To Pump or not to Pump VM28's

I recently removed my carbs to sort out the bad running inherited from the PO's mechanic. One of the float levels was too high and one too low. I reset these having also reverted to the stock 15 idle jet, from 20's, and reducing the mains to 110. - I'm at 5,000 feet + of altitude. I did leave the shim washers under the needles figuring as these are carbs from a 1980. the needle set up is likely on the lean side. I also replaced some missing check valve parts in one of the float bowls, for the accelerator pump system with some parts from another set of carbs I had lying around. I put the carbs back on quickly to try them, although I had some suspicions about the accelerator pump diaphragm etc. from the feel of it, but didn't want to get it apart as it wasn't leaking, I had no spare parts to hand and it appeared to have been redone in recent history. The bike fired up almost immediately and ran great, much smoother,no bogging and hesitation off idle and a nice idle ( but I haven't ridden it yet) - but no gas squirting from the accelerator pump nozzles no matter how much pumping of the lever I did, and the pump just felt limp, no resistance. I can get a rebuild kit, but I've read some negative comments regarding the reliability of this set up on bikes not used regularly, that they dry out when the bike sits and then often don't work or take forever to get fuel circulating again.

I'd like to hear experience and opinions on this from people who are running accelerator pumps, if it's going to be troublesome and need attention every spring, I'm inclined to just remove the whole thing and trust it will prove an unnecessary complication if I'm running the whole thing richer, as was the way on the early bikes and Z1's .

I can't comment on one on a kawi as my kz1000 doesn't have it on the vm26's I have. I do however have accelerator pumps on the carbs on my 77 cb750, they work well and I use them always for cold starts. 2-3 twists of the throttle and it always fires up on the first crank. No bog either when opening the throttle quickly when riding. So take that as you will, I wish my kz1000 had them.

redhawk4 wrote: I recently removed my carbs to sort out the bad running inherited from the PO's mechanic. One of the float levels was too high and one too low. I reset these having also reverted to the stock 15 idle jet, from 20's, and reducing the mains to 110. - I'm at 5,000 feet + of altitude. I did leave the shim washers under the needles figuring as these are carbs from a 1980. the needle set up is likely on the lean side. I also replaced some missing check valve parts in one of the float bowls, for the accelerator pump system with some parts from another set of carbs I had lying around. I put the carbs back on quickly to try them, although I had some suspicions about the accelerator pump diaphragm etc. from the feel of it, but didn't want to get it apart as it wasn't leaking, I had no spare parts to hand and it appeared to have been redone in recent history. The bike fired up almost immediately and ran great, much smoother,no bogging and hesitation off idle and a nice idle ( but I haven't ridden it yet) - but no gas squirting from the accelerator pump nozzles no matter how much pumping of the lever I did, and the pump just felt limp, no resistance. I can get a rebuild kit, but I've read some negative comments regarding the reliability of this set up on bikes not used regularly, that they dry out when the bike sits and then often don't work or take forever to get fuel circulating again.

I'd like to hear experience and opinions on this from people who are running accelerator pumps, if it's going to be troublesome and need attention every spring, I'm inclined to just remove the whole thing and trust it will prove an unnecessary complication if I'm running the whole thing richer, as was the way on the early bikes and Z1's .

One of the float levels was too high and one too low. I reset these -- Hopefully the FUEL level was confirmed with the clear tube test, as merely setting the upside down dry measured float height is woefully unreliable toward achieving the correct fuel level inside the float bowl.

reverted to the stock 15 idle jet, from 20's -- Might result in a too lean pilot mixture when actually riding the bike (especially without a functioning fuel pump), where a strong pull-away from idle is desirable.

did leave the shim washers under the needles figuring as these are carbs from a 1980. the needle set up is likely on the lean side -- The jet needle to needle jet configuration has little if any effect on the pilot circuit. If the objective is to enrichen the mid-range, shimming the needles should help accomplish that by slightly raising the needles to sit slightly higher in the needle jets.

reducing the mains to 110 -- As known, main jets have most influence at wide open throttle position, and not much influence at mid-range throttle positions.

I concur with the idea of either removing or ignoring the non-functioning fuel pump, as it adds more clogging potential incident to carburetion.

Would assure all fuel levels are within spec via clear tube tests.

After careful tuning, including valve clearance checks and adjustments if needed, assuring correctly timed strong fat sparks on brand new plugs, carb sync, pilot screw adjustments, etc., spark plug readings at various throttle positions for pilot mixture, mid-range, and wot, will help indicate whether the pilot jets and main jets are correctly sized, and whether the jet needle to needle jet configurations are correct.

Good Fortune!

I used the clear tubes I had for my 650 to verify the levels. Time will tell on the other jets etc. I made my best guess based on stock settings and where I've gone with other bikes taking into account the altitude and how weak the stock setup sometimes is. Getting rid of the 20 idle jets was IMO an essential change, 15's might be too small, but I've found on other bikes with the altitude you can soon get too big on pilot jets and the engine bogs, then clears and takes off under acceleration, the bike was doing that big time as originally configured. I'm waiting on a Z1 airbox, before making final adjustments, but bearing in mind I was running it without any filters, it seemed pretty close to me. the addition of the airbox and filter will undoubtedly improve things - I allowed for that in my estimation. Incidentally stock is 102.5 for these carbs with the stock needle and #2 slide cut away etc.

I really don't want to mess with the Accelerator pump if they are prone to problems with clogging and premature failure. Using non ethanol fuel and draining the carbs at season end, has usually been sufficient to keep my carbed bikes running for years without issue, once initially cleaned and sorted and using fuel filters. While I'm pretty experienced with carbs, it's not something I want to be constantly tinkering with. My KZ650 is "pre-pump" and seems to run fine, I don't know if after 77 they went to pumpers because they improved performance or were forced to run the bikes leaner.

I'm interested in anyone's experience with the pumper carbs over time. PFD is the Honda a similar setup?

Most people recommend deleting them and rejetting accordingly. IT's much more consistent then. My buddy did that on his KZ1000 shaft and said there is no way he would go back to the pump.

I just realized the float bowls from VM24 carbs will fit the 28's, I have a set of parts carbs with 3 bowls on them, if I can find one more then it would be easy to remove the accelerator pump, but also replace it if I ever needed to, as I could just swap the whole float bowl assembly and reattach the linkage. I have some reassembly to do before I can take it for a run, but assuming it works on the open road I think I'm going to do away with the pump for simplicity, one less thing to go wrong and some reduced clutter around the carbs.

The problem I have always had with the pumps is if the carbs sit, the pumps won't pump because they have no gas in them. Hard to explain, hut kind of the same idea as pumping brake fluid through a dry system. You can pump all day with the lever and never build pressure until brake fluid finally works it's way in. In other words probably there is no gas there to prime the system. It's a downright pain to get them squirting once they dry out from sitting. I gave up keeping them working.

redhawk4 wrote: I just realized the float bowls from VM24 carbs will fit the 28's, I have a set of parts carbs with 3 bowls on them, if I can find one more then it would be easy to remove the accelerator pump, but also replace it if I ever needed to, as I could just swap the whole float bowl assembly and reattach the linkage. I have some reassembly to do before I can take it for a run, but assuming it works on the open road I think I'm going to do away with the pump for simplicity, one less thing to go wrong and some reduced clutter around the carbs.

If you get rid of the pump, make sure either the gaskey covers the hole for the pump nozzle OR you solder the hole shut or something, don't know if it makes a difference but when I delete pumps I push the nozzle out and solder the hole

I don't think I'd remove the tubes until I was sure about never going back, but if there's no opposing hole in the float bowl the "O" ring should seal the passage way to the nozzle against the float bowl unless I'm thinking of it wrong?

RonKZ650 wrote: The problem I have always had with the pumps is if the carbs sit, the pumps won't pump because they have no gas in them. Hard to explain, hut kind of the same idea as pumping brake fluid through a dry system. You can pump all day with the lever and never build pressure until brake fluid finally works it's way in. In other words probably there is no gas there to prime the system. It's a downright pain to get them squirting once they dry out from sitting. I gave up keeping them working.

That seems to be a somewhat common complaint and the one that got me thinking about removing it. With the hot summers here, they'd be constantly drying out if it sits for long, never mind during the winter layoff, and if it doesn't work consistently, any benefit it may have will be lost. Thanks for the feedback. I ran the bike today with the "Breadbox" filter back on and it seems it will be OK without the pumps to me, can't wait to ride it and assess it then. Might have got round to it today but it was raining, but really I need to wait for my airbox to arrive to get a true test with my actual configuration..

Got everything back together today, and rose it about 15 miles, it ran really well and I couldn't see I needing the accelerator pump based on how it pulled etc. I do think I need to go to 17.5 pilot jets though, I couldn't have the air screws out much at all with the 15's.

Got everything back together today, and rode it about 15 miles, it ran really well and I couldn't see needing the accelerator pump based on how it pulled etc. I do think I need to go to 17.5 pilot jets though, I couldn't have the air screws out more than a fraction of a turn with the 15's when I was synching the carbs