Thanks.


I set the air screws back to two turns out.Is this enough or too much? Guessing 1-3/8 or 1-1/2 would be better, but go by factory specs per FSM.

Question -- any results with the starter fluid?

Don't dispair! :cheer:
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215777

  • MentalMike
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Well as far as I could find, there are no factory specs for the air screw on the U.S. model, as it states it should be set and sealed at the factory and does not need adjustment. But to do the soak cleaning I drilled through the cap to get the air screw out. The spec for European models is 2 turns out and this is what I went by.

I still get the same result with the starting fluid, it fires and dies once it's burnt off.
I swear to God, it's like I live in a trailer of common sense, and stare out the window at a tornado of stupidity.

1982 Kawasaki KZ1000J ELR
1984 Kawasaki ZX750A2 GPz
1978 Kawasaki KZ650 Custom
1986 Kawasaki ZX900A3 GPz
1985 Kawasaki ZX900A2 GPz (Project Bike)
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215879

  • Patton
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MentalMike wrote:
Well as far as I could find, there are no factory specs for the air screw on the U.S. model, as it states it should be set and sealed at the factory and does not need adjustment. But to do the soak cleaning I drilled through the cap to get the air screw out. The spec for European models is 2 turns out and this is what I went by.

I still get the same result with the starting fluid, it fires and dies once it's burnt off.

If not already done, would do compression test
(hold throttle wide open during testing).
What are the psi figures?

Immediately after attempting to crank while
using choke, what is appearance of plugs?
Are they dry?
Are they wet, with gasoline odor?
Are these the same old plugs that were
in the bike after sitting for 5 years?

Included here for reference is the carb
parts diagram from Kawasaki.com which
shows these as constant vacuum style carbs.
Am presuming the choke plunger part# 16016
has been removed and cleaned and the choke
passages inside the carbs also cleaned.

Keep the faith! :)

[click image to enlarge view]

84gpz750carbCV.JPG
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215891

  • MentalMike
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Patton, thanks for the response.

The plugs are new and yes I did remove the choke plunger when I soaked and cleaned the innards.

I will do the compression test today and let you know how I make out.
I swear to God, it's like I live in a trailer of common sense, and stare out the window at a tornado of stupidity.

1982 Kawasaki KZ1000J ELR
1984 Kawasaki ZX750A2 GPz
1978 Kawasaki KZ650 Custom
1986 Kawasaki ZX900A3 GPz
1985 Kawasaki ZX900A2 GPz (Project Bike)
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215939

  • MentalMike
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Ok compression test on each cylinder was 150 psi, throttle open, choke out. Plugs were dry and clean. I also pulled exhaust baffles to see if any critters had made a nest in there - all clear.

I turned air screws back to 1 turn out, and started her with starting fluid. After a few attempts, I was able to keep her running with the choke 3/4 to a 1/2 out. I let her warm up holding the choke like this, but even after warm she would still die if I let the choke in. Any touch of the throttle and she would burp and want to die. Idle screw is only set a couple turns out.

Having made sure the pilot circut was completely clear on all carbs, I don't understand why I'm not getting fuel at low idle.

Any thoughts? Thanks.
I swear to God, it's like I live in a trailer of common sense, and stare out the window at a tornado of stupidity.

1982 Kawasaki KZ1000J ELR
1984 Kawasaki ZX750A2 GPz
1978 Kawasaki KZ650 Custom
1986 Kawasaki ZX900A3 GPz
1985 Kawasaki ZX900A2 GPz (Project Bike)
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215959

  • Makarth
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have you checked to see if you're manifolds are not cracked and/or leaking. Try cranking it spraying starting fluid outside the carb where the manifold is but keep an extinguisher handy in case it backfires.

Edit: if it runs while spraying starting fluid outside the manifold you got a leak.

1977 kz1000 - Megasquirt project @ 40% wiring, plenum, and exhaust<--(done!)
Last Edit: 6 years 3 months ago by Makarth.
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215970

  • RetroRiceRocketRider
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This may sound like a no-brainer, but sometimes the little things are forgotten by over thinking it and assuming that it's a more complicated/serious issue - are the rubber caps for the intake manifold fittings installed and in good shape, and is the petcock vacuum hose connected correctly and in good condition? :huh:
Covina, So Calif!
78 KZ650-B2 = IN A COMA
84 ZN700 LTD = SLEEPING
84 ZX750 GPz = SOLD
89 GSX1100F Katana = RIDING! :-)
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215979

  • Patton
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MentalMike wrote:
Ok compression test on each cylinder was 150 psi, throttle open, choke out. Plugs were dry and clean. I also pulled exhaust baffles to see if any critters had made a nest in there - all clear.

I turned air screws back to 1 turn out, and started her with starting fluid. After a few attempts, I was able to keep her running with the choke 3/4 to a 1/2 out. I let her warm up holding the choke like this, but even after warm she would still die if I let the choke in. Any touch of the throttle and she would burp and want to die. Idle screw is only set a couple turns out.

Having made sure the pilot circut was completely clear on all carbs, I don't understand why I'm not getting fuel at low idle.

Any thoughts? Thanks.

The good even compression figures are not surprising due to the low mileage. Also indicates rings are doing their job and likely not sticking in the piston groves.

Is there still a good fat spark on the plugs?

Because plugs appear dry, am wondering if fuel level in float bowls is for some reason too low, whereby fuel is not getting to the pilot jet. Would check service fuel level inside the float bowls by performing the clear plastic tube test (may be done without removing carbs from the bike).

If fuel level is obviously too low, there may an assembly issue. Or if the float tabs were adjusted during reassembly using the upside-down measuring method, the float height is likely wrong anyhow.

Good Luck! :)
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1984 ZX750 GPz - START AND RUN, THEN NO START AND NO RUN. HELP PLEASE! 6 years 3 months ago #215982

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Forgot to mention -- would assure integrity of the vacuum line from carb to petcock. Tightly fit at each end. No cracks or splits allowing air intrusion from outside.

When attempting to crank the bike, would put petcock in PRI (prime) position, so as to assure free flow of fuel without worrying about whether petcock diaphram is properly functioning.

Regarding ample supply of clean fresh fuel from tank to carbs --is the tank clean inside (might need flushing to remove any grit or crud suspended and hovering about the petcock intake tube screens up inside the tank)? Are all the petcock screens clean? Is fuel readily flowing from the petcock when in PRI position? Is a good clean in-line fuel filter installed? Am wanting to assure that an ample supply of fuel is reaching the carbs.

As known, if in-line fuel filter(s) are not being utilized, perfectly clean carbs can be instantly re-clogged.

Are the orifices in the float needle seats positively open and clean, so as to permit ample fuel flow into the float bowls?

Are the float needles moving freely inside the seats (and not stuck inside the seats up against the orifices)?

Are the seats loose (lightly snug is okay -- not Godzilla tight)?

Are the clamps tight that hold the carbs into the carb holders?

Is the air filter in place and properly fitted?

Good luck! :)
Last Edit: 6 years 3 months ago by Patton.
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