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Classic, Vintage & Veteran For Coventry and Meriden Models. Anything pre-Hinckley goes.

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Old 10-30-2012, 10:48 PM   #11 (permalink)
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...thanks. Did what you suggested with a plug grounded and I get good spark. Re the timing...the left side starts first kick and this thing runs great as a single. I was very careful to lock everything in place so the timing is very close and the idler gear has not been moved so cam timing will not have changed. Apparently the Mikunis are good when they are set up. They look like a mistake right now.
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Old 10-31-2012, 12:31 AM   #12 (permalink)
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This has to be a carburettor problem.Take the carb from the good cylinder and fit it to the bad cylinder.
I wouldn't even bother to fit the bad carb back on;there is something wrong with it.I'd just plug the balance tube between the manifold flanges (put a 5/16" ball in it).

Then see if that bad cylinder can run with the good carb.I'm sure it will.

If that's the case,something is wrong in the other carb:wrong parts or incorrect assembly.
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Old 10-31-2012, 01:50 AM   #13 (permalink)
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Mikunis are no more difficult than Amals, especially the VM (Round Slide) Type. Difference in circuit layout, but same principles in function. As Mr. Pete suggests, would try swapping the carb from left to right, easily done and best way to make sure this is your concern. I would remove the right hand carb and go through it again.

As it really seems you are running rich/flooding, pay careful attention to the enrichner (choke), idle air/fuel screw and float height. Enrichner should move smoothly and fit snug in the body. Several options out there to replace the plunger if you like (plunger, cable, lever types). Would verify the float height. Don't remeber spec off hand for the VM's, but quick search should pull it up. Check the needle and seat while your at it, just for kicks. Remove the idle air/fuel screw and make sure the passage is clean with carb clean and blow compressed air through it from the body out. Port should be just in front of the slide if memory serves. Check the oring, washer, and spring are all in good shape, as well as the needle itself. Run them in until LIGHTLY seated, then back out 1 1/2 turns (baseline). Don't over torque the air/fuel screw as you can mushroom the tip and break it off in the body. Carb is typically junk at that point, as almost impossible to get the tip out.

Last thing would be to check the carb slide and needle. Make sure the needle is true, and on the middle clip groove. If it is raised (not seating into the body/emulsion tube completely) whether bent, wrong clip position, or otherwise, even at idle you will pull a huge amount of fuel through. Same if the slide is sticking open.
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Old 11-03-2012, 04:17 PM   #14 (permalink)
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Thanks again everyone for all your responses...I've never gotten this much help before on a forum. I removed the RH carb and took a good look at the enrichment circuit. I could not find a problem. There is no 'o' ring in the plunger and it is as I thought a simple mechanical piston plunger connected directly to the choke lever. You'd have to get pretty crazy to bend that lever. The float needle seemed a little sticky but worked when I tested it. Blew out all the jets one more time and looked at the needle jet seat and it was clean. I replaced the leaking pet cock and then swapped carbs one more time. I found the slide on the LH side was holding off the seat so I loosened the cable set nut and adjusted it down. Pulled both plugs and cleaned them just to be sure. fired it up and it idled perfectly for about a minute ...for a moment I thought it was a Japanese bike. I then started blipping the throttle and the LH side started missing, cutting out and emmiting black smoke. The RH side runs perfectly...no smoke, no miss. The LH side would not run too well after the brief idle time. As I played with the LH side at about 2000rpm I found that oddly it would kick in and run better if I actuated the choke lever...yet it blows black smoke when it runs without it. I'm going to change out the float needle cartridge and get two new B7ES plugs and see what happens. At least now I know that the rebuild was good and that the problem swaps sides with the carbs.
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Old 11-10-2012, 08:18 PM   #15 (permalink)
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...further update. Both petcocks started leaking but I was able to repair them. Swapped carbs again and the problem switched this time! Pulled of the bad carb and got some 'Gunk' carb cleaner...went nuts on the float needle valve, soaked and blew out every jet and orifice I could find. Cleaned the float pins and guides (the VM's have separate floats with a pin that goes up the middle of the float and a pin at the bottom that contacts the float valve arm). Fired it up and it idled perfectly. Huge improvement. No more fuel slopping around. Still have a bit of a miss on the bad carb side but very tolerable. Shut it down and the RH carb started overflowing...ripped it apart and Gunked the needle valve and blew it out and all is well again. Gotta get that little miss sorted out and I think it's going to be very nice. Thanks for all the help so far guys.
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Old 11-10-2012, 09:55 PM   #16 (permalink)
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Glad you are getting it sorted out and also appreciative that you are sharing what you are doing. My only regret is you are doing things without noticing what may or may not be changing. The engine's ability to run seems to be the only indicator.

When you said that you pinched a fuel line and it started to run better says something was causing the carb to flood.

The comment about it running better with the choke/enrichener on is not logical, but probably a clue. Something sounds ass-backwards in that carb. Can the enrichener be put in backwards and act like a slide in backwards. I don't suppose the slide itself is in backwards, is it. I think I mentioned this before. I've had that happen to me with square slide Dellortos. Sorry if I'm repeatin myself. This tread is taking some time with lags in between.

I would suggest you take that carb or both to somebody that truly knows carbs. You may have an obvious error or issue that you just don't see because of inexperience. We've all been there at one time or another so it happens.

I know you are learning in the process here. But sometimes, it's okay to get a little help. It's kinda like telling a little kid that the stove is hot.

regards,
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Old 11-11-2012, 07:55 PM   #17 (permalink)
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Thanks Rob, I pinched the balance feed between the two carbs when it was flooding and tried to regulate fuel using the petcock. That didn't work. As I said, I swapped the carbs and the problem went with the carbs so I took the 'bad' carb off an took it down to the local Honda shop that supposed to be Mikuni experts. They could not find anything wrong with the carb. I took the float valve apart at that point and used the gunk etc....re-installed and there was a huge difference. By the way, the RH carb started dumping fuel out the over flow so it came off and I gave it the same treatment. I have been trying to eliminate things in some kind of logical fashion and it looks like I've eliminated ignition issues and nailed it down to one carb. That could only be done after I got rid of the oil issue with the Morgo set up. That is solved now and there's no leaks. Putting in the original style pump, eliminating the oil cooler and rigging up a PCV valve worked good. The oil pressure is now normal. The bike starts first kick now and idles very well.
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Old 11-11-2012, 08:19 PM   #18 (permalink)
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Well, there might have been crud that prevented the float valve from sealing and that is why she was flooding. Or the float may have been hanging up and when you took it apart, you tweaked the float or the gasket and not it is not hanging up.

When I said I'm not familiar with Miks, I meant the Miks used on Triumphs. I have experience with Miks and Keihins from Japanese bikes.

Do these carbs have dual floats? If so, it is very common for the floats to hang up either on a part of the carb or the bowl gasket. It's very important to inspect how the float moves with the bowl off to make sure that any side play in the pivot point does not result in the carb rubbing/handing up on something in the bowl area. This includes the gasket.

I had an issue last year with a brand new Monobloc that worked fine at first and apparently worked fine for the owner that bought the carb. But it started to flood and it was a matter of trimming some flash from the float and relieving a boss inside the carb. I thought I had it fixed and it worked fine. Then a month or so later, did it again. I had to removed a little more material.

So, the point is, be very anal about your floats' abilities to move freely inside the bowls in any position.

regards,
Rob
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Old 11-12-2012, 01:54 PM   #19 (permalink)
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I think the float needle valve was sticking open and closed whenever it felt like it. That would explain flooding and occasional lean running where hitting the enrichment lever helped. These carbs are the same as the old Honda 750 four types, round bore VM30-83 and they were used on a few other early 70's Japanese bikes. Sudco makes a kit to convert to Triumph. Other's have said that the Amal Mk2's are a better fit. Yes, the VM's have dual floats. One of the things I focused on was cleaning up those little pins that the floats ride up and down on as they seemed a little sticky. I think a combination of previous issues such as a bad ignition system ground, too much oil pressure, garbage in the tank from sitting and varnish build up were the main problems. Ya, I think it's time to methodically set these carbs up and see where that takes me from here....it may not be over yet.
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