KZ750H Restoration

The bike does have a vacuum petcock but it's connected to carb #2. The thing that I don't get is that the idle is so much better when #3 is 3 turns out, although this should be too rich (and is too rich going by the plug).

[quote="calum" post=834838]The bike does have a vacuum petcock but it's connected to carb #2. .......................[/quote]

As far as I know, the vacuum petcock will always be connected to carb #2. I've never heard of one ever being connected to carb #3, so maybe Kaylinator had a typo or maybe he's thinking of a different model? Ed

I think it was maybe just to rule it out as #3 is too rich.

I thought that it may be to do with the float levels. When I took the carbs off #3 was the only one where the overflow tube wasn't dry. It was also the highest by about 1.5mm when I checked the float height - although this was done dry and I still haven't got round to checking them with a clear tube.
I'll check them later and correct them if needed. I'll go for a test ride tomorrow. With any luck the level will be good and the plugs will all be closer to the same colour (I'll pull number three and brush the soot off before the ride).

1978 KZ1000. VM26SS. Vacuum off carb # 3, vent off 2 & 4.

Thought if yours was the same, it could rule it out. I had an issue where the diaphragm leaked and pulled fuel through the vacuum, making #3 run SUPER rich.

I've been working away slowly, trying to iron out the last couple of kinks. I made some new spacers to reduce preload on the forks, handling is a lot better now (see here: kzrider.com/forum/5-chassis/614165-kz750h-forks-topping-out ). Everything is smooth except occasionally when I go over a big bump - something seems to rattle around up front. I figure it could be the connectors in the headlight bucket, or maybe the speedo or clutch cable. Everything is nice and tight and there's no play in the steering head, so I'm not too worried. Would be nice to figure it out though.

I've been trying to fix the flat spot in the upper mid-range. I figure I need to sort out the rich condition on #3 and see if I still have a problem. I've done the following so far:
- swapped the plugs multiple times
- swapped the float valve, float and float bowl with #4
- swapped the plug cap and lead with #2
- new secondary main
- swapped the needle and vacuum piston with #4

Each time #3 was still way too rich and #1,#2 and #4 slightly lean - probably due to the float level being on the lower side (5mm) and the open exhaust.
I will swap the needle jet and the main jet with #4 on the weekend, after that I'm out of ideas. As far as I can see it must be one of those two as any other problems (blockages etc.) would cause it to run too lean. All the idle mixture screws are 2.5 turns out.

Finished the second set of carbs today (see here: kzrider.com/forum/3-carburetor/614410-ke...kits?start=12#837896 ). Went to swap them out and ended up standing in a puddle of petrol when I took the fuel line off. I'm guessing the additives I tried (for cleaning the carbs out) have ruined the petcock membrane and it now has three settings: on, on and on.
As I don't really like vacuum petcocks (for exactly this reason - there's no off), I ordered a pingel. I figure with the number of other things that aren't stock an aftermarket petcock wouldn't make much of a difference. I will repair the stock one and stick it on the shelf.

After cleaning up I managed to get the carbs swapped out. I vacuum synced and set the idle on the new carbs and will head out for a test when the roads are dry. One promising sign is that the vacuum is a lot higher at idle (it's within spec now).

:woohoo: :woohoo: :woohoo: :woohoo:

Went for a ride and finally felt all 74 horses (well not quite, hit about 8000rpm max). It pulled smoothly through the entire rev range and there was no bogging except low down when it was still a bit cold. I had the stock Delkevic baffle in, I'll try the quiet baffle before I put it away for the winter. I imagine that will be better low down but not quite as good in the upper rev range. Will make a few different baffles over winter so I can find the sweet spot.


The second set of carbs isn't quite as shiny as the others - still pretty good though as I had the caps and choke lever zinc plated. Given that they actually work I can't complain
I'm stoked that I can just roll her out the garage next year and ride. Shouldn't have put off building a second set of carbs for so long!

Great success. Way more fun to ride a correctly tuned bike than to just ride. Quality time in the shop is rewarded with performance and reliability.

Put the new Pingel petcock in today (no pics as it was already dark when I did the job). I'm thinking of ditching the inline filter. The Pingel screen is pretty good and the inline filter is almost always in the way (and is also another source for potential leaks). Any advice?
I screwed the petcock in to the adapter plate with fuel resistant thread sealant instead of Teflon tape. I let it cure for a few days before it saw any fuel. Figure I could see if it leaked over winter when the bike is up on stands. Not a fan of thread tape.

Speaking of winter, should I drain the carbs before I put her to bed? I've only every had year round bikes before this so not really sure.

I left fuel in may carbs without starting the bike for several months and seriously regretted it! The fuel will deposit a varnish-like substance on the needles, jets. etc. that will definitely cause problems. I had to remove the carbs and thoroughly clean them to get the bike running properly. Now I start the bike and let it run for about 15 minutes once a week even during the winter. I've been doing this for about the past 18 years and have had zero problems. If you cannot start the bike once a week you should drain the carbs, otherwise you may experience the same issue that I had.

As far as an inline filter, I installed a Golan Super Mini fuel filter. It is great, is small, is all metal, can be cleaned, and will last forever. It filters out particles as small as 10 microns (.000392”), so nothing significant can foul the carbs. It was not inexpensive, but I'll never need to replace it. Pingel makes a good product, but I don't think I would rely on any petcock screen to keep stuff out of the carbs. Does Pingel give filtration specs? Ed

650ed wrote: I left fuel in may carbs without starting the bike for several months and seriously regretted it! The fuel will deposit a varnish-like substance on the needles, jets. etc. that will definitely cause problems. I had to remove the carbs and thoroughly clean them to get the bike running properly. Now I start the bike and let it run for about 15 minutes once a week even during the winter. I've been doing this for about the past 18 years and have had zero problems. If you cannot start the bike once a week you should drain the carbs, otherwise you may experience the same issue that I had.

As far as an inline filter, I installed a Golan Super Mini fuel filter. It is great, is small, is all metal, can be cleaned, and will last forever. It filters out particles as small as 10 microns (.000392”), so nothing significant can foul the carbs. It was not inexpensive, but I'll never need to replace it. Pingel makes a good product, but I don't think I would rely on any petcock screen to keep stuff out of the carbs. Does Pingel give filtration specs? Ed

Fuel stabilizer will eliminate the issue of gummed up carbs from inactivity. I use marine version Stabil and haven't had any issues since even though my bike sometimes goes months between starts. And speaking of starting, it's bad to start the bike unless you plan to ride it and burn off all the condensation that naturally forms when hot gasses contact cold metal. Exhaust systems in particular are prone to rusting out.

calum wrote:
Speaking of winter, should I drain the carbs before I put her to bed? I've only every had year round bikes before this so not really sure.

Yes. Definitely.
Drain the carbs. Even in a sub zero temperatures gasoline will evaporate over a Winter and leave crud behind. It only takes a couple of minutes to drain and a few seconds to fill / prime in the spring.