85 GPz 750 Cafe Project

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?

ajsfirehawk wrote: But that would suggest the pilot circuit is tuned correctly would it not?

It would, but there seems to be a couple of conflicting rich vs. lean indications. I only mention the overly-rich possibility because in my case I thought I was too lean when I was actually just right. I had always read that the EPA-regulated bikes with CV carbs were jetted way too lean from the factory so I was biased towards thinking I needed to increase the pilot when in fact the factory jet was just about perfect, even with a low-backpressure exhaust.

I was also surprised to measure less than a .001" difference between a 37.5 and a 42.5 (both jets were new genuine Mikuni parts). Really surprising that such a small change in ID makes such a large difference in operation. Almost scary that they are that sensitive.

You may well be correct ayeckly. It smells rich to me which isn't scientific but I'm also getting black soot on the plugs in just 15 minutes of running. 130 main jets are 8 sizes up from stock and the only deviation from stock is the pods. Those are going in the trash can. I've purchased some K&N two into two air cleaners. RC-2382's
www.knfilters.com/search/product.aspx?pr...c-2382&mp_mt=b&pdv=c
You are making reference to the pilot jets. I've got 42.5a but I suppose they could be rich as well. They are running at 2 turns out. Anything less than that and I can see the cylinder misfiring. You can literally see it shut off as your turn the pilot screw in. The tuning process will start anew when the K&N's arrive. They are what I wanted to go with in the first place.

I installed the K&N filters yesterday. Hooked up the remote fuel bottle, turned the key on, hit the starter button, all instrument lights flashed on and off, dead. No lights no anything. Turned it off, pulled all the fuses (blade type) nothing is blown. Today I start electrical debugging after I pull the carbs and put in 125 main jets. Possessed, absolutely possessed. On the plus side the K&N's look good and they do not have any 'lip' on the inside to interfere with the openings in the intake bell.

Checked the battery terminals, check the ground. Buffed up all ground mating surfaces and read continuity through the ground connection. 13.2 on the battery. I started working through the wiring diagrams, removed the ignition switch and bussed it out. All good. I was headed for the starter switch when it hit me. I kept the voltmeter on the battery terminals and turned the switch on. .03V. New gel mat battery from a year ago kept on a battery tender. Just flat zero juice. We shall see how well the Tatu battery return process works. Carb coming apart tomorrow for new jets.

125 main jets installed, float levels verified on the bike. K&N filters back on the bike. All set for a fire up test once I get a battery. Tomorrow afternoon I'll find a way to get a battery connected from another bike. In case others have had the problem, when I'm swapping jets I often have to pull the top caps off the carbs to get the needles back in the main jets. I used bobby pins to keep them from falling into the top.

Can't seem to get Imgur to play nice tonight. I'll just attach the pic below.

I've made a ridiculous mistake. I've got the needles on the wrong side of the puck inside the carb sliders. The KZ650 dudes just fished me out of my brain fart. I'll update when I address this and try to restart.

Needles in the proper location now. I installed 37.5 pilot jets at two turns on the pilot screw. 125 main jets. I pulled the enrichner rod out. Hit the starter button and it almost died first time. Then nothing, never even coughed...again, I tried another three times. I pulled the plugs #2,3,4 were damp, but not shiney. #1 was wet and shiney. I'm running out of ideas. I've got a set of Dyna coils and wires on the shelf. I'm going to give that a try.