85 GPz 750 Cafe Project

I should remind any readers: 42.5 pilot at 2.5 turns; 135 mains. Stock cams and pipes and those damnable pods.

ajsfirehawk wrote: . . . no idle combustion on carb #1 . . . isn't a coil issue. I re-re-re-removed the #1 carb, broke it down and shot carb cleaner through every passage. All clear. Any thoughts on next steps are greatly appreciate. . . . .

Does spraying some starting fluid into carb #1 intake produce momentary combustion? If so, would suspect that the carb pilot circuit is still failing to provide fuel mixture into the carb bore despite all the cleaning effort. :pinch:

Could remove the #4 spark plug immediately after the lack of combustion scenario during the starting procedure to determine whether or not there's fuel on the business end of the spark plug, which would indicate that fuel mixture is indeed entering the combustion chamber but for whatever reason isn't combusting.

Good Fortune!

I'll be out there this afternoon Patton. Good thought on the starting fluid. Also had a recommendation to open the enricher circuit and see if I get combustion. Same thought as yours "introduce fuel another way to prove fuel is the only missing element". I will advise later today.

I uncapped the pilot jet and I now have a pilot circuit functioning on #1. Letting the bike fully warm up it is back to tuning. What now becomes clear is I'm running too rich on the main jets. I've dropped the needles all the way down and any application of throttle makes it go yellow and when the RPMs flatten out it bounces between yellow and blue on the Colortune.. The plugs after running for many minutes come out black and sooty. I fine tuned the pilot circuits. I could never get them to go white with the color tune, but when they got too lean they would misfire (dark). I've got to see if I have 130 main jets and pull these suckers apart again.
Meanwhile I'm not confident the ignition system is 100%. Stock coils and wires that measure good but I'm skeptical. I don't even remember if I did the Wired George mod to apply battery voltage to the coils. I'll do that at a minimum and possibly order new Dyna coils and wires.

No joy, I don't have 132.5 or 130 mains.

I went to Tri City Cycle chasing main jets. They had three 132.5's (as useful as balls on a priest) and four 130 main jets. I installed the 130's to see how it responded. Spins like crazy, but doesn't light. I'm ever more convinced the ignition is sub par. 13.2 volts on the coils at rest. I have not done the Wired George mod. This puppy should light. Great compression, (145 to 150) I watched the enricher function properly with the Colortune. Pull the enricher and each cylinder turns bright yellow. I've got air, fuel, compression...I have to believe the spark is weak. It should fire up immediately and just nothing. Not even a cough. I'll work through the ignition diagnostics in the service manual and then if nothing jumps out as a problem I think I'm going to order Dyna coils and new plug wires. Do the Wired George mod. Get another 132.5 jet and give it a go. Back to waiting for parts. JFC this just never ends.

I'm going to call this a starting problem. It flatass won't start cold, won't even cough. But bump it once with starting fluid and it runs like a deer. Also starts very well once it is warm. I'm at a loss regarding how to make this puppy start on its own.

Too lean.
Steve

Or possibly too rich. I tried 42.5 pilots on my 83 GPz750 and could barely get it to start when cold (regardless of choke position). Switched back to stock 37.5 and all was well. I'm running a stock air box and filter with an old school 2" Kerker racing exhaust/baffle. Mains are 115 (stock is 110) and needles are stock 4BC7/Y270 at position #4 (one position richer than stock). If anything, this setup is rich on mine.

Super-stupid suggestion;

Make sure the throttle cable isn't binding. If it is binding and holding the throttle butterflies open it will lean it out too much to start on CV carbs. Happened to me when I got my KZ1100 running this spring. It had me completely stumped for awhile.

When you do get it started does it idle too high? It might not if you have adjusted the idle to compensate for the skewed throttle position.

ayeckley wrote: Or possibly too rich. I tried 42.5 pilots on my 83 GPz750 and could barely get it to start when cold (regardless of choke position). Switched back to stock 37.5 and all was well. I'm running a stock air box and filter with an old school 2" Kerker racing exhaust/baffle. Mains are 115 (stock is 110) and needles are stock 4BC7/Y270 at position #4 (one position richer than stock). If anything, this setup is rich on mine.

Interesting thought. But with Colortune I get the proper blue color at idle with the pilot screws 2 turns out. Less turns and I see the cylinder go dark, no ignition. (Once warm) But that would suggest the pilot circuit is tuned correctly would it not?

GPzMOD750 wrote: Super-stupid suggestion;

Make sure the throttle cable isn't binding. If it is binding and holding the throttle butterflies open it will lean it out too much to start on CV carbs. Happened to me when I got my KZ1100 running this spring. It had me completely stumped for awhile.

When you do get it started does it idle too high? It might not if you have adjusted the idle to compensate for the skewed throttle position.

No such thing as stupid questions so thanks for the thought. I'll double check but I don't believe so based on the snap back of the throttle and the idle dropping in a 1000rpms when warm.

I took the pods apart and it does appear there could be some interference. While the gasket for the pod doesn't directly cover the ports in the intake bell, it does obscure it. I suspect it makes the air tumble around it as opposed to a direct shot into the end. Even the metal edge on the pod filter encroaches a bit so there is not a direct path into either intake bell port for the main jet or the enrichner. I cut out the area on the rubber pod mount that aligns with the ports. See below. New behavior, when I hit the starter with the enricher on I get some ignition now. I tried 6 times and it begrudgingly started but it did start! It does not start like it should but the change in behavior based on the changes I made to the pod suggest I've got my hands on something. Pablo (crazy smart) on KZ650 brought up the intake bell covered by the pod rubber idea. When I had the carbs apart the second time, I shot carb cleaner from the choke backwards through the small brass tube that feed into the carb bowl. They are clear. I think the right answer is to get air filters that do not have a lip on them that encroaches on the O.D. of the carb bell. Thoughts?