hi , i am trying to get my commando mk 111 up and running with a mikuni vm 36 (new), i have just rebuilt the engine and rebored out to +40s , i am able to get the bike running but when i give it throtle it just dies ,then if i leave the throtle the bike will run on idle ,my pilot jet is a 37.5 and main jet is a290 with air mix screw 1 1/2 tunrs out , i have tryed adjusting the air screw but the bike dose not want to rev when i turn the throtle (unless it is turned very slowly) any help would be aprishiated . bigspyke ,scotland
mikuni vm 36
- Thread starter bigspyke
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Stupid question I know but do you have the choke lever on? (Down is on) I had a similar problem a while ago and after almost giving up I checked the new slide i'd fitted (after advice from moto carb) and lo and behold it was the wrong way round i.e the cutaway was at the front (towards the engine) seems I'd been sent the wrong sided slide (they come in LH & RH Variants) Seemingly not uncommon, i did feel a bit of an idiot though!
Where in Scotland are you?
Where in Scotland are you?
These thing are all about the needle and needle jet. Main jet are quite veriable and the pilot seem ok.
Needle jets can be anywhere fro P2 to a Q2 with the P2 as the starting point the needle is generally a 6DH3. You need to raise or lower the needle.
You also need to find out what needle and needle jet you have.
It can be elusive but when you find the sweet spot, you will love it.
Needle jets can be anywhere fro P2 to a Q2 with the P2 as the starting point the needle is generally a 6DH3. You need to raise or lower the needle.
You also need to find out what needle and needle jet you have.
It can be elusive but when you find the sweet spot, you will love it.
Gino Rondelli said:
thanks gino , the choke is off ,i only know as i phoned and asked allens performance where i bought the carb what was on or off ,dhaw ,. when i was talking to them they did mention having the cutaway to the back of the carb (pointing to the back the air fillter) whitch i could not figure out as there is a only one way the slide will fit ! so hopfully i can ring them tomorrow and get things sorted , thanks a lot for your help and will let you know how i get on . bigspyke , lanark .
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True that a MIkuni slide will only fit with its notch only one way, BUT it is also possible you have a slide with the cutaway facing the wrong way, even if it does fit.
This happened to me, be very careful which way it faces and talk with them about this.
Also, your needle is in the middle clip we assume? Check it make sure also that the circlip is fully seated in the ring.
Check that the top of the carb is fully screwed on the body, and that both pilot and main jet are fully screwed in.
This happened to me, be very careful which way it faces and talk with them about this.
Also, your needle is in the middle clip we assume? Check it make sure also that the circlip is fully seated in the ring.
Check that the top of the carb is fully screwed on the body, and that both pilot and main jet are fully screwed in.
I have a 36 VM on my 1972 750 and it takes a long time before it will run well without the choke on. If I close the choke too early it will pop and bang like mad on the road and no revs/stall at low speeds. I would try leaving the choke on until the motor is really warmed up. On the road this takes about 2/3 miles, but once warmed up runs very well. I have met other owners who have had the same problem. I got an adaptor from Rocky Point so that I could use a lever on the handlbars to close the choke. As an aside I also had to fit an Amal spring inside the Mikuni spring, as the throttle would not close in wet/cold weather, which was an alarming experience. My suggestion is to get it up to full working temperature with the choke on, then experiment with closing the choke. Mine takes a long, long time before you can close the choke.
Hope this helps,
Les
Hope this helps,
Les
have just checked the slide and its as should be , the bike starts with no choke but will not rev ! when running and i put the choke on it will rev but runs ritch and after 20-30 secs will foul the plugs , if you then turn the choke off then its back to ok at tick over but will not rev without dying ! strange .
bigspyke
bigspyke
have just checked the slide and its as should be , the bike starts with no choke but will not rev ! when running and i put the choke on it will rev but runs ritch and after 20-30 secs will foul the plugs , if you then turn the choke off then its back to ok at tick over but will not rev without dying ! strange .
bigspyke
bigspyke
Have you measured the float level? On a VM36 it should be 22-24mm. As its starting without choke that appears to be logical thing to check first.
PS - for the other mentioned post that has to have the choke on for 3 - 3 miles before it can run well, the simple answer is - the PIlot Jet is too small. Common problem with Mikunis fitted straight out of the box. It must have either a 35 or 40 to start on the choke and switch off under 1 minute.
Mick
PS - for the other mentioned post that has to have the choke on for 3 - 3 miles before it can run well, the simple answer is - the PIlot Jet is too small. Common problem with Mikunis fitted straight out of the box. It must have either a 35 or 40 to start on the choke and switch off under 1 minute.
Mick
hi again , just back from holidays ( in sunny scotland) and got back to getting my commando running , i changed the needle that was wrong,( which i thought was going to be the problem ) but did not solve the problem , i put a bigger pilot jet in as well to see if that would help (37.5 up to 40) but still the same , will start and idle with no choke but will not rev , but when choke is on she will rev but too rich and will foul plugs , Mrnorton and somone else did mention float levels ! can enyone tell me how to measure and adjust the float ! any help would be apresiated .
bigspyke LANARK SCOTLAND
bigspyke LANARK SCOTLAND
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If you're sure there's no air leaks, the carb is near book set up, the float level is OK, just a bit of lateral thought;
Sometimes a weak spark can give the same symptoms. I'll cost nothing to check the plugs and caps aren't both the resistive type or to try another set of coils.
Stick with it,
Cash
Sometimes a weak spark can give the same symptoms. I'll cost nothing to check the plugs and caps aren't both the resistive type or to try another set of coils.
Stick with it,
Cash
- Joined
- Nov 16, 2010
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- 1,275
Did the bike run ok with the OE Amal carbs fitted? If so maybe it would be a good idea to refit them and see if it still runs well? Obviously you have checked things like ignition timing, valve clearances, cam timing, and are 100% sure they are correct?
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