High Revving GPz750?

Thinking 1982 GPZ750 carbs have enrichener circuits as opposed to choke flaps.

Would return pilot adjustment screws to default position per FSM.

At normal engine operating temperature, adjust the idle thumb screw to set idle rpm at say 1000~1200 rpm.

When starting a cold engine, apply full choke, DO NOT TOUCH THE THROTTLE GRIP while cranking over the engine (or using a kick starter, where applicable).

An enrichener circuit is designed to properly function with the carb slides closed fully down at idle position where the belcrank contacts the idle thumb screw.

Good Fortune!

Would also assure:

--- ignition coils are receiving full battery voltage;

--- ignition timing advancer is properly functioning;

--- visually observed spark at plug tips is fat blue, not wimpy thin orange.

Good Fortune!

Thanks Patton. I'll check on those. While I was looking at the FSM supplement for 1982, I came across the spec for float level of 3mm. Mine measured 1mm, so it looks like mine are too high.

Also, back when I was troubleshooting the high idle issue, I adjusted the carb butterflies to be slightly open at rest. The manual describes the starter enrichment system working based on the butterflies being closed. I'm wondering if that could be contributing to the issue.

Nick

nicksorg wrote:

Thanks Patton. I'll check on those. While I was looking at the FSM supplement for 1982, I came across the spec for float level of 3mm +- 1mm. Mine measured 1mm, so it looks like mine are too high.

Also, back when I was troubleshooting the high idle issue, I adjusted the carb butterflies to be slightly open at rest. The manual describes the starter enrichment system working based on the butterflies being closed. I'm wondering if that could be contributing to the issue.

Nick

When I had the high idle issue, I checked the advancer and it was moving in and out based on rpm. With the engine off, I made sure all of the parts were free and moving.

I visually checked the spark on #1 and #4 plugs. Both had a yellow spark of varying strengh as the starter was spinning. So no blue spark. My starter is doing something weird. When I press the starter button, the starter engages but after a few turns of the engine, it starts making a clicking/spinning noise. I can't tell whether its mechanical or electrical. I put the battery on the charger to make sure its charged, so I'll try later.
Nick

Voltage received by coils should equal battery voltage (from a good fully charged battery).

Inadequate voltage to coils results in weak spark.

Good Fortune!

Here's what I did when I got home tonight. Put full choke on and bike started but only revved up to about 1,500 - 2,000. It took about 10 sec to start. After about a minute it started to drop a little. I took off the choke and it would only stay running with throttle. Once it stalled, it wouldn't turn over again.

Now that my high idle problem is gone, I noticed something today. At low idle, the engine makes some rattling and knocking noises. Its probably time to pull the valve cover and check valves and cam chain.

Lastly, I checked the voltage at the red bullet connector for each coil and it was 11.76 and 11.79 at each coil. Battery was about 12.5 volts.

Nick

nicksorg wrote:

...Put full choke on and bike started but only revved up to about 1,500 - 2,000. It took about 10 sec to start. After about a minute it started to drop a little. I took off the choke and it would only stay running with throttle. Once it stalled, it wouldn't turn over again.

...At low idle, the engine makes some rattling and knocking noises. Its probably time to pull the valve cover and check valves and cam chain.

...checked the voltage at the red bullet connector for each coil and it was 11.76 and 11.79 at each coil. Battery was about 12.5 volts....

It took about 10 sec to start. Should start running in less than 2 seconds.

After about a minute it started to drop a little. I took off the choke and it would only stay running with throttle. Would remove choke ASAP to avoid fuel-fouling spark plugs.

voltage at the red bullet connector for each coil and it was 11.76 and 11.79 at each coil. Battery was about 12.5 volts. Loosing too much voltage between battery and coil, likely due to issues with old wiring and connectors. (See image below). Best to consult particular bike's actual wiring diagram to track voltage in and out of each connection and switch between battery and coils. If not already at hand, there's probably a wiring diagram here on KZR (see following post).

Once it stalled, it wouldn't turn over again. Would suspect a failing battery. Or maybe needing to clean and snug connections at terminals. Also check integrity of connection where negative battery cable attaches (grounds) to rear of engine.

At low idle, the engine makes some rattling and knocking noises. Its probably time to pull the valve cover and check valves and cam chain. Would follow FSM instruction regarding cam chain tension adjustment as applicable. Would also consider that good carb sync often reduces cam chain noise at idle and low rpm.

Good Fortune!

[Click on image to enlarge view.]

[Click on image to enlarge view.]

Thanks Patton. To clarify, when I said it wouldn't turn over, after running for a short while, I meant that it wouldn't start. Battery was purchased new in July.

I pulled the valve cover and checked valve clearances:

Intake:

#1 = .004
#2 = .012
#3 = .009
#4 = .008

Exhaust:

#1 = .005
#2 = .005
#3 = .004
#4 = .004

Looks like Exhaust are in spec, while Intake #2,3,4 are out of spec range of .003 - .007.

So here's a summary of where I am with this bike:

I go the bike in June. It had a solenoid and wiring problem. I replaced the solenoid and wiring harness. Carbs were off the bike and had sat for years. I cleaned the carb, multiple times and put in new float needles and seats. I had a high idle problem due to carbs not installed correctly in the intake holders. I rode this bike multiple times, while trying to resolve the high idle issue. Once I fixed the high idle problem, it's now hard starting and won't idle on its own. Could the idle problem still be carb-related (e.g pilot jets)?
Nick

nicksorg wrote:

...Battery was purchased new in July...Could the idle problem still be carb-related (e.g pilot jets)?
Nick

Possibly carb related:
--- pilot jet, or other pilot circuit issues
--- enrichener circuit
--- adjustments to butterflies
--- too high fuel level

Or perhaps the weak spark.

In this instance, I don't suspect the idle problem is related to valve clearance.

Good Fortune!

I'm going to pull the carbs and go through them again. I'm not a big fan of making wholesale changes, but maybe its time to install the new jets, and needle that came with the Z1 rebuild kits I bought. I'm also going to drop the float levels and bench sync them. I'll also check the voltage at all the points in between battery and coils.
Thanks
Nick