Author Topic: F3 Accelerator Pump Operation (Read 4220 times)

Wayne Meuir · « **on:** June 30, 2008, 08:54:12 AM »

I put a new accelerator pump in my carbs and I am a little confused about how it is supposed to work. The Clymer manual says the gap between the top of the pumps shaft and the arm that operates it should be .024-.032" and to bend the tab to adjust it. That is clear and I have done that. Then it says to set the clearance between the top of the operating arm and its stop to like .410" and that seems clear enough (I assumed that meant with the throttle in the closed position) and I have done that.

The problem that I am having is that when I operate the throttle by hand (carbs are still on the bench) the pump arm does not operate the accelerator pump. It is as though the spring is not strong enough to pull the pumps operating arm down onto the pumps shaft. I took the spring off and sorta shortened it to increase the tension, but it still does not work. If I take the spring off, the arm moves freely with no binding. If I operate the throttle shaft to WOT, I can then move the pump actuating arm by hand and it will operate the pump as I think it should.

Any ideas?

Wayne

eldar · « **Reply #1 on:** June 30, 2008, 09:05:13 AM »

They clymer is really off there. The gap between the tab and the arm is only .008.

Wayne Meuir · « **Reply #2 on:** June 30, 2008, 09:25:53 AM »

OK, I can fix that easily enough. Now what do I do to make it work? There was almost no gap at all when I first started and it still did not operate.

Wayne

eldar · « **Reply #3 on:** June 30, 2008, 09:35:28 AM »

What you need to do is download the shop manual and use that. The clymer covers the models all together and if yours is like the one I have, does not show much on the 77/78 carbs.

good-times.webshots.com/album/551597157aFDIkf

www.mediafire.com/?5ttzdg9yyuz

Try the mediafire first

TwoTired · « **Reply #4 on:** June 30, 2008, 09:46:41 AM »

Did you put the diaphragm spring on the correct side (opposite the actuating rod)?

Wayne Meuir · « **Reply #5 on:** June 30, 2008, 11:12:11 AM »

Yes, sir, I installed the spring so that it rides against the bottom of the diaphram and seats against the inside of the cover, so it is basically pushing upward on the diaphram.

I downloaded the shop manual and I am going there to see if I can learn anything.

Wayne

Wayne Meuir · « **Reply #6 on:** June 30, 2008, 12:27:01 PM »

OK, I reset the clearance according to the shop manual to .008". Then I sprayed silicone lube on the pivot point on the lever arm and it seems to be moving a little better and it is actually moving the accellerator pump rod the way I think it should.

I hooked up a temporary fuel can and hooked it to the carbs and ran gas into them. #4 leaked like a sieve out of the overflow even though it had a brand new needle in it and the float height was 14.5mm. I replaced the needle with another new one and that fixed the leak. The rack has been setting for about 10 minutes with gas flowing to them with no leaks that I can detect.

BUT, when I work the throttle by hand and the accelerator pump is activated by the control arm, shouldn't I see a burst of fuel coming into the venturi of the carb out of the the little brass standpipe?
If so, it ain't happening and I made absolutely sure those things would spray before I put them back together, so they ain't stopped up. I have a new accelerator pump from Parts-N-More in it. If it is not supposed to do that, then I may be OK, but I surely can't see why it would not squirt gas if the pump is working.

The shop manual devoted one whole paragraph to the accelerator pump, about three sentences.

Wayne

TwoTired · « **Reply #7 on:** June 30, 2008, 12:41:10 PM »

Quote from: Wayne Meuir on June 30, 2008, 12:27:01 PM

BUT, when I work the throttle by hand and the accelerator pump is activated by the control arm, shouldn't I see a burst of fuel coming into the venturi of the carb out of the the little brass standpipe?

Yes you should.

The pump must be primed first. Usually through repeated pumping.
There are two check valves for that pump that must function. These are behind the square plugs that you see in the pump cover and in the bowl mating surface.

One is closed (output) when the pump draws fuel from the bowl supply, the other is closed (input) when the diaphragm makes pressure to supply the squirt nozzles.
I test these with aerosol carb cleaner to prove they allow fluid transfer in one direct only. I've not seen them, but I think they are ball check valves.

Cheers,

eldar · « **Reply #8 on:** June 30, 2008, 02:04:47 PM »

I have that same pump kit. I put mine on and away it went. Should not need any priming. Are you sure fuel is getting to the carbs? You may need to clean the fuel passages in the carbs to make sure there are no blockages.

Wayne Meuir · « **Reply #9 on:** June 30, 2008, 04:14:26 PM »

The rack has been totally dissassembled and cleaned thoroughly. I squirted spray carb cleaner through every orifice on the carb and made sure fluid was making the trip. I did not, however, check the check valves to see if fluid was only going one direction.
The carbs are getting fuel into the bowls fine. The new float needle I put in #4 would not seal, so I had to change it out and put another new one in and it seems to be working fine.
When I got the Parts-N-More accel pump, I noticed that the two Mickey Mouse ears were slightly smaller than the cavity that they fit in while on the pump I took out they fit that cavity perfectly. The holes in the MM ears on the new pump did line up with the holes in the body so I don't see how that could cause a problem.

If priming is required, how is that accomplished. I have probably pumped this thing 25 times and have seen no raw fuel squirt into the bore of the carbs even though I can see the pump rod being depressed on every stroke.

Wayne

TwoTired · « **Reply #10 on:** June 30, 2008, 04:35:13 PM »

Quote from: Wayne Meuir on June 30, 2008, 04:14:26 PM

When I got the Parts-N-More accel pump, I noticed that the two Mickey Mouse ears were slightly smaller than the cavity that they fit in while on the pump I took out they fit that cavity perfectly. The holes in the MM ears on the new pump did line up with the holes in the body so I don't see how that could cause a problem.

I agree...unless...Mickey's ears swelled shut when squished on installation.

Quote from: Wayne Meuir on June 30, 2008, 04:14:26 PM

If priming is required, how is that accomplished. I have probably pumped this thing 25 times and have seen no raw fuel squirt into the bore of the carbs even though I can see the pump rod being depressed on every stroke.

Priming only took a couple, maybe five, slow actuation cycles to fill the lines with fuel all the way to the nozzles. This was after the check valves were finally proven to work, and mickey's ears were opened up for flow.
Have you taken the diaphragm off since gas was put in? The diaphragm ought to have gas on one side of it, if so. This would tell you if it is getting gas to pump. But, if the supply check valve is stuck open, it could simply move the gas back into the float bowl instea of toward the nozzles.

You can check the pump operation with the float bowl assembly in your hand, off the carb body. Fill it with gas and work the pump rod. If it's working, you might consider eye protection.

Good thing I wear glasses.

Cheers,

Wayne Meuir · « **Reply #11 on:** June 30, 2008, 07:09:48 PM »

Lloyd, I didn't get that far today, had to do some yard work

I will pull the bowl off and see if the pump is working. I may open up the holes in the MM ears if that appears to be a problem. The fear I have with those is that they have room to move around when the cover is tightened because they don't fit precisely, and it might be possible for them to block the holes, then get tightened that way, sealing off the fuel. Right about NOW I am wishing I would have just sucked it up and paid Honda the $61 they wanted for a new pump. I only saved about $40, and I'd give $40 right now not to be having to screw with this anymore.

I'll work on it some more tomorrow and see what I can figure out.

Thanks for the help guys I'm a little lost right now. The freakin' carbs on this bike have more parts that my entire Kawasaki H1.

Wayne

Wayne Meuir · « **Reply #12 on:** July 01, 2008, 04:03:57 PM »

OK, the saga continues.

I pulled the float bowl with the pump still attached and it had plenty of gas in the bowl. I manually operated the pump rod about 20 times--nothing.
I took the pump cover off and the pump kinda came out with it so I was not able to tell if the MM ears were covering the holes causing the pump not to work. I sprayed carb cleaner through the one way valve. It flowed gas going from the pump to the carb, but not the other way, so I guess it is working right.
I sprayed carb cleaner into the pump inlet going from the pump to the #2 carb and gas squirted out all 4 stand pipes into the carb throats.
I then put the pump back on the carb bowl aligning it very carefully and filled it with gas. Pumped it by hand and it squirted fuel straight up from the one way valve.
Reassembled the bowl to the carb thinking all was well.
Well, that's what I thought anyway.
Now the resistance created by the pump trying to move fuel to the carbs overcomes the spring on the pumps actuating arm. The arm then stops moving and the pump barely puts any fuel into the carbs throats. I can actuate the arm by hand and all 4 orfices will squirt gas completely through the carbs.
Not sure what to do. If the spring is weak from age, a new one might fix it if it is still available, but the spring is pretty light to begin with. There is absolutely NO binding in the movement of the arm, it is simply the resistance created by the fuel being pressurized that is causing the problem.
Any suggestions?

Wayne

TwoTired · « **Reply #13 on:** July 01, 2008, 04:34:05 PM »

So, if I understand correctly, your pump arm moves freely, but the pump rod doesn't? Is the rod bent or binding in the rubber guide?

What size holes would you estimate mickey's ears had in them? I was able to reuse an old diaphragm by carefully drilling out those holes to better match the passageways they sealed. After that, it pumped strongly and rebounded quickly.

It's not clear if you checked operation of both one way valves.

Cheers,

Wayne Meuir · « **Reply #14 on:** July 01, 2008, 07:20:49 PM »

Lloyd, the pump rod moves freely and squirts a strong stream of fuel if I depress the arm manually BUT the little coil spring mounted at the top of the arm that actuates the pump is not strong enough to overcome the pressure inside the pump. It moves part of the way and a very small (I mean VERY small) amout of fuel is pumped and then the pressure of the diaphram becomes more than the spring can overcome and it will not push the rod any farther, so it stops squirting.

I could only find one of the one way valves you were talking about. It was on the outlet side of the pump going to the squirter nozzles in the carb throats. The inlet side of the pump does not have one. All that is there is a hole in the bottom of the float bowl that exits into the pumps chamber in the side of the pump cover. There is no valve there and there seems to be no place for one to have ever been there, BUT the pump would still squirt a strong stream if the arm had enough force to actuate the pump.

Wayne

TwoTired · « **Reply #15 on:** July 01, 2008, 10:25:01 PM »

Wayne, it's been a while since I did one of these. But, as I recall, one check valve was in the pump cover and one was in the bowl body.
There has to be two valves. One valve will keep the fuel flow toward the nozzles only on the down stroke of the rod, and not allow back flow from the nozzles on the up stroke of the rod. Another valve will keep the the flow going to the pump from the float bowl on the upstroke of the rod and not allow the pump to push fuel back to the bowl on the down stroke of the rod.

Also, there is a coil spring between diaphragm and pump cover. If you are missing this spring, there is nothing to push the rod back up toward the actuator arm.

http://www.cmsnl.com/honda-cb750f-750-super-sport-78-us_model7240/partslist/E++2001.html

Cheers,

Wayne Meuir · « **Reply #16 on:** July 02, 2008, 05:43:02 AM »

Lloyd, coil spring is there, in fact it is new, it came with the pump kit.
Even though I only found one of the check valves, they both must be working fine. The reason I say this is that if I hold the slides open and then actuate the pump manually by moving the pumps actuating arm by hand, the carbs will squirt fuel all the way through the carbs and onto the work bench behind the carbs, so the squirter is working fine, which means the check valves are working as well.

Problem I have is that the arm will not exert enough force on the upper end of the pump rod to squirt the fuel. It starts to move the rod, squirts just a dribble of fuel into the carbs, then the pressure inside the pump(resistance caused by trying to move the fuel out of the pump chamber and into the carbs through a very small orifice) overcomes the little coil spring and it can no longer move the pump rod, so it stops pumping.

Wayne

eurban · « **Reply #17 on:** July 02, 2008, 06:22:35 AM »

Can't know for sure, but I doubt that you have a problem with the pump itself, if you are able to push the actuating rod by hand and get a good squirt of fuel from all the nozzles. Problem is more likely in the linkages involved. How about a good picture of the the linkages and springs on your carb setup? I would guess that something is bent, frozen up, improperly installed/adjusted or you may have incorrect or damaged springs. The system is a bit complicated as there is a "buffering" linkage that transmits the movement of the main throttle linkage to the rod and I have often found issues with adjustments being way off (thanks Clymer!) and the pivot points not moving freely. Can you show us what you got?

Wayne Meuir · « **Reply #18 on:** July 02, 2008, 07:31:55 PM »

OK, I took some pics but I have a really crummy camera, so that may not help. The clearance between the arm at the top and it stop is about 9.5-10mm. The clearance between the top of the pump rod and the actuating arm is .008".

eurban · « **Reply #19 on:** July 02, 2008, 08:04:35 PM »

You say the clearance between the pump rod and the actuating arm is .008 inches? Looks a hell of lot bigger than that in your third pic (but maybe thats the pic?) Spec I have seen in the shop manual actually calls for between .008 inches and 0 inches. This means that with the throttle closed the rod end and the arm should be essentially touching but allowing the rod to rest at its highest point of travel. Is this really how you have it set up? Also does your actuating arm move completely freely, flopping back in forth in its full range of motion with ease (with the spring removed and the rod out of the way)? I have seen a number of carb sets with the pivot adding resistance due to corrosion. Hope this helps . . .

Wayne Meuir · « **Reply #20 on:** July 02, 2008, 08:31:37 PM »

Pump arm is totally free with the spring removed through its entire range of motion. There is no corrosion on these carbs anywhere, I completely dissassembled the rack and soaked and cleaned the carbs, replaced all o-rings and gaskets. The clearance is .008" set with a feeler guage. Pic is not very good, but the top of the rod has a round profile and the .008" is from the highest contact point on the dome of the rod where it contacts the underneath side of the tab on the actuating arm. The gap was measured with the throttle slides closed and the actuating arm in the at rest position.

Wayne

eurban · « **Reply #21 on:** July 03, 2008, 05:17:11 AM »

Kind of grasping at straws here. . .Could it be that the pump spring that came with your new kit is too stiff? There is a balance of sorts required between the spring on the linkage and the spring in the pump. Your linkage spring looks stock but its hard to say for sure. Do you have the rubber seal for the where the pump rod enters the carb body properly installed? Its locating lip tends to push out when you shove the rod in during assembly and might be somehow creating too much resistance or allowing the rod to become offset and rub on metal. I put a bit of grease on the rod before assembly. Do you have a spare carb rack?

Wayne Meuir · « **Reply #22 on:** July 03, 2008, 06:55:39 AM »

I slid the rubber boot on the rod up out of the way to eliminate it as a possible cause, so it is not touching anything. I think I will take the cover off and replace the new spring with the old one and see if that helps.

I don't have a spare carb rack like these. I have a set off an earlier model CB750, I think they came off a '72. They don't have the pump but they have screw in pilot jets. I may have to rebuild them and use them instead. How much conversion is required to do that?

Wayne

eurban · « **Reply #23 on:** July 03, 2008, 07:14:19 AM »

Sounds like you have spent a good amount of time, effort and $ on these carbs. I wouldn't give up on them; problem should be solvable. When you have the boot out of the way, does the shaft cock to one side or the other when the arm pushes it? I doubt that is the issue but the boot may serve as a bushing to keep the rod properly located. A working set of carbs would be helpful as a comparison to your rack; perhaps there is someone within range out there? To install the older style carbs you would need a set of the earlier rubber intakes. You might also need earlier throttle cables but I am not sure.

eurban · « **Reply #24 on:** July 03, 2008, 08:19:20 AM »

One other thought here. The accel pump will only squirt significant fuel when the throttle is abrubtly whacked open, not "gently" opened. If you are diagnosing things without the throttle cables installed it may be difficult to open up the throttle fast and far enough to get a good squirt. Just a thought . . .

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Author Topic: F3 Accelerator Pump Operation (Read 4220 times)

eldar

eldar

eldar